JPH034607A - Optical detection amplifier - Google Patents

Abstract

PURPOSE:To amplify the DC signal being a detection signal from an optical sensor and output it without using a capacitor by adopting the constitution such that the optical sensor section connects directly to a gate electrode of a thin film transistor(TR) electrically. CONSTITUTION:An amorphous silicon semiconductor layer 15 of P-I-N junction is coated on a transparent electrode 14. Moreover, a heat resistance metallic electrode 16 is coated on the semiconductor layer 15 to form an optical sensor section S. In a thin film TR, a gate electrode 17 is coated with the same film forming condition as the transparent electrode 4 in the optical sensor section on the light shield film 11 and the insulation film 12 formed on the transparent board 10. Then the optical sensor section S is connected directly in terms of DC without using a coupling capacitor to the gate electrode of the tin film TR. As a result, the DC signal being a detection signal by the optical sensor S is amplified.

Description

Detailed Description of the Invention (Industrial Application Field) This invention is applied to automatic exposure devices such as cameras and video cameras, and other various optical measurement devices, etc. Detected.

The present invention relates to a photodetection amplifier configured to amplify the amount of light, convert it into an electrical signal, and output it.

(Prior art) Generally, the output of a photosensor is converted into a field effect transistor (F).
In order to obtain sufficient gain when amplifying by ET), a predetermined DC voltage must be applied between the gate and drain of the field effect transistor so that the operating point moves to approximately the center of the linear part, that is, It is necessary to apply a bias voltage,
In order to maintain this bias voltage, conventionally a capacitor has been used to couple the optical sensor and the gate of the field effect transistor.

Figure 1θ is a circuit diagram of a conventional photodetection amplifier;
shows a voltage mode circuit that outputs a voltage signal, and the same figure (
B) shows a current mode circuit that outputs a current signal. In each of these figures, 1 is an optical sensor, 2 is a field effect transistor, R1 and R2 are voltage dividing resistors, RL is a source resistor,
Vcc is the power supply voltage, and in both voltage mode and current mode, the bias voltage V is as follows.Therefore, if the photosensor 1 and the gate of transistor 2 are directly connected without using a capacitor, the bias voltage will be The voltage VIE depends on the internal resistance of the optical sensor-1,
It fluctuates greatly as the electromotive force fluctuates (fluctuates in the amount of light received), and as a result, an abnormality occurs in the operating point, making it impossible to obtain constant output characteristics.

Therefore, a capacitor C is required to maintain the bias voltage VB& and to keep the output characteristics constant regardless of fluctuations in the electromotive force of the optical sensor 1.

A so-called CR coupling amplifier circuit was used in which the optical sensor 1 and the gate of the transistor 2 were coupled through the capacitor C.

(Problem to be Solved by the Invention) In the case of the conventional photodetection amplifier configured as described above, since a coupling capacitor is used between the photosensor and the gate of the transistor, Although the resistor is small and a predetermined amplification effect can be obtained, the capacitor only performs a charging function for DC signals, and it is not possible to obtain the amplification effect of DC signals by an optical sensor.

Furthermore, even if transistors can be made thinner and lower in cost by applying amorphous silicon semiconductor film formation technology due to the existence of the coupling capacitor as described above, capacitors and optical sensors must be externally attached to these thin film transistors. Therefore, the optical sensor and the transistor cannot be integrated and formed on the same substrate, making the manufacturing process and circuit configuration as a whole complicated and expensive. There were drawbacks.

In particular, in the case of a photodetector amplifier that obtains a current mode output, the output level of the photosensor changes over several orders of magnitude depending on changes in illuminance. It is necessary to combine a Jlog conversion circuit that logarithmically compresses the output, that is, a logarithmic amplifier circuit.

Such a logarithmic amplifier circuit has a very complicated structure, further increasing the cost. On the other hand, when used in voltage mode, it has the disadvantage of poor linearity when a small signal is input, that is, at low illuminance.

This invention was made in view of the above-mentioned circumstances, and therefore not only can DC signals from optical sensors be amplified, but also can be integrated as a whole on one substrate.

It is an object of the present invention to provide a photodetection amplifier that is small and can be realized at low cost.

