A gas sensor based on a reverse-biased bipolar transistor

Abstract

The application belongs to the technical field of gas sensors, and specifically provides a gas sensor based on a reverse bipolar transistor, which is used to solve the problems of single detection concentration signal path, dependence on calibration, poor anti-interference ability and the like of an existing resistance type gas sensor; and specifically comprises a heavily doped p-silicon layer 1, a silicon dioxide layer 2, a metal electrode 3, a molybdenum ditelluride thin film 4, a molybdenum disulfide thin film 5, the heavily doped p-silicon layer is used as a gate electrode, and the silicon dioxide layer is arranged on the gate electrode; the molybdenum ditelluride thin film and the molybdenum disulfide thin film constitute a heterojunction gas sensitive unit and are arranged on the surface of the silicon dioxide layer; the two metal electrodes are used as a drain electrode and a source electrode and are arranged on the molybdenum ditelluride thin film and the molybdenum disulfide thin film, respectively. The application fully utilizes the special transfer characteristics of the reverse bipolar transistor, converts the concentration information of a sensitive gas into frequency domain information of an output signal, has better anti-interference ability, does not need baseline calibration, and brings a brand-new concentration information coding form.

Description

Technical Field

[0001] This invention belongs to the field of gas sensor technology, specifically providing a gas sensor based on an inverse bipolar transistor. Background Technology

[0002] Gas sensors primarily rely on the physical adsorption or chemical reaction of gas molecules on the surface of sensitive materials to achieve detection by altering the carrier concentration or conductivity of the material. This approach is simple and easy to operate. However, traditional resistive or current-based detection modes mainly rely on changes in the amplitude of channel conductance to reflect gas concentration. Changes in ambient temperature and humidity often cause baseline drift in the amplitude signal, reducing responsivity and requiring additional signal calibration. Furthermore, a single amplitude signal also suffers from weak anti-interference capability when transmitting signals over long distances. These problems stem from the fact that traditional resistive gas sensors rely solely on absolute amplitude signals to reflect gas concentration, limiting the potential for further performance improvements and application versatility of new gas sensors. Therefore, it is necessary to seek a universal method to expand the detection dimensions of gas sensor output signals, guiding the design and operation of new gas sensors and enabling the use of real-time gas-sensing information for long-distance lossless transmission. Summary of the Invention

[0003] The purpose of this invention is to provide a gas sensor based on an inverse bipolar transistor to solve the problems of existing resistive gas sensors, such as single detection signal path, reliance on calibration, and poor anti-interference capability. This invention makes full use of the special transfer characteristics of the inverse bipolar transistor to convert the concentration information of the sensitive gas into the frequency domain information of the output signal, bringing a brand-new form of concentration information encoding.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A gas sensor based on an inverse bipolar transistor, characterized in that it comprises: a heavily doped p-silicon layer 1, a silicon dioxide layer 2, a metal electrode 3, a molybdenum telluride thin film 4, and a molybdenum disulfide thin film 5; wherein:

[0006] The heavily doped p-silicon layer serves as the gate, and a silicon dioxide layer is stacked on top of it.

[0007] The molybdenum ditelluride thin film and the molybdenum disulfide thin film constitute a heterojunction gas-sensitive unit, and the heterojunction gas-sensitive unit is disposed on the surface of the silicon dioxide layer;

[0008] The two metal electrodes, serving as the drain and source electrodes, are respectively disposed on a molybdenum ditelluride thin film and a molybdenum disulfide thin film.

[0009] Furthermore, the molybdenum ditelluride thin film serves as a p-type two-dimensional material layer, and the molybdenum disulfide thin film serves as an n-type two-dimensional material layer. The molybdenum disulfide thin film is partially overlapped on the molybdenum ditelluride thin film to form electrical contacts, or the molybdenum ditelluride thin film is partially overlapped on the molybdenum disulfide thin film to form electrical contacts, thus constituting a type II heterojunction.

[0010] Furthermore, the thickness of the metal electrode is 35nm~50nm.

[0011] Furthermore, the thickness of the molybdenum ditelluride film is 3nm~13nm, and the thickness of the molybdenum disulfide film is 0.6nm~12nm.

[0012] Furthermore, the work function of the metal material used in the metal electrode is in the range of 5.1 eV to 5.2 eV.

