JP2006047229A - Surface acoustic wave device sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave device sensor, capable of simultaneously and precisely detecting environmental variable factors represented by physicochemical parameters (temperature, humidity, load, atmospheric pressure, gas component, magnetism, material damages, biological sample microanalysis and the like) resulting from various environmental information and biological medical factors, based on changes in a surface acoustic wave propagation properties, by making a surface acoustic wave (SAW) multichanneled and multifunctional which is generated on a piezo-electric type substrate. <P>SOLUTION: In the surface acoustic wave (SAW) device sensor 1, high-frequency current or high-frequency voltage is applied to an element made up by bonding an IDT 3 to the piezo-electric type substrate 2, whereby the surface acoustic wave (SAW) 5 is generated near the surface of the piezo-electric type substrate 2, and an environmental variable factor is detected on the basis of the propagation property of the SAW 5. A SAW propagating path 4, made up of a plurality of functional thin films 6, is formed to be multichanneled on the piezo-electric type substrate 2, thereby simultaneously detecting the plurality of environmental variable factors. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention adds a special functional material that reacts to multiple environmental change factors on the SAW propagation path in a surface acoustic wave (SAW) device that propagates energy concentrated near the surface of the elastic body. Multi-functionalization, focusing on changes in the propagation characteristics of SAW, through which various physical and chemical quantities (temperature, stress, strain, humidity, trace gas) related to the surrounding environment and biological (health) problems The present invention relates to a basic technology for the development of a multifunctional SAW device sensing system characterized by a non-power-feeding method and wireless that can measure ionization concentration, biological component microanalysis, etc.) with high sensitivity.

  The ultrasonic waves currently used in the engineering and medical fields are mainly elastic waves (bulk waves) that propagate in water or solids. On the other hand, surface acoustic waves (SAW) that propagate by concentrating energy near the surface of an elastic body have recently been utilized as elements for electronic / communication equipment and have played an important role in the progress of this direction.

  One of the related technologies that are the basis for the development of functions of such SAW devices is the piezoelectric effect. This piezoelectric effect is generally referred to as a piezoelectric effect, where a charge or a stress is induced when a strain or stress is applied (forward effect), and a strain or stress is generated when a voltage is applied (reverse effect). In particular, the forward effect was discovered by Curie brothers (J. Curie, P. Curie, 1880) for tourmaline, and the reverse effect was found the following year by G. Lippmann. Whether or not the crystal exhibits a piezoelectric effect is determined by the point group symmetry of the crystal, and among the 32 crystal groups, the crystal effect is the 20 crystal group.

Electromechanical transducers using the piezoelectric effect are the mainstream of current ultrasonic application parts. Piezoelectric elements include single crystals such as quartz, Rochelle salt (calcium sodium tartrate), LiTaO ₃ , LiNbO _3, etc., and polycrystals such as barium titanate (BaTiO ₃ ), lead zirconate titanate (PbZrO ₃ , PbTiO ₃ ), niobic acid Typical examples are salt. The piezoelectric vibrator is one elastic vibration body configured by using a piezoelectric body having electrodes as a whole or a part thereof, and has a function of electrically exciting and detecting its own elastic vibration by piezoelectric conversion.

  Table 1 shows the piezoelectric basic formula described above. Piezoelectricity is a linear interaction between electrical and mechanical systems, and is a type of energy conversion. In that type of classification, of the transformations that occur through changes in physical variables, it enters a quasi-static transformation in which the changes occur slowly (in a form close to thermal equilibrium). The physical variables are an electric field E and an electric flux density D (or polarization P) in an electrical system, and a stress T and a strain S in a mechanical system (dynamic system). In dealing with this interaction, it is necessary to distinguish between strong (inclusive) variables and explanatory (external) variables. Here, E and T are the former, and D (or P) and S are the latter.

  A surface acoustic wave (SAW) propagates in a rectangular parallelepiped or a piezoelectric medium, but is basically a Rayleigh wave that propagates on the surface of an isotropic body. The Rayleigh wave guided by Lord Rayleigh in 1885 propagates along the free surface of a semi-infinite elastic body (the surface of a sufficiently thick plate), so the wave behavior is similar to that of the water surface. is doing. That is, first, wave energy is concentrated near the surface, and 90% or more is included within one wavelength from the surface. Further, the displacement portion has only the wave traveling direction and the depth direction, and the phase difference between the two components is 90 °, so each point draws an elliptical orbit. FIG. 13 schematically shows the state of the displacement distribution of the surface wave and Rayleigh wave of water. The difference from the case of water is that the surface has a backward elliptical motion in the direction of travel, the displacement is only in the depth direction at a position of about 1/5 wavelength, and the forward elliptical rotation is made deeper than that. That is.

