A surface acoustic wave gas sensor using a gas sensitive thin film heating

Abstract

This invention discloses a surface acoustic wave (SAW) gas sensor heated by a gas-sensitive thin film. The SAW gas sensor includes an electrical pin (1), a metal base (2), electrical leads (3), a SAW device (4), a protective film (5), and a gas-sensitive film (6). The gas-sensitive film (6) includes a serpentine gas-sensitive film and a block gas-sensitive film. The serpentine gas-sensitive film has the same shape as the interdigital transducer in the SAW device (4), and the block gas-sensitive film has the same shape as the acoustic propagation path between the interdigital transducer in the SAW device (4). The serpentine gas-sensitive film and the block gas-sensitive film are connected to the electrical pin (1) in parallel or series via the electrical leads (3). This invention can effectively enhance the adsorption characteristics of the gas-sensitive film, adjust and control the device temperature and surface temperature distribution, thereby improving the response speed, sensitivity, and stability of the SAW gas sensor.

Description

Technical Field

[0001] This invention belongs to the field of surface acoustic wave gas sensors, and in particular to a surface acoustic wave gas sensor that utilizes a gas-sensitive thin film for heating. Background Technology

[0002] Gas sensors play a vital role in numerous fields such as industry, aerospace, nuclear power, and medicine. Currently, gas sensors are broadly categorized into thermal conductivity, electrochemical, catalytic combustion, and fiber optic types. As the application demands for gas sensors increase and application scenarios become more complex, gas sensors require characteristics such as high accuracy, fast response / recovery, high stability, and wide measurement range. However, the aforementioned gas sensors cannot meet all gas detection requirements. Since its introduction in the 1980s, the surface acoustic wave (SAW) gas sensor has found applications in defense, counter-terrorism, and aerospace fields due to its miniaturization, high sensitivity, fast response, low power consumption, and low cost.

[0003] Surface acoustic wave (SAW) gas sensors utilize a gas-sensitive thin film deposited along the propagation path of SAW waves. The adsorption of gas alters the Young's modulus, density, and conductivity of the film, which in turn affects the SAW propagation speed, allowing gas information to be decoupled from this velocity change. Currently, to improve the performance of SAW gas sensors, numerous studies have focused on designing porous, nano-hybrid, and multilayer composite structures for the gas-sensitive materials to enhance the device's gas-sensing capability. However, these methods suffer from complex fabrication processes and issues with device consistency and long-term stability. Summary of the Invention

[0004] The purpose of this invention is to provide a surface acoustic wave (SAW) gas sensor that utilizes a gas-sensitive thin film for heating, thereby enhancing the adsorption characteristics of the gas-sensitive thin film and improving the response speed and sensitivity of the SAW gas sensor. This invention proposes a method that combines the adsorption characteristics of the gas-sensitive thin film with its electrical performance, directly converting input electrical energy into film thermal energy to raise the temperature of the gas-sensitive thin film, enhancing its adsorption performance, and achieving the dual functions of heating and gas sensing in the SAW gas sensor. A gas-sensitive thin film combining serpentine and block shapes is used to regulate the surface temperature distribution of the device. By utilizing the relationship between the resistance and temperature characteristics of the gas-sensitive thin film, the temperature coefficient of resistance of the gas-sensitive thin film is determined, thus raising the SAW gas sensor to a specific temperature is beneficial for improving the response speed, stability, and sensitivity of the SAW gas sensor.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A surface acoustic wave (SAW) gas sensor utilizing a gas-sensitive thin film for heating includes electrical pins 1, a metal base 2, electrical leads 3, a SAW device 4, a protective film 5, and a gas-sensitive film 6. The metal base 2 has several electrical pins 1, and the SAW device 4 is disposed on its upper surface. The protective film 5 covers the SAW device 4, and the gas-sensitive film 6 covers the protective film 5. The gas-sensitive film 6 includes a serpentine gas-sensitive film and a block gas-sensitive film. The serpentine gas-sensitive film has the same shape as the interdigital transducers in the SAW device 4, and the block gas-sensitive film has the same acoustic propagation path shape as the interdigital transducers in the SAW device 4. The serpentine gas-sensitive film and the block gas-sensitive film are connected to the electrical pins 1 via electrical leads 3 in parallel or series connection.

