High-temperature stable elastic wave device

Abstract

The invention relates to a 10000 elastic wave device in the field of elastic wave-based components for fields such as telecommunications. The elastic wave device 1000 of the invention comprises a variable impedance means 1003, 2003, 3003, 10400, a first electromechanical device 3, 11130, in particular a first transducer 3, 11130, and a second electromechanical device 5, 11140, in particular a second transducer 5, 11140 or an electrode array configured to reflect at least partially elastic waves emitted by the first electromechanical device 3, an array 4000, 11150 of at least one electrode 1000, 2000, 3000 located between the first electromechanical device 3 and the second electromechanical device 5 in the direction of propagation of the elastic waves, and a temperature determination means 10200 configured to determine a temperature of an operating region of the wave device elastic bands.Figure for the abbreviation: Figure 12.

Description

Title of the invention: High-temperature stable elastic wave device

[0001] The invention relates to an elastic wave device in the field of elastic wave-based telecommunication components, in particular surface acoustic waves (SAW).

[0002] Devices using elastic surface waves have recently seen a marked increase in their use for a variety of applications such as filtering, signal manipulation and processing, and detection. An example of a device comprising two transducers and an electrode array is described in EP 3 599 720 AL

[0003] In the telecommunications context, numerous radio frequency (RF) bands are used to receive and transmit information. Each RF band defines a channel to which filtering operations must be applied in order to process, manipulate, or store information. In this context, the industry requires filters with as many resonant frequencies as there are RF bands to process. Furthermore, they must be able to switch from one RF band to another within a single device.

[0004] However, a serious problem for the reliable operation of elastic wave devices arises due to frequency shifts of the relevant operating (center / resonance) frequencies caused by temperature variations.

[0005] The present invention aims to compensate for the impacts of temperature variation on the reliability of operation of an elastic wave device by dynamically adjusting the elastic wave device to its natural operating frequency.

[0006] The object of the invention is achieved by an elastic wave device comprising one (or more) variable impedance means, a first electromechanical device, in particular a first transducer and more specifically an interdigitated transducer (IDT) consisting of the entanglement of at least two electrode combs connected to electrical sources of opposite polarization, forming a periodic network, and a second electromechanical device, in particular a second transducer or an IDT or an electrode network configured to reflect at least partially the elastic waves emitted by the first electromechanical device and a network of at least one electrode located between the first electromechanical device and the second electromechanical element in the direction of propagation of the elastic waves, in which at least one electrode of the network of at least one electrode is connected to a predetermined electrical potential via the variable impedance means.In addition, the elastic wave device includes a configured temperature determination means. to determine the temperature of an operating region (e.g., being or including a resonance region) of the elastic wave device, and at least one (potentially several) control means configured to control the variable impedance means based on the temperature determined by the temperature-determining means. In the context of the invention, an electrode array can be constructed with a single electrode or with a plurality of electrodes. Each electrode in the array of at least one electrode can be connected to a variable impedance means from among a plurality of variable impedance means, and each variable impedance means from among a plurality of variable impedance means can be controlled by a control means from among a plurality of control means (see also the detailed description below).Controlling a variable impedance medium involves controlling one or more impedances of the variable impedance medium, for example, controlling / adjusting one or more capacitances of one or more capacitors. Elastic waves can be surface acoustic waves. The elastic wave device can be, for example, a filtering device (SAW).

[0007] The elastic wave device can adjust its operating frequency according to a varying temperature thanks to the electrode array connected to the variable impedance means controlled by the control means (all electrodes being connected to a predetermined electrical potential, in particular ground). Determining the temperature makes it possible, for example, to estimate a drift in the filter center and to determine a correction applied by the variable impedance means to compensate for the temperature-dependent drift in the filter center. In particular, a phase match between the first and second electromechanical devices (transducers) can be maintained precisely even in the case of temperature variations due to the provision of the variable impedance means and the control means.

[0008] In one embodiment of the invention, each of the variable impedance means may include a voltage-controlled capacitor and the control means are configured to control the variable impedance means by supplying a voltage determined on the basis of (in deduction of) the temperature determined by the temperature-determining means to achieve an adjustment of the elastic wave device to its operating frequency as a function of the determined temperature.

[0009] Furthermore, it should be noted that, in principle, a variable capacitor allows the network of at least one electrode to which it is connected to be switched from a configuration corresponding to an open circuit (OC), i.e., a floating connection and therefore a low coupling capacitance, to a configuration corresponding to a short-circuit (SC) connection, i.e., a connection with a predetermined electrical potential such as ground, and therefore with a high coupling capacitance. A low coupling capacitance is small compared to the static capacitance of the IDT or the network to which it is connected—for example, two orders of magnitude lower—and a high coupling capacitance is high compared to the static capacitance of the IDT or the network to which it is connected—for example, one order of magnitude higher. By using an impedance with a variable capacitance, the phase of the elastic waves traveling through the gap between the two transducers can be changed, resulting in a change in the bandwidth. In particular, by switching from the OC configuration to the SC configuration, the device's bandwidth can then transition smoothly from a high-frequency range to a low-frequency range.

[0010] According to one embodiment, the temperature-determining means is configured to determine an electrical resistance in the operating region of the elastic wave device and to determine the temperature based on the determined electrical resistance. Determining the electrical resistance can prove to be a reliable way of determining the temperature and, consequently, of controlling the variable impedance means, for example, by determining the appropriate supply voltage to be provided to a voltage-controlled capacitor. Alternatively, the temperature-determining means may include or be a surface acoustic wave resonator. The operating / resonant or antiresonant frequency depends on the temperature variations and can be used to precisely control the variable impedance means, for example, by determining the appropriate supply voltage to be provided to a voltage-controlled capacitor.

[0011] In an alternative configuration, the control means can also be configured to open or close an electrical connection between at least one electrode and a predetermined electrical potential, in particular ground. In particular, several or all of the electrodes can be configured in this way. In this manner, agility can be achieved and controlled, in particular by means of a simple switch. This is technically relatively easy and inexpensive to manufacture.

[0012] According to one embodiment, the array of at least one electrode may comprise several electrodes, in particular, in the form of parallel bands, several of which have variable impedances; in particular, each electrode may be connected to a separate variable impedance. The number of parallel bands modifies the frequency agility of the device, in particular the frequency range accessible to the device. It is thus even easier to adapt the agility of the device to the desired operating criteria for a particular case, as well as to the desired cost and complexity of the overall configuration.

[0013] According to one embodiment, the electrode array can be configured to change the phase of the elastic waves and / or configured to reflect them at least partially. The introduction of an electrode array configured to reflect the elastic waves at least partially creates resonant cavities, notably reducing the frequency width of the transition between the device's passband and the frequency rejection band, which corresponds to all frequencies not included in the device's operating bandwidth. Depending on the situation, those skilled in the art will know how to define the limits of the passband and the rejection band. The transition between the passband and the rejection band is called the transition band.The frequency width of the transition band is defined as the attenuation of the transmitted signal from the device's minimum insertion loss to the same value plus 30 dB, 40 dB, or 50 dB, depending on the device specifications.

[0014] According to one embodiment, the electrodes of a first subset of electrodes of the network of at least one electrode are connected by means of variable impedance.

[0015] In another embodiment of the invention, the electrodes of a second subset of electrodes in the array of at least one electrode may be connected to each other and to a floating electrical potential or connected to a predetermined electrical potential, in particular to ground. This configuration of the device makes it possible, for example, to create a mirror for elastic waves whose spectral range of the reflection function varies according to the connection conditions.

[0016] According to one embodiment of the invention, the first electrode subset and the second electrode subset can be arranged such that the electrodes of the first subset and those of the second subset are interdigitated with respect to each other, forming the aforementioned IDT described above. This electrode arrangement makes it possible to create an air gap coupler (AGC) that allows the phase of the device to be changed and monitored. The frequency agility potentially achievable by the device can depend on the number of fingers composing the two interdigitated electrode arrays and, in particular, by increasing the number of finger pairs in the IDT subsets, it is possible to broaden the frequency range of the device's frequency agility.

[0017] According to one embodiment of the invention, a plurality of electrode arrays can be included between the first electromechanical device, in particular a first transducer (IDT), and the second electromechanical device, in particular a second transducer (IDT), the arrays being separated from each other by free and / or metallized propagation gaps. The distances between two adjacent electrode arrays can be identical. In particular, by introducing more electrode arrays configured to reflect waves at least partially With elastic transducers, the number of cavities in the device is increased, thus allowing for a modification and, in particular, a reduction in the frequency width of the transition between the device's passband and the frequency rejection band, the transition band defined previously. Furthermore, by adjusting the distance between adjacent electrode arrays, it becomes possible to achieve phase quadrature between the elastic waves propagating in the cavities located in the space between the two transducers and those originating from the transducers, in particular to increase the electromechanical coupling coefficient.

