A semiconductor gas sensor based on a dual-pass porous substrate

Abstract

The application relates to a semiconductor gas sensor based on a double-through porous substrate, which at least comprises: a first electrode used for conducting electrical changes in a sensing reaction in a powered state; a second electrode used for forming a current path with the first electrode; a sensing layer composed of a double-through porous substrate with a gas-sensitive material for detecting gas deposited on the surface, and the double-through porous substrate is formed by a plurality of nanotube arrays. The first electrode and the second electrode are staggered on both sides of the sensing layer in a third direction in a non-overlapping manner, so that at least one tube opening of the nanotube on the sensing layer can be connected with the outside. The sensing electrode is improved, the phenomenon that part of the nanotubes cannot detect gas due to the nanotubes being covered when the sensing electrode is arranged is avoided, and the detection efficiency of the semiconductor gas sensor is improved.

Description

Technical Field

[0001] This invention relates to the field of sensor devices, and more particularly to a semiconductor gas sensor based on a dual-channel porous substrate. Background Technology

[0002] Gas sensors have been widely applied in three major fields: industry, civil use, and environmental monitoring. Currently, there are numerous methods and techniques for gas detection, mainly including catalytic combustion, electrochemical, thermal conductivity, infrared absorption, and semiconductor gas sensors. Semiconductor gas sensors include resistive and non-resistive types. Resistive gas sensors detect gas concentration by utilizing changes in resistance. Due to their advantages such as high sensitivity, ease of operation, small size, low cost, and short response and recovery times, resistive semiconductor sensors are the most widely used, especially in the detection of flammable and explosive gases (such as CH4 and H2) and toxic and harmful gases (such as CO and NOx).

[0003] Semiconductor gas sensors typically use metal oxides as gas-sensitive materials. These materials detect target gases by adsorbing gases onto their surface and causing changes in their surface resistance due to surface reactions. The larger the specific surface area of ​​the gas-sensitive material, the higher its sensitivity and the easier it is to adsorb target gases. Many methods exist for preparing gas-sensitive materials, such as chemical vapor deposition and chemical bath deposition. These methods produce gas-sensitive materials with large specific surface areas and high chemical activity, enabling the detection of target gases at relatively low concentrations.

[0004] In the prior art, patent document CN113092542A discloses a planar nano gas sensor, array and its fabrication method, relating to the field of gas sensor technology. The gas sensor includes, from top to bottom, a planar sensing electrode, a sensing layer, an electrically insulating layer and a micro heater. The sensing layer is formed by depositing nanoscale sensing material in a dual-hole substrate. The dual-hole substrate is composed of multiple dual-hole nanotubes. The dual-hole nanotubes are nanotubes with openings at both ends and connected to each other. The nanoscale sensing material is deposited on the wall of the dual-hole nanotubes. The heating area of ​​the micro heater overlaps with the sensing area of ​​the planar sensing electrode in the vertical direction.

[0005] Chinese patent CN110412084A relates to a gas sensor and a method for manufacturing and using the sensor. The gas sensor includes an insulator template comprising an array of nanotubes formed by parallel-aligned open nanotubes; a sensing material deposited at least on the inner surface of the nanotubes; and optionally catalyst nanoparticles dispersed on the sensing material. The sensor also includes an electronic controller activating electrodes made of different conductive materials to obtain multiple resistance measurements on the insulator template. The resistance measurements can be compared with stored resistance curves to determine the gas type, concentration, and mixture in the nanotube array gas sensor.

[0006] The aforementioned application proposes to increase the specific surface area of ​​the gas-sensitive material by depositing it on a dual-channel AAO template, thereby giving the sensor a higher detection area. However, it does not consider how to configure the sensing electrodes to accurately and quickly conduct the current changes during the sensing response, thus failing to improve the detection sensitivity and resulting in poor practicality.

[0007] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the inventors studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0008] To address at least some of the shortcomings of the prior art, this application provides a semiconductor gas sensor based on a dual-channel porous substrate, comprising at least: a first electrode for conducting electrical changes during sensing when energized; a second electrode for forming a current path with the first electrode; and a sensing layer composed of a dual-channel porous substrate with a gas-sensitive material deposited on its surface for gas detection. The dual-channel porous substrate can be formed by an array of multiple nanotubes. The first and second electrodes are staggered on both sides of the sensing layer in a vertically intersecting, non-overlapping manner, ensuring that at least one opening of the nanotube on the sensing layer remains connected to the outside. By arranging the first and second electrodes in a vertically intersecting, non-overlapping manner, this invention avoids the phenomenon where the width of the interdigitated ends of the sensing electrodes is greater than the pore size of the nanotubes, resulting in both ends of the same nanotube being covered and closed by the sensing electrodes, preventing the gas to be detected from entering the nanotube for detection, thereby improving the utilization rate of the nanotubes on the sensing layer.

