CN117321914A

CN117321914A - Resonator device

Info

Publication number: CN117321914A
Application number: CN202280035465.3A
Authority: CN
Inventors: G·皮亚扎; G·维达尔·阿尔瓦雷斯
Original assignee: Sibaichuang Microsystems Co ltd
Current assignee: Sibaichuang Microsystems Co ltd
Priority date: 2021-05-19
Filing date: 2022-05-18
Publication date: 2023-12-29
Also published as: WO2022243908A2; IT202100013004A1; WO2022243908A3

Abstract

A resonator device comprising a layer of piezoelectric material (2), the layer of piezoelectric material (2) having a pair of end faces (3, 4) thereon to selectively produce acoustic waves propagating from the end faces (3, 4); at least one layer (5) of metallic material, which is placed directly on the respective end face (3, 4) of the piezoelectric material (2). The metal material layer (5) constitutes an electrode adapted to interact with a corresponding face (3, 4) of the piezoelectric material layer (2). The metal material layer (5) also constitutes a reflector for the acoustic waves generated by the piezoelectric material (2).

Description

Resonator device

Technical Field

The present invention relates to the technical field of electronic devices for generating and processing electrical signals, the subject of which is a resonator device.

Background

It is well known in the field of miniaturized electronic devices that it is necessary to make devices suitable for filtering electrical signals, in particular electrical signals having a small form factor.

A typical solution to this need is to construct an acoustic resonator on the basis of thin films of piezoelectric material arranged layer by layer.

These acoustic resonators are greatly reduced in size compared to circuits based on electromagnetic counterparts.

The operation of the acoustic resonator is based on the generation and processing of sound waves, and a part of these circuits is used for synthesizing radio frequency filters (RF filters).

In particular, there are two main classes of acoustic resonators currently used in microelectronic circuits, such as those used in mobile radio technologies (4G and 5G).

The first type of resonator is represented by Surface Acoustic Wave (SAW) resonant acoustic devices, which mainly employ a relatively simple structure and can be obtained at relatively low cost.

SAW resonators are used in electronic circuits with frequencies below 2 GHz.

The second type of resonator comprises a Bulk Acoustic Wave (BAW) resonant acoustic device. Such devices are more complex and expensive than SAW resonators, and are mainly used in applications with frequencies above 2 GHz.

Some BAW devices may also be used for frequencies below 2GHz when design data requires high performance in terms of efficiency and thermal drift stability.

The 5G standard requires that the acoustic resonator be capable of performing a filtering function at frequencies above 3 GHz.

In fact, the new Wi-Fi standard also requires that the filtering system operate between 5GHz and 7 GHz.

The selected thickness of the other components defining the piezoelectric film layer and resonator determines the resonant frequency of the BAW device.

The new 5G standard presents problems for BAW technology because extremely thin piezoelectric films must be used in order for the filter device to be able to operate at frequencies above 3 GHz.

Furthermore, in current electronic devices, the radio frequency filtering must be performed in a very small form factor.

Therefore, acoustic resonators based on thin films of piezoelectric material arranged layer by layer are used, which has the advantage of being smaller than electromagnetic devices themselves. There is a large class of acoustic resonators that have been put on the market for synthesizing RF filters.

Thus, new communication standards require that BAW devices be manufactured based on very thin films, enabling the BAW devices to be used at higher frequencies than those currently used.

For example, resonator devices with operating frequencies above 5GHz require the use of piezoelectric films with a thickness of about 300 nm.

In addition, the shrinking of the electrode requires the use of metals having a thickness of less than 100 nm.

This extreme reduction in thickness of the layers making up the piezoelectric device is associated with an increase in electrical losses and a significant reduction in device operating signal power.

If the size is further reduced so that the operating frequency exceeds 10GHz, the difficulty is great, and in fact, if the thickness is extremely reduced, it is difficult to accurately set the operating frequency of the device.

As a result, the electrical losses can increase significantly, thereby compromising the overall efficiency of the resonator device.

Disclosure of Invention

The present invention aims to overcome the above-mentioned technical drawbacks and to provide a resonator device which enables high efficiency even when operating in a particularly high frequency range.

In particular, the main object of the present invention is to provide a resonator device consisting of several layers, the thickness of which is easily obtainable by means of existing production techniques.

Another object of the invention is to provide a resonator device that is particularly inexpensive to manufacture.

Another object of the invention is to provide a resonator device that is capable of operating in a particularly accurate manner at very high frequencies, even above 5GHz or 10 GHz.

It is a further object of the invention to provide a resonator device whose electrical characteristics remain unchanged over time, i.e. a device which is minimally affected by changes in environmental parameters such as temperature and humidity.