[0007] According to a preferred embodiment of the present invention, a surface acoustic wave (SAW) gas sensor utilizing a gas-sensitive thin film for heating comprises an electrical pin 1, a metal base 2, electrical leads 3, a SAW device 4, a protective film 5, and a gas-sensitive thin film 6. The gas-sensitive thin film 6 is connected to the electrical pin 1 via the electrical leads 3, thereby realizing the heating function of the gas-sensitive thin film. The gas-sensitive thin film 6 is composed of a combination of a serpentine gas-sensitive thin film and a block gas-sensitive thin film. The gas-sensitive thin film 6 deposits a serpentine pattern of gas-sensitive material on the interdigitated electrodes (above the structure of the protective film 5) of the corresponding SAW device 4, according to the interdigitated electrode spacing, width, and aperture deposition period, along the sound propagation path. The SAW device 4 is bonded to the surface of the metal base 2. The protective film 5 is deposited on the surface of the SAW device 4 using a semiconductor planarization process. The gas-sensitive thin film 6 is deposited on the surface of the protective film 5 using a semiconductor planarization process. The SAW device 4 and the electrical pin 1 are connected via the electrical leads 3, thereby realizing the input and output of sensing signals.

[0008] Preferably, the electrical signal of the electrical pin 1 is transmitted to the gas-sensitive film 6 using the electrical lead 3, thereby converting electrical energy into heat energy of the gas-sensitive film 6, thus increasing the temperature of the gas-sensitive film and the surface acoustic wave device.

[0009] Preferably, the gas-sensitive film 6 is composed of a serpentine gas-sensitive film and a bulk gas-sensitive film. The serpentine gas-sensitive film 6 arranges the serpentine pattern gas-sensitive material according to the deposition cycle of the interdigital electrode spacing, width, and pore size. The interdigital electrode pattern can be selected as uniform fingers, weighted fingers, or SPUDT structures, etc. The thickness of the serpentine gas-sensitive film is set according to the required heating temperature. Preferably, the thickness of the serpentine gas-sensitive film is 10 nm to 100 nm. The bulk gas-sensitive film is deposited along the sound propagation path. Its thickness determines the sensitivity and loss of the surface acoustic wave gas sensor. Preferably, the thickness is 10 nm to 500 nm.

[0010] Preferably, the serpentine gas-sensitive film and the bulk gas-sensitive film can each convert electrical energy into heat energy through electrical pin 1, thereby allowing independent control of the temperature in the interdigital transducer region and the sound propagation path region, achieving control of the surface temperature distribution of the device. Alternatively, they can be connected in series to form a serpentine-bulb gas-sensitive composite film, using electrical pin 1 to transfer electrical energy to the film, thereby increasing the film temperature.

[0011] This invention relies on the correlation characteristics between the resistance of a gas-sensitive thin film and temperature to determine the temperature coefficient of the gas-sensitive thin film resistance, thereby achieving temperature calibration and enabling the gas-sensitive thin film to be heated to a specific temperature.

[0012] In this invention, the protective film 5 is used to isolate the electrical crosstalk between the gas-sensitive film 6 and the surface acoustic wave device 4. Preferably, the material of the protective film 5 can be insulating materials such as silicon dioxide, SU-8, and polyimide, and the film thickness is in the nanometer to micrometer range.

[0013] Preferably, the gas-sensitive thin film 6 can be a pure metal, an alloy metal, or a metal oxide, such as zinc oxide, pure palladium, tin oxide, palladium, nickel, platinum, tin oxide, zinc oxide, palladium-nickel, palladium-copper, palladium-magnesium, palladium-cobalt, palladium-nickel-platinum, copper phthalocyanine, etc., or it can be a multilayer metal thin film structure such as palladium / copper / palladium, palladium / magnesium / palladium.

