CN106788318B - Method for manufacturing film bulk acoustic resonator on flexible substrate - Google Patents
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- CN106788318B CN106788318B CN201611029211.3A CN201611029211A CN106788318B CN 106788318 B CN106788318 B CN 106788318B CN 201611029211 A CN201611029211 A CN 201611029211A CN 106788318 B CN106788318 B CN 106788318B
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Images
Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
- H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
- H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/15—Constructional features of resonators consisting of piezoelectric or electrostrictive material
- H03H9/17—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator
- H03H9/171—Constructional features of resonators consisting of piezoelectric or electrostrictive material having a single resonator implemented with thin-film techniques, i.e. of the film bulk acoustic resonator [FBAR] type
- H03H9/172—Means for mounting on a substrate, i.e. means constituting the material interface confining the waves to a volume
- H03H9/174—Membranes
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H3/00—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators
- H03H3/007—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks
- H03H3/02—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks
- H03H2003/023—Apparatus or processes specially adapted for the manufacture of impedance networks, resonating circuits, resonators for the manufacture of electromechanical resonators or networks for the manufacture of piezoelectric or electrostrictive resonators or networks the resonators or networks being of the membrane type
Abstract
The invention discloses a method for manufacturing a film bulk acoustic resonator on a flexible substrate, which comprises the following steps: selecting a silicon substrate, and sequentially coating a water-soluble high-molecular polymer film layer and a polyimide film layer on the silicon substrate; manufacturing a film bulk acoustic resonator above the polyimide film layer; manufacturing a metal column on the top end face of an electrode on the film bulk acoustic resonator; coating a polymethyl methacrylate film layer on the top end face of the electrode on the film bulk acoustic resonator; coating the adhesive of the used flexible substrate on the silicon substrate and curing; putting the whole manufactured structure into water to separate the polyimide film layer from the silicon substrate; removing the metal column by using corrosive liquid; placing the structure in an acetone solution, and dissolving the polymethyl methacrylate film layer to form an air gap; and removing the polyimide film layer below the film bulk acoustic resonator. The method for manufacturing the film bulk acoustic resonator on the flexible substrate can improve the resonance performance of the device and ensure the processing quality of the device.
Description
Technical Field
The invention belongs to the technical field of micro electro mechanical systems, and particularly relates to a method for manufacturing a film bulk acoustic resonator on a flexible substrate.
Background
Film bulk acoustic resonators are a new type of mems device that has been developed in recent years. The basic structure of the film bulk acoustic resonator is composed of a piezoelectric film and electrodes, and the working frequency reaches several gigahertz. The working principle of the device is that the piezoelectric effect of a piezoelectric film in the device is utilized to convert input electric energy into mechanical energy, and standing wave resonance is formed in the piezoelectric film in a sound wave mode. The film bulk acoustic resonator has the advantages of lower insertion loss, larger power capacity, higher Q value, integration and miniaturization. Thus, the thin film bulk acoustic resonator exhibits a great performance advantage as compared with the conventional surface acoustic wave resonators and ceramic resonators. At present, the device is applied to the construction of a GHz band radio frequency filter and a high-sensitivity biochemical sensor. The process for manufacturing the film bulk acoustic resonator is based on silicon-based semiconductor manufacturing technology, and therefore, at present, the devices are mainly manufactured and applied on a silicon substrate.
On the other hand, the development of flexible thin film electronics in recent years has urgently required the development of a technique for manufacturing various functional electronic devices on a flexible substrate. The film bulk acoustic resonator is used as a resonance device with a tiny size and a high Q value, can be integrated in a high-speed flexible film circuit to serve as a core function device of a high-sensitivity sensor of a high-frequency oscillator, and has huge potential application in wearable electronic systems. Currently, there are two main methods for manufacturing a film bulk acoustic resonator on a flexible substrate.
