CN109756203B - Method for establishing corresponding relation between FBAR resonant frequency and thickness of each layer of oscillation film - Google Patents
Method for establishing corresponding relation between FBAR resonant frequency and thickness of each layer of oscillation film Download PDFInfo
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Abstract
The invention discloses a method for establishing a corresponding relation between FBAR resonance frequency and thicknesses of layers of an oscillation film. The invention establishes the corresponding relation between the resonance frequency of the FBAR and the thickness of each layer of material of the oscillation film, so that the two can be mutually deduced and predicted. In the design of the FBAR, the film thickness of each oscillation layer is predicted according to the determined frequency, and the resonance frequency is predicted according to the determined film thickness of each oscillation layer, so that a simple, quick and effective method is provided, and the research and development and production progress can be accelerated.
Description
Technical Field
The invention relates to the technical field of radio frequency technology and FBAR filters, in particular to a method for establishing a corresponding relation between FBAR resonant frequency and thickness of each layer of an oscillation film.
Background
To meet more communication functions and better communication experience, modern communication technologies need to meet the requirements of higher efficiency and integration. The filter constructed by the FBAR cascade has the advantages of high Q value, low insertion loss, good rectangular coefficient, good direction selectivity, good zero depth, good out-of-band rejection and the like, and is small in size, compatible with the COMS process and capable of being integrated. In addition, the working frequency can be high, so that the filter constructed by the FBAR cascade can well meet the requirements of modern communication technology.
FBAR (film bulk acoustic resonator) is a structured component having a piezoelectric effect material and being capable of forming an (inverse) piezoelectric effect structure. Are manufactured by means of MEMS technology and thin-film technology using silicon backplanes. The FBAR works on the principle that, in the core part of a "sandwich" structure of electrodes-piezoelectric material-electrodes, the piezoelectric material is deformed by applying a voltage to the electrodes, and when an alternating voltage is applied, the structure has an inverse piezoelectric effect. In the process, electric energy is converted into mechanical energy, the mechanical energy is transmitted in the structure through sound waves, vibration is caused, and meanwhile, an electric signal is generated through vibration, namely, the mechanical energy is converted into the electric energy through the piezoelectric effect, and the electric signal is output. The piezoelectric effect and the inverse piezoelectric effect exist at the same time, interact with each other and can generate resonance in the interaction process, so that the signal is selected.
At present, aiming at the research, design and manufacture of the FBAR filter, a good method is not provided for predicting the resonant frequency and the thickness of each layer of film, so that the theoretical design needs to obtain results by other various tools and methods, and on the other hand, the research, the verification and the guidance of the design and the manufacture of a new FBAR filter cannot be realized by researching the FBAR filter with good detection performance.
Disclosure of Invention
In view of the problems in the prior art, embodiments of the present invention provide a method for establishing a correspondence between FBAR resonant frequency and thicknesses of layers of an oscillation film, where the establishment of the correspondence between the thicknesses of the layers of the FBAR oscillation film and the resonant frequency is known. The resonant frequency of the FBAR can be predicted by obtaining the thickness of each layer of the FBAR in the FBAR filter, and the operating frequency of the FBAR filter can be obtained. The research on the FBAR filter with good detection is realized by comparing the predicted FBAR resonance frequency with the actual resonance frequency, and design comparison parameters are provided for further designing the FBAR filter, so that the design and the manufacture of the FBAR filter are guided.
The embodiment of the invention provides a method for establishing a corresponding relation between FBAR resonance frequency and thickness of each layer of an oscillation film, which is known to establish the corresponding relation between the thickness of each layer of the FBAR oscillation film and the resonance frequency and comprises the following steps:
establishing a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR according to the resonance condition of the ideal piezoelectric layer of the FBAR;
establishing a correlation model of the electromechanical coupling coefficient and the FBAR resonant frequency according to the corresponding relation of the electromechanical coupling coefficient and the FBAR resonant frequency;
acquiring the thickness of each layer of structure aiming at each FBAR in the FBAR filter, wherein each layer of structure at least comprises a piezoelectric layer, an upper electrode layer and a lower electrode layer;
converting the obtained thickness of each layer of structure into the thickness of an ideal piezoelectric layer, substituting the thickness of the ideal piezoelectric layer into a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR, and obtaining the parallel resonance frequency of the FBAR;
and obtaining the electromechanical coupling coefficient of the material used by the piezoelectric layer, substituting the obtained electromechanical coupling coefficient of the material used by the piezoelectric layer and the FBAR parallel resonance frequency into a correlation model of the electromechanical coupling coefficient and the FBAR resonance frequency, and obtaining the FBAR series resonance frequency.
