JP2008277797A - Image sensor - Google Patents

Abstract

An image pickup device with high sensitivity is provided by integrating charges generated by light irradiation at specified timings.
An imaging element includes an imaging region where a plurality of imaging elements Px each including a photoelectric conversion unit D1 that generates charges by light irradiation, and charges generated in the imaging region E1 are transferred at a specified timing. A storage region E2 in which a plurality of storage elements Py each storing charge for each imaging element Px is arranged is provided on the semiconductor. Each storage element Py includes an addition unit F1 that accumulates charges generated for each image pickup element Px by delivering a charge that has a larger saturation charge amount than the image pickup element Px and is received from the image pickup area E1.
[Selection] Figure 1

Description

  The present invention relates to an image sensor having a sensitizing function.

  In general, in an image sensor that generates a charge by light irradiation and extracts a light reception output corresponding to the amount of received light, the light reception output also changes according to the amount of light received. Although the amount of received light increases as the exposure time increases, the upper and lower limits of the effective received light output that reflects the received light amount are limited by the size and impurity concentration of the part that generates and transfers charges. That is, simply increasing the exposure time cannot saturate the portion where charge generation or charge transfer occurs and cannot obtain a light reception output reflecting the amount of received light, and therefore cannot increase sensitivity.

Since the exposure time can be adjusted with the image sensor, the dynamic range is obtained by capturing multiple times with multiple exposure times and obtaining the received light output using the charge with the appropriate exposure time. (For example, refer to Patent Document 1).
JP 2006-84430 A

  By the way, in the structure of patent document 1, since the structure which adjusts light reception light quantity by adjusting the length of exposure time is employ | adopted, the electric charge amount taken out as a light reception output although the dynamic range with respect to light reception intensity becomes large However, the dynamic range of the received light output does not increase.

  The present invention has been made in view of the above-mentioned reasons, and its object is to increase the sensitivity by accumulating the charges generated by light irradiation at each specified timing and to increase the saturation charge amount of the light receiving output. Accordingly, an object of the present invention is to provide an image pickup device in which the dynamic range of light reception output is increased.

  According to the first aspect of the present invention, there is provided an imaging region in which a plurality of imaging elements each including a photoelectric conversion unit that generates charges by light irradiation, and charges generated in the imaging region are transferred at a specified timing, and the charges for each imaging element. And a storage region in which a plurality of light-shielded storage elements are arranged on a semiconductor, and each storage element has a larger saturation charge amount than the imaging element, and the charge received from the imaging region is delivered multiple times. It has the addition part which accumulate | stores the electric charge produced | generated for every imaging element, It is characterized by the above-mentioned.

  According to a second aspect of the present invention, in the first aspect of the present invention, the imaging region and the storage region are formed in different regions adjacent to each other on the semiconductor.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the storage element includes a transfer unit that receives charges transferred from the imaging region, and adds the charges received by the transfer unit from the imaging region. It is characterized in that the charge is accumulated by handing it over to the unit.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, a plurality of basic units each including a plurality of the imaging elements and the storage elements are arranged on the semiconductor, and the imaging elements and the storage elements are Each of the plurality of control electrodes arranged on the semiconductor via an insulating layer is provided, and charge transfer from the imaging region to the storage region is performed by controlling a voltage applied to the control electrode, and the transfer The control unit provided in the imaging element and the control electrode provided in the transfer unit are straight lines in the first direction in which the imaging region and the storage region are arranged in the basic unit. The control electrode provided in the transfer unit and the control electrode provided in the addition unit are arranged on a line and are aligned on a straight line in the second direction intersecting the first direction.

  According to a fifth aspect of the present invention, in the fourth aspect of the invention, the imaging region further includes a charge holding unit that determines an amount of unnecessary charges to be removed from the charge generated by the photoelectric conversion unit, and the charge holding unit and the addition Are arranged in a line in the first direction.

  According to a sixth aspect of the present invention, in the invention according to any one of the third to fifth aspects, a separation band is formed between the transfer section and the addition section, and the transfer section is disposed on the main surface of the semiconductor. The addition unit has an addition control electrode arranged on the main surface of the semiconductor, and controls the height of the potential barrier in the separation band by controlling the voltage applied to the transfer control electrode and the addition control electrode. It is characterized in that the charge transfer between the unit and the adding unit is controlled.

  According to a seventh aspect of the present invention, in the invention according to any one of the third to fifth aspects, a separation band is formed between the transfer section and the addition section, and the transfer section is disposed on the main surface of the semiconductor. The addition portion has an addition control electrode disposed on the main surface of the semiconductor, and further, the height of the potential barrier of the separation band between the transfer control electrode and the addition control electrode on the main surface of the semiconductor. And a movement control electrode for controlling charge movement between the transfer section and the adding section is arranged.

  According to an eighth aspect of the present invention, in any one of the third to seventh aspects, the addition unit has an impurity concentration higher than that of the transfer unit.

  According to a ninth aspect of the present invention, in the sixth or seventh aspect of the present invention, a slit region having a higher impurity concentration than the transfer unit and the addition unit is provided between the transfer unit and the addition unit. It is characterized by that.

  According to a tenth aspect of the present invention, in the sixth or seventh aspect of the present invention, the first slit region formed between the transfer portion and the separation band and having a higher impurity concentration than the transfer portion, and the addition And at least one of a second slit region formed between the separation portion and the separation band and having an impurity concentration higher than that of the addition portion.

  According to an eleventh aspect of the present invention, in the invention according to any one of the third to tenth aspects, in the accumulation region, on both sides of the accumulation element, a first overflow drain adjacent to the addition unit, and the transfer unit And a second overflow drain adjacent to the second overflow drain.

  In the invention of claim 12, in the invention of claim 11, a third overflow drain adjacent to the photoelectric conversion unit is formed in the imaging region, and an overflow drain is provided between the imaging region and the accumulation region. It is characterized in that no buffer region is formed.

  According to the configuration of the first aspect of the present invention, the storage element for storing the charge for each image pickup element is provided separately from the image pickup element, and the charge generated for each image pickup element is greater than that of the image pickup element. Since the addition unit is provided in the storage element, it can be sensitized by accumulating charges in the addition unit. In addition, since the addition unit is provided separately from the photoelectric conversion unit, the occupied area in the semiconductor can be increased or the impurity concentration can be increased to increase the saturation charge amount. It can be easily realized. In addition, since the charges can be integrated without taking them out of the image sensor, the charges can be integrated without reducing the response speed (frame rate).

  Note that storing the charge for each imaging element by the storage element does not necessarily mean that the imaging element and the storage element have a one-to-one correspondence, but the storage element is an integral multiple of the imaging element. (2 times or 4 times) may be sufficient. That is, it is possible to associate two or four storage elements with one imaging element.

  According to the configuration of the second aspect of the present invention, since the imaging region and the storage region are formed in different regions on the semiconductor, an increase in dark current of the imaging element can be prevented. In particular, when the impurity concentration in the accumulation region is increased to increase the saturation charge amount in the accumulation region, if the imaging region and the accumulation region are provided in the same region, the electric field strength at the boundary increases and dark current is increased. However, dark current can be suppressed by providing the imaging element and the accumulation region in different regions.

  Also, if the imaging area and the storage area are provided in the same area, charges flow from the imaging area to the storage area due to the potential difference between the imaging area and the storage area, but the imaging area and the storage area are different areas. By providing, it is possible to prevent the charge from flowing out naturally from the imaging region to the accumulation region.

  According to the configuration of the invention of claim 3, the transfer unit that receives the charge from the imaging element in the accumulation region is provided separately from the addition unit, and the charge from the imaging element is transferred to the addition unit via the transfer unit. The photoelectric conversion unit can generate charges during the period in which the charge is moved from the addition unit to the addition unit, and the photoelectric conversion unit can be used for charge generation other than the period during which the charge is transferred from the photoelectric conversion unit to the transfer unit. It becomes possible. As a result, it is possible to increase the period during which charges are generated in a unit time and to increase the sensitivity.

  According to the fourth aspect of the invention, the imaging element and the storage element each have a plurality of control electrodes, and a plurality of basic units each including a plurality of imaging elements and storage elements are arranged on the semiconductor. In each basic unit, the control electrode provided in the imaging element and the control electrode provided in the transfer unit are arranged in a straight line, and provided in the transfer unit on a straight line in a direction intersecting this direction. Since the control electrode and the control electrode provided in the addition unit are arranged, the image pickup device is configured by repeating the basic unit, and the transfer unit and the addition unit are alternately arranged in the accumulation region. Since this structure is similar to a frame transfer type CCD image sensor, it can be realized by using the technology of a frame transfer type CCD image sensor that has been conventionally provided, and can be easily realized. Become.

  According to the configuration of the fifth aspect of the invention, the charge holding unit provided for determining the amount of unnecessary charge to be removed from the charge generated by the photoelectric conversion unit is arranged in a line in the first direction with the addition unit. In the basic unit, the accumulation region uses two columns of the addition column and the transfer column, and the imaging region uses an area corresponding to two columns of the imaging element and the charge holding unit, resulting in the semiconductor. The above space can be used without waste.

