Nanometer structured gas sensor array and device comprising the same

Abstract

A gas sensor array and a device including the gas sensor array are provided. The gas sensor array includes: an electrically insulating three-dimensional porous template including a plurality of first pores and a plurality of second pores; a plurality of electrically conductive first metal-modified metal oxide films each formed within a corresponding first pore and including a first metal oxide film and first metal-modified particles, a first inner surface of the first metal oxide film attached to an inner wall of the corresponding first pore, the first outer surface modified with the first metal-modified particles; and a plurality of electrically conductive second metal-modified metal oxide films each formed within a corresponding second pore and including a second metal oxide film and second metal-modified particles, a second inner surface of the second metal oxide film attached to an inner wall of the corresponding second pore, the second outer surface modified with the second metal-modified particles. The first metal-modified particles and the second metal-modified particles are made of different metals.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 995,165, filed January 16, 2020, which is incorporated herein by reference in its entirety. Technical Field

[0003] This disclosure generally relates to nanostructured gas sensor arrays and devices including such gas sensor arrays for performing gas detection and concentration level identification. Background Technology

[0004] In connecting things to the world, sensing takes precedence. With the immense opportunities presented by the Internet of Things (IoT) and even future 5G networks permeating every aspect of buildings, homes, and cities, the need for massive data collection is driving the increasing prevalence of smaller, smarter, lower-power, and more integrated sensors. Smart gas sensors, capable of sensing the surrounding environment (including detecting chemical analytes, exhaled gases, and flammable or explosive gases for public and home safety purposes), detecting gas leaks, conducting environmental monitoring, and diagnosing diseases, play a crucial role in some of the most important technologies in our daily lives. Particularly for indoor air quality monitoring and gas leak detection, gas sensors need to be spatially distributed throughout houses or buildings to continuously monitor and identify complex environments over long periods, protecting humans from fire hazards and explosive gas leaks (such as H2 and NO2) and parts-per-billion (ppb) levels of chemical analytes (such as formaldehyde and toluene) released from home renovations.

[0005] Since a heater must be used, most gas sensor devices have poor selectivity and high power consumption, which not only reduces stability and service life, but also hinders the integration and miniaturization of a new generation of portable wireless IoT devices. Moreover, the device system is usually powered by a battery, which needs to be replaced or charged regularly due to its limited life and limited energy density and capacity, which sets a great obstacle to the implementation of a sensor network deployment requiring hundreds or thousands of gas sensors in smart home and building applications. Therefore, it is highly desirable to develop a self-powered gas sensor system that can successfully implement continuous and high-precision home / building indoor air quality monitoring to ensure health and safety. The self-powered system using solar, mechanical vibration, bioenergy, wind field, and thermal energy power sources has proven to be an effective method for self-powering gas sensor nodes with unlimited life. For smart home and / or building applications, solar cells can fully utilize light sources and can convert light waves directly into electrical energy through the photovoltaic effect, which is considered the most ideal power source to drive sensor devices. Indoor lighting energy is not affected by region, weather, and sunshine time, and is expected to become an indoor power source that overcomes the limitations of traditional batteries. Indoor light sources can produce a power density of about 100 μW cm -2 horizontal, which can generate enough power to operate the sensor device, however, an indoor light-driven self-powered gas sensor array system for smart home and building applications has not been previously reported, mainly due to challenges in the manufacture of ultra-low power gas sensor devices and system integration of functional units.

[0006] Therefore, there is a need in the art for a gas sensor device and system with ultra-low power consumption. SUMMARY

[0007] Provided herein is a nanostructured gas sensor array, particularly a gas sensor array based on a 3D nanostructured SnO2 thin film and an apparatus including the same, for performing gas recognition and concentration detection.

[0008] One aspect of the present disclosure is to provide a gas sensor array including a gas sensing substrate. The gas sensing substrate includes: a three-dimensional (3D) porous template made of an electrically insulating material and including a plurality of first pores penetrating through the three-dimensional porous template and a plurality of second pores penetrating through the three-dimensional porous template; a plurality of first metal-modified metal oxide films, each first metal-modified metal oxide film being electrically conductive, formed within a corresponding first pore and including a first metal oxide film and first metal-modified particles, the first metal oxide film having a first inner surface attached on an inner wall of the respective first pore and a first outer surface on which the first metal-modified particles are modified; and a plurality of second metal-modified metal oxide films, each second metal-modified metal oxide film being electrically conductive, formed within a corresponding second pore and including a second metal oxide film and second metal-modified particles, the second metal oxide film having a second inner surface attached on an inner wall of the respective second pore and a second outer surface on which the second metal-modified particles are modified. The first metal-modified particles and the second metal-modified particles are made of different metals, such that each first metal-modified metal oxide film and each second metal-modified metal oxide film provide different resistances in response to a same concentration of a gas, such that a first gas sensor formed by the respective first metal-modified metal oxide film and a second gas sensor formed by the respective second metal-modified metal oxide film provide different sensitivities in response to the concentration of the gas.

[0009] In certain embodiments, the 3D porous template further comprises a plurality of third pores extending through the three-dimensional porous template and a plurality of fourth pores extending through the three-dimensional porous template. The gas sensing substrate further comprises a plurality of third metal-modified metal oxide films, each third metal-modified metal oxide film being electrically conductive, formed within a corresponding third pore and comprising a third metal oxide film and third metal-modified particles, the third metal oxide film having a third inner surface attached to an inner wall of the respective third pore and a third outer surface decorated with the third metal-modified particles; and a plurality of fourth metal-modified metal oxide films, each fourth metal-modified metal oxide film being electrically conductive, formed within a corresponding fourth pore and comprising a fourth metal oxide film and fourth metal-modified particles, the fourth metal oxide film having a fourth inner surface attached to an inner wall of the respective fourth pore and a fourth outer surface decorated with the fourth metal-modified particles. The first metal-modified particles, the second metal-modified particles, the third metal-modified particles, and the fourth metal-modified particles are made of different metals, such that each first metal-modified metal oxide film, each second metal-modified metal oxide film, each third metal-modified metal oxide film, and each fourth metal-modified metal oxide film provides a different electrical resistance in response to a same concentration of a gas, such that the first gas sensor, the second gas sensor, a third gas sensor formed by the respective third metal-modified metal oxide film, and a fourth gas sensor formed by the respective fourth metal-modified metal oxide film provide different sensitivities in response to the concentration of the gas.

[0010] In certain embodiments, the first metal-modified particles, the second metal-modified particles, the third metal-modified particles, and the fourth metal-modified particles are made of a metal selected from platinum (Pt), silver (Ag), palladium (Pd), gold (Au), nickel (Ni), copper (Cu), iridium (Ir), and ruthenium (Ru).

[0011] In certain embodiments, each of the first metal-modified particles, the second metal-modified particles, the third metal-modified particles, and the fourth metal-modified particles has a diameter between 1 nm and 50 nm.

[0012] In certain embodiments, the first metal oxide film, the second metal oxide film, the third metal oxide film, and the fourth metal oxide film are made of a metal oxide selected from tin dioxide (Sn02), titanium dioxide (Ti02), zinc oxide (ZnO), nickel (II) oxide (NiO), and iron (III) oxide (Fe203), and each of the first metal oxide film, the second metal oxide film, the third metal oxide film, and the fourth metal oxide film has a thickness between 1 nm and 100 nm.

[0013] In certain embodiments, the first metal oxide film and the second metal oxide film are made of the same metal oxide.

