Surface acoustic wave sensor device

Abstract

The present invention relates to an acoustic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) comprising a first interdigitated transducer (T, T1), a first reflecting structure (M1), a second reflecting structure (M2), a first resonant cavity including a first top surface and formed between the first interdigitated transducer (T, T1) and the first reflecting structure (M1), and a second resonant cavity including a second top surface and formed between the first interdigitated transducer (T, T1) and the second reflecting structure (M2), wherein at least one of the first and second top surfaces is at least partially covered by a metallization or passivation layer. The present invention also relates to an acoustic wave sensor assembly.

Description

Technical Field

[0001] The present invention relates to elastic wave type sensors, and more particularly to surface acoustic wave sensor devices including interdigitated transducers and resonant cavities.

[0002] The importance of sensors is increasing and they are widely spread in daily life. Microelectromechanical systems (MEMS) are an attractive option for meeting the requirements for improving sensor performance along with miniaturization and cost reduction. Surface acoustic wave (SAW) sensors, and to a lesser extent bulk acoustic wave (BAW) sensors or Lamb wave acoustic sensors or Love wave acoustic sensors, provide particularly advantageous options for a wide variety of measurable ambient parameters including, for example, temperature, pressure, strain, and torque.

[0003] Elastic wave sensors utilize the piezoelectric effect to convert an electrical signal into a mechanical wave / elastic wave. SAW-based sensors are constructed on single crystal piezoelectric materials such as quartz (SiO2), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), langasite (LGS), or polycrystalline piezoelectric materials such as aluminum nitride (AlN) or zinc oxide (ZnO), which are deposited particularly on silicon, and further, if necessary, on a piezo-on-insulator (POI) composite material including a layer of a single crystal material such as lithium tantalate or lithium niobate, for example, a piezoelectric material bonded to a support substrate such as silicon by a bonding layer such as a silicon oxide layer (generally, any combination of a single crystal piezoelectric material and a non-piezoelectric substrate can be used from the perspective of specific characteristics such as thermoelastic characteristics or acoustic quality).

[0004] In surface acoustic wave sensors, an alternating mating transducer (IDT) converts the electrical energy of an electrical signal into acoustic wave energy. The acoustic wave propagates across the surface (or bulk) of the device substrate via a so-called delay line to another transducer, particularly an IDT, which converts the acoustic wave back into a detectable electrical signal. Some devices are equipped with mechanical absorbers and / or reflectors to prevent interference patterns and reduce insertion loss. In some devices, the other (output) IDT is replaced by a reflector that reflects the generated acoustic wave back to an (input) IDT, which can be coupled to an antenna for remote questioning of the sensor device. Advantageously, measurements can be performed entirely passively, i.e., the sensor does not need to be powered by a power supply.

[0005] Certain classes of acoustic wave sensors include resonators that exhibit a resonant frequency that changes in accordance with changing ambient conditions. Figure 1 shows an example of a resonant acoustic wave sensor. The surface acoustic wave resonator includes an electroacoustic interleaved transducer IDT in which interleaved comb electrodes C and C' are positioned between Bragg mirrors M. The comb electrodes are set to opposite potentials +V and -V, respectively. The geometric shape of the electrodes is defined by the pitch p, i.e., the spatial repetition frequency of the interleaved electrodes C and C' in the propagation direction of the excited surface acoustic wave, the length of the gap between electrodes C and C' in a direction perpendicular to the propagation direction of the excited surface acoustic wave, the length of the acoustic aperture region given by the lengths of electrodes C and C' between the gaps, and the width a of electrodes C and C', which determines the so-called metallization ratio a / p. The IDT can operate, for example, under Bragg conditions where the wavelength λ of the excited surface acoustic wave is equal to twice the pitch p.

[0006] At the resonant frequency, the synchronization conditions between reflectors are met, enabling the coherent summation of various reflections occurring beneath the reflectors. Within the resonant cavity, the maximum acoustic energy is observed, and from an electrical standpoint, the maximum amplitude of the current allowed by the transducer is observed. In principle, a differential elastic wave sensor can comprise two or more resonators exhibiting different resonant frequencies, or a resonator operating in multimode (several resonant frequencies), where the difference in measurement frequencies reflects variations in ambient parameters (measured quantities) measured as, for example, temperature, pressure, or strain.

[0007] However, despite recent engineering advances, the entire interrogation process—in which the interrogator transmits a suitable high-frequency signal, this signal is received by an elastic wave sensor via a receiving antenna, converted into a surface acoustic wave (or bulk wave in the case of bulk elastic wave sensor type devices) by a transducer, and this surface acoustic wave is converted into a high-frequency signal retransmitted via a radiating antenna, received by the interrogator, and analyzed—still presents significant technical challenges. Furthermore, the relatively bulky configurations known in the art require a considerable amount of space.

[0008] To obtain reliable measurement results, it is necessary to accurately observe true differential measurements based on the appropriate differential sensitivity of the resonator resonance used for the measured quantity. This imposes stringent requirements on manufacturing process tolerances and the reproducibility of the physical characteristics of each wafer. In addition, any relative movement between the sensor device and the interrogator can significantly affect the measurement results due to the inductive, capacitive, or radiative RF links formed by the sensor device and interrogator. Other environmental influences in the measurement environment, such as temperature changes, also affect the reliability of the measurement results.

[0009] Therefore, an object of the present invention is to provide an elastic wave sensor that enables a higher signal-to-noise ratio, more reliable measurement results, and / or a more compact design compared to elastic wave sensor devices in the art.

[0010] The present invention addresses the above object by providing an elastic wave sensor device comprising, in particular, a first alternating-fit transducer including comb-type electrodes, a first reflective structure, a second reflective structure, a first resonant cavity formed between the first alternating-fit transducer and the first reflective structure, including a first upper surface, and a second resonant cavity formed between the first alternating-fit transducer and the second reflective structure, wherein at least one of the first and second upper surfaces is at least partially covered by a metallization layer or a passivation layer. Alternatively, or in addition, at least one of the first and second upper surfaces may be physically and / or chemically modified by other means, for example, by denting the respective surfaces.

[0011] The present invention addresses the above object by providing an elastic wave sensor device comprising a first alternating-fit transducer, a first reflective structure, a second reflective structure, a first resonant cavity formed between the first alternating-fit transducer and the first reflective structure, including a first upper surface, and a second resonant cavity formed between the first alternating-fit transducer and the second reflective structure, including a second upper surface, wherein the first and second resonant cavities differ from each other in that one of them exhibits some physical and / or chemical modification compared to the other.

[0012] Either the first or second upper surface may be at least partially covered by a metallization layer or a passivation layer. Alternatively, the first and second upper surfaces may be covered by different materials.

