Elastic wave device with frequency self-adjustment

Abstract

The invention relates to an elastic wave device 10000 that comprises one or more variable impedance means 1003, 2003, 3003, 10400, wherein each variable impedance means 1003, 2003, 3003, 10400 comprises a capacitor configured to change capacity depending on temperature variation to compensate for a frequency shift of an operating frequency of the elastic wave device caused by the temperature variation; 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; and 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.

Description

[0001] Elastic wave device with frequency self-adjustment

[0002] [1] The invention concerns an elastic wave device in the field of telecommunication components based on elastic waves, in particular surface acoustic waves (SAW).

[0003] [2] Devices using elastic surface waves have recently seen a marked increase in use, for a variety of applications such as filtering, signal manipulation and processing, and sensing. An exemplary device comprising two transducers and an electrode array is described in EP 3 599 720 A1.

[0004] [3] In the context of telecommunications, numerous radio frequency (RF) bands are used to receive and transmit information. Each RF band defines a channel to which it is necessary to apply filtering operations in order to process, manipulate or store information. In this context, the industry requires filters with as many natural frequencies as there are RF bands to process. What is more, they need to be able to switch from one RF band to another in a single device.

[0005] [4] However, a severe problem for the reliable operation of elastic wave devices is posed by frequency shifts of the relevant operating (central / resonance) frequencies caused by temperature variations.

[0006] [5] The present invention aims to compensate for temperature variation impacts on the operation reliability of an elastic wave device by dynamically adjusting the elastic wave device to its natural operating frequency.

[0007] [6] The object of the invention is achieved by an elastic wave device comprising one or more variable impedance means each comprising a capacitor, a first electromechanical device, in particular, a first transducer, and a second electromechanical device, in particular, a second transducer or an array of electrodes configured to reflect at least partially the elastic waves emitted by the first electromechanical device and an array 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, wherein at least one electrode of the array of at least one electrode is connected to a predetermined electrical potential via the variable impedance means. Here and in the following the transducers may be, for example, interdigitated transducers (IDTs). The capacitor(s) is (are) configured to change capacity depending on temperature variation to compensate for a frequency shift of an operating frequency of the elastic wave device caused by the temperature variation, since by varying the capacitance(s) the electric potential(s) applied to the electrode(s) of the array of at least one electrode is (are) varied and, thereby, the operation frequency is adjusted (brought back to the operation frequency). In the context of the invention, an electrode array can be constructed with just one electrode or with a plurality of electrodes. Each electrode of the array of at least one electrode may by connected to an individual one of a plurality of variable impedance means and each individual one of the plurality of variable impedance means may be further controlled by an individual one of a plurality of control means (see also detailed description below). The elastic waves may be surface acoustic waves, for example, used in a surface acoustic wave (SAW) device. The elastic wave device may be a (SAW) filter device, for example.

[0008] [7] The elastic wave device can passively adjust its operating frequency depending on a varying temperature thanks to the array of electrodes being connected to the variable impedance means comprising the capacitor having the temperature dependent capacity (all electrodes being connected to a predetermined electrical potential, in particular, ground, via the variable impedance means). Thus, the change of capacitance as a function of temperature is such that the temperature dependency of the working frequency is compensated at least partially. In particular, the capacity of the variable capacitor oppositely varies in function of the temperature compared to the working frequency. For example, if the working frequency of the device increases when the temperature arises, the capacity of the variable capacitor will passively vary under temperature variation so as to decrease the working frequency. In that way, the passively temperature-dependent capacitor allows for compensating and at least partially correcting the working frequency drift due to temperature variations.

[0009] [8] The capacitor does not need any commanding signal during operation of the device for changing its capacity and correcting the temperature variation effects. It allows the elastic wave device for passively adjusting its operating frequency when the temperature varies. The device is capable of correcting the temperature variation effects by itself, without a sensor or a parameter / voltage conversion. For example, a filter center drift caused by temperature variations can be compensated by means of the temperature dependent capacitor obeying a capacitor-temperature law suitable for counteracting a frequency-temperature law of the frequency shift caused by the temperature variations (see also detailed description below). The capacitor may suitably comprise a class 1 capacitor dielectric, in particular, a ceramic capacitor dielectric. Capacitors showing a temperature dependence of the capacities suitable to counteract the temperature dependent frequency drift of the operation frequency of the elastic wave device can be readily found on the market. Particularly, phase matching of the first and second electromechanical devices (transducers) can be accurately maintained even in the case of temperature variations due to the provision of the variable impedance means comprising the temperature dependent

[0010] capacitor(s). [9] In particular, connecting the variable impedance means to the array of at least one electrode disposed between the two electromechanical devices, in particular being transducers, allows the device for passively modifying the elastic wave propagating between the first and the second electromechanical devices. Thanks to this configuration, the phase matching of the first and the second electromechanical devices is passively maintained by the variable impedance means - of which the capacity passively varies under temperature variations - that adjusts passively the elastic wave propagating in-between.

[0011]

[0010] In this context, passively means that the array of electrodes does neither directly receive an incoming radio-frequency (RF) electric signal nor transmits an outgoing RF electric signal but only receives and transmits elastic waves.

[0012]

[0011] The working frequency of the device is maintained independently of the temperature at least in a predetermined range, for example from -20°C to 50°C, only by the passive change of the electrical conditions of the array of at least one electrode under temperature variations. In particular, the electrical conditions of the array of at least one electrode have - thanks to the variable capacitor - an opposite temperature dependency compared to the remainder of the device, and in particular compared to the piezoelectric layer. The invention allows for at least partially correcting the frequency drift due to temperature variations without needing to modify electrical conditions of the first and second electromechanical devices, in particular being transducers. More particularly, pure shear waves on POI (piezoelectric on insulator) substrates based on the combination of single-rotation LiTaO3layers, SiC>2 layers and silicon tend to exhibit a positive temperature coefficient of frequency whereas variable impedance means such as variable capacitor or inductor exhibits a negative temperature coefficient of their characteristic value (capacitance C or inductance L)

[0013]

[0012] According to an embodiment of the invention wherein the first and the second electromechanical devices are both transducers, in particular being interdigitated transducers, the RF (radio frequency) signal of interest entering the device is only applied to the first or to the second transducer. The RF signal of interest is not actively applied to the array of at least one electrode. Indeed, the array of at least one electrode passively interacts with the signal of interest propagating from the first to the second transducer. In the context of the invention, the signal of interest means an incoming radiofrequency signal to be processed via the elastic wave device.

[0014]

[0013] The frequency adjusting elements, namely the array of at least one electrode and the variable impedance means, do not participate to excite or generate a new electromechanical RF signal, in other words a radiofrequency signal that may interact with signal of interest processed by the elastic wave device. Indeed, the frequency adjusting elements only participate to modify an electromechanical RF wave, in particular the RF signal of interest, propagating from the first electromechanical device to the second electromechanical device.

[0015]

[0014] The compactness of the device according to the invention permits to reduce the time needed by the device to be operational. Moreover, since the electromagnetic waves propagate 105times faster than the elastic waves, the electrical conditions of the device are modified instantly from the point of view of the elastic wave. The device is thus capable of changing its operating frequency, in particular to correct the temperature variations effects, instantly, without generating latency in the signal of interest.

[0016]

[0015] Preferably, the present invention is not a single port device. It comprises at least two ports being the first and the second electromechanical devices.

[0017]

[0016] According to an embodiment of the invention, the first and the second electromechanical devices may be transducers formed by interdigitated comb electrodes. It allows for creating a double-port device that passively corrects temperature variation effects thanks to its coupling structure comprising a passive temperature-dependent capacitor, namely the array of at least one electrode.

[0018]

[0017] The elastic wave device may comprise control means configured to control the variable impedance means, particularly, to vary the capacitance of the capacitor(s) in addition to the temperature-dependent variation. For example, on the one hand, active control by the control means may be used to fine tune the center frequency of the elastic wave device, i.e. its operating frequency, to a desired operation frequency and, on the other hand, compensation for temperature dependent drift of the operation frequency of the elastic wave device in order to maintain the desired operation frequency can be provided by the temperature dependent capacitor(s).

[0019]

[0018] In principle, a variable capacitance actively controlled by the control means enables the array 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. By using an impedance comprising a variable capacitance, the phase of the elastic waves passing through the space between the two transducers can be altered, resulting in a change in the bandwidth position. In particular, by switching from the OC configuration to the SC configuration, the device's bandwidth can then shift continuously from a high-frequency range to a low-frequency range.