  According to the configuration of the invention of claim 6 and claim 7, since the separation band is provided between the transfer unit and the addition unit, the charge of the transfer unit is received during the period in which the transfer unit receives charge from the photoelectric conversion unit. Can be prevented from mixing with the charge of the adder. In addition, after the charge is transferred to the storage element associated with the imaging element, the charge of each imaging element is imaged by controlling the height of the potential barrier of the separation band and moving the charge from the transfer unit to the adding unit. Integration can be performed in the addition unit in the storage element associated with the element. In particular, since the movement control electrode is provided in order to control the height of the potential barrier of the separation band in the invention of claim 4, the voltage applied to the movement control electrode can be controlled together with the transfer control electrode and the addition control electrode. Thus, the charge can be easily transferred from the transfer unit to the addition unit.

  According to the configuration of the eighth aspect of the invention, since the impurity concentration of the addition unit is higher than that of the transfer unit, the saturation charge amount of the addition unit can be increased without increasing the area occupied by the addition unit. it can. In other words, it is possible to increase the saturation charge amount and suppress sensitization while suppressing the increase in size of the image sensor.

  According to the configuration of the ninth aspect of the invention, by providing the slit region having a higher impurity concentration than the transfer unit and the adder unit between the transfer unit and the adder unit, the transfer unit and the adder unit respectively. A potential gradient can be formed, and the slit region is formed between the transfer unit and the addition unit, so that charge transfer from the transfer unit to the addition unit is facilitated. In addition, when a plurality of pairs of transfer units and addition units are alternately arranged, a potential barrier is formed between the transfer unit and the addition unit between the adjacent groups, and the charge between the adjacent sets Mixing can be suppressed.

  According to the configuration of the invention of claim 10, in the configuration including the separation band between the transfer unit and the addition unit, the impurity concentration is at least one between the transfer unit and the separation band and between the addition unit and the separation band. By providing a slit region having a high concentration, a potential gradient is formed in at least one of the transfer unit and the addition unit, and the movement of charges from the transfer unit to the addition unit can be facilitated.

  According to the configuration of the eleventh aspect of the present invention, since the first overflow drain adjacent to the addition section and the second overflow drain adjacent to the transfer section are formed in the accumulation region, the charge in the transfer section or the addition section When it is likely to saturate, discarding the charge through the overflow drain prevents the adjacent storage element from overflowing and suppresses blooming. In addition, since the first overflow drain and the second overflow drain are arranged on both sides of the storage element, charge transfer from the transfer unit to the addition unit is not hindered.

  According to the configuration of the twelfth aspect of the present invention, since the buffer region in which the overflow drain is not provided is formed between the imaging region and the storage region, the potentials of the first and second overflow drains and the third overflow drain are formed. The charge of the imaging region and the storage region can be prevented from flowing to the other overflow drain, and the amount of charge that accurately reflects the amount of received light is integrated in the adder. Can do. In addition, the buffer area can be used as a wiring space.

  In the embodiment described below, by forming a main row L in which a plurality of imaging elements Px are arranged in the vertical direction Dv as an imaging device, and by arranging a plurality of main rows L in the horizontal direction Dh, Assume a two-dimensional (area) image sensor in which pixels are arranged in a matrix.

  Further, in the embodiment described below, a distance measuring device that calculates a distance to an object existing in a target space is exemplified as an active type spatial information detecting device configured by combining an imaging element with a light emission source. As a spatial information detection device, the technical idea of the present invention can be applied to a device that obtains the reflectance of an object and the transmittance of a medium in space in addition to a distance measuring device.

(Basic structure)
In the embodiment described below, as shown in FIG. 1, a structure in which a vertical transfer register is also used as a photoelectric conversion unit D1 as in the frame transfer (hereinafter abbreviated as “FT”) system in a CCD image sensor. As shown in FIG. 9, the vertical transfer register Rv is disposed adjacent to the photoelectric conversion unit D1 as in the configuration of the interline transfer (hereinafter abbreviated as “IT”) system, as shown in FIG. The technique of the following embodiment can also be adopted in the imaging device 1 having the above structure. Further, since it can be applied to the structure of the FT method and the IT method, the technique of the following embodiment can be applied even to a structure similar to the structure of the frame interline transfer (hereinafter abbreviated as “FIT”) method. It is possible to adopt.

  Hereinafter, a structure similar to the FT method will be described as an FT type, a structure similar to the IT method will be described as an IT type, and a structure similar to the FIT method will be described as an FIT type. In the case of the FT type, it is assumed that the imaging region E1 including the photoelectric conversion unit D1 and the storage region E2 that stores the charge generated in the imaging region E1 are provided in the semiconductor, and the storage region E2 is shielded from light. . On the other hand, in the case of the IT type, an area where the photoelectric conversion units D1 are arranged is an imaging area E1, and a vertical transfer register Rv provided adjacent to the photoelectric conversion unit D1 is an accumulation area E2. Accordingly, one imaging region E1 and one accumulation region E2 are provided in the FT type, while a plurality of imaging regions E1 and a plurality of accumulation regions E2 are provided in the IT type.

  A large number of imaging elements Px each having a photoelectric conversion unit D1 and generating charges are arranged in the imaging area E1, and a storage element for storing charges generated by the imaging elements Px in the imaging area E1 is arranged in the storage area E2. Many Py are arranged. The number of storage elements Py may or may not match the number of imaging elements Px. When the number of imaging elements Px and storage elements Py is different, a plurality of storage elements Py are associated with the imaging elements Px, and the storage elements Py are preferably integer multiples (2 or 4 times) of the imaging elements Px. ).

  The storage element Py provided in the storage area E2 includes an integration element Py1 and a transfer element Py2. The charge generated by the imaging element Px is transferred to the integration element Py1 through the transfer element Py2. In the storage region E2, an addition unit F1 in which a plurality of integration elements Py1 are arranged on a straight line and a transfer unit F2 in which a plurality of transfer elements Py2 are arranged on a straight line are formed in a plurality of columns on the semiconductor. The adding unit F1 and the transfer unit F2 are arranged in parallel, and the transfer element Py2 is arranged beside the integrating element Py1. The same number of integration elements Py1 and transfer elements Py2 are provided. Although the integration element Py1 and the transfer element Py2 do not necessarily correspond one-to-one, as described later, the addition control electrode 41 arranged in the addition unit F1 in which the integration elements Py1 are arranged and the transfer element Py2 are arranged. The transfer control electrodes 42 arranged in the transfer unit F2 are arranged on a straight line in the horizontal direction Dh.

  In the FT type, as will be described later, the storage element Py is configured by the addition unit F1 and the transfer unit F2, and in the IT type, the storage element Py is configured by only the addition unit F1 without providing the transfer unit. The charge weighing unit F3 described later is preferably provided in the FT type. However, even in the IT type, the structure corresponding to the photoelectric conversion unit of the CCD image sensor is replaced with the structure of the imaging element Px described later. Can be realized.

  Hereinafter, only the FT type will be described, but if the above description is taken into consideration, the technology can be easily transferred to the IT type or the FIT type.

〔Construction〕
FIG. 1 shows an overall schematic structure of the image sensor 1 as viewed from the front. The vertical direction in FIG. 1 is the vertical direction Dv in the image, and the horizontal direction is the horizontal direction Dh in the image. The imaging element 1 is formed on a single semiconductor, and is divided into an imaging area E1 and an accumulation area E2 in the vertical direction Dv.

  In the imaging area E1, charges are generated by light irradiation, and in the accumulation area E2, charges generated in the imaging area E1 are temporarily accumulated and the charges are taken out of the imaging element 1. In the imaging region E1, a main row L in which a large number of imaging elements Px are arranged on a straight line in the vertical direction Dv is formed, and the plurality of main rows L are spaced apart in the horizontal direction Dh and arranged in parallel, whereby the imaging element Px Are arranged in a matrix.

  FIG. 2A shows the configuration of one imaging element Px, and FIG. 2B shows the configuration of one storage element Py. 3 and 4 are cross-sectional views of the imaging element Px, and FIG. 5 is a cross-sectional view of the storage element Py.

  2A and 2B is a basic unit of the image sensor 1, and the image sensor 1 is formed by arranging a plurality of these basic units on a semiconductor. The basic unit is provided with a plurality of imaging elements Px and storage elements Py.

As shown in FIGS. 3 and 4, the imaging element Px is disposed on the main surface side of the element forming layer 11 made of a first conductivity type (p-type in the illustrated example) semiconductor (assuming silicon in the illustrated example). A well 12 made of a semiconductor of the second conductivity type (n-type in the illustrated example) is formed, and a sensitivity control electrode 21 and a separation electrode are formed on the main surface of the well 12 via an insulating layer (for example, silicon oxide or silicon nitride) 13. 22, a storage electrode 23, and a barrier control electrode 24 are arranged. In the element forming layer 11, a holding well 14 having the second conductivity type and an impurity concentration higher than that of the well 12 (that is, n ^{++ type} ) is formed in the range of the well 12. One end 25 of a connection line 26 is connected to the holding well 14 in an ohmic manner, and a barrier control electrode 24 is connected to the other end of the connection line 26. However, an electrode may be provided at one end portion 26 of the connection line, and the electrode may be arranged with respect to the holding well 14 via the insulating layer 13.