[0013] The first reflective structure may include or consist of Bragg mirrors (including elongated electrodes arranged parallel to each other), and / or the second reflective structure may include or consist of Bragg mirrors (including other elongated electrodes arranged parallel to each other). Alternatively, at least one of the first or second reflective structures may comprise a groove or edge reflective structure or a short reflector including three or fewer electrodes. Such reflective structures can be easily formed and can provide high reflectivity. Those skilled in the art will know how to adjust the groove depth or electrode thickness to provide a reflectivity of more than 20% that is achievable for a given crystal orientation, wave polarization, and electrode properties.

[0014] The elastic wave sensor device may include a substrate comprising a piezoelectric layer and a non-piezoelectric bulk substrate, or it may include a (uniform) piezoelectric substrate. The non-piezoelectric bulk substrate may be a silicon substrate and optionally include a so-called trap-rich layer (e.g., provided by a layer of polycrystalline silicon) on its surface. The trap-rich layer can reduce insertion loss and RF loss due to charge traps induced at the interface with the silicon substrate.

[0015] The metallization layer or passivation layer may be formed on or above the piezoelectric layer or piezoelectric substrate, respectively. The metallization layer may contain or consist of at least one of AlCu and Ti, and the passivation layer may contain, but is not limited to, at least one of Si3N4, Al2O3, AlN, Ta2O5, and SiO2, or consist of these. The metallization layer may be made of the same material as the electrodes of the first transducer (and therefore may be formed using the same processing steps as those used to form the electrodes).

[0016] When a Bragg mirror is used as a reflective structure, the Bragg mirror may be made of the same metallic material used to form the metallization layer and / or the electrodes of the first transducer.

[0017] By modifying one of the first or second upper surfaces of the resonant cavity with a metallization layer or passivation layer, it is possible to obtain a result in which the propagation characteristics of elastic waves generated by the alternating-fit transducer differ between the second and first resonant cavities. This makes it possible to provide a highly reliable and sensitive differential sensor device.

[0018] If no modification is performed, the first and second upper surfaces are free (exposed) surfaces, particularly the free surfaces of the piezoelectric layer (see description below). A material layer may be formed only on the second upper surface, or a material layer may be formed on the second upper surface and another material layer (made of a different material than the material layer formed on the second upper surface) may be formed on the first upper surface.

[0019] According to one embodiment, the first transducer may be located on one side of the first resonant cavity, and the second resonant cavity may be located on the other side of the first resonant cavity, with the first reflecting structure separating the first resonant cavity from the second resonant cavity. Thus, the second resonant cavity may be formed between the first reflecting structure and the second reflecting structure. In such a configuration, the separation of the resonant cavities is provided not by the transducer, but by the intermediate reflecting structure (i.e., the first reflecting structure). Such a configuration allows for a compact design.

[0020] In such a configuration, a third reflective structure may be provided, and the alternating-fit transducer may be positioned between the third reflective structure and the first resonant cavity. The third reflective structure can improve the reflectivity provided by the first transducer (acting as both a source and reflector of surface acoustic waves). The third reflective structure may include or consist of Bragg mirrors (including elongated electrodes arranged parallel to each other). Those skilled in the art will know how to adjust the first reflective structure so that energy can be transferred to the second resonant cavity.

[0021] According to one embodiment, the elastic wave sensor device further comprises a second alternating-mating transducer and a fourth reflective structure positioned between the first and second alternating-mating transducers. The first alternating-mating transducer comprises a first number of electrodes, and the second alternating-mating transducer comprises a second number of electrodes, the first number of electrodes being different from the second number. In addition, or alternatively, the lengths of at least some of the electrodes of the first number of electrodes may be different from the lengths of at least some of the electrodes of the second number of electrodes (i.e., the lengths of the two transducers in a direction perpendicular to the propagation direction of the surface acoustic wave). Furthermore, the apertures of the first and second transducers may be different from each other. Such methods make it possible to fine-tune to compensate for intrinsic losses caused by the metallization or passivation layer due to scattering, changes in wave velocity, changes in optimal resonance conditions, etc.

[0022] In the embodiments described above, the first and second transducers may be considered as divided portions (operating in parallel) of a single transducer. Such a configuration is advantageous in operating conditions where the reflection coefficient of the first transducer is not strong enough to sufficiently isolate the individual resonant cavities.

[0023] Furthermore, in the elastic wave sensor device according to one of the embodiments described above, a cascade resonant cavity can be formed to reduce the number of resonances and obtain a unique measurement result. Therefore, the elastic wave sensor device according to one of the examples described above may be configured such that the first resonant cavity comprises a first subcavity separated from each other by a first reflective substructure of the first reflective structure, and the second resonant cavity comprises a second resonant subcavity separated from each other by a second reflective substructure of the second reflective structure. Each of the reflective substructures may consist of elongated electrodes arranged parallel to each other.

[0024] According to one embodiment, the elastic wave sensor device further comprises a quartz material layer including a flat surface, a first alternating interlocking transducer and first and second reflective structures formed on or above the quartz material layer, first and second resonant cavities including a portion of the quartz material layer, and the flat surface of the quartz material layer is defined by the crystal cut of the quartz material layer having angles φ in the range of -14° to -24°, angles θ in the range of -25° to -45°, and angles ψ in the range of +8° to +28°, in particular angles φ in the range of -17° to -22°, angles θ in the range of -30° to -40°, and angles ψ in the range of +10° to +25°, more specifically angles φ in the range of -19° to -21°, angles θ in the range of -33° to -39°, and angles ψ in the range of +15° to +25°. In particular, the crystal cut angles may be φ=-20°, θ=-36°, and ψ=15°~25°, especially 17°.

[0025] It should be noted that the above definition is equivalent to angles φ in the range of +14° to +24°, θ in the range of -25° to -45°, and ψ in the range of -8° to -28°, according to the symmetry conditions of the crystal cut rotated around the Z axis (i.e., the non-zero angles φ and ψ of a given crystal cut). More precisely, according to the symmetry rule, it can be stated that the (YXwlt) / +φ / +θ / +ψ cut is equivalent to the (YXwlt) / -φ / +θ / -ψ cut.

