JPH02210877A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To reduce difference in gain and difference in noise quantity by using a phototransistor which is partially formed of non-single crystal as a photoelectric converting element and providing a driving circuit therefor and a thin-film transistor on the same substrate. CONSTITUTION:A solid image pickup device comprises an N-type thin-film transistor 101 produced from polycrystalline silicon and uses a non-single crystal phototransistor, 102 as a photoelectric converting element. The source line of the thin-film transistor 101 is connected to a bias power supply 103. A gate line 103 is formed from polycrystalline silicon and, as a control signal line for a switch, it turns the transistor 101 ON and OFF according to input data. In such a manner, difference in gain can be reduced. Further, difference in noise quantity also can be reduced because a scanning section can be provided very close to the photoelectric converting element 102.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state imaging device in which a photoelectric conversion element has an amplification effect.

[Prior Art] Conventionally, there has been an idea for a solid-state imaging device in which an optical signal is amplified pixel by pixel and an output signal is extracted. Now that improvements in sensitivity and signal-to-noise ratio are becoming increasingly difficult to hope for due to the inherent physical characteristics of element devices, their practical application is increasingly desired, and there is a growing demand for solid-state imaging devices capable of high-speed readout with high image quality, high sensitivity, and high signal-to-noise ratio. Therefore, specifically, the format shown in the Journal of the Television Society Vol. 41 No. 11 (19B?) is being studied.

Also, SOI technology is being actively developed for large-area, high-performance devices.

[Problems to be solved by the invention] However, in conventional solid-state imaging devices that have an amplification function, it is difficult to maintain uniformity in the characteristics of the amplification element and photoelectric conversion element, resulting in large variations in the gain of the amplification element and further noise. There was a problem that only those with characteristics on the same level as those with an external amplifier existed because the variation in the amount was large. This is because in conventional devices, in addition to variations in photoelectric conversion elements, variations in amplification elements are added independently.

On the other hand, with the miniaturization of devices, there is a strong need for large-area photoreceptor arrays, and the advantage of being able to form a device on a transparent substrate as an imaging device is that the light is incident on the substrate side. Therefore, an element array in which the size of the element chip is limited by the size of the silicon wafer is not suitable for use in a large area as a contact type solid-state imaging device. In a large-area sensor that integrates the sensor part and the scanning circuit part, it is possible to arrange a large number (such as 10) of elements formed on a silicon wafer, but the mounting efficiency is very poor, and the inter-chip problems such as sensitivity etc. Since the variation becomes large, there is no point in incorporating an amplification function in multiple chips even though the variation is large even in a single chip. However, if the area of the chip is increased, the effects of the above-mentioned performance deterioration factors may become even greater.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a large single-area solid-state imaging device that has a high amplification gain, has small variations in gain, suppresses variations in noise amount, and enables high-speed readout. be.

[Means to solve the problem]

The solid-state imaging device of the present invention is characterized in that a phototransistor, at least a part of which is made of a non-single crystal, is used as a photoelectric conversion element, and a thin film transistor is used for a drive circuit thereof, and the phototransistor is provided on the same substrate. Furthermore, a part of the photoelectric conversion element and a part of the thin film transistor are formed of the same non-single crystal material.

Hereinafter, the details of the present invention will be shown by examples.

[Examples] Example 1 FIG. 1 is an example of the configuration of a solid-state imaging device according to the present invention, and FIG. 2 is an example of an enlarged cross-sectional view of the solid-state imaging device. 1
In this example, 01.206 consists of an n-type thin film transistor made using polycrystalline silicon, and 102.2
It works as a switch connected to the non-single crystal phototransistor 04. Polycrystalline silicon is deposited by LPCVD at approximately 60°C, then a gate film is formed by thermal oxidation at approximately 1100°C, a gate electrode is formed of polycrystalline silicon, and a source is formed by ion implantation using a self-alignment method. A drain part is formed.If characteristics are important, it is also a good idea to use a crystal grown by heat or light after depositing a silicon film (so-called SOI structure).In this example, a quartz plate is used for the substrate 201. Since it uses a thin film transistor, there are fewer problems with applying heat during gate oxidation, etc., and since the substrate is transparent, light can enter from the substrate side, and the mounting structure can ensure high reliability.If it operates as a thin film transistor, other There is no problem when using this method, and of course, the range of substrate material selection is expanded (substrates cheaper than quartz can be used), and it is also preferable that everything can be processed at low temperatures (for example, about 650 degrees Celsius or less). Source lines of thin film transistors. is 10
It is connected to the bias power source No. 3, and any wiring material may be used for the wiring, but in this example, aluminum mixed with a small amount of silicon and copper is used. Thin film transistor (10
The gate line (105) of 1) is formed using polycrystalline silicon, and is turned on and off according to input data as a control signal line for a switch.