[0009] Preferably, at least the contact portions of the first and second electrodes at their connection with the sensing layer are provided with a conductive film. This conductive film forms a barrier at the connection point with a reduced contact barrier width, facilitating electron tunneling. This ensures that the electrical property changes conducted through the first and second electrodes originate entirely from the electrical property changes during the sensing response of the sensing layer. The present invention provides a conductive film between the sensing electrode and the sensing particle to achieve ohmic contact between them. This allows the electrical property changes of the sensing response to be accurately conducted to the sensing electrode, unaffected by the Schottky junction generated by the semiconductor-metal contact between the sensing electrode and the sensing particle. Furthermore, the present invention anneales the sensing particle, sensing electrode, and conductive film at the connection point, resulting in a higher carrier concentration in the sensing particle and a thinner contact barrier at the connection point, making electron tunneling easier and achieving better ohmic contact performance.

[0010] Preferably, the conductive thin film disposed on the surfaces of the first and second electrodes gives them thicker interdigitated ends, increasing the proportion of nanopores covered by these interdigitated ends on the dual-channel porous substrate to form more nanotubes in the first state. The opening of the nanotube in the first state near the second electrode is covered by the second electrode, resulting in a "U"-shaped layer structure within the nanotubes. This "U"-shaped layer structure increases the sensing area of ​​the sensing particles on top of the original deposition, allowing the dual-channel porous substrate to accommodate more sensing particles, generate more sensing potentials, and further enhance the sensor's practicality.

[0011] Preferably, the sensing particles within the nanotube in the first state comprise a first portion with a relatively high and non-uniform thickness and a second portion with a uniform thickness. The first portion has a higher heating rate than the second portion, and the portion of the first portion closest to the second electrode in the vertical direction directly contacts and maintains an electrical connection with the second electrode. This allows changes in the electrical properties of the first portion to be conducted to the second electrode more quickly and sensitively than those of the second portion. Growing a conductive thin film on the sensing electrode increases the width of the sensing electrode, at least at the interdigitated ends, encouraging the formation of more nanotubes in the first state. The first portion of the nanotube in the first state has a higher heating rate and a faster conductivity rate than the second portion and any other portion in the other states, enabling the sensor to operate intermittently for energy saving. Specifically, the first portion can quickly reach the sensing condition when the external power is turned on and directly conducts the changes in electrical properties during the sensing response through the second electrode connected to the bottom, greatly increasing the sensor's detection efficiency and practicality.

[0012] Preferably, in the second state, the two ends of the nanotube are connected, and the gas inside the nanotube has high fluidity, which makes it easier for the sensing particles deposited on the inner wall of the nanotube to come into contact with the gas molecules inside the tube and to react with the gas molecules to be detected.

[0013] Preferably, the semiconductor gas sensor further includes a heating layer and an isolation layer. The isolation layer is disposed between the heating layer and the sensing layer. The isolation layer can transfer the heat generated by the heating layer to the functional area in a uniform conduction manner. The isolation layer has reserved heating electrode holes for the heating layer to be led out to an external heating power supply.

[0014] Preferably, the sensing layer includes functional areas and non-functional areas, which are connected by a suspension, and the shape of the non-functional areas is matched to the interdigital space.

[0015] Preferably, the heating layer includes a heating electrode and a thermal resistance wire. The heating electrode is electrically connected to the thermal resistance wire via a connecting wire. The shape of the heating electrode matches the heating electrode hole, so that the heating electrode can be nested in the heating electrode hole and maintain electrical connection with an external heating power supply. The heating area formed by the meandering thermal resistance wire matches the shape of the functional area, so that the thermal resistance wire can heat the functional area as a whole.

[0016] Preferably, the semiconductor gas sensor further includes a support layer disposed on the other side of the thermal resistance wire relative to the sensing layer. The support layer is provided with a bearing area to prevent the heat generated by the thermal resistance wire from being dissipated from one side of the support layer. The bearing area is configured to match the heating area formed by the thermal resistance wire.

[0017] Preferably, the semiconductor gas sensor further includes a substrate disposed on the other side of the support layer, and the substrate has a slotted hole extending through the substrate. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0019] Figure 2 This is a top view of the sensing electrode of the present invention;

[0020] Figure 3 This is a schematic diagram of the heating layer of the present invention;

[0021] Figure 4 This is a schematic diagram of the sensor layer partitioning of the present invention;

[0022] Figure 5 This is a schematic diagram of a single nanotube in the third state of the present invention.

[0023] List of reference numerals

[0024] 1: First electrode; 11: Interdigitated electrode; 12: Interdigitated region; 13: Interdigitated end; 14: Interdigitated panel; 2: Sensing layer; 21: Functional area; 22: Non-functional area; 23: Suspension; 24: Channel; 3: Sensing particle; 4: Isolation layer; 41: First overlapping area; 42: Heating electrode hole; 5: Heating layer; 51: Heating electrode; 52: Connecting wire; 53: Thermal resistance wire; 6: Support layer; 61: Second overlapping area; 7: Substrate; 71: Hole; 8: Second electrode; 9: Conductive thin film; 31: First part; 32: Second part. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings.

