JP2007019701A - Spherical surface acoustic wave element and surface acoustic wave exciting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spherical surface acoustic wave element and a surface acoustic wave exciting method that can minimize distortion of exposure even when electrodes of the spherical surface acoustic wave element using a plurality of frequencies are formed by using plane type photolithography. <P>SOLUTION: The surface acoustic wave element provided with projection portions alternately from a first electrode and a second electrode on an annular surface acoustic wave path on a piezoelectric crystal sphere or a sphere having a piezoelectric material film formed on its surface is characterized in that a third electrode is provided between a projection section of each first electrode and a projection portion of each second electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spherical surface acoustic wave device used in a method for measuring a physicochemical property of an object to be measured in a sample, and a surface acoustic wave excitation method necessary for temperature calibration thereof.

  Usually, the electrode of the surface acoustic wave element formed on the piezoelectric material substrate is formed by photolithography using a flat mask.

  Patent Document 1 discloses a surface acoustic wave device having a plurality of frequencies. In the case of a planar type surface acoustic wave element, an element is generally used in which surface acoustic waves of each frequency pass through different paths. In addition, the patent literature includes an element that propagates surface acoustic waves having a plurality of frequencies in one waveguide. In this case, the surface acoustic waves having a plurality of frequencies are converged by disposing the comb-shaped electrodes having protrusions alternately protruding from both sides of the annular surface acoustic wave path.

Patent documents are as follows.
Japanese Patent Laid-Open No. 11-340772 Japanese Patent Laid-Open No. 7-50548

  When forming a comb-shaped electrode on the surface using a photolithographic technique in a spherical surface acoustic wave element, it is ideally desirable to use an optical system that focuses light along a spherical spherical surface. It becomes a complicated optical system and the cost becomes high. On the other hand, as shown in FIG. 2, when a spherical surface is exposed using a flat mask as in the case of forming an electrode pattern on a flat substrate, the cost can be reduced, but the peripheral portion is more spherical on the periphery due to the influence of curved surfaces. As a result, the pattern is exposed greatly, and the image is blurred due to out of focus. Here, 1 is a plane mask, 2 is a pattern on the plane mask, 5 is a material ball, and 4 is a photosensitive material film formed on the surface of the material ball. Obviously, this effect becomes more prominent as the electrode pattern to be exposed becomes larger.

  In the spherical surface acoustic wave element, since the frequency used is about 10 MHz to 100 GHz, the attenuation characteristic of the surface acoustic wave is an important factor. One of the causes for attenuating the surface acoustic wave is an electrode for exciting the surface acoustic wave. In order to excite the surface acoustic wave, an electrode is required on the surface, but the electrode also attenuates the surface acoustic wave. Therefore, in order to suppress attenuation due to this effect, it is preferable to reduce the number of electrodes. However, a large number of electrodes are required for strong excitation.

In a spherical surface acoustic wave element, the temperature can be calibrated by using surface acoustic waves having a plurality of frequencies. However, to do this, it is necessary to form an electrode structure that can excite surface acoustic waves of a plurality of frequencies. At this time, if a plurality of surface acoustic waves can be excited in one path, variation in characteristics may be suppressed. In the spherical surface acoustic wave element, the technique as in Patent Document 2 cannot be used. This is because, in a spherical surface acoustic wave device, one path makes a belt around the surface of the sphere, and this surface acoustic wave needs to be excited on this path, and the electrodes cannot be arranged in a concave shape. One way to solve this is to arrange two electrodes with different frequencies side by side in the circuit path. However, in this case, since electrodes having two frequencies are formed separately, the electrode pattern to be exposed becomes large, and the electrode pattern is eventually distorted accordingly.

  In order to solve the above problem, in the invention according to claim 1, the first electrode and the second electrode are arranged on the annular surface acoustic wave path on the piezoelectric crystal sphere or the sphere formed with the piezoelectric material film on the surface. In a spherical surface acoustic wave element in which protrusions are alternately provided, a third electrode is provided between the protrusion of each first electrode and the protrusion of the second electrode. A spherical surface acoustic wave device is provided.

  In order to solve the problem, in the invention according to claim 2, in the spherical surface acoustic wave device according to claim 1, the third electrode is continuous between the first electrode and the second electrode. A spherical surface acoustic wave device is provided.

  Furthermore, in order to solve the problem, in the invention according to claim 3, the spherical surface acoustic wave device according to claim 1 or 2 is used to excite the first electrode and the second electrode, and the first electrode And a surface acoustic wave excitation method having a plurality of frequencies, wherein excitation is performed between a second electrode and a third electrode.

  Specifically, for example, as shown in FIG. 1, the first electrode and the second electrode, which are simple saddle-shaped electrodes in which protruding portions alternately protrude from both sides of the annular surface acoustic wave path, are connected to each other. A third electrode is used that passes in a zigzag so as to sew between the first electrode and the second electrode. This eliminates the need to provide a new counter electrode corresponding to the third electrode by utilizing the existing first electrode and second electrode, and can reduce the exposure area, thereby minimizing distortion. It has become possible.

