RU2616222C1 - Device for amplifying signal from matrix photodetector cell - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: photosensitive cell and amplifier, configured as a thin-film field transistor, are produced monolithically on a common substrate transparent to the radiation detectable range in the device for amplifying the signal from the matrix photodetector cell. In addition, the photosensitive organic layer is made of the organic materials on the basis of the polymethine dyes in the photosensitive cell.

EFFECT: realisation of the possibility of manufacturing the monolithic lines and matrices of the organic photodetectors in the version with the active amplification of small charge and photoconductivity current, which will amplify the signal from the photodetector cell and avoid the hybrid assembly.

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Description

The invention relates to the field of semiconductor, organic and hybrid optoelectronics and can be used in optical information processing systems.

A device for reading and storing signals from multi-element infrared photodetectors (description of the patent of the Russian Federation No. 2498456 for the invention, IPC: H01L 27/14), which consists in the fact that the read cell is made up of an integrating amplifier, a sample and storage cell, a comparator, a trigger - latches, logical element "AND". Analog elements - an integrating amplifier, a sampling and storage cell, a comparator are connected in series in the indicated order relative to one of the inputs of each with analog buses. The integrating amplifier is connected to a photodetector.

The disadvantages of this device include the fact that the device for reading and storing signals is made on a silicon substrate opaque in the visible and near infrared range, then a hybrid assembly of the photosensitive matrix and the device for reading and storing the signal (multiplexer) is performed, i.e., the device is not monolithic , and, in addition, the design of the device is such that organic photosensitive layers cannot be used as the photosensitive element.

A device for amplifying signals from a photodetector (description of US patent No. 7935917 B2 for invention, IPC: H01L 27/14 and G05D 25/02), which consists in the fact that the photodetecting device includes a module that amplifies a signal that has electrical contact with a photosensitive transistor. The module is able to cut off the dark (background) current and amplify the signal current. The second module, amplifying the signal, has electrical contact with the first module and is capable of detecting a constant component of the signal current.

The disadvantages of this device include the fact that the photosensitive device is a phototransistor, and not a photodiode or photo resistance, it is more difficult to perform, which does not allow using organic photosensitive layers as a photosensitive element.

As the closest analogue, we took a photodetector signal amplification device (description of RF patent No. 2296303 for the invention, IPC: G01J 1/44)), which means that the photodetector includes a photodiode, one output of which is connected to the photodiode power source, and the second - with load resistance and pre-amplifier input.

The disadvantage of this device is that it is not possible to amplify signals from cells of organic photodetectors made in a linear or matrix design. The reason for this is not the monolithic design of the amplification circuit and photosensitive cells on a substrate that is transparent in the detected range.

The technical result of the invention is the realization of the possibility of monolithic manufacturing of rulers and matrices of organic photodetectors in the embodiment with active amplification of a small charge and photoconductivity current, which will enhance the signal from the cell of the photodetector, as well as avoid hybrid assembly.

The technical result is achieved by the fact that in the device for amplifying the signal from the matrix photodetector cell, the photosensitive cell and amplifier, made as a thin-film field effect transistor, are made integrally on one transparent substrate in the range of detectable radiation, namely, a buffer dielectric is sequentially applied to a transparent substrate in the range of detectable radiation a layer that simultaneously represents an antireflection coating in the required sensitivity range, on a buffer d the electric layer is sequentially coated with a transparent electrode, a photosensitive organic layer and a tunnel-thin electrode blocking minority carriers, in addition, in parallel with the above layers, a thin-film field-effect transistor with a gate is sequentially made in the desired sensitivity range in parallel with the coating layer in the required sensitivity range dielectric, and on the surface of the tunnel-thin electrode that blocks minority carriers behind a row and a gate dielectric, a gate electrode is made on which a passivating protective dielectric is located.

The photosensitive organic layer is made of organic materials based on polymethine dyes.

The substrate is made of glass or plastic.

The proposed device for amplifying a signal from a cell of a matrix photodetector by performing a photosensitive cell and an amplifier as a thin-film field effect transistor monolithically on a common substrate transparent in the range of detectable radiation and performing a photosensitive organic layer in a photosensitive cell provides the possibility of obtaining the claimed technical result, namely: the implementation of the possibility of monolithic of manufacturing rulers and matrices of organic photodetectors in a variant with amplification small photoconductivity and charge current, which will amplify the signal from the photodetector cells, and also to avoid the hybrid assembly.

The essence of the invention is illustrated by the following description and the accompanying figures.

FIG. Figure 1 shows the structure of a photosensitive cell (PCF) with amplification.

FIG. 2 shows the connection diagram of the PCF with amplification in a line.

FIG. Figure 3 shows a diagram of the active line of the PCF operating in the photovoltaic mode.

FIG. Figure 4 shows a diagram of the active line of the PCF operating in the photodiode mode.

