A field effect transistor gas sensor and method of manufacture

Abstract

This invention relates to the field of sensor technology, and more particularly to a field-effect transistor gas sensor and its fabrication method. From bottom to top, the sensor comprises a doped semiconductor substrate, a composite insulating layer, an interdigitated layered back gate electrode, a graphene film, a boron nitride transition layer, a multi-element alloy ultrathin layer, a source electrode, and a drain electrode. The sensing material is a composite structure of the graphene film, the boron nitride transition layer, and the multi-element alloy ultrathin layer. This invention effectively solves the problems of high control voltage and uneven electric field distribution in traditional devices through structural innovation in the composite insulating layer and the interdigitated layered back gate electrode. The composite insulating layer, composed of an Al2O3 bottom layer and a HfO2 top layer, achieves a high dielectric constant ≥25 with a thickness ratio of (2-3):1, with a total thickness of only 20-50 nm. While ensuring insulation performance, it reduces the control voltage. Combined with the layered back gate structure with an interdigital spacing of 50-100 μm and 8-12 pairs of interdigitates, it significantly improves the electric field uniformity and control coverage, increasing device response consistency by more than 50% and reducing the control voltage by 40% compared to traditional structures.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically to a field-effect transistor gas sensor and its fabrication method. Background Technology

[0002] With the deep penetration of IoT technology into fields such as environmental monitoring and smart homes, the demand for miniaturization, low power consumption, high responsiveness, and long-term stability in gas sensors is becoming increasingly urgent. Graphene-based field-effect transistor gas sensors have become a core research direction for room temperature gas detection due to graphene's excellent carrier mobility and specific surface area. Existing technologies have improved response performance and recovery speed to some extent by depositing ultrathin multi-metal layers on the graphene surface and optimizing the back gate structure, but key technical bottlenecks still exist: traditional insulating layers mostly use single SiO2 or Al2O3 materials, which makes it difficult to simultaneously meet the requirements of high dielectric constant and low thickness, resulting in high device control voltage and large system power consumption; the back gate electrode is mostly a planar single-layer structure with uneven electric field distribution, which limits the control coverage of the graphene channel and affects the consistency of device response.

[0003] Furthermore, the metal modification layers of existing sensors are mostly single metal or binary metal stacked structures, which have insufficient catalytic synergy and weak selective response to low concentration target gases. Moreover, the interface between the metal layer and graphene lacks an effective transition structure, resulting in poor adhesion and easy shedding after long-term use, leading to a decline in the cycle stability of the device. At the same time, there are many interface defects after the metal layer is deposited, which further restricts the electron transport efficiency and the lifespan of the device. These problems seriously limit the expansion of practical application scenarios for graphene-based field-effect transistor gas sensors. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a field-effect transistor gas sensor and its fabrication method, solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a field-effect transistor gas sensor, comprising, from bottom to top, a doped semiconductor substrate, a composite insulating layer, an interdigitated layered back gate electrode, a graphene film, a boron nitride transition layer, a multi-element alloy ultrathin layer, a source electrode, and a drain electrode; The sensitive material is a composite structure of graphene film, boron nitride transition layer and multi-element alloy ultrathin layer, the composite insulating layer is a stacked structure of Al2O3 bottom layer and HfO2 top layer, and the interdigitated layered back gate electrode is a stacked structure of Cr bottom layer and Au top layer.

[0006] Preferably, the multi-element alloy ultrathin layer is an Au-Pt-In ternary alloy with a molar ratio of (45-55):(35-45):(5-10) and a thickness of 0.8-1.2 nm.

[0007] Preferably, the thickness of the boron nitride transition layer is 0.2-0.5 nm, and the boron nitride transition layer is prepared by atomic layer deposition.

[0008] Preferably, the interdigitated layered back gate electrode has an interdigitated spacing of 50-100 μm, an interdigitated number of 8-12 pairs, a Cr bottom layer thickness of 5-8 nm, and an Au top layer thickness of 50-70 nm.

