Composite substrates for SAW tags for RFID and sensor applications

Abstract

The present invention relates to a surface acoustic wave tag device, which comprises an acoustic wave propagation substrate (202), at least one transducer structure (204) comprising staggered comb electrodes (216), and at least one reflecting device, wherein the reflecting device comprises at least one reflector (206, 208, 210), characterized in that the acoustic wave propagation substrate (202) is a composite substrate (202) comprising a base substrate (226) and a piezoelectric layer (224), wherein the crystal orientation of the piezoelectric layer (224) relative to the base substrate (226) enables shear waves to propagate in the piezoelectric layer (224) and in a propagation direction corresponding to the acoustic wave. The present invention also relates to a physical quantity determination device and a method for manufacturing such a surface acoustic wave tag device (200).

Description

[0001] The present invention relates to a surface acoustic wave tag device for RFID and sensor applications, and more particularly, to a composite substrate for a surface acoustic wave tag device.

[0002] Since the late 1980s, surface acoustic wave (SAW) tag devices have been used as radio frequency identification device (RFID) tags. According to the prior art, a SAW tag device includes a piezoelectric substrate having a single transducer and a set of reflectors and an antenna, wherein the set of reflectors are positioned on one side of the transducer at various delays. An incident RF signal is captured by the antenna attached to the SAW tag, which activates the SAW tag and is retransmitted as a reflected response of the SAW tag device.

[0003] The quality factor to be considered in designing such a device is the electromechanical coupling coefficient ks 2 , the temperature stability of the operating frequency and the reflection coefficient of the reflector under Bragg conditions.

[0004] The SAW tag device relies on the use of Rayleigh waves traveling on the surface of bulk piezoelectric lithium niobate (LiNbO3) with a crystal orientation given by (YX / ) / 128°. 2 In between 5% and 6% of cases, this construction makes it possible to produce a SAW tag operating in a frequency band centered around 2.45 GHz that can be remotely interrogated at distances ranging from a few centimeters to a few meters.

[0005] However, it is not possible to obtain an electromechanical coupling coefficient ks greater than 6% in bulk lithium niobate using Rayleigh waves. 2 , thus limiting the distance at which the device can be interrogated.

[0006] Furthermore, lithium niobate in fact exhibits a strong temperature drift, which is a minimum of about 70 ppm / K for the temperature coefficient of retardation (TCD), which makes it difficult to realize an architecture that can be used as a sensor for measuring any other physical parameter than temperature.

[0007] The object of the present invention is to overcome the above mentioned drawbacks by providing a surface acoustic wave (SAW) tag device deposited on a composite substrate having improved performance for RFID and sensor applications, in particular for measuring physical parameters other than temperature.

[0008] The objective of the present invention is achieved through a surface acoustic wave tag device, which comprises an acoustic wave propagation substrate, at least one transducer structure including staggered comb electrodes arranged on the substrate, and at least one reflection device, which comprises at least one reflector, and the at least one reflector is positioned at a distance relative to the at least one transducer structure in the propagation direction of the acoustic wave, characterized in that the acoustic wave propagation substrate is a composite substrate including a base substrate and a piezoelectric layer, wherein the crystal orientation of the piezoelectric layer relative to the base substrate enables shear waves to propagate within the piezoelectric layer and in the propagation direction corresponding to the acoustic wave.

[0009] In such a device, shear waves are the dominant waves propagating in the piezoelectric layer, rather than Rayleigh waves as in the prior art SAW tag devices, due to the relative crystal orientation of the piezoelectric layer with respect to the base substrate. Since the temperature stability of the shear waves is improved using the proposed composite substrate compared to the one of the Rayleigh waves on bulk LiNbO3, the application of the SAW tag device can be extended to measuring mechanical parameters such as force, pressure, etc., in addition to measuring temperature. Moreover, the shear wave mode in the considered composite substrate presents a stronger electromechanical coupling coefficient ks than the Rayleigh wave mode on bulk LiNbO3 2 , and using this relative crystal orientation of the piezoelectric layer with respect to the base substrate will also result in an electromechanical coupling coefficient ks 2 The increase is by a factor of about 2 up to about 5. Thus, a SAW tag device with an increased range for long-range interrogation can be obtained.

[0010] According to a variant of the invention, the piezoelectric layer of the composite substrate may be lithium tantalate (LiTaO 3 ) or lithium niobate (LiNbO 3 ).

[0011] According to a variant of the invention, the piezoelectric layer is lithium niobate LiNbO3, and the crystal orientation of the piezoelectric layer relative to the base substrate is (YX / ) / θ according to the standard IEEE 1949Std-176, where θ is an angle of crystal orientation between 0° and 100°, in particular between 0° and 50°, or between 140° and 180°, with 180° as the modulus. Within this specific range of crystal orientation, shear wave modes travel in the piezoelectric layer, and fast propagation speeds of 4000 m / s or more and absolute maximum TCF values ​​of about 65 ppm / K and ks higher than 20% can be observed. 2 Typically, the shear wave mode exhibits a sufficiently large electromechanical coupling coefficient ks 2To allow SAW tag operation, however only cut angles close to the (YX / ) / 128° orientation allow the use of Rayleigh waves for this purpose. Therefore, cut angles in the ranges [0°-100°] and [140°-180°] are favorable for the use of shear wave modes, and any crystal cut in the range [100°-180°] can be used to utilize Rayleigh waves.

[0012] According to a variant of the invention, the piezoelectric layer is lithium tantalate (LiTaO3), and the crystal orientation of the piezoelectric layer relative to the base substrate is (YX / ) / θ according to the standard IEEE 1949Std-176, wherein θ is an angle of crystal orientation between -30° and 90°, in particular between 0° and 90°, with 180° as the modulus. In this specific range of crystal orientation, the shear wave mode is dominant over the Rayleigh mode, and a fast propagation speed of about 4000 m / s and a TCF of less than -20 ppm / K and a ks of about 3% to 12% can be observed. 2 In particular, for a range of θ between 20° and 60°, more particularly for θ of about 36° or about 42°, modulo 180°, the TCF may be close to zero.

[0013] According to a variant of the invention, the base substrate of the composite substrate is silicon. To transfer the piezoelectric layer on silicon, a SmartCut TM A mass production method using ion implantation in a piezoelectric source substrate to define the layer to be transferred, attaching the source substrate to a silicon substrate and transferring the layer by thermal or mechanical treatment. Alternatively, a base substrate such as diamond, sapphire, silicon carbide, fused quartz or quartz crystal can be used. Preferably, the base substrate of the composite substrate can be a silicon-on-insulator substrate (SOI), corresponding to a layered silicon-insulator-silicon substrate, and the insulating layer can be a SiO2 layer.

[0014] According to a variant of the invention, the base substrate may also include a Bragg mirror consisting of alternating low / high acoustic impedance layers, such as silicon dioxide and tungsten or silicon dioxide and silicon nitride or silicon dioxide and aluminum nitride. The Bragg mirror reduces energy losses toward the base substrate because it can reflect the radiated portion of the mode toward the piezoelectric layer and may also add mechanical stability to the device structure.

