Integrated active QCM humidity sensor and preparation method thereof

Abstract

The invention discloses an integrated active quartz crystal microbalance (QCM) humidity sensor and a preparation method thereof. The integrated active quartz crystal microbalance (QCM) humidity sensor is characterized by comprising a piezoelectric wafer (1), a metal electrode layer (2), a humidity sensitive layer (3), an oscillating circuit wafer (4), leads (51 and 52), a base (6) and a pin bonding pad (7), the metal electrode layer (2) comprises a first metal electrode layer (a bottom electrode) (21) and a second metal electrode layer (a top electrode) (22), and a humidity sensitive layer (3) is arranged on the surface of the second metal electrode layer (22). According to the small-size and high-fundamental-frequency integrated active QCM humidity sensor disclosed by the invention, the humidity-sensitive material is formed on the second metal electrode layer, so that the QCM humidity sensor attached with the humidity-sensitive film is obtained. The sensor is internally provided with the oscillating circuit, and stable high-quality oscillating signals can be generated. The integrated active QCM humidity sensor is simple in preparation method, low in cost, small in size and capable of being mounted, and has the advantages of being high in sensitivity, good in linearity, high in response speed and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of humidity sensors, and in particular relates to an integrated active QCM humidity sensor and a preparation method thereof. Background Art

[0002] Among different types of humidity sensors, humidity sensors based on QCM (Quartz Crystal Microbalance) have attracted widespread attention due to their digital frequency output characteristics. The core component of the QCM humidity sensor is a piezoelectric chip. Based on the inverse piezoelectric effect, the mass change of the piezoelectric chip surface load can be converted into a frequency change. The humidity-sensitive film has a significant impact on the performance of the QCM humidity sensor. Increasing the amount of humidity-sensitive film is a common method to improve the sensor response sensitivity. On the one hand, it will increase the amount of water molecules adsorbed, and on the other hand, the increase in the viscosity of the humidity-sensitive film will also cause additional frequency offset response. However, with the increase in the amount of humidity-sensitive film, the increase in the viscosity of the humidity-sensitive film will cause the stability of the QCM humidity sensor to deteriorate. In addition, the response sensitivity of the QCM humidity sensor under high humidity conditions is usually much higher than that under low humidity, resulting in nonlinear humidity-frequency response in the full humidity range, making the conversion of humidity from frequency complicated. The nonlinear humidity-frequency response is one of the important factors restricting the performance of the QCM humidity sensor. Generally, when a trace amount of humidity-sensitive film is loaded on the surface of the QCM humidity sensor, the sensor has a good linear response, but its response sensitivity is low. The contradiction between the high sensitivity and nonlinearity of the QCM humidity sensor is an urgent problem to be solved. Summary of the invention

[0003] The present invention discloses an integrated active QCM humidity sensor and a preparation method thereof, which is intended to solve the nonlinear humidity-frequency response problem of the QCM humidity sensor mentioned in the background technology, and at the same time to solve the mutual restriction problem between high linearity and high sensitivity of the QCM humidity sensor.

[0004] One of the technical solutions adopted by the present invention is: an integrated active QCM humidity sensor, comprising a QCM device and an oscillating circuit wafer connected with the QCM device to form a series loop; the QCM device and the oscillating circuit wafer are integrated in a package;

[0005] The QCM device comprises: a piezoelectric chip, metal electrode layers arranged on the upper and lower surfaces of the piezoelectric chip, and a humidity sensitive layer arranged on the metal electrode layer on the upper surface of the piezoelectric chip.

[0006] Furthermore, the QCM device and the oscillation circuit wafer are arranged on a base.

[0007] Furthermore, a pin pad is arranged under the base.

[0008] Furthermore, the piezoelectric chip is a piezoelectric quartz chip or a piezoelectric ceramic chip.

[0009] Furthermore, the fundamental frequency of the piezoelectric chip is 5 to 100 MHz.

[0010] Furthermore, the size of the piezoelectric chip is 3.5 mm×2.0 mm.

[0011] Furthermore, the material of the first metal electrode layer and the material of the second metal electrode layer are gold or silver.