  As shown in FIG. 2, the sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, and the barrier control electrode 24 are rectangular or strip-shaped in the plan view and are formed to have the same dimensions, and the width direction (vertical direction Dv). Arranged on a straight line. That is, the sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, and the barrier control electrode 24 are arranged with their centers aligned on a straight line perpendicular to the longitudinal direction (that is, the vertical direction Dv). It becomes the vertical direction Dv. There is one barrier control electrode 24, but there are a plurality of sensitivity control electrodes 21, separation electrodes 22 and storage electrodes 23 (in the example shown, there are six sensitivity control electrodes 21, and each of the separation electrodes 22 and the storage electrodes 23). 3) provided. The sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, and the barrier control electrode 24 do not necessarily have the same dimensions. For example, the longitudinal direction (horizontal direction Dh) of the barrier control electrode 24 is set to the separation electrode 22 and the storage electrode. It may be larger than 23.

  The holding well 14 is disposed adjacent to one side in the horizontal direction Dh of the pixel array with respect to the central separation electrode 22 of the three separation electrodes 22. In addition, an overflow drain 15 is formed in the element forming layer 11 adjacent to the sensitivity control electrode 21 and the separation electrode 22, and the drain electrode (provided at the same site as the overflow drain 15) without the insulating layer 13 being interposed in the overflow drain 15. Are directly connected. Overflow drain 15 is formed, for example, as a region having the same conductivity type as well 12 and having an impurity concentration higher than that of well 12. The overflow drain 15 is formed on the same side as the holding well 14 in both sides of the sensitivity control electrode 21 in the longitudinal direction (horizontal direction Dh of the pixel array). The reason for this will be described later. In the element formation layer 11, the well 12 is formed so as to protrude in the region where the holding well 14 is formed, but the well 12 is not formed in the region where the drain electrode is formed. The element forming layer 11 is formed on the second conductivity type substrate 10.

  Of the sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, and the barrier control electrode 24, at least the sensitivity control electrode 21 has translucency. The separation electrode 22, the storage electrode 23, and the barrier control electrode 24 are preferably not translucent, but have translucency because they are formed simultaneously with the sensitivity control electrode 21. Therefore, the main surface of the element formation layer 11 in the imaging element Px is entirely formed by the light shielding film 30 (see FIGS. 3 to 5) except for the opening window 31 (see FIG. 4) formed in the region corresponding to the sensitivity control electrode 21. Covered. In the following description, an example of using electrons among the charges generated by light irradiation will be described. However, when holes are used as the charges, the conductivity type of the semiconductor is changed, and the polarity of the voltage described later is changed. Will be replaced.

  The region where the sensitivity control electrode 21 is arranged in the element formation layer 11 and the well 12 functions as a photoelectric conversion unit D1 that generates charges when irradiated with light through the opening window 31. In the well 12, the region where the separation electrode 22 is disposed functions as the charge separation portion D2, and the region where the storage electrode 23 is disposed functions as the charge storage portion D3. A region where the holding well 14 is disposed in the well 12 functions as the charge holding portion D4.

  The barrier control electrode 24 is electrically connected to the holding well 14 through the connection line 26. The connection line 26 is a metal wiring, and the barrier control electrode 24 has the same potential as the holding well 14. Therefore, when the charge is held in the holding well 14, a voltage corresponding to the charge amount of the holding well 14 is applied to the barrier control electrode 24 (or the barrier control electrode 24 corresponds to the charge amount of the holding well 14. Charged).

  Since electrons are held in the holding well 14, a negative voltage can be applied to the barrier control electrode 24, and the potential barrier against electrons increases. That is, the potential barrier for electrons is higher than that of the charge separation unit D2 corresponding to the separation electrode 22 and the charge storage unit D3 corresponding to the storage electrode 23, and a potential barrier is formed between the charge separation unit D2 and the charge storage unit D3. Will be. The height of the potential barrier immediately below the barrier control electrode 24 changes according to the amount of charge in the holding well 14. In other words, the height of the potential barrier changes according to the amount of charge held in the charge holding unit D4.

  The potentials of the barrier control electrode 24 and the holding well 14 are determined by the amount of charge held in the charge holding portion D4, but the voltages applied to the sensitivity control electrode 21, the separation electrode 22, and the storage electrode 23 are controlled separately. There is a need. For example, two types of positive and negative voltages (+10 V, −5 V) are applied at appropriate timing. Therefore, one of the two power supply wires 27a and 27b is ohmically connected to the sensitivity control electrode 21, the separation electrode 22, and the storage electrode 23. The power supply wirings 27a and 27b are preferably metal wirings. Further, when the power supply wires 27 a and 27 b are not connected to the sensitivity control electrode 21, the separation electrode 22, and the storage electrode 23, the power supply wires 27 a and 27 b are connected via the insulating layer (for example, silicon oxide or silicon nitride) 16. Is insulated.

Meanwhile, the reset gate electrode 28 and the reset drain 17 are formed on the main surface of the element forming layer 11 so as to be aligned in the direction Dv perpendicular to the holding well 14. In plan view, the holding well 14 and the reset drain 17 are arranged with the reset gate electrode 28 interposed therebetween. The reset gate electrode 28 and the reset drain 17 are disposed on the photoelectric conversion unit D1 side with respect to the holding well 14. The reset drain 17 is formed as a region of the second conductivity type (ie, n ⁺⁺ ) having a high impurity concentration, for example, and the reset electrode (provided at the same site as the reset drain 17) does not pass through the insulating layer 13. Connected directly to. A fixed reset voltage is applied to the reset electrode.

  Further, a transfer gate electrode 29 is disposed between the separation electrode 22 and the holding well 14. When an appropriate voltage is applied to the transfer gate electrode 29, a channel is formed immediately below the transfer gate electrode 29, and charge can be transferred from the charge separation unit D2 to the charge holding unit D4.

  The region where the separation electrode 22, the storage electrode 23, the barrier control electrode 24, the reset gate electrode 28, the transfer gate electrode 29, the reset drain 17, and the charge holding portion D 4 are arranged (the region surrounded by the alternate long and short dash line in FIG. 2). The charge weighing unit F3 is configured. In the charge weighing unit F3, the separation electrode 22, the storage electrode 23, and the barrier control electrode 24 are aligned with the photoelectric conversion unit D1 in the direction along the main row L (that is, the vertical direction Dv), and the charge holding unit D4. The reset gate electrode 28, the transfer gate electrode 29, and the reset drain 17 are disposed at different locations from the straight line on which the photoelectric conversion units D1 are arranged. In other words, it is shifted in the horizontal direction Dh with respect to the straight line.

  On the other hand, the storage area E2 includes storage elements Py that individually store the charges generated by the imaging elements Px. Here, a case where the imaging element Px and the storage element Py are associated one-to-one will be described as an example. However, if one image pickup element Px is associated with two or four storage elements Px, it is possible to distribute and store charges corresponding to the amount of received light received at different timings to the storage elements Px. This operation can be used to distribute and accumulate charges corresponding to a plurality of received light amounts corresponding to a plurality of phases of intensity-modulated light whose intensity is modulated at a constant frequency in a spatial information detection apparatus to be described later. .

  Each storage element Py includes an adding unit F1 that integrates the charges delivered from the imaging element Px, and a transfer unit F2 that receives the charges generated in the imaging region E1 and delivers them to the adding unit F1. The transfer unit F2 and the photoelectric conversion unit D1 are arranged on a straight line in the vertical direction Dv. The adding unit F1 is disposed adjacent to the transfer unit F2, and the adding unit F1 and the transfer unit F2 are alternately arranged in the horizontal direction Dh. In addition, the charge holding unit D4 and the adding unit F1 in the charge weighing unit F3 are arranged on a straight line in the vertical direction Dv.

  In the addition part F1, the addition control electrode 41 is arranged on the main surface of the well 12 via the insulating layer 13, and in the transfer part F2, the transfer control electrode 42 is arranged on the main surface of the well 12 via the insulating layer 13. . There are no particular restrictions on the number of addition control electrodes 41 and transfer control electrodes 42 constituting one storage element Py, but in the present embodiment, the addition control electrodes 41, transfer control electrodes 42, It is assumed that the same number is provided.

  In addition, the shape and size of the addition control electrode 41 and the transfer control electrode 42 are not particularly limited, but in this embodiment, the addition control electrode 41 and the transfer control electrode 42 have the same shape and the same size as the sensitivity control electrode 21. It shall be formed. Furthermore, the arrangement pitch of the sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, the barrier control electrode 24, the addition control electrode 41 and the transfer control electrode 42 is made equal, and the difference in shape from the FT CCD sensor is different. It is configured to decrease.

  That is, the photoelectric conversion unit D1 and the transfer unit F2 are arranged on a straight line in the vertical direction Dv, and the separation electrode 22, the storage electrode 23, and the barrier control electrode 24 are also on a straight line in the vertical direction Dv with respect to the photoelectric conversion unit D1. Since the sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, the barrier control electrode 24, and the transfer control electrode 42 are formed in the same shape and the same size, the voltage applied to these electrodes is controlled. As a result, charge can be transferred from the imaging region E1 to the storage region E2. That is, it is possible to transfer charges from the imaging element Px to the storage element Py and further to extract the charge from the storage element Py to the outside of the imaging element 1. In other words, the sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, and the barrier control electrode 24 are used without distinction as control electrodes when used for transferring charges from the imaging region E1 to the storage region E2.