Preferably, after acquiring the FBAR parallel resonance frequency and the FBAR series resonance frequency, the method further comprises the following steps: and acquiring the working frequency of the FBAR filter.
The method for establishing the corresponding relation between the FBAR resonant frequency and the thicknesses of the layers of the oscillation film provided by the embodiment of the invention is used for establishing the corresponding relation between the thicknesses of the layers of the FBAR oscillation film and the resonant frequency. The resonant frequency of the FBAR is predicted by measuring the thickness of each layer of the FBAR in the FBAR filter, and then the working frequency of the FBAR filter is calculated. The research on the FBAR filter with good detection is realized by comparing the predicted FBAR resonance frequency with the actual resonance frequency, and design comparison parameters are provided for further designing the FBAR filter, so that the design and the manufacture of the FBAR filter are guided. The determined thickness of each layer of material can be used for predicting the resonant frequency, and the method is generally applied to performance prediction of a prepared device and provides reference for further analysis or adjustment. Or determining the thickness of each layer of material according to specific process conditions, and predicting the performance of the device.
The embodiment of the invention provides a method for establishing a corresponding relation between FBAR resonance frequency and thicknesses of layers of an oscillation film, wherein the known FBAR resonance frequency and the corresponding relation between the thicknesses of the layers of the oscillation film comprise the following steps:
establishing a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR according to the resonance condition of the ideal piezoelectric layer of the FBAR;
establishing a correlation model of the electromechanical coupling coefficient and the FBAR resonant frequency according to the corresponding relation of the electromechanical coupling coefficient and the FBAR resonant frequency;
acquiring the working frequency of the FBAR filter, determining the working frequency band of the FBAR filter according to the working frequency of the FBAR filter, and determining the parallel resonance frequency and the series resonance frequency of each FBAR in the FBAR filter according to the working frequency band and the FBAR cascade construction principle;
substituting the obtained FBAR parallel resonance frequency and FBAR series resonance frequency into an association model of the ideal piezoelectric layer and the FBAR parallel resonance frequency to obtain the thickness of the ideal piezoelectric layer;
determining the actual piezoelectric layer thickness according to the actual piezoelectric layer thickness proportion;
substituting the obtained FBAR parallel resonance frequency and FBAR series resonance frequency into a correlation model of an electromechanical coupling coefficient and the FBAR resonance frequency to obtain an electromechanical coupling coefficient of the piezoelectric material, and determining the piezoelectric material according to the electromechanical coupling coefficient;
obtaining the equivalent piezoelectric layer thickness through the ideal piezoelectric layer thickness and the determined actual piezoelectric layer thickness;
and obtaining the thickness of the materials of other layers except the piezoelectric layer by combining the materials selected for the layers except the piezoelectric layer according to the thickness of the equivalent piezoelectric layer, wherein the layers except the piezoelectric layer at least comprise an upper electrode layer and a lower electrode layer.
The method for establishing the corresponding relation between the FBAR resonant frequency and the thickness of each layer of the oscillation film is characterized in that the FBAR resonant frequency is known and is established corresponding to the thickness relation of each layer of the oscillation film, the working frequency of the FBAR filter is obtained by detecting the FBAR filter with good performance, and the parallel resonant frequency and the series resonant frequency of each cascaded FBAR of the FBAR filter are calculated according to the working frequency, so that the thickness of each layer of the FBAR material in the FBAR filter is predicted. The obtained thickness of each layer of FBAR material can be substituted into FBAR simulation software for simulation research so as to be compared with the FBAR filter, find out a better method for optimizing and designing the FBAR, and also provide design parameters for the FBAR design.