Furthermore, it is another and equally important object of the present invention to provide a resonator device configured to allow filtering of signals associated with high data capacities.

These objects, as well as other objects, which will be described in more detail below, are achieved by a resonator device of the type according to claim 1.

Other objects, which will be described in more detail below, are achieved by a resonator device according to the dependent claims.

Drawings

The advantages and features of the invention will become apparent from the following detailed description of some preferred but non-limiting embodiments of the acoustic device, with particular reference to the following drawings, in which:

FIG.1 shows a schematic top view of a first embodiment of an acoustic resonator device;

fig.2 shows a cross-section of the device according to the invention in a first embodiment;

fig.3 shows a cross-section of the device according to the invention in a second embodiment.

Detailed Description

The present invention relates to an acoustic resonator device for generating and/or filtering electrical signals having frequencies within a predetermined range in the electronic field.

More specifically, the acoustic resonator device, which is the subject of the present invention, is particularly suitable for facilitating the generation/filtering of electrical signals belonging to the radio frequency range, typically in the frequency range of 1.5GHz to 30 GHz.

The term "acoustic resonator device" as used herein refers to an electronic oscillator device capable of converting an electrical signal into a mechanical wave (referred to as an acoustic wave) that is generated inside the device due to dimensional deformation (or mechanical vibration) of the component.

The working principle of an acoustic resonator device is therefore based on the propagation of mechanical waves (also called acoustic waves) inside it, said waves having a predetermined amplitude and mode trend. By propagation of these acoustic waves, an electrical signal having a predetermined characteristic can be generated across the respective electrodes associated with the resonator.

Thus, a resonator device may be defined as a device adapted to convert an electrical signal across an electrode into an acoustic wave propagating inside the device (and vice versa).

By utilizing such characteristics, an electronic oscillator, i.e., a device adapted to generate a periodic electric signal centered on a predetermined frequency band, can be manufactured.

In addition, resonator devices may also be used to fabricate electronic filtering elements to provide at their outputs a portion of the frequency spectrum associated with the input signal (e.g., selective bandpass filters, high-pass or low-pass filters, bandstop filters, etc.).

The resonator device, which is the subject of the present invention, is indicated in the accompanying drawing by reference numeral 1, and is mainly used as a filtering element for radio frequency devices used in 5G technology and related new standards.

In particular, fig.1 to 3 show a resonator 1 designed for operation above 5GHz, in particular above 10 GHz.

However, it is to be understood that these embodiments of the invention are merely illustrative and that the innovative features described below can also be reproduced in other types of RF resonators whose operating frequency bands differ from the frequency bands described above.

Furthermore, the acoustic resonator 1 described below can also be used as an oscillator and/or filter element adapted to different frequency intervals, but not necessarily belonging to the radio frequency range.

The acoustic resonator 1 as subject of the invention has a laminated structure, which is laminated from different types of materials.

The cross-sectional view of the structure can be seen in fig.2 and 3, whereas in the plan view seen in fig.1, the shape of the layers may vary depending on the design specifications or installation environment of the device 1.

Fig.2 and 3 show resonator devices of different geometries obtained by modifying the planar shape of the layers.

The device 1 comprises first a layer 2 of piezoelectric material extending between a pair of end faces 3, 4.

The geometry of the layer 2 in plan view may correspond to a regular polygon (e.g. square, rectangular, trapezoid or any other polygon) with n sides.

Advantageously, the piezoelectric material 2 is of monocrystalline type or polycrystalline type, chosen from the group comprising one of the following materials: aluminum nitride, lithium niobate, lithium tantalate, quartz, zinc oxide, lead zirconate titanate, and other materials having similar electromechanical properties.

The material used for manufacturing the piezoelectric layer 2 may be selected from the materials specified above, but may be obtained at different doping values of the materials specified above.

The resonator device 1 further comprises one or more additional layers in direct contact with the respective face 3 or the respective face 4 (or both respective faces 3, 4) of the layer 2 of piezoelectric material.

This additional layer is denoted in the figures by reference numeral 5 and is mainly characterized in that it is made of a metallic material or an alloy of metallic materials.

This, in combination with the other characteristics mentioned below, enables the metallic material layer 5 to have two functions:

first, said layer 5 constitutes an electrode of the resonator device, which is capable of exciting the layer 2 of piezoelectric material in a manner that promotes the generation of acoustic waves;

secondly, said layer 5 also constitutes a reflector, which is capable of (at least partially) reflecting the acoustic waves generated by the layer 2 of piezoelectric material.