Another object of the present invention is to provide a logarithmic compression output with good linearity in the voltage mode.

(Means for Solving the Problems) In order to achieve the object E, a photodetection amplifier according to the present invention includes a heat-resistant amorphous semiconductor layer having a transparent electrode and a P-I-N junction on a transparent substrate. A photosensor section is formed by sequentially stacking the metals, and a gate electrode 6 insulating film, an I-
A thin film transistor is formed by sequentially stacking an N-junction amorphous semiconductor layer and interlocking comb-shaped source and drain electrodes, and the gate electrode of this thin film transistor is connected to the transparent electrode of the photosensor section. Features.

In addition, in the photodetection amplifier having the above configuration, a partial pressure resistor is formed by sequentially stacking a ■-type amorphous semiconductor layer and a metal electrode on the same transparent substrate on which a light-shielding film is formed and which is close to the photosensor section and the thin film transistor. A portion and a source resistance portion are formed, and the photosensor portion is connected between the voltage dividing resistance portion and the gate electrode of the thin film transistor.

Furthermore, in the photodetection amplifier according to the invention set forth in claim 3, the thin film transistors are formed by connecting the thin film transistors in a plurality of stages on the same substrate in Darlington, and the first stage of the thin film transistors causes the voltage output of the photosensor section to become non-linear. It is characterized by being configured to correct the gender.

(Function) According to the present invention, by configuring the photosensor section to be electrically connected directly to the gate electrode of the thin film transistor,
It is possible to amplify and output the DC signal of the detection signal from the optical sensor section without using a capacitor, and since a coupling capacitor is not required, there is no need to attach an external optical sensor, and the optical sensor section and Thin film transistors can be easily integrated and integrated on the same substrate by a film formation technique using an amorphous semiconductor.

Furthermore, the voltage dividing resistor and source resistor for bias voltage application are also layered on the same substrate as the photosensor and transistor using amorphous semiconductor film formation technology, resulting in a one-chip device. A photodetector amplifier can be obtained.

Furthermore, multiple stages of thin film transistors are formed by Darlington connection on the same substrate using amorphous semiconductor film formation technology, and the first stage of the thin film transistors is configured to correct the nonlinearity of the voltage output of the photosensor section. By appropriately setting the amplification factor of this thin film transistor, it is possible to obtain a logarithmically compressed output with good linearity by utilizing the nonlinearity of the gain.

(Example) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows an external plan view of the entire voltage mode photodetection amplifier of the present invention, and FIGS. 2 to 4 show the cross-sectional structure taken along the ■-■ line, the lo-m line, and the ff-IV line in FIG. 1. shows.

In FIG. 1, S is a photosensor section, Tr is a thin film transistor, R1 and R2 are voltage dividing resistors for bias voltage application, RL is a source resistor, T (V) is an input terminal, and T (
0) is an output terminal portion, T (GMD) is a ground terminal portion, and as shown in Figs. 2 to 4, these elements are formed on the same heat-resistant transparent substrate lO, such as glass. ing.

Further, on the entire surface of the transparent substrate 10F, there is a light shielding layer 11911 such as a metal film or a resin containing a pigment, and silicon oxide (SiOz) or silicon nitride (SiOz) for insulating the elements.
An insulating film 12 made of SiN+) or the like is formed.
Of the light-shielding film 11, only the region where the photosensor section S is formed is removed by an etching technique or the like to form the light entrance window 13.

As shown in FIG. 2, tin oxide (Sn02) or ITO (
A transparent electrode 14 made of a material such as indium oxide (tin oxide) is formed by a thermal decomposition method, an electron beam method, a sputtering method, etc. 5
A P-1-N bonded amorphous silicon semiconductor layer 15 is deposited on the transparent electrode 14 to a film thickness of 00 to 200 OA. aluminum (1) and nickel (Ni),
The optical sensor section S is formed by depositing a heat-resistant metal electrode 16 such as chromium (Or) or titanium (Ti).