[0013] Furthermore, the gas sensor based on the inverse bipolar transistor operates as follows:

[0014] The drain is connected to a DC voltage source 6, the source is connected to ground 7, and the gate is connected to an AC voltage source 8.

[0015] A periodic triangular wave voltage signal with frequency f is input from an AC voltage source. The frequency of the output current is monitored, and the time it takes for the output current frequency to change from 2f to f is recorded, thereby characterizing the concentration of the sensitive gas.

[0016] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0017] This invention provides a gas sensor based on an inverse bipolar transistor. Utilizing the unique transfer characteristics of the inverse bipolar transistor, the concentration information of the sensitive gas is converted into frequency domain information of the output current. The specific detection principle is as follows:

[0018] The inverting bipolar transistor integrates p-type and n-type channels on the same substrate. Its structural layout and transfer characteristic curves are similar to those of an inverter based on CMOS circuits, but their underlying principles differ. Because the inverting bipolar transistor has two conductive channels, it exhibits higher positive gate voltage (V0) in the higher positive gate voltage range. G > V th,p V G For gate voltage, V th,p (This refers to the threshold voltage of the p-type material.) Although the n-type channel remains on, the p-type channel is off, thus affecting the overall It. D (Drain current) is suppressed, forming an off state; in the higher negative gate voltage range (V G < V th,n V th,n (This is the threshold voltage of the n-type material). Although the p-type channel remains on, the n-type channel is off, thus causing I...D When suppressed, it also forms an off state; while in the middle range of the gate voltage (V th,n <V G < V th,p Within this channel, both the p-type and n-type channels are simultaneously conducting, resulting in a source-drain current I0. D The current increases significantly, forming a peak current. It is evident that the conduction current in the unique Λ-shaped transfer characteristic curve of the inverted bipolar transistor includes the synergistic contribution of the p-type and n-type channel conduction currents. Simultaneously, the different changes in conductivity of the p-type and n-type channels after adsorbing the same sensitive gas directly affect the gate voltage at which the peak current appears in the Λ-shaped transfer characteristic curve. That is, assuming a gate voltage scan range of -50V to 50V, the original peak current appears at gate voltages of -10V and -50V. <V G <10V: Source and drain current increase; -10V <V G <50V: Source and drain currents decrease; taking the sensitive gas nitrogen dioxide as an example, in a 10ppm nitrogen dioxide atmosphere, the gate voltage point where the peak current appears shifts to 0V, -50V. <V G <0V: Source and drain currents increase; 0V <V G <50V: The source-drain current decreases slowly or remains basically unchanged; if the input periodic gate voltage scanning range is fixed at -10V to 10V and the frequency is f, the original source-drain current frequency of the output is 2f, while in a nitrogen dioxide atmosphere, the source-drain current frequency of the output after a certain time is f; it can be seen that by using the gate voltage scanning method, the information of gas concentration change can be mapped to the frequency change of the output current. That is, the gas concentration information is not directly reflected in the absolute magnitude of the signal at a certain instant, but is encoded in the change of the duration of the frequency signal, that is, the concentration information of the sensitive gas is converted into the frequency domain information of the output current.

[0019] Compared with existing technologies, this invention has obvious advantages: traditional resistive gas sensors use amplitude information to reflect gas concentration information, while the inverse bipolar transistor structure can use frequency information to reflect gas concentration information. In the case of fluctuations in ambient temperature and humidity and signal transmission, frequency-modulated signals have better anti-interference ability than amplitude-modulated signals. This invention encodes concentration information in frequency changes, and amplitude interference during transmission is easily filtered out without affecting the restoration of the original signal. In addition, since the core of sensitive gas concentration characterization lies in the time it takes for the output signal frequency to change from 2f to f, the device is minimally affected by fluctuations in the absolute amplitude of the conduction current. In actual testing, frequency 2f is the reference point for each test. The gas concentration can be determined simply by judging the time it takes for frequency f to appear after frequency 2f, without the need for the baseline calibration steps required by traditional resistive gas sensors. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of a gas sensor based on an inverse bipolar transistor provided by the present invention.

[0021] Figure 2 The real-time transfer characteristic curve of the gas sensor based on the anti-bipolar transistor provided by the present invention under the condition of continuous introduction of 10ppm nitrogen dioxide.

