TWI420717B - Method for making surface acoustic wave sensor - Google Patents

Description

Surface acoustic wave sensor manufacturing method

The invention relates to a method for fabricating a surface acoustic wave sensor.

With the improvement of living standards, people pay more and more attention to the management of environmental quality, and various kinds of sensor products have begun to respond. Among them, surface acoustic wave sensors are high in sensitivity, high in reliability, light in size and low in cost. The price and other advantages have been developed into a large number of sensor components (see P3K-3 Surface Acoustic Waves in an Infinite Plate of Functionally Graded Materials, Ultrasonics Symposium, 2006. IEEE, 2-6 Oct. 2006, Page (s ): 2242-2245). For example: gas sensors for detecting airborne particles, liquid sensors for detecting aqueous solutions, pressures for measuring environmental factors, temperature, humidity sensors, and various types of biosensors for use on living organisms Wait. The sensors are combined with a specific sensing film to further subdivide the function and the object to be tested.

The surface acoustic wave sensor comprises a piezoelectric substrate, an input interdigital transducer (IDT) disposed on the surface of the piezoelectric substrate, an output interdigital electrode, and an electrode disposed on the surface of the piezoelectric substrate and located at the input interdigital electrode The sensing film between the interdigital electrodes is output, and the sensing film is used to adsorb a trace amount of the molecule to be tested in a gas or a liquid. When an AC signal is applied to the input interdigital electrode, the piezoelectric substrate is strained by the inverse piezoelectric effect, and the electric energy is converted into acoustic energy, thereby generating surface acoustic waves, via the piezoelectric substrate. The piezoelectric material transmits acoustic energy to the output interdigital electrode, and then converts the acoustic signal into an electrical signal output through a positive piezoelectric effect to provide an external instrument to accurately interpret the change of the signal on the surface of the sensing film. When the surface acoustic wave propagates to the piezoelectric substrate, the adsorption of the sensing film causes a slight change in the quality of the sensing film, and the sound wave energy of the sensing film is absorbed by the adsorption of the specific gas due to the influence of the mass loading effect. It will change its original propagation characteristics, and cause a certain amount of drift in the phase velocity and attenuation of the acoustic wave. Detecting the drift signal of these resonant frequencies can quantitatively analyze the concentration of the molecule to be tested adsorbed on the surface of the piezoelectric material. .

The sensing film is usually formed on the surface of the piezoelectric substrate by Chemical Vapor Deposition (CVD). However, this method is liable to cause unevenness in the surface of the sensing film and a small contact area with the object to be tested.

In view of the above, it is necessary to provide a method of fabricating a surface acoustic wave sensor that senses a uniform surface of the film and has a large contact area with the object to be tested.

A surface acoustic wave sensor manufacturing method comprises the steps of: plating a sensing material layer on a surface of a piezoelectric substrate; forming a predetermined pattern on the surface of the sensing material layer by using a nano imprinting method; and plating the sensing material After the step of layer or after preparing a predetermined pattern on the surface of the sensing material layer, an input interdigital electrode and an output interdigital electrode are formed on opposite sides of the sensing material layer on the surface of the piezoelectric substrate to obtain a surface acoustic wave sensing. Device.

Compared with the prior art, the surface acoustic wave sensor is manufactured by using a nanoimprint method to achieve a predetermined pattern on the surface of the sensing material layer with an accuracy of nanometer level, thereby making the surface of the sensing film uniform; The dimensional accuracy of the pattern formed on the surface of the sensing film is nanometer, which can make a large contact area with the substance to be tested, and improve the sensing efficiency and precision. In addition, the process of forming the sensing film by using the nano imprint method is simple, Suitable for mass production.

20‧‧‧Piezo substrate

22‧‧‧Input finger electrode

24‧‧‧ Output finger electrode

26‧‧‧Sensor material layer

28‧‧‧ Polymer layer

30‧‧‧Men

302, 462‧‧‧ substrates

304, 464‧‧ ‧ raised

32‧‧‧Sensing film

40‧‧‧Surface Acoustic Sensor

42‧‧‧Organic transition layer

44‧‧‧ Imprint

46‧‧‧Men

48‧‧‧UV beam

1 is a flow chart of a method for fabricating a surface acoustic wave sensor according to an embodiment of the present invention.

2 is a schematic perspective view of a piezoelectric substrate having an interdigital electrode formed on its surface.

3 is a schematic perspective view of a piezoelectric substrate having an interdigital electrode and a sensing material layer formed on its surface.