[0026] The crystal cut, and thus the angles defining the flat surfaces, are defined according to IEEE 176 1949 Standards on Piezoelectric Crystals, 1949 from 12-12-1949. A quartz crystal can have a cut surface (X”, Z”) defined in a reference system (X”, Y”, Z”) with respect to the cut surfaces (X, Z), where X, Y, Z are the crystal axes of the quartz, the wave propagation direction is defined along the axis X''', the first cut surface (X', Z') is defined by a rotation of an angle φ about the axis Z of the plane (X, Z) so as to define a first reference system (X', Y', Z') where the axis Z' is the same as the axis Z, the second cut surface (X”, Z”) is defined by a rotation of an angle θ about the axis X' of the plane (X', Z') so as to define a second reference system (X'', Y'', Z'') where the axis X'' is the same as the axis X', and the propagation direction along the axis X''' is defined by a rotation of an angle ψ of the axis X'' in the plane (X'', Z'') about the axis Y''. According to the present disclosure, φ ranges from -14° to -24°, θ ranges from -25° to -45°, and ψ ranges from +8° to +28°.

[0027] According to experiments, it has been shown that a quartz material layer for an elastic wave sensor device obtained from such a type of crystal cut has low sensitivity to mechanical stress and can provide measurement robustness against environmental influences. A linear sensitivity of the differential frequency sensitivity (linearity of the temperature-frequency dependence) can be achieved. In fact, the resulting resonance frequency sensitivity enables a measurement sensitivity exceeding 1 ppm per Kelvin in the context of temperature measurement by the provided elastic wave sensor device. 2 ppbK -2 Or even 1 ppbK -2 variation of the second-order temperature coefficient of the differential frequency can be achieved.

[0028] The quartz material layer can be a quartz layer formed on a quartz bulk substrate or a non-piezoelectric bulk substrate. In the latter case, the non-piezoelectric bulk substrate may be a silicon substrate, and optionally, its surface includes a so-called trap-rich layer (e.g., provided by a layer of polycrystalline silicon). The trap-rich layer reduces the insertion loss and makes it possible to reduce the RF loss due to the charge traps induced at the interface with the silicon substrate. It is also possible to use a sapphire substrate, which is very interesting for maximizing the quality factor of resonance by minimizing the viscoelastic loss of the substrate. Sapphire is known to be one of the most advantageous materials in its aspect (along with yttrium-based garnet, more specifically yttrium aluminum garnet - YAG).

[0029] The elastic wave sensor device according to one of the above examples may be a POI device, and thus may include a bulk substrate, particularly a Si bulk substrate or a quartz substrate, and a dielectric layer formed on the bulk substrate, particularly a SiO2 layer. Further, the elastic wave sensor device may include a piezoelectric layer, particularly a LiNbO3 or LiTaO3 layer, formed on or above the bulk substrate. In this case, the first interdigitated transducer and the first and second reflection structures are formed on or above the upper surface of the piezoelectric layer, and the first and second resonance cavities include (a part of) the piezoelectric layer.

[0030] In all of the above-described embodiments, in order to more clearly separate the spectral response of the resonance of the first resonance cavity from the spectral response of the resonance of the second resonance cavity, the extension length of the first resonance cavity and the extension length of the second resonance cavity (in the propagation direction of the elastic wave) may be different from each other.

[0031] Generally, the elastic wave sensor device according to one of the above examples may be a passive surface elastic wave sensor device configured to sense one of ambient parameters such as temperature, chemical species, strain, pressure, or torque of the rotation axis.

[0032] In one embodiment, the first alternating-fit transducer, the first reflective structure, the second reflective structure, the first resonant cavity, and the second resonant cavity may be arranged along a single line. If one of the first and second upper surfaces of the resonant cavity is modified, in particular by a metallization layer or passivation layer, such that the propagation characteristics of the elastic waves generated by the alternating-fit transducer differ between the second resonant cavity and the first resonant cavity, a sensor device having a single-line architecture, particularly a differential sensor device, can be provided, which corresponds to a more compact design compared to a sensor design using two lines.

[0033] Furthermore, an elastic wave sensor assembly is provided comprising one or more elastic wave sensor devices according to one of the examples described above. In particular, the elastic wave sensor assembly may comprise an elastic wave sensor device according to one of the examples described above, and may further comprise other elastic wave sensor devices connected in series or in parallel to the elastic wave sensor device according to one of the examples described above, the other elastic wave sensor devices comprising a third alternating mating transducer, a fifth reflective structure and a sixth reflective structure, a third resonant cavity formed between the third alternating mating transducer and the fifth reflective structure, including a third upper surface, and a fourth resonant cavity formed between the third alternating mating transducer and the fifth reflective structure.

[0034] In such an elastic wave sensor assembly, both the first and second upper surfaces may be at least partially covered by a metallization layer or passivation layer, for example, a metallization layer or passivation layer made of or containing the same material on the first upper surface of the first resonant cavity and the second upper surface of the second resonant cavity, while the third and fourth upper surfaces of the resonant cavities of other elastic wave sensor devices may not be covered, or may be covered with different metallization layers or different passivation layers relative to the first and second upper surfaces.

[0035] An elastic wave sensor assembly comprising two surface acoustic wave sensor devices connected in series (for anti-resonance-based measurements, see U.S. Patent Application Publication 2017 / 033840A1) or in parallel (for resonance-based measurements) may improve the differential sensitivity of measurements compared to employing a single elastic wave sensor device. The resonances provided by the first and second resonant cavities may not be equal to each other due to the formation of one or more metallization or passivation layers. In particular, the quality factor provided by a metallized resonant cavity may be lower compared to a resonant cavity with a free surface. When two elastic wave sensor devices are connected to each other, each of the two elastic wave sensor devices may be configured separately from each other (for example, with respect to the length and number of electrodes of the transducers of each of the two surface acoustic wave sensor devices) to improve the dynamics of the response and to satisfy any desired operating point given by the actual working specification.

[0036] Furthermore, a system is provided for monitoring / measuring ambient parameters, such as temperature, strain level, pressure or torque level of a rotating shaft, chemical species, etc., and this system comprises a questioning device and an elastic wave sensor device and / or elastic wave sensor assembly according to one of the above embodiments, which is communicably coupled to the questioning device.

[0037] An interrogation device for interrogating an elastic wave sensor may include a transmitting antenna configured to transmit a high-frequency interrogation signal to the elastic wave sensor device, a receiving antenna configured to receive a high-frequency response signal from the elastic wave sensor device (which may also include a transmitting and receiving antenna), and processing means for processing / analyzing the high-frequency response signal to determine ambient parameters to be sensed.