- When used as a solid-state imaging device such as dimensional or two-dimensional,
Connected to a circuit that has data transfer and creation functions,
．． Although not shown in Figure 2, signals are transferred using a CMO8-type O8 register made of p- and n-type thin film transistors made of polycrystalline silicon similar to 101. If this method is used, it is possible to form a switch and a scanning station excluding part or all of the photoelectric conversion element in almost the same process, so if the conditions permit, the cost and other advantages are very large. This figure shows an example of a circuit diagram of a static operation master-slave type shift register. Only the starting part is shown, but by repeating 404 cells, it is possible to obtain the required number of stages of phototransistor density and number depending on the reading resolution and reading range. A signal is sequentially sent by the start pulse 401 to sequentially open the switches of the thin film transistors, thereby forming a phototransistor selection circuit. Furthermore, since it is formed on an insulating substrate, there is no need for element isolation, and stray capacitance is small, which is very advantageous in terms of scanning speed.

The drain line of the thin film transistor 101 is connected to the emitter of a non-single-crystal (hereinafter referred to as a non-single-crystal) phototransistor (102), and a bias voltage is applied through the thin-film transistor (101). In the example, the phototransistor is S i H
n1p made using amorphous silicon decomposed by glow discharge of a gas containing H4, PH3, B2Hg, etc.
In this example using an in-type transistor, the thickness of each layer is 500A, 8000A, and 250A from the collector side.

Although it is necessary to consider the doping amount of 1,500 people and 500 people, in this example, the collector side is considered to be close to the optimum value. Impurities are added using PH3, B2 He, or the like. For the purpose of window effect, blocking characteristics, high amplification characteristics, high-speed performance, heat resistance, reliability improvement, etc. on the light used, it is also possible to mix carbon into each layer to create a wide gap and make it as silicon carbide. In this example, the n-layer is made of silicon carbide and the band gap is around 2 eV to form a film. Although it is highly dependent on the device, the parallel plate type (
Amorphous silicon and amorphous silicon carbide were deposited by inputting a power of 1.10 W to 80 W using a capacitively coupled plasma device (30 cm round).

In addition, in this example, each layer of n1pin is simply stacked to form a pattern with the same area, and the electrodes are taken out from the collector and emitter at both ends. It is also possible to take out the electrode and form part or all of the electrode (pinip% npin
% n1pn, npnS pnip, pinp or pnp
Alternatively, a small amount of impurity may be mixed into part or all of the i-layer, a highly doped layer may be used for contact, and each layer may have a gradient or step of impurity concentration or band gab to form a junction or contact with an electrode. Bias application, light utilization efficiency, etc. can be optimized, and the structure uses amorphous, microcrystalline, or polycrystalline only for the emitter, and several optimizations can be made with the configuration of the present invention. is first made into a non-single crystal, formed to a thickness of 3.5 μm on an interlayer insulating film, and then thermally annealed to improve crystallinity.
In this example, CVD silicon formed at 515°C is heated to 20°C at 615°C using the commonly used SOIO technique.
After annealing for 8 hours, a crystal grain size of 1.2 μm to 2.3 μm was obtained. In the structure of the present invention, a scanning circuit section and a switch section are already formed of non-single crystal silicon under the interlayer insulating film. During the above annealing, the crystallinity of the thin film transistor portion is also improved at the same time. Therefore, the characteristics of both the light receiving section, the scanning circuit section, and the switch section can be greatly improved by one annealing (which may take more than one day and night).

Regarding thin film transistors, the crystallinity of the channel portion has increased, and the mobility has increased by about 5 times or more. Although the film thickness was increased in the emitter section of the light receiving section, the effect on the layer width ratio and speed was tremendous. Although the overall variation increases, the effect of forming a light receiving section on a silicon wafer using this emitter section due to high amplification factors can also be considered from the optimization of the scanning section. During the entire process, after creating a thin film transistor, a silicon oxide film and a video line (203) are formed.
The video line also serves as the electrode of the phototransistor, and is made of a transparent electrode material (for example, an I TO film).

