A gate-sensitive transistor gas sensor based on atomic-level thickness heterojunction and its preparation method

Abstract

The present invention discloses a gate-sensitive transistor gas sensor based on an atomically thin heterojunction and a method for preparing the same. This sensor, which belongs to the field of micro-nano gas sensors, comprises a heterojunction transistor and a sensitive gate. The heterojunction transistor comprises, from bottom to top, a base layer, a channel layer, and a dielectric layer. The sensitive gate is located on top of the dielectric layer and is an electrically floating gate. The channel layer is in contact with a metal electrode, which is connected to a signal acquisition device. The present invention uses the sensitive gate as a gas molecule-specific adsorption material, while the channel layer is responsible for conducting electrical signals. The two are spatially separated, reducing the requirements for the sensing material.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano gas sensors, and in particular relates to a gate-sensitive transistor gas sensor based on an atomic-level thickness heterojunction and a preparation method thereof. Background Art

[0002] Gas sensors play a vital role in identifying and quantifying the properties of toxic gases and organic vapors, and are widely used in fields such as emission control, military and public safety, industrial and agricultural production, environmental monitoring, and medical diagnosis. Currently, gas sensors based on metal oxide thin film semiconductors are widely used due to their high sensitivity and low cost. However, metal oxide thin film semiconductor gas sensors also have many drawbacks, such as high operating temperature, high power consumption, and low selectivity, which severely limit their application in flexible wearable and portable devices. Therefore, it is necessary to explore new gas sensors with high sensitivity, low operating temperature, and high mechanical flexibility.

[0003] Two-dimensional materials have attracted significant attention due to their excellent mechanical properties, high transparency, high carrier mobility, and large specific surface area, making them promising applications in gas sensors. Researchers have employed a variety of two-dimensional materials, including graphene, transition metal dichalcogenides, and layered III-VI semiconductors, to achieve highly sensitive and rapid responses to various gases. Existing gas sensors based on two-dimensional materials primarily employ a two-terminal resistive device design. The large specific surface area of ​​the two-dimensional material allows the sensitive material to effectively adsorb gas molecules, resulting in charge transfer between the two, which in turn changes the material's resistance and enables detection of the target gas. Patent CN109632906A discloses a resistive gas sensor based on a graphene-metal heterojunction capable of detecting the type and concentration of the gas being sensed. However, resistive devices rely on the sensitive material for both gas molecule adsorption and sensing, placing high demands on the material. Some oxidizing gases can also irreversibly damage the sensitive material. Patent CN116908248A discloses a graphene-based gas sensor that uses intrinsic graphene and, in combination with ultraviolet light, can quickly respond to H2. However, since it only uses intrinsic graphene and does not contain other specific gas adsorption materials, its sensitivity to other gases is low. Patent CN116259667A discloses a thin-film transistor gas sensor and its preparation method, which uses a bottom-gate structure transistor. The channel active layer adopts a double-layer thin-film heterojunction structure. The upper layer is a gas-sensitive layer, the surface of which has adsorption and reaction activity for gas molecules, and the lower layer is a one-dimensional or two-dimensional semiconductor transport layer with high mobility. The charge transfer at the gas-solid interface of the gas-sensitive layer has a regulatory effect on the channel heterojunction interface band structure, causing the channel conductivity to change and converting it into a change in the transistor output characteristics. Combined with the control of the gate voltage, multiple characteristic parameters of the sensor's gas-sensitive response are extracted, which helps to improve selectivity. The disadvantage of this prior art is that it adopts a back-gate design, which increases the complexity of the device structure. Summary of the Invention

[0004] The purpose of the present invention is to provide a gate-sensitive transistor gas sensor based on an atomic-level thickness heterojunction and a preparation method thereof, so as to solve the problems existing in the above-mentioned prior art.

[0005] One of the technical solutions provided by the present invention:

[0006] A gate-sensitive transistor gas sensor based on an atomic-level thickness heterojunction includes a two-dimensional material heterojunction transistor and a sensitive gate. The two-dimensional material heterojunction transistor includes a base layer, a channel layer, and a dielectric layer from bottom to top. The sensitive gate is located on the upper part of the dielectric layer and is an electrically floating gate. The channel layer is in contact with a metal electrode, and the metal electrode is connected to a signal acquisition device.