[0018] According to one embodiment of the invention, the distance between the first electromechanical device and the directly adjacent electrode array, and the distance between the second electromechanical device and the directly adjacent electrode array, can be identical and, in particular, equal to the distance between two adjacent electrode arrays. This arrangement can thus improve the resonance conditions of the device, and consequently the coupling performance of the elastic wave device.

[0019] According to one embodiment of the invention, an even number of electrode arrays configured to change the phase of elastic waves can be included in the space between the transducers, which is configured to at least partially reflect the elastic waves. In particular, the electrode array configured to at least partially reflect the elastic waves can be a Bragg mirror arranged to form two resonant cavities, located on either side of this Bragg mirror or the reflecting structure, which can achieve a quadrature of the phase of the elastic waves between the space between the transducers and the reflecting structure(s).Increasing the number of pairs of electrode arrays configured to change phase with or without an electrode array configured to at least partially reflect elastic waves increases the number of resonant cavities in the device and, in particular, reduces both the frequency width of the transition between the device's bandwidth and frequency rejection band, and increases the device's operating bandwidth width.

[0020] According to one embodiment, the elastic wave device further comprises a first reflection structure (mirror) and a second reflection structure (mirror) to facilitate the formation of resonance spaces, the first electromechanical device being positioned between the first reflection structure and the array of at least one electrode, and the second electromechanical device being positioned between the second reflection structure and the array of at least one electrode.

[0021] In another embodiment of the invention, the first and second electromechanical devices (for example, transducers - IDT) may be arranged above or within a piezoelectric substrate, in particular, a composite substrate comprising a base substrate and a piezoelectric layer, the thickness of the piezoelectric layer being less than or equal to 1.5 x X, where X is the wavelength of the fundamental mode of elastic surface waves. By using a composite substrate designed for this purpose, it is possible to guide shear waves that allow a higher electromechanical coupling between the elastic waves and the electromechanical elements of the device than was possible with elliptically (Rayleigh type) or longitudinally polarized modes.

[0022] According to one embodiment of the invention, a dielectric layer and / or a trapping layer and / or a Bragg mirror may be included between the base substrate and the piezoelectric layer. This layer, rich in electrical charge traps, improves the insulating properties of the base substrate and, consequently, the performance of the device.

[0023] According to one embodiment of the invention, the polarization of the elastic waves can correspond to a guided shear wave or a guided longitudinal wave within the piezoelectric layer. In particular, the thickness of the piezoelectric layer can influence the efficiency of the shear wave or longitudinal wave guidance. Specifically, a piezoelectric layer with a thickness less than the elastic ground wavelength improves the guidance of the shear and longitudinal modes of the elastic waves and reduces acoustic radiation energy losses in the composite substrate. The use of these elastic wave modes improves the performance of the elastic device, particularly by minimizing energy losses in the passband in the case of a passband filter.The composite substrate can be selected such that its bulk surface skimming wave velocity, i.e. the velocity above which the substrate no longer guides waves, is equal to or greater than the wave velocity that occurs at the end of the stopband of the grating, which could be advantageous, for example, for resonant space filters.

[0024] The invention will be better understood and other advantages will become apparent with the aid of the following non-limiting description and the accompanying figures, among which:

[0025] [Fig.1] is a diagram illustrating an elastic wave device according to a first embodiment of the invention.

[0026] [Fig.2] illustrates an elastic wave device according to a second mode of realization in which the space between the two transducers comprises only a single electrode connected to a variable impedance and its control means, all connected to a predetermined electrical potential.

[0027] [Fig.3] illustrates an elastic wave device according to a third embodiment in which the space between the two transducers comprises an electrode array formed by two interdigitated combs.

[0028] [Fig.4] is a graphical representation of the gain in decibels of the function of transfer of the device according to the third embodiment, which in this case presents a variable impedance comprising a variable capacitor, depending on the value of the variable capacitor.

[0029] [Fig.5] is a graphical representation of the gain in decibels of the function of transfer of the device according to the third embodiment, which in this case has a variable impedance comprising a variable inductance, depending on the value of the variable inductance.

[0030] [Fig.6] illustrates an elastic wave device according to a fourth mode of realization in which the space between the two transducers comprises three electrode arrays, two of which are configured to allow continuity of guidance between neighboring resonant cavities with a low level of elastic wave reflection.

[0031] [Fig.7] is a graphical representation of the gain in decibels of the function of transfer of the device according to the fourth embodiment, which in this case has a variable impedance comprising a variable inductance and a variable capacitance, depending on the value of the variable capacitance.

[0032] [Fig.8] is a graphical representation of the gain in decibels of the function of transfer of the device according to the fourth embodiment, which in this case has a variable impedance comprising a variable inductance and a variable capacitance, depending on the value of the variable inductance.

[0033] [Fig.9] illustrates an elastic wave device according to a fifth mode of embodiment in which the space between the two transducers comprises three electrode arrays, two of which are configured to transmit but only weakly reflect elastic waves emitted by the transducers (IDT) with an overall reflection coefficient of the corresponding array less than 50% or even less than 20%.

[0034] [Fig. 10] illustrates an elastic wave device according to a sixth embodiment in which the space between the two transducers (IDT) comprises five electrode arrays, three of which are configured to transmit mainly but not or only marginally reflect elastic waves, unlike the other two which are configured to reflect mainly elastic waves with an overall reflection coefficient of the corresponding array greater than 50% and more preferably 80%) and are interposed between each of the three preceding arrays.

[0035] [Fig. 11] illustrates an elastic wave device according to an embodiment including a control means configured to control a variable impedance means as a function of temperature determined by a temperature determination means.

[0036] [Fig. 12] illustrates an elastic wave device according to an embodiment comprising three ports, a reflection means, and a configured control means to control a variable impedance means as a function of temperature determined by a temperature determination means.

[0037] [Fig. 13] illustrates an example of a capacity-frequency law applicable to an elastic wave device according to one embodiment.

[0038] The invention will be described in more detail using advantageous embodiments, by means of examples and with reference to the drawings. The embodiments described are simply possible configurations such that individual features as described can be provided independently of one another or can be omitted when implementing the present invention.

[0039] Here, an elastic wave device is provided which can be adjusted to its operating frequency by compensating for frequency drifts caused by temperature variations by means of a temperature determination means, a control means and a variable impedance means connecting an array of one or more electrodes positioned between two electromechanical devices (for example, transducers converting electromagnetic waves into elastic waves, and vice versa) at electrical potentials.

[0040] In [Fig. 11], a general embodiment of such an elastic wave device 10000 is illustrated in a schematic sketch. The elastic wave device 10000 illustrated in [Fig. 11] comprises an active part 10100 including two electromechanical devices (representing two ports), for example, a first and a second transducer (IDT) or a first transducer and an electrode array configured to reflect at least partially elastic waves emitted by the first electromechanical device and an additional electrode array (for example, representing a third port) arranged between the electromechanical devices (for further details, see the description of different embodiments below).Furthermore, the elastic wave device 10000 includes a temperature determination means 10200 for determining the temperature of an operating region of the active part 10100 of the elastic wave device 10000. The temperature determination means 10200 may include a temperature sensor, for example, a SAW temperature sensor. The temperature determination means 10200 may alternatively include a means for determining the electrical resistance of the active part 10100 of the elastic wave device 10000. Variations in the determined electrical resistance result in variations in the ambient temperature to which the elastic wave device 10000 is subjected. In addition, the elastic wave device 10000 includes control means 10300 and a variable impedance means 10400 connecting at least some of the electrodes of the electrode array arranged between the electromechanical devices. (IDT) at electrical potentials. The control means 10300 controls the variable impedance means 10400 according to the temperature determined by the temperature-determining means 10200. It should be noted that the temperature-determining means 10200 can be integrated into the control means 10300. In particular, an impedance or impedances of the variable impedance means 10400 can be controlled / adjusted by the control means 10300 in order to adjust the elastic wave device 10000 to its operating frequency in the event of temperature variations detected by the temperature-determining means 10200. The elastic wave device 10000 is considered to be (almost) perfectly tuned to its operating frequency, for example, its resonant frequency. For example, an permissible temperature sensitivity is approximately 10 ppm / K at most.If subsequent tuning has been completed, a temperature change occurs, resulting in a frequency shift. This temperature change is detected by the temperature determination means 10200, and the control means 10300 receives information about the detected temperature change. In response, the control means 10300 controls the impedance(s) of the variable impedance means 10400, which connects the electrodes arranged between the electromechanical devices (IDTs), to electrical potentials in order to retune the elastic wave device 10000 to its operating frequency. For example, the variable impedance means 10400 includes a voltage-controlled capacitor, and the control means 10300 provides supply voltages to the variable impedance means 10400 to adjust the capacitor(s) to retune the elastic wave device 10000 to its operating frequency. .