  Further, in the case of water, the propagation speed is a function of frequency, whereas in Rayleigh waves it is always constant regardless of frequency. Thus, the fact that the velocity is constant is said to be nondispersive, which is a major feature of Rayleigh waves. As in the case of an isotropic body, a Rayleigh wave propagates to the surface of a piezoelectric medium that is an anisotropic medium, but generally has all displacement components. However, it is the same that speed does not have frequency characteristics.

The propagation characteristics of surface acoustic waves propagating through a piezoelectric substrate include values such as propagation velocity v, electromechanical coupling coefficient K2, delay time temperature coefficient TCD, and power flow angle PFA. The characteristics of a SAW device using surface acoustic waves largely depend on the piezoelectric substrate used. Therefore, the characteristics required for a better piezoelectric substrate are listed as follows.
(1) The electromechanical coupling coefficient (K2) is large.
(2) Good temperature characteristics (TCD).
(3) Spurious response is small.
(4) The power flow angle (PFA) is zero.
(5) Propagation loss is small.

  The electromechanical coupling coefficient is a value indicating the conversion efficiency from electric energy to surface wave energy. TCD indicates the coefficient of variation of surface wave velocity or delay time with temperature. The spurious response is a phenomenon in which the attenuation amount deteriorates due to the unnecessary vibration mode. The power flow angle is an angle representing the difference between the direction of the phase velocity that propagates and the direction of the group velocity when SAW is excited in the comb-shaped electrode. If the propagation velocity V is high, it is advantageous for high frequencies, and if it is slow, it is advantageous for delay lines.

  SAW devices using the piezoelectric effect and surface acoustic waves contribute to technological innovation of devices used in mobile communication terminals along with the rapid expansion of the mobile communication market represented by mobile phones in recent years. . Such a SAW device is regarded as one of key parts for realizing miniaturization and high functionality of mobile communication terminals, and is mainly used as a band pass filter for RF and IF stages, and is manufactured by a photolithography process. Therefore, microfabrication is possible, and now it is put into practical use in several GHz band.

  In the SAW device, a piezoelectric body is used as a substrate for exciting and receiving SAW. The piezoelectric body is required to have a smoothness of the order of μm, which is the wavelength of the elastic wave, and a reproducibility of a frequency of several hundred ppm or less, so that it was formed on a piezoelectric single crystal or a single crystal with small variations in material constants. A piezoelectric thin film or the like is used. As means for exciting the SAW, an electrode in which plus and minus intersect as shown in FIG. 14, that is, a so-called IDT (Interdigital Transducer) comb-shaped electrode is used. Since this IDT has frequency characteristics, a filter or a resonator can be formed.

FIG. 15 shows the principle of a SAW filter using the SAW device. This SAW filter is generally composed of a piezoelectric substrate and a transmission / reception IDT. The center frequency f of the filter can be expressed as f = V / λ where V is the SAW sound velocity and λ is the wavelength determined by the IDT pitch. Therefore, since this center frequency band is excited most, it is possible to take out an arbitrary frequency band by controlling this value. At this time, in order to obtain an arbitrary frequency with higher accuracy, several stages of filters are used. FIG. 16 shows an example of a reception block of a mobile phone using the SAW filter. The radio wave taken in from the antenna passes through the first-stage filter, drops the frequency through the mixer, and is finally sent to the baseband unit. Since the SAW filter covers a frequency range of several tens of MHz to several GHz, for example, in a 1.5 GHz digital mobile phone, it is used as a first-stage IF filter of RF 1.5 GHz and 130 MHz.
T. Nomura, A. Saitoh, and S. Furukawa, Proceedings of 1999 IEEE Ultrasonics Symposium, pp477-480 (1999) 2) Toshio Fujiyoshi, New Nondestructive Inspection Handbook (Japan Nondestructive Inspection Association), 19923 Shibayama Inui, Acoustic Wave Device Handbook (Japan Society for the Promotion of Science), 19914 T.Nomura, A.Saitoh, Wireless acoustic wave sensor system (JTTAS Study Group), 20025 Shibayama Inui, SAW Engineering, 19836 VKVaradan et al., Microsencors, MEMS and Smart Devices (published by John Willey & Sons, Ltd) 20017 Yoshihisa Tanaka, Shuichi Miyazaki, Mechanical properties of shape memory alloys (Yokendo Publishing), pp31-33, 44-45

  In a high-frequency surface acoustic wave (SAW) device composed of a piezoelectric material and a comb-shaped electrode (IDT), many developments have been made as a radio wave filter using a resonance phenomenon incorporated in a radio wave receiver such as a television or a cellular phone. There was a track record. However, conversely, the acoustoelastic properties of the SAW substrate material itself accompanying changes in the external environment (deformation (phase, amplitude, attenuation, etc.) of the propagating elastic wave) are extracted and used as the leading-edge of a non-powered and wireless sensing device. At present, there are few research examples that can be developed as measurement and analysis techniques and methods, and developed and utilized as basic elemental technologies for the IT technology society.

