TW536868B - Piezoelectric substrate working method of surface acoustic device - Google Patents

Abstract

The present invention is a piezoelectric substrate working method of surface acoustic device. The surface acoustic device is formed of a piezoelectric substrate and the input electrode, output electrode on its surface, wherein the circuit patterns of input/output inter-digital transducers (IDT) are fabricated on the piezoelectric substrate by photolithography technology or screen printing. By varying the design of the density and member composition of the pattern, the surface acoustic wave triggering/receiving device (such as reflector) is matched with the IDT, different operation frequencies can be associated and generated for application. At the same time, sand blast processing with appropriate roughness is applied on the back side of the piezoelectric substrate to make a surface with appropriate roughness, so as to inhibit the block body wave signal excited by the input IDT for improving the ripple response of the band-pass band and the inhibition of band-rejection band, and to be processed by the output IDT.

Description

536868 _ + Case No.91111fl22_ Revised Year, Month, and Day V. Description of the Invention (1) The present invention is a method for processing a piezoelectric substrate (piezoeiectric substrate) of a surface acoustic wave (Surface Acoustic Wave: SAW) device, especially a surface acoustic wave element. A piezoelectric substrate made of piezoelectric materials is used in the device, and a surface finger electrode is designed on the piezoelectric substrate to perform signal processing. The special processing method of the present invention is used for the piezoelectric substrate of the device. Effectively reduce the influence of the bulk wave generated by the surface acoustic wave excitation of the surface finger electrode on the frequency response of the design element. In the early days, surface acoustic wave elements were first used in radars as pulse compression filters for spectrum analysis. At the same time, their applications were also seen in various fields. Today, due to the advantages of high performance, small size, low cost, and high reproducibility, surface acoustic wave components make them important in both the electronics industry and communication systems. Currently, the conventional piezoelectric substrate 1 used to make a surface acoustic wave wave transformer is generally provided with surface finger electrodes 2 (interdigital transducers: IDT) on one surface (as shown in the first figure), and the other surface (that is, the back surface). It is left untreated, and is kept flat. While such a substrate device can normally exert its piezoelectric effect, there is still room for improvement in suppressing bulk wave 1. In order to improve this shortcoming, it is disclosed in US Patent No. 5708402 that a rough surface is formed by cutting or grinding on the back surface of a piezoelectric substrate in a surface acoustic wave device, as shown in the second figure. In order to achieve the purpose of suppressing block waves. However, the above-mentioned method of processing the back surface of piezoelectric substrates has some disadvantages such as difficulty in processing and practical implementation. Because the thickness of the substrate is not large, it is very difficult to perform side cutting, especially to cut into irregular It is more difficult to control the depth of the rough surface. In addition, the rough surface is processed by cutting or grinding, which makes it difficult to completely cut the rough surface into a uniform rough surface.

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The wafer is fully maintained. Furthermore, the finger electrodes on the cut surface of the piezoelectric piezoelectric substrate are damaged, which is a big disadvantage. The rough regularity is that the substrate must be cut on the surface first, so it is very easy to even break it, causing sugar surface, that is, the function of the piezoelectricity is not greatly reduced; the finger electrode is used to cut the surface after cutting. The yield rate is greatly reduced for each of the defects on the baryon. The present invention provides a method for processing a substrate of a surface acoustic wave device to improve the following effects: 1 · S electrical substrate processing, a more gentle sandblasting method The formation of a roughened surface will not cause damage to the piezoelectric substrate. 2. The piezo substrate is processed by sandblasting and thickening, which makes it easy to control the thickness. 3. The roughness formed by sand blasting is easier to be processed into a uniform rough surface. ^ The technical means for applying the above-mentioned objects and advantages achieved by the present invention 'are combined with simple drawings, and the preferred embodiments are described later. Specific implementation examples The method for processing a piezoelectric substrate of the present invention can be applied to several types of surface acoustic waves. A surface acoustic wave filter is taken as an example (please refer to FIG. 3A and FIG. 3B). The electric substrate is composed of an input electrode and a set of output electrodes on its surface. The surface of the piezoelectric substrate 1 is produced by optical development technology or screen printing technology. The surface finger electrode 2 is provided with the finger electrode 21 and the output finger. The circuit pattern of the electrode 22, and the design change of the density and component composition of the electric case, combined with the installation of a radio wave trigger / receiving device (such as a reflector, etc.), the operating frequency of the long P that is different from the electricity generation is At the same time, at the same time, the back of the piezoelectric substrate 1 is sandblasted on the back with an appropriate roughness to create a proper degree of surface, which can effectively suppress the excitation of the wheel-in finger electrode 2 丨