One method is disclosed in Chinese patent with publication number CN 103929149A, a flexible piezoelectric film bulk acoustic resonator and a preparation method thereof. The method directly deposits a bottom electrode, a piezoelectric film and a top electrode layer on a flexible substrate to form the film bulk acoustic resonator.
Another type of method is disclosed in 2015 3, volume 5, page 9510, in journal SCIENTIFIC REPORTS, in the paper "Film bulk acidic detectors integrated on the acquisition metadata utilization elementary support layer". The method mainly comprises the following steps: (1) etching a groove on a silicon substrate; (2) directly coating polyimide on a silicon substrate; (3) manufacturing a film bulk acoustic resonator on the surface of polyimide; (4) and stripping the device on the silicon substrate.
The main disadvantage of the above solution is that the manufactured film bulk acoustic resonators all have one side in direct contact with the flexible substrate. Due to the viscous damping property of the flexible material to mechanical vibration, bulk acoustic waves in the piezoelectric film are severely lost in the flexible substrate, and the performance of the device is attenuated. In addition, in the first method, the hardness of the flexible substrate is poor, and the processing precision and the film quality of the device manufactured directly on the flexible substrate are affected. For the second method, the fabrication of the device after coating polyimide on the silicon substrate can solve the problems of the processing accuracy and the film quality, but the kinds of flexible substrates that can be used are limited. For example, commonly used dimethyl siloxane (PDMS), which has good biocompatibility, has a large difference in thermal expansion coefficient from the deposited material, and easily causes excessive residual stress of the thin film. The process of peeling the device from the silicon substrate is also prone to damage to portions of the device.
It will thus be seen that the prior art is susceptible to further improvements and enhancements.
Disclosure of Invention
In order to avoid the defects of the prior art, the invention provides the method for manufacturing the film bulk acoustic resonator on the flexible substrate, which can improve the resonance performance of the device and ensure the processing quality of the device.
The technical scheme adopted by the invention is as follows:
a method of fabricating a thin film bulk acoustic resonator on a flexible substrate, comprising the steps of:
step 1, selecting a silicon substrate, and sequentially coating a water-soluble high-molecular polymer film layer and a polyimide film layer on the silicon substrate from bottom to top;
step 3, manufacturing a metal column on the top end face of the upper electrode of the film bulk acoustic resonator;
step 5, coating the adhesive of the used flexible substrate on the silicon substrate and curing to enable the film bulk acoustic resonator, the metal column and the polymethyl methacrylate film layer to be integrally arranged on the flexible substrate;
step 7, removing the metal column by using corrosive liquid;
and 9, removing the polyimide film layer below the film bulk acoustic resonator.
In the step 1, the water-soluble high molecular polymer film layer comprises polyvinyl alcohol, polyethylene glycol, polyacrylamide or polyvinylpyrrolidone, and the thickness of the water-soluble high molecular polymer film layer is 1 micron to 5 microns.
In the step 1, the thickness of the polyimide film layer is 0.5 to 2 micrometers.
In the step 2, two upper electrodes are arranged in parallel.
In the step 2, the film bulk acoustic resonator further comprises a lower electrode, and the upper electrode, the piezoelectric film and the lower electrode are sequentially stacked from top to bottom.
In the step 3, the material of the metal column is different from the material of the upper electrode of the film bulk acoustic resonator, the cross-sectional area of the metal column is smaller than one tenth of the cross-sectional area of the upper electrode of the film bulk acoustic resonator, and the top end of the metal column is positioned outside the flexible substrate.
In the step 4, the cross sectional area of the polymethyl methacrylate film layer is the same as that of the upper electrode of the film bulk acoustic resonator, and the thickness of the polymethyl methacrylate film layer is 500 nanometers to 2 micrometers.
In step 5, the flexible substrate comprises dimethyl siloxane, polyethylene terephthalate or polyimide.
In the step 6, the temperature of the water is 40-70 ℃.
