Aln ceramic-based four-cantilever bridge micro-hotplate gas sensor array and preparation method thereof

Abstract

The present invention relates to an AlN ceramic-based four-cantilever bridged micro-hotplate gas sensor array and its fabrication method. The purpose of this invention is to address the problems of poor mechanical properties, thermal interference, and insufficient thermal stability in existing micro-hotplate sensors. The AlN ceramic-based four-cantilever bridged micro-hotplate gas sensor array of this invention features a substrate with four cantilever arms arranged within a rectangular frame, forming a cross-shaped structure. Each cantilever has an interdigitated signal electrode on its front side and a heater electrode on its back side. The heater electrodes and signal electrodes are symmetrically arranged. A sensitive film is placed between the signal electrodes to form a sensor array unit. The heater electrodes have a serpentine structure, and the substrate is an AlN ceramic substrate. In this invention, the heater electrodes and signal electrodes are platinum film structures, symmetrically positioned, and the patterned structure is achieved through a double-sided flexible mechanical photolithography lift-off process, resulting in improved mechanical properties of the AlN ceramic substrate.

Description

Technical Field

[0001] This invention relates to a ceramic-based multi-cantilever bridged micro-hot plate gas sensor array and its fabrication method. Background Technology

[0002] Currently, existing micro hot plate gas sensor arrays are mainly silicon-based, forming micro thermal films or micro thermal bridge structures through wet etching processes. Generally, the upper and lower layers of the heating electrode use silicon dioxide and silicon nitride composite films as insulating substrates and thermal insulation layers. Since micro hot plate gas sensors need to be heated to high temperatures, even reaching several hundred degrees Celsius, there is a problem of thermal stress mismatch instability of multilayer heterogeneous films. Such complex multilayer films have disadvantages such as complex integration processes, low mechanical properties, small heat collection area volume and low heat capacity of the hot film structure, serious thermal interference, and unsatisfactory high temperature resistance and thermal stability. These disadvantages restrict the further improvement of the performance and application development of microstructure gas sensors, especially in complex environments. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of poor mechanical properties, thermal interference and insufficient thermal stability of existing micro hot plate sensors, and to provide an AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array and its preparation method.

[0004] The AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array of the present invention includes: a substrate, a heater electrode, a first thermal isolation via, a second thermal isolation via, a third thermal isolation via, a signal electrode, and a sensitive film; the substrate has four cantilever arms arranged in a rectangular frame, the four cantilever arms forming a cross-shaped structure, a second thermal isolation via opening in the center of the cross-shaped structure, a first thermal isolation via opening between adjacent cantilever arms (a total of four first thermal isolation vias), and a third thermal isolation via opening on each cantilever arm;

[0005] An interdigitated signal electrode is provided on the front side of each cantilever, and a heater electrode is provided on the back side of each cantilever. The heater electrode and the signal electrode are arranged symmetrically on opposite sides. A sensitive film is provided between the electrodes of the signal electrode to form a sensor array unit. The heater electrode has a serpentine structure, and the substrate is an AlN ceramic substrate.

[0006] The fabrication method of the AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array of the present invention is carried out according to the following steps:

[0007] Step 1: Clean the substrate.

[0008] Using an AlN ceramic substrate as a base, the AlN ceramic substrate was ultrasonically cleaned and dried to obtain a clean AlN ceramic substrate.

[0009] Step 2: Apply photoresist to both sides:

[0010] A homogenization process is performed on the front and back sides of a clean AlN ceramic substrate, and after drying, a double-sided coated AlN ceramic substrate is obtained.

[0011] Step 3: Double-sided exposure:

[0012] Using photolithography with photoresist as a mask, double-sided ultraviolet exposure was performed according to the sensor array structure pattern to obtain the photolithographically lithographic AlN ceramic substrate.

[0013] Step 4: Double-sided development and etching:

[0014] The photolithographically patterned AlN ceramic substrate is placed in a positive resist developer for development, rinsed off with deionized water, and dried to obtain an AlN ceramic substrate with a photoresist pattern.

[0015] Step 5: Double-sided Pt film coating:

[0016] An AlN ceramic substrate with a photoresist pattern is placed in a magnetron sputtering coating machine, a vacuum is drawn and argon gas is introduced, and a platinum (Pt) film is deposited on both sides by magnetron sputtering using a platinum metal target. The result is an AlN ceramic substrate coated with heater electrodes and signal electrodes.