4 is a schematic view showing the process of the method for forming a sensing film in the manufacturing method of FIG. 1.

Figure 5 is a perspective view of a surface acoustic wave sensor fabricated by the method of Figure 1.

Fig. 6 is a schematic view showing the process of forming another method of sensing a film in the manufacturing method of Fig. 1.

The invention will now be described in further detail with reference to the accompanying drawings.

Referring to FIG. 1 , an embodiment of the present invention provides a method for fabricating a surface acoustic wave sensor, which includes the following steps: Step 102: forming an input interdigital electrode and an output interdigital electrode on a surface of a piezoelectric substrate; Step 104: The surface of the piezoelectric substrate between the input interdigital electrode and the output interdigital electrode is plated with a sensing material layer; Step 106: using a nanoimprint method to form a predetermined pattern on the surface of the sensing material layer to form a sensing film, A surface acoustic wave sensor.

Referring to FIG. 2 to FIG. 5, the method for fabricating the surface acoustic wave sensor is as follows:

Referring to FIG. 2, in step 102, a piezoelectric substrate 20 is provided. The piezoelectric substrate 20 can be a piezoelectric substrate or a piezoelectric film layer formed on the surface of the substrate. In this embodiment, the pressure is The electrical substrate 20 is a piezoelectric substrate. The piezoelectric substrate 20 has a rectangular parallelepiped shape and is made of a piezoelectric material, which may be, but not limited to, the following types: single crystals such as quartz, lithium niobate (LiNbO3), lithium niobate. (LiTaO3), etc.; thin films such as aluminum nitride (AlN), zinc oxide (ZnO); ceramics such as barium titanate, lead zirconate titanate (PZT), etc.; polymers such as polyvinylidene fluoride ( Polyvinylidene Fluoride, PVDF).

An input interdigital electrode 22 and an output interdigital electrode 24 are formed on the surface of the piezoelectric substrate 20. The input interdigital electrode 22 and the output interdigital electrode 24 can be fabricated on the piezoelectric substrate by a method such as photolithography or microelectromechanical processing. The surface of the material 20.

Referring to FIG. 3, in step 104, a surface of the piezoelectric substrate 20 between the input interdigital electrode 22 and the output interdigital electrode 24 is plated with a sensing material layer 26, which may be, but is not limited to, Sputtering is formed on the surface of the piezoelectric substrate 20. The sputtering method includes glow discharge, magnetron sputtering, radio frequency sputtering, reactive sputtering, cyclotron sputtering, and the like.

The material selection of the sensing material layer 26 depends on the substance to be sensed. For example, zinc oxide (ZnO) may be used for sensing ultraviolet light, zinc oxide or palladium (Pd) may be used for sensing hydrogen gas, and carbon monoxide may be used for sensing carbon monoxide. Tin dioxide (SnO2).

Referring to FIG. 4, in step 106, a predetermined pattern is formed on the surface of the sensing material layer 26 by using a nano imprinting method to form a sensing film. In this embodiment, a hot pressing type nano imprinting method is adopted, and heat is applied. The process of forming a predetermined pattern on the surface of the sensing material layer 26 by the pressure nanoimprint method is as follows:

Referring to FIG. 4(a) and FIG. 4(b), a layer of high score is applied on the surface of the sensing material layer 26. The sub-material layer 28 heats the polymer material layer 28 at a heating temperature higher than the glass transition temperature of the polymer material layer 28 to soften the polymer material layer 28. The heating temperature of this step should not be too high, otherwise the molding cycle will be extended. In this embodiment, the material of the polymer material layer 28 is polymethyl methacrylate (PMMA), and the glass transition temperature is 104 ° C. The heating temperature in this step may be 105 ° C to 110 ° C.

Referring to FIG. 4(c), a nanoimprint mold core 30 is provided. The nanoimprint mold core 30 includes a substrate 302 and a plurality of protrusions 304. The plurality of protrusions 304 are disposed on the surface of the substrate 302. And formed integrally with the substrate 302. The plurality of protrusions 304 form a predetermined pattern for embossing the polymer material layer 28 to form a pattern corresponding to the plurality of protrusions 304 on the surface of the polymer material layer 28. In the embodiment, the protrusions 304 are cylindrical. shape. The material of the mold core 30 generally has the following properties: high hardness, large compressive strength, and large tensile strength, so that deformation and wear of the mold core 30 can be reduced; high thermal conductivity and low thermal expansion coefficient, so that the mold core 30 during heating The thermal deformation is small. The mold core 30 is usually made of a material such as tantalum, niobium oxide, tantalum nitride or diamond. The size of the protrusion 304 can reach 10 nm.