[0007] The base layer provides a relatively flat interface for the channel material, ensuring a smooth, defect-free surface and providing insulation protection for the device. The dielectric layer isolates the sensitive gate from the channel layer, preventing direct contact between the two materials and preventing gas molecules from adsorbing directly into the channel layer. The presence of the dielectric layer allows the conductivity of the channel to be controlled by varying the work function of the sensitive gate. When gas adsorbs onto the surface of the sensitive gate, the generated electric field passes through the dielectric layer, modulating the conductivity of the channel material and achieving sensing.

[0008] The "local field effect" two-dimensional material heterojunction transistor (gate-sensitive transistor) has a base layer, a channel layer, and a dielectric layer from bottom to top, and a thin film serving as a sensitive gate is prepared above the dielectric layer.

[0009] Preferably, the material used to prepare the base layer is an insulating material with atomic-level thickness, and the insulating material includes one or both of h-BN (hexagonal boron nitride) and HfO2 (hafnium oxide).

[0010] Preferably, the material used to prepare the channel layer is a high carrier mobility two-dimensional material with atomic-level thickness, and the high carrier mobility two-dimensional material includes one or both of Graphene and MoS2 (molybdenum disulfide).

[0011] Preferably, the material used to prepare the dielectric layer is a two-dimensional material with atomic-level thickness, and the two-dimensional material includes one or both of h-BN (hexagonal boron nitride) and HfO2 (hafnium oxide).

[0012] Preferably, the material used to prepare the electric floating gate is a two-dimensional material, a one-dimensional material or a zero-dimensional material with atomic-level thickness.

[0013] Preferably, the two-dimensional material is a two-dimensional MOFs (metal organic framework), the one-dimensional material is a one-dimensional metal oxide nanowire, and the zero-dimensional material is a zero-dimensional metal particle, wherein the zero-dimensional metal particle includes Ag or Ru, and the metal oxide nanoparticles include SiO x .

[0014] The second technical solution provided by the present invention is:

[0015] A method for preparing the above-mentioned gate-sensitive transistor gas sensor based on an atomic-level thickness heterojunction includes the following steps: using a silicon substrate as the substrate, and using flexible transfer technology to sequentially transfer the material for preparing the base layer, the material for preparing the channel layer, and the material for preparing the dielectric layer to the silicon substrate, thereby sequentially forming the base layer, the channel layer, and the dielectric layer to complete the construction of the atomic-level thickness two-dimensional material heterojunction, depositing metal electrodes on both sides of the channel layer, connecting the metal electrodes to a signal acquisition device, and preparing the sensitive gate above the dielectric layer.

[0016] The technical principle of this invention is that it provides a gate-sensitive transistor gas sensor based on an atomically thin heterojunction. Its main structure is a two-dimensional material heterojunction transistor. The sensitive gate (electrically floating gate) serves as both the transistor's gate and a specific receptor for gas molecules, exhibiting selectivity for different target gases. In operation, a voltage is applied between the source and drain electrodes, while no additional voltage is applied to the gate. When gas molecules contact the sensitive gate, charge transfer occurs between them, altering the charge distribution on the sensitive gate surface. This changes the gate's work function or surface potential, which in turn alters the current in the channel material between the source and drain, achieving the sensing purpose. Figure 1 Schematic diagram of the gas sensing process and mechanism of the gate-sensitive transistor gas sensor based on atomic-level thickness heterojunction provided by the present invention, from Figure 1 It can be seen that:

[0017] The present invention constructs a "local field effect" gate-sensitive transistor gas sensor, where Vs is the source, Vd is the drain, and Vg is the sensitive gate (electric floating gate). The sensitive gate is responsible for gas adsorption, and the two-dimensional material transistor platform is responsible for sensing. This can not only improve the gas response performance, but also avoid damage to the two-dimensional material by some target gases.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects:

[0019] (1) Compared with traditional transistor sensors, the gate-sensitive transistor gas sensor based on atomic-thick heterojunction provided by the present invention has the following advantages: the sensitive gate is used as the gas molecule-specific adsorption material, and the channel layer is responsible for electrical signal conduction. The two are spatially separated, which reduces the requirements for sensing materials.

[0020] (2) Two layers of atomically thick insulating two-dimensional materials (such as h-BN, HfO2, etc.) are used to encapsulate and protect the middle channel material. The insulating material isolates the oxygen and water vapor in the air from direct contact with the channel material, preventing the channel material from being oxidized and improving the stability of the device.

[0021] (3) By changing the sensitive gate material, the sensor can show high sensitivity to a single target gas in a multi-gas environment, while having almost no response to the remaining gases, thus achieving selective recognition of different target gases.