[0026] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, 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.

[0027] This invention provides a semiconductor gas sensor based on a dual-channel porous substrate, such as... Figure 1 As shown, it can include the following parts stacked from top to bottom:

[0028] The first electrode 1, which is located at the very top of the entire sensor, is used to transmit electrical signals when the sensor generates a sensing response.

[0029] The sensing layer 2 is disposed on the bottom layer of the first electrode 1 in such a way that it at least partially overlaps the first electrode 1 vertically, and has sensing particles 3 for sensing reactions with the gas to be detected.

[0030] The second electrode 8, together with the first electrode 1, makes contact-type electrical connection to the sensing layer 2, so that changes in the electrical properties of the sensing particles 3 can be conducted through the first electrode plate 1 and the second electrode plate 8.

[0031] An isolation layer 4, which is disposed on the other side of the second electrode 8 opposite to the sensing layer 2, is used to uniformly and stably transfer the heat required for the sensing particles 3 to undergo a sensing response to the sensing layer 2.

[0032] The heating layer 5, which is located at the bottom of the isolation layer 4, is used to provide heat to the sensing layer 2. This heat can be evenly conducted to the sensing layer 2 after being blocked by the isolation layer 4.

[0033] A support layer 6 is disposed on the side of the heating layer 5 opposite to the isolation layer 4 to prevent the heat generated by the heating layer 5 from being lost from the side located on the support layer 6.

[0034] Substrate 7, which is located at the bottom layer of the entire sensor structure, serves as a carrier structure to support all the layers above.

[0035] According to a preferred embodiment, such as Figure 1 As shown, the first electrode 1 is disposed on the surface of the sensing layer 2, and the second electrode 8 is disposed on the opposite side of the sensing layer 2 relative to the surface. The first electrode 1 and the second electrode 8 are respectively in contact with and electrically connected to the sensing particles 3 on the sensing layer 2. Under the premise that the voltage across the first electrode 1 and the second electrode 8 is constant, when the sensing particles 3 come into contact with the gas to be detected that can react with the sensing particles 3, a sensing reaction occurs, causing a change in their own resistance, and further changing the current in the circuit. By monitoring the change in current within the circuit, it can be determined whether there is a gas capable of being sensed in the scene where the sensor is located. Preferably, as... Figure 1 The first electrode 1 and the second electrode 8 can be composed of a pair of interdigitated electrodes 11 with an interlaced structure. The interdigitated electrodes 11 are arranged vertically without overlapping, and the interdigitated interval 12 between the two interdigitated electrodes 11 is electrically connected to the interdigitated ends 13 of the interdigitated electrodes 11 through the sensing particles 3 on the sensing layer 2, so that a closed loop is formed between the two interdigitated electrodes 11.

[0036] According to a preferred embodiment, such as Figure 1 As shown, the first electrode 1 and the second electrode 8 are respectively deposited on two vertical surfaces of the sensing layer 2. Specifically, an example of the sensing layer 2 can be a dual-channel porous alumina template. Specifically, the orifices of the dual-channel porous alumina template face the first electrode 1 and the second electrode 8, respectively. Two interdigitated electrodes 11, formed by interlocking vertically without overlapping, are deposited at the orifice positions on both sides of the dual-channel porous alumina template. The two interdigitated electrodes 11 are electrically connected by being deposited on both sides of the sensing layer 2 and contacting the sensing particles 3 within the interdigitated region 12. The sensing particles 3 within the interdigitated region 12 include sensing particles on the surface outside the orifices and sensing particles deposited on the inner wall of the alumina template within the orifices. Preferably, the interdigitated region 12 can be any shape conceivable to those skilled in the art, matching the contour formed by its mating interdigitated electrodes 11. Here, it is set as a triangle. The two interdigitated electrodes 11 are led out through their respective interdigitated panels 14, which are used to connect to an external voltage source. The first electrode 1 and the second electrode 8 are preferably made of metal Al.

[0037] According to a preferred embodiment, the sensing layer 2 may be formed from a dual-porous alumina template on which sensing particles 3 are deposited. It should be understood that the dual-porous alumina template described in this invention is merely a preferred example of the sensing layer 2. In some alternative embodiments, the dual-porous substrate or sensing layer 2 described in this invention may also be formed from one or more of titanium oxide, silicon oxide, tantalum oxide, zirconium oxide, or gallium nitride.