[0012] Furthermore, the material of the humidity sensitive layer is a combination of two single materials among polyimide (PI), graphene oxide (GO) and carboxylated ultra-high purity single-walled carbon nanotubes (SWCNTS-COOH).

[0013] Furthermore, the size range of the base is (3.0-7.0) mm×(2.5-6.0) mm.

[0014] Furthermore, the type of the oscillation circuit wafer may be a Pierce oscillator or a Colpitts oscillator.

[0015] Furthermore, the oscillation circuit wafer is respectively connected to the second metal electrode layer (top electrode) and the first metal electrode layer (bottom electrode) on the base through leads.

[0016] The second technical solution adopted by the present invention is: a method for preparing an integrated active QCM humidity sensor, comprising the following preparation steps:

[0017] Step 1: Prepare a QCM device; prepare a strong oxidizing cleaning solution, place the piezoelectric chip in it for cleaning for 30 minutes, then rinse with deionized water, and then blow dry with nitrogen. Subsequently, place the piezoelectric chip in anhydrous ethanol for ultrasonic cleaning for 30 minutes, then rinse with deionized water, blow dry with nitrogen, and finally place the piezoelectric chip in a 50°C vacuum drying oven for drying for 1 hour. After drying, metal electrode layers are formed on the upper and lower surfaces of the piezoelectric chip. The metal electrode layer on the lower surface of the piezoelectric chip is the first metal electrode layer, and the metal electrode layer on the upper surface of the piezoelectric chip is the second metal electrode layer, thereby obtaining a QCM device; connect the QCM device in series with the oscillation circuit wafer through leads to form a loop, and finally package and integrate to obtain an active QCM device, and place the prepared active QCM device in a dry and clean container for standby use;

[0018] Step 2: preparing a moisture-sensitive material solution; mixing the solutions of the two selected materials and ultrasonically treating them for 30 minutes to obtain a moisture-sensitive material solution;

[0019] Step 3: Prepare a QCM sensitive material device; form a film of the moisture-sensitive material solution on the second metal electrode layer of the piezoelectric chip, and place it in a vacuum drying oven at 30°C for 2 hours. After drying, a layer of moisture-sensitive material coating is attached to the surface of the second metal electrode layer of the piezoelectric chip.

[0020] The third technical solution adopted by the present invention is: an application of an integrated active QCM humidity sensor to measure humidity by changing the resonant frequency of a QCM piezoelectric chip coated with a humidity-sensitive film.

[0021] The QCM humidity sensor prepared by the above steps is connected to a universal frequency meter and placed in a humidity generating device. When the humidity-sensitive material on the QCM piezoelectric chip adsorbs water molecules, the universal frequency meter detects and collects the resonant frequency changes of the QCM humidity sensor under different humidity in real time, and the humidity-sensitive characteristic curves of the sensor can be obtained, such as: response curve, response-recovery curve, hysteresis curve, etc.

[0022] The integrated active QCM humidity sensor prepared as described above can be widely used in real-time detection of ambient humidity.

[0023] Based on the above technical scheme, the present invention has at least the following advantages: a small-sized, high-base-frequency integrated active QCM humidity sensor of the present invention is connected to an oscillation circuit to generate a stable, high-quality oscillation signal; the QCM humidity sensor of the present invention can use any one of the three composite materials of PI / GO, PI / SWCNTS-COOH, and GO / SWCNTS-COOH as a humidity-sensitive membrane material, and the humidity-sensitive membrane has the characteristics of good hydrophilicity; the QCM humidity sensor of the present invention has the characteristics of high sensitivity and good linearity; the QCM humidity sensor of the present invention integrates an active oscillator, has the advantages of small size, high output frequency stability, and can be mounted; the preparation process of the QCM humidity sensor of the present invention is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The quartz crystal microbalance used in the present invention is used for humidity detection due to its highly sensitive mass-frequency response characteristics. The present invention will be described by way of example and with reference to the accompanying drawings, in which:

[0025] Figure 1 It is a schematic diagram of the structure of the integrated active QCM humidity sensor device of the present invention.

[0026] Figure 2 FIG. 4 is a top view of the integrated active QCM humidity sensor of the present invention.

[0027] Figure 3 It is a dynamic response-recovery characteristic curve diagram of the integrated active QCM humidity sensor of the present invention.