[0038] Further features and advantages of the present invention will be described with reference to the drawings. The description will refer to the accompanying drawings, which are intended to illustrate preferred embodiments of the present invention. It should be understood that such embodiments do not represent the entire scope of the present invention. [Brief explanation of the drawing]

[0039] [Figure 1] This is an example of a surface acoustic wave sensor device using conventional technology. [Figure 2a] This is an example of a surface acoustic wave sensor device according to one embodiment of the present invention, in which a resonant cavity is located on only one side of the transducer. [Figure 2b] This is an example of a surface acoustic wave sensor device according to another embodiment of the present invention, in which a resonant cavity is located on only one side of the transducer. [Figure 2c] This is an example of a surface acoustic wave sensor device according to yet another embodiment of the present invention, in which a resonant cavity is located on only one side of the transducer. [Figure 3a] This is an example of a surface acoustic wave sensor assembly according to one embodiment of the present invention. [Figure 3b] This is an example of a surface acoustic wave sensor assembly according to another embodiment of the present invention.

[0040] The present invention provides an elastic wave sensor, particularly a passive SAW sensor, characterized by a high signal-to-noise ratio, sensitivity, and reliability. Regarding temperature measurement, for example, the attainable resonant frequency sensitivity allows for measurement sensitivities exceeding 1 ppm per Kelvin. The elastic wave sensor can be interrogated by any interrogator configured to determine the response spectrum from the interrogated elastic wave sensor. The interrogated elastic wave sensor can be, for example, a resonator device, such as a differential SAW sensor. Needless to say, the present invention can be implemented with any device using an elastic wave sensor or a dielectric resonator, RLC circuit, etc.

[0041] An interrogation device (also called a unit) for interrogating one of the elastic wave sensor devices of the present invention may comprise a transmitting antenna for transmitting a high-frequency interrogation signal to the sensor device and a receiving antenna for receiving a high-frequency response signal from the sensor device. The high-frequency interrogation signal transmitted by the transmitting antenna may be generated by a signal generator which may comprise a high-frequency synthesizer or control oscillator and, optionally, some signal shaping module that provides appropriate frequency conversion and / or amplification of the signal transmitted by the transmitting antenna. The high-frequency interrogation signal generated by the signal generator may be a pulsed signal or a burst signal whose frequency is selected according to the resonant frequency of the elastic wave sensor device. It should be noted that the radiating antenna and the receiving antenna may be the same antenna. In this case, the radiating process and the receiving process should be synchronized with each other, for example, by a appropriately controlled switch.

[0042] Furthermore, the interrogation device may include processing means connected to a receiving antenna. The processing means may include filtering means and / or amplification means and may be configured to analyze the high-frequency response signal received by the receiving antenna. For example, the sensor device operates at a resonant frequency of 434 MHz, 866 MHz, 915 MHz, or 2.45 GHz (the ISM band).

[0043] The question device can transmit long high-frequency pulses, and after transmission stops, the resonant cavity of the sensor device is Q f They discharge at their resonant natural frequencies with a time constant τ equal to / πF, where F is the center frequency and Q f Q is the quality factor of resonance. f This corresponds to the ratio of the resonant center frequency to the half-width of the bandpass used in the questioning process. For example, Q fThis corresponds to a resonance quality coefficient estimated based on the real part of the resonator admittance (conductance) of the resonator, if the resonator is designed to operate at the aforementioned resonance. Spectral analysis performed by the processing means of the interrogation device can calculate one or more resonator frequencies, thereby allowing the ambient parameters to be sensed. The received high-frequency response signal can be mixed by the processing means with the high-frequency interrogation signal according to the so-called IQ protocol, as known in the art, to extract the real and imaginary parts (in-phase component I=Ycosφ and orthogonal component Q=Ysinφ, where signal amplitude is Y and signal phase is φ), from which the modulus and phase can be derived.

[0044] Figure 2a shows an exemplary embodiment of the surface acoustic wave (SAW) sensor device 20a of the present invention. A SAW sensor device according to one embodiment of the present invention, for example, the SAW sensor device 20a shown in Figure 2a, comprises a transducer T. The transducer T is constructed in the form of an interlocking (comb-type) transducer (IDT) that receives an electromagnetic wave E1 (high-frequency interrogation signal) and is connected to an antenna (not shown in Figure 2a) for converting the electromagnetic wave E1 into a surface acoustic wave.

[0045] The surface acoustic wave sensor device 20a comprises a first Bragg mirror structure M1 and a second Bragg mirror structure M2. A first resonant cavity of length g1 is defined between the first Bragg mirror structure M1 and the second Bragg mirror structure M2, and a second resonant cavity of length g2 is defined between the transducer T and the first Bragg mirror structure M1. Thus, the transducer T converts the high-frequency interrogation signal E1 received by the antenna into a surface acoustic wave, which is reflected back by the Bragg mirrors M1 and M2 in the resonant cavities of lengths g1 and g2, respectively, and inversely converted back into a high-frequency signal S1 by the transducer. The inversely converted acoustic wave is, of course, transmitted by the antenna (or another antenna) as a high-frequency response signal. The surface acoustic wave sensor 20a (and the devices described below with reference to other devices in the figure) can operate under Bragg conditions where the wavelength of the excited surface acoustic wave is several times the pitch of the comb electrodes of the comb transducer T. When operation is performed under Bragg conditions, the comb transducer T itself functions substantially as a mirror. It should be noted that the efficiency of this mirroring function depends on the polarization of the wave, the nature and shape of the obstacles, and the characteristics of the substrate. It should be noted that those skilled in the art will know how to adapt the first Bragg mirror structure M1 (for example, by reducing the number of electrode fingers) so that energy can be exchanged between the first and second resonant cavities.

[0046] The mirror grids of the first Bragg mirror structure M1 and the second Bragg mirror structure M2 may be different from each other (as shown in Figure 2a) and may be appropriately configured to yield optimal resonance conditions. The lengths g1 and g2 of the resonant cavities (along the direction of surface acoustic wave propagation) may be different from each other, and changing the length of one of the resonant cavities will lead to a localized change in wave propagation characteristics. According to different embodiments, two or more resonant cavities may be provided. Note that a compact design can be achieved with the SAW sensor device according to the embodiment shown in Figure 2a. Furthermore, satisfactory response dynamics can be achieved with the illustrated configuration.

[0047] The sensor device 20a may include SAW-based sensors constructed on single-crystal piezoelectric materials such as quartz (SiO2), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and langasite (LGS), particularly deposited on silicon, or on polycrystalline piezoelectric materials such as aluminum nitride (AlN) or zinc oxide (ZnO). Furthermore, it may include SAW-based sensors constructed on piezo-on-insulator (POI) composite materials that include layers of piezoelectric material, particularly single-crystal materials such as lithium tantalate or lithium niobate, bonded to a support substrate such as silicon by a bonding layer, for example, a silicon oxide layer, if necessary. As already mentioned, so-called trap-rich layers (e.g., polycrystalline silicon) may be present at the interface with the silicon support substrate.

