WO2024218009A1

WO2024218009A1 - Cmos sensor and method for processing detection signals, computer program and computer-readable data carrier

Info

Publication number: WO2024218009A1
Application number: PCT/EP2024/060011
Authority: WO
Inventors: Joel Bertomeu Mestre; Rafael Serrano-Gotarredona; Jose Manuel Garcia
Original assignee: Ams Sensors Belgium BV
Current assignee: Ams Sensors Belgium BV
Priority date: 2023-04-18
Filing date: 2024-04-12
Publication date: 2024-10-24
Anticipated expiration: 2025-10-18

Abstract

A CMOS sensor (10) comprises a plurality of pixels (100), each of the pixels (100) comprising a photodiode (111, 112) and a switch (114, 115), the photodiodes (111, 112) being arranged in rows and columns, respectively. The CMOS sensor (10) further comprises a processing circuit (105) for activating the switches (114, 115). The processing circuit (105) is configured to simultaneously bias a first photodiode (111) and a second photodiode (112) to accomplish readout, to obtain a first readout result. The processing circuit (105) is further configured to bias the first photodiode (111) to accomplish readout while the second photodiode (112) is not biased to accomplish readout, to obtain a second readout result. The processing circuit is further configured to bias the second photodiode (112) to accomplish readout while the first photodiode (111) is not biased to accomplish readout, to obtain a third readout result. The processing circuit (105) further is configured to determine a spatial distribution of incoming photons on the basis of a difference between the first readout result and the second readout result and a difference between the first readout result and the third readout result.

Description

CMOS SENSOR AND METHOD FOR PROCESSING DETECTION SIGNALS , COMPUTER PROGRAM AND COMPUTER-READABLE DATA CARRIER

SUMMARY

The present disclosure relates to a CMOS sensor and to a method for processing detection signals .

CMOS image sensors are widely used in a variety of applications . Generally, CMOS sensors comprise an array of pixels , each comprising a photodiode and a readout circuit . Attempts are being made to improve the performance of CMOS sensors .

It is an obj ect of the present invention to provide an improved CMOS sensor and an improved method for processing detection signals .

According to embodiments , the above obj ect is achieved by the claimed matter according to the independent claims . Further developments are defined in the dependent claims .

A CMOS sensor comprises a plurality of pixels , each of the pixels comprising a photodiode and a switch for connecting and disconnecting the photodiode to a readout circuit . The photodiodes are arranged in rows and columns . The CMOS sensor further comprises a processing circuit for activating the switches . The proces sing circuit is configured to simultaneously bias a first photodiode and a second photodiode to accomplish readout , the first photodiode and the second photodiode being arranged in one row and adj acent columns , respectively, or in one column and adj acent rows , respectively, or in adj acent columns and adj acent rows , respectively, to obtain a first readout result . The processing circuit is further configured to bias the first photodiode to accomplish readout while the second photodiode is not biased to accomplish readout , to obtain a second readout result and to bias the second photodiode to accomplish readout while the first photodiode is not biased to accomplish readout , to obtain a third readout result . The processing circuit is further configured to determine a spatial distribution of incoming photons on the basi s of a di f ference between the first readout result and the second readout result and a di f ference between the first readout result and the third readout result .

Further embodiments are directed to a method for processing detection signals of pixels comprising a photodiode , the photodiodes being arranged in rows and columns . The method comprises simultaneously biasing a first photodiode and a second photodiode to accomplish readout , the first photodiode and the second photodiode being arranged in one row and adj acent columns , respectively, or in one column and adj acent rows , respectively, or in adj acent columns and adj acent rows , respectively, to obtain a first readout result . The method further comprises biasing the first photodiode to accomplish readout while the second photodiode is not biased to accomplish readout , to obtain a second readout result and biasing the second photodiode to accomplish readout while the first photodiode is not biased to accomplish readout , to obtain a third readout result . The method further comprises determining a spatial distribution of incoming photons on the basis of a di f ference between the first readout result and the second readout result and a di f ference between the first readout result and the third readout result .

For example , according to a first readout pattern the first and the second photodiode are arranged in one row and adj acent columns , respectively .

The method may further comprise repeating the method using a second readout pattern di f ferent from the first readout pattern . For example , according to the second readout pattern the first and the second photodiode are arranged in adj acent rows and in adj acent columns , respectively .

The method may further comprise repeating the method using a third readout pattern .

For example , according to the third readout pattern the first and second photodiode are arranged in one column and in di f ferent rows , respectively .