[0041] A particular embodiment implementing the general embodiment shown in [Fig. 11] is illustrated in [Fig. 12]. The elastic wave device 11000 illustrated in [Fig. 12] comprises an active part 11100 including reflective structures / mirrors 11110 and 11120, transducers 11130 and 11140 (IDT corresponding to ports 1 and 2), and an additional interdigitated electrode array 11150 (port 3, coupler) located between the transducers 11130 and 11140. The unit 11200 is a combined temperature determination and control means. Unit 11200 determines the electrical resistance R of an operating region of the active part 11100 of the elastic wave device 11000. The temperature T of the operating region of the active part 11100 is determined from the measured resistance R. Based on the determined temperature T, a supply voltage V is determined.

[0042] The elastic wave device 11000 illustrated in [Fig. 12] further comprises one or more voltage-controlled capacitors 11400 whose capacitance is controlled by the supply voltage V provided by the unit 11200. Electrical potentials The electrodes of the interdigitated electrode array 11150, located between the transducers 11130 and 11140, can be controlled by means of the voltage-controlled capacitor 11400, which connects the electrodes to electrical potentials in order to adjust the elastic wave device 11000 to its nominal operating frequency (the frequency defined, for example, at the midpoint of the filter's operating temperature range, e.g., 25 °C) in the event of temperature variations causing a certain frequency shift. In one example, the electrical potential of the interdigitated electrode array 11150 is controlled by a voltage-controlled capacitor 11400, and in another example, individual electrodes of an electrode array are adjusted with respect to their electrical potentials by different individual capacitances (voltage-controlled capacitors 11400 or other means of variable impedance).

[0043] In general, the temperature sensitivity of an elastic wave device, for example, the elastic wave device 10000 shown in [Fig. 11] or the elastic wave device 11000 shown in [Fig. 12], is known (both theoretically and experimentally). Based on this knowledge, the variable impedance means, for example, the variable impedance means 10400 shown in [Fig. 11] or the voltage-controlled capacitor 11300 shown in [Fig. 12], can be controlled to adjust the electrical potentials of the array of electrodes positioned between the transducers so as to allow the elastic wave device to adjust to its operating frequency in the event of temperature variations causing a certain frequency shift. A detailed example is given below.

[0044] The temperature sensitivity of an elastic wave device, for example operating as a filtering device, can for example be expressed by a third-degree polynomial function: A<0 = (ff^ = TCÆlxCT-T0)+TCÆ2xC^ where / 0 denotes the frequency Filter center (operating frequency) at T0 = 25°C and TCF^ denotes the temperature coefficients of order 1, 2 and 3 of the frequency. The values ​​in the table below indicate a frequency variation of approximately 7.0 MHz in the temperature range of -40 / +85°C, with less than 3 MHz from 0 to +85°C: [Table 1] Equation 1 Parameter Lower Bandwidth Upper Bandwidth (MHz) 1901.100 1942.62 TCF (ppm.K1) 12.50 13.25 TCF2 (ppm.K-2) -310.20 -204.89 TCF3 (ppm.K'3) 4622.52 3037.47 Table 1. Example of TCF of a SCAW / RG-SAW filter built on a standard Connect-POI substrate to operate near 1.9 GHzTemperature measurement allows estimation of the filter's center frequency drift based on the formula above. Adjusting the filter's center frequency can be achieved, for example, using a thermistor and a variable capacitance diode, i.e., a voltage-controlled capacitor. A processing unit can convert a defined resistance from an operating region (resonance) of the elastic wave device into a temperature and voltage to be applied to the variable capacitance diode. Resistance variations can be directly converted into voltages in a suitable manner. The system can also be based on other types of sensors and voltage-controlled components, without restriction, provided that the control range covers the entire frequency change excursion.The temperature can be detected by a thermistor connected to the filter or any temperature sensor that provides a means of converting resistance or another suitable electrical parameter into voltage. The sensor can also be a SAW resonator operating at a frequency close to the filter center frequency of the elastic wave device, or at other frequencies to maximize its temperature sensitivity.For example, an MHB (1.5-2.5 GHz) filter built on a standard piezoelectric-on-insulator (POI) substrate (e.g., LT42 600 nm / BOX 500 nm / TR / Si, where LT42 denotes LiTaO3 (YXl) / 42°, a crystal cut definition according to IEEE 176 Piezoelectricity Standard, BOX means buried oxide, TR is a trap-rich layer, and Si is a silicon substrate) can be fitted with a resonator operating at 1 GHz to maximize temperature sensitivity, but it could also be tuned to the filter center frequency to allow direct conversion of the frequency change into the tuning voltage.

[0045] Voltage control as a function of a determined temperature is based on a known capacitance-frequency law, as illustrated by way of example in [Fig. 13]. In the example given, the capacitance-frequency law is quasi-linear on a logarithmic scale. from 0.1 to 1 pF with a frequency excursion of ~25 MHz, that is, much more than the 7.0 MHz (-40 / +85°C) observed, for example, for a typical 1.9 GHz SCAW filter. For example, a linear drift of 40 ppm Kl would correspond to an absolute frequency variation of 10 MHz. The most important thing is to model the quasi-linear part of the function [Math 1] dlog(fC+ [Fig. 13] with exemplary values [Math 2] a = 1610.73, 0 = -23.40, y = 2.44, 6 = -0.44, ^ = -1.22xl03, q = 1.31

[0046] An example of temperature sensitivity of the elastic wave device is considered, with TCF values: TCFX = 13 ppm«K ', TCF2 = -300 ppb«K2, TCF3 = 3500 ppt«K 3 (close to the example in Table 1). The starting capacitance value (corresponding to the operating condition at 25 °C) can be set in the middle of the variable capacitance diode frequency excursion, for example, 0.6 pF, and the filter design must take this point into account to be truly satisfactory. Using the third-degree temperature-frequency law, it is possible to estimate the frequency variation due to any temperature change and convert it into a capacitance variation by solving the equation f(C) above, but limited to the exponential part [Math 3] which corresponds well to the section of the curves for which the capacitance / frequency dependence is strongest (i.e., from 0.1 to 1 pF for the example shown in [Fig. 13]). With / (Co) and / (O) denoting the frequency corresponding to / 0, the initial frequency at To and Co, and the current temperature T for which the capacitance C must be found, respectively, we obtain the capacitance to be adjusted C(T) in the form [Math 4] To give a numerical example, we can assume that ΔC0 = 1620 MHz, which gives a value of C0 of 0.376 pF. Let's assume the determined temperature is 5°C. The resulting frequency shift given by the temperature-frequency law is 1619.339 MHz = f(T). Substituting this value into the formula above provides the new capacitance value to adjust to bring the filter back to its operating frequency of 1620 MHz: 0.3498 pF – the frequency shift actually corresponds to 0.66 MHz. It should be noted that this assumes the capacitor actually used is not temperature-sensitive. In real-world applications, there are in fact many commercially available capacitors that are (almost) temperature-insensitive within the actual temperature ranges involved.

[0047] The active part 10100 of the elastic wave device 10000 shown in [Fig. 11] can alternatively be implemented in various other embodiments in the form of a plurality of configurations as described below, in which the terms "variable impedance means" and "variable impedances" are used interchangeably. Furthermore, the function of the control means can be supplemented as described below. The description of the materials and substrates used can be applied to all embodiments.

[0048] [Fig. 1] represents the elastic wave device 100 as described in a first embodiment of the invention. The elastic wave device 100 represents a dual-port resonator that can be used as a filter. The elastic wave device 100 comprises a first electromechanical device, in particular, here a first transducer (IDT) 3 forming a first port, and a second electromechanical device, in particular, here a second transducer (IDT) 5 forming a second port, which in alternative embodiments may be an array of electrodes configured to at least partially reflect the elastic waves emitted by the first electromechanical device 3.

[0049] The device 100 further comprises an array 4000 of at least one electrode 1000, 2000, 3000 situated between the first transducer 3 and the second transducer 5 in the direction of propagation of elastic waves, in which at least one electrode of the array is connected to a predetermined electrical potential 1005, 2005, 3005 via a variable impedance 1003, 2003, 3003, and a control means 1007, 2007, 3007 for changing the variable impedance, all arranged on a piezoelectric substrate 9.

[0050] In this first embodiment, the piezoelectric substrate can be a composite substrate comprising a piezoelectric layer 11 with crystallographic axes X, Y and Z, a dielectric layer 13 and a base substrate 15.

[0051] In this embodiment, the piezoelectric layer 11 is LiTaO3 or LiNbO3. In particular, using IEEE 1949 Std-176 standards, the orientations of the crystallographic cross-section of the piezoelectric layer are defined by (YXZ) / 0, with 0 denoting the crystallographic orientation angle corresponding to a rotation around the crystal axis X between 0 and 60 degrees or between 90 and 150 degrees.

[0052] The piezoelectric layer 11 can also be made of potassium niobate, KNbO3, or any other material of similar composition, such as KTN. It is also possible to use for the piezoelectric layer 11 a film formed epitaxially or sprayed, for example, of aluminum nitride AIN, scandium-doped aluminum nitride AIScN, zinc oxide ZnO, PZT, GaN, or any other composition of AIN and GaN.