FIG. 1 shows the structure of a photosensitive cell (PCF) with amplification, where 1 is a substrate that is made of glass or plastic transparent in the detectable range; 2 - buffer dielectric layer, which is an antireflection coating; 3 - transparent electrode; 4 - photosensitive organic layer; 5 - tunnel-thin electrode blocking minority charge carriers; 6 - channel thin-film field effect transistor (TPT); 7 - gate dielectric; 8 - gate electrode; 9 - passivating protective dielectric.

The thickness of the substrate 1 is determined by its mechanical strength and ranges from 50 μm to 5 mm. The thickness of the buffer layer 2, which is an antireflection coating, is determined by the wavelength of the detected light signal and the refractive index of the material from which it is made, and ranges from 50 to 300 nm. The thickness of the transparent electrode 3 is determined by the optimal ratio between surface resistance and transmittance and ranges from 50 to 300 nm. The thickness of the photosensitive organic layer 4 is determined by the absorption coefficient of the material from which it is made, as well as by the diffusion length of the photoinduced charges and ranges from 10 to 1000 nm. The thickness of the tunnel-thin electrode that blocks minority charge carriers 5 is determined by the band gap of the material from which it is made and ranges from 1 to 30 nm. The thickness of the channel of the thin-film field effect transistor 6 is determined by the required value of the current in the closed state and ranges from 50 to 500 nm. The thickness of the gate dielectric 7 is determined by the magnitude of the operating voltage and ranges from 20 to 500 nm. The thickness of the gate electrode 8 is determined by the required value of the tire resistance and ranges from 50 to 300 nm. The thickness of the passivating protective dielectric is determined by the material from which it is made, and ranges from 50 to 200 nm.

The lateral dimensions of the cell are determined by the material of the photosensitive layer and the required resolution of the matrix and are from 5 to 1000 microns.

A device for amplifying a signal from a cell of a matrix photodetector is organized as follows (Fig. 1).

The substrate 1 is made of glass or plastic and is transparent in the range of detectable radiation, a buffer dielectric layer 2 is applied to it, which at the same time is an antireflection coating in the required sensitivity range. On the buffer dielectric layer 2, a transparent electrode 3, a photosensitive organic layer 4 and a tunnel-thin electrode blocking minority charge carriers 5 are sequentially deposited. On the buffer dielectric layer 2, which at the same time is an antireflection coating in the required sensitivity range, the following are successively made: a thin-film field channel transistor 6 and gate gate dielectric 7. On the surface of the tunnel-thin electrode blocking minority charge carriers - 5 and gate gate lektrika - 7 sequentially formed the gate electrode 8 and a passivation protective insulator 9.

The transparent electrode 3, the photosensitive organic layer 4 and the tunnel-thin electrode blocking minority charge carriers 5 are the working layers of the organic photodiode.

In FIG. 2 shows the connection diagram of the PCF with the amplifier in a line, where 10 is the photosensitive cell (PCF), 11 is the gate of the thin-film field effect transistor (TPT), 12 is the drain (TPT), 13 is the source (TPT).

In FIG. Figure 2 shows the connection diagram of individual PSFs with amplifying TPT in the active (amplifying) line. The drain-source current (12-13 of Fig. 2) of each TPT of the line element generates voltage signals at the load resistances (not shown in Fig. 2) that are read by a switching device assembled integrally on a substrate or by an external switching device. The proposed structure and connection scheme make it possible to create a matrix of individual PSF 10 with amplifying TPT.

There are two possible approaches for implementing a signal amplification device from the PCF 10. In the first one, an additional operating voltage is applied to the gate 11 of the TFT, such that the steepness of the TFT (the ratio of the source-drain current to the change in gate-source voltage S) at this operating point is maximum. In the second, the parameters of the TFT are selected such that its slope S is maximum at the operating voltage of the gate-source near zero, while there is no need to apply additional operating voltage to the gate 11 of the TFT.

The proposed device can be solved in two versions - n-channel and p-channel TPT.

Consider the operation of a device for amplifying a signal from a cell on an array photodetector.

Two possible schemes are proposed for realizing the lines of organic photodetectors in the embodiment with active amplification of a small charge (Fig. 3) and photoconductivity current (Fig. 4). The diagrams show the first three photosensitive cells 10 of the line with amplifiers based on thin-film field-effect transistors (N-channel MOS transistors, N-MOS). The fourth transistor, or transistor with the number K + 1 for a line of K active cells is the transistor of the operating point (TPT). TPT, together with an operational amplifier (OA), serves to create an initial bias voltage for K amplification transistors of the line (UTL). This bias is produced by TRT. The value of the initial current TPT is set by the resistor R _set in the source circuit of the TPT. The offset corresponding to the given current is transmitted through the op-amp to the combined sources of the overcurrent protection circuit. Thus, all UTLs are put into active mode with average initial currents corresponding to those established for TRT. The spread of the characteristics of the CTL should be taken into account when choosing the current TRT.

