RU2633658C2 - Surface acoustic wave resonator - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: surface acoustic wave resonator comprises a substrate made of a piezoelectric material with high electromechanical coupling coefficient, on which surface an interdigital transducer is formed and at least two reflecting structures consisting of arrays of reflectors made with width and repetition period multiple to certain fraction of wave length. The interdigital transducer of the resonator is divided into two sections of electrodes by an acoustic cavity, which length between the two sections of the interdigital transducer is selected from the range 0.01 λ/δfR<L<3.0 λ/δfR, where L is the length of the acoustic cavity, δfR is the relative width of the reflection band of the reflecting structures which can take a value δfR=0.003..0.03, λ - the length of the surface acoustic wave on the free surface at the resonant frequency.

EFFECT: improvement of resonator quality on the surface acoustic waves.

17 cl, 4 dwg

Description

The invention relates to the field of radio engineering, in particular to piezoelectric engineering and acoustoelectronics, and can be used in radio electronics to create frequency-setting devices, including high-frequency signal generators, as well as physical quantity sensors.

The master oscillator generates electrical oscillations of a certain frequency and is designed in such a way that harmonic oscillations in it are excited without external influences. In this process, the main element is a resonator, for example a resonator based on surface acoustic waves (SAWs), which is an oscillating circuit in which, when energy enters it, current oscillations decaying over time. The resonator must have a high Q factor to compensate for the losses that determine the damping of the oscillations. The quality factor determines the width of the resonance and characterizes the ability of the resonator to store the stored energy. The achieved level of technology with the right structural solutions allows us to create resonators with high Q factor. High-Q resonators typically have higher temporal frequency stability (less aging). For resonators with a small value of the quality factor, more aging is more often observed.

From the prior art it is known that the main piezoelectric material for high-Q surfactant resonators are highly stable sections of quartz. Surfactant quartz resonators are used in highly stable frequency-setting oscillators due to the high thermal stability of quartz, which is directly related to its structure and is reflected in the value of the electromechanical coupling coefficient (CEMS), which makes it possible to obtain high-quality resonators. Other piezoelectric materials, such as lithium niobate (LiNbO ₃ ) or lithium tantalate (LiTaO ₃ ), are used in resonators that are used in surfactant filters (I. Zelenka. Piezoelectric resonators based on volume and surface acoustic waves. - M.: Mir, 1990 , 584 p.).

The disadvantage of quartz resonators on surfactants is the propagation loss of the acoustic wave, which increases at high frequencies, causing signal attenuation and a decrease in the quality factor of the resonators. In resonators based on lithium niobate or lithium tantalate at high frequencies, the acoustic loss is much less than in quartz resonators, which is due to the crystal lattice parameters of materials. However crystals on substrates of LiNbO ₃ or LiTaO ₃ also have a low quality factor at high frequencies caused by the large energy losses in the metal structural elements related to high surfactants KEMS for distribution on a free surface, due to the nature of the material.

A resonator based on surface acoustic waves is known from the prior art (European patent for invention EP 0481733 A1, IPC Н03Н 9/02, Н03Н 9/145, Н03Н 9/25, publ. 04/22/1992) containing a piezo-plate made of lithium niobate (LiNbO ₃ ) , on the surface of which an interdigital transducer (IDT) is formed and at least two reflective structures (OS), consisting of arrays of reflectors. An increase in the Q-factor of the resonator in this technical solution is achieved by apodizing (weighting) the interdigital transducer, that is, by selectively changing the overlap (aperture) of the electrodes along the IDT length according to a certain law described by the equation, so that the overlap maximum is in a certain place of the IDT for example in the middle.