[0015] According to a variant of the invention, at least a portion of the base substrate may be deformable. Thus, it is possible to have a SAW tag device that can measure mechanical parameters caused by deformation, such as pressure or vibration resulting in a difference in the flight time of reflected shear waves.

[0016] According to a variant of the invention, at least one reflector of the reflecting device comprises one or more metal strips, which can be connected to each other or to the ground. Connecting them as described above leads to an improvement in the reflection coefficient of the reflector under Bragg conditions, contrary to the prior art situation of Rayleigh waves on a single piece (YX / ) / 128° LiNbO3. The improved reflection coefficient of the reflector under Bragg conditions leads to a better detection of the reflected wave by the transducer structure. Therefore, a SAW tag device with an improved response signal can be obtained compared to the SAW tag device of the prior art.

[0017] According to a variation of the present invention, a physical quantity determination device comprising two or more SAW tag devices (at least one SAW tag device as described above) may also include only one tag antenna connected to the transducer structure of the two or more SAW tag devices. The device can measure two or more parameters that can be sent using only one antenna. Using only one antenna simplifies the structure.

[0018] According to a variant of the present invention, one of the two or more SAW tag devices included in the physical quantity determination device can be a surface acoustic wave resonator, and at least one of the SAW tag devices can be as described above. In the physical quantity determination device, the SAW resonator allows identification of the device on which the measurement of the physical parameter is to be performed. The SAW resonator allows identification, and at least one of the SAW tag devices allows measurement of a physical quantity, such as temperature or pressure.

[0019] According to a variant of the invention, the surface acoustic wave resonator of the physical quantity determination device can be positioned relative to at least one of the surface acoustic wave tag devices of the physical quantity determination device so that they have two different surface acoustic wave propagation directions. Preferably, the surface acoustic wave propagation direction of the surface acoustic wave resonator is parallel to one of the crystal axes of the piezoelectric layer and forms an angle Ψ with the surface acoustic wave propagation direction of at least one of the surface acoustic wave tag devices. As a result, the angle Ψ can be selected so that the surface acoustic wave resonator can generate the type of acoustic wave required for the desired application of the physical quantity determination device. Both devices can use the same type of acoustic waves, both shear waves or Rayleigh waves or any other type of acoustic waves that can be achieved by the orientation of the piezoelectric layer and the selected propagation direction.

[0020] In a variation of the present invention, the surface acoustic wave resonator can be configured to use Rayleigh waves, and at least one of the surface acoustic wave tag devices of the physical quantity determination device can be configured to use shear waves. Thus, the surface acoustic wave resonator can perform identification, and at least one of the surface acoustic wave tag devices can perform measurement.

[0021] According to a variant of the invention, the physical quantity determination device is configured to measure temperature and / or pressure and / or force and / or to allow identification.Thus, in one SAW device it is possible to allow identification of the device and measurement of one or more of its physical parameters.

[0022] The object of the present invention is also achieved by a method for manufacturing a SAW tag device, the method comprising the steps of: a) arranging a piezoelectric layer on a base substrate, and b) arranging a transducer structure on the piezoelectric layer, wherein in step a), the piezoelectric layer is arranged such that the crystal orientation of the piezoelectric layer relative to the base substrate enables propagation of shear waves corresponding to acoustic waves. Layer transfer can be used, for example using SmartCut TM technology.

[0023] According to a variation of the present invention, the above method of manufacturing a SAW tag device further comprises the step of thinning the base substrate. For example, the thinning of the base substrate can produce a seismic mass or membrane. In this configuration, the SAW tag device can measure force or deformation.

[0024] According to a variant of the invention, the step of thinning the base substrate comprises thinning a portion of the surface opposite to the surface to which the piezoelectric layer is attached. Thus, the SAW tag device can be positioned right on the thinned portion of the base substrate such that it becomes sensitive to deformations.

[0025] According to a variant of the invention, the step of thinning the base substrate is performed by etching, wet or dry methods, grinding or chemical mechanical polishing.

[0026] According to a variation of the invention, the base substrate may be a semiconductor on insulator (SOI) substrate, so that the insulator layer of the semiconductor on insulator (SOI) substrate may be used as an etch stop for the step of thinning the base substrate. Using such an SOI substrate as the base substrate allows precise control of the thickness of the etched portion of the back side of the base substrate.

[0027] The present invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which reference numerals indicate features of the invention.

[0028] FIG. 1 shows a surface acoustic wave tag device according to the prior art.

[0029] Figure 2 A surface acoustic wave tag device according to a first embodiment of the present invention is shown.

[0030] Figure 3a and Figure 3b The characteristics of a surface acoustic wave tag device using a composite substrate according to the present invention with a 100 nm SiO2 layer between the piezoelectric layer and the base substrate are described.

[0031] Figure 4The beam steering effect η and the electromechanical coupling coefficient ks are plotted as a function of the angle θ of the crystal orientation on the X-axis and the angle Ψ of the propagation on the Y-axis for a composite substrate according to the invention. 2 The value of .

[0032] Figure 5a A physical quantity determining apparatus including two surface acoustic wave tag apparatuses according to a second embodiment of the present invention is described.

[0033] Figure 5b A physical quantity determining apparatus according to a third embodiment of the present invention is described, the physical quantity determining apparatus including a surface acoustic wave tag device and a SAW resonator device according to the present invention.

[0034] Figure 5c A physical quantity determining apparatus including two surface acoustic wave tag apparatuses according to a fourth embodiment of the present invention is described.

[0035] Figure 6 A schematic diagram showing the steps of a method for manufacturing a surface acoustic wave tag device according to the present invention.

[0036] Figure 7 A schematic diagram showing steps of a method for manufacturing a surface acoustic wave tag device according to another embodiment of the present invention.

[0037] FIG. 1 shows a surface acoustic wave tag device 100 according to the prior art.

[0038] The SAW tag device 100 includes a substrate 102 having a transducer structure 104 and a set of reflectors 106, 108 and 110 positioned on one side of the transducer structure 104 at various delays in the direction of propagation X as shown in FIG1. ​​These reflectors 106, 108 and 110 include one or more aluminum strips 112. The SAW tag device also includes an antenna 114 connected to the transducer structure 104.

[0039] The transducer structure 104 includes two interleaved comb electrodes 116 and 118, each of which includes a plurality of electrode fingers 120, 122, respectively.

[0040] The substrate 102 on which the transducer structure 104 is arranged is a piezoelectric material having the crystal axes X, Y and Z shown in Fig. 1. The piezoelectric material 102 described as an example here may be lithium niobate LiNbO3, in particular having a crystal cut (YX / ) / 128° or YZ.

[0041] 1 schematically illustrates the working principle of a reflector-based SAW tag device 100. A remote reader 124 transmits an electromagnetic request pulse 126, which is received by a tag antenna 114 directly connected to a transducer structure 104. The transducer structure 104 converts the electromagnetic signal 126 into a surface acoustic Rayleigh wave 128, which propagates along the surface of the substrate 102, along the crystal direction X of the piezoelectric material 102 shown in FIG.