  One storage element Py includes, for example, eight addition control electrodes 41 and transfer control electrodes 42, respectively, and is driven in four phases. Further, a separation band 43 that forms a potential barrier is formed between the addition unit F1 and the transfer unit F2. The addition control electrode 41 and the transfer control electrode 42 are formed in the same shape and the same dimensions as the control electrodes (the sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, and the barrier control electrode 24) in the imaging region E1. Further, the addition control electrode 41 and the transfer control electrode 42 are arranged in a relationship facing each other. That is, the addition control electrode 41 and the transfer control electrode 42 that are each formed in a rectangular shape are arranged with their short sides facing each other.

  In order to form the separation band 43, an appropriate voltage is applied to the addition control electrode 41 and the transfer control electrode 42, and as shown in FIG. 5A, immediately below the addition control electrode 41 and the transfer control electrode 42. Potential wells W1 and W2 are formed. Thus, if potential wells W1 and W2 are formed in addition part F1 and transfer part F2, respectively, potential barrier B1 will be formed between addition part F1 and transfer part F2, and this potential barrier B1 will be formed. It can be used as the separation band 43.

Further, as described above, the well 12 of the second conductivity type (n-type) is formed on the main surface of the element formation layer 11 of the first conductivity type (p-type in the configuration example of FIG. 2). Since the electrode 41 and the transfer control electrode 42 are arranged with respect to the well 12 via the insulating layer 13, the well 12 is provided at a portion corresponding to the addition unit F1 and the transfer unit F2, respectively, as shown in FIG. If the structure to provide is employ | adopted, the element formation layer 11 from which the conductivity type differs from the well 12 will interpose between the addition part F1 and the transfer part F2 (in the above-mentioned example, n type-p type-n type) The element formation layer 11 functions as the separation band 43. However, if the conductivity types of the well 12 and the separation band 43 are different, the potential barrier formed as the separation band 43 is increased. Therefore, as shown in FIG. the same west impurity concentration (in the above example the n ^- type) low concentrations against the well 12 by a, may be caused to function as a separator 43.

  By providing the separation band 43 as described above, when the charge is transferred from the imaging region E1 to the transfer unit F2, it is possible to prevent the charge of the transfer unit F2 and the charge of the addition unit F1 from being mixed. it can. Further, by controlling the relationship between the voltages applied to the addition control electrode 41 and the transfer control electrode 42, the potential barrier B1 formed in the separation band 43 is lowered to transfer the charge of the transfer unit F2 to the addition unit F1. Can do.

When transferring charges from the transfer unit F2 to the adding unit F1, it is desirable that no charges remain in the transfer unit F2. Therefore, as shown in FIG. 6A, a slit region 44 whose impurity concentration is higher (for example, n ^{+ -type} ) than the addition unit F1 and the transfer unit F2 between the addition unit F1 and the transfer unit F2. It is desirable to form. By providing the slit region 44, as shown in FIG. 6B, a potential gradient is formed in the adding unit F1 and the transfer unit F2 so as to incline the charge C into the other.

  Therefore, when the relationship between the voltages applied to the addition control electrode 41 and the transfer control electrode 42 is controlled so that the charge C of the transfer unit F2 overcomes the potential barrier B1 of the separation band 43 (for example, the potential well W2 in the transfer unit F2). When a positive voltage is applied to the transfer control electrode 42 when forming the voltage, the voltage applied to the transfer control electrode 42 is stopped or the voltage is applied). As shown in FIG. As the potential well disappears (the potential of the transfer part F2 approaches the height of the potential barrier B1), the charge C passes over the separation band 43 and flows into the addition part F1.

  In the above-described operation, since the potential well W1 of the adding unit F1 remains, the charge C does not flow backward and flow into the transfer unit F2. In addition, since the potential gradient is also formed in the addition unit F1 by the slit region 44, the electric charge hardly moves between the storage element Py adjacent in the horizontal direction Dh together with the potential gradient in the transfer unit F2, and the adjacent storage is performed. Charge mixing between elements Py is prevented.

  The slit region 44 is provided between the adding unit F1 and the transfer unit F2, and may be provided in any form as long as the potential gradient can be controlled as shown in FIG. For example, it is also possible to form the slit region 44 over the entire area between the adding section F1 and the transfer section F2 including immediately below the separation band 43. In the illustrated example, the slit region 44 is provided both between the addition unit F1 and the separation band 43 and between the transfer unit F2 and the separation band 43. However, only one slit region 44 may be provided. . Further, the slit region 44 near the adding unit F1 only needs to have a higher impurity concentration than the adding unit F1, and the slit region 44 close to the transferring unit F2 only needs to have a higher impurity concentration than the transferring unit F2.

  An overflow drain 45.46 in the vertical direction Dv is disposed in the vicinity of the adder F1 and the transfer unit F2. Similarly to the overflow drain 15 formed in the imaging region E1, each overflow drain 45, 46 is directly connected to a drain electrode (provided at the same site as the overflow drains 45, 46) without the insulating layer 13 interposed therebetween. Overflow drains 45 and 46 are formed, for example, as regions having the same conductivity type as well 12 and having a higher impurity concentration than well 12.

  The storage element Py is formed between both overflow drains 45 and 46. That is, overflow drains 45 and 46 are disposed on both sides of the storage element Py. Here, the overflow drains 45 and 46 between the storage elements Py adjacent in the horizontal direction Dh may be combined into one. The overflow drains 45 and 46 have a function of discarding the charges overflowed in the adding unit F1 and the transfer unit F2, and the charges overflowed by saturation in any of the storage elements Py are stored in the storage elements Py adjacent to the horizontal direction Dh. It is prevented from being mixed in the electric charge, and as a result, the occurrence of blooming is suppressed.

  Further, as described above, since the overflow drain 15 is disposed in the imaging region E1 so that the charges of the photoelectric conversion unit D1 and the charge holding unit D4 can be discarded, as shown in the upper part of FIG. In the conversion unit D1, a potential gradient is formed so that charges easily flow into the charge holding unit D4.

  By the way, it is conceivable to provide the overflow drains 45 and 46 between the addition unit F1 and the transfer unit F2 so as to form a potential gradient similar to that of the slit region 44 in the accumulation region E2, but adopting such a configuration. The charge cannot be transferred from the transfer unit F2 to the adding unit F1.

  On the other hand, in the configuration of the present embodiment, the overflow drains 45 and 46 are provided, so that the transfer unit F2 has one end near the separation band 43 and the other end as shown in the lower part of FIG. A potential gradient is formed so that an electric charge flows.

  This potential gradient does not necessarily have an advantageous effect on the movement of charges from the transfer unit F2 to the addition unit F1, but promotes the movement of charges during the movement of charges from the imaging region E1 to the storage region E2. It is possible to apply a potential gradient, and it is possible to increase the charge transfer efficiency from the imaging region E1 to the storage region E2. When used in combination with the above-described slit region 44, the efficiency of charge transfer from the imaging region E1 to the storage region E2 is slightly reduced, but the efficiency of charge transfer from the transfer unit F2 to the addition unit F1 is increased. Therefore, it is desirable to adjust the efficiency of charge transfer by using the slit region 44 and the overflow drains 45 and 46 together.

  Since the overflow drain 15 provided in the imaging region E1 and the overflow drains 45 and 46 provided in the storage region E2 are electrically independent, they can be electrically separated so as not to affect each other. desirable. Therefore, as shown in FIG. 7, a buffer region E3 in which the overflow drains 15, 45, 46 are not provided is formed between the imaging region E1 and the storage region E2. Although the addition control electrode 41 and the transfer control electrode 42 can be provided in the buffer region E3, they may be used as a space for wiring without providing electrodes. When the addition control electrode 41 and the transfer control electrode 42 are provided, the addition control electrode 41 and the transfer control electrode 42 are formed in such a width that about 10 pieces can be provided. When used as a space for wiring, it is desirable to adopt a configuration such as a shield so that the electric field around the wiring does not affect the charge generated in the imaging region E1.

  Note that the overflow drain 15 in the imaging region E1 is used for discarding the residual charge in the photoelectric conversion unit D1 together with discarding the waste charge in the charge separation unit D2, but when the residual charge in the photoelectric conversion unit D1 is not discarded. Is omitted, and the technology similar to that of the charge holding unit D4 may be adopted for discarding the discarded charge of the charge separation unit D2. In this case, the overflow drain 15 is omitted.

  By the way, the addition unit F1 is provided to integrate the charges generated in the imaging region E1, and needs to have a larger saturation charge amount than the transfer unit F2. In addition, the charge generated by the photoelectric conversion unit D1 is transferred to the transfer unit F2, and each integrating element Py1 integrates the charge delivered from each imaging element Px. Therefore, the saturation charge amount is higher than that of each imaging element Px. Is enlarged. In order to increase the saturation charge amount, it is conceivable to increase the occupied area (volume). However, there arises a problem that the imaging element 1 is increased in size and the material cost is increased. Further, when the area occupied by the adding unit F1 is increased, the number of pixels per unit area is reduced.