[0009] Preferably, the thickness ratio of the Al2O3 bottom layer to the HfO2 top layer in the composite insulating layer is (2-3):1, the total thickness is 20-50nm, and the dielectric constant is ≥25.

[0010] A method for fabricating a field-effect transistor gas sensor as described above includes the following steps: S1: An Al2O3 bottom layer and an HfO2 top layer are sequentially prepared on the surface of a doped semiconductor substrate by atomic layer deposition to form a composite insulating layer; S2: Interdigitated layered back gate electrodes were prepared by overlay and electron beam evaporation processes, and then annealed after deposition; S3: The graphene film prepared by CVD method is transferred to the surface of the composite insulating layer and then patterned and etched. S4: Deposit a boron nitride transition layer on the surface of a graphene film using atomic layer deposition; S5: An ultrathin Au-Pt-In ternary alloy layer is deposited on the surface of the boron nitride transition layer using an electron beam co-evaporation process, followed by rapid annealing. S6: The source and drain electrodes are fabricated at both ends of the graphene film by overlay and electron beam evaporation processes to obtain the sensor.

[0011] Preferably, in step S5, the vacuum level of the electron beam co-evaporation deposition chamber is ≥10. -7 torr, deposition rate is 0.1-0.15 Å·s -1 The rapid annealing conditions are: temperature 200℃, time 15min.

[0012] Preferably, in step S2, the annealing conditions are: temperature 150℃, time 30min; in step S3, the patterning etching adopts reactive ion etching in an O2 atmosphere, with an etching gas flow rate of 20sccm, a gas pressure of 5Pa, an RF power of 100W, and an etching time of 8 seconds.

[0013] Preferably, the resistivity of the doped semiconductor substrate is (1-5)×10⁻⁶. -3 The source and drain are Cr / Au stacked structures with a thickness of 8nm and a thickness of 80nm, and the source-drain distance is 1.5-2mm.

[0014] Preferably, it is used for the detection of ammonia, hydrogen sulfide or carbon monoxide at concentrations of 1-200 ppm at room temperature, and has high selectivity for ammonia, with a performance retention rate of ≥95% after 10 consecutive cycles of testing.

[0015] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a field-effect transistor gas sensor and its fabrication method: 1) This invention effectively solves the problems of high control voltage and uneven electric field distribution in traditional devices through the structural innovation of composite insulating layer and interdigitated layered back gate electrode: The composite insulating layer composed of Al2O3 bottom layer and HfO2 top layer achieves a high dielectric constant of ≥25 with a thickness ratio of (2-3):1, and the total thickness is only 20-50nm. While ensuring insulation performance, it reduces control voltage. Combined with the layered back gate structure with interdigital spacing of 50-100μm and 8-12 pairs of interdigitals, it significantly improves electric field uniformity and control coverage, improves device response consistency by more than 50%, and reduces control voltage by 40% compared with traditional structures; 2) This invention addresses the pain points of metal layer shedding, insufficient selectivity, and poor stability through a composite sensitive structure design of a boron nitride transition layer and a multi-element alloy ultrathin layer. The 0.2-0.5 nm thick boron nitride transition layer is prepared by atomic layer deposition, constructing a tight interface between the graphene film and the multi-element alloy layer, avoiding interlayer delamination during long-term use. The Au-Pt-In ternary alloy ultrathin layer with a molar ratio of (45-55):(35-45):(5-10) enhances the selective adsorption and desorption capacity of ammonia through the synergistic catalytic effect of the three metals. Combined with a rapid annealing process of 200℃ / 15min to optimize crystallinity and reduce interface defects, the device's response intensity to 1-200 ppm ammonia at room temperature is significantly improved, and the performance retention rate is ≥95% after 10 consecutive cycles. At the same time, it achieves accurate detection of hydrogen sulfide and carbon monoxide, greatly expanding the practical value of the device. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is one of the structural schematic diagrams of the present invention; Figure 3 This is a schematic diagram showing the disassembled parts of the present invention; Figure 4 This is a schematic diagram of the process of the present invention.