From the above-mentioned SAW device using only the piezoelectric (PZT example, crystal element, LiNbO ₃ etc.) substrate material, the temperature coefficient of the piezoelectric material itself, the temperature and stress (strain) due to the stress acoustoelastic effect are only the measurable parameters. As a sensor device for measuring environmental factors, there is a drawback that its application range and expandability are narrow. For this reason, there is a need for a system that can simultaneously measure multi-parameter environmental change factors.

  Furthermore, in the conventional SAW device consisting of IDT bonded to a piezoelectric substrate, incompletely bonded portions of IDT and PZT substrate, PZT inhomogeneity on the propagation path, and poor surface finish (discontinuity) are affected. In addition, electrical noise (disturbance) may enter during input and output, and it may be difficult to separate and extract sensing signals from environmental change factors (temperature, stress (strain), etc.). Sometimes it became a problem.

  Due to the technical problems in developing and applying the above SAW device as a sensor for detecting environmental change factors, in the present invention, a special functional film material that reacts to multiple environmental change factors is added to the SAW propagation path. Focus on changes in propagation characteristics through interaction with environmental change factors, and also make IDT multi-channel, through which various physical stoichiometry related to the environment and living body (health) problems It is an object of the invention to obtain a basic technology for developing a sensing system using a multifunctional SAW device capable of measuring (temperature, stress, strain, humidity, trace gas, ionization concentration, biological component trace analysis, etc.) with high sensitivity.

  And further selection of piezoelectric substrate material and IDT densification, SAW propagation high frequency in ultra short wavelength range above GHz, multi-channel, miniaturization of micro device, wireless transmission / reception system improvement, signal transmission / reception analysis software The purpose is to develop and establish it as an internationally unique and superior IT, advanced measurement and analysis technology and technique for ubiquitous society.

  In the present invention, in a surface acoustic wave (hereinafter referred to as SAW) device that propagates energy concentrated near the surface of an elastic body, a special functional material that reacts to an environmental change factor is added to the SAW propagation path. Multifunctionalization, focusing on changes in the propagation characteristics of SAW, through which various physical and chemical quantities (temperature, stress, strain, humidity, trace gas, etc.) related to the surrounding environment and biological (health) problems It is an object of the present invention to provide a SAW device sensor capable of measuring ionization concentration, biological component microanalysis, etc.) with high sensitivity.

  In order to solve the above-described problems, the surface acoustic wave device sensor of the present invention applies a high-frequency current or a high-frequency voltage to an element composed of comb-shaped electrodes bonded to a piezoelectric substrate, and has a surface near the surface of the piezoelectric substrate. An elastic wave is generated, and an environment change factor is detected by the propagation characteristic of the surface acoustic wave.

  In addition, the surface acoustic wave device sensor of the present invention reduces electrical noise by electrically short-circuiting the propagation surface of an element composed of comb-shaped electrodes joined to a piezoelectric substrate with a conductive metal and grounding it. The detection sensitivity has been improved by extracting the signal reception in both the surface acoustic wave propagation paths at the same time. It is characterized by.

  Therefore, it is designed to enable parameter sensing in which a plurality of IDTs are installed on a SAW device. In addition, by forming a functional thin film on the propagation path of each channel, the physicochemical reaction between the environmental change factor and the film formation is caused, and the film formation characteristics denatured at that time are indirectly determined. If captured as a change in SAW, various physicochemical environmental change factors can be measured simultaneously.

  Furthermore, it can be developed as a basic technology for a wireless multi-functional SAW sensing system of a non-power-feed type in which a small-sized SAW chip having a multi-functionality and a characteristic of wireless is arranged on the net. It has technological advantages such as internationally unique and superior IT, advanced measurement and analysis technology and techniques for ubiquitous society.

  SAW devices that focus on changes in the propagation characteristics of high-frequency SAWs composed of piezoelectric materials and IDTs have many achievements as filters built into radio wave receivers such as mobile phones in Japan.・ Currently, there are almost no research examples that have been developed as advanced measurement analysis technology / methods as wireless sensing devices and developed and utilized as fundamental elemental technologies for the IT technology society.

  In the present invention, paying attention to the change in propagation characteristics of SAW, a functional thin film is formed on a surface acoustic wave propagation path (hereinafter referred to as SAW propagation path), and various physicochemical environmental change factors are simultaneously applied. It can be developed as a basic technology for a wireless multi-function SAW sensing system of a non-powered system in which small SAW chips capable of remote measurement are arranged on the net. FIG. 1 is a schematic configuration diagram of a SAW device sensor according to the present invention.