[0022] Figure 3 The transfer characteristic curves of the gas sensor based on the anti-bipolar transistor provided by the present invention after continuous introduction of nitrogen dioxide at different concentrations for 100s.

[0023] Figure 4 The graph shows the measured output signal frequency of the gas sensor based on the anti-bipolar transistor provided by this invention in air and 10ppm nitrogen dioxide atmosphere.

[0024] In the above figures: 1. Heavily doped p-silicon layer; 2. Silicon dioxide layer; 3. Metal electrode; 4. Molybdenum ditelluride thin film; 5. Molybdenum disulfide thin film; 6. Voltage source; 7. Ground terminal; 8. AC voltage source. Detailed Implementation

[0025] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] This embodiment provides a gas sensor based on an inverse bipolar transistor, the structure of which is as follows: Figure 1 As shown, it includes: a heavily doped p-silicon layer 1, a silicon dioxide layer 2, a metal electrode 3, a molybdenum ditelluride thin film 4, and a molybdenum disulfide thin film 5; wherein, the silicon dioxide layer 2 is stacked on the heavily doped p-silicon layer 1, and together they form the substrate portion; the molybdenum ditelluride thin film 4 and the molybdenum disulfide thin film 5 constitute a heterojunction gas-sensitive unit, the molybdenum ditelluride thin film 4 and the molybdenum disulfide thin film 5 are disposed on the silicon dioxide layer 2, and a type II heterojunction is formed at their overlapping portion, the molybdenum ditelluride thin film serves as a p-type two-dimensional material layer, the molybdenum disulfide thin film serves as an n-type two-dimensional material layer, the molybdenum disulfide thin film is located on the molybdenum ditelluride thin film and forms good electrical contact; two metal electrodes serve as the drain and source, respectively disposed on the molybdenum ditelluride thin film 4 and the molybdenum disulfide thin film 5, the drain is connected to a DC voltage source 6, and the source is connected to a ground terminal 7; the heavily doped p-silicon layer 1 serves as the gate and is connected to an AC voltage source 8.

[0027] In this embodiment, the thickness of the metal electrode is 35nm~50nm, and the work function of the metal thin film material is in the range of 5.1eV~5.2eV; the thickness of the molybdenum ditelluride thin film is 3nm~13nm, and the thickness of the molybdenum disulfide thin film is 0.6nm~12nm.

[0028] In this embodiment, the two-dimensional material thin films in the gas sensor are all obtained by mechanical peeling, and the two-dimensional heterojunction is constructed by dry transfer process; the metal electrode is prepared by a series of processes including spin coating, photolithography, development, coating and peeling.

[0029] In this embodiment, a forward bias voltage of 1V is applied to the source and drain electrodes, and a periodic triangular wave voltage signal of -40V to 10V is input from an AC voltage source to the bottom gate electrode to monitor the frequency and amplitude changes of the output current (source-drain current). Specifically, in this embodiment, a triangular wave gate voltage signal of -40V to 10V is selected, covering the characteristic gate voltage region of the inverse bipolar transistor. That is, when the gate voltage changes from -40V to 10V, the current first increases and then decreases; when the gate voltage changes from 10V to -40V, the source-drain current first increases and then decreases. However, after continuously passing 10ppm nitrogen dioxide for 100s, when the gate voltage changes from -40V to 10V, the source-drain current maintains a monotonically increasing trend. Figure 2 As shown, during the gate voltage scanning process, the transfer characteristic curve can reflect the real-time response of the inverse bipolar transistor gas sensor to 10 ppm nitrogen dioxide. Ultimately, the change in the concentration of the gas being measured is reflected by the frequency change of the output current signal. That is, if the frequency of the fixed input periodic gate voltage is f, then the frequency of the output current (source-drain current) is 2f. However, in a nitrogen dioxide atmosphere, the frequency of the output current will change to f after a certain period of time. Furthermore, different concentrations of nitrogen dioxide cause different times for the transfer characteristics of the inverse bipolar transistor to begin to change significantly. That is, when the gate voltage changes from -40 V to 10 V, the source-drain current changes from a trend of first increasing and then decreasing in an air atmosphere to a trend of continuous increase in a nitrogen dioxide atmosphere, with different durations of change. Figure 3 As shown, nitrogen dioxide at concentrations of 1 ppm, 2 ppm, 5 ppm, and 10 ppm was continuously introduced. After 100 seconds, the nitrogen dioxide concentrations of 2 ppm, 5 ppm, and 10 ppm essentially enabled the device to complete the transition to mono-incremental transfer characteristics (and the time required for this transition decreased with increasing gas concentration). In contrast, 1 ppm of nitrogen dioxide required a relatively longer gas flow time to complete the transition to mono-incremental transfer characteristics. Therefore, this invention can characterize the nitrogen dioxide concentration by measuring the duration of frequency changes in the output current (source-drain current).