[0014] In certain embodiments, the 3D porous template has a honeycomb-like structure and a thickness between 100 nm and 100 pm. The electrically insulating material is aluminum oxide (AI2O3), silicon dioxide (SiO2), or titanium dioxide (TiO2). The first plurality of pores extends substantially parallel to each other. The second plurality of pores extends substantially parallel to each other, and each of the first plurality of pores and the second plurality of pores has a pore diameter between 100 nm and 1 pm.

[0015] In certain embodiments, the first plurality of pores is located in a first region of the 3D porous template; the second plurality of pores is located in a second region of the 3D porous template, the first region and the second region do not overlap.

[0016] In certain embodiments, the gas sensor array further comprises: one or more first top electrodes and one or more first bottom electrodes, each first top electrode contacting a respective first metal-modified metal oxide film at a top surface of the three-dimensional porous template, each first bottom electrode contacting a respective first metal-modified metal oxide film at a bottom surface of the three-dimensional porous template, thereby forming one or more first gas sensors; and one or more second top electrodes and one or more second bottom electrodes, each second top electrode contacting a respective second metal-modified metal oxide film at the top surface of the three-dimensional porous template, each second bottom electrode contacting a respective second metal-modified metal oxide film at the bottom surface of the three-dimensional porous template, thereby forming one or more second gas sensors.

[0017] Another aspect of the present disclosure is to provide a method of manufacturing a gas sensor array, comprising: providing a three-dimensional porous template made of an electrically insulating material and comprising a plurality of first holes and a plurality of second holes; forming a first metal-modified metal oxide film on an inner surface of the first holes, the first metal-modified metal oxide film being electrically conductive and comprising a first metal oxide film and first metal-modified particles, the first metal oxide film having a first inner surface attached to an inner wall of the first holes and a first outer surface modified with the first metal-modified particles; and forming a second metal-modified metal oxide film on an inner surface of the second holes, the second metal-modified metal oxide film being electrically conductive and comprising a second metal oxide film and second metal-modified particles, the second metal oxide film having a second inner surface attached to an inner wall of the second holes and a second outer surface modified with the second metal-modified particles. The first metal-modified particles and the second metal-modified particles are made of different metals.

[0018] In certain embodiments, the first metal oxide film is formed on the inner wall of the first holes by atomic layer deposition, and the first metal-modified particles are modified on the outer surface of the first metal oxide film by a vacuum pump suction filtration method. The second metal oxide film is formed on the inner wall of the second holes by atomic layer deposition, and the second metal-modified particles are modified on the outer surface of the first metal oxide film by a vacuum pump suction filtration method.

[0019] Another aspect of the present disclosure is to provide a gas sensor array, comprising: a gas sensing substrate. The gas sensing substrate comprises: a first three-dimensional porous template made of a first electrically insulating material and comprising a plurality of first pores passing through the three-dimensional porous template; a second three-dimensional porous template made of a second electrically insulating material and comprising a plurality of second pores passing through the three-dimensional porous template; a plurality of first metal-modified metal oxide films, each first metal-modified metal oxide film being electrically conductive, formed within a corresponding first pore and comprising a first metal oxide film and first metal-modified particles, the first metal oxide film having a first inner surface attached on an inner wall of the respective first pore and a first outer surface decorated with the first metal-modified particles; and a plurality of second metal-modified metal oxide films, each second metal-modified metal oxide film being electrically conductive, formed within a corresponding second pore and comprising a second metal oxide film and second metal-modified particles, the second metal oxide film having a second inner surface attached on an inner wall of the respective second pore and a second outer surface decorated with the second metal-modified particles. The first metal-modified particles and the second metal-modified particles are made of different metals, such that each first metal-modified metal oxide film and each second metal-modified metal oxide film provides different electrical resistance in response to a same concentration of a gas, such that a first gas sensor formed by the respective first metal-modified metal oxide film and a second gas sensor formed by the respective second metal-modified metal oxide film provide different sensitivities in response to the concentration of the gas.

[0020] Another aspect of the present disclosure is to provide a gas detection device, comprising: a transmission unit; a microprogrammed controller unit (MCU); a power management unit; and a gas sensor unit comprising a gas sensor array according to the present disclosure and a sensor printed circuit board. The gas sensor array is packaged on the sensor PCB. The gas sensor array comprises a plurality of electrodes and a common plane for connection to the sensor PCB.

[0021] In certain embodiments, the plurality of electrodes are located on a top surface of the three-dimensional porous template and contact the respective first metal-modified metal oxide film or second metal-modified metal oxide film at the top surface of the three-dimensional porous template. The common plane is located on a bottom surface of the three-dimensional porous template.

[0022] In certain embodiments, the MCU is configured to identify and quantitatively detect a gas species passing through the gas sensor unit by performing a pattern recognition technique based on a sensed voltage across each electrode of the plurality of electrodes.

[0023] In certain embodiments, the pattern recognition technique comprises a principal component analysis, a support vector machine algorithm, or an artificial neural network.

[0024] In certain embodiments, the gas detection device includes a multi-channel processor configured to sequentially receive the sensed voltage across each of the plurality of electrodes and transmit the sensed voltage to the MCU.

[0025] In certain embodiments, the MCU includes an analog-to-digital converter for converting the sensed voltage to a digital value. The transmission unit includes a Bluetooth Low Energy module for communicatively sending the digital value to one or more receiving ends.

[0026] In certain embodiments, the power management unit includes a solar panel positioned on an outer surface of the gas detection device and used to collect light energy in the surrounding environment, the collected light energy used to power the gas detection device and continuously charge a rechargeable battery.

[0027] The above summary is provided to introduce some concepts in a simplified form that will be further described below in the detailed description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used in determining the scope of the claimed subject matter. Other aspects and advantages of the present application will become apparent from the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0028] The drawings contain further illustrations and explanations of the above and other aspects, advantages and features of the present disclosure. It should be understood that these drawings only depict certain embodiments of the present disclosure and are not intended to limit the scope thereof. It should also be understood that the drawings are shown for simplicity and clarity and are not necessarily drawn to scale. The present disclosure will now be described and explained in detail with reference to the drawings, in which:

[0029] FIG. 1A is a schematic illustration of a cross-sectional view of a first metal-modified metal oxide film of

[0030] FIG. 1B is a schematic illustration of a cross-sectional view of a second metal-modified metal oxide film of FIG. 1A

[0031] FIG. 1C is a schematic illustration of a cross-sectional view of a second metal-modified metal oxide film of FIG. 1A

[0032] FIG. 2A is a schematic illustration of a process for fabricating a gas sensing substrate based on 3D porous anodized aluminum oxide (AAO) templates by atomic layer deposition and vacuum pump suction filtration for metal modification, according to certain embodiments of the present disclosure;

[0033] FIG. 2B ​​is a flow chart of a method for fabricating a gas sensing substrate based on a 3D porous AAO template according to certain embodiments of the present disclosure;

[0034] FIG. 3A is a scanning electron microscope (SEM) image of a top view of a porous AAO template according to certain embodiments of the present disclosure;

[0035] FIG. 3B is FIG. 3A a SEM image of a cross-sectional view of a porous AAO template;

[0036] FIG. 3C is a SEM image of a top view of a Sn02 thin film according to certain embodiments of the present disclosure;

[0037] FIG. 3D is FIG. 3A a SEM image of a cross-sectional view of a Sn02 thin film;

[0038] FIG. 3E is a SEM image of a cross-sectional view of a Sn02 thin film FIG. 3A shown at a higher magnification;