  In this SAW device sensor 1, a comb-shaped electrode (IDT) 3 is formed on a piezoelectric substrate 2, and a high-frequency current or a high-frequency voltage is applied to the IDT 3 from the outside, whereby surface acoustic waves ( SAW). A plurality of functional thin films 6 are formed on the piezoelectric substrate 2, and a SAW propagation path 4 is set corresponding to the functional thin film 6. The functional thin film 6 reacts with environmental change factors (trace gas, humidity, light, temperature, stress (strain), electromagnetic, radioactivity, ion concentration, liquid viscosity, biological reaction, pathogen, etc.) Changes, polarization, weight changes, residual stresses, etc. are caused, and through this, a plurality of external environment information can be detected (sensing) at a time. The SAW device sensor 1 of the present embodiment includes three channels (Ch. 1 to Ch. 3) of the SAW propagation path 4 made of the functional thin film 6, but is not limited to this, and further increases the number of channels. Thus, it is possible to realize multi-function sensing with a single chip.

  FIG. 2 shows a circuit configuration example when the SAW device sensor 1 is made non-powered and wireless. By using the wireless function shown here, the use environment as the sensor can be greatly expanded. Further, since the SAW device sensor 1 is manufactured by a photolithography process, the SAW device sensor 1 is easily reduced in size and is inexpensive, and the frequency characteristic thereof is determined by the interval between the linear electrodes of the IDT 3. For this reason, the frequency becomes higher with the development of the microfabrication technology, and it becomes possible to have a more advanced sensing function such as a bio-factor analysis sensor.

For the design and trial manufacture of the SAW device sensor 1, two types of piezoelectric substrates 2 of quartz (ST cut) and LiNbO ₃ (128 ° YX cut) having dimensions of 20 mm × 35 mm were used. Table 2 below shows the basic characteristics of the used piezoelectric substrate (quartz, LiNbO ₃ ). The IDT 3 was designed using Au and P (pitch) 20 μm, crossing width 3 mm, and propagation length L = 16 mm. Further, when the respective center frequencies were measured with an oscilloscope, it was 39.8 MHz for the quartz substrate and 66.82 MHz for the LiNbO ₃ substrate. FIG. 3 shows the shape of the SAW device sensor actually designed and the dimensions of each part.

  Next, the functional thin film 6 was formed on the SAW propagation path 4 of the piezoelectric substrate 2. FIG. 4 shows the basic configuration of the magnetron sputtering apparatus used at that time. In the magnetron sputtering method, a concentric magnet whose center and outer periphery are excited with opposite polarities is installed on the backside of the cathode to which the target (thin film material) is attached, and a leakage magnetic field connecting the center and the outer periphery is generated on the target surface. . Using the chamber and the substrate holder as an anode, for example, an inert gas such as Ar gas is introduced so as to be about 0.01 Torr, and a voltage of several hundred volts is applied to generate glow discharge. The positively ionized Ar gas is accelerated by the cathode fall voltage, obtains kinetic energy, and collides with the cathode. Therefore, a part of the target material exchanging momentum with positive ions jumps out of the cathode, reaches the substrate on the anode, and deposits a film.

The target material is Fe-Pd, which is a magnetic shape memory alloy (FSMA), and the chamber of the sputtering apparatus is evacuated (4 × 10 ^-4 Pa) using a rotary pump and a turbo pump. Film formation was performed on the intermediate portion of the SAW propagation path 4 using a magnetron sputtering method at an argon pressure of 3.0 Pa, a film formation time of 3 hours, and a substrate temperature of 100 ° C. In addition, the film was formed using a mask so that the thin film dimensions were 3 mm × 6 mm and the thickness was 3 μm.

  In order to confirm the presence or absence of the transformation point of the formed functional thin film, the Fe-Pd thin film of the same composition prepared on the aluminum substrate under the same sputtering conditions was measured with a differential scanning calorimeter (DSC) and compared. did. When DSC raises the temperature of a substance and a reference material (in this case alumina) simultaneously while applying the same amount of heat according to a controlled program, the sample absorbs the heat of fusion and heat of transition when melting and phase transition occur, The temperature rise is delayed and a temperature difference is generated between the reference material and the reference material. A record of the electrical energy required to keep the temperature difference at zero is a differential calorimetric curve. Melting and phase transitions appear as peaks on the curve, and the peak area corresponds to the amount of heat. The sample purity is determined from the analysis of the peak shape. The heat capacity is determined as a value relative to the reference substance from the position of the baseline.