The closest in technical essence analogue (prototype) to the claimed invention is a resonator on surface acoustic waves (European patent for invention EP 2239846 A2, IPC Н03Н 9/02, Н03Н 9/145, publ. 13.10.2010), consisting of a piezoelectric plate made from lithium tantalate or lithium niobate, on the surface of which an interdigital transducer and reflective structures located on both sides of the IDT are formed. An increase in the quality factor of the resonator in this technical solution is achieved through the joint use of apodization of the electrodes of the interdigital transducer and the application of a laminating coating on the resonator surface, which improves the temperature characteristics of the device and reduces the piezoelectric activity of the single-crystal substrate material, while not strongly suppressing and not absorbing acoustic waves. Silicon dioxide (SiO ₂ ) or silicon oxynitride (SiON) can be used as a coating.

The disadvantage of the surfactant resonators proposed in the patents EP 0481733 A1 and EP 2239846 A2 is their low quality factor due to the high CEMS of the piezoelectric board material (LiNbO ₃ or LiTaO ₃ ), and signal losses associated with the presence of conductive structural elements in the structure regions determining the quality factor resonator.

The technical result of the present invention is to increase the quality factor of a resonator on a surfactant.

The technical result is achieved by the fact that in a resonator based on surface acoustic waves containing a substrate of piezoelectric material with high ECM, on the surface of which an interdigital transducer IDT and at least two reflecting structures are formed, consisting of arrays of reflectors made with a width and repetition period, a multiple of a certain fraction of the wavelength, the IDT is divided into two sections by an acoustic cavity, the length of which between two sections of IDT electrodes is selected from the range

0.01 λ / δf _R <L <3.0 λ / δf _R ,

where L is the length of the acoustic cavity, δf _R is the relative width of the reflection band of the reflecting structures, which can take the value δf _R = 0.003..0.03, λ is the length of the surface acoustic wave on the free surface at the resonant frequency.

The most important parameters when designing devices for surfactants are, CEM, the reflection coefficient of the surfactant from the electrodes and the speed of the acoustic wave under the electrode structure. The surfactant resonator substrate, as in the prototype, is made of a dense piezoelectric material with high CEM, which leads to a high reflectance of the surfactant from the electrodes, determined by the ratio of acoustic impedances (product of the speed of sound to the density of the material) in the piezoelectric material and metal. The resulting parasitic reflections in the IDT lead to a distortion of the target single-mode characteristic with high Q and to the appearance of many resonances with a lower Q factor. Energy losses increase.

In the proposed technical solution, in contrast to the prototype, separation of IDT, consisting of a small number of electrodes, into two parts and their location along the edges of the region with the free surface of the piezoelectric material is used. This area is an acoustic cavity. It is necessary to increase the length of the IDT, that is, the length of the region in which the interference of the signal reflected from the OS occurs. Together, the two sections of IDT and the free cavity between them represent the IDT of the prototype, but with a much smaller number of electrodes. The removal of metallization that overlaps the IDT aperture helps to conserve the stored energy of the oscillatory system. Reducing the relative wavelength of the wave under the IDT metal with respect to the wavelength of the wave along the free surface reduces the energy loss associated with the reflection of surfactants from metallization. The ratio of the accumulated energy (growing with the path length) to the lost energy for each period of oscillations increases, that is, the quality factor of the oscillatory system increases.

Reducing the distortion of the target signal and increasing the quality factor of the resonator is also achieved by reducing the effective CEMS in the structure. It is known that CEMS can be determined through the relative difference in the velocities of surfactants on metallized and non-metallized surfaces, that is, CEMS is an expression of the deceleration of an acoustic wave. Under metallization, the surfactant speed is lower than on a free surface. When using the known IDT structure in the resonator, with electrodes instead of an acoustic cavity, the effective CEMS is close to the CEMS of a surfactant on a free surface. In the proposed technical solution in IDT there is a section without metallization - a significant part of the electrodes is removed with the formation of a free acoustic cavity. The total change in the speed of the surfactant IDT is the sum of the changes in the speed of the surfactant in the areas under the electrode structures and on the free surface of the piezoelectric material. In the acoustic cavity, the speed of the surfactant does not change, therefore, the total change in the speed of the surfactant is less than in known IDTs. The relative average SAS deceleration averaged over the distance between the OSs, i.e., the effective CEMS, is smaller than in the case of a single IDT, which leads to a decrease in the effective reflection coefficient in IDT and an increase in the quality factor of the resonator.