Therefore, in this embodiment, in order to increase the saturation charge amount, a technique is adopted in which the impurity concentration of the addition unit F1 is higher than that of the transfer unit F2. For example, when the transfer unit F2 is an n-type, the adder F1 is an n ^{+ type} . In this case, the slit area 44 of the transfer unit F2 is set to ^{n +} -type, the slit area 44 of the adder unit F1 is the ^{n ++} type. Since the impurity concentration of the addition unit F1 is higher than that of the transfer unit F2, the potential well W1 of the addition unit F1 becomes deeper than the potential well W2 of the transfer unit F2, as shown in FIG. The amount of saturation can be increased. In addition, since only the impurity concentration is adjusted, the occupied area is not affected, and the enlargement of the image sensor 1 and the decrease in the number of pixels per unit area do not occur. The impurity is doped by, for example, diffusion.

  The storage area E2 is also provided with a horizontal transfer register Rh made up of a CCD in the same manner as the CCD image sensor, as a charge extraction unit for taking out the charge accumulated in the storage element Py to the outside of the imaging device 1. The horizontal transfer register Rh is basically used to read out the charge from the adder F1, but can also read out the charge from the transfer unit F2 as necessary. The charge transferred through the horizontal transfer register Rh is converted into a voltage corresponding to the amount of charge at an output unit provided in the image sensor 1, and is taken out of the image sensor 1 as a light reception output. Since the configuration of the horizontal transfer register Rh and the output unit is a known technique in a CCD image sensor, it is not particularly described here.

  In the configuration example described above, the portion excluding the photoelectric conversion unit D1 is covered with the light shielding film 30, but in the imaging region E1, the light shielding film 30 is formed so as to cover the separation electrode 22, the storage electrode 23, and the barrier control electrode 24. A configuration in which the charge holding portion D4 is not shielded from light may be employed. However, it is necessary to cover the entire accumulation region E2 with the light shielding film 30.

  In the configuration example described above, the potentials of the addition unit F1 and the transfer unit F2 with respect to the potential of the separation band 43 are controlled by controlling the voltage applied between the addition control electrode 41 and the transfer control electrode 42, and the addition is performed from the transfer unit F2. As shown in FIG. 8, the movement control electrode 47 is provided in the separation band 43, and together with the voltage applied to the addition control electrode 41 and the transfer control electrode 42, the movement control electrode 47 is moved to the portion F <b> 1. The movement of charges from the transfer unit F2 to the adder unit F1 may be promoted by adjusting the voltage applied to. The movement control electrode 47 is disposed on the surface of the element forming layer 11 that becomes the separation band 43 with the insulating layer 13 interposed therebetween.

  Therefore, from the state where the charge C exists in the transfer unit F2 as shown in FIG. 8B and the potential barrier B1 is formed between the transfer unit F2 and the addition unit F1, as shown in FIG. 8C. If an appropriate voltage is applied to the movement control electrode 47 so that the potentials immediately below the transfer control electrode 42, the addition control electrode 41, and the movement control electrode 47 are equal, a part of charge is transferred from the transfer unit F2 to the addition unit F1. C moves.

  Next, as shown in FIG. 8D, when the voltage applied to the transfer control electrode 42 is controlled so as to eliminate the potential well W2 formed as the transfer portion F2, the charge C is added to the addition control electrode 41 and the movement control electrode 47. When the applied voltage of the movement control electrode 47 is controlled so that the potential barrier B1 is formed immediately below the movement control electrode 47, the charge moves to the potential well W1 formed as the adding portion F1. To do. That is, the charge can be moved from the transfer unit F2 to the addition unit F1 by the procedure of FIG.

[Operation]
The operation of the image sensor 1 having the configuration shown in FIG. 1 will be described below. The basic operation is the same for other configurations in which a part of the configuration of FIG. 1 is changed, and the operation of the changed part is described in conjunction with the description of the configuration. The operation of the element 1 will be described. The charge to be used will be described as electrons.

  Now, assume that light is irradiated in a state where electrons in the well 12 are depleted. In order to deplete the electrons in the well 12, the electrons remaining in the photoelectric conversion unit D1 and the charge separation unit D2 are discarded through the overflow drain 15, and a reset voltage is applied to the reset gate electrode 28 to A channel is formed between the reset drain 17 and the electrons remaining in the charge holding portion D4 are discarded through the reset drain 17.

  Further, if the photoelectric conversion unit D1 is defined as the upstream side in the direction from the photoelectric conversion unit D1 to the charge storage unit D3 in the vertical direction Dv, the charge in the charge storage unit D3 is the photoelectric of the downstream imaging element Px aligned in the vertical direction Dv. It can be discarded through the overflow drain 15 provided adjacent to the converter D1.

  After the electrons in the well 12 are depleted, when an appropriate voltage is applied to the sensitivity control electrode 21 of the photoelectric conversion unit D1 to irradiate light in a state where a potential well for electrons is formed in the photoelectric conversion unit D1, the well 12 Among the electrons and holes generated in the element formation layer 11 including, electrons are accumulated in the potential well, and the holes are discarded through the substrate 10. That is, an amount of electrons corresponding to the amount of received light is accumulated in the potential well. A specific example of controlling the voltage applied to the sensitivity control electrode 21 will be described later.

  After the amount of electrons corresponding to the amount of received light (hereinafter, the electrons are indicated by hatched portions) is accumulated in the photoelectric conversion unit D1, first, a voltage is applied to the separation electrode 22 as shown in a period Ta in FIG. A potential well is formed in the part D2, and the electrons accumulated in the photoelectric conversion part D1 are moved to the charge separation part D2 (see FIG. 10A). That is, electrons move from the photoelectric conversion unit D1 to the charge separation unit D2. The electrons moved to the charge separation part D2 apply an appropriate voltage to the transfer gate electrode 29 to form a channel between the charge separation part D2 and the holding well 14 and move to the charge holding part D4. (See FIG. 10B).

In other words, the n ^{++ type} holding well 14 surrounded by the n type well 12 has a higher potential than the well 12 (lower potential for electrons), and the potential is higher in the charge holding unit D4 than in the charge separation unit D2. Is higher. Therefore, when a channel is formed by applying an appropriate voltage to the transfer gate electrode 29, electrons move from the charge separation unit D 2 toward the charge holding unit D 4, and electrons flow into the holding well 14.

  As electrons flow into the holding well 14, the potential of the holding well 14 decreases, and the potential of the barrier control electrode 24 electrically connected to the holding well 14 decreases (see FIG. 10D). That is, a potential barrier is formed immediately below the barrier control electrode 24. Further, since a part of the charges accumulated in the holding well 14 moves to the barrier control electrode 24, a potential barrier having a height corresponding to the amount of the moved charge is formed immediately below the barrier control electrode 24.

  Note that, during the period Ta, no voltage is applied to the storage electrode 23 so that electrons are not accumulated in the charge storage portion D3. Whether to apply a voltage to the transfer gate electrode 29 after applying a voltage to the separation electrode 22 or to apply a voltage to the separation electrode 22 and the transfer gate electrode 29 at the same time can be appropriately selected.

  When electrons move to the charge holding unit D4, the voltage application to the transfer gate electrode 29 is stopped to hold the electrons in the charge holding unit D4 as in the period Tb, and further, the overflow drain 15 is controlled to control the charge separation unit D2. Are discarded (see FIGS. 10B and 10C). When discarding electrons, if the voltage application to the separation electrode 22 is stopped, the electrons can be discarded quickly.

  The light received by the photoelectric conversion unit D1 in the above-described operation is incident not for obtaining a light reception output corresponding to the amount of received light but for determining the height of the potential barrier immediately below the barrier control electrode 24. The operation after the potential barrier height is determined by the above-described operation is an operation for actually obtaining a light reception output.

  Before receiving the light for obtaining the light reception output, as in the period Tc, first, electrons in the portion of the well 12 excluding the charge holding portion D4 are depleted through the overflow drain 15, and the photoelectric conversion portion D1 and the charge separation are separated. Electrons are removed from the part D2 (see FIG. 10C).

  When electrons corresponding to the amount of received light are integrated in the photoelectric conversion unit D1, a potential barrier B2 is formed immediately below the barrier control electrode 24 as shown in FIG. After accumulating electrons according to the amount of received light in the photoelectric conversion unit D1, an appropriate voltage is applied to the separation electrode 22 to form a potential well for electrons in the charge separation unit D2 and the sensitivity control electrode as in the period Td. By controlling the voltage applied to 21, electrons are moved from the photoelectric conversion unit D1 to the charge separation unit D2 (see FIG. 10A). That is, as shown in FIG. 11B, electrons move to the charge separation unit D2.