The amorphous silicon semiconductor scrap 15 in the optical sensor section S is produced by plasma CVD, which decomposes a reaction film-forming gas in which a silicon compound gas such as silane or disilane and a carrier gas such as hydrogen are mixed in a predetermined ratio by glow discharge. The P layer is formed to a film thickness of 100 to 500A using a reaction gas obtained by mixing a P-type doping gas such as Siborane (B2H6) with the above-mentioned reaction film forming gas. , the first layer is a non-doped reactive film forming gas on top of it,
The 8 layers are formed to a film thickness of 0.3 to 2 ILvi, and the 8 layers are further coated with a reaction gas obtained by mixing an N-type doping gas such as phosphine with the above-mentioned reaction film forming gas to form a film of 500Ai! It is formed to have a film thickness after I.

The thin film transistor T" is formed on the transparent substrate 10 as shown in FIG.
A gate electrode 17 is deposited on the insulating film lz under the same film forming conditions as the transparent electrode 14 in the photosensor section S, and silicon oxide (
An insulating thin film 18 made of silicon nitride (SiOz) or silicon nitride (SiN4) is coated with a film of 500 to 2
The insulating film 1118 is coated with a thickness of 000A, and I
A -N junction amorphous silicon semiconductor layer 19 is deposited, and an active element consisting of a comb-shaped source electrode 20 and a drain electrode 21 is formed on the amorphous silicon semiconductor layer 19 to a thickness of 1 μm. It is constituted by forming.

The amorphous silicon semiconductor layer 19 in this thin film transistor Tr forms a channel between the source electrode 20 and the drain electrode 21 depending on the voltage applied to the gate electrode 17.

The first layer is formed to a thickness of 50G-10000λ FfJ using a non-doped reactive film-forming gas in which a silicon compound gas such as silane or disilane and a carrier gas such as hydrogen are mixed at a predetermined ratio using plasma CVD or optical CVD. The N layer is coated with a reactive gas containing an N-type doping gas such as phosphine in the above-mentioned reactive film-forming gas.
It is formed to have a film thickness of ~500λ.

Further, the source electrode 20 and the drain electrode 21 are made of nickel (Xi), nickel (Xi),
Aluminum (1), titanium (Ti), chromium (Or)
After depositing a metal film such as by vacuum evaporation, sputter song, etc., it is patterned into a predetermined comb shape by photolithography, resist etching, etc. That is, a channel is formed in the amorphous silicon semiconductor layer 19 according to the voltage applied to the gate electrode 17, and electrons are moved to the opposing portions of the source electrode 20 and the drain electrode 21 that are interlocked with each other. There is.

Furthermore, the voltage dividing resistance sections R1 and R2 and the source resistance section RL are as follows:
As clearly shown in FIGS. 4 and 3, the above insulation P
On a12, an amorphous silicon semiconductor layer 22 having only a ■-type layer is deposited, and on top of that, a nickel (N layer) is deposited as in the active element in the S-film transistor Tr.
, aluminum (AIL), titanium (Ti), chromium (
After depositing gold Jtill such as Cr), an electrode 23 patterned into a predetermined comb shape is formed by photolithography, resist etching, or the like.

It is configured.

In the photodetection amplifier consisting of the following elements, electrical connections between the elements are made by patterning the electrodes 17, 20, 21 and 23, as shown in the equivalent circuit diagram of FIG. 5(A). , the optical sensor section S is directly connected between the gate electrode 17 of the thin film transistor Tr and the connection point of the voltage dividing resistor sections R1 and R2.

In addition, in FIG. 1 to No. 41iid, 24 represents each of the above-mentioned terminal portions T(V), T(0), T(GND).
This is an insulating protective film formed to cover all parts except for.

According to the photodetection amplifier having the above configuration, when light is irradiated from the transparent electrode 14 side through the transparent substrate lO and the light incidence window 13, the light reaches the amorphous silicon semiconductor layer 15 via the transparent electrode 14. , this amorphous silicon semiconductor layer 15
Carriers are generated from one layer according to the spectral sensitivity of the carrier. Then, carriers are collected in the P layer and NN3 due to the electric field at the interface with the PM and N layers sandwiching this one layer, and the metal electrode 1
Photovoltaic force is derived from between the transparent electrode 14 and the transparent electrode 14 .