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_Case No. 91111Q22 V. Description of the invention (3) Block wave to improve the chain wave response of its bandpass band and the rejection band ^. Suppression (as shown in Figure 4). In addition, the above-mentioned blasted 12-sided piezoelectric substrate with a rough surface has different types of finger electrodes 2 on the surface, which can provide different frequencies, and can also produce an additive effect with the back surface of the piezoelectric substrate. , Has a positive effect on improving its bandpass frequency band < chain wave response and band rejection frequency band signal suppression, such as the surface finger electrode or its reflector can be: split finger electrode b (gp 1 i 卜 Finger IDT ) (As shown in the fifth figure A), the finger electrode c (Electrode Width Controlled IDT) (as shown in the fifth picture b), the short-structure reflector d (Structure of Short Reflectors) ( As shown in the fifth figure C) or an open circuit structure e (Structure of 〇pen Reflectors) (as shown in the fifth figure D). Continuing, please refer to the sixth figure. On the rough curve of the rough sandblasted back surface of the above-mentioned piezoelectric substrate, a section of measurement length L is taken, and the center line of the rough depth within the measurement length L is taken as the X axis. The vertical line of the centerline is the y-axis, then the rough curve is represented by y = f (x), and the lower curve is reverse-folded based on the X-axis of the centerline, and then all the curves covered by the reverse-folding above the centerline are calculated. The area is then divided by the measured length L. The resulting value is centerline with # m as the unit and the average roughness is [^. The mathematical expression of Ra is

L The value of R a between 0 · 8 // in and 1 · 9 // in is the preferred embodiment. The comparison of the gain of its effect can be seen in the seventh graph (the thickness of the piezoelectric substrate is 350 um)

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Case No. 91111Q22 5. In the description of the invention (4), the horizontal axis is the frequency and the vertical axis is the insertion loss. This is the back-cut GC # 1 0 0 0 is a piezoelectric substrate without sandblasting on the general back) and the eighth X When the thickness of the piezoelectric substrate is 50 Um, the horizontal axis is frequency, vertical = insertion loss, Ra is average roughness, and GC # 1000 is a rational piezoelectric substrate). It can be known from the treatment that the present invention applies sandblasting to the lunar surface of the substrate in the surface acoustic wave device element. In addition to improving the construction yield and efficiency, it is easier to control the roughness of the rough surface. Improve the chain wave response of its band-pass frequency band and the quality filter waveband with rejection frequency band.1 This technology has not been published before the application. The actual U: :: invention patent application is #. The application for an invention patent has been filed according to law, Although the present invention is disclosed in a preferred embodiment as above, the bran is limited to the present invention. Anyone skilled in the art can use it within the scope of God and the scope, and can make various changes without departing from the essence of this matter. Regulations, the scope of protection of property inventions? : Month Defined by the range. J π ^ Jun Fuzhi's patent application

536868 _Case No. 911Π922_ Year Month Day __ ^ __ Brief Description of the Drawings [Simplified Illustration of the Drawings] The first diagram is a cross section of the piezoelectric substrate and the surface finger electrodes in the conventional surface acoustic wave device. The second figure is a schematic cross-sectional view of the bottom surface of the piezoelectric substrate processed by back cutting (grinding). The third figure A is a schematic cross-sectional view of a piezoelectric substrate and finger electrodes on its surface in the surface acoustic wave device of the present invention. The third figure B is a schematic cross-sectional view of a piezoelectric substrate and finger electrodes and reflectors on the surface of the surface acoustic wave device of the present invention. The fourth figure is a preferred embodiment a of the surface finger electrode type on the piezoelectric substrate of the present invention. The fifth figure A is an embodiment of the surface acoustic wave device of the present invention in which the surface is a segmented finger electrode. The fifth figure B is an example of a finger electrode type in which the surface of the surface acoustic wave device of the present invention is a controllable electrode width. The fifth figure C is an embodiment of a reflector in which the surface of the surface acoustic wave device of the present invention has a short-circuit structure. The fifth figure D is an embodiment of a reflector in which the surface of the surface acoustic wave device of the present invention has an open circuit structure. The sixth figure is a graph showing the center line average roughness of the processed surface of the bottom of the piezoelectric substrate of the present invention. The seventh figure is a conventional schematic diagram of a piezoelectric substrate having a flat back surface and backcut processing at different depths. The eighth figure is a comparison diagram of the sandblasting and flat spectrum response characteristics of the back surface of the piezoelectric substrate with different roughnesses.