In various measurements, a SAW device sensor attached to a polymer substrate and connected was used. FIG. 5 shows the external appearance of the SAW device sensor 1 after connection. The left in the figure is based on the LiNbO ₃ substrate, and the right in the figure is based on the quartz substrate. In the connection method, first, a copper substrate attached to a polymer substrate was etched, and the copper foil was formed into an arbitrary shape. Next, the prototype SAW device sensor is fixed to the center of the polymer substrate, and the copper foil on the polymer substrate and the SAW device are wired with copper tape, and each joint is conductive to improve the flow of electricity. Glue with an adhesive (doutite etc.).

(Temperature change test conditions)
In order to verify whether the SAW device can be used as a temperature sensor or phase transformation sensing, the amplitude and phase change of the SAW extraction signal when the temperature was changed were measured. FIG. 6 shows a configuration diagram of the experimental system. In the experiment, two types of prototyped SAW devices were used, and the respective center frequencies were measured with a quartz substrate: 39.8 MHz and a LiNbO ₃ substrate: 66.82 MHz. The measuring instrument was a vector voltmeter capable of measuring changes in amplitude and phase from the input / output potential difference. First, a prototype SAW device sensor is installed in a temperature control chamber, and a pulse voltage of each center frequency is applied using a function generator to generate SAW. Using the amplitude and phase at room temperature as a reference at this time, the phase difference and amplitude ratio when the temperature was changed from room temperature to 90 ° C. were measured with a vector voltmeter. The temperature was measured using a digital thermometer close to the SAW device sensor.

In order to verify whether the SAW device can be used as a stress (strain) or internal damage sensor, changes in the amplitude and phase of the SAW were measured when a load was applied. The measurement was performed using two types of prototyped substrates, and the respective center frequencies were measured with a quartz substrate: 39.8 MHz and a LiNbO ₃ substrate: 66.82 MHz. The amplitude and phase were measured using a vector voltmeter as in the previous experiment.

  FIG. 7 shows a configuration diagram of an experimental system using a load. One end of a polymer substrate on which a SAW device is mounted is fixed in a cantilever manner, and a pulse voltage having a center frequency is applied by a function generator to generate SAW. The amplitude and phase at this time (no load) were used as a reference, and changes in the phase and amplitude when the weight was loaded up to 600 g were measured with a vector voltmeter. The strain was measured using a strain gauge attached near the Fe-Pd thin film. The dimensions of the polymer substrate were 45 mm × 70 mm and thickness 1 mm, and the dimensions of the piezoelectric substrate constituting the SAW device were 20 mm × 35 mm and thickness 0.5 mm.

  Here, temperature changes in the prototyped SAW device and changes in SAW propagation characteristics due to load are measured, and measurement as a temperature sensor and a stress (strain) sensor is attempted. Furthermore, a functional film (magnetic shape memory alloy, Ferromagnetic SMA) is formed on the device, and sensing of crystal phase transformation / physical property change using stress-induced phase transformation phenomenon accompanying temperature change, which is a major feature of FSMA materials, stress induction To verify the possibility as an evaluation sensor of the degree of mechanical internal damage through phase transformation.

  Quartz (ST cut) substrates are greatly affected by noise, and various measurements are impossible. This means that the electromechanical coupling coefficient, which means energy conversion efficiency, is small and the sensitivity is weak. Therefore, the excitation signal of the SAW itself is weak and buried in the disturbance (noise) level. This is because it cannot be evaluated. Therefore, in order to use the SAW device as a sensor, it is necessary to increase the main signal and make it less susceptible to noise by using a material / cut direction having a large electromechanical coupling coefficient.

(About temperature sensor)
FIG. 8 shows a graph of the phase change with respect to the temperature change in the LiNbO ₃ substrate. From this graph, it can be seen that the phase shows a substantially linear change with respect to the temperature change, and there is almost no hysteresis due to the temperature. Since the phase is expressed by θ = 2πfL / v (f: frequency, L: propagation distance, v: SAW propagation velocity), in this case, the change in propagation distance L due to thermal expansion is very small, so the phase changes. The main cause is considered to be a change in the propagation velocity v.

  The velocity of elastic waves is not as strongly dependent on the type of material as you can imagine from the difference in material hardness. This is because the state dependence of the density P and the compression rate Ks almost cancels each other as a result. Differences in materials appear in the temperature dependence of sound speed. Here, the basic equation of sound waves is shown in the next section.

  For example, most solids become softer when warmed. That is, as the temperature rises, the compression rate increases and the sound speed decreases. This tendency, in contrast to gases, is actually a property of many solids. Therefore, it can be used as a temperature sensor by measuring a change in phase, propagation speed, or wave propagation time due to temperature.