[0017] In the figure: 100, doped semiconductor substrate; 110, composite insulating layer; 111, Al2O3 bottom layer; 112, HfO2 top layer; 120, interdigitated layered back gate electrode; 121, Cr bottom layer; 122, Au top layer; 130, graphene film; 140, boron nitride transition layer; 150, multi-element alloy ultrathin layer; 160, source electrode; 170, drain electrode. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0020] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "configuration" should be interpreted broadly. For example, they can refer to a fixed connection or configuration, a detachable connection or configuration, or an integral connection or configuration. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] Example like Figures 1-4As shown, the present invention proposes a field-effect transistor gas sensor, which, from bottom to top, includes a doped semiconductor substrate 100, a composite insulating layer 110, an interdigitated layered back gate electrode 120, a graphene film 130, a boron nitride transition layer 140, a multi-element alloy ultrathin layer 150, a source electrode 160, and a drain electrode 170. The sensitive material is a composite structure of graphene film 130, boron nitride transition layer 140 and multi-element alloy ultrathin layer 150. The composite insulating layer 110 is a stacked structure of Al2O3 bottom layer 111 and HfO2 top layer 112. The interdigitated layered back gate electrode 120 is a stacked structure of Cr bottom layer 121 and Au top layer 122.

[0023] Specifically, in the room temperature gas detection scenario, the doped semiconductor substrate 100 provides a stable support for the entire device and forms the basis for the electrical contact between it and the bottom of the interdigitated layered back gate electrode 120; the Al2O3 bottom layer 111 of the composite insulating layer 110, with its excellent stability and the high dielectric constant of the HfO2 top layer 112, achieves reliable insulation between the upper and lower layers of the device and can efficiently conduct the electric field generated by the interdigitated layered back gate electrode 120. The Cr bottom layer 121 of the interdigitated layered back gate electrode 120 enhances the adhesion of the composite insulating layer 110, while the Au top layer 122 ensures excellent conductivity. Together, they output a uniformly modulated electric field that acts on the graphene film 130. The graphene film 130 serves as the core carrier transport channel, and is tightly connected to the multi-element alloy ultrathin layer 150 through the boron nitride transition layer 140. After the multi-element alloy ultrathin layer 150 adsorbs the target gas, it triggers electron transfer, changing the carrier concentration of the graphene film 130. The closed loop formed by the source electrode 160 and the drain electrode 170 converts this change into a quantifiable current signal, ultimately achieving precise sensing of gas concentration.

[0024] In this embodiment: the multi-element alloy ultrathin layer 150 is an Au-Pt-In ternary alloy with a molar ratio of 45-55:35-45:5-10 and a thickness of 0.8-1.2 nm.

[0025] Specifically, in the detection of low-concentration gases, the high conductivity of Au in the Au-Pt-In ternary alloy of the multi-element alloy ultrathin layer 150 ensures rapid electron transport, the strong catalytic activity of Pt accelerates the adsorption and reaction of gas molecules, and In further enhances the adsorption affinity for target gases such as ammonia. The molar ratio of the three components, 45-55:35-45:5-10, precisely balances catalytic activity and electron transport efficiency. The ultrathin thickness design of 0.8-1.2nm ensures that the multi-element alloy ultrathin layer 150 has sufficient gas adsorption sites, while avoiding the inhibition of carrier mobility of the graphene film 130 by an excessively thick metal layer. When gas molecules come into contact with the device, the multi-element alloy ultrathin layer 150 quickly captures the gas molecules and triggers interfacial electron transfer. The electrons are transferred through the multi-element alloy ultrathin layer 150 to the boron nitride transition layer 140, and then smoothly introduced into the graphene film 130, causing a significant change in the conductivity of the graphene film 130. Combined with the current monitoring of the source electrode 160 and the drain electrode 170, a recognizable signal can be generated even for a low concentration of ammonia gas of 1 ppm, achieving high-sensitivity detection.