[0028] Figure 4 This is the response characteristic curve of the integrated active QCM humidity sensor of the present invention.

[0029] Figure 5 Schematic diagram of the oscillation signal generated by the integrated active QCM humidity sensor of the present invention.

[0030] Explanation of the reference numerals: 1. piezoelectric chip; 2. metal electrode layer; 21. first metal electrode layer; 22. second metal electrode layer; 3. humidity sensitive layer; 4. oscillation circuit wafer; 51. lead; 52. lead; 6. base; 7. pin pad. DETAILED DESCRIPTION

[0031] All other embodiments obtained without creative work are protected by this application. In order to make the purpose, technical solutions and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. The components of the embodiments of this application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for which protection is claimed, but merely represents selected embodiments of the present application.

[0032] See also Figure 1 and Figure 2 As shown, an integrated active QCM humidity sensor of the present invention includes a piezoelectric chip 1, a metal electrode layer 2, a first metal electrode layer 21, a second metal electrode layer 22, a humidity sensitive layer 3, an oscillation circuit wafer 4, leads 51 and 52, a base 6 and a pin pad 7.

[0033] The three humidity-sensitive materials used in the present invention are polyimide (PI), graphene oxide (GO), and carboxylated ultra-high purity single-walled carbon nanotubes (SWCNTS-COOH). The humidity-sensitive film can be prepared by compounding the above three single materials in pairs and mixing them in different concentrations and ratios.

[0034] The humidity sensitive film of the integrated active QCM humidity sensor of the present invention is composited by PI solution, GO solution and SWCNTS-COOH solution. PI is mainly synthesized by dianhydride and diamine. There are many varieties of dianhydride and diamine. Different combinations can obtain PI with different performances. GO, as one of the important derivatives of graphene, has high hydrophilicity because it contains a large number of oxygen-rich functional groups, such as hydroxyl, epoxy, carboxyl, etc. According to current research, GO has potential application prospects in the development of high-stability QCM humidity sensors. SWCNTS-COOH is often used in composite materials because of its unique structure and excellent chemical properties. It can significantly improve the strength and toughness of the material. In addition, its large specific surface area can provide more sites for the adsorption of water molecules. It is precisely because of these characteristics that this material is often used in the humidity field.

[0035] The following examples will illustrate the present invention in conjunction with the accompanying drawings. The raw materials used in this embodiment are all compounds that can be purchased in the pharmaceutical market or obtained by known synthetic methods. The following examples of the present invention are described in detail in conjunction with the accompanying drawings.

[0036] Example 1

[0037] The present invention also provides an integrated active QCM humidity sensor and a preparation method thereof, comprising the following steps:

[0038] Step 1: Prepare the QCM device. Prepare a strong oxidizing cleaning solution with a volume ratio of 5:1:1 of deionized water: ammonia water: hydrogen peroxide, place the piezoelectric chip in the strong oxidizing cleaning solution for 30 minutes, then rinse with deionized water, and blow dry with nitrogen. Then, place the piezoelectric chip in anhydrous ethanol for ultrasonic cleaning for 30 minutes, then rinse with deionized water, blow dry with nitrogen, and finally place the piezoelectric chip in a 50°C vacuum drying oven for 1 hour. After drying, metal electrode layers are formed on the upper and lower surfaces of the piezoelectric chip. The metal electrode layer on the lower surface of the piezoelectric chip is the first metal electrode layer, and the metal electrode layer on the upper surface of the piezoelectric chip is the second metal electrode layer, thereby obtaining a QCM device; the QCM device is connected in series with the oscillation circuit wafer through leads to form a loop, and finally packaged and integrated to obtain an active QCM device, and the prepared active QCM device is placed in a dry and clean container for standby use;

[0039] Step 2: Prepare a hygroscopic material solution. Mix 18% PI solution and 10 mg / mL GO solution in a ratio of 1:1 and perform ultrasonic treatment for 30 minutes to prepare a hygroscopic material solution.

