JP2963182B2 - Light receiving element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-receiving element having an amplifying function used for an image sensor, an optical sensor, and the like, and particularly to a high-sensitivity light-receiving element having a large output current.

[Related Art] A light receiving element is widely used for an image sensor, an optical sensor, and the like, and research and development are being vigorously conducted in various places. Especially,
In the field of imaging devices in which the development of charge-coupled devices (CCDs) has been remarkably progressing, with the improvement in resolution, they have come to be used not only for consumer cameras but also for broadcast cameras. However, in order to renovate the conventional image pickup tube method, although it has the advantages of small size and light weight, it is still inferior in resolution and sensitivity, and it is in a state where future progress is expected.

In order to improve the resolution, it is necessary to produce a huge number of fine light receiving elements in a small area to take advantage of the above advantages. That is, high integration of the light receiving element is required. In this case, since the light receiving area becomes narrow, the intensity of the output signal is reduced, and accordingly, there is a concern that the light receiving sensitivity is reduced. Therefore, in order to realize high resolution,
Development of a fine and highly sensitive light receiving element is an important issue.

On the other hand, in the field of optical computers, which has recently attracted attention, a spatial light modulator (SLM: Spatial Light
Modulator) is strongly desired. In the SLM, cells composed of a light receiving element that senses input light and a modulator that changes the properties of light such as liquid crystal are arranged in a matrix.
Parallel light calculation and the like are performed by controlling the intensity and traveling direction of the output light with the input light. in this case,
In order to further increase the parallel processing capability, it is necessary to form the above cells finely. Therefore, just as in the case of the image pickup device, development of a technique for forming a fine and high-sensitivity light receiving element on a transparent insulating substrate such as a glass substrate is an important issue.

In recent years, in order to increase the sensitivity, a light receiving element having an amplifying function in the element itself (hereinafter, referred to as an amplification type light receiving element) has attracted attention. In a conventional element, an output signal from a light receiving element is amplified by an external amplifier after passing through a transfer line. However, in such a method, it is difficult to realize a high S / N ratio because noise is mixed during transfer. However, in the case of an amplification type light receiving element, since the output signal is directly amplified, the S / N ratio can be increased even with weak incident light, and as a result, high sensitivity can be realized. One of such amplifying light receiving elements is an optical thin film transistor.

FIG. 6 is a schematic cross-sectional view showing a schematic structure of an optical thin film transistor. The active region is composed of two regions, that is, an n-type region 1 ′ and a p-type region 1 ″, and a pn junction is formed in the active region. Here, when the transistor is irradiated with light, electron-hole pairs are generated in the active region, and when a negative potential is applied to the gate electrode 3, the electrons are converted into the n-type region 1 '.
The holes flow into the p-type region 1 ". The electrons flowing into the n-type region 1 'flow as they are into the drain electrode 5 as a photocurrent and are taken out as an output signal. An optical thin film transistor is used for manufacturing a liquid crystal display or the like. There is an advantage that the active matrix can be formed on a substrate having a large area at a high density by using the active matrix forming technique, but as described above, the output current basically depends on the electrons and holes generated by photoexcitation. Since only a pair is used, a large output current cannot be obtained, and the sensitivity is low.

[Problems to be Solved by the Invention] As described above, in the related art, even if a high density can be achieved to some extent, a large output current cannot be obtained and the sensitivity is low due to the basic restrictions of the configuration. Challenges remained.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-sensitivity photodetector capable of solving the above-mentioned problems of the prior art and obtaining a high density and a large output current.

[MEANS FOR SOLVING THE PROBLEMS] The object is to provide a semiconductor device having a source / drain region in an active region, a part of the source / drain region having p-type conductivity, and a remaining source / drain region. A light-receiving element using a thin film transistor having n-type conductivity, wherein the p / drain region is constituted by a pin junction between the p-type conductive source / drain region, the n-type conductive source / drain region, and the active region; Electrical connection between the solar cell and the gate electrode of the thin film transistor,
Thin film transistor with amplifying function and light receiving function
This can be achieved by forming a light receiving element having a configuration shared with a pin type solar cell.

[Operation] FIG. 5 is a diagram showing a basic configuration of the light receiving element of the present invention.
Pin type solar cell and thin film transistor gate electrode 3
It is shown that the light receiving element is electrically connected in parallel between the drain electrode 5 and the operation principle of the light receiving element of the present invention will be described below with reference to FIG.

As shown in FIG. 3A, when light is irradiated from the substrate side to the active region, the drain region and the cathode region or the anode region forming the pin structure, for example, the gate electrode 3 is formed according to the principle of the pin type solar cell. An electromotive force is generated between the gate electrode and the drain electrode 5, and the potential of the gate electrode increases. For this reason, in the case of an n-type thin film transistor, as shown in FIG. 3B, an n-type channel region is formed in the active region, and when a potential difference is generated between the source and the drain, the drain electrode is formed together with the photocurrent. It starts to flow rapidly, and its current value can be taken out as an output signal. Also, in the case of a p-type thin film transistor, exactly the same operation is performed as shown in FIG. In the above description, the case where light is incident from the substrate side has been described.
When an ITO (Indium Tin Oxide) electrode is used, a similar operation is performed even when light is incident from the gate electrode side.