It is known that in the structure of the resonator there are longitudinal modes of oscillations located over a certain frequency interval. It is generally accepted to choose one of these modes as the operating oscillation of the resonator. When choosing the length of the acoustic cavity corresponding to the range 0.01 λ / δfR <L <3.0 ω / δfR, in the region of high reflection OS there is one main vibration mode and the appearance of the nearest longitudinal cavity modes is limited.

The maximum length of the acoustic cavity is limited by the appearance of resonances from the resonator modes in addition to the main resonance. Additional resonant peaks make it difficult or impossible for the electronic system to work with such a resonator. With decreasing L, the relative path length under the IDT metal increases, which reduces the quality factor. In addition, with a decrease in the IDT, the longitudinal modes will remain, reduced on the slopes of the amplitude-frequency characteristic (AFC) of the main mode. Therefore, the IDT sections are close to the reflecting structures and spaced apart by a distance at which the spatial distribution of the amplitude of the generated surfactants in the IDT is carried out in such a way that the frequencies of the nearest longitudinal resonator modes fall at zero frequency response of the main mode. The attenuation of a standing wave is reduced, and the energy loss in the system is reduced.

The specified range for choosing the length of the acoustic cavity allows you to arrange the electrode sections in the spatial minimum of the amplitude of the main mode of the acoustic waves reflected from the OS and the associated components of electromagnetic waves, which leads to the appearance of a single resonance of the main mode during the interference of waves in the acoustic cavity and reduces rereflection and energy loss in IDT, affecting the quality factor.

The use of the combination of the above distinctive features in the invention leads to a significant decrease in the effective CEMS compared to the CEMS surfactant on the free surface of the piezoelectric substrate and can improve the quality factor of the resonator.

The formula 0.01 λ / δfR <L <3.0 λ / δfR relates the frequency response of the reflection coefficient with the possible limits of the choice of distance L. The parameters are chosen so that only one vibration mode is present in the region of high reflection of the OS. The length of the acoustic cavity L in the general case is a multiple of an integer half-wave, but adjusted for different speeds of surfactants in the region of the OS, acoustic cavity, and in sections of IDT electrodes. This formula closes the entire range of L values useful for achieving a technical result and is specified in the variants proposed in the invention.

The length of the acoustic cavity between the IDT electrode sections can be selected from a smaller range of 0.01 λ / δfR <L <0.5 λ / δfR + λ, which additionally ensures the presence of one resonant peak in the frequency response and increases the operational characteristics of the resonator, since with increasing The resonant peaks travel more often, and then they enter the reflection band and appear in the frequency response.

Based on the principle of the invention, it is necessary to minimize the relative amount of metallization in the IDT resonator. This implies the maximum possible size of the free surface. The IDT acoustic cavity length, selected from the range 0.25 λ / δf _R <L <3.0 λ / δf _R , is close to half the maximum distance L and ensures the size of the acoustic cavity, from which a significant improvement in the resonator Q factor is already observed.

The range of 0.5 λ / δf _R - λ / 10 <L <0.5 λ / δf _R + λ / 10 for selecting the IDT cavity length is sufficient to compensate for the spread in the additional phase incursion in IDT sections using various piezoelectric substrate materials and spraying materials, their various thicknesses and metallization coefficients.

An additional refinement to obtain one resonant peak in the frequency response that increases the operational characteristics of the resonator is possible using two alternative ranges for choosing the length of the IDT acoustic cavity:

0,5 λ / δf _R + λ / 4 - λ / 10 _{<L <0,5 λ / δf R} + λ / 4 + λ / 10 or

0.5 λ / δf _R - λ / 4 - λ / 10 <L <0.5 λ / δf _R - λ / 4 + λ / 10,

where + λ / 4 or -λ / 4 provide the position of the frequency response of a pair of IDT sections in the desired frequency range near the resonant frequency of the resonator, and -λ / 10 and + λ / 10 reflect possible refinements of the position associated with the calculation options. This arrangement of the electrodes allows for the excitation and reception of the useful component of acoustic vibrations in the resonator. The +/- sign is selected for positive or negative reflectance from an individual reflective element in reflective structures. The operational characteristics of the resonator are improved due to an increase in the quality factor without the appearance of spurious resonances.