More advantageously, the metallic material layer 5, which is directly placed on one (or both) of the faces 3, 4 of the piezoelectric material layer 2, can perform both functions (electrode and reflector) at the same time.

The presence of the metallic material layer 5 has some important advantages, the metallic material layer 5 being advantageously designed to be in direct contact with the faces 3, 4 of the material forming the piezoelectric layer 2.

In general, in resonators known in the art, the electrodes do not have reflective properties, and therefore the element is integrated in the resonant cavity of the device.

In the present invention, the term "resonant cavity" refers to a geometrical space having a predetermined size in which most of the energy associated with the mechanical wave generated when the active material (i.e., the piezoelectric material 2) oscillates is located.

Generally, the energy associated with an acoustic wave residing within a resonant cavity exceeds 95% of the total energy associated with the acoustic wave generated by the piezoelectric material.

It is known that a resonant device can only work properly when the resonant cavity has a predetermined size selected according to the wavelength, typically a multiple of half the wavelength.

Therefore, the thickness of the electrode should be reduced as much as possible to minimize its effect in the resonant cavity; thus, the thickness of the resonant cavity is primarily determined by the layer of piezoelectric material.

In the resonator device of the invention, the electrodes have been incorporated into the metal layer 5, and the metal layer 5 also has the additional function of reflecting the sound waves generated by the layer 2 of piezoelectric material.

In this configuration the electrode is no longer part of the resonator (the resonator is entirely determined by the thickness of the piezoelectric material) but is "buried" in the layer 5, the layer 5 also functioning as an acoustic reflector.

This solution has many advantages: first, compared with the known technique, the thickness s of the piezoelectric material ₂ May be larger because the entire resonant cavity is composed and defined only of piezoelectric material (and no longer a combination of piezoelectric material and electrodes).

In addition to the above, the thickness of the electrodes is much thicker than in the presently known resonators, since the dimensions of these elements must now correspond to the dimensions of the reflector, which is known to be equivalent to a quarter wavelength or a multiple thereof.

In a first configuration of the resonator device 1, the layer 5 of metallic material suitable for constituting the electrodes and acoustic reflectors may be a single layer and may therefore be in contact with the faces 3, 4 of the layer 2 of piezoelectric material.

This example is illustrated in the device shown in fig.2, in which a single metal layer 5 on the lower surface 3 of the piezoelectric material 2 is used.

For the device to function properly, the layer 2 of piezoelectric material must always be located between a pair of electrodes.

In this case the resonator 1 has an additional electrode, indicated with reference number 6, comprising a layer of conductive material.

This configuration is clearly illustrated in fig.2 and 3.

However, the electrode 6 is not suitable for use as an acoustic reflector and thus functions entirely similar to the electrodes known in the prior art.

The electrode 6 is in direct contact with the face 4 of the layer 2 of piezoelectric material, the face 4 of the layer 2 of piezoelectric material being opposite to the face on which the layer 5 of metal is arranged.

In the case shown in the figures, the electrode 6 is in direct contact with the upper surface 4 of the layer 2 of piezoelectric material.

Advantageously, the electrode 6 may have a predetermined thickness s ₆ 。

In another embodiment of the resonator device 1, multiple layers of metallic material 5 may be used.

For example, there may be two layers of metallic material 5, each located in a relative position to the layer of piezoelectric material 2.

The layer 2 of piezoelectric material is then sandwiched between two layers 5 of metallic material, the two layers 5 of metallic material being in direct contact with the respective faces 3, 4 of the layer 2 of piezoelectric material.

This configuration is not shown in the figure.

Alternatively, the resonator device 1 may comprise a stack of metal material layers 5, i.e. a plurality of metal layers 5 superimposed on each other.

Thus, the stacked first layers 5 are in direct contact with one face 3 of the piezoelectric material layer 2.

Fig.3 illustrates this configuration.

In this case the electrodes are distributed over substantially the entire thickness of the stack of layers of metallic material 5, since each layer of the stack has conductive properties.

Furthermore, each metal layer 5 in the stack also has the function of a reflector, and therefore by stacking these layers, a cascade of acoustic reflectors can be obtained, each adapted to reflect a portion of the incident acoustic wave propagating from the piezoelectric material 2.

As shown more clearly in fig.1, the conductive metal material layer 5 as an electrode may be dimensioned to entirely or partially cover the end faces 3, 4 of the piezoelectric material 2 with which it is in contact.

Advantageously, as shown more clearly in fig.1, the metallic material layer 5 may be sized to cover only a portion of the end faces 3, 4 of the piezoelectric material 2.