[0019] In an alternative configuration, the control means can also be configured to open or close an electrical connection between the at least one electrode and a predetermined electrical potential, in particular, ground. In particular, several or all electrodes can be configured in this way. In this way, agility can be achieved and controlled, in particular, piloted with the use of a simple switch. This can be manufactured relatively easily in an inexpensive manner.

[0020]

[0020] According to an embodiment, the array of at least one electrode can comprise several electrodes, in particular, in the form of parallel strips, several of which have variable impedances, in particular, each of the electrodes can be connected to a separate variable impedance. The number of parallel bands modifies the frequency agility of the device, in particular, the range of frequencies accessible to the device. This makes it even easier to tailor the device's agility to the desired operating criteria for a particular case.

[0021]

[0021] According to an embodiment, the electrode array can be configured to change the phase of the elastic waves and / or configured to at least partially reflect them. The introduction of an array of electrodes configured to at least partially reflect elastic waves creates resonant cavities, which makes it possible, in particular, to reduce the frequency width of the transition between the device's passband and the frequency rejection band, which corresponds to the set of frequencies not included in the device's operating passband. Depending on the situation, the person skilled in the art will know how to define the ends 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 minimum insertion loss of the device to the same value plus 30 dB, 40 dB or 50 dB, depending on the device specifications and filter efficiency.

[0022]

[0022] According to an embodiment, the electrodes of a first electrode subset of the array of at least one electrode are connected to the variable impedance means.

[0023]

[0023] In an alternative embodiment of the invention, the electrodes of a second electrode subset of the array of at least one electrode can be connected to each other and to a floating electrical potential or connected to a predetermined electrical potential, in particular, 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.

[0024]

[0024] In an alternative embodiment of the invention, the first subset and the second subset can be arranged so that the electrodes of the first subset and those of the second subset are interdigitated with respect to each other, forming a so-called interdigitated transducer (IDT), the most common transducer used for exciting and detecting surface acoustic waves and the key part of SAW filters. This arrangement of electrodes makes it possible to create a gap coupler (GC) that enables the phase of the device to be changed. The frequency agility potentially achievable by the device can depend on the number of fingers making up the two inter-digitated electrode arrays and, in particular, by increasing the number of finger pairs of the inter-digitated sub-assemblies, it is possible to widen the frequency range of the device's frequency agility.

[0025]

[0025] In an alternative embodiment of the invention, a plurality of electrode arrays can be included between the first electromechanical device, in particular, a first transducer, and the second electromechanical device, in particular, a second transducer, the arrays being separated from one another by free and / or metallized propagation spaces. The distances between respective two adjacent electrode arrays may be the same. In particular, by introducing more electrode arrays configured to at least partially reflect elastic waves, the number of cavities in the device is then increased, thus enabling modification and, in particular, reduction of the frequency width of the transition between the device passband and the frequency rejection band. In addition, by adjusting the distance between adjacent electrode arrays, it becomes possible to obtain phase quadratures 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.

[0026]

[0026] In an alternative 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 the same 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.

[0027]

[0027] In an alternative embodiment of the invention, an even number of arrays of electrodes configured to change the phase of the elastic waves can be included in the space between the transducers that is configured to at least partially reflect the elastic waves. In particular, the array of electrodes configured to at least partially reflect the elastic waves can be a Bragg mirror arranged in such a way as to form two resonant cavities, located on either side of this Bragg mirror or the reflecting structure, which can achieve phase quadrature 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 the elastic waves increases the number of resonant cavities in the device and, in particular, both reduces the frequency width of the transition between the device's passband and the frequency rejection band and increases the width of the device's operating passband.

[0028]

[0028] According to an embodiment, the elastic wave device further comprises a first reflection (grating mirror) structure and a second reflection (mirror) structure for facilitating the formation of resonance gaps, wherein the first electromechanical device is positioned between the first reflection structure and the array of at least one electrode and the second electromechanical device is positioned between the second reflection structure and the array of at least one electrode.

[0029]

[0029] In an alternative embodiment of the invention, the first and second electromechanical devices (for example, transducers) can be arranged above or in a piezoelectric substrate, in particular, a composite substrate comprising a base substrate and a piezoelectric layer, in which the thickness of the piezoelectric layer is less than or equal to 1.5 × λ, where A is the wavelength of the fundamental mode of surface elastic waves. By using a composite substrate designed for this purpose, it is possible to guide the shear waves that enable a higher electromechanical coupling between the elastic waves and the electromechanical elements of the device than it were possible with elliptically or longitudinally polarized modes.

[0030] It is noted that, in general, it is possible according to the present invention to guide elastic waves using a composite substrate to obtain characteristics that cannot be provided by single crystal substrates. Surface modes on single crystals might also be implemented, however, in accordance with the invention.

[0031]

[0030] In an alternative embodiment of the invention, a dielectric layer and / or a trapping layer and / or a Bragg mirror can be included between the base substrate and the piezoelectric layer. A trapping layer, rich in electrical charge traps, improves electrical isolation of the piezoelectric layer and, consequently, the performance of the device. A Bragg mirror consisting of an alternation of layer with different acoustic impedances improves the acoustic isolation of the piezoelectric layer.

[0032]

[0031] In an alternative embodiment of the invention, the polarization of the elastic waves may 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 shear wave or longitudinal wave guidance. In particular, a piezoelectric layer with a thickness less than the wavelength of the elastic wave improves the guidance of shear and longitudinal modes of elastic waves, and reduces acoustic radiation energy losses in the composite substrate. The use of these modes of the elastic wave improves the performance of the elastic device, in particular, minimizing energy losses in the passband in the case of a band filter.

[0032] When a device has its bandwidth, defined by a lower frequency f1 and a higher frequency f2, at and around the anti-resonance frequency but exclusive of the resonance frequency of its electromechanical structures, namely the first transducer, the second transducer and the array of electrodes, their susceptance is close to zero and the device thus operates mainly conductively.

[0033]

[0033] Therefore, the energy of the signal of interest is not stored but mostly transmitted by the electromechanical structures to the piezoelectric layer. In particular, when the device operates at or close to the anti-resonance frequencies of its electromechanical structures, their conductance is lower compared to when the device operates at or close to their resonance frequencies. Therefore, the parasitic effects and transverse modes are lowered when the device works at the antiresonance frequency.

[0034]

[0034] Moreover, the conductance presents a linear and almost constant behavior in the vicinity of the anti-resonance frequency. Thus, if the electromechanical structures of the elastic wave device are parameterized so as to optimize the adaptation of impedance of the device at the anti-resonance frequency, then the frequencies close to the anti-resonance frequency also almost optimize the adaptation of impedance of the device as the corresponding conductance at these frequencies are close to the one at the anti-resonance frequency.

[0035]

[0035] In an embodiment of the invention, the elastic wave device may be configured to have a bandwidth comprised between a first frequency f1 and a second frequency f2, and at least the first electromechanical device, the second electromechanical device, and the array of at least one electrode may be configured so that their respective antiresonance frequency fAR is higher than the first frequency f 1, and so that their respective resonance frequency fR is lower than the first frequency f 1, in particular lower than the lower frequency of the transition band.

[0036]

[0036] As explained in more details above, the parasitic effects and transverse modes are therefore lowered. These features permits to have a filter device wherein frequencies close to the anti-resonance frequency also almost optimize the adaptation of impedance of the device as the corresponding conductance at these frequencies are close to the one at the anti-resonance frequency.

[0037]

[0037] In an embodiment of the invention, the elastic wave device may be configured to have a bandwidth comprised between a first frequency f1 and a second frequency f2, and at least the first electromechanical device, the second electromechanical device, and the array of at least one electrode may be configured so that their respective resonance frequency fR is comprised between f1 and f2, and so that their respective resonance frequency is lower than f1, in particular lower than the lower frequency of the transition band.

[0038]

[0038] These features further increase the above-outlined advantageous effects.

[0039]

[0039] The invention will be better understood and other advantages will become apparent from the following non-limiting description and from the attached figures, which include:

[0040]

[0040] [Fig. 1] is a schematic diagram illustrating an elastic wave device according to a first embodiment of the invention.

[0041]

[0041] [Fig. 2] illustrates an elastic wave device according to a second embodiment 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.

[0042]

[0042] [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.