In the step 7, the selected corrosive liquid does not corrode the flexible substrate and the upper electrode of the film bulk acoustic resonator; in the step 8, when the polymethyl methacrylate film layer is dissolved in the acetone solution, the dissolution can be accelerated by using auxiliary means, wherein the auxiliary means comprises stirring and/or ultrasound.
Due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. the film bulk acoustic resonator manufactured by the method is released from the silicon substrate to form a suspended structure, and the resonance performance of the device is improved.
2. The invention adopts the process sequence of firstly manufacturing the device and then manufacturing the substrate, and the device processing is not influenced by the flexible substrate material, thereby ensuring the processing quality of the device and simultaneously using the prior various flexible substrate materials.
3. By using the method of the invention, the silicon wafer used in the device manufacturing process is not damaged and can be reused after being cleaned, thereby reducing the manufacturing cost.
4. By using the method of the invention, the sacrificial layer is used in the separation process of the device from the silicon substrate, and the polyimide layer is used as protection, so that the structure of the device is not damaged.
Drawings
Figure 1 shows a typical thin film bulk acoustic resonator structure made using the present invention.
Figure 2 illustrates another exemplary thin film bulk acoustic resonator structure made using the present invention.
Fig. 3 shows the main steps of fabricating a thin film bulk acoustic resonator on a Polydimethylsiloxane (PDMS) flexible substrate using the method of the present invention.
Figure 4 illustrates a top view of a thin film bulk acoustic resonator fabricated in an embodiment of the present invention.
Fig. 5 shows the return loss test results of the thin film bulk acoustic resonator manufactured by using the embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following drawings and specific examples, but the present invention is not limited to these examples.
The invention can be applied to manufacturing film bulk acoustic resonators with various structures, and has no requirements on the material, the structure and the electrode shape of the film bulk acoustic resonator. Fig. 1 and 2 show two typical film bulk acoustic resonator structures fabricated using the present invention, respectively. The film bulk acoustic resonator shown in fig. 1 has a sandwich structure including a piezoelectric film 101, and an upper electrode 102 and a lower electrode 103 disposed on both sides of the piezoelectric film 101. The film bulk acoustic resonator shown in fig. 2 is a transverse electric field excitation structure composed of a piezoelectric film 101 and upper electrodes 102 parallel to each other. The film bulk acoustic resonator with the two structures can be manufactured by adopting the invention. The shape of the upper electrode and the lower electrode can be square, circular, annular, interdigitated or other irregular shapes, etc. The piezoelectric film 101 may be any piezoelectric material that has been applied to a film bulk acoustic resonator at present, such as zinc oxide, aluminum nitride, lead zirconate titanate, or the like. The flexible substrate suitable for the present invention mainly includes substrate materials commonly used in the flexible electronics industry, such as dimethyl siloxane (PDMS), polyethylene terephthalate (PET), or Polyimide (PI).
The method of using the present invention will be described below by taking as an example the main steps of fabricating a thin film bulk acoustic resonator on a flexible substrate of Polydimethylsiloxane (PDMS) as shown in fig. 3. In this embodiment, the film bulk acoustic resonator to be manufactured has a sandwich structure, in which the upper electrode 102 and the lower electrode 103 are made of molybdenum and have a thickness of 150 nm. The piezoelectric film is made of aluminum nitride and has a thickness of 1 micron. The thickness of the flexible substrate was 50 microns.
The steps for manufacturing the film bulk acoustic resonator are as follows:
step 1, coating a water-soluble high molecular polymer film layer and a polyimide film layer on a silicon substrate from bottom to top in sequence.
The water-soluble high molecular polymer film layer is used as a sacrificial layer for stripping the device from the silicon substrate, and the polyimide film layer above the water-soluble high molecular polymer film layer plays a role in protecting the water-soluble high molecular polymer film layer in the subsequent process. In specific implementation, the water-soluble polymer film layer may be one of polyvinyl alcohol (PVA), polyethylene glycol (PEG), Polyacrylamide (PAM), and polyvinylpyrrolidone (PVP), and the thickness of the water-soluble polymer film layer is 1 micrometer, 5 micrometers, or any value within a range from 1 micrometer to 5 micrometers. The thickness of the polyimide film layer is 0.5 microns, 2 microns, or any value in the range of 0.5 microns to 2 microns. The method for coating the water-soluble high molecular polymer film layer and the polyimide film layer can adopt common organic film preparation methods such as spin coating, evaporation coating or screen printing. In order to protect the water solubility of the water-soluble polymer film, the polyimide film cannot undergo imidization, and the heat treatment temperature is generally less than 150 ℃.
