Abstract:
A method for manufacturing a surface acoustic wave device comprises depositing a detecting material layer on a substrate, forming a predetermined pattern on the detecting material layer using a nanoimprint method to obtain a detecting film with a predetermined pattern formed thereon, and forming an input interdigital transducer and an output interdigital transducer on two opposite sides of the detecting material layer on the substrate, thus obtaining a surface acoustic wave device comprising the detecting film.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure relates generally to a method for manufacturing a surface acoustic wave device. 
         [0003]    2. Description of Related Art 
         [0004]    Surface acoustic wave devices utilize electromechanical conversion and rely on surface acoustic waves that propagate elastic energy, concentrated on the surface of a solid. Generally, a surface acoustic wave device is provided with an input interdigital transducer (IDT), an output IDT and a detecting film on a piezoelectric substrate. The detecting film is positioned between the two IDTs. Each IDT includes a pair of comb-shaped electrodes interdisposed with each other. 
         [0005]    The detecting film absorbs adjacent gas molecules or liquid molecules. When an electrical signal is applied to the input IDT, the piezoelectric substrate is stressed, creating a surface acoustic wave. The surface acoustic wave passes through the substrate and is transmitted to the output IDT, at which point the acoustic wave signal is converted to an electric signal for output. Absorption of the detecting film increases mass thereof. When the surface acoustic wave passes through the substrate, because of mass loading effect on the detecting film, an excursion occurs in phase velocity and attenuation of the output signal. The molecular concentration of the gas or liquid to be detected can be read from the excursion. 
         [0006]    The detecting film, generally formed on the substrate via Chemical Vapor Deposition (CVD), may exhibit an uneven surface with only limited area for detection. 
         [0007]    Therefore, a method for manufacturing a surface acoustic wave device is needed that can overcome the limitations described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. 
           [0009]      FIG. 1  is a flowchart of a method for manufacturing a surface acoustic wave device. 
           [0010]      FIG. 2  is a schematic, isometric view of a substrate with two IDTs thereon. 
           [0011]      FIG. 3  is a schematic, isometric view showing a substrate with two IDTs and a detecting material layer thereon. 
           [0012]      FIG. 4  shows a method for forming a detecting film on the substrate according to a first embodiment. 
           [0013]      FIG. 5  is a schematic, isometric view showing a surface acoustic wave device formed by the method in  FIG. 4 . 
           [0014]      FIG. 6  shows a method for forming a detecting film on the substrate according to a second embodiment. 
       
    
    
       [0015]    Corresponding reference characters indicate corresponding parts. The exemplifications set out herein illustrate at least one present embodiment of the present method for manufacturing a surface acoustic wave device, in one form, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0016]    Reference will now be made to the drawings to describe embodiments of the present method for manufacturing a surface acoustic wave device in detail. 
         [0017]    Referring to  FIG. 1 , a method for manufacturing a surface acoustic wave device includes Step  102 , in which a substrate of piezoelectric material is provided. In Step  104 , an input IDT and an output IDT are formed on the substrate. In Step  106 , a detecting film is coated on the substrate between the input IDT and the output IDT. In Step  108 , a predetermined pattern is formed on a surface of the detecting film using a nanoimprint method, resulting in a surface acoustic wave device. 
         [0018]    Referring to  FIGS. 2 to 5 , a method for manufacturing a surface acoustic wave device according to a first embodiment is detailed as follows. In step  102 , a rectangular substrate  20  is provided. The substrate  20  is piezoelectric material such as single crystal, such as quartz, LiNbO 3 , and LiTaO 3 , thin film specie, such as AlN, or ZnO; ceramic species, such as barium titanate, lead zirconate-titanate, or polymer such as polyvinylidene fluoride. 
         [0019]    In step  104 , an input IDT  22  and an output IDT  24  are formed on a surface of the substrate  20  by micro-etching or micro-electromechanical process. 
         [0020]    Referring to  FIG. 3 , in step  106 , a detecting layer  26  is formed on the substrate  20  between the input IDT  22  and the output IDT  24  by glow discharge, magnetron sputtering, radiofrequency sputtering, reactive sputtering, or cyclotron wave sputtering. 
         [0021]    Material of the detecting layer  26  may be ZnO, to detect ultraviolet radiation, ZnO or Pd to detect hydrogen gas, or SnO 2  to detect carbon monoxide. 
         [0022]    Referring to  FIG. 4 , in step  108 , a predetermined pattern is formed on a surface of the detecting layer  26  using nanoimprinting. In this embodiment, hot pressing forms the predetermined pattern, detailed as follows. 
         [0023]    Referring to  FIGS. 4(   a ) and  4 ( b ), a polymer layer  28  is deposited on a surface of the detecting layer  26 . The polymer layer  28  is heated beyond a glass transition temperature of the polymer layer  28 , whereby the polymer layer  28  is softened. The temperature must be prevented from rising too high, otherwise time required for solidifying the polymer layer  28  will be increased. In this embodiment, the polymer layer  28  is polymethyl methacrylate (PMMA). A glass transition temperature of the PMMA is 104° C., thus the temperature for heating the polymer layer  28  may be from 105° C. to 110° C. 