[0039] FIG. 4A is a SEM image of a cross-sectional view of a 5 nm thick Sn02 thin film according to certain embodiments of the present disclosure;

[0040] FIG. 4B is a SEM image of a cross-sectional view of a 10 nm thick Sn02 thin film according to certain embodiments of the present disclosure;

[0041] FIG. 4C is a SEM image of a cross-sectional view of a 15 nm thick Sn02 thin film according to certain embodiments of the present disclosure;

[0042] FIG. 5A is a high resolution transmission electron microscope (HRTEM) image of a Pt-modified Sn02 thin film in an AAO template according to certain embodiments of the present disclosure;

[0043] FIG. 5B is a HRTEM image of a Pt-modified Sn02 thin film FIG. 5A shown at a higher magnification;

[0044] FIG. 5C is an elemental map of Al in conjunction with the Pt-modified Sn02 thin film FIG. 5A ;

[0045] FIG. 5D is an elemental map of Sn in conjunction with the Pt-modified Sn02 thin film FIG. 5A ;

[0046] FIG. 5E Is with FIG. 5A Elemental mapping of Pt-modified SnO2 thin films with Pt bound to them;

[0047] FIG. 6A The sensitivity of Pt-modified SnO2 films with thicknesses of 5 nm, 10 nm, 15 nm, and 20 nm under hydrogen atmosphere is shown as a function of time according to certain embodiments of the present disclosure.

[0048] FIG. 6B The resistance of Pt-modified SnO2 thin films under different concentrations of hydrogen according to certain embodiments of this disclosure;

[0049] FIG. 6C The resistance of Pd-modified SnO2 thin films under different concentrations of hydrogen according to certain embodiments of this disclosure;

[0050] FIG. 6D The resistance of Au-modified SnO2 thin films under different concentrations of hydrogen gas according to certain embodiments of this disclosure;

[0051] FIG. 6E The resistance of Ag-modified SnO2 thin films under different concentrations of hydrogen gas according to certain embodiments of this disclosure;

[0052] FIG. 6F It is under different concentrations of hydrogen gas, FIG. 6B to FIG. 6E The sensitivity of Pt-modified SnO2 films, Pd-modified SnO2 films, Au-modified SnO2 films and Ag-modified SnO2 films;

[0053] FIG. 7A The response curves of Pt-modified SnO2 films, Pd-modified SnO2 films, Au-modified SnO2 films and Ag-modified SnO2 films with a thickness of 15 nm under different concentrations of formaldehyde according to certain embodiments of the present disclosure are shown.

[0054] FIG. 7B It was under different concentrations of toluene. FIG. 7A Response curves of Pt-modified SnO2 films, Pd-modified SnO2 films, Au-modified SnO2 films and Ag-modified SnO2 films.

[0055] FIG. 7C It is under different concentrations of NO2, FIG. 7A Response curves of Pt-modified SnO2 films, Pd-modified SnO2 films, Au-modified SnO2 films and Ag-modified SnO2 films;

[0056] FIG. 7D This is under different concentrations of formaldehyde. FIG. 7AThe sensitivity of Pt-modified SnO2 films, Pd-modified SnO2 films, Au-modified SnO2 films and Ag-modified SnO2 films;

[0057] FIG. 7E It was under different concentrations of toluene. FIG. 7A The sensitivity of Pt-modified SnO2 films, Pd-modified SnO2 films, Au-modified SnO2 films and Ag-modified SnO2 films;

[0058] FIG. 7F It is under different concentrations of NO2, FIG. 8 The sensitivity of Pt-modified SnO2 films, Pd-modified SnO2 films, Au-modified SnO2 films and Ag-modified SnO2 films;

[0059] FIG. 9A Two-component principal component analysis of Pt-modified SnO2 films, Pd-modified SnO2 films, Au-modified SnO2 films and Ag-modified SnO2 films for hydrogen, formaldehyde, toluene and NO2, according to certain embodiments of this disclosure.

[0060] FIG. 9B This is a top view of an electrode mask according to certain embodiments of the present disclosure;

[0061] FIG. 10 This is a bottom view of an electrode mask according to certain embodiments of the present disclosure;

[0062] FIG. 11A This is an exploded perspective view of a gas sensor unit according to certain embodiments of the present disclosure;

[0063] FIG. 11B These are images of a main PCB for connecting a gas sensor unit according to certain embodiments of this disclosure;

[0064] FIG. 11A It is connected to FIG. 12 Image of the main PCB of the gas sensor unit;

[0065] FIG. 13 This is a schematic diagram of a gas detection device according to certain embodiments of the present disclosure;

[0066] FIG. 12 It shows FIG. 14 A simplified system diagram showing the connection of gas detection equipment; and

[0067] FIG. 12 Is using FIG. 1A An exemplary smart home configuration of a gas detection device. Detailed Implementation

[0068] The present disclosure relates generally to a gas sensor array. More specifically, but not exclusively, the present disclosure provides a gas sensor array based on a 3D nanostructured Sn02 thin film, a method of manufacturing the gas sensor array, and a device including the gas sensor array for performing gas identification and concentration detection.

[0069] The following detailed description is merely exemplary in nature and is not intended to limit the disclosure or the application thereof. The detailed description conveys the

[0070] The present application, or any portion thereof, can be implemented by hardware, software, firmware, middleware, microcode, hardware description language or any combination thereof. When implemented in software, firmware, middleware or microcode, the program code or code segments to perform the necessary tasks can be stored in a machine readable medium such as a non-transitory storage medium. A processor(s) can perform the required tasks. Code segments can represent processes, functions, subprograms, programs, routines, subroutines, modules, software packages, classes, or any combination thereof. A code segment can be coupled to another code segment or hardware circuit by the passage of information, data, arguments, parameters or memory contents, by

[0071] Unless otherwise indicated, the term "cloud" is interpreted and explained in the sense of cloud computing or synonymously as distributed computing over a network. "Server" as used herein is explained in the sense of computing. The database(s) can be, for example, circuitry, hard disks and / or other solid state disks for storing data. Typically, a server is equipped with processor(s) for executing program instructions and / or memory(ies) for storing data. The server can be a standalone computing server or a distributed server in the cloud.

[0072] The term "Internet of Things (IoT) device" is used to refer to any device that has an addressable interface (e.g., an Internet Protocol (IP) address, a Bluetooth identifier (ID), a near field communication (NFC) ID, etc.) and can send information to one or more other devices through a wired or wireless connection. An IoT device can have an active communication interface, such as a modem, a transceiver, etc. If a sensor device does not have Internet connectivity, the device can be connected to a communication device, a cell phone, a desktop computer, a laptop computer, or a tablet computer, etc. to form a connected system, such that the connected system can be an IoT device. An IoT device can be controlled or monitored by a central processing unit (CPU), a microprocessor, an ASIC, etc. and configured to connect to an IoT network or the Internet.

[0073] Benefits, advantages, solutions to problems, and any one or more elements of any of the implementations presented in this disclosure can be apparent, without being expressly discussed in priority to other elements. The present disclosure is only defined by the appended claims, which include all equivalents as permitted by the applicable law.

[0074] Terms such as "first," "second," and the like can be used herein to describe various elements, components, regions, parts, and the like, and are not intended to be limiting.

[0075] When introducing elements of the present disclosure or the preferred embodiments thereof, the articles "a," "an," and "the" are intended to mean that there are one or more of the elements. The terms of "comprising," "having," and "including" are intended to be inclusive and mean that there can be additional elements other than the listed elements.