[0042] The surface acoustic wave 128 is then partially reflected 130, 134, 138 and partially transmitted 132, 136 by reflectors 106, 108 and 110, which are placed on the substrate 102 at predetermined locations from the transducer structure 104. The reflected surface acoustic waves 130, 134 and 138 that return to the transducer structure 104 carry a code based on the location of the reflectors 106, 108, 110. This encoding method is based on the time delay of the reflected pulses. When the reflected surface acoustic waves 130, 134 and 138 return to the transducer structure 104, the acoustic signal is then reconverted into electrical form and retransmitted by the tag antenna 114. The reader 124 then detects and decodes the response signal.

[0043] The SAW tag device uses Rayleigh waves as surface acoustic waves that propagate in a propagation direction of a crystal direction X of a piezoelectric material.

[0044] SAW tag devices are used as sensors that can be interrogated remotely, providing wireless measurements of a physical quantity. Whatever that physical quantity is, it is best to put a differential measurement in place to ensure measurement of the absolute physical quantity or to reject relevant external disturbances that affect the sensor.

[0045] Due to the sensitivity of SAW sensors to changes in many environmental parameters, some kind of reference signal or multiple reference signals are usually used in the sensor, or one or more reference devices are used in the sensor system.

[0046] Due to thermal drift of a SAW tag device of tens of ppm / K, when the SAW tag device is used to measure mechanical parameters, such as force, pressure, etc., the temperature must be measured to subtract this quantity from the total measurement accessible by the SAW tag device.

[0047] Figure 2 A surface acoustic wave tag device according to the present invention is shown.

[0048] The SAW tag device 200 includes a substrate 202 having a transducer structure 204, and in particular only one transducer structure, and a set of reflectors 206, 208 and 210, the set of reflectors being arranged in a manner such as Figure 2The reflectors 206, 208 and 210 are positioned on one side of the transducer structure 204 at various delays in the direction of propagation X shown. The reflectors 206, 208 and 210 typically include one or more metal strips 212, such as aluminum strips. The SAW tag device 200 also includes an antenna 214 connected to the transducer structure 204.

[0049] In variations, the reflectors 206, 208, and 210 may also be positioned on either side of the transducer structure 204. In another variation, the set of reflectors includes more or fewer reflectors, wherein each reflector may have more or fewer metal strips 212.

[0050] In a variation of the invention, the metal strips 212 of the reflector can be connected to each other and / or shortened. This results in an improvement in the reflection coefficient of the reflector under Bragg conditions, contrary to the prior art situation of Rayleigh waves on a monolithic (YX / ) / 128° LiNbO3. Under Bragg conditions, the reflected waves generated due to electrical and mechanical loads are in phase, so that the improved reflection coefficient of the reflector under Bragg conditions results in better detection of the reflected waves by the transducer structure 204.

[0051] The transducer structure 204 includes two interleaved comb electrodes 216 and 218, each of which includes a plurality of electrode fingers 220, 222, respectively.

[0052] Compared to the prior art, the substrate 202 on which the transducer structure 204 is disposed is a composite substrate. The composite substrate 202 comprises a piezoelectric material layer 224 having crystal axes X, Y and Z formed on top of a base substrate 226.

[0053] In this embodiment, the piezoelectric layer 224 is lithium niobate LiNbO3, preferably LiNbO3 with a crystal orientation defined as (YX / ) / θ relative to the base substrate according to the standard IEEE 1949Std-176, where 0°<θ<100° or 140°<θ<180°, or lithium tantalate LiTaO3, preferably LiTaO3 with a crystal orientation defined as (YX / ) / θ relative to the base substrate according to the standard IEEE 1949Std-176, where θ is between -30° and 90°. The piezoelectric layer 224 is preferably single crystal.

[0054] The thickness of the piezoelectric layer 224 formed on the base substrate 226 is of the order of one wavelength λ or less, in particular about 2 μm or less, in particular λ / 4, even more in particular λ / 10. Here, one wavelength λ is twice the mechanical period of the transducer structure 204, as defined for the Bragg condition. The thickness t of the base substrate 226 must be greater than the thickness of the piezoelectric layer 224 in order to apply its thermal expansion to the piezoelectric layer 224 and reduce the sensitivity of the transducer to temperature changes. A preferred case corresponds to a base substrate 226 thickness that is at least ten times greater than the thickness of the piezoelectric layer 224, in particular 50 to 100 times greater, which corresponds to a base substrate thickness equal to 250-500 μm.

[0055] The base substrate 226 used in the first embodiment of the present invention is a silicon substrate. The orientation of the silicon substrate is preferably (100) due to the higher acoustic wave propagation speed compared to other crystal orientations (such as (110), (111) or (001), however other crystal orientations may be used. Since the temperature expansion coefficient of Si is around 2.6ppm / °C, the combined temperature expansion coefficient of the SAW tag device will generally be in the range of 2.6ppm / °C to the temperature expansion coefficient of the piezoelectric material 224 used, depending on the thickness of the piezoelectric layer 224 and the stress level at the bonding interface 228. The effective reduction in the temperature expansion coefficient of the composite substrate 202 results in a reduction in the temperature coefficient of frequency (TCF) of the transducer structure 204. It is also advantageous to use a base substrate 226 that exhibits a thermal expansion that is smaller, up to ten times smaller, or even larger than that of the piezoelectric layer 224, thereby applying an overall composite thermal expansion and producing a TCF reduction as well as optimal TCF control.

[0056] As previously mentioned, design flexibility can be enhanced by using different materials for base substrate 226. Other substrate materials with high acoustic wave propagation velocities can be selected instead of silicon, such as diamond, sapphire, silicon carbide, aluminum nitride, fused silica, or quartz crystal, and more generally, any material that exhibits a slow shear body wave velocity (SSBW velocity) equal to or greater than 4500 m / s can be selected. The slow shear body wave velocity is sensitive to the orientation of the base substrate, for example, for (111) silicon, the velocity is about 4500 m / s, and for (100) silicon, the velocity is about 5700 m / s.

[0057] Furthermore, materials with a smaller thermal expansion than silicon, ie, for example, some amorphous quartz compositions or pyrex or mica or silicon carbide, may advantageously be used as base substrates to control the TCF of the resulting device.

[0058] In a variation of the present invention, the base substrate may also include a trap-rich layer near the top layer of the piezoelectric material, which improves the insulation properties of the base substrate and may be formed of at least one of polycrystalline, amorphous or porous materials, such as polycrystalline silicon, amorphous silicon or porous silicon, but the present invention is not limited to these materials.

[0059] In a variation, the base substrate may be a semiconductor on insulator (SOI) substrate. A silicon on insulator structure (SOI) corresponds to a layered silicon-insulator-silicon substrate. The insulating layer may be a SiO2 layer.

