CN118090867B - A FET hydrogen sensor and its preparation method - Google Patents

Abstract

The invention discloses an FET hydrogen sensor and a preparation method thereof, relates to the technical field of hydrogen detection equipment, and aims to solve the problems of long response time, low sensitivity, low high concentration detection resolution, high cost, insufficient selectivity and the like of the hydrogen sensor in the prior art. The invention can provide various hydrogen detection schemes, thereby effectively realizing high-resolution detection of low-concentration hydrogen and having wide application scenes.

Description

A FET hydrogen sensor and its preparation method

Technical Field

The invention relates to a FET hydrogen sensor and a preparation method thereof, belonging to the technical field of hydrogen detection equipment.

Background technique

With the continuous development of hydrogen energy, fuel cell technology has become an important part of clean energy. Accurate monitoring of hydrogen concentration is crucial to the safety of the production process in the chemical, pharmaceutical, and electronic industries. The application of hydrogen sensors can detect potential leakage risks in a timely manner and effectively prevent accidents. Therefore, the demand for hydrogen sensors in industrial production is constantly expanding, and high-performance hydrogen sensors are preferred to monitor hydrogen concentration and ensure the safe operation of fuel cell systems.

At present, the research on hydrogen sensors focuses on improving safety and performance. Traditional capacitor film and thermal conductivity principle sensors have problems of difficulty in integration and high power consumption. Room temperature high-sensitivity sensors achieve sensitive detection of low-concentration hydrogen through palladium-doped tungsten trioxide and graphene, but the recovery speed and basic stability still need to be improved.

Tin oxide-based sensors have the characteristics of simple manufacturing, low production cost, and high sensitivity, and have broad application prospects. In applications, metal oxide nanomaterials are more often used as gates of FETs (field effect transistors) to achieve miniaturization and integration of hydrogen sensors. FET sensors are made using silicon planar technology and are suitable for low-concentration gas detection, but they have challenges such as long response time, low sensitivity, low resolution for high-concentration detection, high cost, and insufficient selectivity.

Summary of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art and provide a FET hydrogen sensor and a preparation method thereof, which can provide a variety of hydrogen detection schemes, thereby effectively achieving high-resolution detection of low-concentration hydrogen.

To achieve the above object, the present invention is implemented by adopting the following technical solutions:

On the one hand, the present invention provides a FET hydrogen sensor, which includes, from bottom to top, a substrate, a channel layer, a gate dielectric layer, a FET electrode, an isolation layer, a buffer layer, a hydrogen sensing layer and an interdigital electrode;

The substrate is arranged at the bottom layer of the FET hydrogen sensor;

The channel layer includes a P-type epitaxial layer and three N-doped regions, the P-type epitaxial layer is arranged on the substrate, the N-doped region is arranged on the surface of the P-type epitaxial layer, and from left to right are N-doped region A, N-doped region B and N-doped region C, a first channel is arranged between the N-doped region A and the N-doped region B, and a second channel is arranged between the N-doped region B and the N-doped region C;

The gate dielectric layer is disposed above the channel layer and covers the channel layer;

The FET electrode comprises a source electrode, a first gate electrode, a second gate electrode and a drain electrode arranged in sequence from left to right, and the source electrode, the first gate electrode, the second gate electrode and the drain electrode are all composed of a main body part and an epitaxial part in sequence from bottom to top;

The isolation layer is arranged above the gate dielectric layer and covers the main body of the FET electrode and the gate dielectric layer.

The buffer layer is disposed above the isolation layer and covers the isolation layer;

The hydrogen sensing layer is arranged above the isolation layer, and comprises a symmetrically distributed hydrogen sensitive area and a semiconductor resistance area;

The interdigital electrodes are distributed on the surface of the hydrogen sensing layer, including a first interdigital electrode, a second interdigital electrode, a third interdigital electrode and a fourth interdigital electrode. The first interdigital electrode and the fourth interdigital electrode are arranged above the hydrogen sensitive area, and the second interdigital electrode and the third interdigital electrode are arranged above the semiconductor resistance area. The first interdigital electrode is connected in series with the second interdigital electrode, and the connection point of the first interdigital electrode and the second interdigital electrode is a first voltage dividing point. The first voltage dividing point covers the part of the epitaxial part of the first gate electrode extending out of the surface of the hydrogen sensing layer. The third interdigital electrode and the fourth interdigital electrode are connected in series, and the connection point of the third interdigital electrode and the fourth interdigital electrode is a second voltage dividing point. The second voltage dividing point covers the part of the epitaxial part of the second gate electrode extending out of the surface of the hydrogen sensing layer. By connecting the corresponding interdigital electrodes in series, the semiconductor resistance area can be connected to the hydrogen sensitive area to form a working point control circuit composed of a hydrogen sensitive resistor and a semiconductor resistor in series.

Preferably, the substrate is one of aluminum oxide, silicon, silicon carbide, gallium nitride, and aluminum nitride.

Preferably, the P-type epitaxial layer adopts a P-type doped semiconductor film, the material of the P-type doped semiconductor film is one of silicon, silicon carbide, gallium nitride, and gallium arsenide, and the doping concentration is 1×10 ¹⁵ cm ^-3 to 5×10 ¹⁶ cm ^-3 , and the thickness is 0.5 to 2 μm;

The length of the N-doped region is 2-25 μm, the doping concentration is 5×10 ¹⁸ cm ^-3 ～5×10 ¹⁹ cm ^-3 , and the gate width of the channel layer is 10-100 μm;

The lengths of the first channel and the second channel are both 2-15 μm.

Preferably, the gate dielectric layer is made of one of silicon oxide, silicon nitride and gallium oxide, wherein the thickness of silicon oxide is 5-20 nm, the thickness of silicon nitride is 5-20 nm, and the thickness of gallium oxide is 6-25 nm. The thickness of the gate dielectric layer is set according to different gate dielectric layer materials so that the maximum breakdown voltage of the gate dielectric layer is greater than 50 V.