[0026] In this embodiment, the thickness of the boron nitride transition layer 140 is 0.2-0.5 nm, and the boron nitride transition layer 140 is prepared by atomic layer deposition.

[0027] Specifically, during long-term stable operation of the device, the boron nitride transition layer 140 serves as a connector between the graphene film 130 and the multi-element alloy ultrathin layer 150. Its ultrathin thickness of 0.2-0.5 nm does not hinder electron transport while forming a dense interface transition structure. Combined with the high-precision fabrication advantages of atomic layer deposition, the boron nitride transition layer 140 can tightly adhere to the surfaces of the graphene film 130 and the multi-element alloy ultrathin layer 150, effectively suppressing interlayer delamination. Simultaneously, the boron nitride transition layer 140 itself possesses excellent chemical stability and insulation, reducing the diffusion of metal atoms from the multi-element alloy ultrathin layer 150 to the graphene film 130, lowering the interface defect density, and ensuring efficient carrier transport between the graphene film 130 and the multi-element alloy ultrathin layer 150. During repeated gas adsorption-desorption cycles, the boron nitride transition layer 140 maintains the integrity of the sensitive material composite structure, ensuring that the device retains ≥95% of its performance after 10 consecutive cycle tests, significantly improving its service life.

[0028] In this embodiment: the interdigitated layered back gate electrode 120 has an interdigitated spacing of 50-100μm, an interdigitated number of 8-12 pairs, a Cr bottom layer 121 thickness of 5-8nm, and an Au top layer 122 thickness of 50-70nm.

[0029] Specifically, in detections requiring uniform electric field control, the combination of the 50-100μm interdigitated spacing and 8-12 pairs of interdigitated fingers in the interdigitated layered back gate electrode 120 enables the electric field to uniformly cover the entire channel region of the graphene film 130, avoiding inconsistent response caused by excessively strong or weak local electric fields. The Cr bottom layer with a thickness of 1215-8nm enhances the adhesion with the composite insulating layer 110, preventing the back gate electrode from falling off, while the Au top layer with a thickness of 12250-70nm ensures excellent conductivity and reduces energy loss during electric field transmission. When a control voltage is applied, the interdigitated layered back gate electrode 120 is stably in contact with the composite insulating layer 110 through the Cr bottom layer 121. The Au top layer 120 efficiently conducts the electric field, which acts on the graphene film 130 through the composite insulating layer 110. This precisely controls the carrier concentration and mobility of the graphene film 130, making the signal change after the multi-element alloy ultrathin layer 150 adsorbs gas more significant. Combined with the current detection of the source electrode 160 and the drain electrode 170, the response consistency and control efficiency of the device are greatly improved.

[0030] In this embodiment: the thickness ratio of the Al2O3 bottom layer 111 to the HfO2 top layer 112 in the composite insulating layer 110 is 2-3:1, the total thickness is 20-50nm, and the dielectric constant is ≥25.

[0031] Specifically, in low-power detection scenarios, the Al2O3 bottom layer 111 provides good structural stability and insulation reliability, while the HfO2 top layer 112 enhances electric field conduction efficiency with its extremely high dielectric constant. The two work together to enable the composite insulating layer 110 to maintain a high dielectric constant of ≥25 even with a thin total thickness of 20-50nm. This reduces the leakage risk of the insulating layer and can generate a sufficiently strong control electric field at a lower back gate voltage, thereby reducing system power consumption. The composite insulating layer 110 of appropriate thickness shortens the electric field transmission path between the interdigitated layered back grid electrode 120 and the graphene film 130, making electric field control faster. Combined with the rapid response of the sensitive material composite structure to gas, it achieves a balance between low power consumption and high response speed, which is suitable for the use of portable gas detection equipment.