In this example, a 2 μm polyvinyl alcohol film layer was prepared as a water-soluble polymer film layer and a 1 μm polyimide film layer by a spin coating method. The process for spin coating the polyvinyl alcohol film layer comprises the following steps: a40% polyvinyl alcohol aqueous solution is adopted, spinning is carried out at 3000 rpm for 30 seconds, and hot plate treatment is carried out at 100 ℃ for 5 minutes. The process for spin coating the polyimide film layer comprises the following steps: spin coating was performed using photosensitive polyimide glue at 5000 rpm for 30 seconds, and hot plate treatment was performed at 130 ℃ for 5 minutes. The polyimide film was then irradiated with ultraviolet light at a power of 30 mw/cm for 30 seconds, so that it was insoluble in the developing solution used in the subsequent steps.
And 2, manufacturing a film bulk acoustic resonator structure above the polyimide film layer.
In specific implementation, the film bulk acoustic resonator structure can be manufactured by a general semiconductor process method, and the main process comprises sputtering or evaporating an electrode, and patterning the electrode by adopting a photoetching or Lift-off process (stripping process); preparing a piezoelectric film by sputtering and patterning the piezoelectric film by adopting a dry method or a wet method.
In this embodiment, the upper electrode and the lower electrode of the film bulk acoustic resonator are both manufactured by a dc sputtering method, and patterning is performed by a Lift-off process (Lift-off process). The piezoelectric film is manufactured by adopting a radio frequency reactive sputtering method, an aluminum target is used, and the sputtering atmosphere is mixed gas of argon and nitrogen. The aluminum nitride piezoelectric film is patterned by adopting a chlorine-based gas reactive ion etching method.
Step 3, manufacturing a metal column on the top end surface of the upper electrode of the film bulk acoustic resonator;
the metal posts will form through holes for releasing the film bulk acoustic resonator structure in subsequent steps. In specific implementation, in order to ensure that the upper electrode of the film bulk acoustic resonator is not damaged in the subsequent step of corroding the metal column, the material of the metal column is different from that of the upper electrode of the film bulk acoustic resonator. Meanwhile, in order to ensure that the manufactured device has enough mechanical strength, the through hole generated after corrosion cannot be too large, and the cross section area of the metal column is required to be less than one tenth of that of the electrode on the film bulk acoustic resonator. In order to ensure that the corrosive liquid can smoothly enter from the outside of the flexible substrate, the top end surface of the metal column is positioned at the outer side of the flexible substrate. Depending on the different sizes and heights required, the metal posts can be fabricated by either a thick-paste Lift-off process (Lift-off process) or by micro-electroforming.
In this embodiment, the metal pillar is made of copper and has a height of 100 μm, and is fabricated by a micro-electroforming method, which includes: firstly, sputtering a copper seed layer on the surface of an upper electrode of the film bulk acoustic resonator, wherein the thickness of the copper seed layer is 100 nanometers; coating 100-micron positive photoresist and patterning to expose the metal column region; electroplating in a standard copper electroplating solution; and removing the photoresist and drying.
the polymethyl methacrylate film layer is used as a sacrificial layer released by the film bulk acoustic resonator structure in the subsequent step. In specific implementation, the cross-sectional area of the polymethyl methacrylate film layer is the same as that of the upper electrode of the film bulk acoustic resonator. In order to ensure that the air gap has enough height after the device is released and the mechanical strength of the device, the thickness of the polymethyl methacrylate film layer is 500 nanometers, 2 micrometers or any value in the range of 500 nanometers to 2 micrometers. The method for coating the film layer can adopt common organic film preparation methods such as spin coating, evaporation coating or screen printing.