Preferably, the FET electrode material is one of nickel, platinum, aluminum, copper, gold and silver;

The main parts of the source electrode and the drain electrode are respectively arranged above the two sides away from each other of the N-doped A region and the N-doped C region, and pass through the gate dielectric layer to make ohmic contact with the N-doped A region and the N-doped C region below; the main parts of the first gate electrode and the second gate electrode are respectively arranged on the gate dielectric layer located above the first channel and the second channel;

The epitaxial part is arranged at the center of the main body part, and the upper part of the epitaxial part passes through the isolation layer and the buffer layer to the surface of the hydrogen sensing layer and is connected with the outside.

Preferably, the width of the main body of the source electrode and the drain electrode is the same as the width of the N-doped A region and the N-doped C region, respectively, and the length of the main body of the source electrode and the drain electrode is smaller than the length of the N-doped A region and the N-doped C region, respectively, and both are 1 to 15 μm;

The length and width of the first gate electrode are the same as those of the first channel, and the length and width of the second gate electrode are the same as those of the second channel;

The length of the epitaxial part is the same as that of the main part, and the width is 5-15 μm, and the thickness of the main part is 50-500 nm.

Preferably, the isolation layer is made of one of silicon oxide, silicon nitride, and aluminum oxide, and has a thickness of 1 to 2 μm. The isolation layer is provided to prevent the operating point control circuit from affecting the operation of the FET electrode, improve the signal-to-noise ratio of the sensor during operation, and protect the FET electrode.

Preferably, the buffer layer is made of gallium nitride or aluminum oxide, and has a thickness of 50 to 200 nm. Providing a buffer layer can improve the film quality, thereby improving the sensor's responsiveness to hydrogen, signal-to-noise ratio and other performances.

Preferably, the hydrogen sensitive area includes a gallium oxide film, a tin oxide film, and a hydrogen catalyst nanocluster arranged in sequence from bottom to top;

The thickness of the gallium oxide film is 50-100 nm; the gallium oxide film is selected from a gallium oxide nanobelt film or a β-phase gallium oxide film.

Preferably, the tin oxide film is a tin oxide quantum dot film, and the diameter of the quantum dots is 1 to 20 nm; wrapping the gallium oxide film with a tin oxide film can further improve the hydrogen responsiveness of the tin oxide film at room temperature, reduce the response and recovery time of the material to hydrogen, improve the resolution of hydrogen, and further achieve efficient monitoring of hydrogen.

Preferably, the material of the hydrogen catalyst nanoclusters is one or more of platinum, palladium, and nickel. The diameter of the nanoclusters is 1 to 10 nm, and the content of the nanoclusters does not exceed 5% of the total area. The hydrogen catalyst nanoclusters have a selective catalytic effect on hydrogen, preferentially catalyzing the cracking of hydrogen into hydrogen atoms, making it more reactive, so as to improve the selectivity and sensitivity of the sensor to hydrogen. The selection of the catalyst only needs to satisfy the requirement of having good catalytic properties and selectivity for hydrogen, so it is not limited to common hydrogen catalysts, and various compound catalysts that meet the other conditions are also applicable to the present invention.

Preferably, the semiconductor resistance region is made of polysilicon with a thickness of 60-130 nm.

Preferably, the hydrogen sensitive resistor is respectively composed of the first interdigitated electrode and the area within the interdigitated electrode gap and the fourth interdigitated electrode and the area within the interdigitated electrode gap in the hydrogen sensitive region, and the semiconductor resistor is composed of the second interdigitated electrode and the area within the interdigitated electrode gap and the third interdigitated electrode and the area within the interdigitated electrode gap in the semiconductor resistor region, the overall upper surface area composed of the hydrogen sensitive region, the semiconductor resistor region and the interdigitated electrodes is larger than the area occupied by the channel layer, and the overall upper surface area composed of the hydrogen sensitive region, the semiconductor resistor region and the interdigitated electrodes ranges from 150μm×150μm to 500μm×500μm.

Preferably, the material of the interdigital electrodes is one of nickel, platinum, palladium, aluminum, copper, gold, and silver. Further preferably, the material of the interdigital electrodes is nickel, platinum, and palladium. Using precious metals that have a catalytic effect on hydrogen to make interdigital electrodes can further improve the selectivity and resolution of the sensor for hydrogen and shorten the response time of the sensor.

In another aspect, the present invention provides a method for preparing a FET hydrogen sensor, the method being used to prepare the FET hydrogen sensor described in any one of the above items, comprising:

Preparation of channel layer: a P-type doped semiconductor film is arranged on a substrate to obtain a P-type epitaxial substrate;

Doping an N-doped A region, an N-doped B region, and an N-doped C region on a P-type doped semiconductor film by using an ion implantation process;

Preparing a gate dielectric layer: preparing a gate dielectric layer on the channel layer by using one of plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD), atomic layer deposition (ALD), and magnetron sputtering;

Prepare FET electrodes: remove the gate dielectric layer above the N-doped A region and the N-doped C region by photolithography until the source electrode and the drain electrode windows are completely exposed, and prepare the source electrode and the drain electrode on the source electrode and the drain electrode windows by vacuum evaporation, magnetron sputtering, or electron beam evaporation, respectively, and prepare the first gate electrode and the second gate electrode on the first channel and the second channel, respectively;

Prepare the isolation layer: deposit the isolation layer on the gate dielectric layer by one of PECVD, LPCVD and magnetron sputtering techniques, so that the isolation layer covers the FET electrode and the gate dielectric layer;