[0076] Certain embodiments of the present disclosure provide a wireless, self-powered, high-performance 3D nanostructured material-based gas detection device, which generally includes a power management unit, a gas sensor unit, a microprogram controller unit, and a transmission unit.

[0077] Since the gas sensor based on 3D nanostructured materials provides more surface active sites, reduces the activation energy of gas adsorption and activation, which can achieve excellent room temperature gas sensing performance with ultra-low power consumption, therefore the sensor array system thus manufactured can operate at room temperature, and the average power consumption of each sensor unit is significantly reduced to 4.3 μW, less than one thousandth of the power consumption of commercial Sn02 thin film sensors. Due to the ultra-low power consumption of the sensor device, a self-powered indoor light-collecting solar cell can collect light power to effectively drive the sensor system while charging the battery. In addition, such integrated self-powered system can be laid in any location in the house, which can realize sustainable remote monitoring and identify complex gas environments (such as H2, CO, CH4, NO2, H2S, SO2, NH3, formaldehyde, toluene, benzene, acetone, ethanol, methanol, etc.) through mobile applications using pattern recognition technology. In addition, for smart home applications, a wireless data transmission unit using Bluetooth will establish a connection between the sensor array system and the mobile phone, thus demonstrating the ability to monitor and distinguish gases in real time remotely, and even track the source of gas leakage through an array composed of multiple gas sensors.

[0078] FIG. 1B A gas sensor array 100 according to certain embodiments of the present disclosure is shown. The gas sensor array 100 includes a gas sensing substrate 110, a first top electrode 120, a first bottom electrode 121, a second top electrode 130, and a second bottom electrode 131. The gas sensing substrate 110 includes a three-dimensional (3D) porous template 140, a plurality of first metal-modified metal oxide films 150, and a plurality of second metal-modified metal oxide films 160.

[0079] The 3D porous template 140 is made of an electrically insulating material, has a top surface 141 and a bottom surface 142, and includes a plurality of first pores 170 and a plurality of second pores 180. Each first pore 170 has a first top opening 171 at the top surface 141 and a first bottom opening 172 at the bottom surface 142. Each first pore 170 penetrates through the 3D porous template 140. Each second pore 180 has a second top opening 181 at the top surface 141 and a second bottom opening 182 at the bottom surface 142. Each second pore 180 penetrates through the 3D porous template 140.

[0080] As FIG. 1CAs shown, each first metal-modified metal oxide film 150 is electrically conductive, formed within a respective first hole 170, and includes a first metal oxide film 151 and first metal-modified particles 152. The first metal oxide film 151 has a first inner surface 153 attached to an inner wall 173 of the respective first hole 170 and a first outer surface 154 modified with the first metal-modified particles 152. As shown, the first metal-modified particles 152 are attached to the first outer surface 154 of the first metal oxide film 151. FIG. 2A As shown, each second metal-modified metal oxide film 160 is electrically conductive, formed within a respective second hole 180, and includes a second metal oxide film 161 and second metal-modified particles 162. The second metal oxide film 161 has a second inner surface 163 attached to an inner wall 183 of the respective second hole 180 and a second outer surface 164 modified with the second metal-modified particles 162.

[0081] The first top electrode 120 is attached to the top surface 141 of the 3D porous template 140 and contacts the first metal-modified metal oxide film 150 at the top surface 141. The first bottom electrode 121 is attached to the bottom surface 142 of the 3D porous template 140 and contacts the first metal-modified metal oxide film 150 at the bottom surface 142, thereby forming the first gas sensor 190. The second top electrode 130 is attached to the top surface 141 of the 3D porous template 140 and contacts the second metal-modified metal oxide film 160 at the top surface 141. The second bottom electrode 131 is attached to the bottom surface 142 of the 3D porous template 140 and contacts the second metal-modified metal oxide film 160 at the bottom surface 142, thereby forming the second gas sensor 191.

[0082] The first metal-modified particles 152 and the second metal-modified particles 162 are made of different metals, such that the first metal-modified metal oxide film 150 and the second metal-modified metal oxide film 160 provide different resistances in response to the same concentration of gas, thereby causing the first gas sensor 190 and the second gas sensor 191 to have different sensitivities in response to the gas at the concentration to improve accuracy of gas identification based on pattern recognition techniques.

[0083] In certain embodiments, the first metal-modified particles are made of a first metal selected from the group consisting of platinum (Pt), silver (Ag), palladium (Pd), gold (Au), nickel (Ni), copper (Cu), iridium (Ir), and ruthenium (Ru); and the second metal-modified particles are made of a second metal selected from the group consisting of Pt, Ag, Pd, Au, Ni, Cu, Ir, and Ru.

[0084] In certain embodiments, each of the first metal-modified particles and the second metal-modified particles has a diameter between 1 nm and 50 nm.

[0085] In certain embodiments, the first metal oxide film and the second metal oxide film are made of the same metal oxide.

[0086] In certain embodiments, the first metal oxide film and the second metal oxide film are made of a metal oxide selected from the group consisting of tin dioxide (Sn02), titanium dioxide (Ti02), zinc oxide (ZnO), nickel(II) oxide (NiO), and iron(III) oxide (Fe203).

[0087] In certain embodiments, each of the first metal oxide film and the second metal oxide film has a thickness between 1 nm and 100 nm.

[0088] In certain embodiments, the 3D porous template is a 3D porous AAO template.

[0089] In certain embodiments, the electrically insulating material is aluminum(III) oxide (AI2O3), silicon dioxide (Si02), or titanium dioxide (Ti02).

[0090] In certain embodiments, the plurality of first pores are arranged substantially parallel to each other; and the plurality of second pores are arranged substantially parallel to each other.

[0091] In certain embodiments, each of the plurality of first pores and the plurality of second pores has a width between 100 nm and 1 pm.

[0092] In certain embodiments, the plurality of first pores are located in a first region of the 3D porous template; and the plurality of second pores are located in a second region of the 3D porous template.

[0093] In certain embodiments, the gas sensing substrate includes 2 to 10 types of metal-modified metal oxide films. Each type of metal-modified metal oxide film is modified by metal-modified particles made of a specific metal.

[0094] FIG. 2Bis a schematic diagram of a process for fabricating a gas sensing substrate based on 3D porous anodization of aluminum oxide (AAO) template by Sn02atomic layer deposition and vacuum pumping for metal modification according to certain embodiments of the present disclosure. A 3D porous AAO template 210 is provided. The 3D porous AAO template 210 has a top surface 211, a bottom surface 212, and a plurality of pores 213, and each pore 213 has an inner wall 214 and two openings 215a, 215b on the top surface 211 and the bottom surface 212, respectively, for allowing a gas to be determined to enter the pore 213. Then, a Sn02thin film 221 is deposited on the inner wall 214 of each pore 213 by atomic layer deposition, thereby forming a Sn02coated 3D porous AAO template 220.