[0043]

[0043] [Fig. 4] shows a graphical representation of the gain in decibels of the transfer function of the device according to the third embodiment, which in this case has a variable impedance comprising a changeable capacitor, as a function of the value of the changeable capacitor.

[0044]

[0044] [Fig. 5] shows a graphical representation of the gain in decibels of the transfer function of the device according to the third embodiment, which in this case has a variable impedance comprising a variable inductance, as a function of the value of the variable inductance.

[0045]

[0045] [Fig. 6] illustrates an elastic-wave device according to a fourth embodiment in which the space between the two transducers comprises three electrode arrays, two of which are configured to allow guidance continuity between neighboring resonant cavities with a low level of elastic-wave reflection.

[0046]

[0046] [Fig. 7] shows a graphical representation of the gain in decibels of the transfer function of the device according to the fourth embodiment, which in this case has a variable impedance comprising a variable inductance and a variable capacitance, as a function of the value of the variable capacitance.

[0047]

[0047] [Fig. 8] shows a graphical representation of the gain in decibels of the transfer function of the device according to the fourth embodiment, which in this case has a variable impedance comprising a variable inductance and a variable capacitance, as a function of the value of the variable inductance.

[0048] [Fig.9] illustrates an elastic wave device according to a fifth embodiment in which the space between the two transducers comprises three electrode arrays, two of which are configured to transmit but not reflect elastic waves.

[0048]

[0049] [Fig. 10] illustrates an elastic wave device according to a sixth embodiment in which the space between the two transducers comprises five electrode arrays, three of which are configured to transmit primarily but not reflect elastic waves, in contrast to the other two which are configured to reflect primarily elastic waves and are interposed between each of the previous three arrays.

[0049]

[0050] [Fig. 11] illustrates an elastic wave device according to an embodiment comprising control means configured to control one or more variable impedance means, each comprising a temperature dependent capacitor.

[0050]

[0051] [Fig. 12] illustrates an elastic wave device according to an embodiment comprising three ports, reflection structures and a temperature dependent capacitor.

[0051]

[0052] [Fig. 13] illustrates an exemplary capacity-frequency law applicable to an elastic wave device according to an embodiment on temperature.

[0052]

[0053] [Fig. 14] illustrates exemplarily the effect of a temperature dependent capacitance on frequency adjustment for different capacitors.

[0053]

[0054] The invention will be described in more detail using advantageous embodiments, by way of example and with reference to the drawings. The embodiments described are merely possible configurations so that individual features as described may be provided independently of one another or may be omitted when implementing the present invention.

[0054]

[0055] Herein, it is provided an elastic wave device capable of adjusting, in particular passively, its operation frequency by compensating for frequency drifts caused by temperature variations of an operation (for example, resonance) region of the elastic wave device by variable impedance means comprising temperature dependent capacitor(s) 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 (for example, interdigitated transducers - IDTs - which represent the most used solution for SAW device and filter implementation) to electrical potentials.

[0055]

[0056] In [Fig. 11] a general embodiment of such an elastic wave device 10000 is illustrated in a principle sketch. The elastic wave device 10000 illustrated in [Fig. 11] comprises an active part 10100 comprising two electromechanical devices (representing two ports), for example, a first and a second transducers or a first transducer and an electrode array configured to reflect at least partially elastic waves emitted by the first electromechanical device and an array of additional electrodes (for example, representing a third port) arranged between the electromechanical devices (for details, see description of different embodiments below). Further, the elastic wave device 10000 comprises control means 10300 and variable impedance means 10400 connecting at least some of the electrodes of the array of electrodes arranged between the electromechanical devices to electrical potentials. The variable impedance means 10400 comprises one or more temperature dependent capacitors, the impedance of which varies with varying temperature. The control means 10300 can control the variable impedance means 10400. The control means 10300 may control the variable impedance means 10400 in order to tune the elastic wave device 10000 to a particular desired operation frequency. However, the control means 10300 are optional. The passive correction of the frequency shift due to temperature variations is achieved thanks to the passive temperature-dependent capacitor being connected to the array of at least one electrode. Consider, the elastic wave device 10000 is (almost) perfectly tuned to its operation frequency, for example, its resonance frequency. After tuning, some temperature variation may occur which results in a frequency shift according to some frequency-temperature law. In response to the temperature variation, the capacitance of the capacitor(s) of the variable impedance means 10400 that connect the electrodes arranged between the electromechanical devices to electric potentials also passively varies according to a capacitance-temperature law. According to the invention, the capacitor(s) are selected such that the temperature dependent capacitance counteracts the frequency shift of the operation frequency caused by the temperature variation to allow passive re-tuning by the elastic wave device of its operation frequency.

[0056]

[0057] A particular embodiment realizing 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 comprising reflection structures / mirrors 11110 and 11120, transducers 11130 and 11140 (ports 1 and 2) and an additional array of interdigitated electrodes 11150 (port 3, coupler) located between the transducers 11130 and 11140. The elastic wave device 11000 illustrated in [Fig. 12] further comprises one or more passive temperature dependent capacitors 11300, the capacitance of which passively varies with varying temperature. The temperature dependent capacitor(s) 11300 connecting the electrodes to electrical potentials passively control the electrical potentials of the electrodes of the array of interdigitated electrodes 11150 located between the transducers 11130 and 11140 in order to adjust the elastic wave device 11000 to its operation frequency in case of temperature variations causing some frequency shift. According to an example, a temperature dependent capacitor 11300 controls the electrical potential of the array of interdigitated electrodes 11150 and according to another example, different individual temperature dependent capacitors 11300 respectively adjust the electrical potential of an array of electrodes.

[0057]

[0058] The change of capacitance of the capacitor 11300 as a function of temperature is such that the temperature dependency of the working frequency of the device 11000 is compensated at least partially. In particular, the capacity of the variable capacitor 11300 oppositely varies in function of the temperature compared to the working frequency. For example, if the working frequency of the device 11000 increases when the temperature arises, the capacity of the variable capacitor 11300 will passively vary under temperature variation so as to decrease the working frequency. That way, the passively temperature-dependent capacitor 11300 allows for compensating and at least partially correcting the working frequency drift due to temperature variations.

[0058]

[0059] 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 from experiments). Based on that knowledge, the employed temperature dependent capacitor(s) 11300 can be chosen to have such a temperature dependent capacitance to allow the elastic wave device to self-adjust to its operation frequency in case of temperature variations causing some frequency shift. A concrete example is given in the following.

[0059]

[0060] The temperature sensitivity of an elastic wave device, for example, functioning as a filter device, may, for example, be expressed by a polynomial function of third order: Af / fo = (f-fo) / fo = TC / zix(T-To)+TC / z2x(T-To)2+TC / z3x(T-To)3wherein f0denotes the filter center frequency (operation frequency) at 7o = 25°C and TCFI,2,3 denote the 1st, 2ndand 3rdorder temperature coefficients of frequency. Values of the table below indicate a frequency variation of about 7.0 MHz in the temperature range -40 / +85°C with less than 3 MHz from 0 to +85°C:

[0060] Table 1: Example of TCF values for a Surface Cavity Acoustic Wave / Resonant Gap SAW filter operating near 1.9 GHz relative to each edges of the filter passband [Table 1]

[0061] Eq,(1) parameter Band-pass lower edge Band-pass upper edge

[0062] fo (MHz) 1901.100 1942.62

[0063] TCFi (ppm. K’1) 12.50 13.25

[0064] TCF2(ppb. K-2) -310,20 -204,89

[0065] TCFz (ppt. K'3) 4622.52 3037.47

[0066]

[0067]

[0061] The dependence of the capacitance of the time dependent capacitor(s) 13000 on temperature may be expressed by a polynomial function of second order: AC / Co = (C-Co) / Co = TCCIX(T-TO)+TCC2X(T-TO)2(3) with TCCI,2 denoting the 1stand 2ndorder temperature coefficients of capacitance.

[0068]

[0062] On the other hand, a known capacitance-frequency law is, exemplarily, illustrated in [Fig. 13]. The capacitance-frequency law is quasi linear in log scale from 0.1 to 1 pF with a ~25 MHz frequency excursion, i.e., much more than about 7.0 MHz (- 40 / +85°C) observed for instance for a typical SCAW filter at 1.9 GHz (cf. Table 1 ). For instance, a 40 ppm K'1linear drift would correspond to a 10 MHz absolute frequency variation. Most important is to model the quasi-linear part (from about 0.1 to about 1 pF showing the highest variation) of the function

[0069] [Math 1]

[0070]

[0071] f ( C ) = a- 7?exp"" *s'v+ <5 log ( £C + / / C2)

[0072] shown in [Fig. 13] with exemplary values

[0073] [Math 2]

[0074] a 1610,73, 6 -23.40, y = 2.44, 5 = -0.44, = -1.22xl0’3, 1.31

[0075]

[0063] Consider an exemplary elastic wave device temperature sensitivity with TCF values:

[0076] TCFi = 13 ppm-K’1, TCF2= -300 ppb K’2, TCF3= 3500 ppt K’3.