[0040] Step 3: Use a microsyringe to take 5 μL of the PI / GO humidity sensitive material solution prepared in step 2, and spray it on the center of the second metal electrode layer of the QCM piezoelectric chip. Then place the QCM humidity sensor in a drying oven at 30°C for 2 hours. After drying, a layer of PI / GO sensitive material coating is attached to the surface of the second metal electrode layer of the QCM piezoelectric chip.

[0041] Step 4: After the QCM humidity sensor prepared by the above steps is connected to a universal frequency meter, it is placed in a corresponding humidity generating device. When the humidity-sensitive material on the QCM piezoelectric chip absorbs water molecules, the universal frequency meter detects and collects the resonant frequency changes of the QCM humidity sensor in different humidity environments in real time. Figure 3 The dynamic response-recovery characteristic curve of the sensor shown in Figure 4 As can be seen from the response characteristic curve shown in the figure, the response sensitivity of the QCM humidity sensor in this embodiment is 69.71 Hz / % RH, and the linearity is high (R 2 =0.9962), the response / recovery time is 3 / 4s.

[0042] Those skilled in the art will know that the Sauerbery equation Describes the linear relationship between the sensor frequency change and the mass change; combined with this embodiment Figure 4 The response characteristic curve shown in the figure shows that the integrated active QCM humidity sensor of the present invention meets the requirements of the Sauerbery equation and can achieve high linearity of humidity-frequency response in the full humidity range. In the Sauerbery equation, f0 represents the fundamental frequency of the piezoelectric crystal, △m(g) represents the mass of the additional material on the crystal electrode, A represents the surface area of ​​the chip, and μ q represents the crystal shear modulus, ρ q represents the crystal density, and △f represents the frequency shift.

[0043] Since the widely used QCM devices usually have low fundamental frequency and large wafer surface area, resulting in low mass frequency sensitivity and poor linearity. The present invention uses a piezoelectric chip with a fundamental frequency of 5 to 100 MHz and a small-sized quartz crystal to ensure that the sensor has high mass frequency sensitivity and linear response.

[0044] The present invention uses a base to protect and support the oscillation circuit so that the oscillation circuit is connected to the package substrate through the lead wire. If the base size is too large, it will make it difficult for the sensor to be integrated and packaged; if the size is too small, it will affect the contact area between the oscillation circuit and the sensor base. Therefore, it is necessary to select a base of appropriate size. The base size range of the present invention is (3.0-7.0) mm×(2.5-6.0) mm.

[0045] Example 2

[0046] An integrated active QCM humidity sensor and a preparation method thereof, comprising the following steps:

[0047] Step 1: Prepare the QCM device. Prepare a strong oxidizing cleaning solution with a volume ratio of 5:1:1 of deionized water: ammonia water: hydrogen peroxide, place the piezoelectric chip in the strong oxidizing cleaning solution for 30 minutes, then rinse with deionized water, and blow dry with nitrogen. Then, place the piezoelectric chip in anhydrous ethanol for ultrasonic cleaning for 30 minutes, then rinse with deionized water, blow dry with nitrogen, and finally place the piezoelectric chip in a 50°C vacuum drying oven for 1 hour. After drying, metal electrode layers are formed on the upper and lower surfaces of the piezoelectric chip. The metal electrode layer on the lower surface of the piezoelectric chip is the first metal electrode layer, and the metal electrode layer on the upper surface of the piezoelectric chip is the second metal electrode layer, thereby obtaining a QCM device; the QCM device is connected in series with the oscillation circuit wafer through leads to form a loop, and finally packaged and integrated to obtain an active QCM device, and the prepared active QCM device is placed in a dry and clean container for standby use;

[0048] Step 2: Prepare a hygroscopic material solution. Mix a 0.5% PI solution with a 5 mg / mL GO solution in a ratio of 1:1 and perform ultrasonic treatment for 30 minutes to prepare a hygroscopic material solution.

[0049] Step 3: Use a microsyringe to take 0.1 μL of the PI / GO humidity sensitive material solution prepared in step 2, and apply it to the center of the second metal electrode layer of the QCM piezoelectric chip by drop coating. Then place the QCM humidity sensor in a drying oven at 30°C for 2 hours. After drying, a layer of PI / GO sensitive material coating is attached to the surface of the second metal electrode layer of the QCM piezoelectric chip.