  Thereafter, when the voltage application to the separation electrode 22 is stopped in a state where a suitable voltage is applied to the storage electrode 23 and the potential well is formed in the charge storage portion D3 as in the period Te, as shown in FIG. In addition, a certain amount of electrons determined by the height of the potential barrier formed immediately below the barrier control electrode 24 and the size of the charge separation portion D2 are left as unnecessary charges in the charge separation portion D2, and the potential barrier is separated from the charge separation portion D2. The charge exceeding the value flows into the charge storage portion D3 (see FIG. 10E). However, before the voltage application to the separation electrode 22 is stopped, sensitivity control is performed so that a potential barrier higher than the potential barrier immediately below the barrier control electrode 24 is formed between the charge separation unit D2 and the photoelectric conversion unit D1. The voltage applied to the electrode 21 is controlled.

  By the above-described operation, a certain amount of electrons are separated as unnecessary charges from the accumulated electrons according to the amount of light received by the photoelectric conversion unit D1, and the remaining charges obtained by separating the unnecessary charges are charged as effective charges. Accumulated in the accumulation unit D3.

  After the effective charge is accumulated in the charge accumulation unit D3, unnecessary charges remaining in the charge separation unit D2 are discarded from the overflow drain 15 and the charges held in the charge holding unit D4 are discarded as in the period Tf. Therefore, an appropriate voltage is applied to the reset gate electrode 28 to form a channel between the holding well 14 and the reset drain 17, and after the electrons in the holding well 14 are discarded, the voltage to the reset gate electrode 28 is The application is stopped (see FIGS. 10C and 10F). Thereafter, the charge accumulated in the charge accumulation unit D3 is taken out of the imaging device as a light reception output.

  By the series of operations described above, a light reception output corresponding to an image of one frame is obtained. Here, in the above-described operation, electrons in the holding well 14 are discarded every frame, but it is also possible to perform an operation in which electrons in the holding well 14 are discarded every plural frames. However, in this case, since the potential barrier B2 is formed immediately below the barrier control electrode 24, the voltage applied to the separation electrode 22 and the storage electrode 23 is adjusted so that electrons can move before and after the potential barrier B2. There is a need to.

  Incidentally, as described above, it is necessary to move electrons from the charge separation unit D2 to the charge holding unit D4. Since the overflow drain 15 has a function of discarding unnecessary charges from the charge separation part D2, the potential of the overflow drain 15 is set higher than the potential of the charge separation part D2 (lower than electrons). That is, the potential gradient around the charge separation unit D2 is inclined in the direction in which electrons flow from the charge separation unit D2 to the charge holding unit D4, and the efficiency of electron transfer from the charge separation unit D2 to the charge holding unit D4 is increased. Can be increased.

  In the imaging element Px, as described above, unnecessary charges are separated and the remaining charges are accumulated in the charge accumulation unit D3 as effective charges. By the above-described operation, effective charges are accumulated in the charge accumulation unit D3 in each imaging element Px in the imaging region E1. Effective charges are transferred to the accumulation region E2. In transferring the effective charge, the same operation as that of the FT type CCD image sensor is performed. That is, since the sensitivity control electrode 21, the separation electrode 22, the storage electrode 23, the barrier control electrode 24, and the transfer control electrode 42 are formed in the same shape and the same size, the timing of applying a voltage to these electrodes is controlled. Thus, the effective charge can be transferred to the storage region E2 as in the CCD image sensor.

  The effective charges generated in the imaging area E1 are transferred to the transfer unit F2 in the accumulation area E2. Here, a case where each imaging element Px in the imaging region E1 and each storage element Py in the storage region E2 are associated one-to-one is illustrated, so that the effective charges generated in each imaging element Px are It is transferred to the transfer unit F2 of the storage element Py associated with the imaging element Px.

  As described in the configuration, since the potential barrier B1 is formed between the transfer unit F2 and the addition unit F1, the effective charge is transferred to the addition unit F1 when the effective charge is transferred to the transfer unit F2. Never get in. Next, in order to move the effective charge transferred to the transfer unit F2 to the addition unit F1, the relationship between the applied voltages of the addition control electrode 41 and the transfer control electrode 42 is controlled. When the movement control electrode 47 is provided, the voltage applied to the movement control electrode 47 is also controlled. By such voltage control, effective charges can be moved from the transfer unit F2 to the addition unit F1.

  By the way, the present invention does not take out the effective charge to the outside of the image sensor 1 every time the effective charge is transferred from the imaging region E1 to the storage region E2, but integrates the effective charge during a plurality of times of transfer. An adder F1 is provided in order to extract the subsequent charges to the outside of the image sensor 1. That is, the effective charge transferred from the imaging region E1 to the transfer unit F2 is moved to the addition unit F1 for each transfer, and the charge of the addition unit F1 is held while the transfer is performed a plurality of times. By this operation, the addition unit F1 of each storage element Py adds the effective charges for a plurality of times transferred from the imaging region E1 to the storage region E2, and adds even when the amount of effective charges transferred at a time is small. The amount of charge can be increased by accumulating effective charges in the part F1. That is, it is substantially sensitized.

  The number of times of accumulation in the adder F1 is set appropriately. After accumulating the effective charge for the set number of times, the charge is transferred from the adder F1 to the horizontal transfer register Rh and taken out of the imaging device 1. It is.

[Detection device for spatial information]
In the following, as an application example using the above-described imaging device 1, a detection device that detects the presence or absence of an object in the imaging space (that is, the target space) and the reflectance of the object, and the distance to the object existing in the imaging space are measured. The example which uses the image pick-up element mentioned above for the detection apparatus to perform is shown. The spatial information detection device described below is an active detection device using a light emitting source 2 that projects light into a target space, as shown in FIG. 12, and images the target space with the imaging element 1 described above. The light receiving output of the image sensor 1 is given to the signal processing unit 3 and the calculation described later is performed to determine the amount of reflected light from the object or the distance to the object 5 existing in the target space. Further, the control unit 4 controls the operation timing of the image sensor 1 and the light source 2. The control unit 4 also instructs the signal processing unit 3 to calculate timing.

  The light emission source 2 is configured by arranging a plurality of infrared light emitting diodes in parallel, and light from the target space is incident on the image sensor 1 through an infrared transmission filter. That is, by using infrared rays as light used for distance measurement, it is possible to suppress the light in the visible light region from entering the imaging element 1. The signal processing unit 3 and the control unit 4 are configured by a microcomputer that executes an appropriate program.

  In order to obtain the presence / absence of the object 5 and the reflectance (intensity detection operation), as shown in FIG. 13A, a lighting period T1 for turning on the light source 2 and a turning-off period T2 for turning off the light source 2 are provided. The difference between the received light amount and the received light amount in the extinguishing period T2 is obtained. The intensity-modulated light from the light source 2 is modulated with a rectangular wave.

  As shown in FIG. 13 (b), the signal light projected from the light source 2 and reflected by the object 5 and the ambient light existing in the target space are incident on the image sensor 1 and turned off. Only ambient light is incident on the image sensor 1 during the period T2. Therefore, when the difference (C0−C2) between the received light amount C0 in the lighting period T1 and the received light amount C2 in the extinguishing period T2 is obtained, the influence of the ambient light is removed and the degree of reflection of the light on the object 5 is evaluated. Can do.

  If the distance to the object 5 is constant, the reflectance of the object 5 with respect to the wavelength of the projected light can be obtained by the difference in the amount of received light. Since the reflectance depends on the wavelength of the projected light, if the wavelength of the light projected from the light source 2 to the target space is made variable, it is also possible to obtain the reflectance characteristics with respect to the wavelength. Further, since the difference (C0−C2) between the received light amount C2 in the extinguishing period T2 in which only the ambient light exists and the received light amount C0 in the lighting period T1 in which the signal light exists in addition to the ambient light is obtained, the difference is defined. It is also possible to determine that the object 5 that reflects light is present in the region above the threshold value.

  On the other hand, for distance measurement (distance measurement operation), light whose intensity is modulated from the light source 2 (intensity modulated light) is projected onto the target space, reflected by the object 5 existing in the target space, and incident on the image sensor 1. A technique is used in which a phase difference between the phase of the intensity change of the light and the phase of the intensity change of the light from the light source 2 is obtained, and this phase difference is converted into a distance. That is, intensity-modulated light is projected from the light source 2 into the target space as shown in FIG. 14A, and the intensity of light incident on one imaging element Px of the imaging device 1 changes as shown in FIG. If this is the case, the time difference Δt of the same phase reflects the distance L to the object 5. Therefore, when the light speed is c [m / s] and the time difference Δt [s] is used, the distance L to the object 5 is Is represented by L = c · Δt / 2. If the frequency of the modulation signal that modulates the intensity of light is f [Hz] and the phase difference is φ [rad], the time difference Δt is Δt = φ / 2πf. Can be requested.

This phase difference φ may be regarded as a phase difference between the modulation signal for driving the light source 2 and the incident light to the imaging element 1 (each imaging element Px). Accordingly, it is conceivable that the light reception intensity of the incident light to the image sensor 1 is obtained for a plurality of different phases of the modulation signal, and the phase difference φ between the incident light and the modulation signal is obtained from the relationship between the obtained phases and the light reception intensity. Yes. In practice, the image sensor 1 detects the amount of received light for each phase section having a predetermined phase width (time width), and uses the received light output corresponding to this received light amount for the calculation of the phase difference φ. If each phase interval is 90 degrees, four phase intervals with equal phase intervals are periodically obtained for one cycle of the modulation signal. By using the received light amounts A0 to A3 of each phase interval, the phase difference φ is , Φ = tan ⁻¹ {(A0−A2) / (A1−A3)}. Note that the sign of the phase difference φ changes depending on which phase of the modulation signal the received light amounts A0 to A3 correspond to. In the example shown in FIG. 14, each phase section is set to a phase width of 90 degrees, but the phase width can be set as appropriate.