In predicting the thickness of each layer of material for the determined resonant frequency, the structure of the FBAR is predicted for the process of determining the material layers one by one. The determination of the thickness of each layer of material is the result, and the structural hierarchy of the device is also clear given which layers are needed, which layer is of what material, and then the thickness.
Preferably, according to the resonance condition of the ideal piezoelectric layer of the FBAR, a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR is established, which specifically includes:
from the ideal piezoelectric layer resonance condition formula:
obtaining the ideal piezoelectric layer thickness:
where θ is the phase shift angle, k is the wave number, 2HaIs an ideal piezoelectric layer thickness, vaIs the longitudinal wave velocity f of piezoelectric materialpIs the FBAR parallel resonance frequency.
An ideal piezoelectric layer means that, for a basic piezoelectric core structure consisting of an electrode layer, a piezoelectric layer and an electrode layer, sound waves are totally reflected from the surface of the electrode layer, which is in contact with the piezoelectric layer, to the other surface through the electrode layer, and the electrode layer is set to be infinitely thin, namely the electrode layer exists, but the thickness of the electrode layer is ignored, so that the transmission path of the sound waves is totally limited in the piezoelectric layer.
The thickness of each layer can be considered to be distributed from the ideal thickness of the piezoelectric material, and the piezoelectric layer of the same material can be directly subtracted from the thickness, but the thickness of different materials needs to be converted by establishing a relation between the resonant frequency and the thickness of each layer, so that the conversion of the thickness of different materials and the thickness of the piezoelectric material distributed correspondingly is equivalent.
Preferably, according to the corresponding relationship between the electromechanical coupling coefficient and the FBAR parallel resonance frequency and the FBAR series resonance frequency, a correlation model between the electromechanical coupling coefficient and the FBAR resonance frequency is established, specifically:
kt 2is an electromechanical coupling coefficient, fsThe FBAR series resonance frequency.
Preferably, the thickness of each obtained layer structure is converted into an ideal piezoelectric layer thickness, specifically: establishing the relation between the resonant frequency and the thickness of each layer material:
or
Wherein
2Ha＝2ha+2h1+2h2+......+2hn (6)
Wherein, 2hn(n-1, 2,3 … …) is the thickness of the materials of the layers except the piezoelectric layer, vn(n is 1,2,3 … …) is the longitudinal sound velocity of the material represented, 2haIs the actual thickness of the piezoelectric layer.
Equations (4) and (5) are applications to equation (2), where equation (4) is based on
The v in equation (2) is replaced by weighting the time of sound propagation in each material by finding the equivalent rate of sound propagation throughout the oscillating filmaAnd the total thickness is approximated in the numerator and denominator, resulting in equation (4). Equation (5) is for each material layer, assuming that the acoustic wave propagation velocity therein is vaThen, equivalently, the ratio of the thickness of the material of each layer to the velocity of the material is storedIn a proportional relationship, the effective propagation path should be considered as the actual thickness of the respective layer material multiplied by a scaling factor in the established relationship.
Preferably, a corresponding relation between the FBAR resonant frequency and the thickness of each layer of the oscillation film is established, and the parallel resonant frequency and the series resonant frequency of each FBAR are determined according to the following method when the thickness relation between the FBAR resonant frequency and each layer of the oscillation film is established:
determining the difference of the resonant frequencies of the FBARs according to the working frequency of the FBAR filter and the difference of the maximum two times of the resonant frequencies of the FBARs in the working frequency band of the FBAR filter;
for series FBAR, parallel resonant frequency fpIs the highest frequency of the FBAR filter passband, series resonance frequency fsThe intermediate frequency of the passband of the FBAR filter; for parallel FBAR, parallel resonant frequency fpFor the intermediate frequency of the passband of the FBAR filter, the series resonance frequency fsDetermining the FBAR parallel resonance frequency f for the lowest frequency of the FBAR filter passbandpAnd series resonant frequency fs。
Preferably, the equivalent piezoelectric layer thickness is the ideal piezoelectric layer thickness minus the piezoelectric layer initial thickness;
through the equivalent piezoelectric layer thickness, combine the material that each layer chooseed for use, obtain other each layer material thickness outside the piezoelectric layer, specifically do:
by the formula
Or
Converting the equivalent piezoelectric layer thickness into the thickness of other layers except the piezoelectric layer; wherein, 2hn(n-1, 2,3 … …) thickness of other layer materials, vn(n is 1,2,3 … …) represents the longitudinal sound velocity of other materials of each layer, and the following relationship exists:
2Ha＝2ha+2h1+2h2+......+2hn (4)
2hais the initial thickness of the piezoelectric layer.