[0077] The starting capacitance value (corresponding to the 25°C operation condition) may be set in the middle of the varicap frequency excursion, for example, 0.6 pF, and the filter design should take this point into consideration to be actually met.

[0078] Using the 3rdorder temperature-frequency law, one can 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]

[0079]

[0080] which actually fits well the section of the curves for which the capacitance / frequency dependence is the strongest ( / .e., from 0.1 to 1 pF for the example shown in [Fig. 13]). Co might be defined as the capacitance at To at the middle of the sharp frequency / capacitance variation shown in [Fig. 13]: Co = 0.376 pF. This provides a suitable approach to allow for compensating both negative and positive relative temperature variations T-To. Limiting the temperature-capacitance law to the first order vs temperature (linear dependence), according the state of the art for class 1 capacitors, in particular, ceramic capacitors and inserting it into the above f(C) equation yields the following expression

[0081] [Math 4]

[0082]

[0083] with the linear temperature-capacitance coefficient TCC.

[0084]

[0064] The temperature dependent capacitor(s) 11300 have to be chosen to have a linear temperature dependence of TCC in order to counteract temperature dependent frequency shifts of the operation frequency of the elastic wave device 11000. [Fig.

[0085] 14] shows exemplarily the (linear) effect of a temperature dependent capacitor on frequency adjustment for different capacitors with capacitance variations caused by temperature variations in terms of TCC, i.e., the temperature sensitivity of the device adjusted by a capacitance given by TCC. [Fig. 14] shows linear behaviors for a: TCC= 30 ppm K-1, b: TCC= 300 ppm K-1, c: TCC= 750 ppm K-1, and d: TCC= 2000 ppm-K-1, together with a quadratic fit q for TCC= 2000 ppm-K-1. The quadratic fit is used to estimate the temperature sensitivity of an elastic wave device (filter) adjusted by a capacitance with a TCC equal to 2000 ppm-K-1, yielding first and second degree temperature coefficients of -11 ppm K-1and +12 ppb K-2. These values drop down to -4 ppm K-1and +3 ppb K-2for a TCC equal to 750 ppm-K-1. For example, class 1 capacitors, in particular, ceramic capacitors, that exhibit such magnitudes of TCC values are available on the market.

[0086]

[0065] In view of the above, in order to obtain frequency self-compensation for temperature variations one has to obey

[0087] [Math 5] a - peXp~'>'c^'rcc^-T^ = fO (1 + TCF1(T - TO) + T

[0088]

[0089] CF2(T - TO)2+ TCF3(T - TO)3) from which the desired value of TCC for a particular elastic wave device under consideration showing a concrete temperature sensitivity can be determined:

[0090] [Math 6]

[0091] — 1 I / ■'.. d ICC = —7= log 11 - TCF. ( T - ToI +... )

[0092]

[0093]

[0066] By expanding the log function by its Taylor expansion and the approximations of the linear capacitance-frequency and frequency-temperature laws, one can obtain [Math 7]

[0094]

[0095] For example, for TC i = 13 ppm K'1one obtains TCC= -2330 ppm-K’1.

[0096]

[0067] The active part 10100 of the elastic wave device 10000 shown in [Fig. 11] can, alternatively, be realized according to different other embodiments in form of a plurality of configurations as it is described in the following wherein the terms variable impedance means and variable impedance are used interchangeably. Further, control means can be employed that allow for optional additional active control of the variable impedance means for tuning the elastic wave device to a desired operation frequency as described below. Description of materials and substrates used may apply to all embodiments.

[0097]

[0068] [Fig. 1] shows the elastic wave device 100 as described in a first embodiment of the invention. The elastic wave device 100 represents a dual-port resonator which 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 may in alternative embodiments be an array of electrodes configured to at least partially reflect the elastic waves emitted by the first electromechanical device 3.

[0098]

[0069] The device 100 further comprises an array 4000 of at least one electrode 1000, 2000, 3000 located between the first transducer 3 and the second transducer 5 in the direction of elastic wave propagation, wherein 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.

[0099]

[0070] 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.

[0100]

[0071] In this embodiment, the piezoelectric layer 11 is LiTaO3or LiNbOs. In particular, using IEEE 1949 Std-176 standards, the orientations of the crystallographic crosssection of the piezoelectric layer are defined by (YX / ) / 0, with 0 denoting the crystallographic orientation angle corresponding to a rotation about the crystal axis X by between 0 and 60 degrees or between 90 and 150 degrees.

[0101]

[0072] The piezoelectric layer 11 can also be made of potassium niobate KNbOs, or any other material with a similar composition, such as KTN. It is also possible to use for the piezoelectric layer 11 an epitaxially formed or sputtered film of, for example, aluminum nitride AIN, scandium-doped aluminum nitride AIScN, zinc oxide ZnO, PZT, GaN, or any other composition of AIN and GaN.

[0102]

[0073] The thickness of the piezoelectric layer 11 is of the order of magnitude of the wavelength A of the elastic waves or less, in particular, it can be about 10 microns or less, especially 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 can be 50 to 100 times greater, corresponding to a base substrate with a thickness of 50 to 1000 microns. In particular, the substrate thickness can be selected from 100 microns to 500 microns.

[0103]

[0074] The base substrate 15 used in the first embodiment of the invention is a silicon substrate, in particular, a silicon substrate with high electrical resistivity. By high electrical resistivity it is meant an electrical resistivity exceeding 1000 Q cm.

[0104] Preferably, the silicon is in crystalline form, with the substrate orientation preferably in the (100) direction, which results in a higher elastic wave propagation speed than other crystallographic orientations such as (110), (111) or (001 ), which can also be used. The choice of substrate takes into account the speed beyond which elastic waves are no longer guided by the silicon surface, the so-called Surface Skimming Bulk Wave (SSBW) velocity VSSBW. This speed must therefore be higher than the speed of the mode corresponding to the anti-resonance condition, but close enough to it so as not to allow the excitation of other modes which would otherwise degrade the spectral purity of the device's response. Advantageously, the speed 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 Z axes of the substrate and piezoelectric layer along which the respective planes are defined can be ideally aligned in the case of (111 ) silicon or misaligned by 45° for (100) or (111 ) silicon to limit the contributions of spurious modes beyond the antiresonance frequency of the fundamental mode, or misaligned in the angular range [- 10°, +10°] for Si(111) considering the corresponding IEEE angular definition as (YXwlt) / ±457-35.37i with i the misalignment angle or in the angular range [±170°, ±190°] for Si(111) considering the corresponding IEEE angular definition as (YXwlt) / ±457+35.37ip with i the misalignment angle. The base substrate 15 may be made of or comprise other materials, in particular to enable elastic waves to propagate at a higher speed than the elastic waves propagating in the piezoelectric layer 11. In particular, the base substrate 15 can be made of or comprise carbon- diamond, sapphire or silicon carbide. Other suitable materials include aluminum nitride and silicon nitride.

[0105]

[0075] The base substrate 15 may comprise a trapping layer, in particular, 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 can be formed from 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.

[0106]

[0076] In alternative embodiments, the base substrate 15 may comprise a Bragg mirror, located between the piezoelectric layer 11 and the base 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 the elastic wave and the density of the material in which the wave propagates, all expressed in Rayleigh, or preferably MRayleigh, i.e., 106Rayleigh.

[0107]

[0077] This stack of layers forming the Bragg mirror can be composed of a stack of layers alternating, for example, Tungsten and silica, or SisN4 and SiC>2, or Mo and Al. More generally, any pair of materials with 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 with a coefficient of thermal expansion of less than 6 ppm-K’1. The stack may also include a trapping layer to improve insulating properties.

[0108]

[0078] The dielectric layer 13 in [Fig. 1], formed by a thin SiC>2 layer of 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 can be less than or greater than 500 nm and, in particular, can vary between 10 nm and 6 microns.