[0014] Preferably, the electrical pin 1 is electrically connected to the gas-sensitive thin film 6 by wire bonding, thereby converting electrical energy into heat energy and increasing the operating temperature of the device.

[0015] Preferably, the electrical pin 1 and the surface acoustic wave device 4 are electrically connected by wire bonding to realize signal input and output and realize the sensing process.

[0016] Preferably, the surface acoustic wave device 4 adopts a delay line structure or a resonant structure.

[0017] Preferably, the protective film 5 is deposited on the surface of the surface acoustic wave device 4 using a semiconductor planar deposition process, and the gas-sensitive film 6 is deposited on the surface of the protective film 5 using a semiconductor deposition process. Semiconductor deposition processes include, for example, magnetron sputtering and vapor deposition.

[0018] Preferably, the lead material is silicon-aluminum wire.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] By combining the adsorption properties of a gas-sensitive thin film with its electrical performance, electrical energy is directly converted into thermal energy of the film, increasing the temperature of the gas-sensitive thin film and enhancing its adsorption performance. This achieves the dual functions of heating and gas sensing in a surface acoustic wave (SAW) gas sensor. A gas-sensitive thin film combining serpentine and block shapes is designed to regulate the surface temperature and temperature distribution of the device. The temperature coefficient of resistance of the gas-sensitive thin film is determined by utilizing the relationship between its resistance and temperature characteristics, thereby raising the SAW gas sensor to a specific temperature. Compared to traditional SAW gas sensors, the SAW gas sensor proposed in this invention effectively enhances the adsorption characteristics of the gas-sensitive thin film, regulates and controls the device temperature and surface temperature distribution, and thus improves the response speed, sensitivity, and stability of the SAW gas sensor. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the surface acoustic wave gas sensor structure according to Embodiment 1 of the present invention;

[0022] Figure 2 This is a schematic diagram of the surface acoustic wave gas sensor structure according to Embodiment 2 of the present invention;

[0023] Figure 3 This is the unheated response diagram of the gas-sensitive thin film of the surface acoustic wave gas sensor in Embodiment 1 of the present invention;

[0024] Figure 4 This is a diagram showing the heating response of the gas-sensitive thin film of the surface acoustic wave gas sensor in Embodiment 1 of the present invention.

[0025] Figure 5 This is the unheated response diagram of the gas-sensitive thin film of the surface acoustic wave gas sensor in Embodiment 2 of the present invention;

[0026] Figure 6 This is a diagram showing the heating response of the gas-sensitive thin film of the surface acoustic wave gas sensor in Embodiment 2 of the present invention.

[0027] Reference numerals: 1. Electrical pin; 2. Metal base; 3. Electrical lead; 4. Surface acoustic wave device; 5. Protective film; 6. Gas-sensitive film. Detailed Implementation

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] like Figure 1As shown, a surface acoustic wave (SAW) gas sensor utilizing a gas-sensitive thin film for heating is disclosed. The SAW gas sensor includes electrical pins 1, a metal base 2, electrical leads 3, a SAW device 4, a protective film 5, and a gas-sensitive film 6. A plurality of electrical pins 1 are disposed on the metal base 2. The SAW device 4 is disposed on the upper surface of the metal base 2, and the protective film 5 covers the SAW device 4. The gas-sensitive film 6 is further covered by the protective film 5. The gas-sensitive film 6 includes a serpentine gas-sensitive film and a block gas-sensitive film. The serpentine gas-sensitive film has the same shape as the interdigital transducers in the SAW device 4, and the block gas-sensitive film has the same acoustic propagation path shape as the interdigital transducers in the SAW device 4. The serpentine gas-sensitive film and the block gas-sensitive film are connected in series to the electrical pins 1 via the electrical leads 3.