[0038] According to a preferred embodiment, taking a double-pass porous alumina template as an example, the double-pass porous alumina template is composed of multiple single-pore nanotubes, each nanotube having two openings connected at both ends. Specifically, besides the porous double-pass structure, the alumina template can also be a porous single-pass structure, that is, a single-pass alumina template is composed of multiple openings connected at one end. Common double-pass porous alumina templates have a honeycomb structure, composed of hundreds, thousands, or even tens of thousands of regular hexagonal prism-shaped oxide units. For example... Figure 5 As shown, each regular hexagon has a circular channel 24 in the center. The size of the channel 24 is generally at the nanometer level, and the channel is roughly perpendicular to the surface. The pore size is uniform yet relatively adjustable, resulting in a simple and orderly array structure. This special structure makes the preparation process of the dual-channel porous alumina template simple, inexpensive, and suitable for assembling various materials. The ratio between the morphology of the material and particles assembled and deposited within the dual-channel porous alumina template is closely related to the performance of the nanomaterial. The dual-channel porous alumina template can be prepared using a two-step anodizing method. Due to its high temperature resistance, high strength, and monodisperse pore size, this template is an ideal method for preparing nano-alumina materials.

[0039] According to a preferred embodiment, the sensing particle 3 is a nano-zinc oxide material. Preferably, the sensing particle can also be a gas-sensitive material such as tin dioxide or tungsten trioxide (when a gas comes into contact with the gas-sensitive material, it can cause changes in the electrical properties of the gas-sensitive material, such as an increase or decrease in resistance). The sensing particle 3 is disposed on the inner wall of the nanotubes and the surface of the nanotube pores of the dual-channel porous substrate by adsorption deposition. The dual-channel porous substrate has a high specific surface area, which can contact and adsorb as many sensing particles 3 as possible and greatly increase the spread area of ​​the sensing particles 3, making it easier for the gas molecules to be detected to contact the sensing particles 3 and react with them.

[0040] According to a preferred embodiment, when the sensing particle 3 comes into contact with the target gas molecules capable of a sensing reaction, the target gas gains or loses electrons due to its oxidizing and reducing properties. This changes the electrical resistance of the sensing particle 3, altering the current flowing through it, and consequently changing the current magnitude on the first electrode 1 and the second electrode 8 electrically connected to the sensing particle 3. Therefore, by monitoring the degree of current change, it can be determined whether the sensing particle 3 has come into contact with the target gas molecules capable of a sensing reaction. Furthermore, by controlling the temperature environment, the sensing particle 3 can be controlled to only react with the target molecules to be detected.

[0041] The dual-channel porous substrate of the sensing layer 2 can be divided into functional area 21 and non-functional area 22. Functional area 21 and non-functional area 22 are connected by suspension 23. Sensing particles 3 are deposited on both functional area 21 and non-functional area 22. The shape of functional area 21 is adapted to the shape of the first electrode 1, so that the shape of functional area 21 can match the interdigitated area 12. Here, the shape of functional area 21 is set as a triangle matching the contour of the first electrode 1. Non-functional area 22 is used for angular compensation when functional area 21 deforms in a high-temperature environment. Only a single suspension 23 is set to connect with functional area 21 to reduce heat loss of functional area 22. Functional area 21 needs to be at a high temperature when sensing response occurs. Due to the difference in Young's modulus and thermal expansion coefficient of the constituent materials of functional area 21 and the first electrode 1 and the isolation layer 4 stacked on both sides, the surface stress of functional area 21 will increase under high temperature conditions. The stress at the connection with suspension 23 is relatively large, which is prone to cracking and damage. This can be improved by angular compensation. The non-functional area 22, suspension 23, and functional area 21 are integrally formed structures. Preferably, the non-functional area 22, suspension 23, and functional area 21 can be separated from the complete double-through porous substrate by cutting.

[0042] According to a preferred embodiment, the sensing current during a sensing response is mainly distributed on the sensing particles 3, including the sensing particles on the surface of the pores of the dual-channel porous substrate nanotubes and the inner walls of the nanopores. In this invention, the contact surfaces between the first electrode 1 and the second electrode 2 and the sensing layer 2 are the overlapping areas of the interdigitated region 12 and the functional region of the sensing layer 2. That is, the area where the sensing response occurs is mostly concentrated on the nanopore walls with a high unfolded area, with a small portion located within the interdigitated region of the first electrode 1.

[0043] According to a preferred embodiment, an isolation layer 4 is disposed at the bottom of the sensing layer 2 to isolate the sensing layer 2 from the heating layer 5. The isolation layer 4 prevents the sensing particles 3 from malfunctioning due to excessively rapid temperature changes in the heating layer 5. Excessive temperature changes can lead to large variations in thermal stress and rapid thermal expansion, easily causing material deformation and fracture. The isolation layer 4, while ensuring heat conduction, also maintains electrical isolation between the sensing layer 2 and the heating layer 5. The isolation layer 4 can be formed from a silicon oxide layer structure.