  In order to perform the above calculation, it is necessary to generate electrons corresponding to the amount of received light for each phase interval of the modulation signal by the photoelectric conversion unit D1. In order to obtain the amount of received light for each phase section, the voltage applied to the sensitivity control electrode 21 is controlled in synchronization with the modulation signal.

  This operation will be described. The control unit 4 can control whether or not a voltage is applied to each sensitivity control electrode 21, and a potential well is formed immediately below the sensitivity control electrode 21 to which a voltage is applied. That is, by applying a voltage to the adjacent sensitivity control electrodes D1, the opening area corresponding to the number of sensitivity control electrodes 21 to which the voltage is applied (opening area along the main surface of the element formation layer 11) is set. A potential well is formed.

  Since the electrons generated in the photoelectric conversion unit D1 are accumulated in the potential well, the larger the opening area of the potential well (that is, the volume of the potential well), the higher the efficiency of accumulating electrons. Conversely, when a voltage is applied to only one sensitivity control electrode 21, the efficiency of collecting electrons is reduced, and electrons already accumulated in the potential well can be retained. Of course, even when a voltage is applied to only one sensitivity control electrode 21 and electrons are held, electrons are accumulated in the potential well, but a voltage is applied to a plurality of sensitivity control electrodes 21. Since the integration efficiency of electrons is lower than in the case, the amount of accumulated electrons reflects the amount of received light during the period in which voltages are applied to the plurality of sensitivity control electrodes 21. In addition, if the sensitivity control electrode 21 that forms a potential well for holding electrons is shielded from light, accumulation of electrons during a period of holding charges can be suppressed.

  As is clear from the above-described operation, in the photoelectric conversion unit D1, in order to accumulate electrons corresponding to the amount of received light in a specific phase section of the modulation signal, the number of sensitivity control electrodes 21 to which a voltage is applied in the phase section is determined. In many other phases, it is only necessary to hold electrons by applying a voltage to only one sensitivity control electrode 21. The control unit 4 changes the voltage application pattern to the sensitivity control electrode 21 with time. For example, by applying a voltage to the plurality of sensitivity control electrodes 21 in the same section of each period of the modulation signal, an operation of accumulating electrons generated in the section over a plurality of periods is possible. In this operation, even when the amount of received light obtained in one phase period of the modulation signal is small, the amount of electrons can be increased by accumulating electrons in the photoelectric conversion unit D1. Of course, when the received light intensity is high, it is easy to saturate if electrons are accumulated. Therefore, whether or not to accumulate electrons is appropriately determined according to the use environment.

  The signal processing unit 3 uses the received light output corresponding to each phase section for each imaging element Px, obtains the phase difference by the above-described calculation, and measures the distance for each imaging element Px. That is, a distance image with the pixel value of each imaging element Px as a distance is generated.

  By the way, in order to measure the distance based on the above-described principle, it is only necessary to detect only the signal light projected from the light emission source 2 to the target space by the image sensor 1, and the distance measurement accuracy increases as the amount of received light of the signal light increases. It is considered possible. However, not only the signal light but also the ambient light that is present in the surroundings is always incident on the image sensor 1. In addition, there is an upper limit in the range in which the amount of electrons generated in the image sensor 1 changes in accordance with the amount of received light. When the amount of received light increases, the amount of generated electrons is saturated, and the received light output reflects the amount of received light. Disappear. Therefore, it is necessary to increase the amount of electrons corresponding to the signal light while suppressing the saturation of the image sensor 1.

  Since the above-described imaging device 1 has a function of weighing and discarding unnecessary charges corresponding to the amount of electrons held in the charge holding unit D4, the amount of unnecessary charges to be weighed is the amount of ambient light received. , It is possible to increase the ratio of the amount of electrons corresponding to the signal light included in the electrons stored in the charge storage unit D3 with respect to the ratio of the component of the signal light included in the received light amount. In addition, since some of the electrons generated in the photoelectric conversion unit D1 are discarded as unnecessary charges, the possibility that the electrons accumulated in the charge accumulation unit D3 are saturated can be reduced.

  Based on such knowledge, an environment measurement period in which the light source 2 is turned off and an information detection period in which intensity modulated light is projected from the light source 2 are provided to intermittently project the light into the target space. Yes. In the environmental measurement period, electrons generated in the photoelectric conversion unit D1 are held in the charge holding unit D4, whereby an amount of electrons reflecting the intensity of the ambient light is held in the charge holding unit D4, and the charge separation unit D2 The amount of unnecessary charge to be weighed is related to the intensity of ambient light.

  On the other hand, in the information detection period, since a potential barrier corresponding to the amount of received light in the environment measurement period is formed immediately below the barrier control electrode 24, the amount of received ambient light is reflected among the electrons generated in the photoelectric conversion unit D1. It is possible to accumulate the remaining amount of unnecessary electric charge that is weighed and accumulated in the charge accumulating unit D3. Here, the amount of charge weighed as an unnecessary charge is not necessarily proportional to the amount of ambient light received, but changes according to the amount of ambient light received. The amount of unnecessary charge also changes. Therefore, even if the ambient light fluctuates, the ratio of the component corresponding to the signal light in the charge accumulated in the charge accumulation unit D3 can be kept high. That is, by separating unnecessary charges from charges generated by the photoelectric conversion unit D1 during the information detection period of the light emitting source 2, the signal-to-noise ratio can be increased while leaving information on the signal light component.

  As described above, when the amount of electrons generated by the photoelectric conversion unit D1 is small in one cycle of the modulation signal, the electrons are accumulated by integrating the electrons in the photoelectric conversion unit D1 over a plurality of cycles of the modulation signal. However, electrons may be saturated in the photoelectric conversion unit D1. Therefore, instead of immediately reading out the charge accumulated in the charge accumulating unit D3 as a light receiving output, the charge separating unit D2 accumulates electrons in the charge accumulating unit D3 while performing the operation of measuring unnecessary charges a plurality of times, thereby It is also possible to employ a technique for accumulating.

  The electrons accumulated in the charge accumulation unit D3 are the electrons of the ambient light component received as in the case where the electrons are accumulated in the photoelectric conversion unit D1, since unnecessary charges are removed from the electrons generated in the photoelectric conversion unit D1. As compared with the case of accumulating, saturation is less likely to occur because the amount of electrons is small. In addition, as described above, since the ratio of the signal light component to the total charge amount is large, the rate of change of the charge amount with respect to the change of the signal light component is increased, and the distance measurement accuracy is increased accordingly.

  The control unit 4 discards unnecessary charges from the charge separation unit D2 through the overflow drain 15 after electrons flow into the charge storage unit D3. This operation is performed every time electrons are caused to flow into the charge storage portion D3. When the amount of electrons held in the charge holding unit D4 is updated, a voltage is applied to the reset gate electrode 28, and the electrons held in the holding well 14 are discarded from the reset drain 17. The timing at which the electrons in the charge holding unit D4 are discarded may be set to a timing at which ambient light is considered to fluctuate, and may be set as appropriate according to the usage environment. it can. That is, the height of the potential barrier may be adjusted for each frame of the distance image. The unnecessary charge is discarded every time the electrons flow into the charge storage unit D3, but the electrons after being moved to the charge holding unit D4 in the charge separation unit D2 also when shifting from the information detection period to the environment measurement period. Therefore, the electrons in the charge separation part D2 are discarded through the overflow drain 15 before the environmental measurement period.

  In each of the above-described operation examples, the number of the imaging elements Px and the storage elements Py associated with each other has a one-to-one or one-to-two relationship, and when the imaging elements Px and the storage elements Py are paired, a pair of two. However, these numbers are merely examples, and the numbers can be appropriately selected.

  In the configuration example described above, an example in which one photoelectric conversion unit D1 is associated with one imaging element Px is shown. However, a configuration in which one photoelectric conversion unit D1 functions as a plurality of imaging elements Px. Can also be adopted. Hereinafter, an example in which one photoelectric conversion unit D1 functions as two imaging elements Px will be described. As described above, since the six sensitivity control electrodes 21 are provided in the photoelectric conversion unit D1, three sensitivity control electrodes 21 can be used as one imaging element Px as shown in FIG. It is.