[0017] Step Six: Double-sided flexible mechanical peeling:

[0018] An AlN ceramic substrate coated with heater electrodes and signal electrodes is immersed in acetone solution and ultrasonically treated to obtain an AlN ceramic micro hot plate gas sensor array chip with a Pt film pattern structure.

[0019] Step 7: Forming a film of the semiconductor sensitive material:

[0020] A sensitive film is formed between the signal electrodes of an AlN ceramic micro hot plate gas sensor array chip by screen printing. After drying, an AlN ceramic-based micro hot plate gas sensor array chip with a sensitive film is obtained.

[0021] Step 8: Drilling holes:

[0022] A first thermally isolated via, a second thermally isolated via, and a third thermally isolated via were drilled on an AlN ceramic-based micro hot plate gas sensor array chip using a laser scribing machine, resulting in an AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array.

[0023] This invention relates to an AlN ceramic-based four-cantilever bridged micro-hotplate gas sensor array, comprising four sensor array units forming a cross-shaped structure. The heater electrode and signal electrode on each sensor array unit are symmetrically positioned. When the detected airflow flows in perpendicular to the signal electrode on the front of the sensor array, the signals from all four units simultaneously contact the gas being measured, preventing thermal interference between array units due to airflow changes. The thermally isolated through-hole design serves both thermal isolation and reduced heat conduction loss, while also minimizing airflow resistance during gas detection, thus facilitating the dynamic detection of rapid airflow in pipelines.

[0024] The heater electrode and signal electrode of this invention are platinum film structures, and their positions are symmetrical. The pattern structure is realized by a double-sided flexible mechanical photolithography lift-off process. The AlN ceramic substrate has better mechanical properties and features simple process preparation, low cost and good film-substrate bonding quality. Attached Figure Description

[0025] Figure 1 This is a back plan view of the AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array of the present invention.

[0026] Figure 2 This is a front plan view of the AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array of the present invention.

[0027] Figure 3 This is a schematic diagram of the heater electrode structure;

[0028] Figure 4 This is a schematic diagram of the signal electrode structure;

[0029] Figure 5 This is a schematic diagram of the sensitive membrane structure;

[0030] Figure 6 This is a schematic diagram of the substrate structure;

[0031] Figure 7 This is a flowchart of the fabrication process of an AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array;

[0032] Figure 8 Here is a SEM image of the tin dioxide nanoparticles described in the examples;

[0033] Figure 9 This is a test graph of the response recovery rate of the AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array in the embodiment;

[0034] Figure 10 This is a test diagram of the sensitivity response characteristics of the AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array in the embodiment. Detailed Implementation

[0035] Specific Implementation Method 1: The AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array of this implementation method includes: a substrate 1, a heater electrode 2, a first thermal isolation via 3, a second thermal isolation via 4, a third thermal isolation via 5, a signal electrode 6, and a sensitive film 7; the substrate 1 has four cantilever arms 1-2 arranged in a rectangular frame 1-1, the four cantilever arms 1-2 forming a cross-shaped structure, the center of the cross has a second thermal isolation via 4, and the adjacent cantilever arms 1-2 have first thermal isolation vias 3 (a total of four first thermal isolation vias), and each cantilever arm 1-2 has a third thermal isolation via 5;

[0036] An interdigitated signal electrode 6 is provided on the front side of each cantilever 1-2, and a heater electrode 2 is provided on the back side of each cantilever 1-2. The heater electrode 2 and the signal electrode 6 are arranged symmetrically on opposite sides. A sensitive film 7 is provided between the electrodes of the signal electrode 6 to form a sensor array unit. The heater electrode 2 has a serpentine structure, and the substrate 1 is an AlN ceramic substrate.

[0037] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the first thermal isolation through hole 3 is trapezoidal.

[0038] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the third thermal isolation through hole 5 is rectangular.

[0039] Specific Implementation Method Four: This implementation method differs from one of the specific implementation methods one to three in that the heater electrode 2 is a Pt film with a thickness of 500-1000 nm and an electrode linewidth of 20-100 μm.

[0040] Specific Implementation Method 5: This implementation method differs from one of the specific implementation methods one to four in that the signal electrode 6 is a Pt film with a thickness of 500 to 1000 nm.

[0041] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the sensitive film 7 is a metal oxide semiconductor gas sensitive material, and the thickness of the sensitive film 7 is 1 to 5 μm.

[0042] The composition of the sensitive material in this embodiment depends on the type of target gas being detected.