[0044] According to a preferred embodiment, the isolation layer 4 is provided with a first overlapping area 41 for connecting the wires of the interdigital panel 14 portion, including a mating functional area 21, a suspension 23, and interdigital electrodes 11. Figure 1 As shown, the first overlapping area 41 is formed by cutting away several trapezoids from the isolation layer, where the perpendicular bisectors intersect at a point and the shorter sides face each other. In this invention, the first overlapping area 41 is formed by removing three trapezoids. The triangular region enclosed by the trapezoids matches the shape of the functional area 21, and the area of ​​the triangular region is slightly larger than the area of ​​the functional area 21 to ensure that the functional area 21 is completely within the triangular region. A reserved area is reserved between adjacent trapezoids for matching and overlapping with some of the wires of the suspension 23 and the interdigitated electrode 11.

[0045] According to a preferred embodiment, the heating layer 5 is disposed on the side of the isolation layer 4 opposite to the sensing layer 2. The heating layer 5 includes a heating electrode 51 and a thermal resistance wire 53. The thermal resistance wire 53 is connected to the heating electrode 51 via a connecting wire 52. The present invention primarily utilizes the thermal resistance wire 53 to provide the heat source required for the entire sensor's sensing response. The thermal resistance wire 53 is formed by interdigitating triangular regions of a material with high resistivity, matching the first overlapping region 41. This allows the thermal resistance wire 53 to have a relatively long length, enabling concentrated heating of the functional area 21 of the sensing layer 2 through the isolation layer 4, while maintaining a fixed overall shape. The connecting wire 52 can be made of the same material as the thermal resistance wire 53. Even though the connecting wire 52 generates heat when current passes through it, the relatively long heat-generating length of the thermal resistance wire 53 results in more concentrated heat, thus minimizing the impact of the heat from the connecting wire 52 on the sensing response of the functional area 21. The economic benefits of integrally generating the thermal resistance wire 53 and the connecting wire 52 without requiring additional wires for electrical connection to the thermal resistance wire 53 are the highest, and material waste during manufacturing is also saved. The connecting wire 52 is led out to the heating electrode 51 by overlapping it into the reserved area. The heating electrode 51 is preferably rectangular in structure, and has a relatively large area to facilitate electrical connection with a voltage source. The heating electrode 51 is nested in the isolation layer 4 through the reserved heating electrode hole and is disposed on the isolation layer 4, so that one side of the heating electrode 51 is exposed, which facilitates the connection of the voltage source.

[0046] According to a preferred embodiment, the heat generated by the thermal resistance wire 53 can be collected in the isolation layer 4 and evenly conducted to the functional area 21 on one side of the isolation layer 4 when passing through the isolation layer 4, so that the heat generated by the thermal resistance wire 53 will not directly act on the functional area, and avoid the functional area 21 from deforming or falling off due to uneven heating and unbalanced thermal stress.

[0047] According to a preferred embodiment, a support layer 6 is disposed at the bottom of the heating layer 5. A second overlapping region 61 is disposed on the support layer 6 corresponding to the first overlapping region 41. The shape and size of the second overlapping region 61 match those of the first overlapping region 41. The second overlapping region 61 serves as a carrier region for the thermal resistance wire 53 when the heating layer 5 is deposited on the support layer 6. The second overlapping region 61 includes three cantilever beams for connecting to the remaining areas of the support layer 6. When the heat generated by the heating layer 5 is transferred to the carrier region, the heat conduction rate through the cantilever beams is relatively slow because the carrier region is only connected by three cantilever beams. This allows the carrier region to concentrate the heat radiated from the heating layer 5 towards the support layer 6, facilitating the temperature of the working region 21, which is adapted to the first overlapping region 41 and the second overlapping region 61, to reach the sensing temperature. The support layer 6 can be formed by slotting a silicon nitride or silicon oxide layer structure.

[0048] According to a preferred embodiment, the substrate 7 is located at the bottom of the entire sensor device to improve the overall physical strength of the sensor. For example... Figure 1 As shown, the substrate 7 is a cubic structure with a relatively high thickness. A slotted hole 71 is formed on the substrate 7, extending vertically through the entire substrate. In this invention, the slotted hole 71 is shaped as a triangular structure with high stability. Preferably, the shape of the slotted hole 71 can also be square, trapezoidal, or other shapes conceived by those skilled in the art. By slotting the substrate 7, its bending resistance can be increased, further avoiding the risk of the sensor device bending upon impact, thereby further improving the reliability of the sensor device.

[0049] According to a preferred embodiment, the shape of the slotted hole 71 matches the first overlapping region 41 and the second overlapping region 61, and the size of the triangle of the slotted hole 71 is larger than that of the first overlapping region 41, so that the sensor device passes through the slotted hole 71, the second overlapping region 62, the thermal resistance wire 53, the first overlapping region 41, and the sensing layer 2 sequentially from bottom to top. The gas to be detected can enter from one side of the sensor device and exit from the other side, and the device has strong gas flow, making it easier for the gas to be detected to enter for detection.