[0079] As mentioned above, the elastic wave device 100 comprises the two electromechanical transducers 3, 5 and the electrode array 4000 (electrodes 1000, 2000, and 3000) located between the two transducers 3 and 5. Electrode array 4000 (electrodes 1000, 2000, and 3000) is spaced a certain distance ch from the first transducer 3 and a certain distance cfefrom the second transducer 5, as seen in [Fig.

[0109] 1], The three electromechanical elements 3, 5 and 4000 are arranged in the plane (ZX) 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 strips are perpendicular to the axis X of elastic wave propagation.

[0110]

[0080] Gaps 17 and 19 between transducer 3 and 4000 and between transducer 5 and electrode array 4000 have widths ch and dz respectively. These spaces form resonant cavities (gaps) in the X direction of elastic wave propagation. In alternative embodiments of the invention, the device 100 may comprise a single or multiple 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 di and c orthe two spaces 17 and 19. Alternatively, the distances di and cfe can be different from each other.

[0111]

[0081] In [Fig. 1], the 4000 electrode array consists of three interdigitated electrodes 1000, 2000 and 3000. Each of the three electrodes 1000, 2000, 3000 has a straight end 1001, 2001, 3001.

[0112]

[0082] However, the number of electrodes in the 4000 array is not limited to three, in particular, it can be less than or greater than three, in particular, it can be equal to 1. The 4000 array and its 1000, 2000, 3000 electrodes are made of an aluminum-based material such as pure aluminum or an aluminum alloy such as Al doped with Cu, Si orTi. However, other materials can also be used, in particular, those providing a high reflection coefficient (a relative frequency bandgap TTx(fstoP-fstart) / (fstop+fstart) in excess of 5% or even 10%, with fstart and fstop the start and stop frequencies of the spectral bandgap) for a relatively small electrode thickness (less than 10% of the wavelength). Details on the calculation of reflection and scattering parameters can be found in a paper by P. Ventura et al., entitled “Combined FEM and Green’s Function Analysis of Periodic SAW Structure, Application to the Calculation of Reflection and Scattering Parameters”, IEEE Trans, on LIFFC, vol. 48, no. 5, 2001, pp 1259-74. For example, materials such as copper, molybdenum, nickel, platinum or gold can be used. The array 4000 and its 1000, 2000, 3000 electrodes can also include an adhesion layer made, for example, of titanium, tantalum, chromium, zirconium, palladium, iridium, tungsten, etc. This composition of electrodes and combs may also apply to transducers 3 and 5. More complex / multilayer metal combinations can be considered to improve the transducer conductivity or its power handling capability.

[0113]

[0083] The array 4000 is also defined by the pitch p between two consecutive interdigitated electrodes (IDTs), such as the distance between electrodes 1001 and 2001. In particular, this pitch p can be defined by the Bragg condition, which stipulates that p = / 2, with the wavelength of the device's operating elastic waves. 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 in the same structure comprising several electrodes, or even, for example, two interdigitated combs. The electrodes are also defined by the length I of their rectilinear ends, as well as their widths, denoted a in [Fig. 1], In particular, the values of a, I and p can be modified to obtain a desired electromechanical coupling coefficient.

[0114]

[0084] In the embodiment of the invention shown in [Fig. 1], the electrodes 1000, 2000, 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 can be the same, in particular one and the same electrical potential, in particular, this reference potential can be ground. Alternatively, 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 for one or more of the electrodes 1000, 2000, 3000 not to be connected to a variable impedance. In particular, it is possible, and sufficient to achieve the desired frequency agility, for only a single electrode to be connected to a variable impedance, and it is this agility that allows for compensating for temperature variations such that the elastic wave device can passively correct, at least partially, its operation frequency even under the influence of the temperature variations. At least one if the variable impedance means 1003, 2003, 3003 comprises a capacitor having a capacitor configured to passively change its capacity depending on temperature variation to compensate, at least partially, for a frequency shift of the operating frequency of the elastic wave device 100 caused by the temperature variation.

[0115]

[0085] According to an embodiment of the invention, the elastic wave device 100 may further comprise control means 1007, 207, 3007 respectively connected to the variable impedances 1003, 2003, 3003 and further enabling, in addition to the passive correction of the frequency drift, to control and modify the values of the variable impedances 1003, 2003, 3003, in particular, remotely, during operation, or not, of the elastic wave device 100. The impedance may, for example, be a varicap which can be controlled by the voltage applied across the varicap by a variable voltage generator. However, the invention and the passive frequency drift correction is achieved thanks to the passive temperature-dependent capacitor, without needing control means 1007, 207, 3007.

[0116]

[0086] In one embodiment of the invention, electrodes 1000, 2000, 3000 of the 4000 array can each be connected to a second variable impedance which can be modified by their respective control means 1007, 2007, 3007.

[0117]

[0087] In the proposed embodiment of the invention shown in [Fig. 1], transducers 3 and 5 both comprise two interdigitated electrode combs (IDTs), 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 lower or higher, as well as not being the same in the two combs 31 and 33 respectively 51 and 55.

[0118]

[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, 301 and 501 respectively. Comb 31 is connected to an input load 303 and comb 51 to an output load 503.

[0119]

[0089] In this embodiment of the invention, the pitch between two consecutive interdigitated electrodes p, the width a and the length I of the electrodes are the same 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 the two transducers 3 and 5 but different in the electrode array 4000.

[0120]

[0090] By passively varying the value of at least one of the variable impedances 1003, 2003, 3003, the device 100 modifies the reflection conditions of the electrode array 4000 and thus tunes the operating frequency of the device 100. In particular, the variable impedances 1003, 2003, 3003 comprise a capacitance and may comprise an inductance.

[0121]

[0091] However, in alternative embodiments of the invention, it is also possible for two electrodes, for example 1000 and 2000, to be connected to the same variable impedance.

[0122]

[0092] By connecting the electrodes 1000, 2000, 3000 to their respective variable impedances 1003, 2003, 3003, it becomes possible for the device 100to modify as well as to vary, in particular, during its operation, the impedance loads of the variable impedances and consequently the electrical conditions of the electrode array 4000. This makes it possible for the device 100 to modify passively its operating bandwidth, even after it has been designed and manufactured. According to the invention, the 100 device is therefore frequency agile.

[0123]

[0093] The frequency agility of the elastic wave device 100 can, in particular, depend on the number of electrodes making up 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 the device 100 can have its operating frequency.

[0124]

[0094] Alternatively, the variable impedances 1003, 2003, 3003 can be realized by a simple switch, enabling the changeover from a short circuit (SC) to an open circuit (OC).

[0125]

[0095]

[0126]

[0096] Alternatively, the 100 device can be placed between two mirrors to further confine energy in the region of the transducers and the central cavity.

[0127]

[0097] 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.

[0128]

[0098] 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.

[0129]

[0099] 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 made up of three straight electrodes, 711, 713 and 715for comb 71, and 731, 733 and 735 for comb 73, each connected to the other within the same comb.

[0130]

[0100] However, the number of electrodes in each of the combs 71 and 73 is not limited to three; in particular, it may be less or more, and may not be the same in both 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 Al doped with Cu, Si or Ti. However, other materials can also be used, in particular, those that provide a high reflection coefficient for a relatively small electrode thickness. For example, materials such as copper, molybdenum, nickel, platinum or gold can be used. The combs 71 and 73 and their respective electrodes 711, 713, 715, 731, 733 and 735 can also include an adhesion layer made, for example, of titanium, tantalum, chromium, zirconium, palladium, iridium, tungsten, etc.. Compound electrodes may be employed to improve the power handling. This composition of electrodes and combs also applies to transducers 3 and 5.

[0101] Interdigitated electrode combs 71 and 73 are also defined by the pitch p between two consecutive interdigitated electrodes each originating from one of the two combs 71 and 73, such as the distance separating electrodes 731 and 711. In particular, this pitch p can be defined by Bragg's condition, which stipulates that p = λ / 2, with λ the wavelength of the device's operating elastic waves. 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 in the same structure comprising two interdigitated combs. The electrode combs are also defined by the length I of their electrodes and the width a of their electrodes. In particular, the values of a, I and p can be modified to obtain a desired coupling coefficient.

[0131]

[0102] In [Fig. 3], the combs 71 and 73 are configured in such a way that the electrode array 7 at least partially reflects the elastic waves, in a so-called mirror coupler (MC) configuration, thereby modifying the phase of the transmitted wave and that of the reflected wave.