[0053] The thickness of the piezoelectric layer 11 is on the order of the wavelength X of the elastic waves, or less; in particular, it may be approximately 10 microns, or less, in particular between 0.1 and 1.1 microns. The thickness of the base substrate 15 is greater than that of the piezoelectric layer 11. Preferably, the thickness of the base substrate 15 is at least ten times greater than the thickness of the piezoelectric layer 11. In particular, it may be 50 to 100 times greater, corresponding to a base substrate with a thickness of 50 to 1000 microns. In particular, the substrate thickness may be from 100 microns to 500 microns.

[0054] The basic substrate 15 used in the first embodiment of the invention is a silicon substrate, in particular a silicon substrate with high electrical resistivity. High electrical resistivity is understood to mean an electrical resistivity greater than 1000 Ω*cm. Preferably, the silicon is in crystalline form, with the substrate orientation preferably in the (100) direction, which results in a higher propagation velocity of elastic waves than other crystallographic orientations such as (110), (111), or (001), which can also be used. The choice of substrate takes into account the velocity beyond which elastic waves are no longer guided by the silicon surface.This velocity must therefore be greater than the velocity of the mode corresponding to the anti-resonance condition, but sufficiently close to it to prevent the excitation of other modes that would otherwise degrade the spectral purity of the device's response. Advantageously, the velocity is close to the velocity corresponding to the upper edge of the frequency stopband induced by the periodicity of the IDT and mirror gratings of the device. Thus, the crystallographic axes Z of the substrate and the piezoelectric layer, along which the respective planes are defined, can ideally be aligned in . the case of silicon (111) or misaligned by 45° for silicon (100) or (111) in order to limit the contributions of parasitic modes beyond the anti-resonance frequency of the fundamental mode, or misaligned in the angular range [-10°, +10°] for Si(lll) considering the corresponding IEEE angular definition in the form (YXwlt) / +457-35.37^, with rp the misalignment angle, or in the angular range [+170°, ±190°] for Si( 111) considering the corresponding IEEE angular definition in the form (YXwlt) / ±457+35.37'ip, with rp the misalignment angle. The basic substrate 15 may be made of or comprise other materials, in particular to enable elastic waves to propagate at a speed greater than that of elastic waves propagating in the piezoelectric layer 11. In particular, the basic substrate 15 may be made of or comprise carbon-diamond, sapphire, or silicon carbide.

[0055] The base substrate 15 may include a trapping layer, particularly located between the dielectric layer 13 and the base substrate 15, thereby improving the electrical insulation performance of the base substrate 15. This trapping layer may be formed of at least one polycrystalline, amorphous, or porous material, such as polycrystalline silicon, amorphous silicon, or porous silicon. However, the invention is not limited to these materials.

[0056] In alternative embodiments, the basic substrate 15 may include a Bragg mirror, located between the piezoelectric layer 11 and the basic substrate 15. This Bragg mirror consists of a stack of layers periodically alternating the acoustic impedance of the medium, which is defined as the product of the propagation velocity of elastic ground and the density of the material in which ground propagates, all expressed in Rayleighs, or preferably in MRayleighs, i.e. 106 Rayleighs.

[0057] This stack of layers forming the Bragg mirror can be composed of alternating layers of, for example, tungsten and silica, or Si3N4 and SiO2, or Mo and Al. More generally, any pair of materials having an acoustic impedance ratio greater than 2 can be used. The bottom layer can be made of standard silicon, high-resistivity silicon, glass, or, more generally, any material having a coefficient of thermal expansion less than 6 ppm*K*. The stack can also include a trapping layer to improve the insulating properties.

[0058] The dielectric layer 13 in [Fig. 1], formed by a thin layer of SiO2 with a thickness of 500 nm, is located at the interface between the piezoelectric layer 11 and the base substrate 15. However, the thickness of the dielectric layer 13 may be less than or greater than 500 nm and, in particular, can vary between 10 nm and 6 microns.

[0059] As mentioned above, the elastic wave device 100 comprises the two electromechanical transducers (IDT) 3, 5 and the electrode array 4000 (electrodes 1000, 2000 and 3000) located between the two transducers 3 and 5. The electrode array 4000 (electrodes 1000, 2000 and 3000) is spaced from the first transducer 3 by a certain distance d;, and from the second transducer 5 by a certain distance d 2, as seen in [Fig.1]. The three electromechanical elements 3, 5 and 4000 are arranged in the (ZX) plane and oriented so that their electrodes 311, 313, 315, 331, 333, 335, 511, 513, 515, 531, 533, 535, 1001, 2001, 3001 in the form of parallel bands are perpendicular to the X axis of propagation of elastic waves.

[0060] Spaces 17 and 19 between the transducer 3 and the electrode array 4000, and between the transducer 5 and the electrode array 4000, have widths di and d2, respectively. These spaces form resonant cavities (spaces) in the X direction of elastic wave propagation. In other embodiments of the invention, the device 100 may include one or more resonant cavities, in particular, more than two. In the case of the configuration shown in [Fig. 1], two resonant cavities are present, with, in particular, the same distances d and d2 for the two spaces 17 and 19. Alternatively, the distances d and d2 may be different from each other.

[0061] In [Fig.1], the electrode array 4000 consists of three interdigitated electrodes 1000, 2000 and 3000. Each of the three electrodes 1000, 2000, 3000 has a straight end 1001, 2001, 3001.

[0062] However, the number of electrodes in the electrode array 4000 is not limited to three; in particular, it may be less than or greater than three; in particular, it may be equal to one. The electrode array 4000 and its electrodes 1000, 2000, and 3000 are made of an aluminum-based material such as pure aluminum or an aluminum alloy such as Cu-, Si-, or Ti-doped Ai. However, other materials may also be used, particularly those providing a high reflection coefficient for a relatively small electrode thickness. For example, materials such as copper, molybdenum, nickel, platinum, or gold may be used. The 4000 network and its 1000, 2000, 3000 electrodes can also include an adhesion layer made, for example, of titanium, tantalum, chromium, zirconium, palladium, iridium, tungsten, etc.More complex / multilayer metallic combinations can be considered to improve the transducer's conductivity or power handling capacity. This electrode and comb composition can also be applied to transducers 3 and 5.

[0063] The electrode array 4000 is also defined by the spacing p between two consecutive interdigitated electrodes, such as the distance between electrodes 1001 and 2001. In particular, this spacing p can be defined by the Bragg condition, which states that p = Ml, with A being the wavelength of the elastic operating waves of the device. It is also possible to create resonant cavities by varying the distance between two consecutive interdigitated electrodes, which may, in particular, not be the same everywhere within the same structure comprising several electrodes, or even, for example, two interdigitated combs. The electrodes are also defined by the length l of their straight ends, as well as by their widths, denoted a in [Fig. 1]. In particular, the values ​​of a, l, and α can be modified to obtain a desired electromechanical coupling coefficient.

[0064] In the embodiment of the invention shown in [Fig. 1], the electrodes 1000, 2000, and 3000 of the electrode array 4000 are each connected to an individual predetermined electrical potential, here the predetermined electrical potentials 1005, 2005, and 3005, respectively. The potentials 1005, 2005, and 3005 may be the same, in particular the same electrical potential; in particular, this reference potential may be ground. Alternatively, the potentials 1005, 2005, and 3005 may be different. The electrodes 1000, 2000, 3000 of the electrode array 4000 are each respectively connected to a variable impedance 1003, 2003, 3003. In alternative embodiments of the invention, it is possible that one or more of the electrodes 1000, 2000, 3000 are not connected to a variable impedance.In particular, it is possible, and sufficient to obtain the desired frequency agility, for a single electrode to be connected to a variable impedance, and it is this agility that makes it possible to compensate for temperature variations so that the elastic wave device can adjust to its (optimal) operating frequency even under the influence of temperature variations.

[0065] According to the invention, the elastic wave device 100 further comprises control means 1007, 207, 3007 connected respectively to the variable impedances 1003, 2003, 3003, and enabling the values ​​of the variable impedances 1003, 2003, 3003 to be controlled and modified, in particular remotely, during operation or not, of the elastic wave device 100. The impedance can, for example, be a variable capacitance diode which can be controlled by the voltage applied across the terminals of the variable capacitance diode by a variable voltage generator.

[0066] In one embodiment of the invention, the electrodes 1000, 2000, 3000 of the network 4000 can each be connected to a second variable impedance which can be modified by their respective control means 1007, 2007, 3007.

[0067] In the proposed embodiment of the invention shown in [Fig. 1], the transducers 3 and 5 each comprise two interdigitated electrode combs, 31 and 33 for transducer 3, and 51 and 53 for transducer 5. Each of these four combs consists of three interconnected electrodes, 311, 313, 315, 331, 333 and 335 for transducer 3, and 511, 513, 515, 531, 533 and 535 for transducer 5. However, the number of electrodes in each of the combs is not limited to three; in particular, it can be less or more, while not being the same in the two combs 31 and 33, respectively 51 and 55.