[0050] Preferably, to provide high physical strength, the substrate 7 is preferably a silicon substrate. In particular, when the substrate 7 of the present invention is made of silicon material, such as... Figure 1The support layer 6 shown may be unnecessary. However, when the substrate 7 is selected from one or more of sapphire, gallium nitride, or silicon carbide, Figure 1 The support layer 6 shown is usually necessary, taking into account the electrical insulation between the substrate 7 and other layer structures.

[0051] According to a preferred embodiment, the first electrode 1 and the second electrode 8 are electrically connected to the sensing particle 3 through direct contact. The contact between the metallic first electrode 1 and the semiconductor sensing particle 3 is a Schottky contact. In this contact method, a Schottky junction is formed between the first electrode 1 and the second electrode 8 and the sensing particle 3, resulting in a non-linear current-voltage characteristic through the first electrode 1 and the second electrode 8 and the sensing particle 3. This phenomenon is called the rectification effect. In short, the first electrode 1 and the second electrode 8 form a junction similar to a resistor at their contact points with the sensing particle 3. The resistance of this junction is not fixed and is easily changed. This junction affects the magnitude of the current passing through the first electrode 1, the second electrode 8, and the sensing particle 3, especially during a sensing response, where the impact on the sensing current is greatest. This leads to errors in determining whether a sensing response has occurred or the degree of such a response by monitoring the sensing current. In order to eliminate or reduce the problem of sensing errors caused by Schottky junction, the present invention provides a conductive film 9 in the portion of the first electrode 1 and the second electrode 8 that is in contact with the sensing layer 2 before the first electrode 1 is deposited onto the sensing layer 2 and the sensing layer 2 is deposited onto the second electrode 8.

[0052] The conductive thin film 9 is used to achieve ohmic or low-resistance ohmic contact between the first electrode 1, the second electrode 8, and the sensing particle 3. An ohmic contact refers to a metal-semiconductor contact portion whose resistance is negligible compared to the total resistance of the device. An ideal ohmic contact has almost no impact on the performance of the device, and the voltage drop in the ohmic contact region is sufficiently small compared to the voltage drop across the first electrode 1 and the sensing particle 3.

[0053] According to a preferred embodiment, ZnO is an N-type semiconductor and a wide-bandgap semiconductor material. Based on semiconductor-metal contact theory, as long as a metal with a smaller work function than ZnO is selected, such as Al selected in this invention, an ohmic contact between metal and n-type ZnO can be achieved. Preferably, the metal with a smaller work function than ZnO can also be In, Ti, etc. Alternatively, a better ohmic contact with metal ZnO can be obtained using a highly doped contact method. Further, in this invention, a conductive thin film 9 is grown in the region where the first electrode 1 and the second electrode 8 contact the sensing layer 2. The conductive thin film 9 can be aluminum-doped zinc oxide (AZO), preferably with an Al doping amount of 3% by mass. This allows the sensing particle 3, located close to the metal electrode, to be electrically connected to the metal electrode through the conductive thin film 9. At this point, the depletion region is very thin, and due to the electron tunneling effect, the contact at zero bias has very low resistance, thus improving the quality of the ohmic contact between the sensing particle 3 and the metal electrode.

[0054] Specifically, before depositing the sensing layer 2 on the second electrode 8, aluminum-doped ZnO is epitaxially grown on the second electrode 8; before placing the first electrode 1 on the sensing layer 2, the same aluminum-doped ZnO is epitaxially grown on the first electrode 1. To ensure that the thickness of the aluminum-doped ZnO layers grown on the first electrode 1 and the second electrode 8 is consistent, the growth processes of the first electrode 1 and the second electrode 8 should be kept consistent. The first electrode 1 and the second electrode 8 respectively form contact electrical connections with the sensing particles 3 on the sensing layer 2 through conductive thin films 9. Since the work function of Al is not much different from that of the n-type semiconductor ZnO, a contact barrier will appear at the contact position between the metal electrode and the sensing particles 3 before the addition of conductive thin films 9, causing the current I flowing through the metal electrode and the voltage V across the metal electrode to deviate from a linear relationship. At the contact site between the metal electrode and the sensing particle after the addition of the conductive film 9, an Al-AZO-n type ZnO contact is formed. Although a potential barrier exists at the contact surface due to surface states, the AZO layer of the conductive film 9 is a highly doped layer with a sufficiently high carrier concentration, making the contact barrier very thin. Electrons can easily tunnel through the barrier, and the current changes linearly with the applied bias voltage. The first electrode 1 and the second electrode 8 respectively achieve ohmic contact with the sensing particle 3. Furthermore, when the sensor reacts, the change in the electrical properties of the sensing particle 3 can be accurately conducted to the first electrode 1 and the second electrode 8 via the conductive film 9. There is no voltage loss in this process, which greatly improves the accuracy of the sensor. It can be understood that the conductive film 9 can be grown on the first electrode 1 and the second electrode 8 by pre-depositing the conductive film 9 on the first electrode 1 and the second electrode 8. In this process, the first electrode 1 and the second electrode 8 have thicker interdigitated ends 13, which increases the proportion of nanopores covered by the interdigitated ends 13 on the dual-channel porous substrate.