According to embodiments , a computer program comprises instructions which, when the program is executed by a computer, cause the computer to carry out the method as explained above .

Further embodiments relate to a computer-readable data carrier having stored thereon the computer program as described above .

According to embodiments , an electronic device may comprise the CMOS sensor as described above .

For example , the electronic device may be selected from an image sensor, an X-ray medical imaging apparatus and an imaging apparatus for non-destructive testing .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this speci fication . The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles . Other embodiments of the invention and many of the intended advantages will be readily appreciated, as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numbers designate corresponding similar parts.

Fig. 1A shows a general pattern of generated charge carriers.

Fig. IB shows a further pattern of generated charge carriers.

Fig. 1C shows a further example of a pattern of generated charge carriers .

Fig. 2A shows elements of a pixel of a CMOS sensor according to embodiments .

Fig. 2B shows a schematic top view of a CMOS sensor according to embodiments .

Fig. 3A shows an arrangement of pixels.

Fig. 3B shows a potential distribution along a row direction according to implementations.

Fig. 3C shows a potential distribution along the row direction according to embodiments.

Fig. 4A shows a readout pattern according to embodiments.

Fig. 4B shows a readout pattern according to embodiments.

Fig. 4C shows a readout pattern that may be used according to embodiments .

Fig. 5 summarizes a method according to embodiments. Fig. 6 shows an electronic device according to embodiments.

DETAILED DESCRIPTION

In the following detailed description reference is made to the accompanying drawings, which form a part hereof and in which are illustrated by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "over", "on", "above", "leading", "trailing" etc. is used with reference to the orientation of the Figures being described. Since components of embodiments of the invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope defined by the claims.

The description of the embodiments is not limiting. In particular, elements of the embodiments described hereinafter may be combined with elements of different embodiments.

The terms "lateral" and "horizontal" as used in this specification intends to describe an orientation parallel to a first surface of a substrate or semiconductor body. This can be for instance the surface of a wafer or a die.

The term "vertical" as used in this specification intends to describe an orientation which is arranged perpendicular to the first surface of a substrate or semiconductor body.

As employed in this specification, the terms "coupled" and/or

"electrically coupled" are not meant to mean that the elements must be directly coupled together - intervening elements may be provided between the "coupled" or "electrically coupled" elements . The term "electrically connected" may describe a low- ohmic electric connection between the elements electrically connected together .

The term "electrically connected" further comprises tunneling contacts between connected elements .

The present disclosure relates to a CMOS sensor that may be e . g . employed for X-ray imagers in medical applications or non-de- structive testing . The CMOS sensor may be employed in applications , in which it is possible that charge carriers which are generated by incoming photons may be exchanged between adj acent pixels .

Fig . 1A shows an example of a distribution of charge carriers 107 between adj acent photodiodes 111 , 112 . As will be illustrated below with reference to Fig . 2A, a voltage may be applied between a cathode contact and an anode terminal of a photodiode 111 , 112 , in order to collect charges . The anode terminals of the photodiodes are connected to a ground terminal . Accordingly, a voltage is applied to the cathode contact or cathode terminal of the photodiodes . Fig . 1A shows a first cathode contact 1111 which is assigned to the first photodiode 111 , and a second cathode contact 1112 which is assigned to the second photodiode 112 .

As is shown in Fig . 1A, the cathode contacts 1111 , 1112 may be arranged at a distance d which may be in the range of the recombination length of the charge carriers 107 during li fetime . According to embodiments , a distance between adj acent cathode contacts 1111 , 1112 is larger than ( 0 . 8 x the recombination length) and smaller than ( 1 . 5 x the recombination length) . For example , according to the example illustrated in Figs . 1A to 1C, the distance may be 50 pm . Further, there is no speci fic or only a small guard ring that suppresses di f fusion of charge carriers 107 to neighbouring cathode contacts 1111 , 1112 . Accordingly, the charge carriers 107 may di f fuse to neighbouring cathode contacts 1111 , 1112 .

According to the example of Fig . 1A, the charge carriers 107 may be uni formly distributed . The charge carriers 107 which are present in the intermediate zone 108 between the first cathode contact 1111 and the second cathode contact 1112 may be attracted by the first cathode contact 1111 or the second cathode contact 1112 . Accordingly, the first and the second cathode contacts 1111 , 1112 compete for the charge carriers 107 present in the intermediate zone 108 . For example , each of the first and the second cathode contacts 1111 , 1112 may sense an average value of four charge carriers .