By using the light receiving element with the above configuration,
Since the gate modulation can be performed by the solar cell, the output current can be increased. In addition, the i
Since the layer and the active region of the thin film transistor are shared, the occupied area can be reduced, which is suitable for high integration. For example, single-crystal Si on a sapphire transparent substrate
A light receiving element of the present invention is formed using an SOS (Silicon on Sapphire) film on which an active region is deposited, and the size of the active region is 3 μm × 3.
With a size of μm, the sensitivity is about 2
A light receiving element improved by about an order of magnitude was obtained.

EXAMPLES Hereinafter, the configuration of the light-receiving element of the present invention will be specifically described with reference to examples.

FIG. 1 is a plan view showing a schematic configuration of a light-receiving element of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1 and shows an active region 1, a gate insulating film, a gate electrode 3, a source A4, It is shown that it is composed of a drain A5, an anode 7, and an Al wiring 9. The feature here is that the light receiving element has a structure in which drain regions having different conductivity types are connected to the active region of the thin film transistor. That is, as shown in FIG. 3, (a) n-channel thin film transistor is p
(B) In the case of a p-channel thin film transistor, by forming an n-type region (anode region), a pin-type solar cell as a light receiving element is formed between the drain region and the active region of the thin film transistor. A battery will be formed. However, TT and P in FIG.
−P line arrow direction is thin film transistor and pin respectively.
1 shows a configuration of a solar cell (gate electrode 3 is omitted here for convenience). As described above, the light receiving element of the present invention is an element sharing the thin film transistor having the amplifying function and the pin type solar cell having the light receiving function.

Next, the procedure of manufacturing the light receiving element of the present invention will be described with reference to FIG. 4 taking the case of the structure of FIG. 3A as an example. In the drawings, a plan view in each step and a cross-sectional view in the direction of arrows A'-A 'are shown. First, as shown in (a), the pattern of the active region 1 made of a semiconductor film, for example, an amorphous Si film, a polycrystalline Si film, or single-crystal Si is formed on a transparent insulating substrate, for example, a glass substrate. Next, as shown in (b), the pattern of the gate insulating film 2 and then the pattern of the gate electrode 3 were formed by sputtering or CVD. Subsequently, as shown in (c), after forming a mask 6, phosphorus (P) is ion-implanted to form a source A4 and a drain A5 region having n-type conductivity.
After the mask 6 is removed and a mask 6 'is formed, as shown in (d), boron (B) is ion-implanted and the conductivity type becomes p.
Source B7 and drain B8 regions, which are molds, were formed. Lastly, after removing the mask 6 ', activation annealing is performed, and further, a metal wiring (for example, an Al wiring) 9 is formed so as to be electrically connected to the outside, thereby obtaining a finished product (e). .

As can be seen from the above description, the above process is based on the CMOS device manufacturing process used for manufacturing LSIs and the like, and it is not necessary to develop a new process technology in manufacturing the light receiving device of the present invention. Absent.

In the above description, the case where a thin film transistor having one set of source / drain regions is used is described; however, a thin film transistor provided with a plurality of sets of source / drain regions can be used.

[Effects of the Invention] As described above, the light receiving element is configured as the light receiving element of the present invention, that is, the i-layer of the pin type solar cell as the light receiving section and the active region of the thin film transistor as the amplification section are shared. With the light receiving element having the above-described configuration, the problems of the prior art can be solved, and a light receiving element that is integrated at a high density and has significantly improved sensitivity can be provided.

Furthermore, when the light receiving element of the present invention is used for an image sensor, a spatial light modulator, and the like, a normal CMOS manufacturing process can be used, so that the peripheral circuit and the light receiving unit can be easily formed on the same substrate, In addition, there is an advantage that miniaturization of the light receiving element can be easily achieved by using the fine processing technology of the LSI.

[Brief description of the drawings]

FIG. 1 is a plan view showing a schematic configuration of a light receiving element of the present invention, and FIG.
FIG. 1 is a cross-sectional view taken along the line AA of FIG. 1, and FIG. 3 is a view showing a configuration example of a thin film transistor. (A) is an n-type thin film transistor, (b) is a p-type thin film transistor, and FIG.
5A to 5E are diagrams for explaining the procedure of manufacturing the light receiving element of the present invention, FIG. 5 is a diagram for explaining the operation principle of the light receiving element of the present invention, and FIG. 6 is a schematic configuration of a conventional optical thin film transistor. FIG. Reference Signs List 1 ... active region, 1 '... n-type active region, 1 "... p-type active region, 2 ... gate insulating film, 3 ... gate electrode, 4 ... source A, 5 ... drain A, 6 , 6 '... mask, 7 ... anode, 8 ... cathode 9 ... Al wiring.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-143572 (JP, A) JP-A-63-250171 (JP, A) JP-A-59-22360 (JP, A) JP-A-61- 7663 (JP, A) JP-A-63-224373 (JP, A) JP-A-1-83352 (JP, U) JP-A-63-59353 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 31/10 H01L 27/14

Claims (1)

(57) [Claims] An active region having a source / drain region;
In a light-receiving element using a thin film transistor in which part of the source / drain regions has p-type conductivity and the remaining source / drain regions have n-type conductivity, A solar cell formed by a pin junction between the source / drain region of the n-type conductive source / drain region and the active region and a gate electrode of the thin film transistor, and a thin film transistor having an amplifying function. A light-receiving element having a configuration sharing a pin-type solar cell having a light-receiving function.