[0048] In the embodiment shown in Figure 2a, the resonant cavities of lengths g1 and g2 differ from each other in that one of them (length g1) exhibits some physical and / or chemical modification, indicated in black, compared to the other. This physical and / or chemical modification provides different propagation conditions, and therefore different resonant characteristics, to the different resonant cavities. This results in multiple resonances from the multiple resonant cavities, and thus a difference effect when comparing the resonances characterizing each of the multiple resonant cavities.

[0049] Various means exist for physical and / or chemical modification to achieve propagation wave modes exhibiting differential parametric sensitivity. These means include, for example, achieving physical and / or chemical modification by forming a metallization layer and / or a passivation layer. For example, a metallization layer with a thickness of about 100 nm may be formed in the region of a resonant cavity of length g1, and a metallization layer may not be formed in the resonant cavity of length g2. The metallization layer may be formed from the same material as the electrodes of the transducer T and / or Bragg mirror structure M1 and / or Bragg mirror structure M2.

[0050] When the same material is used for forming the comb-type transducer T and Bragg mirror structures M1 and M2, and for the metallization of the electrodes, all of these elements can be deposited using the same deposition process.

[0051] In other embodiments, different materials are used for metallization. For example, one metallization layer or passivation layer of one material is formed on a first resonant cavity of length g1, and another metallization layer or passivation layer of another material is formed on a second resonant cavity of length g2. In another example, a positive temperature-shifted material, such as SiO2 or Ta2O5, is formed on one side of the resonant cavity, and a negative temperature-shifted material, such as Si3N4 or AlN, is formed on the other side of the resonant cavity, or no additional material is formed.

[0052] Passivation may be achieved by forming a passivation layer made of or containing Si3N4, Al2O3, or AlN. According to other embodiments, material layers can be formed on both resonant cavities. Furthermore, material layers formed on one or more resonant cavities may have non-uniform thickness along the direction of elastic wave propagation. Furthermore, multilayers may be formed on one or more resonant cavities. In this regard, it should be noted that generally, when material layers are provided on resonant cavities, particularly when layers of materials with high atomic numbers such as Pt, Au, or W are used, the phase velocity of elastic waves may decrease due to the mass loading effect. This effect can be compensated for by adding layers exhibiting relatively high acoustic velocities, such as AlN, Si3N4, or Al2O3 adjacent to the piezoelectric material layer. Resonant cavities exhibit different sensitivities to the measured quantity because the resulting resonant characteristics differ depending on the surface treatment, thus enabling differential measurements.

[0053] By using cavities with different modification properties, a differential sensor device 20a comprising a transducer structure, first and second reflective structures, and first and second cavities can be formed on the same and single line. In this case, such a device has a single-line architecture that is more compact than a double-line or dual-line architecture.

[0054] According to another embodiment, a first resonant cavity of a surface acoustic wave sensor device 20b, for example in the form of a metal layer, which includes physical and / or chemical modifications, is closer to the transducer than another second resonant cavity which may not include physical and / or chemical modifications (see Figure 2b). Again, all elements of the sensor device 20b are arranged on a single line.

[0055] In both sensor devices 20a and 20b shown in Figures 2a and 2b, respectively, the reflectivity of the transducer T can be increased by an additional reflective structure, such as a third Bragg mirror structure M3 as shown in Figure 2c. In this case, the transducer T is placed between the additional Bragg mirror structure M3 and the resonant cavity. As described above with respect to sensor device 20a, all elements of sensor device 20c, and therefore the transducer T and mirrors M1-M3, can be arranged on the same line to form a single-line architecture sensor device.

[0056] In all of the embodiments described above, Bragg mirrors are provided to form a resonant cavity. However, according to alternative embodiments, one or more of the Bragg mirrors may be replaced with side / edge reflectors for induction in pure shear modes. This allows for a very compact configuration, in that the Bragg reflection is replaced with a planar reflection without energy loss or mode conversion. Configurations with side / edge reflectors for induction in pure shear modes are particularly useful for sensing ambient parameters in liquids. Shear waves are very suitable for probing in liquids. In particular, high-coupling modes (>5%) are attractive for applications in liquids, along with high-k materials (e.g., dielectric constant k greater than 30). According to other embodiments, one or more reflectors are realized in the form of short reflectors containing three or fewer electrodes.

[0057] In all of the above embodiments, including the Bragg mirror, a simple resonant cavity is employed. However, all of these embodiments may employ a cascaded resonant cavity including multiple mirror electrode structures. The spectral distance between two resonances and the coupling coefficient of the resonances can be controlled by the number of mirror electrode structures and resonant subcavities.

[0058] When using cascaded resonator cavities, it is possible to use transducers that do not operate under Bragg conditions. For example, the transducer can have three or four fingers per wavelength, or even five fingers per two wavelengths, and generally any suitable structure that can excite waves with a given synchronization without the waves being reflected by the IDT electrodes.

[0059] Furthermore, it should be noted that this specification also considers operating conditions in which the reflectance coefficient of the transducer is not strong enough to allow sufficiently clear separation between cavity resonances. In this case, (for example, in all of the embodiments described above) to improve the resonance separation of the cavity, the transducer T can be divided into two parts (i.e., two transducers operating in parallel) by providing an additional reflector between the two parts. This is particularly useful for Rayleigh waves, or more generally, elliptic polarization on quartz, langasite, lithium tantalate single crystal substrates, and composite substrates including GaN, AlN, and ZnO layers, because the corresponding modes generally exhibit coupling coefficients of less than 1% and reflectance coefficients of less than 5%, typically less than 3%, and even less than 1% on the intrinsic electrodes. The reflectance coefficient is related to the coupling coefficient to some extent because it generally consists of a mechanical part (elastic loading effect and mass loading effect) and an electrical part (electrical loading effect). The IDT may be divided into two parts in any of the SAW sensor device configurations provided herein, particularly in the configurations shown in Figures 2a to 2c. The two parts (or two transducers) may differ from each other in terms of length (perpendicular to the direction of propagation of surface acoustic waves), number of electrodes, aperture, etc., in order to achieve optimal resonance conditions.

[0060] For POI configurations using LiTaO3 layers with electromechanical coupling exceeding 5%, calculations demonstrate that the reflectivity can be greater than 5%, reaching 10% or even higher (15% experimentally, and over 20% when calculated considering the high atomic number of the metal). In the case of quartz, it can be shown that separation of the two cavity modes can be achieved by adding a central mirror inside the transducer. This consideration is particularly applicable to AlCu-based electrodes. For example, a high reflectivity can be obtained by using electrodes with high atomic numbers such as molybdenum, gold, platinum, or tungsten (especially in the case of single crystals rather than AlN or GaN-based layered substrates). Also in such configurations, it is interesting to use a single-phase unidirectional transducer (SPUDT) to facilitate wave emission in a given direction, again to facilitate separation between cavity resonances.