The plurality of protrusions 304 of the mold core 30 are aligned with the polymer material layer 28, and a pressure is applied to the polymer material layer 28 so that the polymer material layer 28 fills the cavity between the plurality of protrusions 304.

After the molding process is completed, the polymer material layer 28 is cooled below its glass transition temperature to cure the patterned polymer material layer 28 to provide sufficient mechanical strength.

The mold core 30 is removed from the mold, and the pattern of the plurality of protrusions 304 is formed on the polymer material layer 28.

Referring to FIG. 4(d), after the above steps, those portions of the original polymer material layer 28 which are pressed to be recessed become a very thin residual polymer material layer, which is anisotropic reactive ion etching method. The residual polymer material layer is removed.

Referring to FIG. 4(e), the pattern formed by the polymer material layer 28 is transferred to the sensing material layer 26. In this embodiment, the transfer method is an etch method, that is, the patterned polymer material layer 28 formed in the above step is used as a mask, and the sensing material layer 26 is selectively etched, thereby The pattern formed by the bumps is transferred to the layer of sensing material 26. It can be understood that this step can also use a strip process to transfer the pattern, and is not limited to the embodiment.

Referring to FIG. 4(f) and FIG. 5, the polymer material layer 28 remaining on the surface of the sensing material layer 26 is removed to obtain a patterned sensing film 32. So far, a surface acoustic wave sensor 40 is completed. In this embodiment, the pattern of the sensing film 32 formed is an array of circular holes having a radial cross-sectional size that is the same as the radial cross-section of the protrusions 304. It can be understood that the pattern can also be set according to actual needs.

In addition, the steps of forming the input interdigital electrode 22 and the output interdigital electrode 24 may be interchanged with the step of forming the sensing film 32, and are not limited to the embodiment.

Please refer to FIG. 6 , which illustrates another embodiment of forming a predetermined pattern on the surface of the sensing material layer 26 according to an embodiment of the present invention. The embodiment adopts an ultraviolet ray imprinting method, and the specific process thereof is as follows:

Referring to FIG. 6(a) and FIG. 6(b), an organic transition layer 42 is coated on the surface of the sensing material layer 26. The thickness of the organic transition layer 42 is thin, and the organic transition layer 42 is made of an organic material, such as PMMA. The organic transition layer 42 is typically applied to the surface of the sensing material layer 26 by spin coating.

Referring to FIG. 6(c), a surface of the organic transition layer 42 is coated with a laminate layer 44, which is generally a polymer material or an organic solution having good fluidity at room temperature, and the like. The embossed layer 44 has ultraviolet curing properties such as an ultraviolet curable organic hydrazine solution.

Referring to FIG. 6(d) and FIG. 6(e), a nanoimprint mold core 46 is provided. The nanoimprint mold core 46 includes a substrate 462 and a plurality of protrusions 464. The plurality of protrusions 464 are disposed on The surface of the substrate 462 is integrally formed with the substrate 462. The plurality of protrusions 464 form a predetermined pattern, and a cavity is formed between the plurality of protrusions 464. The mold core 46 can be made of quartz glass or polydimethyl siloxane, and the size of the protrusion 464 can reach 20 nm.

The plurality of protrusions 464 of the mold core 46 are aligned with the embossed layer 44 and moved toward the embossed layer 44 such that the material of the embossed layer 44 fills the cavity between the plurality of protrusions 464.

The embossed layer 44 is irradiated with an ultraviolet beam 48 to cure the embossed layer 44.

The mold core 30 is removed from the mold, and the pattern of the plurality of protrusions 464 is formed on the embossed layer 44.

Referring to FIG. 6(f) and FIG. 6(g), the material of the recessed portion of the imprint layer 44 and the organic transition layer 42 corresponding to the recessed portion are removed by halogen etching, reactive ion etching or the like.

Referring to FIG. 6(h), the pattern formed by the organic transition layer 42 is transferred to the sensing material layer 26. In this embodiment, the transfer method is an etching method, that is, the patterned imprint layer 44 and the organic transition layer 42 formed in the above step are used as a mask, and the sensing material layer 26 is selectively etched, thereby The pattern formed by the protrusions is transferred to the sensing material layer 26. It can be understood that this step can also use the stripping technology to transfer the pattern, which is not limited to This embodiment.

