JP5533508B2 - Spherical surface acoustic wave device - Google Patents

Description

  The present invention relates to a spherical surface acoustic wave element for performing various measurements such as a gas state by analyzing a surface acoustic wave (SAW).

  2. Description of the Related Art Conventionally, a plate-like surface acoustic wave element in which electroacoustic transducers are provided at two positions apart from each other on the surface of a substrate 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 on the surface of the substrate and propagates it in a predetermined direction. Can do. The other electroacoustic transducer can receive the surface acoustic wave from 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 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.

  A surface acoustic wave is a surface acoustic wave that propagates while concentrating much of its energy on a material surface, 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 the spherical surface acoustic wave element and the time required for the rotation generally have temperature dependence. Therefore, by measuring the change, it can be used as a highly accurate thermometer. This method of measuring the temperature from the change of the propagation state of the surface acoustic wave is currently used in various applications and is a known technique.

  Conventional plate-like surface acoustic wave devices are used in 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 comb-like electrode as a surface acoustic wave excitation detecting means placed on the surface of a spherical substrate 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. As a result, 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. Such a spherical surface acoustic wave element using a spherical base body generates surface acoustic waves many times without diffusing along the surface acoustic wave circuit in a direction crossing the extending direction of the surface acoustic wave circuit. (I.e., the surface of 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 accurately measure the degree of deceleration of the surface acoustic wave propagation velocity, the degree of phase lag of the surface acoustic wave, and the degree of reduction of the intensity of the surface acoustic wave as the number of laps increases. it can.

  The degree of propagation speed deceleration, the degree of surface acoustic wave phase lag, and the degree of surface acoustic wave intensity decrease depend on changes 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 Patent Document 1, wiring patterns for resistance heating are mounted on both sides of a surface acoustic wave circulation path. While the spherical base material is heated, the phenomenon of heat deprived as the surrounding gas flows is measured to measure the gas flow velocity.

  As a measurement algorithm to be used, there is a method of measuring a heater current value for adjusting the temperature of the circumferential velocity of the surface acoustic wave that circulates the surface acoustic wave element so that the phase velocity becomes constant. Or, more simply, by creating a state in which the same amount of heat is applied to the spherical surface acoustic wave element by flowing a constant current, and measuring the element temperature from the change in the circumferential speed of the surface acoustic wave, The amount of heat taken away by the gas is measured.

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

  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 object of temperature measurement, the temperature measurement position and the heating position are different. In contrast, the temperature in the region where heat dissipation is greatest cannot be measured accurately.

  Patent Document 2 discloses that a resistance temperature sensor is directly formed on a propagation path around a surface acoustic wave, instead of measuring the temperature from the phase velocity of the surface acoustic wave of the surface acoustic wave element.

  In the present invention, description will be made on the assumption that the interdigital electrode is used as the electroacoustic transducer and the interdigital electrode is mounted on the surface of the spherical base material. However, a comb-like electrode is formed on a base material separate from the crystal sphere and the comb-like electrode is brought close to the surface of the crystal sphere to function as a spherical surface acoustic wave element. In the present invention, this case is also expressed as “forms a comb-shaped electrode on the surface of a spherical crystal sphere”.

JP 2007-101450 A JP 2008-082884 A

  Spherical surface acoustic wave elements with heating wiring on the surface are used for measuring changes in the flow of surrounding gas, etc., regardless of their expected use. Since the 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.

  Therefore, the present invention, for example, in applications in which the state of gas is measured by measuring the degree to which the heat is released to the surroundings while heating the spherical substrate, the response speed decreases due to the large heat capacity of the spherical substrate, Alternatively, it is an object to provide a spherical surface acoustic wave element with a heating wiring that does not cause a decrease in measurement accuracy due to a positional shift between a heated portion and a circumferential region of a surface acoustic wave that performs temperature measurement.

  In order to solve the above-mentioned problems, a spherical surface acoustic wave element according to claim 1 of the present invention is a surface region that is formed as a part of a spherical surface and includes an outer circumferential line having the maximum diameter of the spherical surface and extending on an annular ring. A base material in which surface acoustic waves excited along the ring-shaped extending direction of the surface region circulate along the outer circumferential line, and the surface region in the surface region of the base material. The two surface areas sandwiching the electroacoustic transducer for exciting the surface acoustic wave along the extending direction of the ring and the annular spherical area in which the surface acoustic wave propagates are planes, and the two plane shapes And a wiring pattern for heating formed in the surface region.