[0061] In general, an elastic wave sensor device according to one of the examples described above may be a passive surface acoustic wave sensor device configured to sense one of the ambient parameters, such as temperature, chemical species, strain, pressure, or torque of a rotating shaft.

[0062] An elastic wave sensor device according to one of the examples described above may be part of an elastic wave sensor assembly also provided herein. Exemplary embodiments of such an elastic wave sensor assembly are shown in Figures 3a and 3b.

[0063] An elastic wave sensor assembly according to one embodiment of the present invention, for example, the elastic wave sensor assembly 30a shown in Figure 3a, comprises a first SAW sensor device 31a and a second sensor device 32a. The two types of resonators (SAW sensor devices 31a and 32a) can be independently and advantageously optimized with a focus on the idea of ​​benefiting from a balanced resonator response. For example, the dynamics of the response can be improved by changing the aperture of one resonator or the length of the IDT, and any operating point can be satisfied according to the imposed work specification. The first SAW sensor device 31a comprises a first IDT T1, a first Bragg mirror structure M1, and a second Bragg mirror structure M2. A first resonant cavity R1 is formed between the first Bragg mirror structure M1 and the first IDT T1, and a second resonant cavity R2 is formed between the second Bragg mirror structure M2 and the first IDT T1. The first resonant cavity R1 and the second resonant cavity R2 may have the same length g1, or they may have different lengths.

[0064] Furthermore, the second SAW sensor device 32a comprises a second IDT T2, a third Bragg mirror structure M3, and a fourth Bragg mirror structure M4. A third resonant cavity R3 is formed between the third Bragg mirror structure M3 and the second IDT T2, and a fourth resonant cavity R4 is formed between the fourth Bragg mirror structure M4 and the second IDT T2. The third resonant cavity R3 and the fourth resonant cavity R4 may have the same length g2 or different lengths. Lengths g1 and g2 may be the same or different. One or more of the Bragg mirror structures M1 to M4 may be replaced with groove or edge reflection structures or short reflectors containing three or fewer electrodes, as described above. Those skilled in the art will know how to adjust the groove depth or electrode thickness to provide a reflection coefficient of more than 20% that is achievable for a given crystal orientation, wave polarization, and electrode properties.

[0065] According to the embodiment shown in Figure 3a, the first and second resonant cavities R1 and R2 of the first SAW sensor device 31a of the elastic wave sensor assembly 30a include physical and / or chemical modifications (shown in gray in Figure 3a), for example, one of the physical and / or chemical modifications described above, in particular, a metallization or passivation layer. For example, the first and second resonant cavities R1 and R2 of the first SAW sensor device 31a are covered with a metal layer of the same material. On the other hand, in the example shown in Figure 3, the surfaces of the third resonant cavity R3 and the fourth resonant cavity R4 of the second SAW sensor device 32a of the elastic wave sensor assembly 30a are free surfaces. The first SAW sensor device 31a and the second SAW sensor device 32a are connected in parallel to each other (resonant operation), that is, they convert the same electromagnetic wave E1 (high-frequency interrogation signal) received by an antenna (not shown) into a surface acoustic wave in parallel (synchronously), and then retransmit it to an output signal S1.

[0066] In principle, the first transducer T1 of the first SAW sensor device 31a and / or the second transducer T2 of the second SAW sensor device 32a may be divided into two parts, as described above, with an additional reflective structure (e.g., a Bragg mirror structure) positioned between the two parts. Furthermore, instead of providing two resonant cavities symmetrical with respect to the length axis of the first transducer T1, the first transducer T1 may be located to the left or right of the two resonant cavities R1 and R2, in which case its reflectivity can be increased by an additional reflective structure, e.g., a Bragg mirror structure (see the configuration shown in Figures 2a to 2c). Similarly, the second transducer T2 may be located to the left or right of the two resonant cavities R3 and R4, in which case its reflectivity can be increased by an additional reflective structure, e.g., a Bragg mirror structure (see the configuration shown in Figures 2a to 2c).

[0067] All of the above embodiments of the surface acoustic wave sensor device can be mounted on the first SAW sensor device 31a and / or the second SAW sensor device 32a of the acoustic wave sensor assembly 30a. In particular, the acoustic wave sensor assembly 30a may include SAW-based sensors constructed on single-crystal piezoelectric materials such as quartz (SiO2), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), langasite (LGS), or polycrystalline piezoelectric materials such as aluminum nitride (AlN) or zinc oxide (ZnO), particularly deposited on silicon. Furthermore, it may include SAW-based sensors constructed on piezo-on-insulator (POI) composite materials that include layers of piezoelectric material, particularly single-crystal materials such as lithium tantalate or lithium niobate, bonded to a support substrate such as silicon by a bonding layer, for example, a silicon oxide layer, if necessary. As already mentioned, so-called trap-rich layers (e.g., polycrystalline silicon) may be present at the interface with the silicon support substrate.

[0068] The resonances associated with metallized surface cavities and free surface cavities are not strictly equivalent. Metallized surface cavities may have lower quality factors and slower dynamic responses compared to surface cavities with free surfaces. Unbalanced responses can be detrimental to the overall sensor questioning process. Such problems can be mitigated by providing two SAW sensor devices in the elastic wave sensor assembly described above, allowing each SAW sensor device to be individually tuned to optimal resonance conditions.

[0069] Figure 3b shows an alternative embodiment in which the two SAW sensor devices 31b and 32b of the elastic wave sensor assembly 30b are connected in series with each other (anti-resonant operation).

[0070] Therefore, an elastic wave sensor assembly according to another embodiment of the present invention, such as the elastic wave sensor assembly 30b shown in Figure 3b, comprises a first SAW sensor device 31b and a second SAW sensor device 32b. In this case as well, the two types of resonators (SAW sensor devices 31b and 32b) can be advantageously optimized independently of each other. The first SAW sensor device 31b comprises a first IDT T1, a first Bragg mirror structure M1, and a second Bragg mirror structure M2. A first resonant cavity R1 is formed between the first Bragg mirror structure M1 and the first IDT T1, and a second resonant cavity R2 is formed between the second Bragg mirror structure M2 and the first IDT T1. The first resonant cavity R1 and the second resonant cavity R2 may have the same length g1 along the direction of propagation of the surface acoustic wave, or they may have different lengths.