  Since the sensitivity control electrode 21 is disposed in the well 12 via the insulating layer 13 (see FIG. 3 and the like), the potential wells Wa and Wb can be formed by applying a voltage to the sensitivity control electrode 21. In the illustrated example, a voltage is applied to the sensitivity control electrode 21 so that the opening area of the potential well Wa along the main surface of the well 12 is larger than the potential well Wb and the potential well Wa is deeper than the potential well Wb. is doing. Since the potential well Wa has a large opening area and is deep, the potential well Wa has a larger volume than the potential well Wb, and more charges (electrons e) generated by light irradiation are accumulated than the potential well Wb. On the other hand, in the potential well Wb, the accumulation rate of charges (electrons e) generated by light irradiation is lower than that in the potential well Wa, and charges are held. In the illustrated example, the potential well Wb is shallower than the potential well Wa, but charge accumulation and retention are relatively performed even when both are at the same depth. That is, charge accumulation and retention can be performed by changing the opening areas of the potential wells Wa and Wb. The charge is transferred and transferred from the imaging area E1 to the accumulation area E2 after repeating the accumulation and holding of the charges for each imaging element Px a plurality of times.

  By the way, in the example shown in FIG. 15, as described above, two imaging elements Px each including three sensitivity control electrodes 21 are formed in one photoelectric conversion unit D1. In the following example, two imaging elements Px provided in one photoelectric conversion unit D1 are used as a set. Further, in order to distinguish each sensitivity control electrode 21, each sensitivity control electrode 21 is distinguished by being given the numbers (1) to (6). That is, one of the two imaging elements Px in the set includes sensitivity control electrodes (1) to (3), and the other includes sensitivity control electrodes (4) to (6).

  In order to change the opening area of the potential wells Wa and Wb, the number of sensitivity control electrodes 21 to which a voltage is applied is changed. In the illustrated example, a potential well Wa is formed by applying a voltage to three sensitivity control electrodes 21 of one imaging element Px, and a voltage is applied to the central sensitivity control electrode 21 of one imaging element Px. The potential well Wb is formed by application. Further, the voltage applied to the sensitivity control electrode 21 when forming the potential well Wb is smaller than the voltage applied to the sensitivity control electrode 21 when forming the potential well Wa.

  Therefore, in the specific phase section of the intensity-modulated light, as shown in FIG. 15A, in the imaging element Px including the sensitivity control electrodes (1) to (3), the three sensitivity control electrodes (1) to (3) are used. ) To form a potential well Wa that accumulates charges by applying a control voltage that is the same voltage to all of the above), and in the imaging element Px including the sensitivity control electrodes (4) to (6), the central sensitivity control electrode (5) Only a voltage is applied to form a potential well Wb that holds charges. Further, in another phase section, as shown in FIG. 15B, in the imaging element Px including the sensitivity control electrodes (1) to (3), a voltage is applied only to the central sensitivity control electrode (2) to charge the image. In the imaging element Px including the sensitivity control electrodes (4) to (6), a control voltage that is the same voltage is applied to all three sensitivity control electrodes (4) to (6). Thus, a potential well Wa for accumulating charges is formed.

  By repeating the operations of FIG. 15A and FIG. 15B, charge accumulation and holding can be repeated for two different phase sections. For example, the states of FIG. 15A and FIG. 15B are alternately repeated in association with the two phase sections of the phase section corresponding to the received light quantity A0 and the phase section corresponding to the received light quantity A2. Thus, an electric charge corresponding to the received light amount A0 is generated by the imaging element Px including the sensitivity control electrodes (1) to (3), and the received light amount A2 is corresponding to the imaging element Px including the sensitivity control electrodes (4) to (6). Can be generated.

  As can be seen from the above-described operation, if twelve sensitivity control electrodes 21 are used, it is possible to generate charges in four phase sections. In short, by changing the opening area of the potential well using the sensitivity control electrode 21, it is possible to generate charges and hold charges. This operation is also used in each operation example. Here, even when the charge is held in the potential well Wb, the charge generated by light irradiation is accumulated in the potential well Wb. However, the influence of the charge during this period is removed by the calculation when detecting spatial information. The

It is a schematic front view which shows embodiment of this invention. It is a front view which shows the structure of the image pick-up element used for the same as the above. It is the sectional view on the AA line of FIG. FIG. 3 is a sectional view taken along line B-B in FIG. 2. The structural example which provided the isolation | separation band in the same as the above is shown, (a) is operation | movement explanatory drawing, (b) (c) is principal part sectional drawing. The structural example which provided the slit area | region in the same as the above is shown, (a) is principal part sectional drawing, (b) (c) is operation | movement explanatory drawing. It is operation | movement explanatory drawing of the overflow drain in the same as the above. It is a front view which shows the other structural example same as the above. It is a front view which shows the other structural example. It is operation | movement explanatory drawing which shows the operation | movement timing of each part same as the above. It is operation | movement explanatory drawing which shows the change of the potential in the same as the above. It is a block diagram which shows the detection apparatus of the spatial information using the same as the above. It is operation | movement explanatory drawing of the intensity | strength detection operation | movement by the structural example of FIG. It is operation | movement explanatory drawing of the distance measurement operation | movement by the structural example of FIG. It is operation | movement explanatory drawing which shows the operation | movement which performs accumulation | storage and holding | maintenance of an electric charge using a potential well.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up element 10 Substrate 11 Element formation layer 12 Well 13 Insulating layer 14 Holding well 15 (3rd) overflow drain 21 Sensitivity control electrode 22 Separation electrode 23 Storage electrode 24 Barrier control electrode 30 Light shielding film 41 Addition control electrode 42 Transfer Control electrode 43 Separation band 44 Slit region 45 (First) overflow drain 46 (Second) overflow drain 47 Movement control electrode B1 Potential barrier B2 Potential barrier D1 Photoelectric conversion unit D2 Charge separation unit D3 Charge storage unit D4 Charge holding unit E1 Imaging region E2 Storage region E3 Buffer region F1 Adder F2 Transfer unit F3 Charge weighing unit L Main row Px Imaging element Py Storage element Py1 Integration element Py2 Transfer element

Claims (12)

  An imaging region in which a plurality of imaging elements each having a photoelectric conversion unit that generates charges by light irradiation are arranged, and charges generated in the imaging region are transferred at a specified timing, and each of the imaging elements is stored in a light-shielded manner. A storage area in which a plurality of storage elements are arranged is provided on a semiconductor, and each storage element is generated for each image pickup element because the amount of saturation charge is larger than that of the image pickup element and the charge received from the image pickup area is delivered multiple times. An image pickup device comprising an addition unit for integrating electric charges.   The image pickup device according to claim 1, wherein the image pickup region and the storage region are formed in different regions adjacent to each other on the semiconductor.   2. The storage element according to claim 1, further comprising: a transfer unit that receives charges transferred from the imaging region, and transfers the charges received from the imaging region by the transfer unit to the adding unit to perform charge integration. The imaging device according to claim 2.   A plurality of basic units each including a plurality of the imaging elements and the storage elements are arranged on the semiconductor, and the imaging elements and the storage elements are each arranged on the semiconductor via an insulating layer. A plurality of control electrodes, and by controlling the voltage applied to the control electrodes, charge transfer from the imaging region to the storage region is performed, and the transfer unit and the addition unit are arranged in a relationship facing each other. In the basic unit, the control electrode provided in the imaging element and the control electrode provided in the transfer unit are arranged on a straight line in the first direction in which the imaging region and the storage region are arranged, and are added to the control electrode provided in the transfer unit. The image pickup device according to claim 3, wherein the control electrode provided in the section is arranged on a straight line in a second direction intersecting the first direction.   The imaging region further includes a charge holding unit that determines an amount of unnecessary charges to be removed from the charge generated by the photoelectric conversion unit, and the charge holding unit and the addition unit are arranged in a row in the first direction. The image sensor according to claim 4.   A separation band is formed between the transfer unit and the addition unit, the transfer unit has a transfer control electrode arranged on the main surface of the semiconductor, and the addition unit has an addition control electrode arranged on the main surface of the semiconductor 4. The height of the potential barrier in the separation band is controlled by controlling the voltage applied to the transfer control electrode and the addition control electrode, and the charge transfer between the transfer unit and the addition unit is controlled. The imaging device according to claim 5.   A separation band is formed between the transfer unit and the addition unit, the transfer unit has a transfer control electrode arranged on the main surface of the semiconductor, and the addition unit has an addition control electrode arranged on the main surface of the semiconductor Furthermore, a movement control electrode that controls the height of the potential barrier of the separation band between the transfer control electrode and the addition control electrode on the main surface of the semiconductor, and controls the charge transfer between the transfer part and the addition part. The image pickup device according to claim 3, wherein the image pickup device is arranged.   The image pickup device according to claim 3, wherein the adding unit has an impurity concentration higher than that of the transfer unit.   8. The image pickup device according to claim 6, wherein a slit region having an impurity concentration higher than that of the transfer unit and the addition unit is provided between the transfer unit and the addition unit. 9.   A first slit region formed between the transfer unit and the separation band and having a higher impurity concentration than the transfer unit, and an impurity concentration formed between the addition unit and the separation band and having an impurity concentration higher than that of the addition unit. The image pickup device according to claim 6, further comprising at least one of the second slit region having a high concentration.   2. The storage area according to claim 1, wherein a first overflow drain adjacent to the addition unit and a second overflow drain adjacent to the transfer unit are formed on both sides of the storage element. The imaging device according to any one of claims 3 to 10.   A third overflow drain adjacent to the photoelectric conversion unit is provided in the imaging region, and a buffer region without an overflow drain is formed between the imaging region and the accumulation region. Item 12. The imaging device according to Item 11.

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