According to the example which is illustrated in Fig . IB, the charge carriers 107 may be absent from the intermediate zone 108 . For example , the intermediate zone 108 may be covered so that no charge carriers 107 are generated within the intermediate zone 108 . According to this example , the first and the second cathode contacts 1111 , 1112 may sense an average value of four charge carriers 107 .

According to the example of Fig . 1C , the charge carriers 107 are only generated within the intermediate zone 108 . For example , the region of the first photodiode 111 and the second photodiode 112 may be covered . The first cathode contact 1111 and the second cathode contact 1112 compete with each other for the charge carriers 107 within the intermediate zone 108 . For example , each of the first and the second cathode contacts 1111 , 1112 may sense an average value of four charge carriers 107 . As has been shown above, from the detection signals it is hard to distinguish between the situations illustrated in Figs. 1A, IB and 1C.

Fig. 2A shows an example of a pixel 100 of a CMOS sensor according to embodiments. The pixel 100 may comprise two photodiodes 111, 112. As is to be clearly understood, the concepts described herein may be applied to sensors comprising pixels comprising an arbitrary number of photodiodes. In more detail, the specific configuration of the pixel does not largely affect the functionality of the described implementations. Rather, the arrangement and biasing of the single photodiodes 111, 112 particularly determine the functionality of the device.

The pixel 100 further comprises a readout circuit 102. The readout circuit 102 may, for example, comprise a reset transistor 118. A source terminal of the reset transistor 118 may be electrically coupled to a terminal, e.g. a cathode contact of each of the first and the second photodiodes 111, 112. The readout circuit 102 further comprises a readout transistor 123. For example, an output of the first and second photodiodes 111, 112 may e.g. be connected via a floating diffusion region to a gate electrode of the readout transistor 123. A drain terminal of the readout transistor 123 may be electrically coupled to a supply voltage Vdd. A source terminal of the readout transistor 123 may be connected to a drain terminal of a selection transistor 121. A selection signal may be applied to the gate electrode of the selection transistor 121. A source terminal of the selection transistor 121 is connected e.g. to a column line 125. The pixel circuit 102 further comprises a switch 114 for selectively electrically coupling the first photodiode 111 to the readout circuit 102, and a second switch for selectively electrically coupling the second photodiode 112 to the readout circuit 102. The CMOS sensor 10 further comprises a processing circuit 105 that is configured to activate the first switch 114 and the second switch 115.

As is e.g. illustrated in Fig. 2B, the pixels 100 and, hence, the first photodiode 111 and the second photodiodes 112 as well as the first cathode contacts 1111 and second cathode contacts 1112 may be arranged in columns and rows. The processing circuit 105 may be electrically coupled e.g. to the first switch 114 and the second switch 115.

The processing circuit 105 is configured to simultaneously bias a first photodiode 111 and a second photodiode 112 to accomplish readout. The first photodiode 111 and the second photodiode 112 are arranged in one row and adjacent columns, respectively, or in one column and adjacent rows, respectively, or in adjacent columns and adjacent rows, respectively. As a result, a first readout result is obtained.

Within the present disclosure the term "bias a diode to accomplish readout" is intended to mean that a sufficient voltage is applied, e.g. between a cathode contact and an anode terminal of the diode, so that a readout may be accomplished. When the first photodiode 111 and the second photodiode 112 are biased to accomplish readout, the first cathode contact 1111 of the first photodiode 111 and the second cathode contact 1112 of the second photodiode 112 compete for the charges.

The processing circuit 105 is further configured to bias the first photodiode 111 to accomplish readout while the second photodiode 112 is not biased to accomplish readout, to obtain a second readout result. The processing circuit 105 is further configured to bias the second photodiode 112 to accomplish readout while the first photodiode 111 is not biased to accomplish readout, to obtain a third readout result. The term "a diode is not biased to accomplish readout" is intended to mean that a voltage e.g. applied to a cathode contact of the diode is not sufficient to enable or accomplish readout. For example, no voltage or a small voltage may be applied to the cathode contact. Accordingly, when the first photodiode 111 is biased to accomplish readout while the second photodiode 112 is not biased to accomplish readout, a voltage e.g. applied to the first cathode contact 1111 is sufficient to enable readout. The voltage e.g. applied to the second cathode contact 1112 is not sufficient to enable readout. As a result, the second cathode contact 1112 does not compete with the first cathode contact 1111 for the charges.