[0022] (4) Compared with traditional field-effect transistor gas sensors, the dielectric layer in the present invention uses an insulating two-dimensional material with atomic-level thickness (such as h-BN, HfO2, etc.), and its thickness is thinned to the atomic level, making the channel material more sensitive to changes in gate voltage, thereby further improving the sensitivity of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 Schematic diagram of the gas sensing process and mechanism of the gate-sensitive transistor gas sensor based on atomic-level thickness heterojunction provided by the present invention;

[0025] Figure 2 A schematic diagram of the three-dimensional structure of a gate-sensitive transistor gas sensor based on an atomic-thickness heterojunction provided by an embodiment of the present invention, comprising: a silicon wafer 1, a silicon oxide layer 2, a dielectric layer 3, a source electrode 4, a drain electrode 6, a sensitive gate 5, a channel layer 7, and a base layer 8;

[0026] Figure 3 This is a physical picture of the h-BN / Graphene / h-BN structure heterojunction transistor device in the gate-sensitive transistor gas sensor based on atomic-level thickness heterojunction prepared in Examples 1, 3, 5 and 7 of the present invention. DETAILED DESCRIPTION

[0027] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0028] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0029] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0030] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0031] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0032] The raw materials used in the embodiments of the present invention are all purchased from the market.

[0033] The embodiment of the present invention provides a gate-sensitive transistor gas sensor based on an atomic-thickness heterojunction, including an atomic-thickness dielectric layer (atomic-thickness insulating two-dimensional material such as hexagonal boron nitride or hafnium oxide) - a channel layer (atomic-thickness high carrier mobility two-dimensional material such as Graphene or MoS2) - a substrate layer (atomic-thickness insulating material such as h-BN or hafnium oxide) heterojunction transistor and a sensitive gate. The sensitive gate can show selectivity for different target gases. After the gas molecules are adsorbed on the sensitive gate, their surface potential changes, which in turn causes the source-drain current in the underlying channel material to change, thereby achieving the sensing purpose. The present invention uses insulating two-dimensional materials such as hexagonal boron nitride or hafnium oxide to encapsulate and protect the channel layer material, solving the problem of easy oxidation of the sensitive layer material of traditional sensors. In addition, since the heterojunction thickness is only at the atomic level and a specific gas-sensitive gate is used, the prepared sensor has the characteristics of high sensitivity, high selectivity, etc., and can achieve highly reliable gas detection.

[0034] Figure 2This is a schematic diagram of the three-dimensional structure of a gate-sensitive transistor gas sensor based on an atomically thin heterojunction, provided by an embodiment of the present invention. The sensor comprises: a silicon wafer 1, a silicon oxide layer 2, a dielectric layer 3, a source electrode 4, a drain electrode 6, a sensitive gate electrode 5, a channel layer 7, and a base layer 8. The channel layer 7 is responsible for transmitting the sensing signal, the sensitive gate electrode 5 is responsible for adsorbing gas molecules and providing a "gate voltage" for the transistor, and the source electrode 4 and drain electrode 6 are used to extract the source-drain current signal. The sensor's substrate is a silicon substrate. Flexible transfer technology is used to sequentially transfer two-dimensional materials, including the base layer 8, channel layer 7, and dielectric layer 3, onto the silicon substrate, completing the construction of the atomically thin two-dimensional heterojunction. Electrode patterning is achieved using methods such as photolithography and physical masks. Metal electrodes, serving as the source electrode 4 and drain electrode 6, are deposited on both sides of the channel layer using methods such as electron beam evaporation or thermal evaporation. These metal electrodes are connected to a signal acquisition device. The sensitive gate electrode can be fabricated above the dielectric layer using various processes, such as inkjet printing, thermal evaporation, or electron beam evaporation, depending on the material properties. It is essentially an electrically floating gate and does not require an additional gate voltage for operation. When gas molecules are adsorbed onto the surface of the sensitive gate, charge transfer occurs between the gas molecules and the sensitive gate, causing its work function / surface potential to change. This change can be regarded as "gate voltage", which in turn causes the source-drain current of the channel layer 7 to change, thereby achieving the purpose of gas detection.

[0035] In the embodiment of the present invention, the material for preparing the sensitive gate is an atomic-level thickness MOFs material, including Ni-MOF-74, NO2-UiO-66NM and Cu-HHTP, among which Ni-MOF-74 can be synthesized using a solution method, NO2-UiO-66NM can be synthesized using electrospinning, aqueous phase synthesis, etc., and Cu-HHTP can be prepared by LBL deposition method. The preparation methods of the above three atomic-level thickness MOFs materials belong to conventional preparation methods in the field and will not be repeated in the present invention.