  A spherical surface acoustic wave element according to claim 2 of the present invention includes a surface region that is formed of a part of a spherical surface and includes an outer circumferential line having a maximum diameter of the spherical surface and extending on an annular shape, A base material in which a surface acoustic wave excited along the annular extension direction of the surface region on the surface region circulates along the outer circumferential line; and an annular extension of the surface region on the surface region of the base material An electroacoustic transducer for exciting a surface acoustic wave along a direction, a through-hole communicating two surface regions sandwiching an annular spherical region in which the surface acoustic wave propagates, and a surface region other than the annular spherical surface And a wiring pattern for heating formed on the substrate.

  A spherical surface acoustic wave element according to claim 3 of the present invention includes a surface region that is formed of a part of a spherical surface and includes an outer circumferential line having a maximum diameter of the spherical surface and extending on an annular shape, A base material in which a surface acoustic wave excited along the annular extension direction of the surface region on the surface region circulates along the outer circumferential line; and an annular extension of the surface region on the surface region of the base material The two surface regions sandwiching the electroacoustic transducer that excites the surface acoustic wave along the direction and the annular spherical region in which the surface acoustic wave propagates are flat surfaces, and the two planar surface regions communicate with each other. A through-hole, a heating wiring pattern formed in a surface region other than the annular spherical region, and a surface region other than the annular spherical surface in a plane portion excluding the peripheral surface of the through-hole An electric signal is transmitted to and received from the electroacoustic transducer. A first connection portion for performing and a surface region other than the annular spherical surface, which is formed in a plane portion excluding the peripheral surface of the through hole, and supplies power to the wiring pattern for heating. And a second connection portion.

  According to the present invention, for example, in the application of measuring the state of gas by measuring the degree to which the heat is released to the surroundings while heating the spherical base material, the response speed decreases due to the large heat capacity of the spherical base material, Alternatively, it is possible to provide a spherical surface acoustic wave element with a heating wiring that does not cause a decrease in measurement accuracy due to a positional shift between a heated portion and a circumferential region of a surface acoustic wave that performs temperature measurement.

1 is a perspective view schematically showing a configuration 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 spherical surface acoustic wave element concerning the 2nd Embodiment of this invention. The side view which shows schematically the condition which connects with respect to the spherical surface acoustic wave element which concerns on the 2nd Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
First, the first embodiment will be described.

  FIG. 1 schematically shows the configuration of a spherical surface acoustic wave device according to the first embodiment. In FIG. 1, a spherical surface acoustic wave element 10 includes a base material 11 of a trigonal piezoelectric single crystal such as quartz or langasite. In this embodiment, the base material 11 is a crystal having a diameter of 3.3 mm. The base material 11 made of quartz can be formed into a spherical surface after the single crystal base material made of quartz is processed into a spherical shape, and the vicinity of the equator can be used as the circumferential path 12 of the surface acoustic wave with the Z axis of the quartz as the ground axis.

  The piezoelectric crystal base material 11 used in the present embodiment is required to be a piezoelectric crystal base material having temperature dependency in which the circumferential velocity of the surface acoustic wave changes as 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 interdigital electrode 13 is formed on the equator so that the surface of the interdigital transducer 13 is perpendicular to the equator so that the surface acoustic wave circulates along the equator. 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 13 is formed with a period of 21 microns in order to excite the surface acoustic wave of 150 MHz.

  When the spherical base material 11 is made using a trigonal piezoelectric single crystal, the surface acoustic wave circulates along the equator (referred to as the Z-axis cylinder path) with the Z-axis as the ground axis. Although a path can be formed, for example, 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. Multiple laps are possible as long as the lap speed is temperature-dependent, and other than the route along the equator is not excluded.

  The spherical base material 11 has a barrel shape by cutting and polishing both poles with the Z axis as the ground axis. The Z-axis cylinder region 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, and the entire resin is polished on both the north pole side and the south pole side, and then the resin is dissolved and removed to form a barrel-shaped crystal sphere.

  The interdigital electrode 13 is formed by vacuum deposition of an aluminum thin film (1000 Å) or a laminated thin film of chromium (500 Å) and gold (1000 Å) at least in the region of the surface acoustic wave circulation path 12 and then applied to a photolithography method. Therefore, it was formed by patterning. The interdigital electrode 13 has two electrode extraction portions (first connection portions) 14a and 14b.

  After forming the interdigital electrode 13, a chromium thin film is formed by sputtering on the two planar regions 11a and 11b that have been cut and polished, and etching is performed to form wiring patterns 15a and 15b for resistance heating. In addition, what is necessary is just to design the shape and film thickness of wiring pattern 15a, 15b according to the heating use to be used.

  In the present embodiment, the barrel-shaped base material 11 has a volume of a crystal base material of 1/3 or less as compared with the spherical shape, and the heat capacity becomes small. A current is supplied from the heating power supply 16 to the heating wiring patterns 15a and 15b to generate heat, and the temperature of the surface acoustic wave element 10 at that time can be increased by measuring the circumferential speed of the surface acoustic wave.

