JP2012075004A - Spherical surface acoustic wave element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spherical surface acoustic wave element that suppresses a reduction in measuring accuracy due to a positional gap between a heated portion and a circuit region for a surface acoustic wave for temperature measurement, in an application for measuring a degree of heat radiation while heating the spherical surface acoustic wave element to measure a state of gas.SOLUTION: A spherical surface acoustic wave element 10 includes a barrel-shaped piezoelectric crystal substrate 11, and an interdigital electrode 13 and a heating wiring pattern 14 formed on a surface acoustic wave circuit path 12 of the substrate 11.

Description

  The present invention relates to a spherical surface acoustic wave device having a heating function by resistance heating.

  2. Description of the Related Art Conventionally, a surface acoustic wave element in which electroacoustic transducers are provided at two positions apart from each other on a surface of a base material having a flat surface made of a piezoelectric material is known. The electroacoustic transducer is usually a high-frequency excitation / high-frequency receiving means such as an interdigital electrode.

  In this conventional surface acoustic wave element, when a high frequency current is supplied to one electroacoustic transducer, the one electroacoustic transducer generates a surface acoustic wave (SAW) on the surface of the substrate, It can be propagated in a predetermined direction. The other electroacoustic transducer can receive the surface acoustic wave from the one electroacoustic transducer on the surface and generate a high-frequency current corresponding to the received surface acoustic wave. When the electroacoustic transducer is an interdigital electrode, the direction in which the multiple electrode branches of the interdigital electrode are aligned is the direction in which the surface acoustic wave generated by the interdigital electrode propagates, and the surface acoustic wave is efficiently used. It becomes the direction to receive well.

  The surface acoustic wave is a surface acoustic wave that propagates while concentrating much of its energy on the surface of the material, unlike a longitudinal wave or a transverse wave called a normal bulk wave. Examples of the surface acoustic wave include a Rayleigh wave, a Sezawa wave, a pseudo Sezawa wave, a Love wave, and the like, and may also exist on the surface of an anisotropic material.

  The surface velocity of the surface acoustic wave propagating through the circular path of this spherical surface acoustic wave element and the time required for the rotation generally have temperature dependence, so it can be used as a highly accurate thermometer by measuring the change. . The method of measuring the temperature from the change in the propagation state of the surface acoustic wave is currently used in various applications, and the description thereof is omitted here.

  Conventional plate-like surface acoustic wave devices are used for delay lines, oscillation and resonance devices for oscillators, frequency selective filters, chemical sensors, biosensors, remote tags, and the like. The longer the distance between the surface acoustic wave excitation means and the surface acoustic wave detection means on the upper surface of the piezoelectric body, the higher the accuracy of these various devices using surface acoustic wave elements.

  However, in such a conventional plate-shaped surface acoustic wave element, since the piezoelectric body disposed on the flat substrate is flat, the surface acoustic wave excited by the surface acoustic wave excitation means on the upper surface of the piezoelectric body is provided. While propagating along the upper surface of the flat piezoelectric body toward the surface acoustic wave detecting means, it diffuses in a direction perpendicular to the propagation direction and loses its energy. Therefore, the distance between the surface acoustic wave excitation means and the surface acoustic wave detection means that can be set on the upper surface of the flat piezoelectric body is naturally limited.

  A spherical surface acoustic wave element has a interdigital electrode as a surface acoustic wave excitation detecting means placed on the surface of a spherical base body capable of exciting and propagating surface acoustic waves. The frequency and width of the surface acoustic wave excited on the surface of the substrate (the size of the surface acoustic wave in the direction orthogonal to the direction of propagation of the surface acoustic wave on the surface of the substrate) are set to predetermined conditions. Therefore, the surface acoustic wave excited on the surface of the substrate by the interdigital electrode can be propagated without infinitely diffusing in the direction orthogonal to the direction of propagation along the surface of the substrate. It has been clarified that it can be repeatedly circulated.

  The trajectory of the surface acoustic wave that circulates on the surface of the spherical substrate is within a region where a part of the spherical surface including the maximum outer circumference of the spherical substrate is continuous in an annular shape on the surface of the spherical substrate. This area is called a surface acoustic wave circuit. A spherical surface acoustic wave device using such a spherical substrate circulates a surface acoustic wave many times without diffusing in the direction intersecting the extending direction of the surface acoustic wave circuit along the surface acoustic wave circuit. (That is, the number of times the elastic surface circulates until the interdigital electrode cannot accurately detect the surface acoustic wave that circulates the surface acoustic wave circuit after the interdigital electrode excites the surface acoustic wave. Therefore, it is possible to precisely measure the degree of deceleration of the surface acoustic wave propagation speed, the degree of phase delay of the surface acoustic wave, and the degree of reduction of the intensity of the surface acoustic wave as the number of turns increases.