[0095] The Sn02coated 3D porous AAO template 220 is equally divided into four regions 222a, 222b, 222c, and 222d. By a vacuum pump and filtration method and with a shadow mask, the Sn02thin film 221 within each pore 213 in the region 222a is modified with Pt particles 231 to form a Pt-modified Sn02thin film 232. By a similar vacuum pump and filtration method, the Sn02thin film 221 within each pore 213 in the region 222b is modified with Pd particles to form a Pd-modified Sn02thin film, the Sn02thin film 221 within each pore 213 in the region 222c is modified with Au particles to form an Au-modified Sn02thin film, and the Sn02thin film 221 within each pore 213 in the region 222d is modified with Ag particles to form an Ag-modified Sn02thin film, thereby forming a gas sensing substrate 230 having four gas sensing regions 233a, 233b, 233c, 233d. The Pt-modified gas sensing region 233a includes the Pt-modified Sn02thin film, the Pd-modified gas sensing region 233b includes the Pd-modified Sn02thin film, the Au-modified gas sensing region 233c includes the Au-modified Sn02thin film, and the Pt-modified gas sensing region 233d includes the Pt-modified Sn02thin film. Since the Pt, Pd, Au, and Ag particles adhere to the Sn02thin film, respectively, and affect the Sn02thin film differently, the Pt, Pd, Au, and Ag-modified Sn02thin films provide different resistances in response to the same concentration of a gas. Therefore, the four gas sensing regions 233a, 233b, 233c, 233d provide different sensitivities in response to a certain concentration of a gas and are responsible for detecting specific gases and identifying their concentrations.

[0096] FIG. 3Ais a flow chart of a method for fabricating a gas sensing substrate according to certain embodiments of the present disclosure. In step S21, a 3D porous AAO template having a plurality of pores is provided. In step S22, a metal oxide film is deposited on the inner wall of each pore by atomic layer deposition, thereby forming a metal oxide coated 3D AAO template. In step S23, the metal oxide film in some pores is modified with first metal modification particles by vacuum pump filtration to form a first metal modified metal oxide film within the 3D porous AAO template. In step S24, the metal oxide film in other pores is modified with second metal modification particles by vacuum pump filtration to form a second metal modified metal oxide film within the 3D porous AAO template. In step S25, optionally, step S24 is repeated to modify the metal oxide film in other pores with other metal modification particles until a gas sensing substrate is formed.

[0097] Thus, by utilizing atomic layer deposition (ALD) in conjunction with metal modification to construct 3D porous substrates, the operating temperature of gas sensor arrays can be reduced to room temperature and power consumption can be reduced. In certain embodiments, the metal modification based Sn02 thin film porous AAO template for gas sensor arrays only consumes an average power of 4.3 pW, which is less than one thousandth of the power consumption of commercial Sn02 thin film sensors.

[0098] In certain embodiments, the use of low temperature ALD (-150 °C) enables uniform deposition of thin films with controllable thickness even on complex 3D surfaces. This is therefore crucial for maintaining the consistency of the devices and for future mass production. In the ALD process, alternating pulses of two vapor precursors (TDMAS and H20) and purge gas are introduced into the reactor, resulting in thin film growth due to self-saturation reactions with accessible surface groups of the AAO template, leading to self-limited growth of monolayer Sn02 thin films. After Sn02 nanoparticle deposition is complete, four metals (Pt, Pd, Au, Ag) with an average size of 5 nm are modified using a vacuum pump filtration method with a mask.

[0099] In certain embodiments, a nanoscale Sn02 film is deposited in the 3D porous AAO template by ALD. The specific cycle of ALD includes: using tetra(dimethylamino)tin as a tin source; opening the ALD tin source valve for 100 ms, closing the pump valve, allowing the tin source to stay in the chamber for 5 s, opening the pump valve for 20 s for cleaning; closing the pump valve; allowing the precursor source to stay in the chamber for 5 s; opening the pump valve for 25 s for cleaning. By applying different numbers of specific cycles, Sn02 films of different thicknesses are obtained.

[0100] In certain embodiments, the parameters of the ALD cycle are shown in Table 1.

[0101] Table 1

[0102]

[0103] In certain embodiments, different regions of the porous AAO template coated with metal oxide films are modified with different metal nanoparticles by vacuum pump suction filtration method. By controlling the concentration and amount of metal nanoparticles in the vacuum pump suction filtration method, the amount of metal nanoparticles in the metal oxide film coated AAO template can be easily controlled.

[0104] FIG. 3B and FIG. 3C to FIG. 3D A porous AAO template 310 having a plurality of pores 311 is shown, in accordance with certain embodiments. Each pore 311 has an inner wall 312, a top opening 313, and a bottom opening 314.

[0105] FIG. 4A to FIG. 4C A Sn02film coated porous AAO template 320 is shown, in accordance with certain embodiments. The Sn02coated porous AAO template 320 includes a porous AAO template 321 and a Sn02thin film 322 formed on the inner wall 324 of the pores 323 of the porous AAO template 321.

[0106] FIG. 5A A 5 nm thick Sn02thin film 41, a 10 nm thick Sn02thin film 42, and a 15 nm thick Sn02thin film 41 are shown, respectively. To obtain a large surface-to-volume ratio and a high-performance room-temperature gas sensor, the 3D porous AAO template has a thickness of 40 pm, a pitch of 500 nm, and an average pore diameter of 400 nm to provide good support for uniform Sn02layer deposition.

[0107] FIG. 5B A Pt-modified Sn02thin film attached to the inner wall of the pores of the AAO template is shown. FIG. 5C to FIG. 5E A Pt-modified Sn02thin film is shown at a higher magnification. FIG. 6A Elemental mapping of Al, Sn, and Pt in combination with the Pt-modified Sn02thin film is shown. Pt particles are dispersed on the surface of the Sn02thin film.

[0108] FIG. 6B to FIG. 6E The sensitivity versus time of Pt-modified Sn02thin films with thicknesses of 5 nm, 10 nm, 15 nm, and 20 nm under hydrogen (H2) is shown. The 15 nm thick Pt-modified Sn02thin film shows the highest sensitivity at 2000 ppm H2.

[0109] FIG. 6B to FIG. 6EThe resistance of Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film under different concentrations of hydrogen is shown respectively. Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film show different resistance under the same concentration of hydrogen. Their resistance changes are different under different concentrations of hydrogen, which means that Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film provide different sensitivity under the same concentration of hydrogen. Based on the results obtained from FIG. 6F the sensitivity of Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film under different concentrations of hydrogen is summarized and plotted as FIG. 7A .

[0110] FIG. 7D It is shown that Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film provide different resistance under the same concentration of formaldehyde. FIG. 7B It is shown that Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film provide different sensitivity under different concentrations of formaldehyde.

[0111] FIG. 7E It is shown that Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film provide different resistance under the same concentration of toluene. FIG. 7C It is shown that Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film provide different sensitivity under different concentrations of toluene.

[0112] FIG. 7F It is shown that Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film provide different resistance under the same concentration of NO2. FIG. 8 It is shown that Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film and Ag-modified Sn02 thin film provide different sensitivity under different concentrations of NO2.

[0113] Based on the different sensitivities of 15 nm thick Pt-modified Sn02 thin films, Pd-modified Sn02 thin films, Au-modified Sn02 thin films, Ag-modified Sn02 thin films under different concentrations of hydrogen, formaldehyde, toluene, NO2, principal component analysis (PCA) is performed to effectively identify the type and concentration of the above environmental gases. As shown in FIG. 13, the recorded four-dimensional data (corresponding to the four gas sensors) is reduced to two dimensions by PCA for visually visualizing the sensitivity Euclidean distance and correlation between gas types. It shows that each gas has its own cluster area as shown by the circle, which can be clearly distinguished. Each point refers to the PCA-processed sensitivity of each metal-modified gas sensor. The points in the first circular ring refer to the measured gas as hydrogen, the points in the second circular ring refer to the measured gas as formaldehyde, the points in the third circular ring refer to the measured gas as toluene, and the points in the fourth circular ring refer to the measured gas as NO2. FIG. 9A

[0114] In certain embodiments, the sensitivities of different metal-modified metal oxide gas sensors under different gases and corresponding concentrations are predetermined and the results are stored in a memory for performing principal component analysis by a micro control unit (MCU) during actual gas detection with different sensitivities provided by different gas sensors in response to the detected gas type.