(About phase transformation sensing)
FIG. 9 shows a graph of changes in amplitude and phase with respect to temperature changes. Table 3 shows the results of DSC measurement. A large change is seen in both amplitude and phase at 50-60 ° C. during heating and at 40-50 ° C. during cooling. Here, the sample subjected to DSC measurement is a film formed on an aluminum substrate, but even if the shift of the transformation point due to the difference in internal stress is taken into consideration, the temperature related to the change that appears is the result of the DSC measurement. It turns out that it is substantially in agreement. The Fe-Pd thin film deposited on the piezoelectric substrate undergoes a heat-induced phase transformation with temperature change, and the elastic modulus of the thin film has changed significantly.

  However, the change in amplitude does not return to the original amplitude value level even though martensitic transformation occurs during cooling. This is probably because the low temperature side martensitic phase transformation has not been sufficiently completed in the cooling process, and the influence of the high temperature side retained austenite has come out. Therefore, in order to improve this, it can be said that it is necessary to cool to a lower temperature when cooling. From the above, the possibility of sensing the phase transformation can be seen more clearly by paying attention to the change in the phase of the SAW due to the transformation.

(About stress (strain) sensors and internal damage sensors)
FIG. 10 shows a graph of changes in amplitude and phase due to stress. From this graph, it can be seen that the phase changes almost linearly with respect to the distortion and the amplitude does not change. This change in phase due to strain is considered to be due to the acoustoelastic effect. This acoustoelastic effect is that an elastic body that has become anisotropic due to stress exhibits birefringence with respect to sound waves, and the difference in sound speed between the two component waves is proportional to the main stress. That is, the sound velocity is related to the elastic modulus, and the SAW velocity V is given by V≈Vs (0.87 + 1.12σ) / 1 + σ (Vs is the velocity of the transverse wave and σ is the Poisson's ratio). Therefore, the phase change due to strain is caused by the SAW exhibiting birefringence due to the acoustoelastic effect due to the average stress applied to about one wavelength in the SAW propagation path, and the elastic modulus of the substrate slightly changed. It is thought that the speed has changed.

  By using the change in SAW speed due to this acoustic elasticity, it can be used as a stress (strain) sensor. Furthermore, in principle, the acoustoelastic effect can also be applied to the internal residual stress, and the SAW speed changes, so that it can be used for an internal damage sensor.

(About fatigue life nondestructive estimation and evaluation)
In general, for machines and structures, the number of repeated load ranges (△ P) (N) and mechanical damage that occurs and accumulates internally (Df: Destruction damage, damage accumulation per fatigue load = 1 / N linear addition) Life prediction (Nf) can be made by the mutual relation of the law (final fracture is established at 1 / Nf = 1), that is, the so-called minor linear damage accumulation fracture law in fatigue.

  Therefore, we tried to demonstrate SAW multifunctional application that can predict fatigue life. First, a shape having non-linear characteristics with respect to a load stress as shown in FIG. 11 that stores the maximum stress (strain) received by the base material side member on which the SAW is installed on the SAW propagation path having a multi-channel configuration. Memory alloy (low temperature side martensite M phase, for example, Ti50Ni40Cu10 atomic% composition shape memory alloy) and an alloy made of linear superelastic material (high temperature side austenite A phase, for example, Ti50Ni47Co3 atomic% composition alloy) are vapor-deposited. A multifunctional SAW device sensor was designed and prototyped.

  Here, a phase transformation sensing function and a mechanical damage memory function in the multifunctional SAW device sensor will be described with reference to FIG. FIG. 12 shows the concept of the phase transformation behavior accompanying the change in temperature and stress of the functional film (FSMA) formed on the SAW device. Shape memory alloys have a shape recovery behavior that restores the shape to its original shape by the shape memory effect. The shape memory effect is that when a sample of a certain shape is rapidly cooled from a temperature higher than the critical temperature to form a low-temperature phase (martensite phase), and this is deformed and then heated again, when the critical temperature is exceeded, reverse transformation occurs simultaneously. The phenomenon that the shape also recovers. The shape memory effect occurs due to martensitic transformation. The phase before the shape memory alloy undergoes martensitic transformation, that is, the phase at high temperature is called the austenite phase. When the shape memory alloy of the austenite phase is cooled from a high temperature, the martensitic transformation starts when a certain temperature is exceeded. This temperature is referred to as Ms (martensite start temperature).

  If the cooling is continued, the transformation proceeds, and if the temperature drop is stopped, the transformation stops. In other words, the formation of martensite is determined only by temperature, not time. When the temperature is lowered, the temperature at which martensite is first generated is the Ms point. When the temperature is further lowered, the martensite transformation becomes active and the amount of martensite increases rapidly. Thereafter, the progress of the transformation becomes gradual, and finally the entire alloy becomes a martensite phase. When an alloy that is entirely in the martensite phase is heated, a reverse transformation from the martensite phase to the body-centered cubic austenite phase occurs. When heating is continued, the martensite phase decreases according to a curve similar to that during cooling, and the austenite phase increases accordingly. The end temperature of the reverse transformation is called Af (austenite end temperature).