If an electrical signal is applied to the metal material layer 5 as an electrode, the electrical signal is only suitable for promoting excitation of the region of the piezoelectric material 2 covered by the metal material layer 5 (i.e. the region of the piezoelectric material 2 located below the metal material layer 5).

In other words, the portion of the piezoelectric material 2 covered by the metal material layer 5 as an electrode is a portion where the material itself is exclusively suitable for generating acoustic waves. Thus, the acoustic wave will propagate outwards only from the portion of the faces 3, 4 of the piezoelectric material that is in the excited state (corresponding to the area of the faces 3, 4 that is covered by the layer 5 of metallic material).

In general, the lateral extension of the metal material layer 5 as electrode is greater than the lateral extension of the end faces 3, 4 of the piezoelectric material 2, so as to define suitable bosses 7 suitable for being connected to other electrical circuits electrically connected to the resonator.

In particular, the protrusion may be two-dimensional, extending between a small end 8 (suitable for being superimposed on the faces 3, 4 of the layer of piezoelectric material 2) and an opposite end 9, the opposite end 9 protruding from the layer of piezoelectric material 2 and having a maximum dimension for connection to other electrical or electronic circuits.

The metallic material layer 5 may be substantially polygonal in shape in plan view (e.g., regular or irregular polygonal), and may include at least one circular or semicircular portion, as shown in fig. 1.

Advantageously, the layer 2 of piezoelectric material has in fact substantially isotropic physical properties with respect to the two end faces 3, 4.

Thus, energizing the piezoelectric material 2 (e.g., by applying an electrical signal to a pair of electrodes) means facilitating the generation of two substantially identical mechanical waves that propagate in the longitudinal direction Z (extending perpendicular to the faces 3, 4), but in opposite directions.

The propagation direction Z furthermore passes through all other material layers constituting the resonator 1, which material layers face or are superimposed on the two faces 3, 4 of the piezoelectric material layer 2.

As mentioned above, sound waves generated by vibrations applied to the piezoelectric material 2 tend to be "retained" in the device 1 by a plurality of reflectors arranged on opposite sides with respect to said face of the piezoelectric material.

It is possible to induce resonance conditions by retaining acoustic waves in the layers of the device 1, thereby facilitating the generation of resident acoustic waves.

The portion of the oscillating standing wave that is gradually transmitted (not reflected) between the layers represents the loss of the resonator device 1.

Obviously, the device 1 should be designed to minimize this loss, making it easier for the acoustic waves to remain resident.

As is well known, the first acoustic reflector 11 and the second acoustic reflector 12 function to partially reflect the mechanical waves generated by the layer 2 of piezoelectric material (and from the faces 3, 4 thereof) in order to maintain the resonator 1 in an active resonant state for as long as possible.

In this context, reference numeral 5 in fig. 1-3 denotes both the metal layer and the corresponding electrode and acoustic reflector defined by the metal layer.

An additional reflector consisting of layers of materials other than metal is indicated by reference numeral 10 and is described in more detail below.

It is well known that in the prior art of resonators 1, the reflective layers 5, 10 are not capable of totally reflecting incident sound waves, in practice the reflection losses are generally lower than 1% (that is to say, the reflective layers are capable of reflecting more than 99% of the incident mechanical waves and transmitting less than 1% of the sound waves to the next layer).

The layers 5 made of metallic material may also act as reflectors, so that they may consist of a plurality of sub-layers 11, 12, the sub-layers 11, 12 being composed of a low acoustic impedance metallic material and a high acoustic impedance metallic material, respectively.

The metal layer 11 with low acoustic impedance may be made of a thin film or an alloy of one or more of the following materials: copper and aluminum.

The layer 12 having high acoustic impedance may be made of a film or alloy of one or more of the following materials: tungsten, molybdenum, tantalum nitride, gold, platinum, ruthenium, iridium, and alloys of these materials.

Advantageously, each layer of metallic material suitable for defining the reflector may have an X layer of high resistance material 12 and a Y layer of low resistance material 11.

This embodiment can be seen in the device shown in fig. 3.

In particular, the total number of layers X of the high-resistance material sub-layer 12 and the total number of layers Y of the low-resistance material sub-layer 11 contained in the single metal reflector 5 may be the same (x=y) or different (x+notey).

For example, there may be only one sub-layer 11, 12 (x=y=1), and the maximum number of layers of the sub-layers 11, 12 may be variable and determined by construction and/or design requirements.

However, when the number of one of the sublayers 11, 12 is greater than 1 (X >1 and/or Y > 1), the arrangement of sublayers always alternates, i.e. there is one layer of opposite type between two layers of the same type.