[0036] Example 1

[0037] Using silicon substrate as the substrate, Graphene as the channel layer material, h-BN as the dielectric layer material, and h-BN as the substrate material, through flexible transfer technology, the PVA film with good adhesion is attached to the PDMS on the glass slide. Combined with the two-dimensional material transfer platform, the above-mentioned substrate layer material, channel layer material and dielectric layer material are transferred to the silicon substrate in turn, forming the substrate layer, channel layer and dielectric layer in turn, completing the construction of atomic-level thick two-dimensional material heterojunction. The PVA film can be removed with deionized water after each transfer, and the surface of the transferred two-dimensional material is clean and free of residue. The metal electrodes are patterned on both sides of the channel layer using electron beam lithography combined with electron beam evaporation or thermal evaporation. The metal electrodes at both ends of the channel layer are the source and drain, respectively. The metal electrodes are connected to the signal acquisition device. Above the dielectric layer, a sensitive gate is prepared using Ni-MOF-74 (atomic-thick MOFs material) by solution method. A gate-sensitive transistor gas sensor based on atomic-thick heterojunction is obtained. The sensor can show high sensitivity to ppm-level NO2 at 50°C, with a detection limit of less than 0.5ppm. It is selective for NO2 among N2, SO2 and air.

[0038] Example 2

[0039] The same as Example 1, except that MoS2 is used as the channel layer material, HfO2 is used as the dielectric layer material, HfO2 is used as the base layer material, and the top and bottom layers of HfO2 are evaporated using electron beam evaporation or thermal evaporation process.

[0040] Example 3

[0041] Using a silicon substrate as a substrate, Graphene as a channel layer material, h-BN as a dielectric layer material, and h-BN as a substrate layer material, the flexible transfer technology in Example 1 is used to transfer the above-mentioned substrate layer material, channel layer material, and dielectric layer material to the silicon substrate in sequence, forming a substrate layer, a channel layer, and a dielectric layer in sequence, thereby completing the construction of an atomic-level thickness two-dimensional material heterojunction; using an electron beam lithography process combined with an electron beam evaporation or thermal evaporation process, patterning of metal electrodes is completed on both sides of the channel layer, and the metal electrodes at both ends of the channel layer are the source and the drain, respectively, and the source and the drain are connected to a signal acquisition device; above the dielectric layer, an electrospinning combined with an aqueous phase synthesis method is used to prepare a sensitive gate using NO2-UiO-66NM (atomic-level thickness MOFs material) as a raw material, thereby obtaining a gate-sensitive transistor gas sensor based on an atomic-level thickness heterojunction, which can show high sensitivity to ppb-level H2S.

[0042] Example 4

[0043] The same as Example 3, except that MoS2 is used as the channel layer material, HfO2 is used as the dielectric layer material, HfO2 is used as the base layer material, and the top and bottom layers of HfO2 are evaporated using electron beam evaporation or thermal evaporation process.

[0044] Example 5

[0045] Using a silicon substrate as a substrate, graphene as a channel layer material, h-BN as a dielectric layer material, and h-BN as a substrate layer material, the above-mentioned substrate layer material, channel layer material, and dielectric layer material are transferred to the silicon substrate in sequence by the flexible transfer technology in Example 1, forming a substrate layer, a channel layer, and a dielectric layer in sequence, completing the construction of an atomic-level thickness two-dimensional material heterojunction, and using an electron beam lithography process combined with an electron beam evaporation or thermal evaporation process to complete the patterning of metal electrodes on both sides of the channel layer. The metal electrodes at both ends of the channel layer are the source and the drain, respectively, and the source and the drain are connected to a signal acquisition device. Above the dielectric layer, an LBL deposition method is used to prepare a sensitive gate using Cu-HHTP (atomic-level thickness MOFs material) as a raw material, thereby obtaining a gate-sensitive transistor gas sensor based on an atomic-level thickness heterojunction, which can show high sensitivity to ppm-level NH3.

[0046] Example 6

[0047] The same as Example 5, except that MoS2 is used as the channel layer material, HfO2 is used as the dielectric layer material, HfO2 is used as the base layer material, and the top and bottom layers of HfO2 are evaporated using electron beam evaporation or thermal evaporation process.