[0060] In this embodiment, a thin SiO2 layer 230 is provided at the surface 228 between the piezoelectric layer 224 and the base substrate 226 to improve the attachment of the piezoelectric material layer 224 to the base substrate 226. The SiO2 layer 230 is 100 nm thick, but in variations, the thickness of the SiO2 layer 230 may vary and be greater than or less than 100 nm thick, and in particular may vary between 10 nm and 6 μm. The presence of the dielectric SiO2 layer 230 may change the electrochemical coupling coefficient ks 2 , the temperature stability of the composite substrate 202, and the wave phase velocity. This effect depends on the thickness of the layer, for example, increasing the thickness of the SiO2 layer reduces the wave phase velocity. Therefore, the thickness of the SiO2 layer 230 represents the optimization of the properties of the composite substrate 202 to obtain the desired electrochemical coupling coefficient ks 2 and the temperature stability of the composite substrate 202 and the parameters of the wave phase velocity of the desired application of the SAW tag device.

[0061] A composite substrate 202 having a combination of strong coupling from 1% to 25% or even stronger and temperature stability due to a combination of materials with different temperature coefficients of frequency TCF and high acoustic wave propagation speed will enhance the performance of the SAW tag device 200 .

[0062] Furthermore, in this embodiment, according to the present invention, due to the relative crystal orientation of the piezoelectric material layer 224 with respect to the base substrate 226, the shear wave is the main wave propagating in the crystal direction X of the piezoelectric layer 224, rather than the Rayleigh wave as in the SAW tag device of the prior art. Since the temperature stability of the shear wave on the composite substrate 202 is better than the temperature stability of the Rayleigh wave on the monolithic (YX / ) / 128°LiNbO3, in addition to measuring temperature, the application of the SAW tag device can also be extended to measuring mechanical parameters such as force, pressure, etc.

[0063] In addition, the electromechanical coupling coefficient ks 2 Compared with the Rayleigh wave mode on the monolithic (YX / ) / 128° LiNbO3, which is about 5.8%, the shear wave mode on the composite substrate based on the LiTaO3 layer can present a stronger electromechanical coupling coefficient ks2 , higher than 10%. For example, using a LiTaO3 (YX / ) / 42° crystal orientation relative to the base substrate as the piezoelectric material layer, a stronger electromechanical coupling coefficient ks of about 11.3% was obtained. 2 , and will result in an electromechanical coupling coefficient ks 2 An increase of a factor of about 2. For LiNbO3 based composite wafers, an electromechanical coupling coefficient ks of more than 20% can be obtained. 2 , thus an increase in electromechanical coupling of about 5 times can be obtained. This increase in electromechanical coupling will in turn result in a SAW tag device having an increased range for long-range interrogation.

[0064] Finally, the shear wave mode on the composite substrate according to the present invention propagates at a speed greater than or similar to 4000 m / s, which is approximately 5% to 10% faster than the Rayleigh wave mode on the monolithic (YX / ) / 128°LiNbO3, which is advantageous from a technical manufacturing point of view because for a given frequency, such as 2.45 GHz, the electrode finger width of the SAW tag device will be larger using a composite substrate of LiTaO3 / silicon base substrate instead of a monolithic (YX / ) / 128°LiNbO3.

[0065] Figure 3a and Figure 3b The dispersion curves of the Rayleigh mode and the pure shear wave mode of a composite substrate having a silicon base substrate, a 100 nm thick SiO2 dielectric layer and a 500 nm thick piezoelectric layer are shown.

[0066] exist Figure 3a In this case, LiNbO3 is used as the piezoelectric material, and for Figure 3b , using LiTaO3. The operating frequency is 2.45GHz.

[0067] Figure 3a and Figure 3b The phase velocity (m / s) of the guided wave on the left Y-axis and the electromechanical coupling coefficient ks on the right Y-axis are plotted as a function of the rotation angle θ of the cut of the piezoelectric layer relative to the base substrate for shear and Rayleigh modes, respectively. 2 The curve of (%) and TCF (ppm / K) value on the X-axis.

[0068] like Figure 3a As shown, for lithium niobate, virtually all shear modes have an electromechanical coupling coefficient ks suitable for SAW tag device applications. 2Values. Advantageous configurations for using shear waves with lithium niobate correspond to cutting angles between 0° and 100° or between 140° and 180°, in order to exploit the maximum absolute value of TCF between 50 and 65 ppm / K, i.e. a TCD exceeding 50 ppm / K. Note that, for reasons of fundamental symmetry, the characteristics of the wave are found identically every 180° for an angle θ (rotated about the X axis). In practice, the operation of the SAW tag device should be used for angles θ between 0° and +50°, assuming that for these configurations the maximum electromechanical coupling coefficient ks 2 Greater than 20%.

[0069] It is preferred to use the propagation axis of the shear wave along the X crystal axis of the piezoelectric material because for shear waves, the electromechanical coupling coefficient ks 2 is maximized, and for Rayleigh waves, the beam steering effect as the difference between the wavefront direction and the energy direction will not appear in this configuration. However, other propagation directions can still be used for SAW tag applications as long as the corresponding electromechanical coupling coefficient ks 2 Greater than 5%, in particular greater than 3% or more.

[0070] like Figure 3b As shown, the Rayleigh mode of lithium tantalate does not reach an electromechanical coupling coefficient ks exceeding 3%. 2 On the other hand, the electromechanical coupling coefficient ks 2 In between 3% and 12% of the cases, pure shear waves are available within the angular range of -30° / +90° modulo 180°.

[0071] Furthermore, absolute values ​​of TCF below 20 ppm / K are obtained in the angular range from 0° to +90°, values ​​suitable for the measurement of physical parameters different from temperature, such as pressure and any parameter involving stress combinations (torque, acceleration, force, vibration, etc.). These crystal cut configurations appear to be particularly advantageous for any application that is independent of temperature.

[0072] It can also be seen that for the (YX / t) / θ cut of lithium tantalate, where θ is between 20° and 60°, and in particular for θ equal to 36° and thus a (YX / ) / 36° cut, the TCF is close to zero.

[0073] Furthermore, it can be seen that TCF is compatible with temperature measurements in the angular range -30° / 0°.

[0074] Lithium tantalate also exhibits a "tunable" temperature sensitivity from -50 to +5 ppm / K, which is a degree of freedom that can be exploited. In contrast, lithium niobate shows an absolute value of TCF greater than 50 ppm / K.

[0075] The fact of being able to access a substrate that is less sensitive or even insensitive to thermal effects makes it possible to measure physical quantities, in particular mechanical properties, in a simple and effective manner. When the sensor is not affected by thermal effects, the interference caused by thermal changes in the measurement of mechanical properties will be reduced. Therefore, when using a SAW sensor according to the prior art as in FIG. 1 , it will be simpler and more effective to obtain the measurement of the mechanical property of interest.

[0076] Figure 4 The beam steering effect η and the electromechanical coupling coefficient ks are shown as a function of the angle θ of the crystal orientation plotted on the X-axis and the angle Ψ of the propagation plotted on the Y-axis for lithium tantalate on SiO2 on a silicon substrate. 2 The value of .

[0077] For shear waves exhibiting a scalar mechanical displacement field, any propagation direction can be considered. However, once propagating along a crystal direction such as the X-axis, beam steering occurs, which indicates a mixing between shear and sagittal displacement fields. However, there is a family of crystal cuts for which an electromechanical coupling coefficient ks exceeding 3% can be obtained. 2 , and the zero beam steering angle.