[0068] For each of the two transducers 3 and 5, only one of the two combs, in this case comb 33 for transducer 3 and comb 53 for transducer 5, is connected to a predetermined electrical potential, respectively 301 and 501. Comb 31 is connected to an input load 303 and comb 51 to an output load 503.

[0069] In this embodiment of the invention, the pitch between two consecutive interdigitated electrodes p, the width a and the length l of the electrodes are identical in both transducers 3 and 5 as well as in the electrode array 4000. However, in alternative embodiments of the invention, these parameters may be different; in particular, they may be the same in both transducers 3 and 5 but different in the electrode array 4000.

[0070] By varying the value of at least one of the variable impedances 1003, 2003, 3003, it is possible to modify the reflection conditions of the electrode array 4000 and thus tune the operating frequency of the device 100. In particular, the variable impedances 1003, 2003, 3003 may include a capacitance and / or an inductance.

[0071] However, in alternative embodiments of the invention, it is also possible that two electrodes, for example 1000 and 2000, are connected to the same variable impedance.

[0072] By connecting the electrodes 1000, 2000, 3000 to their respective variable impedances 1003, 2003, 3003, it becomes possible, particularly via the control means 1007, 2007, 3007 to which the variable impedances 1003, 2003, 3003 are connected, to modify and vary, especially during the operation of the device 100, the impedance loads of the variable impedances and consequently the electrical conditions of the electrode array 4000. This makes it possible to modify the operating bandwidth of the electromechanical device 100, even after its design and manufacture. According to the invention, the device 100 is therefore frequency-agile.

[0073] The frequency agility of the elastic wave device 100 can, in particular, depend on the number of electrodes constituting the electrode array 4000. In particular, by increasing the number of interdigitated electrodes in the array 4000, it is possible to increase the frequency agility of the elastic wave device 100. In other words, the frequency range in which device 100 can have its operating frequency.

[0074] Alternatively, the variable impedances 1003, 2003, 3003 can be achieved by a simple switch, allowing the transition from a short circuit (SC) to an open circuit (OC).

[0075] Alternatively, the second transducer 5 can be short-circuited. In this way, the device becomes a single-port resonator whose resonant frequency is determined by the reflection conditions of the short-circuited transducer 5 and the electrode array 4000.

[0076] In particular, according to one embodiment of the invention, the second transducer 5 can be replaced by an array of electrodes configured to reflect elastic waves; in particular, it can be a Bragg mirror. The resulting elastic wave device then has only one port, the transducer 3, which is then both the input and output port.

[0077] Alternatively, the device 100 can be placed between two mirrors to further confine the energy in the region of the transducers and the central cavity.

[0078] In a second embodiment of the invention, illustrated in [Fig.2], the device 200 differs from the device 100 illustrated in [Fig.1] in that the electrode array 4000 comprises a single electrode 1000.

[0079] In a third embodiment of the invention, illustrated in [Fig.3], the elastic wave device 300 differs from that illustrated in [Fig.1], 100, in that the electrode array 4000 is replaced by an electrode array 7 consisting of two interdigitated electrode combs 71 and 73.

[0080] In [Fig.3], the electrode array 7 is formed by two interdigitated electrode combs 71 and 73. Each of the two electrode combs 71 and 73 is composed of three straight electrodes, 711, 713 and 715 for comb 71, and 731, 733 and 735 for comb 73, each connected to the other in the same comb.

[0081] However, the number of electrodes in each of the combs 71 and 73 is not limited to three; in particular, it may be lower or higher, and may not be the same in the two combs 71 and 73. The combs 71 and 73, and their respective electrodes 711, 713, 715, 731, 733, and 735, are made of an aluminum-based material such as pure aluminum or an aluminum alloy such as Cu-, Si-, or Ti-doped Ai. However, other materials may also be used, particularly those that provide a high reflection coefficient for a relatively small electrode thickness. For example, materials such as copper, molybdenum, nickel, platinum, or gold may be used. The combs 71 and 73 and their respective electrodes 711, 713, 715, 731, 733 and 735 may also include an adhesion layer made of titanium, tantalum, chromium, zirconium, palladium, iridium, Tungsten, etc. More complex / multilayer metal combinations can be considered to improve transducer conductivity or power handling capacity. This electrode and comb composition also applies to transducers 3 and 5.

[0082] The interdigitated electrode combs 71 and 73 are also defined by the spacing p between two consecutive interdigitated electrodes, each originating from one of the two combs 71 and 73, as the distance separating electrodes 71 and 73. In particular, this spacing p can be defined by the Bragg condition, which states that p = X / 2, where X is the wavelength of the elastic operating waves of the device. It is also possible to create resonant cavities by varying the distance between two consecutive interdigitated electrodes, which may, in particular, not be the same everywhere within the same structure comprising two interdigitated combs. The electrode combs are also defined by the length 1 of their electrodes and the width a of their electrodes. In particular, the values ​​of a, 1, and p can be modified to obtain a desired coupling coefficient.

[0083] In [Fig.3], the combs 71 and 73 are configured so that the electrode array 7 reflects at least partially the elastic waves, in a so-called mirror coupler (MC) configuration, thus modifying the transmitted and reflected ground phases.

[0084] In an alternative embodiment, these same combs can also be configured to primarily modify the phase of the transmitted elastic waves, without wave reflection as their main objective. They are then said to be in an air-gap coupler (AGC) configuration. In the embodiment of the invention shown in [Fig. 3], the electrode array 711, 713, and 715 of the comb 71 is connected to a predetermined electrical potential, in this case ground 701. The electrode array 731, 733, and 735 forming the comb 73 is connected to a variable impedance 703, which in turn is connected to a predetermined electrical potential, in this case ground 705.

[0085] According to the invention, the elastic wave device 300 further includes a control means 707 which is connected to the variable impedance 703 and allows the value of the variable impedance 703 to be controlled and modified, in particular remotely, during the operation, or not, of the elastic wave device 300.

[0086] In one embodiment of the invention, the electrode array 711, 713 and 715 of the comb 71 can be connected to a second variable impedance which can be modified by a control means 707.

[0087] In the proposed embodiment of the invention shown in [Fig. 3], the transducers 3 and 5 both comprise two interdigitated electrode combs, 31 and 33 for transducer 3, and 51 and 53 for transducer 5. As for combs 71 and 73, each of these four combs consists of three interconnected electrodes, 311, 313, 315, 331, 333 and 335 for transducer 3, and 511, 513, 515, 531, 533 and 535 for transducer 5. However, the number of electrodes in each of the combs is not limited to three; in particular, it can be less or more, while not being the same in the two combs 31 and 33, respectively 51 and 55.

[0088] For each of the two transducers 3 and 5, only one of the two combs, in this case comb 33 for transducer 3 and comb 53 for transducer 5, is connected to a predetermined electrical potential, respectively 301 and 501. Comb 31 is connected to an input load 303 and comb 51 to an output load 503.

[0089] In this embodiment of the invention, the pitch between two consecutive interdigitated electrodes p, the width a and the length l of the electrodes are identical in the two transducers 3 and 5 as well as in the electrode array 7. However, in alternative embodiments of the invention, these parameters may be different, in particular, they may be the same in the two transducers 3 and 5 but different in the electrode array 7.

[0090] By varying the value of the variable impedance 703, it is possible to modify the reflection conditions of the electrode array 7 and thus tune the operating frequency of the device 300. In particular, the variable impedance 703 may include or be made up of a capacitance and / or an inductance.

[0091] However, in alternative embodiments of the invention, it is possible that only some of the electrodes on the comb 73 are connected to the variable impedance 703, or that each or a subset of the electrodes are connected to a separate variable impedance. It is also possible that both combs 73 and 71 have electrodes connected to variable impedances.

[0092] By connecting the electrode comb 73 to the variable impedance 703, it becomes possible, particularly by means of the control means 707 to which the variable impedance 703 is connected, to modify and vary, especially during the operation of the device 100, the impedance load of the variable impedance and consequently the electrical conditions of the electrode array 7. This makes it possible to modify the operating bandwidth of the elastic wave device 300, even after its design and manufacture. According to the invention, the device is therefore frequency-agile.

[0093] The frequency agility of the elastic wave device 300 can depend in particular on the number of electrodes constituting the two combs 71 and 73 of the electrode array 7. In particular, by increasing the number of interdigitated electrode pairs in the combs 71 and 73, it is possible to increase the frequency agility of the elastic wave device 300, in other words, the frequency range in which the device 300 can have its operating frequency.

[0094] Alternatively, the variable impedance 703 can be implemented by a simple switch, allowing the circuit to be switched from short circuit (SC) to open circuit (OC).

[0095] Alternatively, the second transducer 5 can be short-circuited. In this way, the device becomes a single-port resonator whose resonant frequency is determined by the reflection conditions of the short-circuited transducer 5 and the electrode array 7.

[0096] Alternatively, the device 300 can be placed between two mirrors to further confine the energy.

[0097] In an embodiment of the invention based on the device 300, illustrated in [Fig.3], the variable impedance 703 of the elastic wave device 300 comprises a variable capacitance.