Preferably, for cascaded FBAR filters, the bandwidth of the band is 2 (f)p-fs) Frequency range fp±(fp-fs) Or fs±(fp-fs) The frequency range is selected primarily by the parallel or series connection at the FBAR. When the parallel resonance frequency f of the FBAR is predictedpAnd series resonant frequency fsThe working frequency band and working frequency of the FBAR filter can be predicted.
In consideration of the frequency requirement, the general index requirement is for the FBAR filter, and is reflected on the FBAR of the cascade structure filter, and is considered to correspond to the FBAR resonance frequency. According to the principle of realizing the filtering function of the most basic FBAR cascade (composed of a series FBAR and a parallel FBAR), the passband of the FBAR filter is at most twice the difference (positive) between two resonant frequencies of the FBAR, so that f is the difference between the two resonant frequencies of the series FBARpIs the highest frequency of the filter passband, fsFor the intermediate frequency of the filter pass band, FBAR, f are connected in parallelpIs the filter passband intermediate frequency, fsThe lowest frequency of the filter passband. Thus, from the resonant frequency, the pass band of the filter can be predicted.
The method provided by the specific implementation of the invention has the following advantages:
1. a method for establishing the corresponding relation between the resonant frequency of FBAR and the thickness of each layer of an oscillation film is characterized in that the resonant frequency of FBAR and the thickness of each layer of material are established into a relational expression, the relevant parameters of FBAR are related, the mutual action relation is quantized and visually embodied, and a guiding effect is provided for research and production.
2. The entrance threshold of the FBAR is reduced, the correlation parameter relationship is reflected through a formula, analysis and research are facilitated, the analysis flow is simplified, and research analysis, design and preparation of the FBAR are promoted and accelerated.
3. The FBAR resonance frequency prediction method and the FBAR layer thickness prediction method provided by the invention are approximately two-directional and are unified into a formula, so that the method is reversible from any direction. The two aspects can be mutually converted, and have important roles in practical application.
Drawings
FIG. 1 is a schematic diagram of an FBAR structure of the present invention;
FIG. 2 is a schematic flow chart of a method for establishing the relationship between the thickness of each layer of a known FBAR oscillation film and the corresponding resonant frequency according to the present invention;
FIG. 3 is a schematic flow chart of the method for establishing the thickness relationship between layers of the oscillation film corresponding to the known FBAR resonant frequency of the present invention.
In the drawings: 21. a silicon substrate; 22. a cavity; 23. a support layer; 24. a lower electrode layer; 25. a piezoelectric layer; 26. an upper electrode layer; 27. a cavity structure.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and the detailed description, and it should be noted that any combination of the embodiments or technical features described below can be used to form a new embodiment without conflict.