  The phase transformation sensing function is enabled by measuring changes in SAW propagation characteristics due to changes in physical properties (such as elastic modulus) associated with the transformation of the FSMA. The memory function of mechanical damage causes an increase in twins and a mutual shift by applying stress at the temperature of the low-temperature martensite phase (Ms) and causing a stress-induced phase transformation in the FSMA. At this time, even if the stress is removed, discontinuous twins remain in the functional film and accumulate as residual strain. This can be achieved by measuring changes in SAW propagation characteristics due to accumulation of residual strain (damage) using the acoustoelastic method. Further, the internal residual strain disappears by heating to the end of the high temperature side austenite (Af) or higher, and is recovered to the A phase, so that the surface film phase can be returned to the initial state (reset).

From the above, in this experiment, at room temperature level,
1) Maximum stress history experienced by a mechanical structure from the thin film adhesion path of a Ti50Ni40Cu10 atomic% composition shape memory alloy having a low-temperature martensite M phase (temperature state below Mf) characterized by nonlinear hysteresis with respect to applied load ( σmax = stored maximum strain level) degree,
2) The load level (stress) that the mechanical structure receives from the thin film adhesion path of the Ti50Ni47Co3 atomic% composition superelastic alloy having the high temperature side austenite A phase (temperature state above Af) characterized by a linear hysteresis with respect to the applied load. Establish and evaluate the fatigue failure life (number of repeated loads Nf) by building a system that constantly monitors the number of times (Δσ = number of load stress levels−frequency). Actually, the above-mentioned multifunctional SAW device sensor signal and the minor linear fatigue damage law with a single swing fatigue load condition (R = Pmin / Pmax = 0) of tension / compression repeated at zero load or more using an Al plate sample The number of sample breaks estimated from (Npf, Nf = 1200 times) is the actual life (Nf, Nf = 1450 times), and it is clear that 30% or less life prediction is possible. The effectiveness was confirmed.

  In order to further develop the multi-functional SAW device sensor system of the present invention and improve the reliability and versatility of the sensor device, it is necessary to select a high-sensitivity, low-temperature coefficient piezoelectric material to be used as a substrate and to increase the IDT density. It is necessary to go ahead and increase the SAW propagation frequency in the ultrashort wavelength range of GHz or higher, increase the number of channels, make a micro device, improve the radio transmission / reception system, and develop signal transmission / reception analysis software. Specifically, 1) Development of high-density, multi-channel SAW sensors, 2) Technological innovations for long-distance, non-feedless wireless sensor systems, 3) Development of SAW multi-function / multi-functional materials process stable production technology 4) Fundamental technology for ultra-micro machining and commercialization.

  If these technical issues can be improved, we will have high sensitivity to physical chemical quantities (temperature, stress, strain, humidity, trace gas, trace analysis of biological components, etc.) related to our everyday environment and biological (health) problems. Investigate and research the basic technology of sensing systems using SAW device sensors that are characterized by wireless power and wireless characteristics, and make SAW device systems that are small and highly mobile as future advanced analysis and measurement equipment. Technological contribution can be realized by developing into an embedded system.

The technical and social significance and application fields of the present invention are as follows.
(1) Development of non-powered wireless sensing technology (2) Proposal of multi-channel SAW device (3) Thin film fabrication process technology for multi-function / complex functional SAW creation (4) Small embedded antenna technology (5) Continuous monitoring of production line ( Process monitor) Technology development (6) Wireless monitoring technology for automobiles, aircraft, etc. (ITS related)
(7) Structural health assessment (health monitoring)
(8) In-situ non-destructive inspection and maintenance cost reduction (9) Contribution to a safe and secure society (Security) and internationally unique IT and advanced measurement and analysis technology for ubiquitous society It can be developed and established as a method.

The following can be considered as specific application fields of the SAW device sensor of the present invention.
(1) Load stress / strain wireless (wireless) measurement of power machine parts, turbine blades (airplanes, power plants) and rotating machine parts (automotive torque sensors)
(2) ・ Measurement of chemical reaction, solution and gas reaction state in factory production process ・ Gas generation and component analysis inside petroleum plant and chemical synthesizer ・ Monitoring management of temperature, gas pressure, etc. of synthesis process and processing line (3) Door open / close sensor (SAW sensor that reacts to magnetic field by magnetostrictive film composite)
(4) Environmental (temperature, lighting, humidity, condition, fire) sensing, energy-saving management in buildings, hospitals, and residences (5) Residual stress (strain) monitoring for construction, bridges, internal damage, remaining life, etc. In-situ evaluation (6) Continuous measurement of distortion and creep elongation of tunnel, bedrock (landslide area), etc. (7) Gas leak detection in gas pipeline (8) Security sensor (combined function with infrared (pyroelectric) sensitive film (Management of suspicious intruders by conversion)
(9) Biosensor (using biofunctional reaction membranes on SAW propagation pathways, ion polarization, viscosity change, attenuation change, bioenzyme reaction, bacteria / virus interaction) Detectable)
(10) Multi-functional and multi-channel SAW device sensor network placement for integrated management system for regional safety and energy saving