  As a result, the specific heat of the piezoelectric crystal sphere is small, and heating and cooling can be performed at a higher speed, so that the transmission and reception of heat with the surrounding gas accurately reflects the temperature of the piezoelectric crystal substrate 11. That is, the surrounding gas condition can be measured more accurately and at high speed.

  In the example of this embodiment, the interdigital electrode 13 is formed as a single unit and serves as an excitation (transmission) and reception, but is separately manufactured for the transmission and reception of surface acoustic waves. can do.

  Thus, by forming the wiring patterns 15a and 15b for heating on the surfaces 11a and 11b cut into a planar shape, the wiring patterns 15a and 15b and the surface acoustic wave circulation path 12 are not only three-dimensionally close. The process of forming the wiring patterns 15a and 15b is simple because it is formed on a plane formed by cutting, and the wiring of the heating power supply 16 to the wiring patterns 15a and 15b is easy. Has a merit.

  Furthermore, it is preferable to form electrode extraction portions (first connection portions) 14a and 14b of the interdigital electrode 13 for detecting excitation of surface acoustic waves on the flat surfaces 11a and 11b generated by the cutting. Connection to the interdigital electrode 13 is possible on the cutting planes 11a and 11b, and mounting is easy.

  The heating wiring patterns 15a and 15b formed on the flat surfaces 11a and 11b generated by cutting may have a simple shape as shown in FIG. 1 or a meandering shape. By forming it in a meandering shape, it is possible to increase the resistance value, make the heat generation distribution uniform, and control for making the distribution uniform.

  While the cutting planes 11a and 11b of the substrate 11 in the present embodiment are heated in the atmosphere by the wiring patterns 15a and 15b for heating, the burst signal is continued at the carrier frequency of 150 MHz with respect to the interdigital electrode 13. A high frequency signal having a time of 1 microsecond is applied to excite a surface acoustic wave. When the voltage generated every time it passes around the interdigital electrode 13 after passing around the circuit 12 is measured and the circuit period is measured, the temperature can be measured at a predetermined time interval according to the temperature.

  For example, in the flow rate measurement, the temperature stabilized at 45 ° C. by the wiring patterns 15a and 15b for heating in a windless state is set to 1 m per second by being installed in an environment of atmospheric flow (wind) to be measured. It can be observed that it drops to about 10 degrees or more in the wind.

  In this embodiment, the decrease in the surface area (proportional to thermal radiation) is smaller than the decrease in the volume (proportional to heat capacity) of the substrate, and it is clear that the temperature change associated with the thermal radiation of the heated substrate 11 is increased. The effect is expected as an improvement in response speed for other applications using the speed of thermal radiation.

Next, a second embodiment will be described.
The same parts as those in the first embodiment described above are denoted by the same reference numerals and description thereof is omitted, and only different parts will be described.

  FIG. 2 schematically shows the configuration of a spherical surface acoustic wave device according to the second embodiment. The second embodiment has a smaller heat capacity than the spherical surface acoustic wave element of the first embodiment described above, and will be described in detail below.

  The crystal sphere used as the substrate 11 is a Langasite sphere having a diameter of 3.3 mm, the plane portions 11a and 11b are formed in both poles, leaving a thickness of 0.7 mm in the vicinity of the Z-axis cylinder path, It has a through hole 17 that communicates the flat portions 11a and 11b along the ground axis. Here, the diameter D of the through hole 17 is 2 mm.

  In the present embodiment, a thin film made of a chromium thin film that acts as the wiring pattern 15 for heating is formed at least on the peripheral surface of the through hole 17 by a sputtering method or the like. Two electrode extraction portions (second connection portions) 18a and 18b for supplying electric power to the heating wiring pattern 15 are formed in the remaining plane portion other than the through hole 17, in this example, the plane portion 11a. . Similarly, the electrode extraction portions (first connection portions) 14a and 14b of the interdigital electrodes 13 are also formed on the flat portions 11a and 11b.

  A larger size of the through hole 17 is desired because the 11 heat capacity of the crystal base material can be made smaller. However, if the through hole 17 is made larger, the rigidity of the crystal base material 11 itself becomes weaker. When the pressure is applied to the crystal substrate 11 in the connection process with the interdigital electrode 13, the crystal substrate 11 itself is destroyed. Further, if the thickness of the surface acoustic wave is not more than 20 times the width of the circumferential path 12 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 quartz crystal is about 21 microns, and [3300 micrometers-(420 micrometers x 2) = 2480 micrometers] to leave a width of 420 microns, Providing the through hole 17 having a diameter of 2480 micrometers or more does not operate as a surface acoustic wave element. As described above, 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 extraction portions (first connection portions) 14a, 14b of the interdigital electrodes 13 and the electrode extraction portions (second connection portions) 18a, 18b of the heating wiring pattern 15 on the flat portions 11a, 11b. Has the following advantages.