[0115] In addition to principal component analysis, in certain embodiments, other pattern recognition techniques (e.g., support vector machine algorithm, artificial neural network, etc.) can be used with the gas sensor array of the present application for gas detection.

[0116] FIG. 9B FIG. 10 ​​Designs of top electrode mask 610 and bottom electrode mask 620 for sputter deposition are shown. Top electrode mask 610 has a predetermined mask pattern comprising a plurality of first electrode patterns 611 and a plurality of connection patterns 612. Each first electrode pattern 611 is connected to a connection pattern 612. Bottom electrode mask 620 has another predetermined mask pattern comprising a plurality of second electrode patterns 622. Second electrode patterns 622 of the same row are interconnected to each other to form an electrode string 623, and all electrode strings 623 are interconnected to each other to form a bottom pattern 621. The drawing shows an embodiment of the present disclosure for depositing 4x4 electrodes. Thus, there are 16 first electrode patterns 611 arranged in four rows and four columns on top electrode mask 610, and 16 second electrode patterns 622 arranged in four rows on bottom electrode mask 620. It is obvious to those skilled in the art that the masks can be patterned for depositing other numbers of electrodes, such as 1x1, 10x10, 2x8, etc. First electrode patterns 611 and second electrode patterns 622 can have a rectangular shape, a square shape, a triangular shape, a quadrilateral shape, a diamond shape, a polygonal shape, or any suitable shape. In certain embodiments, first electrode patterns 611 and second electrode patterns 622 can have a shape of 2.0 mm x 2.5 mm rectangle.

[0117] Top electrode mask 610 and bottom electrode mask 620 are mask plates for performing deposition, such as sputter deposition, on the top surface and the bottom surface of gas sensing substrate 230. Thus, as mentioned above, gas sensor array 100 comprises one or more metal-modified gas sensing substrates 230, a plurality of electrodes, and a common plane for gas detection and concentration level identification. The deposited material can be Au or other noble metal. The thickness of the deposited gold layer can be in the range of 10 nm to 500 nm, or preferably 100 nm. As shown, a plurality of top electrodes 711 are sputtered on the top surface of metal-modified gas sensing substrate 230, and a common GND plane 712 is sputtered on the bottom surface of metal-modified gas sensing substrate 230. FIG. 11B

[0118] After deposition of Au electrodes, gas sensor array 100 is packaged on a sensor printed circuit board (PCB) 720 to obtain a gas sensor cell 700 by connecting the plurality of top electrodes 711 and the common GND plane 712 to signal channel pads 713 on sensor PCB 720 using bonding wires 714 (shown in FIG. 7B). FIG. 11B FIG. 11A ​​The sensor PCB 720 can be a dedicated PCB for a specific kind of gas sensor array 100, which includes a plurality of airflow holes 730 located below the gas sensor array 100 to allow airflow to pass through the airflow holes 730 into the gas sensor array 100 for gas (leakage) detection. The airflow holes 730 can have a circular shape, a rectangular shape, a square shape, a triangular shape, a quadrilateral shape, or any suitable shape.

[0119] The gas sensor unit 700 is further connected to FIG. 11B a main PCB 800 as shown in FIG. 8. The main PCB 800 is an integrated PCB including circuitry for a transmission unit 810, a microcontroller unit (MCU) 830, and a power management unit 840, which can perform data readout, data processing, and transmission. The gas sensor unit 700 is electrically connected to the main PCB 800 by connecting the connector pins 721 to the sockets 820. FIG. 12 The main PCB 800 connected with the gas sensor unit 700 is shown, wherein the gas sensor unit 700 is placed above the main PCB 800.

[0120] FIG. 13A schematic diagram of a gas detection device 500 according to certain embodiments of the present disclosure is described. The gas detection device 500 is an Internet of Things (IoT) device, comprising a transmission unit 810, an MCU 830, a power management unit 840, and a gas sensor unit 700. The gas sensor unit 700 is formed by encapsulating the gas sensor array 100 on a sensor PCB 720, where the gas sensor array 100 comprises a plurality of electrodes and a common plane for connection to the sensor PCB 720. The gas sensor array 100 can be divided into four regions, each region being modified with Pt, Pd, Au, and Ag respectively, to detect the presence of specific gases. According to the different sensitivities of the Pt-modified Sn02 thin film, Pd-modified Sn02 thin film, Au-modified Sn02 thin film, and Ag-modified Sn02 thin film under different concentrations of hydrogen, formaldehyde, toluene, and NO2, the MCU 830 is configured to perform principal component analysis, support vector machine algorithm, or artificial neural network to effectively identify the type and concentration of ambient gases. The four regions are Pt-modified gas sensing region 133a, Pd-modified gas sensing region 133b, Au-modified gas sensing region 133c, and Ag-modified gas sensing region 133d respectively. A power supply voltage Vs is provided to each individual top electrode 711 via a sensing resistor 833. The multi-channel processor 832 is configured to sequentially receive the sensing voltage across each top electrode 711 in the gas sensor array 100 based on a clock signal, such that the sensing voltage across the Pt-modified gas sensing region 133a, Pd-modified gas sensing region 133b, Au-modified gas sensing region 133c, and Ag-modified gas sensing region 133d can be obtained and coupled to the MCU 830. Obviously, the multi-channel processor 832 and the sensing resistor 833 can be connected between the metal-modified gas sensing substrate 230 and the common GND plane 712 without departing from the spirit and scope of the present disclosure. The resistances of the plurality of sensing resistors 833 can be different because the sensitivity of each region can be different.

[0121] MCU 830 is configured to receive signals from the multi-channel processor 832, which includes the sensed voltage at the top electrode 711 in the gas sensor array 100. Synchronized signals that are read in sequence can also be provided by the multi-channel processor 832 to the MCU 830. The MCU 830 can also calculate the sensitivity of the exposed gas, which has a change in the numerical value compared to the sensitivity of the gas analyzed in the algorithm. Thus, the MCU 830 can identify and quantify the gas species in the environment using principal component analysis to determine if the concentration level is safe. The MCU 830 can perform further data optimization on the received signals, such as indexing, noise reduction, filtering, compression, deduplication, and data encoding. In the example shown, the MCU 830 collects voltage signals from 16 gas sensors obtained from 16 channels via the multi-channel processor 832. The MCU 830 can include an analog-to-digital converter for converting the sensed voltage to a digital value. The digital value is then coupled to the Bluetooth Low Energy module 811 of the transmission unit 810 in order to communicatively send the digital value to one or more receiving ends 812. Alternatively, the transmission unit 810 can be configured to support one or more communication protocols for communicating with the receiving ends 812 selected from Bluetooth, wireless body area network (WEAN), Ethernet, internal integrated circuit (I2C) and serial (COM) communication, among other communication protocols. The receiving ends 812 can include a smart phone, a smart watch, a tablet, a personal digital assistant (PDA), a laptop, a desktop computer, other electronic devices, or a cloud database. 2 C) and serial (COM) communication, among other communication protocols. The receiving ends 812 can include a smart phone, a smart watch, a tablet, a personal digital assistant (PDA), a laptop, a desktop computer, other electronic devices, or a cloud database.