The essence of the proposed technical solution is illustrated by drawings:

FIG. 1 - structure of a resonator on surface acoustic waves;

FIG. 2 is a variant of the structure of a resonator on surface acoustic waves with inversion of one of the sections of IDT electrodes;

FIG. 3 - amplitude-frequency characteristic of the proposed resonator on surface acoustic waves;

FIG. 4 - amplitude-frequency characteristic of a resonator on surface acoustic waves when using a single IDT.

The resonator on surface acoustic waves (Fig. 1) contains a substrate 1 of lithium niobate, lithium tantalate or other piezoelectric material with a high coefficient of electromechanical coupling and low acoustic loss at high frequencies, on the surface of which an interdigital transducer 2 is formed by planar technology, divided into two sections of electrodes 3 and 4, and at least two reflective structures 5 are located, consisting of arrays of reflectors. Reflectors are made with a width and a repetition period that is a multiple of a certain fraction of the wavelength, and represent a plurality of grooves or protrusions made of a substrate material or a dielectric material by successive sputtering and etching cycles.

Between the sections of the electrodes 3 and 4 in IDT 2 is an acoustic cavity 6 that does not contain electrodes and the non-uniformities that overlap the aperture of IDT 2. The length of the acoustic cavity 6 between two sections 3 and 4 of IDT 2 is selected from the range

0.01 λ / δfR <L <3.0 λ / δfR,

where L is the length of the acoustic cavity, δfR is the relative width of the reflection band of the reflecting structures, which can take the value δfR = 0.003..0.03, λ is the length of the surface acoustic wave on the free surface at the resonant frequency.

To improve the parameters of resonators based on piezoelectric materials with an isotropy of the propagation of surfactants in the crystallographic direction, it is advisable to use IDTs, sections of which contain the same number of electrodes, as well as IDTs, in which the electrode sections are centrally symmetrical, since, for example, asymmetric structures allow solving certain problems due to the difference in impedances of the connected sections.

The optimal embodiment is a SAW resonator in which each section of the IDT contains from 2 to 20 electrodes. An increase in the number of electrodes leads to an increase in the energy loss in IDT and a decrease in the Q factor of the resonator. With a decrease in the number of electrodes in the IDT section to one, the conductivity of the resonator sharply deteriorates and it cannot be coordinated with conventional circuits of the electric path.

The distance between the edge of the electrode adjacent to the reflective structure of each of the IDT sections of the resonator and the nearby reflector of the corresponding reflective structure is more technologically advanced if it is from 0.25λ to 20λ (for example, when etching excess metal from reflecting structures).

A structure in which the distance between the center of the electrode adjacent to the reflecting structure of each of the IDT sections and the center of the nearby reflector of the corresponding reflecting structure is in the range from (0.5-0.125 + N) ⋅λ-λ / 10 to (0.5 + 0.125 + N) ⋅λ + λ / 10, where λ is the length of the surfactant on the free surface at the resonant frequency, N = 0, 1, 2, ... is an integer, allows you to compensate for the scatter of the additional phase incursion in IDT sections that occurs when using different materials design, to obtain one resonant peak in the frequency response.

By modeling and experimental verification, the most optimal ranges for choosing the pitch of IDT electrodes were selected. Depending on the material of the structure, the pitch of IDT electrodes is in the range from (0.48 + N) ⋅λ to (0.52 + N) ⋅λ or in the range from 0.48⋅ (1 + 2N) ⋅λ to 0 , 52- (1 + 2N) ⋅λ, where λ is the length of the surfactant on the free surface at the resonant frequency, N = 0, 1, 2, ... is an integer.