  The degree of deceleration of the propagation velocity, the degree of phase lag of the surface acoustic wave, and the degree of decrease in the intensity of the surface acoustic wave depend on the change in the environment in which the surface acoustic wave circuit of the spherical surface acoustic wave element is in contact (for example, gas Corresponding to the degree of increase in density). Therefore, measuring the various degrees described above means measuring changes in the environment in which the surface acoustic wave circuit of the spherical surface acoustic wave element is in contact.

  One such application is proposed as an application to an anemometer.

  Patent Document 1 describes a heater that is heated in contact with the surface of a spherical substrate of a spherical surface acoustic wave element or in contact therewith. In particular, in this patent document, wiring for resistance heating is mounted on both sides of a surface acoustic wave circulation path. While the spherical base material is heated, a phenomenon in which heat is taken away with the flow of the surrounding gas is measured to measure the gas flow velocity. As a measurement algorithm used for this measurement, there is a method of measuring the current value of the heater for adjusting the temperature at which the phase velocity of the rotation speed of the surface acoustic wave circulating around the surface acoustic wave element becomes constant. Or, more simply, a constant current is applied to create a state in which the same amount of heat is applied to the spherical surface acoustic wave device, and the ambient temperature is indirectly measured by measuring the device temperature from the change in the surface acoustic wave's circulation speed. It measures the amount of heat taken away by.

  These spherical surface acoustic wave elements with heating wiring are expected to be a thermometer with high accuracy, but since the spherical base material has a large heat capacity, it has a high speed response. It was difficult to get.

  Furthermore, since the conventional spherical surface acoustic wave element with a heating wiring has a heating wiring formed at a position different from the circulation path of the surface acoustic wave element that is the target of temperature measurement, the temperature measurement position and the heating position are different, There is a possibility that the temperature in the region where the heat radiation is greatest cannot be measured accurately.

  Patent Document 2 shows that a resistance temperature sensor is directly formed on a propagation path around a surface acoustic wave rather than measuring the temperature from the phase velocity of the surface acoustic wave of the surface acoustic wave element. Yes.

JP 2007-101450 A JP 2008-082884 A

  As described above, the spherical surface acoustic wave element having the heating wiring on the surface is used for measuring the flow of the surrounding gas, etc. Since the heating wiring is positioned apart from the surface acoustic wave propagation position, there is a problem that the response is slow and accurate measurement cannot be performed.

  The present invention has been made in view of the above circumstances. In an application for measuring the state of a gas by measuring the degree to which the surface acoustic wave element is released while heating the spherical surface acoustic wave element, the heating portion and the temperature measurement are performed. It is an object of the present invention to provide a spherical surface acoustic wave element that suppresses a decrease in measurement accuracy due to positional deviation of the circumferential region of the surface acoustic wave that performs the above-described measurement.

  The spherical base material used in the present invention is a spherical with heating wiring in which the heating area and the propagation area (circulation path) of the surface acoustic wave coincide with each other by forming a resistance heating wiring in the circulation path of the surface acoustic wave. A surface acoustic wave device is provided.

  An embodiment of the present invention is formed by having a surface region that is formed of a part of a spherical surface and includes an outer peripheral line having a maximum diameter of the spherical surface and extending on a ring, and the surface region has a circle of the surface region. A surface acoustic wave excited along the annular extending direction circulates along the outer circumferential line, and a surface acoustic wave formed along the annular extending direction of the surface region formed in the surface region of the substrate. Characterized by a spherical surface acoustic wave device comprising: an electroacoustic transducer that excites a substrate; and a resistance heating wiring pattern that is formed on the surface region of the substrate and controlled by an operation voltage supplied from the outside. And

  According to the present invention, while the spherical surface acoustic wave element has a resistance heating wiring and heats itself, the degree of heat leakage such as the flow rate of the surrounding gas is determined based on the change in the circumferential speed of the surface acoustic wave. Measurement can be performed quickly and accurately.