For example, if x=2, y=1, a single low-resistance metal sublayer 11 is located between two high-resistance metal sublayers 12, whereas in the case of x=y=4, the corresponding reflector 5 is constituted by four identical pairs superimposed, each pair being constituted by a high-resistance metal sublayer 12 and a low-resistance metal sublayer 11 connected.

In addition to the above, the low-resistance sublayer 11 and the high-resistance sublayer 12 may have respective predetermined thicknesses s ₁₁ 、s ₁₂ The method comprises the steps of carrying out a first treatment on the surface of the Thus, the metal layer 5 has a predetermined thickness s ₅ The predetermined thickness is defined by the thickness s of the low-and high-resistance metal sublayers 11, 12 constituting it ₁₁ 、s ₁₂ Sum(s) ₅ ＝s ₁₁ +s ₁₂ ) And obtaining the product.

Thickness s of metal sub-layer 12 made of high resistance material ₁₂ And thickness s of metal sublayer 11 made of low-resistance material ₁₁ Which varies according to the frequency of the acoustic wave generated by the layer 2 of piezoelectric material.

More specifically, the thickness s of each sub-layer 11, 12 of high and/or low acoustic impedance material may be selected ₁₁ 、s ₁₂ Which is made proportional to a part of the period of the acoustic wave lambda propagating in the sub-layer.

The acoustic wave propagates in the respective metal sublayers 11, 12 with a predetermined propagation speed, which varies depending on the material type of the layer itself.

Thus, each sub-layer 11, 12 defines its own acoustic travel time. The time may be defined as the time interval required for each point of the sound wave to pass through the thickness of the end face separating the respective sub-layer 11, 12.

In other words, the propagation time can be calculated as the thickness s of the respective sub-layer 11, 12 ₁₁ 、s ₁₂ And the propagation velocity of the acoustic wave in the same layer.

Advantageously, the thickness s of the metal sublayers 11, 12 can be chosen ₁₁ 、s ₁₂ Such that a predetermined portion of the acoustic wave period propagates through the end face of the material during the propagation time calculated as described above.

For example, the thickness s of the low acoustic impedance sublayer 11 ₁₁ And thickness s of high acoustic impedance layer 12 ₁₂ Alternatively, one quarter cycle (pi/2) or three-quarters cycle (3/2 pi) is allowed to propagate.

Advantageously, the device may comprise, in addition to the layer of metallic material, one or more reflecting layers 10 made of insulating material.

Also in this case, the reflection layer 10 made of an insulating material may include a first sub-layer 13 made of a low acoustic impedance insulating material and a second sub-layer 14 made of a high acoustic impedance insulating material.

Advantageously, the resonator 1 may be configured to comprise a plurality of reflectors 10 made of insulating material and stacked on top of each other.

Thickness s of each reflector 10 made of insulating material ₁₀ Can be formed by the thickness s of the high-resistance sublayer 13 and the low-resistance sublayer 14 constituting the same ₁₃ Sum s ₁₄ Is derived from the sum of (a).

More specifically, the thickness s of the sublayers 13, 14 that make up each reflector 10 ₁₃ 、s ₁₄ It may be chosen such that a variable dimensional relationship is satisfied as a function of the phase length t_p associated with the excitation pattern through the same layer.

Advantageously, in the field of resonator technology, the propagation time is also referred to as the "phase length". The following relationship can be defined by the symbol t_p for the phase time, s for the thickness of a given reflective layer and/or piezoelectric material, and v_p for the propagation velocity of the acoustic wave within the same layer:

t_p＝s/v_p

further, as used herein, "vibration mode" or "excitation mode" refers to a characteristic mode of vibration associated with a system or structure having multiple points of different amplitudes.

The vibration modes include i) temporal variations in vibration, and ii) spatial variations in the amplitude of motion through the structure.

The time variation determines the frequency of the oscillation.

The spatial variation defines different vibration amplitudes from one point of the structure to another.

The sub-layers 13, 14 made of a high-or low-impedance material define each individual reflector 10 of the plurality of reflectors 10 used in the resonator 1, the sub-layers 13, 14 may be selected to have a thickness s that varies according to the following relationship ₁₃ 、s ₁₄ :

s _1x ＝(2N+1)*(π/2)

Wherein:

s _1x is the thickness of the respective sub-layer 13, 14;

n is a positive integer (1, 2, 3.);

pi/2 corresponds to one quarter of the period of the excitation mode (where 2 pi = period of the excitation mode).