  That is, when mounting on a printed wiring board or connecting with an ultrasonic connecting machine, the base 11 is placed on a flat table so as to prevent pressure or ultrasonic vibration applied to the base 11 from destroying the crystal material. It is possible to apply pressure and ultrasonic vibration from above.

  For example, as shown in FIG. 3, an ultrasonic connecting machine usually has a base 11 placed on a flat table (connecting machine surface plate) 21, and ultrasonic vibration is applied from above by a head 22 of the ultrasonic connecting machine. On the other hand, the gold wire 23 and the like are connected while applying a force to the electrode extraction portion (in the example of FIG. 3, the electrode extraction portion 14a) formed of a gold thin film or the like. The connection to the flat portion is suitable for the crystal base material 11 whose rigidity has been weakened by being processed into a ring shape without applying a force leading to breakage.

  In the second embodiment, the example in which the wiring pattern 15 for heating is formed on the peripheral surface of the through-hole 17 is shown. However, it is obvious that the heating wiring pattern 15 may be formed on the flat portions 11a and 11b of the substrate 11. It is.

  As described above, according to the above-described embodiment, the spherical base 11 is formed into a barrel shape in which two regions divided by the surface acoustic wave circulation path 12 are cut in regions other than the circulation path. By making the heat capacity of the material 11 relatively small and forming the wiring patterns 15a and 15b for heating on the flat surfaces 11a and 11b generated by the cutting, the heating region and the surface acoustic wave propagation region (circular path 12) are formed. ) And a spherical surface acoustic wave element 10 with a heating wiring that is close in three dimensions.

  According to the spherical surface acoustic wave element 10 configured as described above, the spherical surface acoustic wave element 10 has the wiring patterns 15a and 15b for heating and heats itself such as the flow rate of the surrounding gas while heating itself. It becomes possible to measure the temperature of the leak based on the change in the circumferential velocity of the surface acoustic wave at high speed and accurately.

  DESCRIPTION OF SYMBOLS 10 ... Spherical surface acoustic wave element, 11 ... Base material, 11a, 11b ... Planar area | region (plane), 12 ... Circulation path | route, 13 ... Interdigital electrode (electroacoustic transducer), 14, 14a, 14b ... Interdigital shape Electrode extraction part (first connection part), 15, 15a, 15b ... heating wiring pattern, 16 ... heating power source, 17 ... through hole, 18a, 18b ... electrode extraction part of wiring pattern (second Connection part).

Claims (3)

A surface region formed of a part of a spherical surface and including an outer circumferential line of the maximum diameter of the spherical surface and extending in an annular shape, and excited in the surface region along the annular extending direction of the surface region A substrate on which a surface acoustic wave circulates along the outer circumferential line;
An electroacoustic transducer that excites a surface acoustic wave along an annular extending direction of the surface region on the surface region of the substrate;
Two surface regions sandwiching the annular spherical region in which the surface acoustic wave propagates are flat, and a heating wiring pattern formed on the two planar surface regions;
A spherical surface acoustic wave device comprising: A surface region formed of a part of a spherical surface and including an outer circumferential line of the maximum diameter of the spherical surface and extending in an annular shape, and excited in the surface region along the annular extending direction of the surface region A substrate on which a surface acoustic wave circulates along the outer circumferential line;
An electroacoustic transducer that excites a surface acoustic wave along an annular extending direction of the surface region on the surface region of the substrate;
A through hole communicating two surface regions sandwiching an annular spherical region through which the surface acoustic wave propagates;
A wiring pattern for heating formed in a surface region other than the annular spherical surface;
A spherical surface acoustic wave device comprising: A surface region formed of a part of a spherical surface and including an outer circumferential line of the maximum diameter of the spherical surface and extending in an annular shape, and excited in the surface region along the annular extending direction of the surface region A substrate on which a surface acoustic wave circulates along the outer circumferential line;
An electroacoustic transducer that excites a surface acoustic wave along an annular extending direction of the surface region on the surface region of the substrate;
Two surface regions sandwiching the annular spherical region through which the surface acoustic wave propagates are flat surfaces, and a through-hole communicating these two planar surface regions;
A wiring pattern for heating formed in a surface region other than the annular spherical region;
A first connection portion that is a surface region other than the annular spherical surface, is formed in a plane portion excluding a peripheral surface of the through-hole, and transmits and receives an electrical signal to and from the electroacoustic transducer;
A second connection portion for supplying power to the heating wiring pattern, which is a surface region other than the annular spherical surface, formed in a plane portion excluding the peripheral surface of the through-hole,
A spherical surface acoustic wave device comprising:

Images