Example 2 A non-single-crystal material of 507, another structure of which is shown in FIG. Here, PECVD silicon formed at 415°C is heated to 600"C.
After annealing for 28 hours, a grain size of 1.8 μm to 3.3 μm was obtained. After roughly forming an oxide film using C, VD or thermal oxidation, an interlayer insulating film for forming a gate electrode is formed in the necessary locations, a contact hole is opened, the emitter part of the phototransistor 504 is formed, and the emitter part of the phototransistor 506 is formed. 505 to form source and drain electrodes
A back electrode 503 and a video line 503 are formed.

Phototransistor materials can be amorphous, microcrystalline, polycrystalline,
Furthermore, it is possible to use a crystal grown version of these, or to combine them to utilize the band gap as mentioned above.It is a structure that uses silicon to have an amplification effect, and at least a part of the light receiving part It is sufficient to form a thin film. Here, the phototransistor is used as a floating base type, but if further speed and stability are required, the amplification factor will be lower, but instead of floating, connect the R resistor as shown in Figure 3. In this example, a line sensor using a one-dimensional photoelectric conversion element array was constructed, but an area where photoelectric conversion elements are arranged two-dimensionally with two systems horizontally and vertically It is also fully possible to use it as a sensor. The collectors of 102 non-single crystal phototransistors are connected to 104 video lines common to each photoelectric conversion element.

In both Examples 1 and 2, further improvement in performance can be achieved by adding a termination process using hydrogen or the like at any process position.

The phototransistor 102, together with the thin film transistor 101, uses an accumulation mode in which charge is accumulated between -line readings to make the amount of charge easy to handle. In operation, when the thin film transistor is turned on, the collector-base capacitance tc of the reverse biased non-single-crystal phototransistor is charged by the bias power supply V. In the case of a structure made of a non-single crystal material as shown in FIG. 2 of this example, the capacitor C is formed by a thin film capacitor together with a junction capacitor. After that, the thin film transistor is turned off until the next readout, and the charge charged by the photonucleus is lost in proportion to the amount of incident light. Therefore, the amount of charge lost at the timing of the next readout is It is recharged and becomes the base current, which is multiplied by the current gain hre > 1 due to the transistor multiplication effect and output from the video line, so an external integration operation is performed and the output is obtained with high sensitivity in proportion to the amount of incident light. It will be done.

Although the embodiments have been described above, the present invention is applicable not only to the above embodiments but also to imaging devices in general, and can be applied to a wide range of devices that handle light and devices that process light.

[Effects of the Invention] As described above, according to the present invention, these elements use the same device and the light receiving part and the amplifying part are formed of the same kind of material, so even if formed over a large area, they can be used as an amplifying element. It is easy to maintain the uniformity of the characteristics of photoelectric conversion elements, and the variation in gain of amplification elements is small.Also, thin film transistors have excellent switching characteristics and are superior to bulk silicon in terms of crystallization, making them extremely suitable for photoelectric conversion elements. Since the scanning section can be formed in close proximity to the scanning section, variations in the amount of noise are also small.

Furthermore, it has the advantage of improving the performance of phototransistors and thin film transistors at the same time by using SOI technology of non-single-crystal materials, improving device characteristics Φ, and eliminating reverse bias between the base and collector. Due to its excellent characteristics, it has excellent performance as a solid-state image sensor such as linearity, and the excellent base and emitter junction allows for high amplification and
It's fast.

It has this effect.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the basic configuration of the present invention. FIG. 2 is a diagram showing an example of an element cross section. FIG. 3 is a diagram showing another example of the present invention. FIG. 4 is a diagram showing an example of the overall configuration of the present invention. FIG. 5 is a diagram showing a separate cross-sectional view of the element of the present invention. 101 ・ ・ 102 ・ ・ 103 ・ ・ 104 ・ ・ 105 ・ ・ 201 ・ ・ 202 ・ ・ 203 ・ ・ 204 ・ ・ 205 ・ 206 ・ ・ 301 ・ ・ ・ Thin film transistor (n) ・ Non-single crystal phototransistor bias power supply・Video line ・Gate line ・Substrate ・Insulating film ・Video line ・Phototransistor ・Back electrode ・Thin film transistor ・Thin film transistor (p) 302...Non-single crystal phototransistor 504...
Phototransistor 506...thin film transistor and above Applicant Seiko Epson Corporation

Claims (2)

[Claims] (1) A solid-state imaging device characterized in that a phototransistor, at least a part of which is made of a non-single crystal, is used as a photoelectric conversion element, and a thin film transistor is used as a drive circuit for the phototransistor, and the phototransistor is provided on the same substrate. (2) The solid-state imaging device according to claim 1, wherein a part of the photoelectric conversion element and a part of the thin film transistor are formed of the same non-single crystal material.