[0122] In certain embodiments, the power management unit 840 of the gas detection device 500 includes a solar panel 842 and a rechargeable battery 841. The solar panel 842 can include a 40 mm x 110 mm solar cell for harvesting indoor light energy. The harvested energy is used to power the gas detection device 500 and also continuously charges the rechargeable battery 841. In certain embodiments, the solar panel 842 can be a built-in module placed on one or more surfaces of the housing of the gas detection device 500 or a separate module connected to the gas detection device 500. Thus, the gas detection device 500 can be installed anywhere in the indoor area with light. The rechargeable battery 841 of the power management unit 840 can be a lithium-ion battery, a lead-acid battery, a nickel-cadmium battery, or a nickel-metal hydride battery. Preferably, the rechargeable battery 841 is a lithium-ion battery with a capacity of at least 800 mAh. Advantageously, the gas sensor array 100 only consumes an average power of 4.3 μW, which is less than a thousandth of the power consumption of a commercial Sn02 thin film sensor. Thus, the rechargeable battery 841 is able to work efficiently with ultra-low power consumption to enable sustainability monitoring using the solar panel 842. Moreover, the rechargeable battery 841 can compensate for dark conditions and intermittent light at night, which provides a stable power source for the gas detection device 500 to work without external power. In certain embodiments, the power management unit 840 can include an input power socket arranged to receive a power source for charging the rechargeable battery 841 and powering the gas detection device 500.

[0123] FIG. 14 is a simplified system diagram showing the connection of the gas detection device 500 according to certain embodiments of the present disclosure. Multiple gas detection devices 500 can be connected together to form a mesh network 530 so that the sensed data can be exchanged. Each gas detection device 500 operates as an IoT device, which can be communicatively connected to a cloud database 510 at a designated server through the Bluetooth Low Energy module 811 or using other communication protocols. It should also be understood that the data communication to the cloud database 510 can be a direct connection or indirectly through a mobile phone or other computer device.

[0124] ​is an exemplary smart home configuration using gas detection devices 500 according to certain embodiments of the present disclosure. Each gas detection device 500 is a self-powered sensing device with a solar panel 842 located on the outer surface of the gas detection device 500 for harvesting indoor light energy. As shown in this example, the gas detection devices 500 are deployed in various locations in the smart home, such as the living room, kitchen, bedroom, and bathroom. To improve detection of any gas leak in the kitchen, four gas detection devices 500 are installed. Preferably, at least one gas detection device 500 is installed within a 10 square meter area to ensure good coverage. Each gas detection device 500 is configured to capture signals and identify complex gas environments (e.g., H2, NO2, formaldehyde, and toluene).

[0125] The installation of multiple gas detection devices 500 in a smart home can extend the indoor detection range and enable tracking of the source of the pollutant. By continuously monitoring the measurement data, predictive analysis and trend analysis can also be performed to minimize the risk of false alarms. The captured signals are sent to the cloud database 510 at a designated server via the transmission unit 810. The transmission unit 810, preferably a Bluetooth Low Energy module 811, is configured to establish a communication connection between the gas detection device 500 and a mobile phone for timely remote monitoring and differentiation of gases, mapping of geographical distribution, and tracking of gas leak sources in the smart home configuration.

[0126] Since the MCU 830 of the gas detection device 500 can identify the gas species and the corresponding concentration level, the MCU 830 can determine whether the concentration level is safe by matching and threshold comparison. In certain embodiments, the gas detection device 500 can include an alarm system to provide an audible warning in the event of a suspected gas leak. Information about the gas species, concentration level, and voltage signal is sent to a mobile phone or the cloud database 510 via the transmission unit 810. This information can be shown in the mobile application 520 and an alert can be generated to the user to indicate a potential gas leak. The alert can also be made through a computer network or by wireless transmission to other electronic devices, and a notification is provided in the form of a pop-up message, automatically generated email, or short message service (SMS) in the mobile application 520. The mobile application 520 can also include a threshold selector for setting the threshold value and acceptable range of concentration level for each gas species, and thereby provide an alert only when the detected concentration exceeds the predetermined threshold.

[0127] The basic structure of the gas sensor array according to the present disclosure and the gas detection apparatus including the same is described herein. Obviously, the above disclosure and other features and functions or variations of alternatives thereof can be combined into many other different structures or apparatuses. Therefore, the present embodiments are considered in all aspects to be illustrative and not restrictive. The scope of the present disclosure is defined by the appended claims rather than by the foregoing description, and thus, all changes coming within the meaning and equivalency of the claims are intended to be embraced therein.

Claims

1. A gas sensor array comprising: a gas sensing substrate comprising: a three-dimensional porous template made of an electrically insulating material and comprising a plurality of first holes therethrough and a plurality of second holes therethrough; a plurality of first metal-modified metal oxide films, each first metal-modified metal oxide film being electrically conductive, formed within a corresponding first hole and comprising a first metal oxide film and first metal-modified particles, the first metal oxide film having a first inner surface attached to an inner wall of the respective first hole and a first outer surface modified with the first metal-modified particles; and a plurality of second metal-modified metal oxide films, each second metal-modified metal oxide film being electrically conductive, formed within a corresponding second hole and comprising a second metal oxide film and second metal-modified particles, the second metal oxide film having a second inner surface attached to an inner wall of the respective second hole and a second outer surface modified with the second metal-modified particles; wherein the first metal-modified particles and the second metal-modified particles are made of different metals, such that each first metal-modified metal oxide film and each second metal-modified metal oxide film provides a different electrical resistance in response to a same concentration of a gas, such that a first gas sensor formed by a respective first metal-modified metal oxide film and a second gas sensor formed by a respective second metal-modified metal oxide film provide different sensitivities in response to the concentration of the gas, wherein the first metal oxide film is made of tin dioxide (Sn02) and has a thickness of 10 nm to 20 nm.

2. The gas sensor array of claim 1, wherein: the three-dimensional porous template further comprises a plurality of third holes therethrough and a plurality of fourth holes therethrough; and the gas sensing substrate further comprises: a plurality of third metal-modified metal oxide films, each third metal-modified metal oxide film being electrically conductive, formed within a corresponding third hole and comprising a third metal oxide film and third metal-modified particles, the third metal oxide film having a third inner surface attached to an inner wall of the respective third hole and a third outer surface modified with the third metal-modified particles; and a plurality of fourth metal-modified metal oxide films, each fourth metal-modified metal oxide film being electrically conductive, formed within a corresponding fourth hole and comprising a fourth metal oxide film and fourth metal-modified particles, the fourth metal oxide film having a fourth inner surface attached to an inner wall of the respective fourth hole and a fourth outer surface modified with the fourth metal-modified particles. ​ wherein the first metal-modified particles, the second metal-modified particles, the third metal-modified particles, and the fourth metal-modified particles are made of different metals, such that each first metal-modified metal oxide film, each second metal-modified metal oxide film, each third metal-modified metal oxide film, and each fourth metal-modified metal oxide film provides a different electrical resistance in response to a same concentration of a gas, such that the first gas sensor, the second gas sensor, a third gas sensor formed by a respective third metal-modified metal oxide film, and a fourth gas sensor formed by a respective fourth metal-modified metal oxide film provide different sensitivities in response to the concentration of the gas.