[0098] By varying the capacitive charge of the variable capacitor, it is possible to continuously vary the operating bandwidth of the device 300 from a high frequency to a low frequency. The high frequency corresponds to a situation where the electrode comb 73, to which the variable impedance is connected, is in, or at least approaches, an open-circuit (OC) configuration. The low frequency corresponds to a situation where the electrode comb 73, to which the variable impedance is connected, is in, or at least close to, a short-circuit (SC) configuration.

[0099] [Fig.4] shows simulated bandwidths using the numerical method described in S. Ballandras et al. “Finite element analysis of periodic piezoelectric transducers (analyse par éléments finis de transducteurs piezoélectriques périodiques)”, Journal of Applied Physics, 93, 702 (2003) to determine the characteristics of a mode propagating on a POI type composite substrate consisting of a 600 nm thick layer of LiTaO3 with an orientation (EV / ) / 42° on a 500 nm thick layer of silicon oxide, a 1 pm thick layer of polysilicon, all on a silicon (100) substrate with a misorientation of 45° between the Z' and Z axes of lithium tantalate and silicon, respectively, these characteristics being then used in a mixed matrix model to simulate the filter response. These bandwidths correspond to those of an elastic wave device as described in [Fig.3], where the variable impedance 703 includes a variable capacitor.

[0100] In this simulation, the simulated device is similar to that shown in [Fig.3], except that transducers 3 and 5 each have 45 pairs of interdigitated fingers in the simulation, and the electrode array 7 has five pairs of interdigitated fingers.

[0101] The step size p in the two simulated transducers 3 and 5 is p = 1.202 in the simulated electrode array 7, it is p = 1.13 The ratio a / p is equal to 0.5.

[0102] On the y-axis, the magnitude, in decibels, of the transfer function of the device as described above is plotted as a function of the crossover frequency, which is plotted in MHz on the x-axis. The various curves shown in [Fig. 4] correspond to the transfer function of the device for the different values ​​of variable capacitance considered in each simulation; in particular, the values ​​are 0.001 pF, 0.1 pF, 0.3 pF, 0.6 pF, 1.0 pF, 2.0 pF, and 10.0 pF, and are represented respectively by curves 4b, 4c, 4d, 4e, 4f, 4g, and 4h in [Fig. 4]. The open circuit CO (curve 4a) and the short circuit SC (curve 4i) are also shown.

[0103] [Fig.4] shows the frequency agility of the device as described above, of which The variable impedance 703 includes a variable capacitor. This device is similar to that shown in [Fig. 3]. By changing the value of the variable capacitor, and therefore the value of the variable impedance, the bandwidth is changed; in particular, its center position varies from 1675 MHz for the open circuit (OC), or from 0.001 pF to 1625 MHz for the short circuit.

[0104] For the lowest value of the variable capacitance of 0.001 pF illustrated by curve 4b, the operating bandwidth of device 100 is close to the bandwidth corresponding to that obtained if the circuit including the variable impedance 703 were open, represented by curve 4a in [Fig. 4]. This situation thus defines the position of the high operating frequency of device 300, corresponding to the OC configuration.

[0105] For a high value of variable capacitance, for example 10.0 pF, represented by curve 4h, the operating bandwidth of device 100 is close to the bandwidth corresponding to that obtained if the circuit including the variable impedance 703 were short-circuited, represented by curve 4i in [Fig. 4]. This situation thus defines the position of the low operating frequency of device 300, corresponding to the DC configuration.

[0106] In this embodiment of the invention, a variable impedance 703 comprising a variable capacitance allows, by increasing the value of the variable capacitance, to continuously shift the operating bandwidth position of the device 300 from the high frequency of the OC configuration, curve 4a, to the low frequency of the SC configuration, curve 4i on the [Fig.4].

[0107] In an embodiment of the invention based on the device 300, illustrated in [Fig.3], the variable impedance 703 of the elastic wave device 300 includes an inductance that can be modified.

[0108] [Fig.5] shows the simulated bandwidths using the numerical method described in S. Ballandras et al., “Finite element analysis of periodic piezoelectric transducers (Finite element analysis of periodic piezoelectric transducers)", Journal of Applied Physics, 93, 702 (2003) with the same parameters as those used for [Fig. 4], except for the use of a variable inductor instead of a capacitor. These bandwidths correspond to those of an elastic wave device 300 as described in [Fig. 3], where the variable impedance 703 includes a variable inductor.

[0109] On the ordinate, the magnitude, in decibels, of the transfer function of the device as described above is plotted as a function of the crossover frequency, which is plotted in MHz on the abscissa. The various curves shown in [Fig. 5] correspond to the different values ​​of variable inductance considered each time in the simulation, in particular the values ​​here are 1.0 nH, 10.0 nH, 50.0 nH and 500.0 nH and are represented respectively by curves 5e, 5d, 5c, 5b and 5a in [Fig. 5].

[0110] [Fig.5] represents the frequency agility of device 300 as described in [Fig.3], whose variable impedance 703 includes a variable inductance.

[0111] By changing the value of the variable inductance, and therefore the value of the variable impedance, the bandwidth is modified, in particular its position changes. For a low value of variable inductance, for example 1.0 nH, illustrated by curve 5e, the operating bandwidth of the device 300 is close to that of the low frequency, around 1625 MHz, corresponding to the DC configuration, represented by curve 5f in [Fig. 5] (and 4i in [Fig. 4]). As the value of the variable inductance increases, for example from 1.0 nH to 10.0 nH, i.e. from curve 5e to curve 5d, the position of the operating bandwidth of the device 300 moves away from that of the low frequency, curve 5f, through frequencies below the low frequency. For a high value of inductance that can be changed, for example 500.0 nH, illustrated by curve 5b on the [Fig.[5], the operating bandwidth of the 300 device approaches that of the high frequency, around 1675 MHz, corresponding to the OC configuration, represented by curve 5a (or 4a on [Fig.4]) and this, by passing through frequencies higher than the high frequency.

[0112] In this embodiment of the invention, as shown in [Fig. 5], it is not possible to reach the frequencies between the low and high frequencies. In this embodiment, the bandwidth of the device 300 approaches the bandwidth corresponding to the SC configuration via frequencies lower than the low frequency. Conversely, in this embodiment, the bandwidth of the device 300 approaches the bandwidth corresponding to the OC configuration by passing through frequencies higher than the high frequency.

[0113] Thus, a variable impedance 703 comprising a variable inductance allows, by increasing the value of the inductance that can be modified, the operating bandwidth position of the device 300 to be shifted from the low frequency of the SC configuration, corresponding to curve 5f on [Fig.5], at the high frequency of the OC configuration, represented by curve 5a, without however being able to reach the frequencies between the low frequency and the high frequency.

[0114] [Fig.6] represents an elastic wave device 400 according to a sixth mode of embodiment of the invention. Compared to device 100 of the first embodiment, device 400 differs in that the electrode array 4000 is replaced by an electrode array 7 consisting of two interdigitated electrode combs 71 and 73, and in that two additional electrode arrays 4 and 6 are present between the transducers 3 and 5, more precisely between the electrode array 7 and the transducer 5. The electrode array 7 is in a GC configuration. The electrode array 6, in an MC configuration, is located between the two electrode arrays 7 and 4, which are in a GC configuration.

[0115] Like the electrode array 7, the electrode array 4 is formed by two interdigitated electrode combs 41 and 43. Each of the two electrode combs 41 and 43 is formed by three straight electrodes, 411, 413, and 415 for comb 41, and 431, 433, and 435 for comb 43, in each case interconnected within the same comb. However, in alternative embodiments, the number of electrodes in each of the combs 41 and 43 may be less than or greater than three. Preferably, the two electrode arrays 4 and 7 have the same parameters regarding the number of fingers, the width a, the pitch p, and the thickness h of the electrodes.

[0116] The electromechanical devices 3 and 7 are separated by the distance d;, 7 and 6 by the distance d2, 6 and 4 by the distance d3, 4 and 5 by the distance d4.

[0117] The electromechanical devices 3, 7, 6, 4 and 5 are separated by distances which may be different. In an advantageous embodiment of the invention, shown in [Fig. 6], these distances may be the same.

[0118] In the embodiment of the invention shown in [Fig. 6], the electrode array 411, 413, and 415 of the comb 41 is connected to a predetermined electrical potential, in this case ground 401. The electrode array 431, 433, and 435 forming the comb 43, meanwhile, is connected to a variable impedance 403, which in turn is connected to a predetermined electrical potential, in this case ground 405. The device 600 also includes a control means 407 that is connected to the variable impedance 403 and allows the value of the variable impedance to be controlled and modified remotely or not during the operation of the elastic wave device 400.

[0119] However, according to other embodiments of the fourth embodiment of the invention, it is possible that only some of the electrodes of the comb 43 are connected to the variable impedance 403, or that each or a subset of the electrodes are connected to a separate variable impedance. It is also possible that the two combs 43 and 41 have electrodes connected to variable impedances.