1 is a perspective view schematically showing a configuration of a main part of a spherical surface acoustic wave element according to a first embodiment of the present invention. The perspective view which shows schematically the structure of the principal part of the spherical surface acoustic wave element which concerns on 2nd Embodiment of this invention. The figure which shows schematically the condition which connects with respect to the spherical surface acoustic wave element which concerns on the said 2nd Embodiment.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, the configuration of the spherical surface acoustic wave device according to the first embodiment of the present invention will be described with reference to FIG. In this embodiment, an interdigital electrode is used as the electroacoustic transducer, but the description will be made on the assumption that the interdigital electrode is mounted on the surface of a spherical substrate. However, a comb electrode is formed on a base material separate from the crystal sphere, and the comb electrode approaches the surface of the crystal sphere to function as a spherical surface acoustic wave element. In the present invention, including this configuration, it is expressed as “forms an interdigital electrode on the surface of a spherical crystal sphere”. The surface velocity of the surface acoustic wave propagating through the circular path of this spherical surface acoustic wave element and the time required for the rotation generally have temperature dependence, so it can be used as a highly accurate thermometer by measuring the change. . The method of measuring the temperature from the change in the propagation state of the surface acoustic wave is currently used in various applications, and the description thereof is omitted in this embodiment.

  A spherical surface acoustic wave element 10 according to the first embodiment of the present invention includes a barrel-shaped base material (piezoelectric crystal base material) 11 in which flat surfaces are formed on both spherical poles, and a circular path of the base material 11. (Surrounding path of surface acoustic wave) For detecting the surface acoustic wave excitation formed on the flat surfaces of the interdigital electrodes 13 and the heating wiring pattern 14 formed on 12 and the poles sandwiching the circumferential path 12 of the substrate 11. An electrode take-out unit 15 is provided. An operating voltage is applied to the heating wiring pattern 14 formed on the circuit path 12 of the substrate 11 from the heating power supply 16 between both ends thereof. The circular path 12 is formed by a surface region which is a part of a spherical surface and includes an outer peripheral line having the maximum diameter of the spherical surface and extends in an annular shape.

  The spherical surface acoustic wave element 10 includes a base material 11 made of a trigonal piezoelectric single crystal such as quartz or langasite. In this embodiment, a Langasite crystal sphere having a diameter of 3.3 mm was used. A base material 11 made of a langasite material processed into a spherical shape has a surface around the equator as a circumferential path 12 of surface acoustic waves with the Z axis as the ground axis.

  For the crystal sphere used in the present invention, it is desired to use a piezoelectric crystal material whose piezoelectric characteristics are hardly changed by heating. The langasite material can excite surface acoustic waves without losing its piezoelectricity even at a high temperature of 1000 ° C. or higher. In order to cause a phase change at a temperature of 300 degrees or more and lose the piezoelectricity, it is necessary to consider that the temperature does not rise too much.

  The piezoelectric crystal base material 11 used in the embodiment of the present invention is required to be a temperature-dependent piezoelectric crystal base material in which the circumferential velocity of the surface acoustic wave changes when the temperature changes. For example, the temperature dependence of a spherical surface acoustic wave element using a crystal sphere is 25 ppm / degree near room temperature, and 40 ppm / degree when a langasite crystal sphere is used. The higher the temperature dependency, the more accurately the temperature can be measured from the circumferential velocity of the surface acoustic wave.

  The electrode branches of the interdigital electrode 13 are formed in a direction perpendicular to the equator so that the surface acoustic wave circulates along the equator of the substrate 11. The period of the interdigital electrode 13 determines the frequency of the surface acoustic wave to be excited or detected. In this embodiment, the interdigital electrode is formed at a period of 15 microns in order to excite the surface acoustic wave of 150 MHz.

  When a spherical base material is made using a trigonal piezoelectric single crystal, a surface acoustic wave orbital path (called a Z-axis cylinder path) is formed along the equator with the Z-axis crystal orientation as the ground axis. It is known that surface acoustic waves circulate in paths other than the Z-axis cylinder path in many piezoelectric crystals such as lithium niobate and lithium tantalate, and the piezoelectric crystal base material used in the present invention is It is only necessary to allow multiple rounds of surface acoustic waves and the speed of the rounds to be temperature-dependent, and this does not exclude other than the path along the equator.