Prepare the buffer layer: deposit the buffer layer on the isolation layer by one of the following techniques: PECVD, LPCVD, ALD, MOCVD (Metal-organic Chemical Vapor Deposition);

Preparation of hydrogen sensing layer: Use one of PECVD, LPCVD, MOCVD, magnetron sputtering, and mechanical transfer technology to prepare a β-phase gallium oxide film on the buffer layer, or use thermal evaporation to prepare a gallium oxide nanobelt film on the buffer layer. Use one of dispensing, spraying, spin coating, and electrospraying technology to prepare a tin oxide film on the β-phase gallium oxide film or gallium oxide nanobelt film. Use ALD technology to prepare hydrogen catalyst nanoclusters on the surface of tin oxide to form a hydrogen sensitive area;

The hydrogen sensitive area is divided into two halves, one half is etched by photolithography until the buffer layer is completely exposed, polysilicon is prepared on the exposed buffer layer by using one of the technologies such as PECVD, LPCVD, MOCVD, etc., and the grain size and grain boundary number of the polysilicon are adjusted by using ion implantation and rapid annealing to form a semiconductor resistance area;

Epitaxially grow FET electrodes: Use photolithography to remove part of the isolation layer, buffer layer and hydrogen sensing layer covering the FET electrodes, expose part of the FET electrodes to form electrode windows, and use vacuum evaporation, magnetron sputtering or electron beam evaporation to deposit metals in the electrode windows to prepare epitaxial electrodes;

Preparation of interdigital electrodes: Interdigital electrodes are prepared on the hydrogen sensing layer using magnetron sputtering to complete the preparation of the FET hydrogen sensor.

Furthermore, the N-type ions implanted are one of phosphorus, arsenic, and antimony, and the energy range of the N-type ions is 15 to 120 Kev. During the formation of the semiconductor resistance region, the resistance value of the polysilicon resistor is adjusted by controlling the energy of the ion implantation and the time and temperature of the rapid annealing.

Furthermore, the rapid annealing temperature is 800-1000°C and the time is 20-30s. When annealing polysilicon, the grain size can be enlarged, the number of grain boundaries can be reduced, and polysilicon resistance can be formed. At the same time, the annealing process can enable the source electrode and the drain electrode to form a good ohmic contact with the semiconductor channel layer.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention combines a dual-gate FET structure, a hydrogen-sensitive gate structure, and an operating point control circuit.

The FET structure is equipped with double gate electrodes, and has the characteristics of stable operation, strong anti-interference ability, low power consumption, high gain and controllable gain, and easy integration. It can fully and reliably amplify the electrical signal converted from the chemical signal;

The hydrogen sensitive gate structure is a composite layer of gallium oxide with hydrogen catalyst nanoclusters dispersed on the surface and wrapped with tin oxide film, wherein the gallium oxide film is wrapped by tin oxide quantum dot film, which has a large specific surface area and high surface activity, and can provide more adsorption sites for gas molecules, and can achieve high-sensitivity detection of low-concentration hydrogen at room temperature; the hydrogen catalyst nanoclusters distributed on the surface of tin oxide quantum dots preferentially catalyze the cracking of hydrogen into hydrogen atoms, making it more reactive and having excellent selectivity for hydrogen. At the same time, the particle size of tin oxide quantum dots and hydrogen catalyst nanoclusters are both nanometer-level, with high surface activity, which can reduce the working temperature of gas-sensitive materials, further improving the high-sensitivity detection of low-concentration gases by the sensor at room temperature, and has a wide range of application scenarios.

Combined with the working point control circuit, a variety of hydrogen detection schemes can be provided. When the sensor is working, the current flowing through the semiconductor resistor and the hydrogen sensitive resistor is weak, and the FET is in the subthreshold region, so that the overall power consumption of the hydrogen sensor or hydrogen sensor array is low. At the same time, by adjusting different electrode voltage settings, the control of the hydrogen resolution of the sensor can be achieved, and the application scenario of the present invention can be greatly expanded, such as: FET is prepared into an integrated array in parallel, the sensor array is connected to an external integration circuit to store the sensing signal, the ADC circuit is used for signal acquisition, the computer is connected to calculate and analyze the data, the sensors in the array are uniformly biased, and the electrical signal is fully amplified by using the amplification effect of the FET and the characteristics of the drain-source current addition of each parallel FET. Gain control is achieved by uniformly adjusting the bias of the second gate electrode, the hydrogen concentration when the current reaches saturation is changed, the hydrogen measurement range is expanded, the resolution of the sensor is changed, and the adjustable gain range of the sensor after integration is expanded, which can cope with the hydrogen detection needs under different conditions; it can also be uniformly biased to make the FET in the subthreshold region or the strong inversion region. Once exposed to hydrogen, the circuit achieves gain traversal within an extremely low hydrogen concentration range, and achieves high-resolution detection of low-concentration hydrogen.

The present invention is based on the existing FET manufacturing process and can greatly reduce production costs. According to application requirements, the sensor matrix is designed, the channel length, gate dielectric layer thickness, finger electrode size are adjusted, and appropriate gate, drain, source bias and other comprehensive parameters are set, so that high-performance hydrogen sensors can be designed and prepared to cope with high-resolution, low-power, and high-efficiency hydrogen detection under different hydrogen concentrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a cross-sectional schematic diagram of a hydrogen sensitive area of a FET hydrogen sensor in an embodiment of the present invention;

FIG2 is a cross-sectional schematic diagram of a semiconductor resistance region of a FET hydrogen sensor in an embodiment of the present invention;

FIG3 is a schematic diagram of a top view of a FET hydrogen sensor in an embodiment of the present invention;

In the figure: 1-substrate, 2-channel layer, 201-P-type epitaxial layer, 202-N-doped A region, 203-N-doped B region, 204-N-doped C region, 205-first channel, 206-second channel, 3-gate dielectric layer, 4-FET electrode, 401-source electrode, 402-first gate electrode, 403-second gate electrode, 404-drain electrode, 5-isolation layer, 6-buffer layer, 7-hydrogen sensitive region, 701-gallium oxide film, 702-tin oxide film, 703-hydrogen catalyst nanoclusters, 8-semiconductor resistance region, 9-interdigitated electrodes, 901-first interdigitated electrodes, 902-second interdigitated electrodes, 903-third interdigitated electrodes, 904-fourth interdigitated electrodes, 905-first voltage dividing point, 906-second voltage dividing point.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

Example 1

As shown in FIG. 1 and FIG. 2 , the method for preparing the FET hydrogen sensor provided by the embodiment of the present invention includes:

An alumina substrate of 1 cm×1 cm was selected as substrate 1 .