By modeling and experimental verification, alternative designs of the resonator structure were also selected in which the most optimal step of the reflectors in the reflective structures is in the range from (0.48 + N / 2) ⋅λ to (0.52 + N / 2) ⋅λ where λ is the length of the surfactant on the free surface at the resonant frequency, N = 0, 1, 2, ... is an integer.

The most optimal distance between the reflecting structures is an integer number of half the acoustic wavelength ± 10%, namely the distance between the reflecting structures is N-λ / 2 + λ / 10 or N⋅λ / 2 - λ / 10, where λ is the SAW length free surface at the resonant frequency, N = 0, 1, 2, ... is an integer. N⋅λ / 2 is necessary to obtain a resonance approximately in the center of the OS reflection range, while -λ / 10 and + λ / 10 reflect possible refinements of the position associated with the calculation options at different levels of losses in the material and are selected for a positive or negative reflection coefficient from a separate reflective element in reflective structures.

A variant of the structure of the resonator on surface acoustic waves with the inversion of one of the sections of the IDT 2 electrodes, for example, section 3 (Fig. 2), is possible. IDT 2 in this design has a centrally symmetrical structure. Moreover, the total number of electrodes connected to the upper IDT bus is equal to the number of electrodes connected to the lower bus, both with an even number of electrodes and with an odd number of electrodes. Thus, a more accurate coincidence of the electrical parameters of each IDT bus is achieved when the resonator is included in a symmetrical balanced circuit, which reduces the influence of spurious components and reduces the loss of electrical signal, which can distort the frequency response and reduce the quality factor of the resonator.

The inventive SAW resonator for high-frequency signal generators can also be used as a physical quantity sensor (for example, a gyroscope, humidity sensor, gas or biochemical sensor), in which periodic or non-periodic inhomogeneities are formed on the IDT acoustic cavity on a substrate of piezoelectric material in the form of strips, dots or other geometric shapes of metal, dielectric or etched in the substrate material.

Periodic inhomogeneities etched in the substrate or made, for example, of tungsten, gold or platinum, with sizes and a repetition period that are multiples of a certain fraction of the wavelength, are used in gyroscopes in which, when the sensor rotates under the influence of the Coriolis force in the acoustic cavity under the heterogeneity structures Surfactant interacting with the main surfactant. The measurement of the angular velocity in a gyroscope is based on measuring the deceleration of the main surfactant or measuring the intensity of the surfactant induced by the Coriolis force.

As non-periodic inhomogeneities in the IDT acoustic cavity, selective dielectric coatings for humidity sensors, as well as gas and biochemical sensors, can be used. In them, due to absorption by sensitive layers or arrays of molecules of the analyte, the speed of the surface acoustic wave changes.

Periodic or non-periodic inhomogeneities formed in the acoustic cavity between two sections of IDT electrodes do not overlap the IDT aperture and contain an insignificant amount of metal, which does not lead to an increase in energy losses in IDT and a decrease in the quality factor of the resonator. Sensors made on the basis of resonators with high quality factor have high operational characteristics.

The resonator on surface acoustic waves operates as follows.

Oscillation energy is supplied and removed from the resonant cavity located between the centers of the reflecting structures 5 of the resonator with an interdigital transducer 2. When an electric signal of high or superhigh frequencies is applied to the sections of electrodes 3 and 4 of IDT 2, electric energy is converted into acoustic wave energy. The generation of surface acoustic waves by sections of electrodes 3 and 4 occurs in phase with a symmetric and antisymmetric design due to the in-phase connection of the electrical signal. Surfactants are emitted by IDT 2 on both sides along the surface of the piezoelectric substrate 1 and reach reflecting structures 5, where they are reflected from the arrays of reflectors forming OS 5 and are directed back to IDT 2. Acoustic waves redirected by OS 5 to IDT 2 practically do not experience reflection from sections of the electrodes 3 and 4 IDT 2 due to the small number of electrodes IDT 2, compared with the number of reflectors OS 5, and go further, getting into the Central region of the resonant cavity of the resonator located in the acoustic cavity 6 between the two sections mi electrodes 3 and 4 IDT 2, where they interfere. When direct and reflected surfactants are superimposed on OS 5, due to their in-phase, energy is accumulated by the dynamic system in the resonance region, which leads to a sharp increase in the amplitude of the wave process, i.e., the interference will be maximum. Surface acoustic waves interfering in the central region of the resonant cavity are reflected to the sections of electrodes 3 and 4 of IDT 2, where the mechanical energy of the acoustic waves is inversely converted to electrical energy.