[0078] according to Figure 4 , the crystal orientation region is defined by (YXw / t) / φ / θ / Ψ, where φ=0°, 80°<θ<150° and 50°<Ψ<80°. In this region, the coupling factor can exceed 7.0% when the beam steering angle is close to or equal to zero.

[0079] For shear waves, the propagation direction along the X axis can be used to make the electromechanical coupling factor ks 2 maximize.

[0080] Figure 5a A physical quantity determining apparatus including two surface acoustic wave tag apparatuses according to a second embodiment of the present invention is described.

[0081] Figure 5a The physical quantity determination apparatus 300 shown in FIG. 1 includes two surface acoustic wave tag apparatuses 302 and 304 according to the present invention. The physical quantity determination apparatus 300 corresponds to a multi-physical sensor in which various physical parameters, such as temperature and pressure, can be measured.

[0082] In a variant, the physical quantity determination device 300 may include more than two surface acoustic wave tag devices according to the present invention.

[0083] Each of the two SAW tag devices 302 and 304 includes a transducer structure 306 and a set of reflectors 308, 310 and 312, the set of reflectors being arranged in a manner similar to that of FIG. Figure 5a306. The transducer structure 306 is shown positioned on one side of the transducer structure 306 with various delays in the direction of propagation X. Reflectors 308, 310, and 312 may also be positioned on either side of the transducer structure 306. The transducer structure 306 includes two interlaced comb electrodes 314 and 316, each of which includes a plurality of electrode fingers 318. The reflectors 308, 310, and 312 typically include one or more metal strips 320.

[0084] The SAW tag device also includes an antenna 322 connected to the transducer structure 306. In this embodiment, the antenna 322 is actually connected to the two transducer structures 306 of the two SAW tag devices 302, 304. According to one aspect of the present invention, only one antenna 322 is used regardless of how many SAW tag devices 302, 304 are used. According to another aspect of the present invention, each SAW tag device can be coupled to its own antenna to facilitate interrogation distance.

[0085] In this embodiment, two surface acoustic wave tag devices 302 and 304 are connected to each other. The connection can be in series or in parallel. In a variation, they may not be connected to each other.

[0086] In this embodiment, the two surface acoustic wave tag devices 302 and 304 have the same structure, which means that their transducer structures 306, reflectors 308, 310 and 312 and their designs have the same size. In a variant of the embodiment, they can also have different sizes to suit the intended use.

[0087] The substrate 324 on which the transducer structure 306 and reflectors 308, 310 and 312 are disposed is the same as the composite substrate 202 of the first embodiment, and therefore its features will not be described in detail again, but reference is made to the description above thereof.

[0088] In this embodiment, both SAW tag devices 302 and 304 can be used as sensors to determine physical quantities, such as temperature or mechanical quantities, respectively.

[0089] In the physical quantity determination device 300, shear waves are the main waves propagating in the piezoelectric layer 224 due to the relative crystal orientation of the piezoelectric layer 224 with respect to the base substrate 226. Since the temperature stability of shear waves is better than that of Rayleigh surface waves used in the prior art devices, the application of the SAW tag device can be extended to measuring parameters other than temperature, especially mechanical parameters such as force, pressure, etc.

[0090] Furthermore, for example, when shear waves were used on LiTaO3(YX / ) / 42° on a composite substrate, the electromechanical coupling coefficient ks was obtained. 2is about 11.3%, which corresponds to about 2 times that when using Rayleigh waves on monolithic (YX / ) / 128° LiNbO3, where an electromechanical coupling coefficient ks of about 5.8% is obtained for these prior art devices 2 For LiNbO3 based composite wafers, considering the (YX / ) / θLiNbO3 cut with angle θ defined in the range [0°-50°], an electromechanical coupling coefficient ks of more than 20% can be obtained. 2 , corresponding to a factor of about 5 times greater than the above-mentioned prior art device. This leads to the possibility of coupling two SAW tag devices to only one antenna, which is at least quite disadvantageous when using the above-mentioned Rayleigh waves. In fact, in the case of Rayleigh waves, the energy losses will be higher due to the lower coupling coefficient. Therefore, the design of the physical quantity determination device 300 is simpler and its applicability is extended.

[0091] Figure 5b A physical quantity determining apparatus including two surface acoustic wave tag devices according to a third embodiment of the present invention is shown, wherein at least one of the two surface acoustic wave tag devices is according to the present invention.

[0092] Figure 5b The physical quantity determination device 400 shown is similar to the physical quantity determination device 300 of the second embodiment, and includes two surface acoustic wave tag devices 402 and 404, except that one of the surface acoustic wave tag devices 402 can be used as a sensor, and the other surface acoustic wave tag device 404 is used for identification. Therefore, the physical quantity determination device 400 can use only one substrate 424 to provide both identification and measurement activities.

[0093] The substrate 424 of the physical quantity determination apparatus 400 is the same as the composite substrate 202 of the first embodiment, and therefore its features will not be described in detail, but reference is made to the above description thereof.

[0094] In a variation, the physical quantity determination device 400 may include more than two surface acoustic wave tag devices according to the present invention, one of which is used for identification and the others are used as sensors.

[0095] SAW tag device 404 or resonator allows identification, SAW tag device 402 allows measurement of physical quantity, such as temperature. SAW resonators typically use the resonant frequency as a measurement parameter, while SAW tag sensors use a delay line or time delay of a compressed signal response as a parameter for indicating the measurement quantity.

[0096] The SAW tag device 402 and the SAW resonator 404 can operate at different frequencies, for example, 2.45 GHz for the SAW tag device and 434 or 866 MHz for the SAW resonator device. Both devices can be fabricated on the same base substrate 226 and different types of modes can be used, since the resonators and delays do not in principle need to have the same quality factor. For example, the SAW tag device 402 can use an electromechanical coupling coefficient ks 2 The SAW resonator device 404 can use a Rayleigh wave with an electromechanical coupling coefficient ranging from 0.1% to 0.5%. The two SAW devices 402, 404 can utilize a specific propagation direction, such as Figure 4 As shown in b, for the SAW tag device 402, it is LiTaO3(YX / ) / 42°, and for the Rayleigh wave of the SAW resonator device 404, it is LiTaO3(YX / t) / 42° / 90°.

[0097] In this embodiment, the SAW tag device 402 and the SAW resonator device 404 have different structures, which means that their respective transducer structures 406, 408 and reflectors 410, 412 and 414 have different designs and / or sizes. In a variation of this embodiment, they can also have the same size and / or design to suit the intended use.

[0098] In this embodiment, the transducer structures 406, 408 and reflectors 410, 412 and 414 have the same features as the transducer structure 306 and reflectors 310, 312 and 314 of the second embodiment, namely, the interlaced comb electrodes 314 and 316, the electrode fingers 318 and the metal strips 320, and reference is made to the description thereof above for more details.