[0055] According to a preferred embodiment, a thin film deposited at a certain temperature contains many defects. By maintaining the film in an environment higher than the deposition temperature for a period of time, the defects in the film can move within the crystal and gradually annihilate or be absorbed by impurities and the surface, thereby improving the crystallinity of the film. In this invention, after the deposition of sensing particles 3 on a dual-channel porous substrate, the Al-AZO-ZnO junction is annealed at 500 degrees Celsius, resulting in a high-quality ohmic contact at the Al-AZO-ZnO junction. Furthermore, the annealed AZO film has a higher carrier concentration, making the contact barrier at the junction thinner and allowing electrons to tunnel through more easily, thus achieving better ohmic contact performance.

[0056] According to a preferred embodiment, such as Figure 5 In this invention, the first electrode 1 and the second electrode 8 are respectively configured as interdigitated electrodes 11, thereby improving the sensing sensitivity of the sensor. When the sensing particles 3 are deposited on the dual-channel porous substrate, some nanopores are completely sealed by the sensing particles 3 due to the interdigitated ends 13 of the second electrode 8 and the conductive film 9 covering the pore openings. Furthermore, the first electrode 1 is arranged in a way that crosses and does not overlap with the second electrode 8 in the vertical direction, resulting in three states for the nanotubes on the dual-channel porous substrate. First state: the end near the first electrode 1 is connected and the connected end is not covered by the interdigitated ends 13 of the first electrode 1, while the end near the second electrode 8 is sealed by the sensing particles 3 and electrically connected to the conductive film 9; Second state: both ends are connected and are not covered by the interdigitated ends 13; Third state: the end near the second electrode 8 is connected and the end near the first electrode 1 is connected but covered by the interdigitated ends 13 of the first electrode 1.

[0057] In the first state, when the sensing particles 3 are deposited on the dual-porous substrate, the openings of some nanotubes near the second electrode 8 are covered by the second electrode 8, forming a "U"-shaped layer structure within the nanotubes. As shown in the figure, the sensing particles 3 at different positions can be divided into a first part 31 and a second part 32 according to their structure. The first part 31 is the part where the layer structure formed by the sensing particles 3 has a relatively high thickness and uneven thickness distribution, while the second part 32 is the part where the layer structure formed by the sensing particles 3 has a uniform thickness. The first part 31 directly contacts the conductive film 9 on the second electrode 8, and the area of ​​the first part 31 that can contact the conductive film 9 includes the cross-sectional area of ​​the sensing particle 3 that is completely deposited and sealed at the orifice and the contact area between the sensing particle 3 on the normal nanotube orifice connection platform and the conductive film 9. The cross-sectional area of ​​the sensing particle 3 that is completely deposited and sealed at the orifice is equal to the area of ​​the axial cross-section of the internal circular channel 24 of the nanotube. The first part 31 has a higher contact area with the conductive film 9, so that the change in electrical properties of the sensing reaction occurring at the first part 31 can be more easily conducted to the second electrode 8 through the conductive film 9, so that the sensor has higher sensing sensitivity.

[0058] Furthermore, since the first part 31 is closer to the heating layer 5 and has a closed structure, it has a higher heating rate than the second part 32 and can reach the sensing temperature faster. Also, the bottom of the first part 31 is in direct contact with the conductive film 9 of the second electrode 8. When a sensing reaction occurs, the change in electrical properties can be directly conducted from the bottom of the first part 31 to the second electrode 8. This means that before the sensor as a whole is heated to the sensing temperature, the first part 31 has the ability to reach the sensing temperature faster than the second part 32 or the entire sensor and to quickly conduct the change in electrical properties when a sensing reaction occurs. This makes the sensor suitable for intermittent detection environments.

[0059] In the second state, the nanotube is connected at both ends, and sensing particles 3 for generating a sensing response are deposited on the inner wall and the connection platform at the nanotube opening. Because the nanotube is connected at both ends, the gas molecules inside have high mobility and can more easily contact the sensing particles 3 on the inner wall of the nanotube, giving the sensor high-sensitivity detection capability. At this time, changes in the electrical properties of the nanotube are conducted to the first electrode 1 or the second electrode 2 via the connection platform at both ends of the nanotube.