Thus, according to this relationship, the sublayers 13, 14 constituting one or more reflectors 10 made of insulating material may have a thickness s chosen according to the following series, with respect to the period 2 pi of the mode excited by the layer 2 of piezoelectric material ₁₃ 、s ₁₄ ：

3*π/2；5*π2；7*π/2；9*π/2；11*π/2；13*π/2...

In addition, other reflectors 10 made of insulating material and intended for the same resonator 1 may have sublayers 13, 14 made of high-or low-impedance material, each of thickness s ₁₃ 、s ₁₄ Is selected to be substantially equal to one quarter of the period of the excitation pattern, i.e. the following relation is satisfied:

s _1x ＝π/2

wherein the method comprises the steps of

s _1x Is the thickness of the respective sub-layer 13, 14;

Thus, in essence, the acoustic resonator 1 as subject of the invention may comprise a stack of reflectors 10 made of metallic material.

The reflector in the stack near the layer 2 of piezoelectric material may be constituted by sublayers 13, 14, the sublayers 13, 14 having a thickness s ₁₃ 、s ₁₄ Is selected to meet the following series of requirements:

3*π/2；5*π/2；7*π/2；9*π/2；11*π/2；13*π/2…

the remaining reflectors 10 made of insulating material are stacked and kept at a larger distance from the piezoelectric material layer (compared to the distance of the reflectors 10 described in the previous paragraph), and the remaining reflectors 10 may be made of sublayers 13, 14, the thickness s of which ₁₃ 、s ₁₄ Is selected to meet the following series of requirements:

s _1x ＝π/2

i.e. equal to a quarter wave of the excitation pattern of the layer 2 of piezoelectric material.

In this way, the thickness of the insulating layer 10 is made greater near the piezoelectric material layer and smaller at a distance therefrom.

Thus, by suitably adjusting the thickness of the sub-layers according to the above-mentioned relation, the reflector 10 of insulating material can effectively reflect different types of sound waves, i.e. i) shear stress waves (the propagation component of which is also substantially in a direction perpendicular to Z), and ii) longitudinal stress waves (the propagation of which is thus substantially parallel to Z), with reduced losses.

The considerations in the preceding paragraphs (with respect to the embodiment of the metal reflector 5) with respect to the location of the sublayers 13, 14, the number and thickness of the sublayers 13, 14 apply equally to reflectors 10 made of an insulating material.

Advantageously, the sub-layer 13 of insulating material with low acoustic impedance may be selected from the group comprising silicon dioxide, spin-on glass, tellurium oxide and silicon oxycarbide.

In addition, the sub-layer 14 of insulating material having a high acoustic impedance may be selected from the group comprising aluminum nitride and respective oxides of tungsten, platinum, molybdenum, ruthenium.

The device may comprise at least one layer 15 of insulating material, which may have a defined low acoustic impedance or a rather high acoustic impedance, as the case may be. The layer 15 may have a predetermined thickness s ₁₅ 。

Layer 15 does not have reflective properties and may be made, for example, of a film of one of the following materials: silicon dioxide, silicon oxide, tellurium oxide, spin-on glass, and other materials based on these materials but with the addition of dopants or impurities.

The low acoustic impedance layer 15 or the high acoustic impedance layer 15 mainly compensates for the thermal drift experienced by the piezoelectric material layer 2.

It is well known that the frequency (and/or frequency band) of oscillation associated with the piezoelectric material 2 varies with the temperature of the environment in which the layer is located.

In the field of resonator technology, this condition is referred to as the "temperature coefficient of frequency", which represents the frequency as a function of temperature (typically, the frequency in units of degrees celsius varies by a few tens of parts per million of standardized frequency). Thus, the temperature coefficient of frequency is 10 parts per million (i.e., the operating frequency value in hertz ^-6 ) Representing the parameters of the change.

When the temperature increases and the oscillation frequency decreases, the frequency temperature coefficient is negative.

Conversely, when the temperature increases, the temperature coefficient of the frequency becomes positive as the oscillation frequency increases.

In general, the temperature coefficient of the frequency of the piezoelectric material 2 over the entire operating range of the material itself is negative (i.e., the oscillation frequency only decreases with increasing temperature).

Therefore, the material layer 15 having low or high acoustic impedance has a positive temperature coefficient of frequency, that is, its internal structure promotes an increase in operating frequency with an increase in temperature.

In this way, the assembly of the piezoelectric material layer 2 and the low-or high-impedance layer 15 can reduce thermal drift (referred to as operating frequency).

In particular, the oscillation frequency variations (caused by temperature variations) associated with the piezoelectric layer 2 are substantially counteracted (or greatly reduced) by the opposite sign of the frequency variations associated with the behaviour of the layer 15 made of low-impedance or high-impedance material.