Preparation of channel layer 2: A 1.5 μm thick P-type epitaxial layer 201 is prepared epitaxially on an alumina substrate using metal-organic chemical vapor deposition (MOCVD). The P-type epitaxial layer 201 is a P-type gallium nitride epitaxial layer with a doping concentration of 1.5×10 ¹⁵ cm ^-3 . An N-doped A region 202, an N-doped B region 203, and an N-doped C region 204 are prepared from left to right on the P-type gallium ^nitride epitaxial layer using an ion ^implantation process. The length of the first channel 205 between the N-doped A region 202 and the N-doped B region 203 is 10 μm, and the length of the second channel 206 between the N-doped B region 203 and the N-doped C region 204 is 12 μm. The gate width of the channel layer 2 formed is 50 μm.

Preparation of the gate dielectric layer 3: A 10 nm thick gallium oxide is prepared on the channel layer 2 by plasma enhanced chemical vapor deposition as the gate dielectric layer 3, and its theoretical breakdown voltage is greater than 80V.

In some embodiments, the plasma enhanced chemical vapor deposition can be adjusted to any one of low pressure vapor deposition, atomic layer deposition, and magnetron sputtering.

Preparation of FET electrode 4: Use standard photolithography process to remove the gate dielectric layer 3 directly above the N-doped A region 202 and the N-doped C region 204 until the N-doped A region 202 and the N-doped C region 204 are completely exposed to form the source electrode 401 and the drain electrode 404 electrode windows. The width of the photolithography area is consistent with that of the N-doped A region 202 and the N-doped C region 204, both of which are 50 μm, and the length is smaller than that of the N-doped A region 202 and the N-doped C region 204, which is 8 μm, and is arranged close to the side away from the N-doped A region 202 and the N-doped C region 204.

The source electrode 401 and the drain electrode 404 are made of silver and have a thickness of 70 nm, respectively, and are formed into an ohmic contact with the channel layer 2 by magnetron sputtering. The first gate electrode 402 and the second gate electrode 403 are made of silver and have a thickness of 60 nm, respectively, and are formed directly above the first channel 205 and the second channel 206 by magnetron sputtering.

In some embodiments, the magnetron sputtering process can be adjusted to any one of vacuum evaporation and electron beam evaporation processes.

Preparation of isolation layer 5 : MOCVD is used to deposit an aluminum oxide isolation layer 5 with a thickness of 1.5 μm on the gallium oxide gate dielectric layer 3 , which completely covers all FET electrodes 4 and the gate dielectric layer 3 .

In some embodiments, MOCVD can be adjusted to any one of plasma enhanced chemical vapor deposition, low pressure vapor deposition, and magnetron sputtering processes.

Preparation of buffer layer 6: Using MOCVD, a gallium nitride buffer layer 6 with a thickness of 100 nm is deposited on the isolation layer 5.

In some embodiments, MOCVD can be adjusted to any one of plasma enhanced chemical vapor deposition, low pressure vapor deposition, magnetron sputtering, and ALD processes.

Preparation of hydrogen sensing layer: A 70 nm thick gallium oxide nanobelt film is prepared on the gallium nitride buffer layer 6 by thermal evaporation. A 25 nm thick tin oxide quantum dot film is prepared on the gallium oxide nanobelt film by spin coating, and the quantum dot diameter is 10 nm. A platinum hydrogen catalyst nanoclusters are prepared on the surface of the tin oxide quantum dot film by ALD technology, and the diameter of the platinum hydrogen catalyst nanoclusters is 7 nm. The content of the platinum hydrogen catalyst nanoclusters is 6% of the total surface area of the tin oxide film 702, thereby forming a hydrogen sensitive area 7.

In some embodiments, the spin coating process can be adjusted to any one of dispensing, spraying, and electrospraying processes.

Using standard photolithography, the lower half of the hydrogen sensitive region 7 (i.e., the semiconductor resistance region 8) is etched until the gallium nitride buffer layer 6 is completely exposed. A polycrystalline silicon film with a thickness of 95 nm is prepared using MOCVD technology. The grain size and grain boundary number of the polycrystalline silicon are adjusted using ion implantation and annealing processes.

The N-type ions implanted are one of phosphorus, arsenic and antimony, and the energy range of the N-type ions is 15 to 120 KeV. During the formation of the semiconductor resistance region 8, the resistance value of the polysilicon resistor is adjusted by controlling the energy of the ion implantation and the time and temperature of the rapid annealing.

The rapid annealing temperature is 800-1000°C and the time is 20-30s. When annealing polysilicon, the grain size can be enlarged, the number of grain boundaries can be reduced, and polysilicon resistance can be formed. At the same time, the annealing process can make the source electrode 401 and the drain electrode 404 form a good ohmic contact with the semiconductor channel layer 2.