The quality factor can be measured by the amplitude-frequency characteristic of the resonator. The quality factor is determined by the ratio of the resonant frequency to the bandwidth of the resonator at half the amplitude of the resonance and is inversely proportional to the CEMS. Bandwidth is directly proportional to CEMS. The measured frequency response of the proposed resonator on surface acoustic waves (Fig. 3) and the measured frequency response of the resonator performed on the same materials on surface acoustic waves using a single-wave IDT (Fig. 4) show that the bandwidth of the proposed resonator is much smaller than the bandwidth resonator with integral IDT. The developed technical solution allowed to reduce the effective CEMS of the SAW resonator and increase its quality factor from a value of 8300 (Fig. 4) to a value of 11200 (Fig. 3).

The topology proposed in the invention allows to reduce the energy loss and improve the quality factor of resonators based on lithium niobate, lithium tantalate or other piezoelectric materials with a high electromechanical coupling coefficient to enable the operation of such resonators at high frequencies.

Information sources

1. Zelenka I. Piezoelectric resonators in bulk and surface acoustic waves. - M .: Mir, 1990, 584 p.

2. European patent for an invention. EP 0481733 A1, IPC Н03Н 9/02, Н03Н 9/145, Н03Н 9/25, publ. 04/22/1992.

3. European patent for invention. EP 2239846 A2, IPC Н03Н 9/02, Н03Н 9/145, publ. 10/13/2010.

Claims (30)