[0043] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the thickness of the AlN ceramic substrate is 0.1 to 0.2 mm.

[0044] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the four sensor array units are connected by microbeams 8 to form a cantilever bridge structure.

[0045] In this embodiment, the bridging effect of the microbeams reduces the impact of airflow on the cantilever array unit and improves the mechanical strength of the array unit structure.

[0046] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the length × width of the AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array is (4-12mm) × (4-12mm).

[0047] Specific Implementation Method 10: The fabrication method of the AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array in this implementation method is carried out according to the following steps:

[0048] Step 1: Clean the substrate.

[0049] Using an AlN ceramic substrate as a base, the AlN ceramic substrate was ultrasonically cleaned and dried to obtain a clean AlN ceramic substrate.

[0050] Step 2: Apply photoresist to both sides:

[0051] A homogenization process is performed on the front and back sides of a clean AlN ceramic substrate, and after drying, a double-sided coated AlN ceramic substrate is obtained.

[0052] Step 3: Double-sided exposure:

[0053] Using photolithography with photoresist as a mask, double-sided ultraviolet exposure was performed according to the sensor array structure pattern to obtain the photolithographically lithographic AlN ceramic substrate.

[0054] Step 4: Double-sided development and etching:

[0055] The photolithographically patterned AlN ceramic substrate is placed in a positive resist developer for development, rinsed off with deionized water, and dried to obtain an AlN ceramic substrate with a photoresist pattern.

[0056] Step 5: Double-sided Pt film coating:

[0057] An AlN ceramic substrate with a photoresist pattern is placed in a magnetron sputtering coating machine, a vacuum is drawn and argon gas is introduced, and a platinum (Pt) film is deposited on both sides by magnetron sputtering using a platinum metal target. The result is an AlN ceramic substrate coated with heater electrodes and signal electrodes.

[0058] Step Six: Double-sided flexible mechanical peeling:

[0059] An AlN ceramic substrate coated with heater electrodes and signal electrodes is immersed in acetone solution and ultrasonically treated to obtain an AlN ceramic micro hot plate gas sensor array chip with a Pt film pattern structure.

[0060] Step 7: Forming a film of the semiconductor sensitive material:

[0061] A sensitive film is formed between the signal electrodes of an AlN ceramic micro hot plate gas sensor array chip by screen printing. After drying, an AlN ceramic-based micro hot plate gas sensor array chip with a sensitive film is obtained.

[0062] Step 8: Drilling holes:

[0063] A first thermal isolation via, a second thermal isolation via, and a third thermal isolation via were drilled on an AlN ceramic-based micro hot plate gas sensor array chip using a laser scribing machine, resulting in an AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array.

[0064] Example 1: The AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array of this example includes: a substrate 1, a heater electrode 2, a first thermal isolation via 3, a second thermal isolation via 4, a third thermal isolation via 5, a signal electrode 6, and a sensitive film 7; the substrate 1 has four cantilever arms 1-2 arranged in a rectangular frame 1-1, the four cantilever arms 1-2 forming a cross-shaped structure, a thermal isolation via 4 is opened in the center of the cross, microbeams 8 are formed around the thermal isolation via 4, one end of the four cantilever arms 1-2 is connected through the microbeams 8, a first thermal isolation via 3 is opened between adjacent cantilever arms 1-2, and a third thermal isolation via 5 is opened on each cantilever arm 1-2;

[0065] An interdigitated signal electrode 6 is provided on the front side of each cantilever 1-2, and a heater electrode 2 is provided on the back side of each cantilever 1-2. The heater electrode 2 and the signal electrode 6 are arranged symmetrically on opposite sides. A sensitive film 7 is provided between the electrodes of the signal electrode 6 to form a sensor array unit. The heater electrode 2 has a serpentine structure, the signal electrode 6 has a comb-shaped interdigitated structure, and the substrate 1 is an AlN ceramic substrate.

[0066] In this embodiment, the four signal electrodes have a total of eight welding pins, and the four heater electrodes have a total of eight welding pins. The welding pins have a tapered structure that is narrow on the inside and wide on the outside. The purpose is to reduce the connection resistance of the platinum film welding pins, which can reduce the temperature interference of the resistance and improve the temperature distribution of the sensor's thermal field.

[0067] Example 2: The fabrication method of the AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array in this example is implemented according to the following steps:

[0068] Step 1: Clean the substrate.