Epitaxially grow FET electrodes: using standard photolithography process, with the center of the gate width as the reference line, remove all semiconductor materials (isolation layer, buffer layer and hydrogen sensing layer) of 8μm×15μm above the source electrode 401 and the drain electrode 404, remove all semiconductor materials of 10μm×15μm above the first gate electrode 402, and all semiconductor materials of 12μm×15μm above the second gate electrode 403 until part of the FET electrode is exposed to form an electrode window, and use vacuum evaporation process or magnetron sputtering or electron beam evaporation process to deposit silver in the electrode window to prepare epitaxial electrode to lead out the FET electrode, so as to form the epitaxial part of the FET electrode.

Preparation of interdigital electrodes: magnetron sputtering is used to sequentially arrange four platinum interdigital electrodes with an interdigital spacing of 4 μm, a pair number of 20, a length of 60 μm, and a thickness of 60 nm in an area of 200 μm×200 μm directly above the center of the hydrogen sensing layer, wherein the first interdigital electrode 901 and the fourth interdigital electrode 904 are arranged above the hydrogen sensitive area 7, and the second interdigital electrode 902 and the third interdigital electrode 903 are arranged above the semiconductor resistance area 8. The hydrogen sensing resistor of the hydrogen sensitive area 7 and the semiconductor resistor of the semiconductor resistance area 8 are both composed of the interdigital electrodes 9 in their area and the area in the gap between the interdigital electrodes 9. The resistance value of the prepared hydrogen sensing resistor when not exposed to hydrogen is in the same order of magnitude as the resistance value of the semiconductor resistor.

The first interdigital electrode 901 is connected in series with the second interdigital electrode 902, and the connection point is the first dividing voltage point 905. The first dividing voltage point 905 covers the part of the epitaxial part of the first gate electrode 402 extending out of the surface of the hydrogen sensing layer. The third interdigital electrode 903 is connected in series with the fourth interdigital electrode 904, and the connection point is the second dividing voltage point 906. The second dividing voltage point 906 covers the part of the epitaxial part of the second gate electrode 403 extending out of the surface of the hydrogen sensing layer. The series interdigital electrodes 9 connect the semiconductor resistance area 8 with the hydrogen sensitive area 7, forming an operating point control circuit composed of a hydrogen sensitive resistor and a semiconductor resistor in series, and completing the preparation of the FET hydrogen sensor, and its top view is shown in Figure 3.

Example 2

The method for preparing the FET hydrogen sensor provided by the embodiment of the present invention comprises:

A 1 cm×1 cm silicon substrate is selected as the substrate 1 .

Preparation of channel layer 2: A P-type epitaxial layer 201 is prepared on a silicon substrate using a standard photolithography process and a thermal diffusion process. The P-type epitaxial layer 201 uses a P-type silicon epitaxial layer with a doping concentration of 2× ^{10 15 cm -3} . An N-doped A region 202, an N-doped B region 203, and an N-doped C region 204 are prepared from left to right on the P-type silicon epitaxial layer using an ion implantation process. The length of the first channel 205 between the N-doped A region 202 ^and the N-doped B region 203 is 8 μm, and the length of the second channel 206 between the N-doped B region 203 and the N-doped C region 204 is 12 μm. The gate width of the channel layer 2 formed is 40 μm.

Preparation of gate dielectric layer 3: Silicon nitride with a thickness of 12 nm is prepared on the channel layer 2 by magnetron sputtering as the gate dielectric layer 3, and its theoretical breakdown voltage is greater than 100V.

Preparation of FET electrode 4: Use standard photolithography process to remove the gate dielectric layer 3 directly above the N-doped A region 202 and the N-doped C region 204 until the N-doped A region 202 and the N-doped C region 204 are completely exposed to form the source electrode 401 and the drain electrode 404 electrode windows. The width of the photolithography area is consistent with that of the N-doped A region 202 and the N-doped C region 204, both of which are 40 μm, and the length is smaller than that of the N-doped A region 202 and the N-doped C region 204, which is 8 μm, and is arranged close to the side away from the N-doped A region 202 and the N-doped C region 204.

The source electrode 401 and the drain electrode 404 are made of gold and have a thickness of 72 nm, respectively, and the source electrode 401 and the drain electrode 404 form an ohmic contact with the channel layer 2. The first gate electrode 402 and the second gate electrode 403 are made of gold and have a thickness of 60 nm, respectively, and are prepared directly above the first channel 205 and the second channel 206 by the magnetron sputtering process.

Preparation of isolation layer 5 : A silicon nitride isolation layer 5 with a thickness of 2 μm is deposited on the silicon oxide gate dielectric layer 3 by using MOCVD, which completely covers all FET electrodes 4 and the gate dielectric layer 3 .

Preparation of buffer layer 6: Using MOCVD, an aluminum oxide buffer layer 6 with a thickness of 50 nm is deposited on the isolation layer 5.

Preparation of hydrogen sensing layer: A 50 nm thick β-phase gallium oxide film was prepared on the aluminum oxide buffer layer 6 using MOCVD. A 30 nm thick tin oxide quantum dot film was prepared on the β-phase gallium oxide film using electrospray printing technology, and the quantum dot diameter was 15 nm. Pd nanoclusters were prepared on the surface of the tin oxide film using ALD technology, and the diameter of the Pd nanoclusters was 3 nm. The content of Pd nanoclusters was 3% of the total surface area of the tin oxide film, thereby preparing a hydrogen sensitive area 7.

Using standard photolithography, the lower half of the hydrogen sensitive region 7 (i.e., the semiconductor resistance region 8) is etched until the aluminum oxide buffer layer 6 is completely exposed. A polycrystalline silicon film with a thickness of 100 nm is prepared using MOCVD technology. The grain size and grain boundary number of the polycrystalline silicon are adjusted using ion implantation and annealing processes.