In the context of the present disclosure the term "readout diode" is intended to describe a diode that is biased so that a readout is accomplished. The term "non-readout diode" is intended to describe a diode that is not biased so that a readout is accomplished. For example, an absolute value of a bias voltage applied to the non-readout diode may be lower than a bias voltage required for accomplishing readout.

The processing circuit 105 is further configured to determine a spatial distribution of incoming photons on the basis of a difference between the first readout result and the second readout result and a difference between the first readout result and the third readout result.

For example, the processing circuit 105 may be configured to extract and reconstruct a unique image from a collection of images taken with different settings (e.g. switches/ transistors and diodes) enabled. The processing circuit may employ machine learning methods. Fig . 3A shows an example of arrangement of the first cathode contacts 1111 and second cathode contacts 1112 , when considering one single row . For example , the rows may extend along the x direction, and the columns may extend along the y direction . As is shown, for example , the first and the second cathode contacts 1111 , 1112 may be arranged alternat ingly in a certain row . As i s schematically illustrated in Fig . 3A, the cathode contacts occupy only a smal l fraction o f the area o f the pixel 100 and is generally arranged at the center of the pixel 100 .

Fig . 3B schematically illustrates a potential distribution in case a voltage is applied to the first cathode contact 1111 and to the second cathode contact 1112 . In this case , a generated charge carrier 107 which is present at the boundary between the first cathode contact 1111 and the second cathode contact 1112 , that is e . g . present in the intermediate zone 108 may likewise be attracted by the potential minimum at the first cathode contact 1111 or the second cathode contact 1112 .

Fig . 3C shows the situation when the charge carrier is arranged at the same position and only the first photodiodes 111 are read out , i . e . a voltage is applied only to the first cathode contact

1111 , and no voltage is applied to the second cathode contact

1112 . As is illustrated in Fig . 3C, the potential minimum for the second cathode contact 1112 is absent in this case . Accordingly, the charge carrier 107 will be attracted by the potential minimum at the first cathode contact 1111 . A similar case applies when a bias voltage suf ficient for readout is applied only to the second cathode contacts 1112 of the second photodiodes 112 whereas the bias voltage appl ied to the first cathode contacts 1111 of the first photodiodes 111 is not suf ficient for readout .

Fig . 4A shows a representation of a first readout pattern . As i s illustrated, the first and the second photodiode 111 , 112 may be arranged in the same row and in adjacent columns, respectively. According to the readout pattern illustrated in Fig. 4A, a column of readout photodiodes 130 is adjacent to a further column of non-readout photodiodes 131.

According to the representation shown in Fig. 4B, the readout photodiodes 130 and the non-readout photodiodes 131 are arranged in a checkerboard pattern. Hence, the first photodiode 111 and the second photodiode 112 may be arranged in adjacent columns and adjacent rows, respectively.

According to a further implementation as e.g. illustrated in Fig. 4C, the readout photodiodes 130 may be arranged in a first row and the non-readout photodiodes 131 may be arranged in a second row which is adjacent to the first row. Hence, the first photodiode 111 and the second photodiode 112 may be arranged in one column and adjacent rows, respectively.

As has been shown with reference to Figs. 4A to 4C, any pattern may be generated by switching on or off the first and second switches 114, 115, thus activating the first or second photodiodes 111, 112. By means of switching on and off the respective photodiodes, it is possible to sense the charge bucket in-between the cathode contacts.

As is shown in Figs. 4A to 4C, each single photodiode has eight competing neighbors. Accordingly, there are eight "charge buckets" for each diode which means that there are eight unknown variables. Using different patterns for reading out the generated charges makes it possible to acquire several images under different conditions. Consequently, it becomes possible to solve these unknown. As a result, it is possible to obtain a final image having an improved resolution. In more detail, a sub-pixel resolution may be reached without the need to reduce the pixel size. Accordingly, the production yield may be improved. Further, cost may be saved.

Fig. 5 summarizes a method according to embodiments. As is shown in Fig. 5, a method for processing detection signals of pixels comprising a photodiode comprises simultaneously biasing (S100) a first photodiode and a second photodiode to accomplish readout, the first photodiode and the second photodiode being arranged in one row and adjacent columns, respectively, or in one column and adjacent rows, respectively, or in adjacent columns and adjacent rows, respectively, to obtain a first readout result. The method further comprises biasing (Slid) the first photodiode to accomplish readout while the second photodiode is not biased to accomplish readout, to obtain a second readout result and biasing (S120) the second photodiode to accomplish readout while the first photodiode is not biased to accomplish readout, to obtain a third readout result. The method further comprises determining (S130) a spatial distribution of incoming photons on the basis of a difference between the first readout result and the second readout result and a difference between the first readout result and the third readout result.