This photovoltaic force is applied to the gate electrode 17 of the thin film transistor Tr.
is applied to the amorphous silicon semiconductor 711 of the thin film transistor Tr in accordance with the voltage applied to the gate electrode 17.
A channel is formed in 9, and electrons move to opposing portions of source electrode 20 and drain electrode 21 that are interlocked with each other. At this time, the operating point is shifted by superimposing a negative bias voltage on the photoelectromotive force generated by the photosensor S that is applied to the gate electrode 17 of the F thin film transistor Tr through the voltage-dividing resistors R1 and R2. Let me vJ
Output characteristics as shown in diagram G can be obtained, and an output that sufficiently amplifies the amount of light produced by one person can be obtained.

By the way, the photodetection amplifier with the above configuration has a photosensor section S.
Since it is directly connected to the gate electrode 17 of the thin film transistor Tr without using a coupling capacitor, the DC signal of the detection signal by the photosensor section S can also be amplified, and -L As mentioned above, Using amorphous silicon semiconductor I & film formation technology, optical sensor section S
It is very easy to integrate and integrate the thin film transistor T and the thin film transistor T on one substrate, and it is possible to obtain a photodetector amplifier that is small and low cost as a whole.

FIG. 5(B) shows an equivalent circuit diagram of a current mode photodetection amplifier. Although the specific structure is omitted in this case, the mold A resistor formed by depositing an amorphous silicon semiconductor layer having only a single layer, and forming a comb-shaped metal electrode of nickel (Xi), aluminum (An, titanium (〒1), chromium (Car), etc.) on the amorphous silicon semiconductor layer. What is necessary is to add a section R and connect this resistor section R in parallel to the optical sensor section S.

FIG. 7 shows an equivalent circuit diagram of a voltage mode photodetection amplifier in another embodiment of the present invention, in which a gate electrode, an insulating thin film, an amorphous silicon semiconductor layer with an I-N junction are formed on a substrate '1 in sequence! Two thin film transistors, Tri and Tr, each having an L layer and a comb-shaped source electrode and a comb-shaped drain electrode formed on the amorphous silicon semiconductor layer.
2 is Darlington connected, and the gate electrode of the first stage thin film transistor Tri and Iy! A transparent electrode and a P-I-N junction were connected between the connection points of the voltage dividing resistors R1 and R2, which are formed by laminating an amorphous silicon semiconductor layer having a Li layer and a metal electrode on the same substrate as above. A photosensor section S formed by laminating an amorphous silicon semiconductor layer and a heat-resistant metal electrode on the same substrate as above is directly connected, and the drain electrodes of the two thin film transistors Tri and Tr2 are connected to
Stabilizing resistors R1 and R2 formed by laminating an amorphous silicon semiconductor layer having a mold layer and a metal electrode on the same substrate as above.
are connected by buttering.

FIG. 8 is a schematic flow diagram showing the operation of the photodetection amplifier having the circuit configuration shown in FIG. 7 above along the flow of signals. At the open end of the section S, a logarithmically compressed voltage (
Voc) is output. This output voltage (Voc) does not have linearity, especially on the low illuminance side, and is distorted so as to draw a curve in the -h direction.

Next, the nonlinear output voltage (V oc) of the photosensor section S is applied to the gate electrode of the first-stage thin film transistor Trl, so that the voltage (V oc)
is amplified, but at this time, the first stage thin film transistor T
The amplification factor (L) with respect to the gate voltage (V) of rl, that is, the gain characteristic, is the amplification factor (L) with respect to the gate voltage (V) of rl, as shown in Fig. 9 (B). It has linearity. Paying attention to this point, the usage range (cross) of the amplification factor (L) of the first stage thin film transistor Tri is
is the output voltage (V oc
), it is possible to correct the nonlinearity of the output voltage (Voc) and obtain a logarithmic output with good linearity.

Next, by superimposing a DC component on the output voltage with good linearity and applying it to the gate electrode of the second-stage thin film transistor Tr2, the J: distribution voltage can be amplified to the required voltage and output. .