  Here, the invention will be described with a simple example. A set of saddle-shaped electrodes having four pairs of protrusions for exciting surface acoustic waves of frequency f and a pair of saddle-shaped electrodes having eight pairs of protrusions for exciting surface acoustic waves of frequency 2 × f When the electrodes are formed on the element surface, if two pairs of electrodes are simply formed, a total of 12 pairs and 24 protrusions are required, which is equivalent to two saddle-shaped electrodes for exciting surface acoustic waves of frequency f. A surface area is required.

  On the other hand, in the case of the pattern as shown in FIG. 1, if the distance between the first electrode and the second electrode corresponds to the frequency f from the relationship between the sound speed and the wavelength, the first electrode and the second electrode By applying an electric signal having a frequency f between them, a surface acoustic wave having a frequency f can be excited. Further, when an electric signal having a frequency of 2 × f is applied between the electrode connecting the first electrode and the second electrode and the third electrode, a surface acoustic wave having a frequency of 2 × f can be excited. In this case, the protrusions on the 16 annular surface acoustic wave paths, that is, the electrodes that excite the surface acoustic waves having the frequency f by using the two-thirds of the protrusions are equivalent to the surface acoustic waves. One area can be formed.

  Thus, by using the first electrode and the second electrode, which are a pair of comb-shaped electrodes, and the third electrode passing through between them, a hook-shaped electrode is formed as a whole, and the number of electrodes is reduced. In addition, the area necessary for forming the electrode can be reduced.

According to the present invention, it is possible to form an electrode of a spherical surface acoustic wave device using a plurality of frequencies with an area smaller than the conventional area. Thereby, it can form easily using normal planar photolithography. As a result, surface acoustic waves having a plurality of frequencies can be excited in one path. Furthermore, by reducing the number of electrodes as a whole, attenuation due to the electrodes can be suppressed, and since the exposure area has become smaller, distortion can be minimized and the performance as a spherical surface acoustic wave device is improved. It has become possible.

  Hereinafter, the present invention will be described in detail based on the illustrated embodiment.

  FIG. 1 is a schematic diagram of electrodes of a spherical surface acoustic wave device according to Embodiment n of the present invention. Reference numerals 6, 7, and 8 denote formed electrodes. When an electric signal having a frequency f is applied between the first electrode 6 and the second electrode 7, a surface acoustic wave 9 having a frequency f is excited as shown in FIG. At this time, the third electrode 8 may be in an electrically floating state.

  When an electric signal having a frequency of 2 × f is applied between the first electrode 6 and the second electrode 7 connected to each other and the third electrode 8, the surface elasticity of 2 × f is obtained as shown in FIG. Wave 9 is excited.

  The excited surface acoustic wave circulates around the spherical surface and outputs an electrical signal from the comb-shaped electrode every time it returns to the excited electrode after one round. By forming a functional film on the spherical surface and observing the surface acoustic wave signal, it can be used as a highly sensitive sensor. Further, by causing the surface acoustic waves of a plurality of frequencies to circulate, it is possible to calibrate signals due to factors other than the sensitive film such as temperature.

  FIG. 5 is a diagram showing the surface acoustic wave circulation phenomenon of the spherical surface acoustic wave device of the present invention. A and B respectively connect the first electrode 6 and the second electrode 7 when an electric signal having a frequency of 30 MHz is applied between the first electrode 6 and the second electrode 7 in the schematic diagram of FIG. 3 shows an output signal indicating that a surface acoustic wave circulates on a sphere when an electrical signal of 60 MHz is applied between the electrode and the third electrode 8. It can be seen that a plurality of frequencies can be excited by changing the connection of the electrodes and the frequency of the input signal.

  The present invention relates to an electrode pattern in a spherical surface acoustic wave device and an electrode pattern in a surface acoustic wave device that can be used for a temperature calibration technique.

Plan view of electrode pattern capable of exciting multiple frequencies according to the present invention Explanatory cross-sectional view of exposure on a spherical surface using a planar mask FIG. 3 is an explanatory diagram of a surface acoustic wave output from a state where the frequency of f is excited using the electrode pattern of FIG. 1. FIG. 2 is an explanatory diagram of surface acoustic waves output from a state where a frequency of 2 × f is excited using the electrode pattern of FIG. 1. FIG. 2 is an explanatory diagram of surface acoustic waves output from a state where f and 2 × f frequencies are excited using the electrode pattern of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Plane mask 2 ... Pattern 4 on plane mask ... Photosensitive material film 5 coated on material sphere surface ... Material sphere 7 ... First electrode (electrode for exciting frequency f and 2xf)
8 ... 2nd electrode (electrode for exciting the frequency of f and 2xf)
9 ... 3rd electrode (electrode for exciting the frequency of 2xf)

Claims (3)

  Surface acoustic wave, which is provided with protrusions alternately from the first electrode and the second electrode on an annular surface acoustic wave path on the surface of a piezoelectric crystal sphere or a sphere formed with a piezoelectric material film. 3. A spherical surface acoustic wave device according to claim 1, wherein a third electrode is provided between the protruding portion of each first electrode and the protruding portion of the second electrode.   2. The spherical surface acoustic wave device according to claim 1, wherein the third electrode is continuous between the first electrode and the second electrode.   Using the spherical surface acoustic wave device according to claim 1 or 2, excitation is performed by the first electrode and the second electrode, and excitation is performed between the first electrode and the second electrode and the third electrode. A surface acoustic wave excitation method having a plurality of frequencies.

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