The circuit proposed in FIG. 3, operates in photovoltaic mode. The transparent contact layer of the line of photodetectors is grounded, and positive charges are generated in the lower contact layer of each pixel, which are directly connected to the gates of the corresponding UTL. The organic photosensitive cell (OFPC) itself is a charged capacitor with spurious leakage (shown by a dotted line in the diagram). This leakage allows, in the absence of illumination, zeroing the previous cell potential and restoring its original “dark” state. During exposure, a charge is integrated on the cell element, and the gate voltage of the UTL increases. The increase in the output current of the CTL begins with units of mV, since the transistor is forcibly biased and the initial current is set by the TPT + OA circuit. The generated OFDM voltage grows nonlinearly, has a logarithmic dependence, and reaches saturation at values of 0.5 ... 0.7 V. In turn, the dependence of the drain current on the gate voltage for MIS transistors has an exponential form. This ratio allows us to expect a relatively linear dependence of the output signal on the integrated exposure in the range of 300 ... 500 rel. units (50 ... 55 dB).

The circuit proposed in FIG. 4, operates in photocurrent mode. The transparent contact layer of the OFPC line is also grounded, a negative bias is applied to the lower layer of the OFPC through the load resistors Rн. ATLs also work at the beginning of the active gain section. In this mode, the resulting photocurrent is converted to the input control voltage of the CTL. Then it is amplified and allocated on the drain resistor. In this scheme, one should expect a noticeable nonlinear dependence of the output signal on the photocurrent, namely, an avalanche increase in the output current at large exposures and suppression of the initial portion of weak exposures. The situation can be corrected by switching on a parallel Rn diode in direct polarity to limit the avalanche. Resistors Rн, like diodes, must be made integrally.

In FIG. Figures 3 and 4 indicate the In switching points of the transition contacts in the case of using the technology of mechanical conjugation of the integrated plate of the active elements with a transparent OFPC layer. The signal is read from resistors in the drains of the UTL in parallel when connected to a multi-channel analog-to-digital converter (ADC) or sequentially when multiplexing the input of a single-channel fast ADC. When constructing rulers with the number of pixels more than 64, it is useful to use the hybrid version, when within a group of pixels of 32-64 elements the signal is read sequentially by synchronous multiplexers, the outputs of which are coupled to a multi-channel (32-64 input) ADC. So you can provide an operational survey of a line of 1024-4096 pixels.

The voltage gain can be estimated as SR _set (if the load resistance R _{set is} comparable to the resistance of the solid-state circuit in the closed state). According to estimates, if amorphous a-Si: H silicon is used as the material of the TFT channel, the voltage gain can reach the same order (in the near-linear mode), and in the case of polycrystalline silicon TFT, the voltage gain can reach 20 -thirty. The values given are obtained for the case of using an organic photodiode with photo-emf saturation of the order of 0.5-0.7 V.

The achievement of the technical result is confirmed by the following embodiments of the invention.

Option 1.

When implementing a device for amplifying a photo signal, an organic photodiode is used as a photosensitive cell, and amorphous silicon is used as a material for the manufacture of TPT.

Option 2

When implementing a device for amplifying a photo signal, an organic photo resistance is used as a photosensitive cell, and amorphous silicon is used as a material for manufacturing TPT.

Option 3

When implementing a device for amplifying a photo signal, an organic photodiode is used as a photosensitive cell, and polycrystalline or single-crystal silicon is used as a material for the manufacture of TPT.

Option 4

When implementing a device for amplifying a photo signal, an organic photo resistance is used as a photosensitive cell, and polycrystalline or monocrystalline silicon is used as a material for the manufacture of TPT.

Claims (5)

1. A device for amplifying a signal from a cell of a matrix photodetector containing a photosensitive cell, an amplifier and a power source connected to an amplifier, characterized in that the photosensitive cell and amplifier, made as a thin-film field effect transistor, are made integrally on a common substrate, and they are made as follows : a buffer dielectric layer is applied to the substrate, on which a transparent electrode, a photosensitive organic layer and a tunnel-thin electrode are applied sequentially, blocks In addition, in parallel with the above layers, on the buffer dielectric layer, a channel of a thin-film field effect transistor and a gate dielectric are sequentially made, and on the surface of the tunnel-thin electrode blocking the minor carrier and gate dielectric, a gate electrode is made on which a passivating electrode is located protective dielectric. 2. The device according to claim 1, characterized in that the photosensitive organic layer is made of organic materials based on polymethine dyes. 3. The device according to p. 1, characterized in that the substrate is made transparent in the range of detectable radiation. 4. The device according to claim 1, characterized in that the buffer dielectric layer at the same time is an antireflection coating in the desired sensitivity range. 5. The device according to p. 3, characterized in that the substrate is made of glass or plastic.

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