Referring to FIG. 6(i), the embossed layer 44 and the organic transition layer 42 remaining on the surface of the sensing material layer 26 are removed to obtain a patterned sensing film 32 as shown in FIG.

It can be understood that the method of forming the sensing film 32 can also adopt other nano imprinting techniques, and is not limited to the embodiment.

Compared with the prior art, the present embodiment uses the nano imprint method to fabricate the sensing film 32. Since the surface of the sensing film 32 forms a predetermined pattern of nanometer dimensional accuracy, the surface of the sensing film 32 can be made uniform, and the sense is felt. The surface of the measuring film 32 is formed with a nano-level precision pattern, which can make a large contact area with the substance to be tested, and improve the sensing efficiency and precision. In addition, the use of the nanoimprint method to form the sensing film is simple and suitable for mass production.

In summary, the present invention has indeed met the requirements of the invention patent, and has filed a patent application according to law. However, the above description is only a preferred embodiment of the present invention, and it is not possible to limit the scope of the patent application of the present invention. Equivalent modifications or variations made by persons skilled in the art in light of the spirit of the invention are intended to be included within the scope of the following claims.

Claims (6)

A method for fabricating a surface acoustic wave sensor, comprising the steps of: plating a layer of a sensing material on a surface of a piezoelectric substrate; coating a layer of a polymer material on the surface of the sensing material layer and heating to a temperature of 105 ° C to 110 ° C Providing a nanoimprinting mold core, the nanoimprinting mold core comprising a substrate and a plurality of nanometer-sized protrusions disposed on the surface of the substrate, the plurality of protrusions constituting the predetermined pattern, the plurality of protrusions Forming a cavity therebetween; aligning the plurality of protrusions of the mold core with the polymer material layer, and applying pressure to the polymer material layer, so that the polymer material layer of the polymer material layer is filled between the plurality of protrusions a cavity; cooling the polymer material layer; demolding; removing the polymer material remaining in the recessed portion of the polymer material layer; transferring a predetermined pattern formed by the polymer material layer to the sensing material layer Removing the polymer material layer remaining on the surface of the sensing material layer to obtain a sensing film having a predetermined pattern; before the step of plating the sensing material layer or after forming a predetermined pattern on the surface of the sensing material layer, Substrate The measured surface located on opposite sides of the sensing material layer is formed of an input interdigital transducer and an output interdigital electrode, to obtain a surface acoustic wave sensor. A method for fabricating a surface acoustic wave sensor according to claim 1, wherein The sensing material layer is zinc oxide, palladium or tin dioxide. The method for fabricating a surface acoustic wave sensor according to claim 1, wherein the material of the polymer material layer is polymethyl methacrylate. The method for fabricating a surface acoustic wave sensor according to claim 1, wherein the method of transferring the predetermined pattern formed by the polymer material layer to the sensing material layer is an etching method or a stripping method. A surface acoustic wave sensor manufacturing method comprises the steps of: plating a sensing material layer on a surface of a piezoelectric substrate; coating an organic transition layer on the surface of the sensing material layer; coating the surface of the organic transition layer a laminate printing layer, wherein the embossing layer is a UV-curable organic cerium solution; providing a nano embossing mold core, the nano embossing mold core comprising a substrate and a plurality of protrusions disposed on the surface of the substrate, the plurality Forming the predetermined pattern, a cavity is formed between the plurality of protrusions; the plurality of protrusions of the mold core are aligned with the embossed layer, and moved to the embossed layer, so that the material of the embossed layer is filled with the plurality a cavity between the protrusions; irradiating the embossed layer with an ultraviolet light beam to cure the embossed layer; releasing the mold, removing the mold core; removing the polymer material or organic matter remaining in the concave portion of the embossed layer and Corresponding to the organic portion of the concave portion of the organic transition layer; transferring the pattern formed by the organic transition layer to the sensing material layer; removing the residual portion of the imprinting layer and the organic transition layer on the surface of the sensing material layer, Sensing with a predetermined pattern Film; coating at the step of sensing the sensing material layer, before or after making a predetermined pattern on a surface layer of the sensing material, the sensing material layer is located on the surface of the piezoelectric substrate opposite two The side forms an input interdigital electrode and an output interdigital electrode to obtain a surface acoustic wave sensor. The method for fabricating a surface acoustic wave sensor according to claim 5, wherein the method of transferring the pattern formed by the organic transition layer to the sensing material layer is an etching method or a stripping method.