[0132]

[0103] In an alternative embodiment, these same combs can also be configured to modify primarily the phase of the transmitted elastic waves, without having wave reflection as their primary purpose. They are then said to be in a Gap Coupler (GC) configuration. In the embodiment of the invention shown in [Fig. 3], the electrode array 711, 713 and 715 of comb 71 is connected to a predetermined electrical potential, in this case ground 701. The array of electrodes 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.

[0133]

[0104] According to an embodiment of the invention, the elastic wave device 300 may further comprise a control means 707 which is connected to the variable impedance 703 and enables, in addition to the passive correction of the frequency drift, to control and modify the value of the variable impedance 703, in particular, remotely, during the operation, or not, of the elastic wave device 300.

[0134]

[0105] In one embodiment of the invention, the electrode array 711, 713 and 715 of comb 71 can be connected to a second variable impedance which can be modified by control means 707.

[0135]

[0106] In the proposed embodiment of the invention shown in [Fig. 3], transducers 3 and 5 both comprise two interdigitated electrode combs, 31 and 33 for transducer 3, and 51 and 53 for transducer 5. As with 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 lower or higher, as well as not being the same in the two combs 31 and 33 respectively 51 and 55.

[0136]

[0107] 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, 301 and 501 respectively. Comb 31 is connected to an input load 303 and comb 51 to an output load 503.

[0137]

[0108] In this embodiment of the invention, the pitch between two consecutive interdigital electrodes p, the width a and the length I of the electrodes are the same in both 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 both transducers 3 and 5 but different in the electrode array 7.

[0138]

[0109] By varying the value of the variable impedance 703, it is possible for the device 300 to passively modify the reflection conditions of the electrode array 7 and thus to tune its operating frequency. In particular, the variable impedance 703 comprises a capacitance, and may comprise an inductance.

[0139]

[0110] However, in alternative embodiments of the invention, it is possible for only some of the electrodes on comb 73 to be connected to variable impedance 703, or for each or a subset of the electrodes to be connected to a separate variable impedance. It is also possible that both combs 73 and 71 have electrodes connected to variable impedances.

[0140]

[0111] By connecting the electrode comb 73 to the variable impedance 703, it becomes possible for the device 300 to modify passively as well as to vary passively, in particular, during its operation, the impedance load of the variable impedance and consequently the electrical conditions of the electrode array 7. This makes it possible for the device 300 to modify passively its operating bandwidth, even after its design and manufacture. According to the invention, the device is therefore frequency agile.

[0141]

[0112] The frequency agility of the elastic wave device 300 can, in particular, depends 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.

[0142]

[0113] Alternatively, the variable impedance 703 can be implemented by a simple switch, enabling the circuit to be switched from short-circuit (SC) to open-circuit (OC).

[0143]

[0114] Alternatively, the 300 device can be placed between two mirrors to further confine the energy.

[0115] According to 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.

[0144]

[0116] By passively varying its capacitive load of the changeable capacitor, it is possible for the device 300 to continuously vary the position of its operating bandwidth of 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 a configuration or at least approaches an OC open-circuit 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 approaching a short-circuit configuration SC.

[0145]

[0117] [Fig. 4] shows bandwidths simulated using the numerical method described in S.

[0146] Ballandras et al. " Finite element analysis of periodic piezoelectric transducers", 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 LiTaO3with (YX / ) / 42° orientation on a 500 nm-thick layer of silicon oxide, a 1pm-thick layer of poly-silicon, all on a silicon substrate (100) with a 45° disorientation between the Z' and Z axes of lithium tantalate and silicon respectively, these characteristics then being used in a mixed-matrix model to simulate filter response. These passbands correspond to those of an elastic wave device as described in [Fig. 3], where the variable impedance 703 comprises a variable capacitor.

[0147]

[0118] 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 interdigital fingers in the simulation, and electrode array 7 has five pairs of interdigital fingers.

[0148]

[0119] The pitch p in the two simulated transducers 3 and 5 is p = 1.202 μm and in the simulated electrode array 7 it is p = 1.13 pm. The a / p ratio is equal to 0.5.

[0149]

[0120] On the y-axis, the modulus, in decibels, of the S12 transfer function of the device as described above is plotted as a function of the pass 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 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 and are represented respectively by curves 4b, 4c, 4d, 4e, 4f, 4g and 4h in [Fig. 4],

[0150]

[0121] [Fig. 4] shows the frequency agility of the Also shown are open-circuit OC (curve 4a) and short-circuit SC (curve 4i). device as described above, whose variable impedance 703 includes a changeable capacitor. This device is similar to the one shown in [Fig. 3]. By passively modifying its value of the variable capacitor and therefore the value of the variable impedance, the device 300 modifies its bandwidth, in particular, its central position varies from 1675 MHz for the open circuit OC or 0.001 pF to 1625 MHz for the short circuit SC.

[0151]

[0122] 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 comprising 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.

[0152]

[0123] 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 comprising variable impedance 703 were short-circuited (SC), represented by curve 4i in [Fig. 4], This situation thus defines the position of the low operating frequency of device 300, corresponding to the SC configuration.

[0153]

[0124] The variable impedance 703 comprising a variable capacitance makes it possible, by passively increasing its 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 in [Fig.

[0154] 4].

[0155]

[0125] 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 changeable inductance.

[0156]

[0126] When a device has its bandwidth at and around the anti-resonance frequency but exclusive of the resonance frequency of its electromechanical structures, namely the first transducer 3, the second transducer 5 and the array 7 of electrodes for the device 300 of [Fig.3], their susceptance is close to zero and the device thus operates mainly conductively.

[0157]

[0127] Therefore, the energy of the signal of interest is not stored but mostly transmitted by the electromechanical structures to the piezoelectric layer 11. In particular, when the device operates at or close to the anti-resonance frequencies of its electromechanical structures, their conductance is lower compared to when the device operates at or close to their resonance frequencies. Therefore, the parasitic effects and transverse modes are lowered when the device works at the antiresonance frequency.

[0158]

[0128] Moreover, the conductance presents a linear and almost constant behavior in the vicinity of the anti-resonance frequency. Thus, if the electromechanical structures of the elastic wave device are parameterized so as to optimize the adaptation of impedance of the device at the anti-resonance frequency, then the frequencies close to the anti-resonance frequency also almost optimize the adaptation of impedance of the device as the corresponding conductance at these frequencies are close to the one at the anti-resonance frequency.

[0159]

[0129] Therefore, the device 300 preferentially operates at or close to the anti-resonance frequency of the transducers 3 and 5 and of the array 7 of electrodes. Preferentially, each of the first transducer 3, the second transducer 5 and the array 7 of electrodes has its anti-resonance frequency comprised in the bandwidth of the device 300 shown in [Fig.4], thus comprised between 1630 and 1680 MHz. In addition, the above-mentioned advantageous effects are further increased when the resonance frequency of the first transducer 3, of the second transducer 5 and of the array 7 of electrodes are out of the operating bandwidth of the device 300, thus not comprised between 1630 and 1680 MHz. In any case, the resonance frequency of the interdigitated transducers is always out of the passband of the filter and even out of the first transition band of the filter defined as the minimum insertion loss of the filter passband ILmin– 3 dB (the lower edge of the filter passband) - 20 dB or even -30dB, these values reflecting the rejection efficiency of the filter. On the other hand, the antiresonance frequency of the interdigitated transducers is always higher than the lower edge of the filter passband defined as the lower frequency for which the losses are corresponding to ILmin-3dB.

[0160]

[0130] The above-mentioned operating preferences and settings also apply for all the embodiments of the present disclosure. In particular, the devices simulated in the [Fig.5], [Fig.7], [Fig.8] and the device of [Fig.11] or [Fig.12] may also preferentially operate at the anti-resonance frequency as described above.

[0161]

[0131] [Fig. 5] shows bandwidths simulated using the numerical method described in S.

[0162] Ballandras et al., " Finite element analysis of periodic piezoelectric transducers", Journal of Applied Physics, 93, 702 (2003) with the same parameters as used for [Fig. 4] except for the use of a changeable inductor instead of a capacitor. These bandwidths correspond to those of an elastic wave device 300 as described in [Fig.

[0163] 3], where the variable impedance 703 comprises a changeable inductor.

[0164]

[0132] On the ordinate, the modulus, in decibels, of the S12 transfer function of the device as described above is plotted as a function of the pass 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].

[0165]

[0133] [Fig. 5] shows the frequency agility of device 300 as described in [Fig. 3], whose variable impedance 703 comprises a variable inductance.