Epitaxially grow FET electrodes: using standard photolithography technology, with the center of the gate width as the reference line, remove all semiconductor materials (isolation layer, buffer layer and hydrogen sensing layer) of 8μm×15μm above the source electrode 401 and the drain electrode 404, remove all semiconductor materials of 8μm×15μm above the first gate electrode 402, and all semiconductor materials of 12μm×15μm above the second gate electrode 403, until part of the electrode is exposed to form an electrode window, use magnetron sputtering technology to deposit silver in the electrode window to prepare epitaxial electrodes to lead out the FET electrodes, and form the epitaxial part of the FET electrodes.

Four platinum interdigital electrodes 9 with an interdigital spacing of 4 μm, a pair number of 20, a length of 60 μm, and a thickness of 60 nm are sequentially arranged in a 200 μm×200 μm area directly above the center of the hydrogen sensing layer by magnetron sputtering, wherein the first interdigital electrode 901 and the fourth interdigital electrode 904 are arranged above the hydrogen sensitive area 7, and the second interdigital electrode 902 and the third interdigital electrode 903 are arranged above the semiconductor resistance area 8. The hydrogen sensing resistor of the hydrogen sensitive area 7 and the semiconductor resistor of the semiconductor resistance area 8 are composed of the interdigital electrodes 9 in the area and the area in the gap between the interdigital electrodes 9. The resistance value of the prepared hydrogen sensing resistor when not exposed to hydrogen is in the same order of magnitude as the resistance value of the semiconductor resistor.

The first interdigital electrode 901 is connected in series with the second interdigital electrode 902, and the connection point is the first dividing voltage point 905. The first dividing voltage point 905 covers the part of the epitaxial part of the first gate electrode 402 extending out of the surface of the hydrogen sensing layer. The third interdigital electrode 903 is connected in series with the fourth interdigital electrode 904, and the connection point is the second dividing voltage point 906. The second dividing voltage point 906 covers the part of the epitaxial part of the second gate electrode 403 extending out of the surface of the hydrogen sensing layer. The series interdigital electrodes 9 connect the semiconductor resistance area 8 with the hydrogen sensitive area 7, forming an operating point control circuit composed of a hydrogen sensitive resistor and a semiconductor resistor in series, and completing the preparation of the FET hydrogen sensor.

The standard photolithography process used in Example 1 and Example 2 may include processes such as coating, exposure, development, and degumming, but is not limited thereto. The specific parameters of all processes in the process of preparing the hydrogen sensor can be set by those skilled in the art according to actual needs, and will not be elaborated or limited here.

working principle:

There are three ways to connect the prepared FET hydrogen sensor during use. Specifically, the first connection method is:

The source electrode 401 and the drain electrode 404 are led out through an external wire or probe and connected in series with the source electrode 401 and the drain electrode 404. The second voltage dividing point 906 is led out through an external wire or probe, and the first interdigital electrode 901 and the second interdigital electrode 902 are led out through an external wire or probe and connected in series with the first interdigital electrode 901 and the second interdigital electrode 902.

A fixed bias is applied between the source electrode 401 and the drain electrode 404, and an adjustable bias is applied at the second voltage dividing point 906 to control the opening degree of the second channel 206. Fixed biases are set at the first interdigital electrode 901 and the second interdigital electrode 902, respectively. The potential of the first interdigital electrode 901 (hydrogen sensitive region 7) is high, and the potential of the second interdigital electrode 902 (semiconductor resistance region 8) is low. The fixed biases set at the first interdigital electrode 901 and the second interdigital electrode 902 are adjusted, and then the potential at the first voltage dividing point 905 is adjusted, so that the first gate electrode 402 is in the subthreshold region.

When the hydrogen sensitive area 7 is exposed to hydrogen, the hydrogen sensitive resistance decreases, the potential of the first voltage dividing point 905 increases, and the chemical signal is converted into an electrical signal. The current signal is amplified by the amplification effect of the FET hydrogen sensor. The sensor is connected to an external integration circuit to store the sensing signal, and the ADC circuit is used for signal acquisition, and the computer is connected to calculate and analyze the data. Gain control can be achieved by adjusting the bias voltage of the second gate electrode 403 (since the second gate electrode 403 is led out by a wire, its bias voltage can be directly adjusted), changing the hydrogen concentration when the current reaches saturation, changing the resolution of the sensor, and expanding the hydrogen measurement range to meet the needs of hydrogen detection in different situations.

The second connection method is:

The source electrode 401 and the drain electrode 404 are led out through an external wire or a probe and connected in series with the source electrode 401 and the drain electrode 404. The first interdigital electrode 901 and the second interdigital electrode 902 are led out through an external wire or a probe and connected in series with the first interdigital electrode 901 and the second interdigital electrode 902. The third interdigital electrode 903 and the fourth interdigital electrode 904 are led out through an external wire or a probe and connected in series with the third interdigital electrode 903 and the fourth interdigital electrode 904.

A fixed bias is applied between the source electrode 401 and the drain electrode 404, and a fixed bias is set at the first interdigital electrode 901 and the second interdigital electrode 902, respectively. The potential of the first interdigital electrode 901 (hydrogen sensitive area 7) is high, and the potential of the second interdigital electrode 902 (semiconductor resistance area 8) is low. The fixed biases set at the first interdigital electrode 901 and the second interdigital electrode 902 are adjusted, and the potential at the first voltage dividing point 905 is adjusted, so that the first gate electrode 402 is in the subthreshold region. Fixed biases are set at the third interdigital electrode 903 and the fourth interdigital electrode 904, respectively. The potential of the fourth interdigital electrode 904 (hydrogen sensitive area 7) is high, and the potential of the third interdigital electrode 903 (semiconductor resistance area 8) is low. The fixed biases set at the fourth interdigital electrode 904 and the third interdigital electrode 903 are adjusted, and the potential at the second voltage dividing point 906 is adjusted, so that the second gate electrode 403 is in the subthreshold region. When the hydrogen sensitive area 7 is exposed to hydrogen, the hydrogen sensitive resistance decreases, the potentials of the first voltage dividing point 905 and the second voltage dividing point 906 both rise, and gain traversal is achieved in an extremely low hydrogen concentration range. The sensor is connected to an external transimpedance amplifier circuit to amplify the signal, the ADC circuit to sample, and the single chip microcomputer circuit to process and display the signal, thereby achieving high-resolution detection of low-concentration hydrogen.