In this example, the film was prepared by spin coating with a photosensitive polymethyl methacrylate adhesive. The specific process comprises the following steps: spin coating at 3000 rpm, hotplate treatment at 120 ℃ for 3 min, and then photolithography using uv light at a power of 30 mw/cm.
Step 5, coating the adhesive of the used flexible substrate on the silicon substrate and curing;
in specific embodiments, the flexible substrate can be manufactured by a common organic film preparation method such as spin coating, evaporation, or screen printing. To ensure that the solubility of the organic film layers applied in the previous step does not change significantly, the curing temperature of the flexible substrate should generally be less than 150 degrees celsius.
In this example, a flexible substrate was prepared by a two-step spin coating method using a dimethyl siloxane (PDMS) paste containing a curing agent. The specific process comprises the following steps: the first step is spin coating at 300 r/min for 10 s; secondly, spin coating at 1000 rpm for 30 seconds; hotplate treatment at 80 ℃ for 15 minutes.
in this step, the water-soluble high molecular polymer film layer below the film bulk acoustic resonator is dissolved in water, so that the device is separated from the silicon substrate. In specific implementation, in order to accelerate the separation process, hot water with a temperature of 40 ℃, 50 ℃, 70 ℃ or any value in the range of 40 ℃ to 70 ℃ can be used for stripping according to the size of the silicon wafer and the size of the device unit. To prevent post-peel adhesion, the separation can be performed using a roll method or a decal method.
In this example, the silicon substrate is a 4-inch silicon wafer, the device unit size is 300 micrometers by 300 micrometers, and the separation is performed using hot water at 60 degrees celsius with a roller.
Step 7, removing the metal column by using corrosive liquid;
in order to ensure that other parts of the device are not damaged, the used corrosive liquid cannot generate corrosive action on the flexible substrate and the electrodes on the film bulk acoustic resonator. In specific implementation, corresponding etching solution is selected according to the metal column material, and wet etching is carried out.
In this example, a mixed solution of 10% ferric chloride and 1% hydrochloric acid was used to corrode the copper metal column. After the etching is completed, through holes appear through the flexible substrate.
in specific implementation, auxiliary means such as stirring and ultrasound can be used to accelerate the dissolution process.
After the step is completed, the film bulk acoustic resonator is released from the silicon substrate to form a suspended structure.
Step 9, removing the polyimide film layer below the film bulk acoustic resonator;
in specific implementation, in order to ensure the structural integrity of the device, oxygen plasma is generally used to etch the polyimide film layer. In this embodiment, the etching process is: the oxygen pressure was 1 pascal, the power was 3 watts per square centimeter, and the etching time was 5 minutes.
Fig. 4 shows a top view of a thin film bulk acoustic resonator fabricated in an embodiment of the present invention. Fig. 5 shows the return loss test results of the thin film bulk acoustic resonator manufactured using the embodiment of the present invention. As can be seen from fig. 5, the thin film bulk acoustic resonator manufactured on a flexible substrate made of Polydimethylsiloxane (PDMS) by the method of the present invention can achieve good operation, and when the flexible substrate is not bent, the resonant frequency is 2.453 ghz, and the return loss is 5.774 dB. After the flexible substrate is bent, the resonant frequency is 2.429 gigahertz and the return loss is 5.187.