[0032] A method for fabricating any of the above-mentioned field-effect transistor gas sensors includes the following steps: S1: An Al2O3 bottom layer 111 and an HfO2 top layer 112 are sequentially prepared on the surface of a doped semiconductor substrate 100 by atomic layer deposition to form a composite insulating layer 110; S2: Interdigitated layered back gate electrode 120 was prepared by overlay and electron beam evaporation processes, and then annealed after deposition; S3: The graphene film 130 prepared by CVD method is transferred to the surface of the composite insulating layer 110 and then patterned and etched. S4: A boron nitride transition layer 140 is deposited on the surface of the graphene film 130 by atomic layer deposition. S5: An Au-Pt-In ternary alloy ultrathin layer 150 is deposited on the surface of boron nitride transition layer 140 using electron beam co-evaporation process, followed by rapid annealing. S6: The source electrode 160 and the drain electrode 170 are fabricated at both ends of the graphene film 130 by overlay and electron beam evaporation processes to obtain the sensor.

[0033] Specifically, in device fabrication and practical application, the composite insulating layer 110 prepared in step S1 provides a flat and stable substrate for the interdigitated layered back gate electrode 120, ensuring effective conduction of the back gate electric field; the annealing treatment in step S2 enhances the structural stability and conductivity of the interdigitated layered back gate electrode 120, preventing performance degradation during use; the graphene film 130 transferred and patterned in step S3 ensures the integrity and precision of the channel region, providing a high-quality channel for carrier transport; the boron nitride transition layer 140 deposited in step S4 pre-constructs the interface between the graphene film 130 and the multi-element alloy ultrathin layer 150, creating conditions for subsequent alloy layer deposition; the electron beam co-evaporation process and rapid annealing treatment in step S5 enable the Au-Pt-In ternary alloy ultrathin layer 150 to form a uniform and stable alloy phase, enhancing catalytic activity; the source electrode 160 and drain electrode 170 prepared in step S6 are precisely aligned with both ends of the graphene film 130, forming a complete current detection circuit, ultimately achieving high-performance device performance in room temperature gas detection.

[0034] In this embodiment: In step S5, the vacuum level of the electron beam co-evaporation deposition chamber is ≥10. -7 torr, deposition rate is 0.1-0.15 Å·s -1 The rapid annealing conditions are: temperature 200℃, time 15min.

[0035] Specifically, in improving the performance of sensitive materials, the electron beam co-evaporation parameters in step S5 are precisely matched with the rapid annealing conditions, and the deposition chamber is ≥10. -7 The high vacuum of the torr prevents contamination of the 150-layer multi-element alloy ultrathin layer by impurities during the deposition process, ensuring the purity of the alloy; 0.1-0.15 Å·s - The slow deposition rate¹ allows Au, Pt, and In atoms to be uniformly spread on the surface of the boron nitride transition layer 140, forming an ultrathin and uniform alloy layer. The rapid annealing treatment at 200℃ for 15min promotes the diffusion and fusion of the three metal atoms, forming a uniform and stable Au-Pt-In ternary alloy phase, which enhances catalytic activity and structural stability. This enables the multi-element alloy ultrathin layer 150 to quickly and efficiently adsorb the target gas, triggering electron transfer, which is smoothly transferred to the graphene film 130 through the boron nitride transition layer 140. This reduces interfacial electron recombination, significantly improving the device's response and recovery speed to gas, while also enhancing the long-term stability of the sensitive material and ensuring the consistency of device performance during repeated use.

[0036] In this embodiment: In step S2, the annealing conditions are: temperature 150℃, time 30min; In step S3, the patterning etching adopts reactive ion etching in an O2 atmosphere, with an etching gas flow rate of 20sccm, a gas pressure of 5Pa, an RF power of 100W, and an etching time of 8 seconds.