         [0024]    Referring to  FIG. 4(   c ), a mold  30  is provided. The mold  30  includes a base  302  and a plurality of protrusions  304  of a predetermined shape. The plurality of protrusions  304  is arranged on a surface of the base  302  and integrally connected with the base  302 . The mold  30  is of a material exhibiting maximum hardness, compression strength, and tension strength, to prevent distortion and abrasion thereof. In addition, the mold  30  should demonstrate high heat conductivity and low thermal expansion coefficient. Material for mold  30  can be silicon, silicon oxide, silicon nitride, or diamond, with required dimensions of the protrusions  304  accurate to about 10 to 100 nanometers (nm). 
         [0025]    The protrusions  304  face polymer layer  28 , and are pressed thereinto, forming compressed regions. 
         [0026]    Referring to  FIG. 4(   d ), the polymer layer  28  is cooled to solidify and the mold  30  removed. The protrusions  304  pressed into the polymer layer  28  do not contact the detecting layer  26 . Thus, a plurality of recesses  282  are formed at the compressed regions which generally conform to the profile of the protrusions  304 . A thin polymer layer  284  remains between each recess  282  and the detecting layer  26 . 
         [0027]    The thin polymer layer  284  of the polymer layer  28  between the recess  282  and the detecting layer  26  is removed, thereby exposing the detecting layer  26 . Removal may be effected utilizing any appropriate process such as reactive ion etching, wet chemical etching or other. The predetermined pattern of the protrusions  304  is transfer printed onto the detecting layer  26  using the polymer layer  28  as a mask, by etching or stripping. As shown in  FIG. 4(   e ), after selectively etching the detecting layer  26 , a plurality of holes  262  are defined in the detecting layer  26 . 
         [0028]    As shown in  FIGS. 4(   f ) and  5 , the remaining polymer layer  28  is removed, leaving a detecting film  32  with predetermined pattern on the surface thereof, with the surface acoustic wave device  40  subsequently obtained. Here, the predetermined pattern is a plurality of holes  262  conforming to the protrusions  304 . 
         [0029]    It is to be understood that formation of the input IDT  22  and the output IDT  24  can be interchanged in the process with formation of the detecting film  32 . 
         [0030]    Referring to  FIG. 6 , a method for forming a predetermined pattern on a surface of a detecting layer  26  according to another embodiment is provided, in which an organic interlayer  42  is deposited on the surface of the detecting layer  26 . The organic interlayer  42  is PMMA and here, the organic interlayer  42  is deposited on the detecting layer  26  by spin coating. 
         [0031]    Referring to  FIG. 6(   c ), an imprinted layer  44  is deposited on the organic interlayer  42 . The imprinted layer  44  can be a polymer or an organic solution having characteristics of fluidity at room temperature and curable by ultraviolet light. Here, the imprinted layer  44  is organic silicon solution. 
         [0032]    Referring to  FIGS. 6(   d ) and  6 ( e ), a mold  46  is provided. The mold  46  includes a base  462  and a plurality of protrusions  464  of a predetermined shape. The plurality of protrusions  464  is arranged on and integrally connected with a surface of the base  462 . The mold  46  can be quartz glass or poly-dimethylsiloxane, with dimensions of the protrusions  304  accurate to 20 nm to 100 nm. 
         [0033]    The protrusions  464  face the imprinted layer  44 , and are pressed thereinto, forming compressed regions. 
         [0034]    Ultraviolet light is applied, irradiating and solidifying the imprinted layer  44 , after which the mold  46  is removed. As shown in  FIG. 6(   f ), the protrusions  464  pressed into the imprinted layer  44  do not contact the organic interlayer  42 , resulting in a plurality of recesses  442  forming at the compressed regions generally conforming to the profile of the protrusions  464 . A thin imprinted layer  444  remains between each recess  442  and the organic interlayer  42 . 
         [0035]    Referring to  FIGS. 6(   g ) and  6 ( h ), the thin imprinted layer  444  of the imprinted layer  44  between the recess  442  and the organic interlayer  42  and the exposed part of the organic interlayer  42  are removed, exposing the detecting layer  26 . Removal can utilize any appropriate process such as reactive ion etching or wet chemical etching. The predetermined pattern of the protrusions  464  is transfer printed onto the detecting layer  26  using the imprinted layer  44  and the organic interlayer  46  as a mask, by etching or a stripping. After etching of the detecting layer  26 , a plurality of holes  262  conforming to the protrusions  464  are defined in the detecting layer  26 . 
         [0036]    Referring to  FIGS. 6(   i ), the remaining imprinted layer  44  and the organic interlayer  42  are removed, resulting in a detecting film  32  with a predetermined pattern on the surface thereof. 
         [0037]    The detecting film  32  formed by the nanoimprint method, having a predetermined nanometer-sized pattern, provides a large area making contact with the substance to be detected, increasing detecting precision and efficiency. In addition, the nanoimprint method presents a simplified process suitable for mass production. 
         [0038]    Finally, it is to be understood that the described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.