[0050] Step 4: After the QCM humidity sensor prepared by the above steps is connected to a universal frequency meter, it is placed in a corresponding humidity generating device. When the hygroscopic material on the QCM piezoelectric chip adsorbs water molecules, the universal frequency meter detects and collects the resonant frequency changes of the QCM humidity sensor in different humidity environments in real time. The experimental test results show that the QCM humidity sensor prepared by mixing a PI solution with a mass fraction of 0.5% and a GO solution with a mass fraction of 5 mg / mL in a ratio of 1:1 has a response sensitivity of 57.46 Hz / % RH and a high linearity (R 2 =0.9957), the response / recovery time is 5 / 6s.

[0051] Example 3

[0052] An integrated active QCM humidity sensor and a preparation method thereof, comprising the following steps:

[0053] Step 1: Prepare the QCM device. Prepare a strong oxidizing cleaning solution with a volume ratio of 5:1:1 of deionized water: ammonia water: hydrogen peroxide, place the piezoelectric chip in the strong oxidizing cleaning solution for 30 minutes, then rinse with deionized water, and blow dry with nitrogen. Then, place the piezoelectric chip in anhydrous ethanol for ultrasonic cleaning for 30 minutes, then rinse with deionized water, blow dry with nitrogen, and finally place the piezoelectric chip in a 50°C vacuum drying oven for 1 hour. After drying, metal electrode layers are formed on the upper and lower surfaces of the piezoelectric chip. The metal electrode layer on the lower surface of the piezoelectric chip is the first metal electrode layer, and the metal electrode layer on the upper surface of the piezoelectric chip is the second metal electrode layer, thereby obtaining a QCM device; the QCM device is connected in series with the oscillation circuit wafer through leads to form a loop, and finally packaged and integrated to obtain an active QCM device, and the prepared active QCM device is placed in a dry and clean container for standby use;

[0054] Step 2: Prepare a hygroscopic material solution. Mix a 9% PI solution and a 0.1 mg / mL GO solution in a ratio of 1:1 and perform ultrasonic treatment for 30 minutes to prepare a hygroscopic material solution.

[0055] Step 3: Use a microsyringe to take 10 μL of the PI / GO humidity sensitive material solution prepared in step 2, and spin coat it on the center of the second metal electrode layer of the QCM piezoelectric chip by spin coating. Then place the QCM humidity sensor in a drying oven at 30°C for 2 hours. After drying, a layer of PI / GO sensitive material coating is attached to the surface of the second metal electrode layer of the QCM piezoelectric chip.

[0056] Step 4: After the QCM humidity sensor prepared by the above steps is connected to a universal frequency meter, it is placed in a corresponding humidity generating device. When the hygroscopic material on the QCM piezoelectric chip adsorbs water molecules, the universal frequency meter detects and collects the resonant frequency changes of the QCM humidity sensor in different humidity environments in real time. The experimental test results show that the QCM humidity sensor prepared by mixing a 9% PI solution with a 0.1 mg / mL GO solution in a ratio of 1:1 has a response sensitivity of 78.01 Hz / % RH and high linearity (R 2 =0.9954), the response / recovery time is 4 / 6s.

[0057] Example 4

[0058] The present invention also provides an integrated active QCM humidity sensor and a preparation method thereof, comprising the following steps:

[0059] Step 1: Prepare the QCM device. Prepare a strong oxidizing cleaning solution with a volume ratio of 5:1:1 of deionized water: ammonia water: hydrogen peroxide, place the piezoelectric chip in the strong oxidizing cleaning solution for 30 minutes, then rinse with deionized water, and blow dry with nitrogen. Then, place the piezoelectric chip in anhydrous ethanol for ultrasonic cleaning for 30 minutes, then rinse with deionized water, blow dry with nitrogen, and finally place the piezoelectric chip in a 50°C vacuum drying oven for 1 hour. After drying, metal electrode layers are formed on the upper and lower surfaces of the piezoelectric chip. The metal electrode layer on the lower surface of the piezoelectric chip is the first metal electrode layer, and the metal electrode layer on the upper surface of the piezoelectric chip is the second metal electrode layer, thereby obtaining a QCM device; the QCM device is connected in series with the oscillation circuit wafer through leads to form a loop, and finally packaged and integrated to obtain an active QCM device, and the prepared active QCM device is placed in a dry and clean container for standby use;

[0060] Step 2: Prepare a humidity-sensitive material solution. Mix 18% PI solution and 5 mg / mL SWCNTS-COOH solution in a ratio of 1:1 and perform ultrasonic treatment for 30 minutes to prepare a humidity-sensitive material solution.