3. The gas sensor array of claim 1, wherein, The first metal-modified particles are made of a first metal selected from the group consisting of platinum (Pt), silver (Ag), palladium (Pd), gold (Au), nickel (Ni), copper (Cu), iridium (Ir), and ruthenium (Ru); and the second metal-modified particles are made of a second metal selected from the group consisting of platinum (Pt), silver (Ag), palladium (Pd), gold (Au), nickel (Ni), copper (Cu), iridium (Ir), and ruthenium (Ru), the first metal being different from the second metal.

4. The gas sensor array of claim 1, wherein, Each of the first metal-modified particles and the second metal-modified particles has a diameter between 1 nm and 50 nm.

5. The gas sensor array of claim 1, wherein, The second metal oxide film is made of a metal oxide selected from the group consisting of tin dioxide (Sn02), titanium dioxide (Ti02), zinc oxide (ZnO), nickel (II) oxide (NiO), and iron (III) oxide (Fe203).

6. The gas sensor array of claim 5, wherein, The second metal oxide film has a thickness between 1 nm and 100 nm.

7. The gas sensor array of claim 5, wherein, The first metal oxide film and the second metal oxide film are made of the same metal oxide.

8. The gas sensor array of claim 1, wherein, The three-dimensional porous template has a thickness between 100 nm and 100 pm; the electrically insulating material is aluminum (III) oxide (AI203), silicon dioxide (Si02), or titanium dioxide (Ti02); the plurality of first pores extends substantially parallel to each other; the plurality of second pores extends substantially parallel to each other; and each of the plurality of first pores and the plurality of second pores has a pore diameter between 100 nm and 1 pm.

9. The gas sensor array of claim 1, wherein, The plurality of first pores is located in a first region of the three-dimensional porous template; and the plurality of second pores is located in a second region of the three-dimensional porous template, the first region being non-overlapping with the second region.

10. The gas sensor array of claim 1, further comprising: one or more first top electrodes, each first top electrode contacting a respective first metal-modified metal oxide film at a top surface of the three-dimensional porous template, and one or more first bottom electrodes, each first bottom electrode contacting a respective first metal-modified metal oxide film at a bottom surface of the three-dimensional porous template, thereby forming one or more first gas sensors; and and one or more second top electrodes, each second top electrode contacting a respective second metal-modified metal oxide film at a top surface of the three-dimensional porous template, and one or more second bottom electrodes, each second bottom electrode contacting a respective second metal-modified metal oxide film at a bottom surface of the three-dimensional porous template, thereby forming one or more second gas sensors.

11. A method of manufacturing an array of gas sensors, comprising: providing a three-dimensional porous template made of an electrically insulating material and comprising a plurality of first pores extending through the three-dimensional porous template and a plurality of second pores extending through the three-dimensional porous template; forming first metal-modified metal oxide films on inner surfaces of the first pores, the first metal-modified metal oxide films being electrically conductive and comprising a first metal oxide film and first metal-modified particles, the first metal oxide film having a first inner surface attached to an inner wall of the first pore and a first outer surface modified with the first metal-modified particles; and forming second metal-modified metal oxide films on inner surfaces of the second pores, the second metal-modified metal oxide films being electrically conductive and comprising a second metal oxide film and second metal-modified particles, the second metal oxide film having a second inner surface attached to an inner wall of the second pore and a second outer surface modified with the second metal-modified particles, wherein the first metal-modified particles and the second metal-modified particles are made of different metals, wherein the first metal oxide film is made of tin dioxide (Sn02) and has a thickness of 10 nm to 20 nm. the first metal oxide film is formed on the inner wall of the first pore by atomic layer deposition, and the first metal-modified particles are modified on the outer surface of the first metal oxide film by a vacuum pump suction filtration method; 12. The manufacturing method of claim 11, wherein, the second metal oxide film is formed on the inner wall of the second pore by atomic layer deposition, and the second metal-modified particles are modified on the outer surface of the first metal oxide film by a vacuum pump suction filtration method.

13. An array of gas sensors, comprising: a gas sensing substrate comprising: a first three-dimensional porous template made of a first electrically insulating material and comprising a plurality of first pores extending through the three-dimensional porous template; a second three-dimensional porous template made of a second electrically insulating material and comprising a plurality of second pores extending through the three-dimensional porous template; a plurality of first metal-modified metal oxide films, each first metal-modified metal oxide film being electrically conductive, formed within a corresponding first pore and comprising a first metal oxide film and first metal-modified particles, the first metal oxide film having a first inner surface attached to an inner wall of the respective first pore and a first outer surface modified with the first metal-modified particles; and a plurality of second metal-modified metal oxide films, each second metal-modified metal oxide film being electrically conductive, formed within a corresponding second pore and comprising a second metal oxide film and second metal-modified particles, the second metal oxide film having a second inner surface attached to an inner wall of the respective second pore and a second outer surface modified with the second metal-modified particles. a plurality of second metal-modified metal oxide films, each second metal-modified metal oxide film being electrically conductive, formed within a corresponding second hole and comprising a second metal oxide film and second metal-modified particles, the second metal oxide film having a second inner surface attached to an inner wall of the respective second hole and a second outer surface modified with the second metal-modified particles; wherein the first metal-modified particles and the second metal-modified particles are made of different metals, such that each first metal-modified metal oxide film and each second metal-modified metal oxide film provides a different electrical resistance in response to a same concentration of a gas, such that a first gas sensor formed by the respective first metal-modified metal oxide film and a second gas sensor formed by the respective second metal-modified metal oxide film provide different sensitivities in response to the concentration of the gas, wherein the first metal oxide film is made of tin dioxide (Sn02) and has a thickness of 10 nm to 20 nm.

14. A gas detection device, comprising: a transmission unit; a microcontroller unit; a power management unit; and a gas sensor unit comprising the gas sensor array of claim 1 and a sensor printed circuit board, wherein the gas sensor array is packaged in the sensor printed circuit board, the gas sensor array comprising a plurality of electrodes and a common plane for connection to the sensor printed circuit board.

15. The gas detection device of claim 14, wherein: the plurality of electrodes are located on a top surface of the three-dimensional porous template and contact the respective first metal-modified metal oxide film or second metal-modified metal oxide film at the top surface of the three-dimensional porous template; and the common plane is located on a bottom surface of the three-dimensional porous template. the microcontroller unit is configured to identify and quantitatively detect a gas species passing through the gas sensor unit by performing a pattern recognition technique based on a sensed voltage across each of the plurality of electrodes.

16. The gas detection device of claim 15, wherein, 17. The gas detection device of claim 14, further comprising a multi-channel processor configured to sequentially receive the sensed voltage across each of the plurality of electrodes and communicate the sensed voltage to the microcontroller unit. the microcontroller unit comprises an analog-to-digital converter for converting the sensed voltage to a digital value, the transmission unit comprises a Bluetooth Low Energy module for communicatively sending the digital value to one or more receiving ends.

18. The gas detection device of claim 17, wherein, the power management unit comprises a solar panel and a rechargeable battery, the solar panel being located on an outer surface of the gas detection device and for collecting light energy in the surrounding environment, the collected light energy being used to power the gas detection device and continuously charge the rechargeable battery.

19. The gas detection device of claim 14, wherein, 20. A mesh network for a smart home configuration having a plurality of the gas detection device of claim 14, wherein: ​ Each gas detection device is communicatively connected to a cloud database at a designated server through the transmission unit; and The plurality of gas detection devices are deployed at various locations in the smart home for detecting gases in the surrounding environment with an extended indoor detection range.

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