  The equipment 11 is manufactured by cutting and polishing both poles with the Z axis of the spherical base material as the ground axis to form a barrel shape. The Z-axis cylinder region (circular path of the surface acoustic wave) leaves a spherical surface over a width of 0.8 mm. In the processing method, the manufactured spherical crystal sphere is embedded in a resin, the resin is polished on both sides of the north pole and the south pole, and then the resin is dissolved and removed to form a barrel shape.

  Next, the interdigital electrode 13 and the heating wiring pattern 14 are formed on a route that is to be the circulation route 12. Here, while rotating a spherical Langasite sphere around the Z-axis, a laminated thin film of chromium (1000 Å) and gold (500 Å) is formed by vacuum film formation on the circulation path.

  After the film formation, the interdigital electrode 13 and the heating wiring pattern 13 are formed according to a photolithography method. Each of the interdigital electrodes 13 and the heating wiring pattern 14 has two electrode extraction portions. However, one of the wires may be taken out as a ground wire, for example.

  The interdigital electrode portion forms an interdigital electrode pattern by etching both metal thin films from a resist pattern patterned using an etching solution of gold and chromium. On the other hand, the heating wiring pattern needs to have a high resistance value in order to perform resistance heating, and a gold film layer can be etched to form a resistance heating wiring only of a chromium film.

  In this embodiment, the formation of the interdigital electrode and the formation of the heating wiring pattern (resistance heating method) can be carried out by forming the metal film once, and there is an advantage that the element can be manufactured at low cost and efficiently. . In this embodiment, a single interdigital electrode is formed to excite and detect surface acoustic waves. However, surface acoustic waves can be separately produced for excitation (transmission) and reception.

  Thus, the surface acoustic wave circulation path and the heating surface forming the spherical surface acoustic wave element with the heating wiring in the same region can be easily manufactured, and the surface acoustic wave propagation path and the heating portion are the same region. Therefore, the timing at which the circulation path is heated matches the timing at which heat is taken away from the heated circulation path by the surrounding gas, so the surrounding gas conditions such as the speed at which the surrounding gas is deprived of heat Can be measured accurately and at high speed.

  In this embodiment, since the region other than the annular surface acoustic wave circulation path is removed by polishing or deletion, the specific heat of the piezoelectric crystal sphere is small, and the surrounding gas is heated and cooled faster. The heat transmission and reception accurately reflects the temperature of the piezoelectric crystal substrate. The temperature of the piezoelectric crystal substrate 11 can be measured because the circumferential speed of the surface acoustic wave changes according to the temperature. That is, the surrounding gas condition can be measured more accurately and at high speed.

  Further, by forming the heating wiring pattern 14 on the annular surface region formed by removing the region other than the annular surface acoustic wave circulation path by polishing or deletion, the heating wiring pattern 14 and the surface acoustic wave For processing such that the circulation path 12 is matched and wiring of the heating power supply (connection) is performed on a flat surface formed by cutting, so that the heating power supply 16 can be easily connected to the heating wiring pattern 14. It has the merit of

  The heating wiring pattern 14 may have a simple shape as shown in FIG. 1 or a pattern shape such as a waveform. As shown in FIG. 2 of Patent Document 1 described above, by forming a meandering shape, the resistance value can be increased, the heat generation distribution can be made uniform, and the distribution can be controlled. However, if the heating wiring pattern is thick, the propagation attenuation of the surface acoustic wave increases in some cases, making it difficult to obtain a large number of turns, and if the film thickness changes, the propagation attenuation increases. Furthermore, it is difficult to form a complex pattern because surface acoustic waves are reflected in a region with a pattern and a region without a pattern to cause propagation attenuation.

  The present invention does not particularly limit the film thickness of the heating wiring. The propagation phenomenon of surface acoustic waves in the case where a conductor film or a semiconductor film is formed on the surface of the piezoelectric crystal has been elucidated by current elasticity, and may be designed as appropriate.

  It is clear that the present invention has an effect of enhancing the thermal radiation response of the heated spherical surface acoustic wave element, and the effect is similar to the improvement of the response speed for other applications using the thermal radiation speed. Expected to be.

  Next, the configuration of the spherical surface acoustic wave device according to the second embodiment of the present invention will be described with reference to FIG. In the second embodiment, a spherical surface acoustic wave element with a heating wiring having a smaller heat capacity than the spherical surface acoustic wave element shown in the first embodiment will be described. Except for the presence of the through hole H, it is the same as in the first embodiment.