In the FBAR resonance frequency prediction method and the FBAR layer thickness prediction method provided in the embodiments of the present invention, a basic structure of the FBAR is as shown in fig. 1, and includes a silicon substrate 21 made of a single crystal, a cavity 22 is etched on the silicon substrate 21, a support layer 23 is disposed on the silicon substrate 21, and the support layer 23 and the silicon substrate 21 together form a closed space for the cavity 22. On the support layer is arranged a lower electrode layer 24, a piezoelectric layer 25, and on the piezoelectric layer an upper electrode layer 26. The upper electrode 26 layer, the piezoelectric layer 25 and the lower electrode layer 24 form a core layer of electrode-piezoelectric layer-electrode. In particular, a cavity structure 27 is provided on the upper electrode layer 26, i.e., a cavity 22 is provided below the core layer, a cavity structure 27 is provided above the core layer, and the cavity 22 and the cavity structure 27 constitute a total reflection surface of the oscillating acoustic wave. Other layers may be added between the electrode-piezoelectric layer-electrode core layers according to other requirements and process conditions, such as a tuning layer or a protective layer for protecting from air on the upper electrode layer 26 during practical fabrication. The support layer 23 is also not necessarily required under the lower electrode layer 24, i.e. the lower electrode and the piezoelectric layer are directly arranged on the silicon substrate 21, or a temperature compensation layer may be arranged at the position of the support layer.
Example 1:
as shown in fig. 2, the method for establishing the relationship between the thickness of each layer of the known FBAR oscillation film and the corresponding resonant frequency provided by the present invention comprises the following steps:
s31, establishing a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR according to the resonance condition of the ideal piezoelectric layer of the FBAR;
s32, establishing a correlation model of the electromechanical coupling coefficient and the FBAR resonant frequency according to the corresponding relation of the electromechanical coupling coefficient and the FBAR resonant frequency;
s33, acquiring the thickness of each layer of structure aiming at each FBAR in the FBAR filter, wherein each layer of structure at least comprises a piezoelectric layer 25, an upper electrode layer 26 and a lower electrode layer 24; the thickness of each layer structure may be obtained by a measuring instrument or any other measurable method, for example, some layers are standard parts, and the thickness of the layer may be obtained by measuring the thickness of the standard parts or by official standards parts;
s34, converting the thickness of each layer of the obtained structure into the thickness of an ideal piezoelectric layer, substituting the thickness of the ideal piezoelectric layer into a correlation model of the ideal piezoelectric layer and the FBAR parallel resonance frequency to obtain the FBAR parallel resonance frequency;
and S35, obtaining the electromechanical coupling coefficient of the material used for the piezoelectric layer, substituting the obtained electromechanical coupling coefficient of the material used for the piezoelectric layer and the FBAR parallel resonance frequency into a correlation model of the electromechanical coupling coefficient and the FBAR resonance frequency, and obtaining the FBAR series resonance frequency.
According to the method for establishing the relation between the thickness of each layer of the known FBAR oscillation film and the corresponding resonant frequency, provided by the embodiment of the invention, the resonant frequency of the FBAR is predicted by measuring the thickness of each layer of the FBAR in the FBAR filter, and then the working frequency of the FBAR filter is calculated. The research on the FBAR filter with good detection is realized by comparing the predicted FBAR resonance frequency with the actual resonance frequency, and design comparison parameters are provided for further designing the FBAR filter, so that the design and the manufacture of the FBAR filter are guided.
According to the resonance condition of the FBAR ideal piezoelectric layer, establishing a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR, specifically comprising the following steps:
from the ideal piezoelectric layer resonance condition formula:
obtaining the ideal piezoelectric layer thickness:
where θ is the phase shift angle, k is the wave number, 2HaIs an ideal piezoelectric layer thickness, vaIs the longitudinal wave velocity f of piezoelectric materialpIs the FBAR parallel resonance frequency.
Establishing a correlation model of the electromechanical coupling coefficient and the FBAR resonance frequency according to the corresponding relation between the electromechanical coupling coefficient and the FBAR parallel resonance frequency and the FBAR series resonance frequency, specifically:
kt 2is an electromechanical coupling coefficient, fsThe FBAR series resonance frequency.
Converting the obtained thickness of each layer of structure into the thickness of an ideal piezoelectric layer, specifically: establishing the relation between the resonant frequency and the thickness of each layer material:
or
Wherein
2Ha＝2ha+2h1+2h2+......+2hn (6)
Wherein, 2hn(n-1, 2,3 … …) is the thickness of the materials of the layers except the piezoelectric layer, vn(n is 1,2,3 … …) is the longitudinal sound velocity of the material represented, 2haIs the actual thickness of the piezoelectric layer.