[0099] exist Figure 5b , the propagation direction of the acoustic wave for the SAW-tag device 402 is along the crystal direction X of the piezoelectric layer 224 of the composite substrate 424, while the propagation direction of the acoustic wave for the SAW resonator device 404 is rotated by an angle Ψ compared to the crystal direction X of the piezoelectric layer 224. Then, according to the standard IEEE 1949 Std-176, the cut of the piezoelectric layer 224 of the composite substrate 424 will be defined as (YX / ) / θ for the SAW tag device 402 and (YX / t) / θ / Ψ for the SAW resonator device 404.

[0100] exist Figure 5b In , the angle Ψ has a value of 90°, but in variations of this embodiment, other values ​​of Ψ may be used depending on the type of acoustic waves generated by the SAW resonator device 404 required for the application.

[0101] exist Figure 5b, the angle Ψ of 90° causes the SAW resonator device 404 to use Rayleigh waves, while the SAW tag device 402 uses shear waves. In a variation of this embodiment, both the SAW tag 402 and resonator 404 devices can use the same type of acoustic waves, both shear waves or Rayleigh waves or any other type of acoustic waves enabled by the selected orientation of the piezoelectric layer 224.

[0102] Positioning the SAW resonator device 404 at an angle Ψ of 90° relative to the SAW tag device 402 means that the transducer structure 406 and reflectors 410 , 412 , and 414 of the SAW resonator device 404 are also positioned at an angle Ψ of 90° relative to the transducer structure 408 and reflectors 410 , 412 , and 414 of the SAW resonator device 404 .

[0103] The SAW tag device 402 and the SAW resonator device 404 are connected to the same antenna 422. In a variation of this embodiment, each SAW device 402, 404 may have its own antenna.

[0104] The SAW tag device 402 and the SAW resonator device 404 are also connected to each other. Assuming that the resonator operates at a lower frequency than the SAW tag, the connection will depend on the resonator contribution at high frequencies. In this case, the SAW tag device acts as a pure capacitor for the resonator, so it can be connected in parallel or in series, but most preferably in series, otherwise the capacitance of the SAW tag device, which is inherently much larger than the capacitance of the resonator, will cut off the electromechanical coupling of the resonator.

[0105] In variations where each SAW device 402, 404 has its own antenna, the SAW tag device 402 and the SAW resonator device 404 may also be independent in that they do not share the same band / frequency operation.

[0106] exist Figure 5b , both devices are also made on the same piezoelectric material 224, but in a variation of this embodiment, the SAW tag device 402 may include a first piezoelectric material and the SAW resonator device 404 may include a second piezoelectric material, and the first and second piezoelectric materials are both on top of the same base substrate 226.

[0107] Figure 5c A physical quantity determining apparatus including two surface acoustic wave tag apparatuses according to a fourth embodiment of the present invention is described.

[0108] Figure 5c The physical quantity determining apparatus 500 shown is similar to the physical quantity determining apparatus 300 of the second embodiment, and includes two surface acoustic wave tag devices 302 and 304 , so their features will not be described in detail, but reference will be made to the above description thereof.

[0109] In a variant, the physical quantity determination device 500 may include more than two surface acoustic wave tag devices according to the present invention.

[0110] The substrate 502 of the physical quantity determination device 500 (on which the transducer structure 306 and the reflectors 308 , 310 and 312 are arranged) is the same as the composite substrate 202 of the first embodiment, so its features will not be described in detail, but reference is made to the above description thereof.

[0111] The physical quantity determining device 500 is different from the physical quantity determining device 300 of the second embodiment in that the base substrate 504 of the composite substrate 502 of the physical quantity determining device 500 can be partially thinned so that the base substrate 504 is hollowed out, and in the side cut view of the physical quantity determining device 500, only a certain thickness of material under one of the surface acoustic wave tag devices is left, such as Figure 5c shown.

[0112] According to the piezoelectric material 506 and the base substrate 504, the base substrate 504 can be hollowed out by a thinning process of its surface 508, leaving only a thickness t2 of the base substrate 504 below the SAW tag device 304, as shown in FIG. Figure 5c As shown. Figure 5c In FIG. 5 , surface 508 of base substrate 504 is the opposite surface from surface 510 where piezoelectric material 506 is attached to base substrate 504 via SiO 2 layer 512. This architecture can be used to compensate for temperature changes, thereby reducing the device's sensitivity to temperature.

[0113] Furthermore, the fact that the silicon base substrate 504 may be thinned on its surface 508 enables the region 514 of the silicon base substrate 504 to be made deformable, since the resulting thickness t2 of the region 514 of the base substrate 504 may be thin enough to react to vibrations, pressure, . . .

[0114] Region 514 is located underneath one of the two SAW tag devices 302 or 304 and is disposed on top of the piezoelectric layer 506. Figure 5c In the embodiment shown in FIG. 5 , the thinned region 514 of the base substrate 504 is only located below the SAW tag device 302 .

[0115] In a variant, the thinned region 514 may also be positioned in the base substrate 524 between two reflectors, ie between 308 and 310 , and ultimately between 310 and 312 .

[0116] Therefore, due to the presence of the thinned region 514 of the base substrate 504 below the SAW tag device 302, the SAW tag device 302 can be used to measure mechanical parameters, such as pressure, vibration, ... Changes in the vibration or pressure of the thinned region 514 in the base substrate 504 will result in changes in the time delay of the mode reflected by the reflector. These changes in time delay will be detected by the transducer structure of the SAW tag device 302 and will enable the measurement of vibration or pressure parameters.

[0117] According to a variation, the surface of the base substrate may be thinned below each SAW tag device as a sensor in the physical quantity measuring device. Figure 4 b shows the structure of the physical quantity measuring device.

[0118] Figure 6 Describes the use of Figure 5c FIG. 1 is a schematic diagram of the steps of a method for a surface acoustic wave tag device according to the present invention.

[0119] The method comprises the step a): disposing a piezoelectric layer 600 having a thickness t on a base substrate 602 to form a composite substrate 604 .

[0120] In order to realize the composite substrate 604 according to the present invention, in step a) of the process, a base substrate 602 is provided. The base substrate 602 is a silicon base substrate, or any other substrate material with a high acoustic wave propagation velocity, such as diamond, sapphire, silicon carbide, aluminum nitride, fused silica or quartz crystal.

[0121] The piezoelectric layer 600 is single crystal lithium niobate (LiNbO3) or lithium tantalate (LiTaO3). The thickness t of the piezoelectric layer 600 formed on the base substrate 602 is of the order of wavelength λ, particularly less than the wavelength, such as λ / 4 or even λ / 10, more particularly 0.5 μm.

[0122] In the composite substrate 602 , as shown in step a), the piezoelectric layer 600 is arranged so that the piezoelectric layer 600 has a crystal orientation relative to the base substrate 602 , thereby enabling propagation of shear waves corresponding to acoustic waves.

[0123] When the piezoelectric material layer 600 is lithium niobate LiNbO3, according to the standard IEEE 1949Std-176, the crystal orientation of the piezoelectric material LiNbO3 relative to the base substrate 602 is (YX / ) / θ, where θ is an angle of the crystal orientation between 0° and 100°, in particular between 0° and 50°, or between 140° and 180°, with 180° as the modulus.