  The spherical surface acoustic wave device according to the second embodiment can realize a spherical surface acoustic wave device with a heating function having a smaller heat capacity than the spherical surface acoustic wave device shown in the first embodiment.

  A spherical surface acoustic wave element 20 according to the second embodiment of the present invention includes a barrel-shaped base material (piezoelectric crystal base material) 21 having a through hole H, and a circular path (surface acoustic wave wave) of the base material 21. (Circular path) 22 interdigital electrode 23 and heating wiring pattern 24, surface acoustic wave excitation detection electrode take-out portion 25 formed on the flat surface of substrate 21, and a pair of heating wiring connection portions 26, 26. Both ends of the heating wiring pattern 24 are circuit-coupled to the pair of heating wiring connection portions 26, 26 on the flat surface, and an operating voltage is applied from the heating power supply 27.

  The crystal sphere constituting the spherical surface acoustic wave element 20 is a Langasite sphere having a diameter of 3.3 mm, the plane portion is formed in both poles with a thickness of 0.7 mm in the vicinity of the Z-axis cylinder path, and the ground axis It penetrates along. The diameter D of the through hole H is 2 mm.

  The larger the size of the hole to be penetrated (the hole diameter D of the through hole H), the heat capacity of the crystal substrate can be further reduced. However, if the hole diameter is increased, the rigidity of the crystal substrate itself becomes weaker, If the pressure is applied to the crystal base material in the connection process for power supply or the connection process with the interdigital electrode 23, the crystal base material itself is destroyed. Furthermore, if the thickness of the surface acoustic wave is 20 times greater than the wavelength of the surface acoustic wave, for example, does not extend over the circumference path width of the surface acoustic wave, a problem arises because the propagation of the surface acoustic wave itself is inhibited.

  In this embodiment, a typical wavelength in a 150 MHz crystal is about 15 microns, and 3300 micrometers-(300 micrometers x 2) = 2600 micrometers to leave a width of 300 microns, 2600 micrometers. Opening a through hole having a diameter of at least a meter does not work as a surface acoustic wave element. The limit for reducing the thickness of the circulation path 12 may be selected so that the surface acoustic wave can propagate in consideration of the surface acoustic wave frequency, propagation mode, and crystal material.

  Positioning the electrode lead-out portion on the flat surface portion has the following advantages. In other words, as shown in FIG. 3, when mounting on a printed wiring board or connecting with an ultrasonic connector, a substrate can be placed on a flat table and pressure or ultrasonic vibration can be applied from above, As a result, the yield and the yield can be improved by avoiding the problem that the pressure and ultrasonic vibration applied to the base material destroy the crystal material.

  In the embodiment, an example in which the heating wiring pattern 24 is formed in a surface region (on the circumferential path 22 of the surface acoustic wave) extending in an annular shape is shown, but a flat surface formed with the surface region interposed therebetween. It may be formed in a region.

  DESCRIPTION OF SYMBOLS 10,20 ... Spherical surface acoustic wave element, 11, 21 ... Base material (piezoelectric crystal base material), 12, 22 ... Circumferential path (circular path of surface acoustic wave), 13, 23 ... Interdigital electrode, 14, 24 ... Heating wiring pattern, 15 and 25... Electrode extraction part for surface acoustic wave excitation detection, 16 and 27... Heating power supply, 27.

Claims (3)

Formed with a surface region formed of a part of a spherical surface and extending in an annular shape including an outer peripheral line of the maximum diameter of the spherical surface, and excited along the annular extending direction of the surface region in the surface region A substrate on which the generated surface acoustic wave circulates along the outer circumferential line,
An electroacoustic transducer that is formed in the surface region of the substrate and excites a surface acoustic wave along an annular extending direction of the surface region;
A wiring pattern for resistance heating, which is formed in the surface region of the base material and is controlled by an operation voltage supplied from the outside;
A spherical surface acoustic wave device comprising:   2. The substrate according to claim 1, wherein the base material has flat surface regions on both sides of the spherical surface sandwiching the surface region, and a surface acoustic wave excitation detection electrode extraction portion is formed in the flat surface region. The spherical surface acoustic wave device described.   The spherical surface acoustic wave element according to claim 1, wherein the base material has a through-hole penetrating between the spherical electrodes sandwiching the surface region.

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