The third connection method:

Lead out the first interdigital electrode 901 and the second interdigital electrode 902 through an external wire or probe and connect them in series. Lead out the third interdigital electrode 903 and the fourth interdigital electrode 904 through an external wire or probe and connect them in series.

When the hydrogen sensor is working, different fixed bias voltages can be set on the interdigitated electrodes 9 above the first gate electrode 402 or the second gate electrode 403, and hydrogen detection can be achieved when no power is supplied to the source electrode 401 and the drain electrode 404 by measuring the voltage change of the first voltage dividing point 905 or the second voltage dividing point 906 before and after exposure to the hydrogen atmosphere.

The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims (10)

1. A FET hydrogen sensor, characterized in that it includes, from bottom to top, a substrate, a channel layer, a gate dielectric layer, a FET electrode, an isolation layer, a buffer layer, a hydrogen sensing layer and an interdigital electrode; The channel layer includes a P-type epitaxial layer and three N-doped regions, the P-type epitaxial layer is arranged on a substrate, the three N-doped regions are arranged on a surface of the P-type epitaxial layer, the three N-doped regions are N-doped A region, N-doped B region and N-doped C region from left to right, a first channel is arranged between the N-doped A region and the N-doped B region, and a second channel is arranged between the N-doped B region and the N-doped C region; The gate dielectric layer is disposed above the channel layer and covers the channel layer; The FET electrode comprises a source electrode, a first gate electrode, a second gate electrode and a drain electrode arranged in sequence from left to right, wherein the source electrode, the first gate electrode, the second gate electrode and the drain electrode are all composed of a main body part and an epitaxial part in sequence from bottom to top; The isolation layer is disposed above the gate dielectric layer and covers the main body of the FET electrode and the gate dielectric layer; The buffer layer is disposed above the isolation layer and covers the isolation layer; The hydrogen sensing layer is arranged above the isolation layer, and the hydrogen sensing layer comprises a symmetrically distributed hydrogen sensitive area and a semiconductor resistance area; The interdigital electrodes are distributed on the surface of the hydrogen sensing layer, including a first interdigital electrode, a second interdigital electrode, a third interdigital electrode and a fourth interdigital electrode. The first interdigital electrode and the fourth interdigital electrode are arranged above the hydrogen sensitive area, and the second interdigital electrode and the third interdigital electrode are arranged above the semiconductor resistance area. The first interdigital electrode is connected in series with the second interdigital electrode, and the connection point of the first interdigital electrode and the second interdigital electrode is a first voltage dividing point. The first voltage dividing point covers the part of the epitaxial part of the first gate electrode extending out of the surface of the hydrogen sensing layer. The third interdigital electrode and the fourth interdigital electrode are connected in series, and the connection point of the third interdigital electrode and the fourth interdigital electrode is a second voltage dividing point. The second voltage dividing point covers the part of the epitaxial part of the second gate electrode extending out of the surface of the hydrogen sensing layer. By connecting the corresponding interdigital electrodes in series, the semiconductor resistance area can be connected to the hydrogen sensitive area to form a working point control circuit composed of a hydrogen sensitive resistor and a semiconductor resistor in series. 2. The FET hydrogen sensor according to claim 1, characterized in that the P-type epitaxial layer adopts a P-type doped semiconductor film, the material of the P-type doped semiconductor film is one of silicon, silicon carbide, gallium nitride, and gallium arsenide, the doping concentration is 1×10 ¹⁵ cm ^-3 to 5×10 ¹⁶ cm ^-3 , and the thickness is 0.5 to 2 μm; The length of the N-doped region is 2-25 μm, the doping concentration is 5×10 ¹⁸ cm ^-3 ～5×10 ¹⁹ cm ^-3 , and the gate width of the channel layer is 10-100 μm; The lengths of the first channel and the second channel are both 2-15 μm. 3. The FET hydrogen sensor according to claim 1 is characterized in that the gate dielectric layer is made of one of silicon oxide, silicon nitride and gallium oxide, wherein the thickness of silicon oxide is 5 to 20 nm, the thickness of silicon nitride is 5 to 20 nm, and the thickness of gallium oxide is 6 to 25 nm. 4. The FET hydrogen sensor according to claim 1, characterized in that the FET electrode material is one of nickel, platinum, aluminum, copper, gold and silver; The main parts of the source electrode and the drain electrode are respectively arranged above the two sides away from each other of the N-doped A region and the N-doped C region, and pass through the gate dielectric layer to make ohmic contact with the N-doped A region and the N-doped C region below; the main parts of the first gate electrode and the second gate electrode are respectively arranged on the gate dielectric layer located above the first channel and the second channel; The epitaxial part is arranged at the center of the main body, and the upper part of the epitaxial part passes through the isolation layer and the buffer layer to the surface of the hydrogen sensing layer and is connected to the outside world; The width of the main body of the source electrode and the drain electrode is the same as the width of the N-doped A region and the N-doped C region, respectively. The length of the main body of the source electrode and the drain electrode is smaller than the length of the N-doped A region and the N-doped C region, respectively, and is 1 to 15 μm. The length and width of the first gate electrode are the same as those of the first channel, and the length and width of the second gate electrode are the same as those of the second channel; The length of the epitaxial part is the same as that of the main part, and the width is 5-15 μm, and the thickness of the main part is 50-500 nm. 5. The FET hydrogen sensor according to claim 1, characterized in that the substrate is