[0069] The AlN ceramic substrate was immersed in acetone solution and cleaned with ultrasonic waves at a frequency of 50 kHz for 10-15 minutes. The AlN ceramic substrate was then removed and immersed in 95% alcohol solution and cleaned with ultrasonic waves at a frequency of 25 kHz at room temperature for 10-15 minutes. The AlN ceramic substrate was then removed and placed in deionized water and cleaned with ultrasonic waves at a frequency of 30 kHz at room temperature for 5-10 minutes. The substrate was then removed and placed in a drying oven at 120 ℃ to dry, thus obtaining a clean AlN ceramic substrate.

[0070] Step 2: Apply photoresist to both sides:

[0071] A homogenization process was performed on the front and back sides of a clean AlN ceramic substrate, with a homogenization thickness of 1-2 μm. The substrate was then dried at 80-100℃ to obtain a double-sided coated AlN ceramic substrate.

[0072] Step 3: Double-sided exposure:

[0073] Using photolithography with photoresist as a mask, double-sided ultraviolet exposure was performed according to the sensor array structure pattern to obtain the photolithographically lithographic AlN ceramic substrate.

[0074] Step 4: Double-sided development and etching:

[0075] The photolithographically etched AlN ceramic substrate is placed in a positive resist developer and developed until the pattern is clear. Then, the developer is rinsed off with deionized water and dried to obtain an AlN ceramic substrate with a photoresist pattern.

[0076] Step 5: Double-sided Pt film coating:

[0077] An AlN ceramic substrate with a photoresist pattern is placed in a magnetron sputtering coating machine, a vacuum is drawn and argon gas is introduced, and a platinum (Pt) film is deposited on both sides by magnetron sputtering using a platinum metal target to obtain an AlN ceramic substrate with a platinum film (film thickness 600nm). At this time, the Pt film pattern of heater electrode and signal is formed.

[0078] Step Six: Double-sided flexible mechanical peeling:

[0079] An AlN ceramic substrate coated with a platinum film is immersed in an acetone solution to dissolve the unexposed photoresist under the metal film. At the same time, the AlN ceramic substrate coated with a platinum film is ultrasonically treated in the acetone solution at a frequency of 20kHz for 50s to accelerate the dissolution of the photoresist and the peeling off of the platinum film. For the Pt film portion that is not completely peeled off, after being removed from the acetone solution, the unwanted platinum metal film is mechanically peeled off using BOPP pressure-sensitive tape to obtain the AlN ceramic micro hot plate gas sensor array chip.

[0080] Step 7: Forming a film of the semiconductor sensitive material:

[0081] A sensitive film with a thickness of 3 μm was formed between the signal electrodes of the AlN ceramic micro hot plate gas sensor array chip by screen printing. After drying, an AlN ceramic-based micro hot plate gas sensor array with a sensitive film was obtained.

[0082] Step 8: Drilling holes:

[0083] A first thermal isolation via, a second thermal isolation via, and a third thermal isolation via were drilled on an AlN ceramic micro hot plate gas sensor array chip using a laser scribing machine to obtain an AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array.

[0084] The semiconductor-sensitive material described in this embodiment is tin dioxide semiconductor nanoparticles. The synthesis method is a hydrothermal method, with a synthesis temperature of 180℃ and a reaction time of 24 hours. The raw materials are stannous chloride and sodium hydroxide, and the catalyst is hexadecanetrimethylammonium bromide. The SEM image of the prepared tin dioxide nanoparticles is shown below. Figure 8 As shown.

[0085] The AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array obtained in this embodiment was packaged and tested.

[0086] Encapsulation and soldering:

[0087] The AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array prepared in this embodiment was PCB packaged and soldered. Pt wire with a diameter of 80 micrometers was used as the connecting lead. The AlN ceramic-based sensor electrode was soldered by 850℃ platinum paste sintering for 10 minutes. The PCB end was soldered to the PCB package board pads by tin soldering.

[0088] Gas-sensitive testing method:

[0089] Standard static gas sensing performance tests were conducted on the encapsulated and soldered AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array to verify the key performance indicators of the prepared sensor array. The heating voltage of the heating electrode was 4-5V, the operating temperature generated by the heater was 300-350℃, and the output resistance signal of the signal electrode was 0.1-10MΩ.