Furthermore, it is also possible/necessary to insert two layers of different low-or high-impedance material 15, 15', each facing a respective face 3, 4 of the layer 2 of piezoelectric material.

Advantageously, the electrode 6 is always superimposed with a layer of insulating material 15 of low or high resistance, the electrode 6 being in direct contact with the faces 3, 4 of the layer 2 of piezoelectric material.

Another layer of low or high impedance material 15' (optional) is then superimposed on the final reflector 10 of insulating material.

Advantageously, any one of the layers of low-or high-impedance insulating material 15, 15' may be made of the same material or of different materials having similar chemical-physical characteristics; thus, the layers 15, 15' have substantially the same dynamic characteristics when acoustic waves generated by the layer 2 of piezoelectric material pass through them.

According to a particular aspect of the invention, the thicknesses of the material layers constituting the resonator 1 subject of the invention are chosen so as to satisfy the dimensional relationships indicated:

thickness s of layer 2 of piezoelectric material ₂ Substantially corresponding to a multiple of half the wavelength of the acoustic wave generated by the layer after excitation (s ₂ ＝N*λ/2)；

Thickness s of the metal reflective layer/electrode 5 in direct contact with one face 3, 4 of the piezoelectric material 2 ₅ Is substantially a multiple of half the wavelength of the acoustic wave generated by the layer of piezoelectric material (s ₁₅ ＝N*λ/2)；

Can be represented by the reference letter (s _{6_15} ) To define the thickness s of the electrode 6 (placed on the faces 3, 4 of the layer 2 of piezoelectric material) ₆ And the thickness s of the low or high acoustic impedance insulating layer 15 superimposed on the electrode 6 ₁₅ And (3) summing; thickness s _{6_15} Is substantially equivalent to a multiple of half the wavelength of the acoustic wave generated by the layer of piezoelectric material (s _{6_15} ＝N*λ/2)。

In the above relationship, the letter N represents a natural integer greater than or equal to 1 (n=1, 2, 3.

According to the above, the thickness s ₂ 、s ₅ Sum s _{6_15} The value of (c) may be equal to λ/2 (minimum) or equal to a multiple of λ/2 (i, 3λ/2).

For example, a predetermined thickness s of the piezoelectric material layer 2 ₂ May be between 100nm and 5000nm, while the thickness s of these layers 15 with low or high acoustic impedance ₁₅ And may be between 50nm and 10 pm.

Thickness s of electrode 6 ₆ And thickness s of the non-reflective insulating-material layer 15 with low acoustic impedance ₁₅ Are less than lambda/2 if considered alone.

However, these thicknesses s ₆ 、s ₁₅ Selected such that their sum s _{6_15} At or near a constant value of lambda/2 (or a multiple of lambda/2).

Furthermore, in case the resonator 1 has an additional non-reflective layer 15' (with low or high acoustic impedance) superimposed on the insulating reflector 10 (or on the last insulating reflector 10 of the stack), even the corresponding thickness s of this additional layer 15 _15' Also at or near N x/2.

As used herein, a "high acoustic impedance layer" and a "low acoustic impedance layer" are relative terms. In fact, the layer made of low impedance material has a first predetermined impedance value (with respect to the passage of the acoustic wave) that is lower than the impedance value of the different layer made of high acoustic impedance material.

In contrast, a layer made of a high impedance material has a second predetermined impedance value (relative to the passage of sound waves) that is higher than the impedance value of a different layer made of a low acoustic impedance material.

In other words, the first impedance value associated with the low acoustic impedance material layer is always lower than the second impedance value associated with the high acoustic impedance material layer (and vice versa).

Advantageously, the resonator may be anchored to the substrate 16, the substrate 16 preferably being made of a high acoustic impedance material. For example, the substrate 16 may be selected from the following materials: silicon, silicon carbide, sapphire, lithium niobate, lithium tantalate, glass, quartz, aluminum nitride, and diamond.

Advantageously, the teachings described with reference to the present invention are also applicable to resonators designed to operate using fundamental mode harmonics (in which case the fundamental mode corresponds to one of the attenuation modes).

The invention is capable of other modifications and all such modifications are intended to be within the scope of the inventive features as claimed and described herein; these technical features may be replaced by different elements and materials that are technically equivalent; the shape and size of the present invention may be any shape and size as long as it matches the use of the present invention.

The numerals and signs included in the claims and description are only for the purpose of increasing the clarity of the text and should not be construed as limiting the technical interpretation of the objects or processes they determine.