Parts which are not described in the invention can be realized by adopting or referring to the prior art.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (9)
1. A method of fabricating a thin film bulk acoustic resonator on a flexible substrate, comprising the steps of:
step 1, selecting a silicon substrate, and sequentially coating a water-soluble high-molecular polymer film layer and a polyimide film layer on the silicon substrate from bottom to top;
step 2, manufacturing a film bulk acoustic resonator above the polyimide film layer, wherein the film bulk acoustic resonator comprises an upper electrode and a piezoelectric film;
step 3, manufacturing a metal column on the top end face of the upper electrode of the film bulk acoustic resonator, wherein in the step 3, the material of the metal column is different from that of the upper electrode of the film bulk acoustic resonator, the cross section area of the metal column is smaller than one tenth of that of the upper electrode of the film bulk acoustic resonator, and the top end of the metal column is positioned outside the flexible substrate;
step 4, coating a polymethyl methacrylate film layer on the top end face of the upper electrode of the film bulk acoustic resonator;
step 5, coating the adhesive of the used flexible substrate on the silicon substrate and curing to enable the film bulk acoustic resonator, the metal column and the polymethyl methacrylate film layer to be integrally arranged on the flexible substrate;
step 6, putting the manufactured whole structure into water, and separating the polyimide film layer, the film bulk acoustic resonator, the metal column, the polymethyl methacrylate film layer and the flexible substrate which are positioned above the polyimide film layer from the silicon substrate;
step 7, removing the metal column by using corrosive liquid;
step 8, integrally placing the polyimide film layer, the film bulk acoustic resonator, the polymethyl methacrylate film layer and the flexible substrate which are positioned above the polyimide film layer into an acetone solution, and dissolving the polymethyl methacrylate film layer to form an air gap;
and 9, removing the polyimide film layer below the film bulk acoustic resonator.
2. The method for manufacturing a thin film bulk acoustic resonator on a flexible substrate according to claim 1, wherein in the step 1, the water-soluble high polymer film layer comprises polyvinyl alcohol, polyethylene glycol, polyacrylamide or polyvinylpyrrolidone, and the thickness of the water-soluble high polymer film layer is 1 to 5 μm.
3. The method for manufacturing a thin film bulk acoustic resonator on a flexible substrate according to claim 1, wherein in the step 1, the thickness of the polyimide film layer is 0.5 to 2 microns.
4. The method for manufacturing a film bulk acoustic resonator on a flexible substrate according to claim 1, wherein in the step 2, the number of the upper electrodes is two, and the two upper electrodes are placed in parallel.
5. The method for manufacturing a thin film bulk acoustic resonator on a flexible substrate according to claim 1, wherein in the step 2, the thin film bulk acoustic resonator further comprises a lower electrode, and the upper electrode, the piezoelectric film and the lower electrode are sequentially stacked from top to bottom.
6. The method for manufacturing a thin film bulk acoustic resonator on a flexible substrate according to claim 1, wherein the cross-sectional area of the polymethylmethacrylate film layer in the step 4 is the same as the cross-sectional area of the upper electrode of the thin film bulk acoustic resonator, and the thickness of the polymethylmethacrylate film layer is 500 nm to 2 μm.
7. The method of claim 1, wherein the flexible substrate in step 5 comprises dimethylsiloxane, polyethylene terephthalate, or polyimide.
8. The method for manufacturing a thin film bulk acoustic resonator on a flexible substrate according to claim 1, wherein the temperature of the water in the step 6 is 40 ℃ to 70 ℃.
9. The method for manufacturing the film bulk acoustic resonator on the flexible substrate according to claim 1, wherein in the step 7, the selected etching solution does not corrode the flexible substrate and the upper electrode of the film bulk acoustic resonator; in the step 8, when the polymethyl methacrylate film layer is dissolved in the acetone solution, the dissolution can be accelerated by using auxiliary means, wherein the auxiliary means comprises stirring and/or ultrasound.
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| CN109450379A (en) * | 2018-09-21 | 2019-03-08 | 天津大学 | Flexible radio frequency oscillator |
| CN109257026A (en) * | 2018-09-30 | 2019-01-22 | 天津大学 | Flexible substrates thin film bulk acoustic wave resonator and forming method thereof |
| CN109474253A (en) * | 2018-09-30 | 2019-03-15 | 天津大学 | A kind of flexible substrates thin film bulk acoustic wave resonator and forming method |
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