one of aluminum oxide, silicon, silicon carbide, gallium nitride, and aluminum nitride; The material of the isolation layer is one of silicon oxide, silicon nitride and aluminum oxide, and the thickness is 1-2 μm; The buffer layer is made of gallium nitride or aluminum oxide, and has a thickness of 50-200 nm. 6. The FET hydrogen sensor according to claim 1, characterized in that the hydrogen sensitive area comprises a gallium oxide film, a tin oxide film, and a hydrogen catalyst nanocluster arranged in sequence from bottom to top; the thickness of the gallium oxide film is 50-100 nm; the tin oxide film is a tin oxide quantum dot film, and the quantum dot diameter is 1-20 nm; the hydrogen catalyst nanocluster is dispersed on the surface of the tin oxide film, and the area of the hydrogen catalyst nanocluster does not exceed 5% of the total surface area of the tin oxide film, and the material of the hydrogen catalyst nanocluster is one or more of platinum, palladium, and nickel, and the diameter is 1-10 nm; The semiconductor resistance region is made of polysilicon with a thickness of 60-130 nm. 7. The FET hydrogen sensor according to claim 1, characterized in that the overall upper surface area composed of the hydrogen sensitive region, the semiconductor resistance region and the interdigital electrodes is larger than the area occupied by the channel layer, and the overall upper surface area composed of the hydrogen sensitive region, the semiconductor resistance region and the interdigital electrodes ranges from 150 μm×150 μm to 500 μm×500 μm; The hydrogen-sensitive resistor is respectively composed of the first interdigital electrode and the area within the interdigital electrode gap and the fourth interdigital electrode and the area within the interdigital electrode gap in the hydrogen-sensitive region; the semiconductor resistor is composed of the second interdigital electrode and the area within the interdigital electrode gap and the third interdigital electrode and the area within the interdigital electrode gap in the semiconductor resistor region; and the resistance value of the hydrogen-sensitive resistor when not exposed to hydrogen is at the same order of magnitude as the resistance value of the semiconductor resistor. 8. The FET hydrogen sensor according to claim 1 is characterized in that the material of the interdigital electrode is one of nickel, platinum, palladium, aluminum, copper, gold, and silver, the interdigital spacing is 3 to 8 μm, the number of pairs is 15 to 25 pairs, the length is 30 to 80 μm, and the thickness is 50 to 150 nm. 9. A method for preparing a FET hydrogen sensor, characterized in that the method is used to prepare the FET hydrogen sensor according to any one of claims 1 to 8, comprising: Preparation of channel layer: a P-type doped semiconductor film is arranged on a substrate to obtain a P-type epitaxial substrate; Doping an N-doped A region, an N-doped B region, and an N-doped C region on a P-type doped semiconductor film by using an ion implantation process; Preparing a gate dielectric layer: preparing a gate dielectric layer on the channel layer by using one of plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, atomic layer deposition, and magnetron sputtering processes; Prepare FET electrodes: remove the gate dielectric layer above the N-doped A region and the N-doped C region by photolithography until the source electrode and the drain electrode windows are completely exposed, and prepare the source electrode and the drain electrode on the source electrode and the drain electrode windows by vacuum evaporation, magnetron sputtering, or electron beam evaporation, respectively, and prepare the first gate electrode and the second gate electrode on the first channel and the second channel, respectively; Preparing an isolation layer: depositing an isolation layer on the gate dielectric layer by one of plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, and magnetron sputtering processes, so that the isolation layer covers the FET electrode and the gate dielectric layer; Preparing a buffer layer: depositing the buffer layer on the isolation layer by one of plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, atomic layer deposition, and metal organic compound vapor deposition processes; Preparation of hydrogen sensing layer: using one of plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, metal organic compound vapor deposition, magnetron sputtering, and mechanical transfer processes to prepare a β-phase gallium oxide film on the buffer layer, or using thermal evaporation to prepare a gallium oxide nanobelt film on the buffer layer; using one of dispensing, spraying, spin coating, and electrospraying processes to prepare a tin oxide film on the β-phase gallium oxide film or the gallium oxide nanobelt film, and using atomic layer deposition technology to prepare hydrogen catalyst nanoclusters on the surface of the tin oxide film to form a hydrogen sensitive area; The hydrogen sensitive region is divided into two halves, and the hydrogen sensitive region is removed from one half by using a photolithography process until the buffer layer is completely exposed, and polysilicon is prepared on the exposed buffer layer by using one of plasma enhanced chemical vapor deposition, low pressure chemical vapor deposition, and metal organic compound vapor deposition processes, and the grain size and grain boundary number of the polysilicon are adjusted by using an ion implantation process and a rapid annealing process to form a semiconductor resistance region; Epitaxially grow FET electrodes: Use photolithography to remove part of the isolation layer, buffer layer and hydrogen sensing layer covering the FET electrodes, expose part of the FET electrodes to form electrode windows, and use vacuum evaporation, magnetron sputtering or electron beam evaporation to deposit metals in the electrode windows to prepare epitaxial electrodes; Preparation of interdigital electrodes: Interdigital electrodes are prepared on the hydrogen sensing layer using magnetron sputtering to complete the preparation of the FET hydrogen sensor. 10. The method for preparing a FET hydrogen sensor according to claim 9 is characterized in that, in the process of preparing polysilicon, the resistance of the polysilicon is adjusted by controlling the ion implantation energy and the annealing time and temperature, the ion is one of phosphorus, arsenic, and antimony, the energy range is 15~120Kev, the annealing temperature is 800~1000℃, and the annealing time is 20~30s.