[0031] A delayed linear surface acoustic wave (SAW) device 4 was fabricated. The SAW interdigitated electrodes adopted a uniform finger structure with an interdigitation width of λ / 4 and an aperture of 100λ, where λ is the SAW wavelength. A 30 nm thick protective silicon dioxide film 5 was deposited on the interdigitated electrodes and the acoustic propagation path of the delayed linear SAW device 4 using magnetron sputtering to protect the surface electrodes. Then, a pure palladium gas-sensitive film 6 was deposited on the protective film 5 using magnetron sputtering to adsorb hydrogen gas. The pure palladium serpentine gas-sensitive film formed serpentine resistance wires with a spacing of λ / 4, a width of λ / 4, and a thickness of 20 nm on the interdigitated electrodes, with the folding length consistent with the interdigitation aperture length. Finally, a 120 nm thick pure palladium bulk gas-sensitive film 6 was deposited on the acoustic propagation path using an overlay process. Simultaneously, the pure palladium serpentine gas-sensitive film and the bulk gas-sensitive film overlap, forming a combined serpentine and bulk pure palladium film. Electrical signals from electrical pins 1 are transmitted to the pure palladium gas-sensitive film using silicon-aluminum wire electrical leads 3, thereby increasing the temperature of the pure palladium film. The prepared delayed linear surface acoustic wave (SAW) gas sensor based on the pure palladium gas-sensitive film is adhesively bonded to the surface of a metal substrate 2. Multiple electrical pins 1 are retained around the perimeter of the metal substrate for signal transmission to the sensor. The relationship between the pure palladium resistance and temperature is calibrated using a high-low temperature chamber to determine the pure palladium resistance at different temperatures and the correlation characteristics between the pure palladium resistance and temperature. Then, a bridge circuit is used to control the temperature of the SAW device at 100℃. Electrical pins 4 are connected to the SAW device 4 using electrical leads 3, thereby realizing the input and output of the sensing signal.

[0032] The test results for different concentrations are as follows Figure 3-4 As shown, without heating, the surface acoustic wave (SAW) hydrogen sensor responds to 2% hydrogen gas in approximately 18 seconds. After passing electrical energy through the pure palladium to raise the temperature of the pure palladium film, the SAW gas sensor's response time is less than 2 seconds at a hydrogen concentration of 2%. The response magnitude increases by 7.284 mV compared to the unheated state.

[0033] Example 2

[0034] like Figure 2 As shown, a surface acoustic wave (SAW) gas sensor utilizing a gas-sensitive thin film for heating is disclosed. The SAW gas sensor includes electrical pins 1, a metal base 2, electrical leads 3, a SAW device 4, a protective film 5, and a gas-sensitive film 6. A plurality of electrical pins 1 are disposed on the metal base 2. The SAW device 4 is disposed on the upper surface of the metal base 2, and the protective film 5 covers the SAW device 4. The gas-sensitive film 6 is further covered by the protective film 5. The gas-sensitive film 6 includes a serpentine gas-sensitive film and a block gas-sensitive film. The serpentine gas-sensitive film has the same shape as the interdigital transducers in the SAW device 4, and the block gas-sensitive film has the same acoustic propagation path shape as the interdigital transducers in the SAW device 4. The serpentine gas-sensitive film and the block gas-sensitive film are connected to the electrical pins 1 via electrical leads 3 in parallel or series connection.

[0035] A delayed linear surface acoustic wave (SAW) device 4 was fabricated. The SAW interdigitated electrodes adopted a uniform finger structure with an interdigitation width of λ / 4 and an aperture of 100λ, where λ is the SAW wavelength. A 30 nm thick protective silicon dioxide film 5 was deposited on the interdigitated electrodes and the acoustic propagation path of the delayed linear SAW device 4 using magnetron sputtering to protect the surface electrodes. Then, a pure palladium gas-sensitive film 6 was deposited on the protective film 5 using magnetron sputtering to adsorb hydrogen gas. The pure palladium serpentine gas-sensitive film formed serpentine resistance wires with a spacing of λ / 4, a width of λ / 4, and a thickness of 20 nm on the interdigitated electrodes, with the folding length consistent with the interdigitation aperture length. Finally, a 30 nm thick pure palladium bulk gas-sensitive film was deposited on the acoustic propagation path using an overlay process. The pure palladium serpentine gas-sensitive film and the bulk gas-sensitive film are separated. Electrical signals from electrical pins 1 are transmitted to the gas-sensitive film using separate silicon-aluminum wire electrical leads 3, thereby increasing the temperature of both the serpentine and bulk pure palladium films. This allows for control of the temperature distribution on the device surface using different voltage signals. The fabricated delayed linear surface acoustic wave gas sensor based on the pure palladium film is adhesively bonded to the surface of a metal substrate 2. Multiple electrical pins 1 are retained around the perimeter of the metal substrate for signal transmission to the sensor. The relationship between the pure palladium resistance and temperature is calibrated using a high-low temperature chamber, determining the pure palladium resistance at different temperatures and establishing the correlation characteristics between the pure palladium resistance and temperature. A bridge circuit is then used to control the device temperature at 100℃. Electrical pins 3 are used to connect the electrical leads to the surface acoustic wave device 4, thus enabling the input and output of the sensing signal.