The following describes a method for establishing the relationship between the thickness of each layer of the known FBAR oscillation film and the corresponding resonant frequency in an embodiment of the present invention.
In the FBAR structure shown in FIG. 1, the silicon substrate 21 is made of single crystal silicon, and the support layer 23 is made of Si3N4The upper electrode layer 26, the upper and lower electrode layers 24 are both Mo, the piezoelectric layer 25 is AlN, and the support layer 23 is Si obtained by a measuring instrument3N4The thickness is 160nm, the thickness of the lower electrode layer 24Mo is 230nm, the thickness of the piezoelectric layer 25AlN is 1200nm, and the thickness of the upper electrode layer Mo is 188 nm.
As can be seen from a review of the manual, the longitudinal wave sound velocities are: the molar ratio of Mo is 6213m/s, that of AlN is 11350m/s, and that of Si3N4 is 11000 m/s.
Knowing the material thickness of each layer, the resonant frequency of the FBAR, and further the operating frequency of the filter, can be extrapolated. And (3) calculating to obtain the parallel resonance frequency according to the formula (4) or the formula (5), and then calculating to obtain the series resonance frequency by using a mathematical expression relation among the parameters in the formula (6). Thus, the resonant frequency of the FBAR is obtained, and the passband bandwidth of the filter formed by the FBAR is 2 (f)p-fs) Frequency range fp±(fp-fs) Or fs±(fp-fs) The frequency is deduced from the thickness of the layers of the FBAR.
And (3) substituting the thickness of each layer of material and the longitudinal sound velocity data of the sound wave propagating in the material into the formula (3) to calculate fp, wherein fp is calculated to be 2.67GHz in the embodiment.
Further, in the known embodiment, the electromechanical coupling coefficient of the piezoelectric material is 0.058, and fs is calculated to be 2.61GHz according to the formula (3), so that if the maximum passband of the cascaded filter is about 120MHz, the operating frequency range is 2.55GHz to 2.79GHz, or 2.49GHz to 2.73 GHz.
Example 2:
as shown in fig. 3, the method for establishing the relationship between the known FBAR resonant frequency and the thickness of each layer of the corresponding oscillation film provided by the present invention comprises the following steps:
s41, establishing a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR according to the resonance condition of the ideal piezoelectric layer of the FBAR;
s42, establishing a correlation model of the electromechanical coupling coefficient and the FBAR resonant frequency according to the corresponding relation of the electromechanical coupling coefficient and the FBAR resonant frequency;
s43, acquiring the working frequency of the FBAR filter, determining the working frequency band of the FBAR filter according to the working frequency of the FBAR filter, and determining the parallel resonance frequency and the series resonance frequency of each FBAR in the FBAR filter according to the working frequency band and the FBAR cascade construction principle;
s44, substituting the obtained FBAR parallel resonance frequency and FBAR series resonance frequency into a correlation model of the ideal piezoelectric layer and the FBAR parallel resonance frequency to obtain the thickness of the ideal piezoelectric layer;
s45, determining the thickness of the compacted boundary electric layer according to the thickness proportion of the actual piezoelectric layer;
s46, substituting the obtained FBAR parallel resonance frequency and FBAR series resonance frequency into a correlation model of an electromechanical coupling coefficient and the FBAR resonance frequency to obtain an electromechanical coupling coefficient of the piezoelectric material, and determining the piezoelectric material according to the electromechanical coupling coefficient;
s47, obtaining the equivalent piezoelectric layer thickness according to the ideal piezoelectric layer thickness and the determined actual piezoelectric layer thickness;
and S48, obtaining the thicknesses of the materials of the layers except the piezoelectric layer by combining the equivalent thickness of the piezoelectric layer with the materials selected for the layers except the piezoelectric layer, wherein the layers except the piezoelectric layer at least comprise an upper electrode layer and a lower electrode layer.