It is a block diagram of the multifunctional SAW device sensor of this invention. It is the circuit block diagram which made the said SAW device sensor wireless. 2-channel SAW (LiNbO ₃ base, Pt deposition) the prototype is a diagram showing a. It is a basic lineblock diagram of magnetron sputtering. It is a figure (left: LiNbO ₃ substrate, right: quartz substrate) showing the SAW device after connection. It is a block diagram of the experimental system for measuring the change of the SAW propagation characteristic with respect to temperature. It is a block diagram of the experimental system for measuring the change of the SAW propagation characteristic by a load. It is the figure which showed the phase change of SAW by temperature. It is the figure which showed the change of the amplitude and phase accompanying the phase transformation of the FePd magnetic shape memory alloy thin film vapor-deposited on the SAW propagation path. It is the figure which showed the change of the amplitude and phase of SAW with respect to distortion. It is a schematic diagram which shows the shape memory effect and superelasticity phenomenon in a shape memory alloy system tensile test. It is a model figure which shows the shape memory effect in a shape memory alloy system, superelastic appearance conditions, and its atomic phase transformation. It is a figure which shows the displacement distribution of water and a Rayleigh wave. It is a figure which shows the excitation state of SAW by an interdigital electrode (IDT). It is a principle diagram of a SAW filter. It is a block diagram of the reception function of the mobile phone using a SAW filter.

Explanation of symbols

1 SAW device sensor (surface acoustic wave device sensor)
2 Piezoelectric substrate 3 IDT (comb electrode)
4 SAW propagation path (surface acoustic wave propagation path)
5 SAW (surface acoustic wave)
6 Functional thin film 7 channels

Claims (9)

A high-frequency current or high-frequency voltage is applied to an element composed of comb-shaped electrodes joined to a piezoelectric substrate, and a surface acoustic wave is generated near the surface of the piezoelectric substrate. A surface acoustic wave device sensor characterized by detecting the above. A free-surface-type surface acoustic wave propagation path that reduces electrical noise by electrically short-circuiting the propagation surface of an element composed of comb-shaped electrodes bonded to a piezoelectric substrate with a conductive metal and grounding And a surface acoustic wave propagation path that is not grounded, and simultaneously detecting signal reception in both surface acoustic wave propagation paths to improve detection sensitivity. A functional thin film using a high-functional material composed of a shape memory effect, a super elastic effect, and a magnetostrictive mechanism is formed on the surface acoustic wave propagation path, and this functional thin film reacts with an environmental change factor to cause an electric resistance. 3. The surface acoustic wave device sensor according to claim 2, configured to cause a change, polarization, weight change, and residual stress, and to detect a plurality of the environmental change factors therethrough. A magnetostrictive material or a magnetic shape memory material that responds to magnetism is formed on the surface acoustic wave propagation path, and a surface acoustic wave based on one of phase, voltage, and attenuation is obtained through a magnetostriction phenomenon caused by an external magnetic field change. The surface acoustic wave device sensor according to claim 2, wherein an external magnetic field is detected by changing propagation characteristics. By forming a shape memory material on the surface acoustic wave propagation path, the external temperature change through the generation of crystal phase transformation accompanying the shape memory effect due to external stress and temperature change, and the accompanying nonlinear shape recovery behavior 3. The surface acoustic wave device sensor according to claim 2, wherein the degree of material damage is indirectly nondestructively inspected. A superelastic material made of TiNiCu or TiNiCo is formed on the surface acoustic wave propagation path, and an external load is applied through the occurrence and extinction of a linear crystal phase transformation accompanying external stress loading / unloading. The surface acoustic wave device sensor according to claim 2, wherein the surface acoustic wave device sensor is indirectly nondestructively inspected. A shape memory material and the superelastic material are deposited on a surface acoustic wave propagation path having a plurality of comb-shaped electrodes, and an external load load and residual damage on the piezoelectric substrate side are indirectly inspected nondestructively. The surface acoustic wave device sensor according to claim 5 or 6. The surface acoustic wave device sensor according to claim 1 or 3, wherein the environmental change factor is any one of a trace gas, humidity, light, temperature, strain, electromagnetics, radioactivity, ion concentration, liquid viscosity, biological reaction factor, and pathogen. . The surface acoustic wave device sensor according to any one of claims 2 to 7, wherein a multichannel configuration is provided by providing a plurality of the surface acoustic wave propagation paths.