[0060] In the third state, the nanotube is located near the second electrode 8. Due to the thickness of the second electrode 8, the nanotube does not directly contact the insulating layer 4, and it is not covered by the second electrode 8. However, the end of the nanotube near the first electrode 1 is covered by the first electrode 1. In this third state, the nanotube is closed near the first electrode 1 and open near the second electrode 2. The deposition method of the sensing particles on the nanotube is the same as in the second state. In this case, changes in the electrical properties of the nanotube can be conducted through direct contact between one end and the first electrode 1, and through connection between the other end and the second electrode 8 via the connection platform at the nanotube opening.

[0061] In the first, second, and third states, the nanotubes are arranged with at least one port connected due to the non-overlapping vertical arrangement of the first electrode 1 and the second electrode 8. This allows any nanopore on the dual-channel porous substrate to accommodate the gas to be detected for detection. Furthermore, the nanotube in the first state has a higher sensing area and a faster sensing response in the first part 31, resulting in higher detection sensitivity and a faster sensing response speed for the sensor.

[0062] It should be noted that the specific embodiments described above are exemplary, and those skilled in the art can devise various solutions inspired by the disclosure of this invention. These solutions all fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification and its accompanying drawings are illustrative and not intended to limit the scope of the claims. The scope of protection of this invention is defined by the claims and their equivalents.

Claims

1. A semiconductor gas sensor based on a double-porous substrate, comprising: a first electrode (1) for conducting electrical changes during a sensing reaction in an energized state; a second electrode (8) for forming a current path with the first electrode (1); a sensing layer (2) composed of a double-porous substrate with a surface deposited with a gas-sensitive material for detecting a gas, the double-porous substrate being formed by a plurality of nanotube arrays, characterized in that the first electrode (1) and the second electrode (8) are staggered on both sides of the sensing layer (2) in a third direction in a manner of crossing without superimposition, so that at least one opening of the nanotube of the sensing layer (2) can be in communication with the outside; the first electrode (1) and the second electrode (8) are provided with a conductive film (9) at least at the contact part of the connection with the sensing layer (2), the conductive film (9) can form a potential barrier with a reduced width at the connection compared to the case without the conductive film (9), which is easy for electron tunneling, so that the change in electrical properties conducted through the first electrode (1) and the second electrode (8) comes from the change in electrical properties of the sensing layer (2) when a sensing reaction occurs.

2. The semiconductor gas sensor according to claim 1, characterized by The conductive film (9) provided on the surface of the first electrode (1) and / or the second electrode (8) makes the first electrode (1) and / or the second electrode (8) have a higher width of interdigital terminal (13), so that the nanotube covered by the interdigital terminal (13) has an increased proportion of nanopores of the double-porous substrate to form a nanotube in a first state, wherein the opening of the nanotube in the first state near one end of the second electrode (8) is covered by the second electrode (8), so that the sensing particles (3) adhere to the nanotube and form a U-shaped layer structure.

3. The semiconductor gas sensor according to claim 2, characterized by The sensing particles (3) in the nanotube in the first state include at least a first part (31) and a second part (32) with different deposition thicknesses, wherein the part of the first part (31) near the second electrode (8) in the upright direction is mechanically and electrically coupled to the second electrode (8).

4. The semiconductor gas sensor according to claim 2, characterized by The nanotube in the second state of the double-porous substrate has both ends in communication to allow the sensing particles (3) deposited on the inner wall of the nanotube to be able to contact the gas molecules in the tube and have a sensing reaction with the gas molecules to be detected.

5. The semiconductor gas sensor according to claim 1, characterized by The semiconductor gas sensor further comprises a heating layer (5) and a separation layer (4), the separation layer (4) is arranged between the heating layer (5) and the sensing layer (2) to allow the heat generated by the heating layer (5) to be transmitted to the functional area (21), and the separation layer (4) is provided with a heating electrode hole (42) for leading out the heating layer (5) to an external heating power supply.

6. The semiconductor gas sensor according to claim 5, wherein The sensing layer (2) comprises a functional area (21) and a non-functional area (22), wherein the functional area (21) and the non-functional area (22) are connected by a suspension (23), and the shape of the functional area (21) matches the interdigital area (12).

7. The semiconductor gas sensor according to claim 6, characterized by The heating layer (5) at least comprises a heat resistance wire (53) which is serpentine to match the functional area (21) in shape to provide heat holding for the functional area (21).

8. The semiconductor gas sensor according to claim 7, characterized by The heating layer (5) further comprises a heating electrode (51) which is electrically connected with the heat resistance wire (53) based on a connecting wire (52), and is connected with an external power supply based on a heating electrode hole (42) embedded on the isolation layer (4).

9. The semiconductor gas sensor according to claim 8, characterized by The semiconductor gas sensor further comprises a support layer (6) which is arranged at the bottom of the heating layer (5), and the support layer (6) is provided with a bearing area which prevents heat generated by the heat resistance wire (53) from dissipating from the side of the support layer (6) to allow the heat generated by the heating layer (5) to be kept in the sensing layer (2).

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