[0124] When lithium tantalate LiTaO3 is used as the piezoelectric material layer 600, according to the standard IEEE 1949Std-176, the crystal orientation of the piezoelectric material LiTaO3 relative to the base substrate 602 is (YX / ) / θ, where θ is an angle of the crystal orientation between -30° and 90°, in particular between 20° and 60°, with 180° as the modulus.

[0125] Before providing the piezoelectric layer 600, a thin 100 nm SiO2 layer 606 is provided on top of the base substrate 602 to improve adhesion. The SiO2 layer may be naturally present on the Si base substrate 602 or may be formed using deposition techniques.

[0126] Prior to attachment, additional processing steps may be added, such as polishing the side of the piezoelectric layer 600 and / or the side 608 of the base substrate 602 where attachment will take place.

[0127] A layer transfer process such as SmartCut can be used TM The process is used to achieve the piezoelectric layer 600 being arranged on the base layer 602. During the layer transfer process, the source substrate including the layer to be transferred is preferably attached to the processing substrate by bonding. After thermal and / or mechanical treatment, the piezoelectric layer 600 is separated at a predetermined segmentation area, thereby being transferred to the processing substrate, which is the base substrate 602 here.

[0128] According to step b), a transducer structure 610 is formed on the piezoelectric layer 600 using a combination of layer deposition and patterning steps. Figure 2 As can be seen in FIG. 6 , the transducer structure 610 comprises two interleaved comb electrodes, each of which comprises a plurality of electrode devices 612 and 614. The interleaved comb electrodes and their respective electrode devices 612 and 614 are formed of a conductive metal, such as aluminum, or an aluminum alloy or tungsten.

[0129] The method further comprises the step of forming a set of reflectors 616, 618 and 620 on the piezoelectric layer 600 using a combination of layer deposition and patterning steps. The reflectors 616, 618 and 620 typically comprise one or more metal strips 622, such as aluminum, and are located on one side of the transducer structure 610, here on the right side in the propagation direction x in FIG. 5 , and are positioned at a predetermined distance from the transducer structure 610.

[0130] The layers used for the SAW tag device 624, their materials, their thicknesses and crystal orientations are selected so as to obtain a predetermined electromechanical coupling coefficient ks 2 , a predetermined temperature coefficient of frequency TCF, and an acoustic wave propagation velocity of an acoustic shear wave traveling in the piezoelectric layer 600.

[0131] The method also includes the step of forming an antenna.

[0132] As mentioned above, more than one SAW tag device may be provided on the piezoelectric layer 600. They may all be fabricated simultaneously.

[0133] To implement the embodiment according to FIG. 5 , the method further comprises a step c) of thinning the base substrate 602 .

[0134] According to a variant of the invention, the step c) of thinning the base substrate 602 comprises thinning 626 a surface 628 of the base substrate 602 opposite to the surface 608, at which the piezoelectric layer 600 is attached to the base substrate 602 via the SiO2 layer 606, in an area 630 defined by a dimension R, which area is located between the transducer structure 610 and the reflectors 616, 618 and 620. This thinning step can be achieved by a dry etching technique, such as deep reactive ion etching or a wet etching process, such as KOH or TMAH etching, grinding or chemical mechanical polishing or any other mechanical process. A mask or protective layer 632 can be used on the side 628 of the base substrate 602 to define the area 630 of dimension R of the base substrate 602 to be etched. This mask or protective layer 632 can then be removed after the thinning step or at the end of the manufacturing process.

[0135] As a result of thinning, Figure 6 d, the thickness t2 of the thinned region 636 of the base substrate 602 is less than the thickness t1 of the remainder of the base substrate 602. The step of thinning 626 provides a deformable region 636 of the base substrate 602 because the resulting thickness t2 of the region 636 of dimension R of the base substrate 602 can be made thin enough to deform under the action of vibration, pressure or force...

[0136] like Figure 6 As shown in the final SAW tag device 638 in d, the thinning step 626 of the surface 628 of the base substrate 602 can occur in an area 636 of size R on the surface 628 of the base substrate 602. However, it is possible to obtain an area 636 of the base substrate 602 of size R1, where R1 is less than or greater than R, i.e., the size of the area where the thinning step 626 occurs, where the thickness t2 is less than t1. Therefore, the area 636 of the base substrate 602 can have a thickness that varies between t1 and t2.

[0137] In a variant, the thinned region 636 may also be positioned in the base substrate 602 between two reflectors, ie between 308 and 310 , and finally between 618 and 620 .

[0138] exist Figure 6d, for the final SAW tag device 638, the thickness t1 of the base substrate 602 at the periphery is greater than the thickness t2 at the center of the base substrate 602. Therefore, the desired temperature stability for making measurements independent of temperature effects can still be achieved because the remaining material of the base substrate 602 in the region 636 imposes the temperature behavior.

[0139] In the case where more than one SAW tag device is used on the composite substrate 604, when the physical quantity measuring device includes at least two SAW tag devices or only some of them, a thinning step 626 of the surface 628 of the base substrate 602 can be performed underneath each of the SAW tag devices used as sensors in the physical quantity measuring device.

[0140] Figure 7 A schematic diagram showing steps of a method for manufacturing a surface acoustic wave tag device according to another embodiment of the present invention.

[0141] This method is based on Figure 6 The method shown in FIG. 1 is similar to the method shown in FIG. 1 , but uses a silicon-on-insulator (SOI) base substrate 704 instead of the base substrate 602 for the surface acoustic wave tag device. Figure 7 a to Figure 7 The steps shown in d correspond to Figure 6 a to the steps shown in 6d.

[0142] Composite substrate 700 includes a piezoelectric material layer 702 formed on top of a base substrate 704, which is a silicon-on-insulator substrate (SOI). The silicon-on-insulator substrate (SOI) corresponds to a layered silicon-insulator-silicon substrate. The insulating layer 706 can be a SiO2 layer. The insulating layer 706 is positioned at a depth d from a surface 708 of the base substrate 704.

[0143] Before providing the piezoelectric layer 702, on top of the base substrate 704, a thin 100 nm SiO2 layer 710 is provided at the surface 712 to improve adhesion. The SiO2 layer may be naturally present on the Si base substrate 704 or may be formed using deposition techniques.

[0144] During step c) of thinning 626 the base substrate 704, the insulating layer 706 may advantageously serve as an etch stop so that the thickness h of the etched base substrate 704 in the region 636 corresponds to the position depth d of the insulating layer 706 in the base substrate 704. The presence of the insulating layer 706 allows controlling and obtaining a desired film thickness t2.

[0145] Using such an SOI substrate as the base substrate 704 allows for precise control of the thickness t2 of the film etched into the back side of the silicon substrate for the final SAW tag device 718 .

[0146] According to the present invention, a composite substrate 604, 700 can be obtained, which provides an electromechanical coupling coefficient ks of at least 3% to 20% and higher. 2 A predetermined level of propagation speed of about 4000 m / s to 7000 m / s and an adjustable temperature stability between -50 and +5 ppm / K can be obtained. For this composite substrate, using the shear wave mode according to the present invention, an electromechanical coupling coefficient Ks can be observed compared to a device using the Rayleigh mode. 2 A factor of about two to about five times of the gain of the SAW tag device can be increased, and thus an increase in the distance for remote interrogation of the device can be observed. Using such composite substrates, the design and performance of SAW tag devices and their range of applications can be improved compared to bulk piezoelectric substrates.