[0071] Furthermore, the second SAW sensor device 32b comprises a second IDT T2, a third Bragg mirror structure M3, and a fourth Bragg mirror structure M4. The third resonant cavity R3 is formed between the third Bragg mirror structure M3 and the second IDT T2, and the fourth resonant cavity R4 is formed between the fourth Bragg mirror structure M4 and the second IDT T2. The third resonant cavity R3 and the fourth resonant cavity R4 may have the same length g2 or different lengths. Lengths g1 and g2 may be the same or different. One or more of the Bragg mirror structures M1 to M4 may be replaced with groove or edge reflection structures or short reflectors containing three or fewer electrodes, as described above.

[0072] According to the embodiment shown in Figure 3b, the first and second resonant cavities R1 and R2 of the first SAW sensor device 31b of the elastic wave sensor assembly 30b include physical and / or chemical modifications (shown in gray in Figure 3b), for example, one of the physical and / or chemical modifications described above, in particular, a metallization or passivation layer. For example, the first and second resonant cavities R1 and R2 of the first SAW sensor device 31b are covered with a metal layer of the same material. On the other hand, the surfaces of the third resonant cavity R3 and the fourth resonant cavity R4 of the second SAW sensor device 32b of the elastic wave sensor assembly 30b are free surfaces.

[0073] In principle, the first transducer T1 of the first SAW sensor device 31b and / or the second transducer T2 of the second SAW sensor device 32b may be divided into two parts, as described above, with an additional reflective structure (e.g., a Bragg mirror structure) positioned between the two parts. Furthermore, instead of providing two resonant cavities symmetrical with respect to the length axis of the first transducer T1, the first transducer T1 may be located to the left or right of the two resonant cavities R1 and R2, in which case its reflectivity can be increased by an additional reflective structure, e.g., a Bragg mirror structure (see the configuration shown in Figures 2a to 2c). Similarly, the second transducer T2 of the second SAW sensor device 32b may be located to the left or right of the two resonant cavities R3 and R4, in which case its reflectivity can be increased by an additional reflective structure, e.g., a Bragg mirror structure (see the configuration shown in Figures 2a to 2c).

[0074] All of the above embodiments of the surface acoustic wave sensor device can be implemented in the first SAW sensor device 31b and / or the second SAW sensor device 32b of the acoustic wave sensor assembly 30b. In particular, the acoustic wave sensor assembly 30b may include SAW-based sensors constructed on single-crystal piezoelectric materials such as quartz (SiO2), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), langasite (LGS), or polycrystalline piezoelectric materials such as aluminum nitride (AlN) or zinc oxide (ZnO), particularly deposited on silicon. Furthermore, it may include SAW-based sensors constructed on piezo-on-insulator (POI) composite materials that include layers of piezoelectric material, particularly single-crystal materials such as lithium tantalate or lithium niobate, bonded to a support substrate such as silicon by a bonding layer, for example, a silicon oxide layer, if necessary. As already mentioned, a so-called trap-rich layer (e.g., polycrystalline silicon) may be present at the interface with the silicon support substrate.

[0075] All embodiments described above are not intended to be limiting, but serve as examples illustrating the features and advantages of the present invention. It should be understood that some or all of the features described above may be combined in different ways.

[0076] In this disclosure, crystal cuts are defined in accordance with IEEE 176 1949 Standards on Piezoelectric Crystals, 1949 from 12-12-1949. In this standard, a crystal cut for SAW applications is uniquely defined by three angles, namely φ and θ, which define the rotation of the crystal according to the basic configuration of the crystal, and the propagation direction ψ, which is defined in a plane (φ, θ) indicating the direction in which the wave propagates, and thus the position of the transducer from which the wave can be emitted. Y and X represent crystal axes that are considered to be reference for defining the initial state of the crystal plate. The first axis is perpendicular to the plate, and the second axis is along the length of the plate. The plate is assumed to be rectangular and is characterized by its length l, its width w, and its thickness t. Given a given (YX) axis system, the length l is along the crystal axis X, the width w is along the Z axis, and the thickness t is along the Y axis.

[0077] Now, assuming that no angle is zero, let's consider the general case of a triple rotation or triple rotation cut. In this situation, the quartz crystal has a cross-section (X'', Z'') defined in a reference frame (X'', Y'', Z'') with respect to the cross-section (X, Z), where X, Y, and Z are the crystal axes of the quartz, and the wave propagation direction is defined along axis X''''. The first cross-section (X'', Z'') is defined by rotating the plane (X, Z) by an angle φ about axis Z, such that axis Z' is the same as axis Z, defining a first reference frame (X', Y', Z'). The second cross-section plane (X'', Z'') is defined by rotating the plane (X', Z') by an angle θ about axis X', such that axis X'' is the same as axis X', defining a second reference frame (X'', Y'', Z''). The propagation direction along axis X'''' is defined by rotating axis X'' by an angle ψ about axis Y'' in the plane (X'', Z'').

[0078] Below, we will review some symmetry rules for quartz. Quartz is a trigonal crystal of class 32. Therefore, quartz is characterized by a ternary axis, or Z-axis, around which the following relationships can be established. (YXw) / φ = (YXw) / φ + 120° The other two axes are binary, and therefore the following symmetry relationship holds. (YXl) / θ=(YXl) / θ+180°, (YXt) / ψ=(YXt) / ψ+180° For simple geometric reasons, it is easy to show that the following set of axes is equivalent. (YXwlt) / +φ / < +θ / +ψ=(YXwlt) / -φ / < +θ / -ψ In practice, assuming the top surface is identified by the positive sign of φ (the surface on which surface waves are assumed to propagate), the bottom surface of the plate can be obtained by changing the sign to negative. Considering that the sign of ψ does not change under symmetry operations, it would seem that the direction of Z''' on the bottom side of ψ remains unchanged, but in reality, it rotates by 180°. Therefore, in order to restore the condition of the top surface, it is essential to add a 180° rotation to ψ, which is actually equivalent to a change in sign. Note that the following symmetries are valid for crystal cuts without rotation around Z (φ=0°).

[0079] (YXlt) / +θ / +ψ=(YXlt) / +θ / -ψ.

Claims

1. A first alternating interlocking transducer (T, T1) arranged in order along the propagation direction of a surface acoustic wave, a first resonant cavity including a first upper surface, a first reflective structure (M1), a second resonant cavity including a second upper surface, and a second reflective structure (M2), Equipped with, At least one of the first and second upper surfaces is at least partially covered by a metallization layer or a passivation layer. Elastic wave sensor devices (20a, 20b, 20c, 31a, 32a, 31b, 32b).

2. A first alternating interlocking transducer (T, T1) arranged in order along the propagation direction of a surface acoustic wave, a first resonant cavity including a first upper surface, a first reflective structure (M1), a second resonant cavity including a second upper surface, and a second reflective structure (M2), Equipped with, The first and second resonant cavities differ from each other in that one of them exhibits some physical and / or chemical modification compared to the other. Elastic wave sensor devices (20a, 20b, 20c, 31a, 32a, 31b, 32b).