[0036] Test results at different concentrations, as follows Figure 5-6As shown, without heating, the surface acoustic wave (SAW) hydrogen sensor responds to 2% hydrogen in approximately 9.434 s. After passing electrical energy into the pure palladium to raise the temperature of the pure palladium film, the SAW gas sensor responds to 2% hydrogen in less than 2 s, and the response magnitude increases by 4.309 mV compared to when it is not heated.

[0037] Clearly, based on the above design method, the adsorption characteristics and electrical properties of the pure palladium thin film are combined to convert electrical energy into film heat energy, thereby increasing the temperature of the pure palladium thin film and the surface acoustic wave (SAW) device. Serpentine and bulk pure palladium thin films with the same width, spacing, and aperture as the SAW interdigitated electrodes can be deposited and heated in series or individually, thus achieving control over the surface temperature distribution of the device. Furthermore, utilizing the temperature coefficient of resistance of the pure palladium thin film in conjunction with a bridge circuit, the gas-sensitive film and the SAW device can be raised to a predetermined temperature. Based on the above invention, the SAW gas sensor can effectively enhance the adsorption performance of the gas-sensitive film and improve the response speed, sensitivity, and stability of the SAW hydrogen gas sensing.

[0038] All aspects not described in detail in this invention can be covered using conventional technical knowledge in the field.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A surface acoustic wave (SAW) gas sensor utilizing a gas-sensitive thin film for heating, the SAW gas sensor comprising electrical pins (1), a metal base (2), electrical leads (3), a SAW device (4), a protective film (5), and a gas-sensitive thin film (6), characterized in that, Electrical pins (1) are provided on the metal base (2), and the gas-sensitive film (6) is connected to the electrical pins (1) through electrical leads (3) to realize the heating of the gas-sensitive film. A surface acoustic wave device (4) is provided on the upper surface of the metal base (2), and a protective film (5) is covered on the surface acoustic wave device (4). The gas-sensitive film (6) is covered on the protective film (5). Among them, the gas-sensitive film (6) includes a serpentine gas-sensitive film and a block gas-sensitive film. The serpentine gas-sensitive film has the same shape as the interdigital transducer in the surface acoustic wave device (4), and the block gas-sensitive film has the same shape as the sound propagation path between the interdigital transducer in the surface acoustic wave device (4). The serpentine gas-sensitive film and the block gas-sensitive film are connected in parallel or in series. The thickness of the serpentine gas-sensitive film is 10nm~100nm, and the thickness of the bulk gas-sensitive film is 10nm~500nm.

2. A surface acoustic wave gas sensor utilizing a gas-sensitive thin film for heating according to claim 1, characterized in that, The gas-sensitive thin film (6) is made of tin oxide, zinc oxide, graphene, palladium, nickel, magnesium-silver alloy, cobalt, palladium-nickel-platinum alloy, copper phthalocyanine, platinum, or a three-layer metal of palladium-magnesium-platinum.

3. A surface acoustic wave gas sensor utilizing a gas-sensitive thin film for heating according to claim 1, characterized in that, The protective film (5) is made of silicon dioxide, SU-8 or polyimide.

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