[0134] By modifying the value of the variable inductance, and therefore the value of the variable impedance, the bandwidth is modified, in particular, its position varies. Fora low value of variable inductance, e.g. 1.0 nH, illustrated by curve 5e, the operating bandwidth of 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 changeable 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 device 300 moves away from that of the low frequency, curve 5f, through the frequencies below the low frequency. For a high value of changeable inductance, e.g. 500.0 nH, illustrated by curve 5b in [Fig. 5], the operating bandwidth of device 300 approaches that of the high frequency, around 1675 MHz corresponding to the OC configuration, represented by curve 5a (or 4a in [Fig. 4]) and this, passing through frequencies higher than the high frequency.

[0166]

[0135] 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 device 300 approaches the bandwidth corresponding to the SC configuration via frequencies below the low frequency. Conversely, in this embodiment, the bandwidth of device 300 approaches the bandwidth corresponding to the OC configuration by passing through frequencies above the high frequency.

[0167]

[0136] Thus, a variable impedance 703 comprising a changeable inductance makes it possible, by increasing the value of the changeable inductance, to shift the operating bandwidth position of the device 300 from the low frequency of the SC configuration, corresponding to curve 5f on [Fig. 5], to 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.

[0168]

[0137] [Fig. 6] shows an elastic wave device 400 according to a sixth embodiment of the invention. Compared to the device 100 of the first embodiment, the 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 transducers 3 and 5, more precisely between electrode array 7 and transducer 5. Electrode array 7 is in GC configuration. Electrode array 6 in the MC configuration is located between the two electrode arrays 7 and 4, which are in the GC configuration.

[0169]

[0138] 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 concerning the number of fingers, width a, pitch p and thickness h of the electrodes.

[0170]

[0139] Electromechanical devices 3 and 7 are separated by the distance d1, 7 and 6 by the distance d2, 6 and 4 by the distance d3, 4 and 5 by the distance d4.

[0171]

[0140] Electromechanical devices 3, 7, 6, 4 and 5 are separated by distances that can be different. In an advantageous embodiment of the invention, shown in [Fig. 6], these distances can be the same.

[0172]

[0141] In the embodiment of the invention shown in [Fig. 6], the electrode array 411, 413 and 415 of comb 41 is connected to a predetermined electrical potential, in this case ground 401. The array of electrodes 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. According to an embodiment of the invention, the device 600 may also comprise a control means 407 which is connected to the variable impedance 403 and enables, in addition to the passive correction of the temperature frequency drift, the value of the variable impedance to be controlled and modified remotely or not during operation of the elastic wave device 400.

[0173]

[0142] However, in alternative embodiments of the fourth mode of the invention, it is possible for only some of the comb 43 electrodes to be connected to the variable impedance 403, or for each or a subset of the electrodes to be connected to a separate variable impedance. It is also possible that both combs 43 and 41 have electrodes connected to variable impedances.

[0174]

[0143] In this embodiment of the invention, the electrode array 6 is a Bragg mirror comprising 16 electrodes, grouped under reference 61 in [Fig. 6]. These 16 electrodes are all interconnected by two base electrodes 62 and 63. The electrode array 6 is in an open circuit OC configuration, i.e. not connected to any electrical potential, so the connection is said to be floating, and the 16 electrodes 61 are isopotential. The mirror can have more or fewer electrodes.

[0175]

[0144] In particular, adding the two electrode arrays 4 and 6 widens the operating bandwidth of the device 400 compared, for example, with the first embodiment of the device shown in [Fig. 1] or the third embodiment shown in [Fig. 3].

[0176]

[0145] In an embodiment of the invention based on device 400, shown in [Fig. 6], variable impedance 703 of device 400 comprises a changeable inductance. According to the invention, the device 400 comprises a variable capacitance.

[0146] [Fig. 7] shows bandwidths simulated 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 pitch p in both simulated transducers 3 and 5 and electrode array 6 is p = 1.202 pm, and in simulated electrode arrays 4 and 7 it is p = 1.13 pm. The a / p (metallization) ratio can suitably be chosen in the range of 0.4 to 0.5 in order to maximize the electrode reflection coefficient.

[0177]

[0147] In this numerical simulation, transducers 3 and 5 (IDTs) each have 45 pairs of interdigitated fingers, and electrode arrays 4 and 7 have three pairs of interdigitated fingers. Electrode array 6 has 16 iso-potential fingers.

[0178]

[0148] In [Fig. 7], only the value of the variable capacitance of electrode array 7 was modified, in particular, through 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.

[0179]

[0149] On the ordinate, the modulus, in decibels, of the S12 transfer function of the device as described above is plotted as a function of the passband center 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 in [Fig. 7] by curves 7b, 7c, 7d, 7e, 7f, 7g and 7h.

[0180]

[0150] [Fig. 7] highlights the frequency agility of the device 400 as described in [Fig. 6], whose variable impedances 703 and 403 comprise a variable capacitance and a variable inductance. By modifying the value of the variable capacitor, and therefore the value of the variable impedances 703 and 403, the bandwidth is modified, in particular, its center frequency. For a low value of the variable capacitance, for example 0.001 pF, corresponding to curve 7b, the operating bandwidth of device 400 is close to the bandwidth corresponding to that obtained if the circuit comprising variable impedance 703 were open, which is illustrated by curve 7a in [Fig. 7], As the value of the variable capacitance 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 towards that of the low frequency, curve 7i. For a high value of variable capacitance, for example 10.0 pF, represented by curve 7h, the operating bandwidth of device 400 is close to the bandwidth corresponding to that of the SC configuration, curve 7i.

[0151] Thus, the variable impedances 703 and 403 comprising a variable capacitance and a changeable 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.

[0181]

[0152] [Fig. 8] is similar to [Fig. 7], except that in contrast to the case of [Fig. 7], only the value of the variable inductance of electrode array 7 is modified, while the value of the variable capacitance included in 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 to curves 8g, 8f, 8e, 8d, 8c and 8b on [Fig. 8] respectively. The fixed inductance of electrode array 4 was 1 nH, and the fixed capacitance of electrode arrays 4 and 7 was 1 pF.

[0182]

[0153] [Fig. 8] shows that, when the variable impedances 703 and 403 of device 400 comprise a variable capacitor and a variable inductance, the operating bandwidth can both reach values between the low frequency around 1607MHz of the SC configuration, curve 8h in [Fig. 8] and 7i in [Fig. 7], and the high frequency around 1643 MHZ of the OC configuration, curve 8a in [Fig. 8] and 7a in [Fig. 7], in particular, through variations in the value of the variable capacitance as visible in [Fig. 7], but also, reach values below the low frequency, curve 8h in [Fig. 8] and 7i in [Fig. 7], and values above the high frequency, curve 8a in [Fig. 8] and 7a in [Fig. 7], in particular, through variations in the value of the changeable inductance.

[0183]

[0154] For example, [Fig. 8] shows that variable impedances 703 and 403 comprising a variable capacitance and a variable inductance enabling the device 400 to have greater frequency agility than if 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.

[0184]

[0155] [Fig. 9] shows an elastic wave device 500 according to a fifth embodiment of the invention with three electrode arrays 4a, 6a and 7a. Compared with 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.

[0185]

[0156] In this embodiment of the invention, arrays 4a and 7a, unlike arrays 4 and 7 of device 400 shown in [Fig. 6], do not have variable impedances. Arrays 4a and 7a each comprise three parallel electrodes, respectively grouped under references 421 and 721. In alternative embodiments, however, it is possible to have more or fewer than three electrodes in parallel strips in arrays 4a and 7a. The parallel electrode strips 421 and 721 are, for each array, connected by two base electrodes, 42 and 44 for array 4a, and 72 and 74 for array 7a. Arrays 4a and 7a are therefore at floating potential, but must still be considered as iso-potential.

[0186]

[0157] In this embodiment of the invention, the array 6a of 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 distinct control means 602, 604 and 606, as well as to a respective distinct determined electrical potential 691, 693 and 695. Alternatively, a single control means can modify impedances 691, 693 and 695 separately or collectively.

[0187]

[0158] Comb 617 is at floating potential, although it forms an iso-potential system. Comb 617 has six electrodes 641, 642, 643, 644, 645 and 646 interdigitated with comb 611 for electrodes 641 and 642, with comb 613 for electrodes 643 and 644 and with comb 615 for electrodes 645 and 646.