As is clearly to be understood, the different readout processes may be performed in arbitrary order before determining the spatial distribution.

Further embodiments relate to a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method as described above. Still further embodiments relate to a computer-readable data carrier having stored thereon the computer program as described above . Fig . 6 shows an imaging apparatus 20 comprising the CMOS sensor 10 which has been explained above . For example , the imaging apparatus 20 may be selected from an image sensor, e . g . a large scale image sensor, an X-ray medical imaging apparatus and an imaging apparatus for non-destructive testing .

While embodiments of the invention have been described above , it is obvious that further embodiments may be implemented . For example , further embodiments may comprise any subcombination of features recited in the claims or any subcombination of elements described in the examples given above . Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein .

LIST OF REFERENCES

10 CMOS sensor

20 electronic device

100 pixel

102 readout circuit

105 processing circuit

107 charge carrier

108 intermediate zone

111 first photodiode

1111 first cathode contact

112 second photodiode

1112 second cathode contact

113 anode terminal

114 first switch

115 second switch

118 reset transistor

121 selection transistor

123 readout transistor

125 column line

130 readout photodiode

131 non-readout photodiode

Claims

1. A CMOS sensor (10) comprising a plurality of pixels (100) , each of the pixels (100) comprising a photodiode (111, 112) and a switch (114, 115) for connecting and disconnecting the photodiode (111, 112) to a readout circuit (102) , the photodiodes (111, 112) being arranged in rows and columns, respectively, the CMOS sensor (10) further comprising a processing circuit (105) for activating the switches (114, 115) , the processing circuit (105) being configured to: simultaneously bias a first photodiode (111) and a second photodiode (112) to accomplish readout, the first photodiode (111) and the second photodiode (112) being arranged in one row and adjacent columns, respectively, or in one column and adjacent rows, respectively, or in adjacent columns and adjacent rows, respectively, to obtain a first readout result; bias the first photodiode (111) to accomplish readout while the second photodiode (112) is not biased to accomplish readout, to obtain a second readout result; bias the second photodiode (112) to accomplish readout while the first photodiode (111) is not biased to accomplish readout, to obtain a third readout result; and determining a spatial distribution of incoming photons on the basis of a difference between the first readout result and the second readout result and a difference between the first readout result and the third readout result.

2. A method for processing detection signals of pixels (100) comprising a photodiode (111, 112) , the photodiodes (111, 112) being arranged in rows and columns, the method comprising: simultaneously biasing a first photodiode (111) and a second photodiode (112) to accomplish readout, the first photodiode (111) and the second photodiode (112) being arranged in one row and adjacent columns, respectively, or in one column and adjacent rows, respectively, or in adjacent columns and adjacent rows, respectively, to obtain a first readout result; biasing the first photodiode (111) to accomplish readout while the second photodiode (112) is not biased to accomplish readout, to obtain a second readout result; biasing the second photodiode (112) to accomplish readout while the first photodiode (111) is not biased to accomplish readout to obtain a third readout result; and determining a spatial distribution of incoming photons on the basis of a difference between the first readout result and the second readout result and a difference between the first readout result and the third readout result.

3. The method according to claim 2, wherein according to a first readout pattern the first and the second photodiode (111, 112) are arranged in one row and adjacent columns, respectively.

4. The method according to claim 3, further comprising repeating the method using a second readout pattern different from the first readout pattern.

5. The method according to claim 4, wherein according to the second readout pattern the first and the second photodiode (111, 112) are arranged in adjacent rows and in adjacent columns, respectively .

6. The method according to any of claims 2 to 5, further comprising repeating the method using a third readout pattern.

7. The method according to claim 6, wherein according to the third readout pattern the first and second photodiode are arranged in one column and in different rows, respectively.

8. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any of claims 2 to 7.

9. A computer-readable data carrier having stored thereon the computer program of claim 8.

10. An electronic device (20) comprising the CMOS sensor (10) according to claim 1.

11. The electronic device (20) according to claim 10, being selected from an image sensor, an X-ray medical imaging apparatus and an imaging apparatus for non-destructive testing.