[0090] Test performance results analysis:

[0091] Taking the testing of one unit of the fabricated sensor array as an example, the gas-sensitive response recovery time T 90 Taking 16ppm as an example, the response times are 6s and 64s respectively, demonstrating a relatively fast response rate. Figure 9As shown. Sensitivity tests were conducted at concentrations of 1 ppm, 2 ppm, 4 ppm, 8 ppm, 16 ppm, and 32 ppm of ethanol gas. The sensitivity at 1 ppm was 2.12 times that of the standard, and at 32 ppm it was 4 times that of the standard. This demonstrates ideal gas-sensing characteristics for trace amounts of ethanol gas, while exhibiting good atmospheric stability. Figure 10 As shown.

Claims

1. An AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array, characterized in that... The AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array includes: a substrate (1), a heater electrode (2), a first thermal isolation via (3), a second thermal isolation via (4), a third thermal isolation via (5), a signal electrode (6), and a sensitive film (7); the substrate (1) is composed of four cantilever (1-2) arranged in a rectangular frame (1-1), the four cantilever (1-2) forming a cross-shaped structure, the center of the cross-shaped structure having a second thermal isolation via (4), and the first thermal isolation via (3) being opened between adjacent cantilever (1-2), the first thermal isolation via (3) being trapezoidal, and a third thermal isolation via (5) being opened on each cantilever (1-2), the third thermal isolation via (5) being rectangular; A signal electrode (6) is provided on the front side of each cantilever (1-2). The signal electrode (6) is an interdigitated electrode. A heater electrode (2) is provided on the back side of each cantilever (1-2). The heater electrode (2) and the signal electrode (6) are symmetrically arranged on opposite sides. A sensor array unit is formed by setting a sensitive film (7) between the electrodes of the signal electrode (6). The signal electrode (6) is a Pt film with a thickness of 500~1000nm. The four sensor array units are connected by microbeams (8) to form a cantilever bridge structure. The heater electrode (2) is a serpentine structure. The heater electrode (2) is a Pt film with a thickness of 500~1000nm and a linewidth of 20~100μm. The substrate (1) is an AlN ceramic substrate.

2. The AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array according to claim 1, characterized in that... The sensitive membrane (7) is a metal oxide semiconductor gas sensitive material, and the thickness of the sensitive membrane (7) is 1~5μm.

3. The AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array according to claim 1, characterized in that... The thickness of the AlN ceramic substrate is 0.1~0.2mm.

4. The AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array according to claim 1, characterized in that... The length × width of this AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array is (4~12mm) × (4~12mm).

5. The method for fabricating the AlN ceramic-based four-cantilever bridged micro-hot plate gas sensor array as described in claim 1, characterized in that... The preparation method is carried out according to the following steps: Step 1: Clean the substrate. Using an AlN ceramic substrate as a base, the AlN ceramic substrate was ultrasonically cleaned and dried to obtain a clean AlN ceramic substrate. Step 2: Apply photoresist to both sides: A homogenization process is performed on the front and back sides of a clean AlN ceramic substrate, and after drying, a double-sided coated AlN ceramic substrate is obtained. Step 3: Double-sided exposure: Using photolithography with photoresist as a mask, double-sided ultraviolet exposure was performed according to the sensor array structure pattern to obtain the photolithographically lithographic AlN ceramic substrate. Step 4: Double-sided development and etching: The photolithographically patterned AlN ceramic substrate is placed in a positive resist developer for development, rinsed off with deionized water, and dried to obtain an AlN ceramic substrate with a photoresist pattern. Step 5: Double-sided Pt film coating: An AlN ceramic substrate with a photoresist pattern is placed in a magnetron sputtering coating machine, a vacuum is drawn and argon gas is introduced, and a platinum film is deposited on both sides by magnetron sputtering using a platinum metal target. The result is an AlN ceramic substrate coated with heater electrodes and signal electrodes. Step Six: Double-sided flexible mechanical peeling: An AlN ceramic substrate coated with heater electrodes and signal electrodes is immersed in acetone solution and ultrasonically treated to obtain an AlN ceramic micro hot plate gas sensor array chip with a Pt film pattern structure. Step 7: Forming a film of the semiconductor sensitive material: A sensitive film is formed between the signal electrodes of an AlN ceramic micro hot plate gas sensor array chip by screen printing. After drying, an AlN ceramic-based micro hot plate gas sensor array chip with a sensitive film is obtained. Step 8: Drilling holes: A first thermally isolated via, a second thermally isolated via, and a third thermally isolated via were drilled on an AlN ceramic-based micro hot plate gas sensor array chip using a laser scribing machine, resulting in an AlN ceramic-based four-cantilever bridged micro hot plate gas sensor array.

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