[0188]

[0159] The comb 617 also comprises two sub-groups of electrodes 631, 633 in isopotential, i.e. they are connected to each other by the common base electrode 699 and, respectively, by the base electrode 681 and 683, as schematized in [Fig. 9]. Subgroups 631 and 633 each have four interconnected parallel strip electrodes.

[0189]

[0160] Combs 611, 613 and 615 each have two parallel strip electrodes, 671 and 673, 661 and 663 and 675 and 677 respectively. However, in alternative embodiments, combs 611, 613 and 615 may have more, or fewer, parallel strip electrodes, in particular, combs 611, 613 and 615 may be reduced to a single straight strip electrode.

[0190]

[0161] Impedances 601, 603 and 605 can be capacitive and / or inductive.

[0191]

[0162] Electromechanical devices 3 and 7a are separated by the distance d5 , 7a and 6a by the distance d6 , 6a and 4a by the distance d7 , 4a and 5 by the distance d8.

[0192] Electromechanical devices 3, 7a, 6a, 4a and 5 are separated by distances that can be different. In an advantageous embodiment of the invention, as shown in [Fig. 9], these distances may be the same.

[0193]

[0163] This mode of implementation of the invention enables frequency agility to be achieved with a change in the value of the maximum of the elastic reflection coefficient of the space between the two transducers that remains low compared to when the operating frequency of the device is changed. For example, when switching from a SC - OC- SC configuration to a OC - SC - OC configuration, the maximum value of the reflection coefficient remains virtually constant.

[0194]

[0164] [Fig. 10] shows an elastic wave device 600 according to a sixth embodiment of the invention. Compared to the embodiment in [Fig. 6] with three electrode arrays 4, 6 and 7, this embodiment has two additional electrode arrays 8 and 10 between transducers 3 and 5. There are therefore five electrode arrays between transducers 3 and 5, two electrode arrays 6 and 8 are in the MC configuration, while the other three arrays 4, 7 and 10 are in the GC configuration.

[0195]

[0165] The arrays are arranged as shown in [Fig. 10], with electrode array 6 sandwiched between electrode arrays 7 and 4, and electrode array 8 sandwiched between electrode arrays 4 and 10.

[0196]

[0166] In this embodiment of the invention, electrode arrays 6 and 8 are identical and comprise Bragg mirrors with 16 electrodes, respectively grouped under references 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. Electrode arrays 6 and 8 are in an open circuit OC configuration; they are not connected to any electrical potential, so their connection is said to be floating, and the 16 electrodes, 61 and 81, are isopotential. Mirrors can comprise more or fewer electrodes. In an alternative configuration, mirrors 6 and 8 may have different numbers of electrodes.

[0197]

[0167] 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 by 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 be different between electrode arrays 4, 7 and 10.

[0198]

[0168] In the embodiment of the invention shown in [Fig. 10], the array of electrodes 111, 113 and 115 of comb 101 is connected to a predetermined electrical potential, in this case ground 999. The array of electrodes 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.

[0199]

[0169] The elastic wave device 600 further comprises a control means 907 which is connected to the variable impedance 903 and enables, in addition to passively correcting the frequency drift due to temperature variations, the value of the variable impedance to be controlled and modified, in particular, remotely, during operation, or not, of the device 600.

[0200]

[0170] Thanks to the optional control means 407, 707 and 907, the variable impedances 403, 703 and 903 can further be controlled individually or jointly.

[0201]

[0171] Electromechanical devices 3 and 7 are separated by the distance d9, 7 and 6 by the distance d10, 6 and 4 by the distance d11, 4 and 8 by the distance d12, 8 and 10 by the distance d13, 10 and 5 by the distance d14. Electromechanical devices 3, 7, 6, 4, 8, 10 and 5 are separated by distances that can be different. In an advantageous embodiment of the invention, as shown in [Fig. 10], these distances may be the same.

[0202]

[0172] 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 just once. In [Fig. 10], the device 600 has the pattern GC - MC - GC - MC - GC, and thus repeats the pattern GC - MC - GC 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 bands (below and above the bandwidth) when compared to the embodiment shown in [Fig. 6].

[0203]

[0173] In a further embodiment, an elastic wave device can be realized which comprises three transducers instead of two. This device comprises at least one electrode array as described for the embodiments of [Fig. 1], [Fig. 2], [Fig. 3], [Fig. 6], [Fig. 9] or [Fig.

[0204] 10] and having a variable impedance arranged between the first transducer and the second transducer and between the second transducer and the third transducer. The result is a dual-mode SAW (DMS) filter that is frequency agile.

[0205]

[0174] In all the alternative embodiments of the invention presented here and in all the other possible alternatives, the second electromechanical device 5 can be a transducer or else an array of electrodes configured to reflect at least partially the waves emitted by the first electromechanical device 3, in particular, it can be a Bragg mirror. Similarly, the predetermined electrical potentials to which electrode arrays 4000, 7, 4, 6a, 10 or any other electrode array between electromechanical elements 3 and 5 present in alternative configurations of the invention are connected may be the same reference potential, in particular, ground, or different from each other.

Claims

CLAIMS1. An elastic wave device (10000) comprising:one or more variable impedance means (1003, 2003, 3003, 10400), wherein each variable impedance means (1003, 2003, 3003, 10400) comprises a capacitor configured to change capacity depending on temperature variation to compensate for a frequency shift of an operating frequency of the elastic wave device caused by the temperature variation;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); andan 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).

2. The elastic wave device (10000) according to claim 1, wherein the first (3, 11130) and the second electromechanical device (5, 11140) are transducers formed by interdigitated comb electrodes.

3. The elastic wave device (10000) according to claim 1 or 2, wherein the capacitor comprises a class 1 capacitor dielectric, in particular, a ceramic capacitor dielectric.

4. The elastic wave device (10000) according to one of claims 1 to 3, wherein the capacitor presents a capacity depending on the temperature and is configured so as its capacity varies in function of a temperature variation to compensate for frequency shift of an operating frequency of the elastic wave device caused by the temperature variation.

5. The elastic wave device (10000) according to one of the preceding claims, further comprising control means (1007, 2007, 3007, 10300) configured to control thevariable impedance means (703, 1003, 2003, 3003, 10400).

6. The elastic wave device (10000) according to claim 5, wherein the control means (707) are configured to open or close an electrical connection of the 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.

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

8. The elastic wave device (10000) according to one of claims 1 to 7, wherein the array of at least one electrode (4000, 7) comprises multiple, in particular, parallel stripshaped, electrodes (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).

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

10. The elastic wave device (10000) according to claim 4 or 5, wherein the electrodes of a second electrode subset of the array of at least one electrode (4000, 7) are connected each other and to a floating electrical potential or connected to a predetermined electrical potential, in particular, ground.

11. The elastic wave device (10000) according to claim 10, wherein the first and second subsets are arranged such that the electrodes of the first subset and the electrodes of the second subset are interdigitated with respect to each other.

12. The elastic wave device (10000) according to one of claims 1 to 11, 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 spaces and wherein, in particular, the distances between respective two adjacent electrode arrays of the plurality of electrode arrays are the same.

13. The elastic wave device (10000) according to one of claims 1 to 12, 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).

14. The elastic wave device (10000) according to one of claims 1 to 13, 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 × λ, where A is the wavelength of the fundamental mode of surface elastic waves emitted by the first electromechanical device (3, 11130).

15. The elastic wave device (10000) according to claim 14, 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 ).

16. The elastic wave device (10000, 11000) according to one of the preceding claims, wherein the device (10000, 11000) is configured to have a bandwidth comprised between a first frequency f1 and a second frequency f2, and at least the first electromechanical device (3, 11130), the second electromechanical device (5, 11140), and the array (4000, 11150) of at least one electrode (1000, 2000, 3000) are configured so that their respective anti-resonance frequency fAR is higher than the first frequency f1, and so that their respective resonance frequency fR is lower than the first frequency f1.

17. The elastic wave device (10000, 11000) according to one of the preceding claims, wherein the elastic wave device (11300, 11500) is configured to have a bandwidth comprised between a first frequency f1 and a second frequency f2, and at least the first electromechanical device (3, 11130), the second electromechanical device (5, 11140), and the array (4000, 11150) of at least one electrode (1000, 2000, 3000) are configured so that their respective anti-resonance frequency fAR is comprised between f1 and f2, and so that their respective resonance frequency is lower than f1.

18. A filter comprising an elastic wave device (10000) according to one of the preceding claims.

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