[0037] Specifically, the annealing treatment at 150℃ for 30 minutes in step S2 makes the Cr bottom layer 121 and Au top layer 122 of the interdigitated layered back gate electrode 120 more tightly bonded, and the conductivity more stable, avoiding the influence of poor electrode contact on electric field control during use. Step S3 uses reactive ion etching in an O2 atmosphere, with a gas flow rate of 20 sccm, a gas pressure of 5 Pa, a radio frequency power of 100 W, and an etching time of 8 seconds precisely matched. This can completely remove excess graphene without damaging the graphene film 130 in the target area, ensuring the integrity of the channel and the smoothness of the edge of the graphene film 130. This allows the graphene film 130 to form a good ohmic contact with the source 160 and drain 170, reducing contact resistance. At the same time, it is tightly connected with the boron nitride transition layer 140 and the multi-element alloy ultrathin layer 150, ensuring carrier transport efficiency and making the device's response signal more stable and accurate.

[0038] In this embodiment: the resistivity of the doped semiconductor substrate 100 is (1-5)×10⁻⁶. -3 The source 160 and drain 170 are Cr / Au stacked structures with a thickness of 8nm for the Cr layer and 80nm for the Au layer. The source-drain spacing is 1.5-2mm.

[0039] Specifically, to ensure both current transmission efficiency and detection sensitivity, a 100 (1-5) × 10⁻⁶ doped semiconductor substrate is used. -3 The resistivity design of Ω·cm ensures good electrical contact with the interdigitated layered back gate electrode 120, enabling the control voltage to be efficiently transmitted to the back gate electrode. The Cr / Au stacked structure of the source 160 and drain 170, with an 8nm thick Cr layer enhancing the adhesion to the graphene film 130 and an 80nm thick Au layer ensuring excellent conductivity, and the 1.5-2mm source-drain spacing adapts to the length requirements of the graphene film 130 channel, avoiding current short circuits caused by too small a spacing or signal attenuation caused by too large a spacing. When the adsorption of gas by the multi-alloy ultrathin layer 150 causes a change in the charge carriers of the graphene film 130, the current injected by the source 160 is smoothly transmitted through the graphene film 130 and efficiently collected by the drain 170. The reduction in contact resistance allows even a weak change in charge carriers to be converted into a significant current signal. Combined with the modulation effect of the interdigitated layered back gate electrode 120, the detection sensitivity of the device is greatly improved, enabling precise capture of low-concentration gases.

[0040] In this embodiment: it is used for the detection of ammonia, hydrogen sulfide or carbon monoxide at concentrations of 1-200 ppm at room temperature, and has high selectivity for ammonia, with a performance retention rate of ≥95% after 10 consecutive cycles of testing.

[0041] Specifically, when detecting specific gases, the composite insulating layer 110 works in conjunction with the interdigitated layered back gate electrode 120 to provide stable electric field modulation at low power consumption at room temperature, enabling the sensitive material composite structure to respond more quickly to gases. The graphene film 130, boron nitride transition layer 140, and multi-element alloy ultrathin layer 150 work synergistically. The multi-element alloy ultrathin layer 150, with its high selectivity of Au-Pt-In ternary alloy, preferentially adsorbs target gases such as ammonia, hydrogen sulfide, and carbon monoxide. The boron nitride transition layer 140 ensures stable interlayer bonding, and the graphene film 130 efficiently transmits carrier signals. The source electrode 160 and drain electrode 170 convert carrier changes into precise current signals, enabling the detection of gases in the concentration range of 1-200 ppm. The stable coordination of each structure ensures that the device's performance degrades slowly during repeated use, maintaining a performance retention rate of ≥95% after 10 consecutive cycles. It exhibits outstanding selectivity for ammonia, enabling accurate identification of target gases in complex gas environments and meeting the detection needs of practical applications.

[0042] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element. Furthermore, it should be noted that the scope of the methods and apparatuses in the embodiments of this application is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0043] The embodiments of this application have been described above with reference to the accompanying drawings. However, this application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of this application.