According to the method for establishing the thickness relation of each layer of the known FBAR resonant frequency corresponding to the oscillation film, provided by the embodiment of the invention, the working frequency of the FBAR filter is obtained by detecting the FBAR filter with good performance, the parallel resonant frequency and the series resonant frequency of each cascaded FBAR of the FBAR filter are calculated according to the working frequency, and the thickness of each layer of the material of each FBAR in the FBAR filter is predicted. The obtained thickness of each layer of FBAR material can be substituted into FBAR simulation software for simulation research so as to be compared with the FBAR filter, find out a better method for optimizing and designing the FBAR, and also provide design parameters for the FBAR.
Preferably, according to the resonance condition of the ideal piezoelectric layer of the FBAR, a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR is established, which specifically includes:
from the ideal piezoelectric layer resonance condition formula:
obtaining the ideal piezoelectric layer thickness:
where θ is the phase shift angle, k is the wave number, 2HaIs an ideal piezoelectric layer thickness, vaIs the longitudinal wave velocity f of piezoelectric materialpIs the FBAR parallel resonance frequency.
An ideal piezoelectric layer means that, for a basic piezoelectric core structure consisting of an electrode layer, a piezoelectric layer and an electrode layer, sound waves are totally reflected from the surface of the electrode layer, which is in contact with the piezoelectric layer, to the other surface through the electrode layer, and the electrode layer is set to be infinitely thin, namely the electrode layer exists, but the thickness of the electrode layer is ignored, so that the transmission path of the sound waves is totally limited in the piezoelectric layer.
The thickness of each layer can be considered to be distributed from the ideal thickness of the piezoelectric material, and the piezoelectric layer of the same material can be directly subtracted from the thickness, but the thickness of different materials needs to be converted by establishing a relation between the resonant frequency and the thickness of each layer, so that the conversion of the thickness of different materials and the thickness of the piezoelectric material distributed correspondingly is equivalent.
Preferably, according to the corresponding relationship between the electromechanical coupling coefficient and the FBAR parallel resonance frequency and the FBAR series resonance frequency, a correlation model between the electromechanical coupling coefficient and the FBAR resonance frequency is established, specifically:
kt 2is an electromechanical coupling coefficient, fsThe FBAR series resonance frequency.
Preferably, the ideal piezoelectric layer thickness is converted into the thickness of each layer structure, specifically: establishing the relation between the resonant frequency and the thickness of each layer material:
or
Wherein
2Ha＝2ha+2h1+2h2+......+2hn (6)
Wherein, 2hn(n-1, 2,3 … …) is the thickness of the materials of the layers except the piezoelectric layer, vn(n is 1,2,3 … …) is the longitudinal sound velocity of the material represented, 2haIs the actual thickness of the piezoelectric layer.
Equations (4) and (5) are applications to equation (2), where equation (4) is based on
The v in equation (2) is replaced by weighting the time of sound propagation in each material by finding the equivalent rate of sound propagation throughout the oscillating filmaAnd the total thickness is approximated in the numerator and denominator, resulting in equation (4). Equation (5) is for each material layer, assuming that the acoustic wave propagation velocity therein is vaThen, equivalently, the ratio of the thickness of the material of each layer to the velocity of the material is proportionalIn the established relationship, the effective propagation path should be considered as the actual thickness of the material of each layer multiplied by a scaling factor.
Preferably, each FBAR parallel resonance frequency and FBAR series resonance frequency is determined according to the following method:
determining the difference of the resonant frequencies of the FBARs according to the working frequency of the FBAR filter and the difference of the maximum two times of the resonant frequencies of the FBARs in the working frequency band of the FBAR filter;
for series FBAR, parallel resonant frequency fpIs the highest frequency of the FBAR filter passband, series resonance frequency fsThe intermediate frequency of the passband of the FBAR filter; for parallel FBAR, parallel resonant frequency fpFor the intermediate frequency of the passband of the FBAR filter, the series resonance frequency fsDetermining the FBAR parallel resonance frequency f for the lowest frequency of the FBAR filter passbandpAnd series resonant frequency fs。
Preferably, the equivalent piezoelectric layer thickness is the ideal piezoelectric layer thickness minus the piezoelectric layer initial thickness;
preferably, for cascaded FBAR filters, the bandwidth of the band is 2 (f)p-fs) Frequency range fp±(fp-fs) Or fs±(fp-fs) The frequency range is selected primarily by the parallel or series connection at the FBAR. When the parallel resonance frequency f of the FBAR is predictedpAnd series resonant frequency fsThe working frequency band and working frequency of the FBAR filter can be predicted.