1. Resonator on surface acoustic waves (SAW), containing a substrate of piezoelectric material with a high coefficient of electromechanical coupling (CEMS), on the surface of which are formed an interdigital transducer (IDT) and at least two reflective structures (OS), consisting of arrays of reflectors made with a width and a repetition period that is a multiple of a certain fraction of the wavelength, characterized in that the IDT is divided into two sections of electrodes by an acoustic cavity, the length of which between two sections of IDT is selected from apazone 0.01λ / δfR <L <3.0λ / δfR, where L is the length of the acoustic cavity, δfR is the relative width of the reflection band of the reflecting structures, which can take the value δfR = 0.003 ... 0.03, λ is the length of the surface acoustic wave on the free surface at the resonant frequency. 2. A SAW resonator according to claim 1, characterized in that the length of the acoustic cavity between two sections of IDT electrodes is selected from the range 0.01λ / δfR <L <0.5λ / δfR + λ, where L is the length of the acoustic cavity, δfR is the relative width of the reflection band of the OS, which can take the value δfR = 0.003 ... 0.03, λ is the length of the surfactant on the free surface at the resonant frequency. 3. The SAW resonator according to claim 1, characterized in that the length of the acoustic cavity between the two sections of IDT electrodes is selected from the range 0.25λ / δfR <L <3.0λ / δfR, where L is the length of the acoustic cavity, δfR is the relative width of the reflection band of the OS, which can take the value δfR = 0.003 ... 0.03, λ is the length of the surfactant on the free surface at the resonant frequency. 4. The SAW resonator according to claim 1, characterized in that the length of the acoustic cavity between the two sections of IDT electrodes is selected from the range 0.5λ / δfR <λ / 10 <0.5λ / δfR + λ / 10, where L is the length of the acoustic cavity, δfR is the relative width of the reflection band of the OS, which can take the value δfR = 0.003 ... 0.03, λ is the length of the surfactant on the free surface at the resonant frequency. 5. The SAW resonator according to claim 1, characterized in that the length of the acoustic cavity between the two sections of IDT electrodes is selected from the range 0.5λ / δfR + λ / 4-λ / 10 <L <0.5λ / δfR + λ / 4 + λ / 10, where L is the length of the acoustic cavity, δfR is the relative width of the reflection band of the OS, which can take the value δfR = 0.003 ... 0.03, λ is the length of the surfactant on the free surface at the resonant frequency. 6. The SAW resonator according to claim 1, characterized in that the length of the acoustic cavity between the two sections of IDT electrodes is selected from the range 0.5λ / δfR-λ / 4-λ / 10 <L <0.5λ / δfR-λ / 4 + λ / 10, where L is the length of the acoustic cavity, δfR is the relative width of the reflection band of the OS, which can take the value δfR = 0.003 ... 0.03, λ is the length of the surfactant on the free surface at the resonant frequency. 7. Resonator on a surfactant according to any one of paragraphs. 1-6, characterized in that the sections of the IDT electrodes are located centrally symmetrical. 8. The resonator on the surfactant according to any one of paragraphs. 1-6, characterized in that the IDT sections contain the same number of electrodes. 9. Surfactant resonator according to any one of paragraphs. 1-6, characterized in that the IDT sections contain from 2 to 20 electrodes each. 10. Surfactant resonator according to any one of paragraphs. 1-6, characterized in that the distance between the edge of the electrode adjacent to the reflecting structure of each of the sections of IDT and the adjacent reflector corresponding reflective structure is from 0.25λ to 20λ, where λ is the length of the surfactant on the free surface at the resonant frequency. 11. The resonator on the surfactant according to any one of paragraphs. 1-6, characterized in that the distance between the center of the electrode adjacent to the reflecting structure of each of the IDT sections and the center of the nearby reflector of the corresponding reflecting structure is in the range from (0.5-0.125 + N) · λ-λ / 10 to (0 , 5 + 0.125 + N) · λ + λ / 10, where λ is the length of the surfactant on the free surface at the resonant frequency, N = 0, 1, 2, ... is an integer. 12. The resonator on the surfactant according to any one of paragraphs. 1-6, characterized in that the pitch of the IDT electrodes is in the range from (0.48 + N) · λ, to (0.52 + N) · λ, where λ is the length of the surfactant on the free surface at the resonant frequency, N = 0, 1, 2, ... is an integer. 13. The resonator on the surfactant according to any one of paragraphs. 1-6, characterized in that the pitch of the IDT electrodes is in the range from 0.48⋅ (1 + 2N) · λ, to 0.52⋅ (1 + 2N) · λ, where λ is the length of the surfactant on the free surface on resonant frequency, N = 0, 1, 2, ... is an integer. 14. The resonator on the surfactant according to any one of paragraphs. 1-6, characterized in that the step size of the reflectors in reflective structures is in the range from (0.48 + N / 2) · λ, to (0.52 + N / 2) · λ, where λ is the length of the surfactant on the free surface at the resonant frequency, N = 0, 1, 2, ... is an integer. 15. The resonator on the surfactant according to any one of paragraphs. 1-6, characterized in that the distance between the reflective structures is N · λ / 2 + λ / 10, where λ is the length of the surfactant on the free surface at the resonant frequency, N = 0, 1, 2, ... is an integer. 16. The resonator on the surfactant according to any one of paragraphs. 1-6, characterized in that the distance between the reflective structures is N · λ / 2-λ / 10, where λ is the length of the surfactant on the free surface at the resonant frequency, N = 0, 1, 2, ... is an integer. 17. Surfactant resonator according to any one of paragraphs. 1-6, characterized in that in the acoustic cavity of IDT on the substrate of piezoelectric material, periodic or non-periodic inhomogeneities are formed that do not overlap the IDT aperture, while periodic inhomogeneities are made with sizes and a repetition period that are multiples of a certain fraction of the wavelength.

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