3. The elastic wave sensor device according to claim 1 or 2 (20a, 20b, 20c, 31a, 32a, 31b, 32b), wherein either the first upper surface or the second upper surface is at least partially covered by a metallization layer or a passivation layer.

4. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to claim 1 or 2, wherein the first and second upper surfaces are covered with different materials.

5. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to any one of claims 1 to 4, wherein the second resonant cavity is formed between the first reflective structure (M1) and the second reflective structure (M2).

6. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to claim 5, wherein the first resonant cavity and the second resonant cavity are formed on the same side of the first alternating-fit transducer (T, T1).

7. The elastic wave sensor device according to any one of claims 1 to 6 (20a, 20b, 20c, 31a, 32a, 31b, 32b), wherein at least one of the first reflective structure or the second reflective structure comprises a groove or edge reflective structure or a short reflector including three or fewer electrodes.

8. The elastic wave sensor device according to any one of claims 1 to 6 (20a, 20b, 20c, 31a, 32a, 31b, 32b), wherein at least one of the first reflective structure or the second reflective structure includes or is composed of a Bragg mirror.

9. The elastic wave sensor device (20c) according to any one of claims 1 to 8, further comprising a third reflective structure (M3), wherein the first alternating-fitting transducer (T) is disposed between the third reflective structure (M3) and the first resonant cavity.

10. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to claim 1 or 3, wherein the metallization layer includes at least one of AlCu and Ti, or is composed of at least one of them.

11. The passivation layer is Si ３ N ４ Al ２ O ３ AlN, Ta ２ O ５ and SiO ２ The elastic wave sensor device according to claim 1 or 3 (20a, 20b, 20c, 31a, 32a, 31b, 32b), comprising or comprising at least one of the above.

12. The elastic wave sensor device according to any one of claims 1 to 11 (20a, 20b, 20c, 31a, 32a, 31b, 32b), further comprising a second alternating-fit transducer and a fourth reflective structure disposed between the first alternating-fit transducer and the second alternating-fit transducer.

13. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to claim 12, wherein the first alternating-fitting transducer (T, T1) comprises a first number of electrodes (C, C'), and the second alternating-fitting transducer comprises a second number of electrodes (C, C'), and the first number of electrodes (C, C') is different from the second number.

14. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to claim 12 or 13, wherein the first alternating-fit transducer (T, T1) comprises a first number of electrodes (C, C'), and the second alternating-fit transducer comprises a second number of electrodes (C, C'), and the length of at least a portion of the electrodes (C, C') of the first number of electrodes (C, C') is different from the length of at least a portion of the electrodes (C, C') of the second number of electrodes (C, C').

15. The elastic wave sensor device according to claim 12, 13, or 14 (20a, 20b, 20c, 31a, 32a, 31b, 32b), wherein the opening of the first alternating-fitting transducer is different from the opening of the second alternating-fitting transducer.

16. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to any one of claims 1 to 15, wherein the first resonant cavity (g1) comprises a first resonant subcavity separated from each other by a first reflective substructure of the first reflective structure (M1), and the second resonant cavity (g2) comprises a second resonant subcavity separated from each other by a second reflective substructure of the second reflective structure (M2).

17. The elastic wave sensor device according to any one of claims 1 to 16 (20a, 20b, 20c, 31a, 32a, 31b, 32b), wherein the first resonant cavity has a first extension length (g1), the second resonant cavity has a second extension length (g2), and the first extension length (g1) and the second extension length (g2) are different from each other.

18. The quartz material layer further comprises a flat surface, The first alternating interlocking transducer (T, T1) and the first and second reflective structures (M1, M2) are formed on or above the quartz material layer, and the first and second resonant cavities include a portion of the quartz material layer. The flat surface of the quartz material layer is defined by the crystal cut of the quartz material of the quartz material layer having angles φ in the range of -14° to -24°, angles θ in the range of -25° to -45°, and angles ψ in the range of +8° to +28°, in particular angles φ in the range of -17° to -22°, angles θ in the range of -30° to -40°, and angles ψ in the range of +10° to +25°, more specifically angles φ in the range of -19° to -21°, angles θ in the range of -33° to -39°, and angles ψ in the range of +15° to +25°, in particular the angles of the crystal cut may be φ = -20°, θ = -36°, and ψ = 15° to 25°, in particular 17°. The elastic wave sensor device according to any one of claims 1 to 17 (20a, 20b, 20c, 31a, 32a, 31b, 32b).

19. Bulk substrates, especially Si bulk substrates, A dielectric layer formed on the bulk substrate, particularly SiO ２ Layers, Piezoelectric layer, especially LiNbO ３ layer or LiTaO ３ layer, and It further includes, The first alternating interlocking transducer (T, T1) and the first and second reflective structures (M1, M2) are formed on or above the piezoelectric layer, and the first and second resonant cavities include the piezoelectric layer. The elastic wave sensor device according to any one of claims 1 to 18 (20a, 20b, 20c, 31a, 32a, 31b, 32b).

20. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to any one of claims 1 to 19, wherein the elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) is a passive surface elastic wave sensor device configured to sense an ambient parameter selected from one of temperature, chemical species, strain, pressure, or torque of a rotating shaft.

21. The elastic wave sensor device (20a, 20b, 20c, 31a, 32a, 31b, 32b) according to any one of claims 1 to 20, wherein the first alternating-fit transducer (T, T1), the first reflective structure (M1), the second reflective structure (M2), the first resonant cavity, and the second resonant cavity are arranged along a single line.

22. An elastic wave sensor assembly (30a, 30b) comprising an elastic wave sensor device (31a, 32a) according to any one of claims 1 to 21, and further comprising another elastic wave sensor device (31b, 32b) connected in series or in parallel to the elastic wave sensor device (31a, 32a) according to any one of claims 1 to 21, wherein the other elastic wave sensor device (31b, 32b) A third alternating mating transducer, A fifth reflective structure and a sixth reflective structure, A third resonant cavity formed between the third interlocking transducer and the fifth reflective structure, including the third upper surface, A fourth resonant cavity is formed between the third interlocking transducer and the sixth reflective structure, including a fourth upper surface. Elastic wave sensor assemblies (30a, 30b).

23. The elastic wave sensor assembly (30a, 30b) according to claim 22, wherein both the first and second upper surfaces are at least partially covered by a metallization layer or a passivation layer, and the third and fourth upper surfaces are not covered by a metallization layer or a passivation layer.

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