[0120] In this embodiment of the invention, the electrode array 6 is a Bragg mirror comprising 16 electrodes, grouped under reference numerals 61 in [Fig. 6]. These 16 electrodes are all interconnected by two base electrodes 62 and 63. The electrode array 6 is not connected to any electrical potential, so the connection is said to be floating, and the 16 electrodes 61 are at isopotential. The mirror may have more or fewer electrodes.

[0121] In particular, the addition of the two electrode arrays 4 and 6 widens the operating bandwidth of the device 400 compared, for example, to the first embodiment of the device shown in [Fig.3].

[0122] In an embodiment of the invention based on the device 400, shown in [Fig.6], the variable impedance 703 of the device 400 comprises a modifiable inductance and a variable capacitance.

[0123] 7] shows the simulated bandwidths using the numerical method described in S. Ballandras et al., “Finite element analysis of periodic piezoelectric transducers,” Journal of Applied Physics, 93, 702 (2003) with the same parameters used for Figures 4 and 5 concerning the piezoelectric substrate 9 and transducers 3 and 5. The step size p in the simulated transducers 3 and 5 and the electrode array 6 is p = 1.202 pm, and in the simulated electrode arrays 4 and 7, it is p = 1.13 pm. The ratio a / p is equal to 0.5.

[0124] In this numerical simulation, transducers 3 and 5 each have 45 pairs of interdigitated fingers, and electrode arrays 4 and 7 have three pairs of interdigitated fingers. Electrode array 6 has 16 isopotential fingers.

[0125] In [Fig. 7], only the value of the variable capacitance of the electrode array 7 was changed, specifically by the values ​​0.001 pF, 0.1 pF, 0.3 pF, 0.6 pF, 1.0 pF, 2.0 pF, and 10.0 pF, which are represented in [Fig. 7] by curves 7b, 7c, 7d, 7e, 7f, 7g, and 7h, respectively. The fixed inductance was 1 nH for both electrode arrays 4 and 7, and the fixed capacitance of electrode array 4 was 1 pF.

[0126] On the ordinate, the magnitude, in decibels, of the transfer function of the device as described above is plotted as a function of the crossover frequency, which is plotted in MHz on the abscissa. The different curves shown in [Fig. 7] correspond to the different values ​​of the variable capacitance considered each time in the simulation, in particular the values ​​here are 0.001 pF, 0.1 pF, 0.3 pF, 0.6 pF, 1.0 pF, 2.0 pF and 10.0 pF, which are respectively represented on [Fig. 7] by curves 7b, 7c, 7d, 7e, 7f, 7g and 7h.

[0127] [Fig. 7] highlights the frequency agility of the device 400 as described in [Fig. 6], whose variable impedances 703 and 403 include a variable capacitance and a variable inductance. By changing the value of the variable capacitor, and therefore the values ​​of the variable impedances 703 and 403, the bandwidth is modified, in particular its center frequency. For a small value of the variable capacitor, for example 0.001 pF, corresponding to curve 7b, the operating bandwidth of device 400 is close to the bandwidth obtained if the circuit including the variable impedance 703 were open, as illustrated by curve 7a in [Fig. 7]. As the value of the variable capacitor increases, for example from 0.001 pF to 0.1 pF, i.e., from curve 7b to curve 7c, the position of the operating bandwidth of device 400 moves away from that of the high frequency, curve 7a, and closer to that of the low frequency, curve 7i.For a high value of the variable capacitance, for example 10.0 pF, represented by curve 7h, the operating bandwidth of the 400 device is close to the bandwidth corresponding to that of the SC configuration, curve 7i.

[0128] Thus, the variable impedances 703 and 403 comprising a variable capacitance and a variable inductance allow, by increasing the value of the variable capacitance, to shift the operating bandwidth position of the device 400 from the high frequency of about 1643 MHz of the OC configuration, corresponding to curve 7a, to the low frequency of about 1607 MHz of the SC configuration, corresponding to curve 7i.

[0129] Fig. 8 is similar to Fig. 7 except that, unlike Fig. 7, only the value of the variable inductance of the electrode array 7 is modified, while the value of the variable capacitance included in the variable impedance 703 of the simulated device 400 is the same in the simulations carried out to edit the curves of Fig. 8. In particular, the inductance values ​​in the simulations of Fig. 8 are 1.0 nH, 10.0 nH, 50.0 nH, 75.0 nH, 100.0 nH and 300 nH, and correspond respectively to curves 8g, 8f, 8e, 8d, 8c and 8b on Fig. 8. The fixed inductance of electrode array 4 was 1 nH, and the fixed capacitance of electrode arrays 4 and 7 was 1 pF.

[0130] Figure 8 shows that when the variable impedances 703 and 403 of device 400 include a variable capacitor and a variable inductor, the operating bandwidth can reach both values ​​between the low frequency around 1607 MHz of the SC configuration, curve 8h in Figure 8 and 7i in Figure 7, and the high frequency around 1643 MHz of the OC configuration, curve 8a in Figure 8 and 7a in Figure 7, in particular, through a variation in the value of the variable capacitor as seen in Figure 7. It can also reach values ​​lower than the low frequency, curve 8h in Figure 8 and 7i in Figure 7, and values ​​higher than the high frequency, curve 8a in Figure 8 and 7a in Figure 7. [Fig.7], in particular, through a variation in the value of the inductance which can be modified.

[0131] For example, [Fig. 8] shows that the variable impedances 703 and 403, comprising a variable capacitance and a variable inductance, allow the device 400 to exhibit greater frequency agility than if the variable impedances 703 and 403 comprised only a variable capacitance or only a variable inductance. This also provides a wider bandwidth than in the cases of Figures 4 and 5.

[0132] [Fig.9] represents an elastic wave device 500 according to a fifth embodiment of the invention with three electrode arrays 4a, 6a and 7a. Compared to the fourth embodiment, the electrode arrays 4a and 7a of the device 500 are in a non-variable GC configuration, and the array 6a located between the two electrode arrays 7a and 4a is in a variable MC configuration.

[0133] In this embodiment of the invention, networks 4a and 7a, unlike networks 4 and 7 of device 400 shown in [Fig. 6], do not exhibit variable impedances. Networks 4a and 7a each comprise three parallel electrodes, respectively grouped under reference numerals 421 and 721. In alternative embodiments, however, it is possible to have more or fewer than three parallel strip electrodes in networks 4a and 7a. The parallel electrode strips 421 and 721 are, for each network, connected by two base electrodes, 42 and 44 for network 4a, and 72 and 74 for network 7a. Networks 4a and 7a are therefore at a floating potential, but must always be considered as being at equal potential.

[0134] In this embodiment of the invention, the network 6a of the device 500 has four electrode combs 611, 613, 615 and 617, with, in particular, combs 611, 613 and 615 interdigitated with comb 617. The three combs 611, 613 and 615 each have a respective variable impedance 601, 603 and 605, each connected to a respective separate control means 602, 604 and 606, as well as to a respective separate determined electrical potential 691, 693 and 695. Alternatively, a single control means can modify the impedances 691, 693 and 695 separately or collectively.

[0135] The comb 617 is at a floating potential, although it forms an isopotential system. The comb 617 has six electrodes 641, 642, 643, 644, 645 and 646 interdigitated with the comb 611 for electrodes 641 and 642, with the comb 613 for electrodes 643 and 644 and with the comb 615 for electrodes 645 and 646.

[0136] The comb 617 also includes two subgroups of isopotential electrodes 631, 633, that is connected to each other by the common base electrode 699 and, respectively, by the base electrodes 681 and 683, as schematically shown in [Fig. 9]. Subgroups 631 and 633 each have four interconnected parallel strip electrodes.

[0137] The combs 611, 613 and 615 each have two parallel band electrodes, respectively 671 and 673, 661 and 663 and 675 and 677. However, in alternative embodiments, the combs 611, 613 and 615 may have more or fewer parallel band electrodes, in particular the combs 611, 613 and 615 may be reduced to a single straight band electrode.

[0138] Impedances 601, 603 and 605 can be capacitive and / or inductive.

[0139] Electromechanical devices 3 and 7a are separated by a distance d; 5, 7a, and 6a by a distance d; 6, 6a, and 4a by a distance d; 7, 4a, and 5 by a distance d; 8. Electromechanical devices 3, 7a, 6a, 4a, and 5 are separated by distances that may be different. In an advantageous embodiment of the invention, as shown in [Fig. 9], these distances may be the same.

[0140] This embodiment of the invention makes it possible to obtain frequency agility with a change in the maximum value of the elastic reflection coefficient of the space between the two transducers that remains small compared to the change in the operating frequency of the device. For example, when switching from an SC-OC-SC configuration to an OC-SC-OC configuration, the maximum value of the reflection coefficient remains practically constant.