[0061] Step 3: Use a microsyringe to take 5 μL of the PI / SWCNTS-COOH humidity sensitive material solution prepared in step 2, and spray it on the center of the second metal electrode layer of the QCM piezoelectric chip. Then place the QCM humidity sensor in a drying oven at 30°C for 2 hours. After drying, a layer of PI / SWCNTS-COOH sensitive material coating is attached to the surface of the second metal electrode layer of the QCM piezoelectric chip.

[0062] Step 4: After the QCM humidity sensor prepared by the above steps is connected to a universal frequency meter, it is placed in a corresponding humidity generating device. When the hygroscopic material on the QCM piezoelectric chip adsorbs water molecules, the universal frequency meter detects and collects the resonant frequency changes of the QCM humidity sensor in different humidity environments in real time. The experimental test results show that the QCM humidity sensor prepared by mixing a PI solution with a mass fraction of 18% and a SWCNTS-COOH solution with a mass fraction of 5 mg / mL in a ratio of 1:1 has a response sensitivity of 62.56 Hz / % RH and high linearity (R 2 =0.9968), the response / recovery time is 4 / 6s.

[0063] Example 5

[0064] The present invention also provides an integrated active QCM humidity sensor and a preparation method thereof, comprising the following steps:

[0065] Step 1: Prepare the QCM device. Prepare a strong oxidizing cleaning solution with a volume ratio of 5:1:1 of deionized water: ammonia water: hydrogen peroxide, place the piezoelectric chip in the strong oxidizing cleaning solution for 30 minutes, then rinse with deionized water, and blow dry with nitrogen. Then, place the piezoelectric chip in anhydrous ethanol for ultrasonic cleaning for 30 minutes, then rinse with deionized water, blow dry with nitrogen, and finally place the piezoelectric chip in a 50°C vacuum drying oven for 1 hour. After drying, metal electrode layers are formed on the upper and lower surfaces of the piezoelectric chip. The metal electrode layer on the lower surface of the piezoelectric chip is the first metal electrode layer, and the metal electrode layer on the upper surface of the piezoelectric chip is the second metal electrode layer, thereby obtaining a QCM device; the QCM device is connected in series with the oscillation circuit wafer through leads to form a loop, and finally packaged and integrated to obtain an active QCM device, and the prepared active QCM device is placed in a dry and clean container for standby use;

[0066] Step 2: Prepare the hygroscopic material solution. Mix 5 mg / mL GO solution and 8 mg / mL SWCNTS-COOH solution in a ratio of 1:1 and ultrasonicate for 30 minutes to prepare the hygroscopic material solution.

[0067] Step 3: Use a microsyringe to take 5 μL of the GO / SWCNTS-COOH humidity sensitive material solution prepared in step 2, and spin coat it on the center of the second metal electrode layer of the QCM piezoelectric chip by spin coating. Then place the QCM humidity sensor in a drying oven at 30°C for 2 hours. After drying, a layer of GO / SWCNTS-COOH sensitive material coating is attached to the surface of the second metal electrode layer of the QCM piezoelectric chip.

[0068] Step 4: The QCM humidity sensor prepared by the above steps is connected to a universal frequency meter and placed in a corresponding humidity generating device. When the hygroscopic material on the QCM piezoelectric chip adsorbs water molecules, the universal frequency meter detects and collects the resonant frequency changes of the QCM humidity sensor in different humidity environments in real time. The experimental test results show that the QCM humidity sensor prepared by mixing 5 mg / mL GO solution and 8 mg / mL SWCNTS-COOH solution in a ratio of 1:1 has a response sensitivity of 73.43 Hz / % RH and high linearity (R 2 =0.9986), the response / recovery time is 3 / 5s.

[0069] In practical applications, the mixing ratio of the two moisture-sensitive materials in step 2 of the above embodiment is not limited to 1:1; it can also be 1:2 or 2:1.