[0048] Example 7

[0049] Using a silicon substrate as the substrate, graphene as the channel layer material, h-BN as the dielectric layer material, and h-BN as the substrate material, the above-mentioned substrate layer material, channel layer material and dielectric layer material are transferred to the silicon substrate in sequence through flexible transfer technology to form a substrate layer, a channel layer and a dielectric layer in sequence, completing the construction of an atomic-level thick two-dimensional material heterojunction. Metal electrodes are deposited on both sides of the channel layer as the source and drain. The metal electrodes are connected to the signal acquisition device. Above the dielectric layer, an electron beam evaporation process (evaporation rate of 0.1 angstroms per second) is used to prepare a sensitive gate using Ag metal micro-nanoparticles (zero-dimensional metal particles) as raw materials, resulting in a gate-sensitive transistor gas sensor based on an atomic-level thick heterojunction. The sensor can show high sensitivity to ppb-level H2S.

[0050] Example 8

[0051] The same as Example 7, except that MoS2 is used as the channel layer material, HfO2 is used as the dielectric layer material, HfO2 is used as the base layer material, and the top and bottom layers of HfO2 are evaporated using electron beam evaporation or thermal evaporation process.

[0052] The gate-sensitive transistor gas sensors based on atomic-thickness heterojunctions prepared in Examples 1, 3, 5, and 7 all include heterojunction transistor devices with h-BN / Graphene / h-BN structures, as shown in the physical diagram. Figure 3 .

[0053] Example 9

[0054] Using silicon substrate as substrate, graphene as channel layer material, h-BN as dielectric layer material, and h-BN as substrate material, the above-mentioned substrate layer material, channel layer material and dielectric layer material are transferred to the silicon substrate in sequence through flexible transfer technology, forming the substrate layer, channel layer and dielectric layer in sequence, completing the construction of atomic-level thick two-dimensional material heterojunction, and depositing metal electrodes on both sides of the channel layer as source and drain. The metal electrodes are connected to the signal acquisition device. Above the dielectric layer, a sensitive gate is prepared using zinc oxide nanowires as raw material by a hydrothermal method, resulting in a gate-sensitive transistor gas sensor based on atomic-level thick heterojunction, which can show high sensitivity to ppm-level ethanol gas.

[0055] Example 10

[0056] The same as Example 9, except that MoS2 is used as the channel layer material, HfO2 is used as the dielectric layer material, HfO2 is used as the base layer material, and the top and bottom layers of HfO2 are evaporated using electron beam evaporation or thermal evaporation process.

[0057] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A gate-sensitive transistor gas sensor based on an atomic-thickness heterojunction, characterized in that: The device comprises a two-dimensional material heterojunction transistor and a sensitive gate. The two-dimensional material heterojunction transistor comprises a base layer, a channel layer and a dielectric layer from bottom to top. The sensitive gate is located on the upper part of the dielectric layer and is an electric floating gate. The channel layer is in contact with a metal electrode, and the metal electrode is connected to a signal acquisition device. The base layer is made of an insulating material with atomic-level thickness, and the insulating material includes one or both of hexagonal boron nitride and hafnium oxide; The material for preparing the channel layer is a two-dimensional material with high carrier mobility and atomic-level thickness, and the two-dimensional material with high carrier mobility includes one or both of graphene and molybdenum disulfide; The material for preparing the dielectric layer is a two-dimensional material with atomic-level thickness, and the two-dimensional material includes one or both of hexagonal boron nitride and hafnium oxide; The material used to prepare the electric floating gate is a two-dimensional material, a one-dimensional material or a zero-dimensional material with atomic-level thickness; The two-dimensional material for preparing the electric floating gate is a two-dimensional metal organic framework, the one-dimensional material is a one-dimensional metal oxide nanowire, and the zero-dimensional material is a zero-dimensional metal particle.

2. A method for preparing a gate-sensitive transistor gas sensor based on an atomic-level thickness heterojunction according to claim 1, characterized in that: The method comprises the following steps: using a silicon substrate as a substrate, and using a flexible transfer technology to sequentially transfer the material for preparing the base layer, the material for preparing the channel layer, and the material for preparing the dielectric layer onto the silicon substrate, sequentially forming a base layer, a channel layer, and a dielectric layer, thereby completing the construction of a two-dimensional material heterojunction with atomic-level thickness, depositing metal electrodes on both sides of the channel layer, connecting the metal electrodes to a signal acquisition device, and preparing the sensitive gate above the dielectric layer.

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