[0141] [Fig. 10] represents a 600 elastic wave device according to a sixth mode of embodiment of the invention. Compared to the embodiment of [Fig. 6] with three electrode arrays 4, 6 and 7, this embodiment includes two additional electrode arrays 8 and 10 between the transducers 3 and 5. There are therefore five electrode arrays between the transducers 3 and 5, two electrode arrays 6 and 8 are in MC configuration, while the other three arrays 4, 7 and 10 are in GC configuration.

[0142] The arrays are arranged as shown in [Fig.10], with the electrode array 6 sandwiched between the electrode arrays 7 and 4, and the electrode array 8 sandwiched between the electrode arrays 4 and 10.

[0143] In this embodiment of the invention, the electrode arrays 6 and 8 are identical and comprise 16-electrode Bragg mirrors, respectively grouped under reference numerals 61 and 81 in [Fig. 10]. These groups of 16 electrodes are, for each of the Bragg mirrors 6 and 8, all connected to each other by means of two base electrodes, 62 and 63 respectively for array 6, and 82 and 83 for array 8. The electrode arrays 6 and 8 are not connected to any electrical potential, so their connection is said to be floating, and the 16 electrodes, 61 and 81, are at the same potential. The mirrors may comprise more or fewer electrodes. In an alternative configuration, the mirrors 6 and 8 may have different numbers of electrodes.

[0144] Like electrode arrays 4 and 7, which have the same structures and properties as those shown in [Fig. 6], electrode array 10 consists of two interdigitated electrode combs 101 and 103. Each of the two electrode combs 101 and 103 is formed of three straight electrodes, 111, 113, and 115 for comb 101, and 131, 133, and 135 for comb 103, each connected to the other within the same comb. However, in alternative embodiments, the number of electrodes in each of the combs of electrode arrays 4, 7, and 10 may be less than or greater than three, and the number of electrodes may differ between electrode arrays 4, 7, and 10.

[0145] In the embodiment of the invention shown in [Fig. 10], the electrode array 111, 113 and 115 of the comb 101 is connected to a predetermined electrical potential, in this case ground 999. The electrode array 131, 133 and 135 forming the comb 103 is connected to a variable impedance 903, which in turn is connected to a predetermined electrical potential, in this case ground 905.

[0146] The elastic wave device 600 further includes a control means 907 which is connected to the variable impedance 903 and allows the value of the variable impedance to be controlled and changed, in particular remotely, during the operation, or not, of the device 600.

[0147] Thanks to the control means 407, 707 and 907, the variable impedances 403, 703 and 903 can be controlled individually or jointly.

[0148] The electromechanical devices 3 and 7 are separated by the distance dg, 7 and 6 by the distance d10, 6 and 4 by the distance dn, 4 and 8 by the distance dn, 8 and 10 by the distance d13, and 10 and 5 by the distance dJ4. The electromechanical devices 3, 7, 6, 4, 8, 10, and 5 are separated by distances that may be different. In an advantageous embodiment of the invention, as shown in [Fig. 10], these distances may be the same.

[0149] In alternative embodiments, the number of resonant cavities can be further increased by increasing the number of times the GC-MC-GC electrode array pattern is repeated. For example, in [Fig. 6], this GC-MC-GC pattern is repeated only once. In [Fig. 10], the device 600 presents the GC-MC-GC-MC-GC pattern, and thus repeats the GC-MC-GC pattern twice. This improves, in particular, the properties and characteristics of the operating bandwidth, such as, for example, a wider plateau and a reduced frequency width of the transition between the device bandwidth and the frequency rejection band, compared to the embodiment shown in [Fig. 6].

[0150] In a further embodiment, an elastic wave device may be made, which includes three transducers instead of two. This device includes at least one electrode array as described for the embodiments of [Fig. 1], [Fig. 2], [Fig. 3], [Fig. 6], [Fig. 9] or [Fig. 10], and featuring a variable impedance arranged between the first and second transducers, and between the second and third transducers. The result is a dual-mode SAW filter that is frequency-agile.

[0151] In all the variant embodiments of the invention presented herein and in all other possible variants, the second electromechanical device 5 may be a transducer, or an electrode array configured to reflect at least partially the waves emitted by the first electromechanical device 3; in particular, it may be a Bragg mirror. Similarly, the predetermined electrical potentials to which the electrode arrays 4000, 7, 4, 6a, 10, or any other electrode array between the electromechanical elements 3 and 5 present in variant configurations of the invention are connected, may be the same reference potential, in particular ground, or different from one another.

Claims

Demands

1. Elastic wave device (10000), comprising: a variable impedance means (1003, 2003, 3003, 10400); a first electromechanical device (3, 11130), in particular a first transducer (3, 11130), and a second electromechanical device (5, 11140), in particular a second transducer (5, 11140), or an electrode array configured to reflect at least partially elastic waves emitted by the first electromechanical device (3, 11130), an array (4000, 11150) of at least one electrode (1000, 2000, 3000) located between the first electromechanical device (3, 11130) and the second electromechanical device (5, 11140) in the direction of propagation of the elastic waves, wherein at least one electrode of the array (4000, 11150) of at least one electrode (1000, 2000, 3000) is connected to a predetermined electrical potential (1005, 2005, 3005) via the variable impedance means (1003, 2003, 3003, 10400);a temperature determination means (10200) configured to determine a temperature of an operating region of the elastic wave device (10000); and a control means (1007, 2007, 3007, 10300) configured to control the variable impedance means (703, 1003, 2003, 3003, 10400) based on the temperature determined by the temperature determination means (10200).

2. Elastic wave device (10000) according to claim 1, wherein each of the variable impedance means (1003, 2003, 3003, 10400) comprises a voltage-controlled capacitor (703, 11300); and the control means (1007, 2007, 3007, 10300) are configured to control the variable impedance means (703, 1003, 2003, 3003, 10400) by supplying a voltage determined on the basis of the temperature determined by the temperature determination means (10200).

3. Elastic wave device (10000) according to claim 1 or 2, wherein the temperature determination means (10300) is configured to determine an electrical resistance of the operating region of the elastic wave device (10000) and to determine the temperature on the basis of the determined electrical resistance.

4. Elastic wave device (10000) according to claim 1 or 2, wherein the temperature determination means (10300) comprises or is a surface acoustic wave resonator.

5. Elastic wave device (10000) according to any one of claims 1 to 4, wherein the control means (707) is configured to open or close an electrical connection of at least one electrode (4000, 7) of the array (4000) of at least one electrode (1000, 2000, 3000) with a predetermined electrical potential (705), in particular ground.

6. Elastic wave device (10000) according to any one of claims 1 to 5, wherein the array (4000) of at least one electrode (1000, 2000, 3000) is configured to change a phase of the elastic waves and / or to reflect at least partially the elastic waves.

7. Elastic wave device (10000) according to any one of claims 1 to 6, wherein the array of at least one electrode (4000, 7) comprises multiple electrodes, in particular in the form of a strip, parallel (711, 713, 715, 731, 733, 735), wherein at least some of the multiple electrodes (711, 713, 715, 731, 733, 735) are connected to the same variable impedance means (703, 1003, 2003, 3003, 10400).

8. Elastic wave device (10000) according to claim 7, wherein the electrodes of a first electrode subset (731, 733, 735) of the array of at least one electrode (4000, 7) are connected by means of variable impedance (703).

9. Elastic wave device (10000) according to claim 7 or 8, wherein the electrodes of a second electrode subset of the array of at least one electrode (4000, 7) are connected to each other to others and to a floating electrical potential or connected to a predetermined electrical potential, in particular ground.

10. Elastic wave device (10000) according to claim 9, wherein the first and second subassemblies are arranged such that the electrodes of the first subassembly and the electrodes of the second subassembly are interdigitated with respect to each other.

11. Elastic wave device (10000) according to any one of claims 1 to 10, comprising a plurality of electrode arrays between the first electromechanical device (3, 11130) and the second electromechanical device (5, 11140), the arrays being separated from each other by free and / or metallized propagation gaps and in which, in particular, the distances between two respective adjacent electrode arrays of the plurality of electrode arrays are the same.

12. Elastic wave device (10000) according to any one of claims 1 to 11, further comprising a first reflection structure (11110) and a second reflection structure (11120), and wherein the first electromechanical device (3, 11130) is positioned between the first reflection structure (11110) and the array (4000) of at least one electrode (1000, 2000, 3000), and the second electromechanical device (5, 11140) is positioned between the second reflection structure (11120) and the array (4000) of at least one electrode (1000, 2000, 3000).

13. Elastic wave device (10000) according to any one of claims 1 to 12, wherein the first electromechanical device (3, 11130) and the second electromechanical device (5, 11140) are arranged above or in a piezoelectric substrate (9), in particular a composite substrate comprising a base substrate (15) and a piezoelectric layer (11), wherein the thickness of the piezoelectric layer is less than or equal to 1.5 x X, where X is the wavelength of the fundamental mode of elastic surface waves emitted by the first electromechanical device (3, 11130).

14. Elastic wave device (10000) according to claim 13, further comprising a dielectric layer (13) and / or a trapping layer and / or a Bragg mirror positioned between the base substrate (15) and the piezoelectric layer (11).

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