[0070] like Figure 5 As shown, on the oscilloscope, it can be seen that the output signal of the QCM humidity sensor of the present invention is a regular square wave waveform, that is, the QCM humidity sensor of the present invention can output a stable high-quality oscillation signal.

[0071] In summary of the above embodiments, when the amount of sensitive material on the surface of the second metal electrode layer of the QCM piezoelectric wafer is 0.1-10 μL, higher sensitivity, linearity and faster response / recovery time can be achieved.

[0072] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. An integrated active QCM humidity sensor, characterized in that: It includes a QCM device and an oscillating circuit wafer connected with the QCM device to form a series loop, wherein the QCM device and the oscillating circuit wafer are integrated in one package; The QCM device comprises: a piezoelectric chip, metal electrode layers arranged on the upper and lower surfaces of the piezoelectric chip, and a humidity sensitive layer arranged on the metal electrode layer on the upper surface of the piezoelectric chip.

2. The integrated active QCM humidity sensor according to claim 1, characterized in that: The piezoelectric wafer is a piezoelectric quartz wafer or a piezoelectric ceramic wafer.

3. The integrated active QCM humidity sensor according to claim 2, characterized in that: The package size is 7050, 5032, 3225 or 2520.

4. The integrated active QCM humidity sensor according to claim 3, characterized in that: The fundamental frequency of the piezoelectric chip is 5 to 100 MHz.

5. The integrated active QCM humidity sensor according to claim 4, characterized in that: The material of the humidity sensitive layer is a combination of two of the three single-element materials of polyimide, graphene oxide and carboxylated ultra-high-purity single-walled carbon nanotubes.

6. The integrated active QCM humidity sensor according to claim 5, characterized in that: The oscillating circuit wafer is interconnected with the metal electrode layer through leads.

7. A method for preparing an integrated active QCM humidity sensor, characterized in that: The method comprises the following preparation steps: Step 1: Prepare the QCM device. Prepare a strong oxidizing cleaning solution, place the piezoelectric chip in it for cleaning for 30 minutes, then rinse with deionized water, and blow dry with nitrogen. Then place the piezoelectric chip in anhydrous ethanol for ultrasonic cleaning for 30 minutes, then rinse with deionized water, blow dry with nitrogen, and finally place the piezoelectric chip in a 50°C vacuum drying oven for 1 hour. After drying, metal electrode layers are formed on the upper and lower surfaces of the piezoelectric chip. The metal electrode layer on the lower surface of the piezoelectric chip is the first metal electrode layer, and the metal electrode layer on the upper surface of the piezoelectric chip is the second metal electrode layer, thereby obtaining a QCM device; the QCM device is connected in series with the oscillation circuit wafer through leads to form a loop, and finally packaged and integrated to obtain an active QCM device, and the prepared active QCM device is placed in a dry and clean container for standby use; Step 2: preparing a humidity-sensitive material solution; mixing solutions of the two selected single materials and ultrasonically treating them for 30 minutes to obtain a humidity-sensitive material mixed solution; Step 3: Prepare a QCM sensitive material device; form a film of the humidity sensitive material solution on the second metal electrode layer of the piezoelectric chip of the integrated active QCM device obtained in step 1, and place it in a vacuum drying oven at 30°C for 2 hours. After drying, a layer of humidity sensitive material coating is attached to the surface of the second metal electrode layer of the piezoelectric chip, thereby obtaining an integrated active QCM humidity sensor.

8. The method for preparing an integrated active QCM humidity sensor according to claim 7, characterized in that: The material of the humidity sensitive layer is a combination of two of the three single-element materials of polyimide, graphene oxide and carboxylated ultra-high-purity single-walled carbon nanotubes.

9. The method for preparing an integrated active QCM humidity sensor according to claim 8, characterized in that: In step 3, the amount of sensitive material on the surface of the second metal electrode layer of the QCM piezoelectric wafer is 0.1 to 10 μL.

10. An application method of an integrated active QCM humidity sensor, characterized in that: The integrated active QCM humidity sensor according to any one of claims 1 to 9 is connected to a frequency meter to measure humidity.

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