536868 _Case No. 91119922_ Simple description of the revised version of the year [Description of the symbols used in the conventional technology] 1. Piezoelectric substrate 11 '. Coarse sugar surface 2 Surface finger electrode Description of the symbols used in the technology of the present invention: a. The preferred embodiments b, c, d, and e of this case · Other preferred embodiments P. Wavelength R a. Average roughness of the center line is L. Measurement length 1. Piezoelectric substrate 11. Surface 1 2. Backside blasting treatment 2 Surface finger electrode 2 1. Input finger electrode 2 2. Output finger electrode 3. Reflector 4. Split finger electrode 5. Finger electrode with controllable electrode width 6. Reflector with short-circuit structure 7. Open circuit structure Reflector

Claims (1)

536868 Case No. 91119922 6. Scope of patent application i. A method for processing a piezoelectric substrate of a surface acoustic wave device, which includes a piezoelectric substrate and a surface finger electrode provided thereon. The processing of the pressing plate includes the following steps:% I = substrate An inorganic or organic substance is coated on the surface with a coating layer, and an electrode composed of the coating layer is etched by photon development or screen printing technology to form a surface acoustic wave device frequency and suppress the generation of reflected waves; Rough sandblaster. 2. 'The method of processing piezoelectric substrate based on surface acoustic wave as described in item 1 of the scope of the patent application', wherein a section of the measurement length L is taken from the f-chain curve of the back surface of the piezoelectric substrate by sandblasting, and Take the center line of the rough ice in this length as the X axis, and take the vertical line of the center line as the 7 axis. The rough curve is expressed by y = f (x). The center curve is used as the reference to fold back the lower curve, and then calculate the center. The area covered by all the curves above the line after re-folding, and then divided by the measured length, the resulting value is # m as the unit. The center line flat roughness is Ra. Then: Ra: Σ J l, Ra value is 0.8 am to 1.9. // m. 3. The method for processing a piezoelectric substrate of a surface acoustic wave device as described in item 丨 or item 2 of the patent application, wherein a reflector is connected to the surface finger electrode. 4 · As described in item 3 of the patent application Method for processing piezoelectric substrate of surface acoustic wave device, wherein surface finger electrode and reflector on the piezoelectric substrate Page 10 Case No. 6. Scope of Patent Application ㈡ = Two groups are formed to form a filter. Levy: Those who surround the electrode of the surface acoustic wave device described in item 3. / 'The surface finger electrode on the piezoelectric substrate 6: The layer of the surface acoustic wave device described in the patent scope No. 3 ^ Method where the surface finger electrode on the piezoelectric substrate "I degree finger Electrode. The layer of the surface acoustic wave device described in item 3 of the patent application = method 'where the reflector on the piezoelectric substrate is a short-circuiter. The surface acoustic wave device described in item 3 of the patent application is clever. = Method, where the reflector on the piezoelectric substrate is an open circuit: electrical substrate plus split finger t electrical substrate plus controllable electrode, electrical substrate plus structure reflection $ electric substrate plus structure reflection 536868 2 The fourth picture 536868 o o ii Y-i- $ k »-t. 9 ύ s o o o4 o -5 o J 01 4 3 334 354 374 394 414 434 454 454 474 Frequency (MHz) Figure 7 536868 J—y. Jzi 1 ^ 2 ^ 4 ^ 5ct} ¥ 2sv Teng ^ 0 2 Eighth picture