[0030] More specifically, in this embodiment, the applied triangular wave voltage signal is applied to the ground gate at a frequency of 2.5 Hz, corresponding to a current signal frequency of 5 Hz at the source and drain electrodes in an air atmosphere; after 10 ppm nitrogen dioxide is continuously introduced for 25 seconds, the inverse bipolar transistor gas sensor completes the transition to mono-incremental transfer characteristics, at which point the frequency of the current signal output from the source and drain electrodes is 2.5 Hz. Figure 4As shown, this demonstrates that a gas sensor based on an anti-bipolar transistor can encode gas concentration information into the frequency domain by utilizing the transition process of anti-bipolar characteristics under a gas atmosphere.

[0031] Based on this, the frequency conversion signal carrying gas information in this embodiment can be used for long-distance signal transmission. Since various environmental interferences during transmission mainly affect the amplitude information while the frequency information is less affected, its anti-interference capability is strong. The frequency information of the current signal in different time periods can be extracted through signal processing at the terminal, and the real-time change process of gas concentration can be finally restored. In addition, in this embodiment, the voltage bias point, voltage swing, and single-point voltage duration of the bottom gate voltage can be freely tuned according to actual needs, and the frequency of the input bottom gate voltage can be freely tuned between 0 and 100 Hz.

[0032] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A gas sensor based on an inverse bipolar transistor, characterized in that, include: Heavily doped p-silicon layer (1), silicon dioxide layer (2), metal electrode (3), molybdenum ditelluride thin film (4), molybdenum disulfide thin film (5); wherein: The heavily doped p-silicon layer serves as the gate, and a silicon dioxide layer is stacked on top of it. The molybdenum ditelluride thin film and the molybdenum disulfide thin film constitute a heterojunction gas-sensitive unit, and the heterojunction gas-sensitive unit is disposed on the surface of the silicon dioxide layer; The two metal electrodes, serving as the drain and source electrodes, are respectively disposed on a molybdenum ditelluride thin film and a molybdenum disulfide thin film.

2. The gas sensor based on an inverse bipolar transistor according to claim 1, characterized in that, The molybdenum ditelluride thin film serves as a p-type two-dimensional material layer, and the molybdenum disulfide thin film serves as an n-type two-dimensional material layer. The molybdenum disulfide thin film is partially overlapped on the molybdenum ditelluride thin film to form electrical contacts, or the molybdenum ditelluride thin film is partially overlapped on the molybdenum disulfide thin film to form electrical contacts, thus forming a type II heterojunction.

3. The gas sensor based on an inverse bipolar transistor according to claim 1, characterized in that, The thickness of the molybdenum ditelluride film is 3nm~13nm, and the thickness of the molybdenum disulfide film is 0.6nm~12nm.

4. The gas sensor based on an inverse bipolar transistor according to claim 1, characterized in that, The thickness of the metal electrode is 35nm~50nm.

5. The gas sensor based on an inverse bipolar transistor according to claim 1, characterized in that, The work function of the metal material used in the metal electrode is in the range of 5.1 eV to 5.2 eV.

6. The gas sensor based on an inverse bipolar transistor according to claim 1, characterized in that, During operation, the gas sensor based on the inverse bipolar transistor works as follows: The drain is connected to a DC voltage source (6), the source is connected to ground (7), and the gate is connected to an AC voltage source (8). A periodic triangular wave voltage signal with frequency f is input from an AC voltage source. The frequency of the output current is monitored, and the time it takes for the output current frequency to change from 2f to f is recorded, thereby characterizing the concentration of the sensitive gas.

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