Claims

1. A field-effect transistor gas sensor, characterized in that, From bottom to top, it includes a doped semiconductor substrate (100), a composite insulating layer (110), an interdigitated layered back gate electrode (120), a graphene film (130), a boron nitride transition layer (140), a multi-element alloy ultrathin layer (150), a source electrode (160), and a drain electrode (170). The sensitive material is a composite structure of graphene film (130), boron nitride transition layer (140) and multi-element alloy ultrathin layer (150), the composite insulating layer (110) is a stacked structure of Al2O3 bottom layer (111) and HfO2 top layer (112), and the interdigitated layered back gate electrode (120) is a stacked structure of Cr bottom layer (121) and Au top layer (122).

2. The field-effect transistor gas sensor according to claim 1, characterized in that, The multi-element alloy ultrathin layer (150) is an Au-Pt-In ternary alloy with a molar ratio of (45-55):(35-45):(5-10) and a thickness of 0.8-1.2 nm.

3. The field-effect transistor gas sensor according to claim 1, characterized in that, The boron nitride transition layer (140) has a thickness of 0.2-0.5 nm and is prepared by atomic layer deposition.

4. The field-effect transistor gas sensor according to claim 1, characterized in that, The interdigitated layered back gate electrode (120) has an interdigitated spacing of 50-100μm, an interdigitated number of 8-12 pairs, a Cr bottom layer (121) thickness of 5-8nm, and an Au top layer (122) thickness of 50-70nm.

5. The field-effect transistor gas sensor according to claim 1, characterized in that, The thickness ratio of the Al2O3 bottom layer (111) to the HfO2 top layer (112) in the composite insulating layer (110) is (2-3):1, the total thickness is 20-50nm, and the dielectric constant is ≥25.

6. A method for fabricating a field-effect transistor gas sensor according to any one of claims 1-5, characterized in that, Includes the following steps: S1: An Al2O3 bottom layer (111) and an HfO2 top layer (112) are sequentially prepared on the surface of a doped semiconductor substrate (100) by atomic layer deposition to form a composite insulating layer (110). S2: Interdigitated layered back gate electrode (120) was prepared by overlay and electron beam evaporation processes and then annealed after deposition; S3: The graphene film (130) prepared by CVD method is transferred to the surface of the composite insulating layer (110) and then patterned and etched. S4: A boron nitride transition layer (140) is deposited on the surface of the graphene film (130) by atomic layer deposition. S5: An Au-Pt-In ternary alloy ultrathin layer (150) was deposited on the surface of the boron nitride transition layer (140) using an electron beam co-evaporation process, followed by rapid annealing. S6: The source electrode (160) and drain electrode (170) are prepared at both ends of the graphene film (130) by overlay and electron beam evaporation processes to obtain the sensor.

7. The preparation method according to claim 6, characterized in that, In step S5, the vacuum level of the deposition chamber for electron beam co-evaporation is ≥10. -7 torr, deposition rate is 0.1-0.15 Å·s -1 The rapid annealing conditions are: temperature 200℃, time 15min.

8. The preparation method according to claim 6, characterized in that, In step S2, the annealing conditions are: temperature 150℃, time 30min; in step S3, the patterning etching adopts reactive ion etching in an O2 atmosphere, with an etching gas flow rate of 20sccm, a gas pressure of 5Pa, an RF power of 100W, and an etching time of 8 seconds.

9. The preparation method according to claim 6, characterized in that, The resistivity of the doped semiconductor substrate (100) is (1-5)×10⁻⁶. -3 The source (160) and drain (170) are Cr / Au stacked structures with a thickness of 8nm for the Cr layer and 80nm for the Au layer. The distance between the source and drain is 1.5-2mm.

10. The application of the field-effect transistor gas sensor according to any one of claims 1-5 in gas detection, characterized in that, It is used for the detection of ammonia, hydrogen sulfide or carbon monoxide at concentrations of 1-200 ppm at room temperature, and has high selectivity for ammonia, with a performance retention rate of ≥95% after 10 consecutive cycles of testing.

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