Also in the photodetection amplifier having the circuit configuration shown in FIG. 7 having the above-mentioned operating characteristics, a photosensor section S, two thin film transistors T rl and T r2, and a resistor section R1゜R2, R
Although L, R1, and R2 are all integrated on the same substrate using an amorphous silicon semiconductor layer deposition technology, it is a one-chip device, but the specific manufacturing method and structure only increase the number of elements. Since this embodiment is substantially the same as the embodiment shown in FIGS. 1 to 4, illustration and description thereof will be omitted.

In each of the above embodiments, the amorphous silicon semiconductor layer may be converted into a crystal structure by injection of energy such as argon laser light.

(Effects of the Invention) As described above, according to the present invention, by directly connecting the photosensor part to the gate electrode of the thin film transistor without using a coupling capacitor, the DC signal detected by the photosensor part can also be detected by the photosensor part. It can be amplified and output, thereby improving the sensitivity characteristics of the photodetection amplifier and expanding its applications.

Moreover, since there is no need to attach the optical sensor section externally, the optical sensor section and thin film transistor can be used together.

By applying film-forming technology, it can be easily integrated and assembled on the same substrate, and therefore, as mentioned above, it is possible to miniaturize and reduce manufacturing costs of photodetector amplifiers with excellent sensitivity characteristics and noise resistance. It has the effect that it can be realized.

In particular, by integrating and fixing the resistor section on the same substrate, the entire photodetection amplifier can be made into a single-chip device, which reduces the size and cost of equipment that incorporates this kind of photodetection amplifier. It also has the effect of contributing to

In addition, by forming multiple stages of thin film transistors in Darlington connection on the same substrate, and configuring the first stage thin film transistor to correct the nonlinearity of the output voltage of the photosensor section, it is possible to achieve compact and low cost photodetection. This has the effect that the logarithm compression output in the amplifier can be made to have good linearity.

[Brief explanation of drawings]

FIG. 1 is a plan view showing an embodiment of a photodetection amplifier according to the present invention, FIG. 2 is a longitudinal sectional view taken along the line ■-■ in FIG. 1, and FIG. A vertical cross-sectional view along the line, Figure 4 is the 1st
Longitudinal cross-sectional view along the line N-IV in Figure 5 (A) (
B) is an equivalent circuit diagram of the circuit shown in Figs. 1 to 4, and Fig. 6
7 is an equivalent circuit diagram of a photodetection amplifier in another embodiment of the present invention, FIG. 8 is a schematic flow diagram explaining the operation of the photodetection amplifier shown in FIG. 7, and FIG. 9 is an amplification characteristic diagram. (A
), (B) are operational characteristic diagrams of each part of the photodetection amplifier shown in FIG. 7, and FIGS. 10 (A) and (B) are conventional diagrams. FIG. 2 is a circuit diagram of a photodetection amplifier of FIG. DESCRIPTION OF SYMBOLS 10... Transparent substrate, 11... Light shielding film, 14... Transparent electrode, 15, 19.22... Amorphous silicon semiconductor layer, 18.23... Metal electrode, 17... Gate electrode. 18... Insulating thin film, 20... Source electrode, 21...
- Drain electrode, S...photo sensor section, Tr...thin film transistor, R1, R2, RL...resistance section. that's all

Claims (3)

[Claims] (1) A transparent electrode, a P-I-N junction amorphous semiconductor layer, and a heat-resistant metal are sequentially laminated on a transparent substrate to form a photosensor part, and a light-shielding film is formed adjacent to the photosensor part. A gate electrode, an insulating film, an I-
A thin film transistor is formed by sequentially stacking an N-junction amorphous semiconductor layer and interlocking comb-shaped source and drain electrodes, and the gate electrode of this thin film transistor is connected to the transparent electrode of the photosensor section. Features of the photodetection amplifier. (2) An I-type amorphous semiconductor layer and a metal electrode are sequentially laminated on the same transparent substrate on which a light-shielding film is formed and which is close to the optical sensor section and the thin film transistor to form a voltage dividing resistor section and a source resistor section. 2. The photodetection amplifier according to claim 1, wherein the photosensor section is connected between the voltage dividing resistor section and the gate electrode of the thin film transistor. (3) A photodetector characterized in that the thin film transistors are formed in multiple stages on the same substrate in Darlington connection, and the first stage of the thin film transistors is configured to correct nonlinearity of the voltage output of the photosensor section. amplifier.