[0147] Several embodiments of the present invention have been described. However, it will be appreciated that various modifications and enhancements may be made without departing from the scope of the appended claims.

Claims

1. A surface acoustic wave tag device, the surface acoustic wave tag device comprising: An acoustic wave propagation substrate (202, 324, 424, 502, 604, 700), at least one transducer structure (204, 306, 610) disposed on the substrate (202, 324, 424, 502, 604, 700) comprising interlaced comb electrodes (216, 218, 316, 318), and at least one reflecting device, the reflecting device comprising a reflector (206, 208, 210, 308, 310, 312, 616, 618, 620) positioned at a distance relative to the at least one transducer structure (204, 306, 610) in the propagation direction of the sound waves, wherein the reflector comprises one or more metal strips connected to each other, It is characterized in that The acoustic wave propagation substrate (202, 324, 424, 502, 604, 700) is a composite substrate (202, 324, 424, 502, 604, 700) comprising a base substrate (226, 504, 602, 704) and a piezoelectric layer (224, 506, 600, 702); wherein the crystal orientation of the piezoelectric layer (224, 506, 600, 702) relative to the base substrate (226, 504, 602, 704) enables propagation of shear waves within the piezoelectric layer (224, 506, 600, 702) and in a direction corresponding to the propagation of the acoustic wave; and The base substrate is thinned in a region between two reflectors, so that the base substrate can respond to vibration and pressure.

2. The surface acoustic wave tag device according to claim 1, wherein: The piezoelectric layer (224, 506, 600, 702) is lithium tantalate LiTaO3 or lithium niobate LiNbO3.

3. The surface acoustic wave tag device according to claim 2, wherein: The piezoelectric layer (224, 506, 600, 702) is lithium niobate LiNbO3; and The crystal orientation of the piezoelectric layer (224, 506, 600, 702) relative to the base substrate (226, 704) is (YX / ) / θ according to standard IEEE 1949 Std-176, where θ is an angle of crystal orientation between 0° and 100°, or between 140° and 180°, with 180° as the modulus.

4. The surface acoustic wave tag device according to claim 3, wherein: θ is the angle of crystal orientation between 0° and 50°, modulo 180°.

5. The surface acoustic wave tag device according to claim 2, wherein: The piezoelectric layer (224, 506, 600, 702) is lithium tantalate LiTaO3; and The crystal orientation of the piezoelectric layer (224, 506, 600, 702) relative to the base substrate (226, 504, 602, 704) is (YX / ) / θ according to standard IEEE 1949 Std-176, where θ is the angle of the crystal orientation between -30° and 90°, modulo 180°.

6. The surface acoustic wave tag device according to claim 5, wherein: θ is the angle of crystal orientation between 20° and 60°, modulo 180°.

7. The surface acoustic wave tag device according to claim 5, wherein: θ is 36°, the angle of crystal orientation modulo 180°.

8. The surface acoustic wave tag device according to claim 5, wherein: θ is 42°, the angle of crystal orientation modulo 180°.

9. The surface acoustic wave tag device according to one of claims 1 to 8, wherein: The base substrate (226, 504, 602, 704) of the composite substrate (202, 324, 424, 502, 604, 700) is one of silicon, diamond, sapphire, silicon carbide, fused quartz or quartz crystal.

10. The surface acoustic wave tag device according to any one of claims 1 to 8, wherein: At least a portion (514, 636) of the base substrate (226, 504, 602, 704) is deformable.

11. A physical quantity determining device, comprising two or more surface acoustic wave tag devices (200, 302, 304, 402, 404, 638, 718), at least one of the two or more surface acoustic wave tag devices being a surface acoustic wave tag device according to any one of claims 1 to 8.

12. The physical quantity determining device according to claim 11, further comprising only one tag antenna (214, 322, 422) connected to the transducer structure (204, 306, 406, 408, 610) of the two or more surface acoustic wave tag devices (200, 302, 304, 402, 404, 638, 718).

13. The physical quantity determining device according to claim 11 or 12, wherein: One of the surface acoustic wave tag devices (200, 302, 304, 402, 404, 638, 718) is a surface acoustic wave resonator (404), and at least one of the surface acoustic wave tag devices (200, 302, 304, 402, 638, 718) is a surface acoustic wave tag device according to any one of the preceding claims 1 to 8.

14. The physical quantity determining device according to claim 13, wherein: The surface acoustic wave resonator (404) is positioned relative to the at least one surface acoustic wave tag device among the surface acoustic wave tag devices (200, 302, 304, 402, 404, 638, 718) so that they have two different surface acoustic wave propagation directions.

15. The physical quantity determining device according to claim 13, wherein: The surface acoustic wave resonator (404) is positioned relative to at least one of the surface acoustic wave tag devices (200, 302, 304, 402, 638, 718) so that a surface acoustic wave propagation direction of the surface acoustic wave resonator parallel to one of the crystal axes of the piezoelectric layer (224, 506, 600, 702) forms an angle Ψ with the surface acoustic wave propagation direction of the at least one of the surface acoustic wave tag devices (200, 302, 304, 402, 638, 718).

16. The physical quantity determining device according to claim 13, wherein: The surface acoustic wave resonator (404) is configured to use Rayleigh waves, and the at least one surface acoustic wave tag device among the surface acoustic wave tag devices (200, 302, 304, 402, 638, 718) is configured to use shear waves. 17 . The physical quantity determining device according to claim 11 , which is configured to measure temperature and / or pressure.

18. The physical quantity determination device according to claim 11 or 12, which is configured to measure force.

19. The physical quantity determination device according to claim 11 or 12, which is configured to allow identification.

20. A method for manufacturing a surface acoustic wave tag device, wherein the surface acoustic wave tag device is a surface acoustic wave tag device according to any one of claims 1 to 8, the method comprising the following steps: a) providing a piezoelectric layer on a base substrate; and b) providing a transducer structure on the piezoelectric layer; Therein, in step a), the piezoelectric layer is arranged so that the crystal orientation of the piezoelectric layer relative to the base substrate enables propagation of shear waves corresponding to the acoustic waves.

21. The method of manufacturing a surface acoustic wave tag device according to claim 20, further comprising the step of thinning the base substrate.

22. The method for manufacturing a surface acoustic wave tag device according to claim 21, wherein: The step of thinning the base substrate includes thinning a portion of a surface opposite to a surface to which the piezoelectric layer is attached.

23. The method for manufacturing a surface acoustic wave tag device according to claim 21, wherein: The step of thinning the base substrate includes etching or grinding.

24. The method for manufacturing a surface acoustic wave tag device according to claim 21, wherein: The step of thinning the base substrate includes chemical mechanical polishing.

25. The method for manufacturing a surface acoustic wave tag device according to any one of claims 21 to 24, wherein: The base substrate is a semiconductor-on-insulator substrate such that an insulator layer of the semiconductor-on-insulator substrate serves as an etch stop for the step of thinning the base substrate.

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