Claims

1. A resonator device, comprising:

-a layer of piezoelectric material (2) having a pair of end faces (3, 4), the layer of piezoelectric material (2) being adapted to selectively generate an acoustic wave having a predetermined wavelength (λ), the acoustic wave propagating from the end faces (3, 4) of the layer of piezoelectric material (2) in a predetermined propagation direction (Z);

-at least one layer (5) made of metallic material in direct contact with a respective face (3, 4) of the layer (2) of piezoelectric material;

-an electrode (6) arranged in contact with the other face (4, 3) of the layer of piezoelectric material (2);

-at least one layer (15) made of insulating material, arranged facing an electrode (6) in contact with the other face (4, 3) of the layer (2) of piezoelectric material;

wherein at least one layer (5) made of metallic material is adapted to define electrodes that interact with respective faces (3, 4) of said layer (2) of piezoelectric material, so that the layer (2) of piezoelectric material is excited and thereby generates acoustic waves;

and wherein at least one layer (5) made of metallic material is adapted to define a reflector for acoustic waves generated by the layer (2) of piezoelectric material;

and wherein the piezoelectric material layer (2), the at least one layer (5) made of a metallic material, the electrode (6) and the at least one layer (15) made of an insulating material have respective predetermined thicknesses (s ₂ 、s ₅ 、s ₆ 、s ₁₅ )；

Characterized in that the thickness (s ₂ ) The thickness(s) of the at least one layer (5) made of a metallic material ₅ ) And a thickness(s) obtained by adding the thicknesses of the electrode (6) and the layer (15) made of an insulating material _6-15 ＝s ₆ +s ₁₅ ) Corresponds substantially to a multiple(s) of half the wavelength associated with the acoustic wave generated by the layer (2) of piezoelectric material ₂ ＝s ₅ ＝s _6-15 ＝N*λ/2)。

2. The device according to claim 1, characterized in that said at least one layer (5) made of metallic material comprises at least one pair of interconnected sublayers (11, 12) made of metallic material, a first sublayer (11) of the pair being made of metallic material with low acoustic impedance and a second sublayer (12) of the pair being made of metallic material with high acoustic impedance.

3. The device according to claim 2, characterized in that the material used for manufacturing the first sub-layer (11) made of a low acoustic impedance metal material is selected from the group comprising aluminum, copper and alloys made of these materials.

4. A device according to claim 2 or 3, characterized in that the material used for the manufacture of the second sub-layer (12) of high acoustic impedance metal material is selected from the group comprising tungsten, molybdenum, tantalum nitride, gold, platinum, ruthenium, iridium and alloys made of these materials.

5. The device according to one or more of the preceding claims, characterized in that it comprises a plurality of layers (5) made of metallic material, which are superimposed on each other so as to form a stack, the first layer (5) made of metallic material of said stack being arranged in direct contact with the respective face (3, 4) of said piezoelectric material (2).

6. The device according to one or more of the preceding claims, characterized in that at least one layer (5) made of a metallic material is larger than the end faces (3, 4) of said layer (2) of piezoelectric material, so that at least one layer (5) made of a metallic material protrudes at least partially from said layer (2) of piezoelectric material.

7. Device according to one or more of the preceding claims, characterized in that said at least one layer (5) made of metallic material is substantially polygonal in plan view.

8. The device of claim 7, wherein at least one metal layer has a shape that is at least partially circular or semi-circular in plan view.

9. The device according to one or more of the preceding claims, characterized in that it comprises one or more reflectors (10) made of insulating material, the reflectors (10) being adapted to reflect at least partially the acoustic waves generated by said layer (2) of piezoelectric material.

10. The device according to claim 11, characterized in that each of said reflectors (10) is constituted by a first sublayer (13) of insulating material of low acoustic impedance and a second sublayer (14) of insulating material of high acoustic impedance.

11. The device according to claim 12, characterized in that the first sub-layer (13) of low acoustic impedance insulating material is selected from the group comprising silicon dioxide, optically active glass, tellurium oxide, silicon oxycarbide.

12. The device according to claim 12 or 13, characterized in that the second sub-layer (14) of high acoustic impedance insulating material is selected from the group consisting of aluminum nitride and the corresponding oxides of tungsten, platinum, molybdenum, ruthenium.

13. The device according to one or more of claims 9 to 12, characterized in that it comprises a plurality of reflectors (10) made of insulating material and stacked on each other along the propagation direction (Z), each reflector (10) made of insulating material having a respective predetermined thickness (s ₁₀ )。

14. The device according to claim 13, characterized in that the thickness (s ₁₀ ) Along the propagation direction (Z) along a path away from the layer of piezoelectric material (2).