In consideration of the frequency requirement, the general index requirement is for the FBAR filter, and is reflected on the FBAR of the cascade structure filter, and is considered to correspond to the FBAR resonance frequency. According to the principle of realizing the filtering function of the most basic FBAR cascade (composed of a series FBAR and a parallel FBAR), the passband of the FBAR filter is at most twice the difference (positive) between two resonant frequencies of the FBAR, so that f is the difference between the two resonant frequencies of the series FBARpIs the highest frequency of the filter passband, fsFor the intermediate frequency of the filter pass band, FBAR, f are connected in parallelpIs the filter passband intermediate frequency, fsThe lowest frequency of the filter passband. Thus, from the resonant frequency, the pass band of the filter can be predicted.
The method for establishing the relationship between the resonant frequency of the known FBAR and the thickness of each layer of the oscillation film according to the present invention is described in detail with an embodiment.
The working frequency range of the FBAR filter is measured to be 2300 MHz-2400 MHz, the insertion loss is less than or equal to 3dB, the out-of-band rejection is greater than or equal to 30dB, and the fundamental frequency f of the resonator is determined according to the principle that the FBAR filter is constructed by the FBAR cascade connectionp. Depending on the operating frequency range, the series FBAR, parallel resonance frequency f can be obtained firstps2400MHz, series resonant frequency fss2350MHz, shunt FBAR, shunt resonance frequency fpp2350MHz, series resonant frequency fsp＝2300MHz。
Calculated according to the formula (3)
Here, the first and second liquid crystal display panels are,
the thickness of the piezoelectric layer in the ideal case is obtained according to the conditions for resonance of the piezoelectric layer in the ideal case. From equation (3), the ideal piezoelectric layer thickness is calculated, with the series FBAR:2Hap being 2.36um and the shunt FBAR:2Haps being 2.41 um.
The thickness of the piezoelectric layer is determined based on structural considerations and thickness ratio considerations. Here, series FBAR piezoelectric layer thickness 2hapIs 1.2um, and the thickness of the parallel FBAR piezoelectric layer is 2hasIs 1.2 um.
The ideal piezoelectric layer thickness minus the determined piezoelectric layer thickness, the remaining thickness is the equivalent piezoelectric layer thickness of the electrodes and other material layers, and therefore this thickness needs to be translated into the thickness of the electrodes and other material layers. A simplified process is performed on the example, the layer structure only remains the "sandwich" structure of the core work, thus the electrode Mo layer remains except the AlN layer.
The equivalent AlN layer thicknesses of the shunt-series FBARs are 1.21um and 1.16um respectively, and the equivalent AlN layer thicknesses are converted into the total electrode thickness by the formula (4) or (5), so that the total parallel electrode thickness is 2h1s659.56nm, total thickness of series electrode 2h1p＝659.39nm。
The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.
Claims (5)
1. A method for establishing a corresponding relation between FBAR resonant frequency and thickness of each layer of an oscillation film is characterized in that the establishment of the corresponding relation between the thickness of each layer of the known FBAR oscillation film and the resonant frequency comprises the following steps:
establishing a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR according to the resonance condition of the ideal piezoelectric layer of the FBAR;
establishing a correlation model of the electromechanical coupling coefficient and the FBAR resonant frequency according to the corresponding relation of the electromechanical coupling coefficient and the FBAR resonant frequency;
acquiring the thickness of each layer of structure aiming at each FBAR in the FBAR filter, wherein each layer of structure at least comprises a piezoelectric layer, an upper electrode layer and a lower electrode layer;
converting the obtained thickness of each layer of structure into the thickness of an ideal piezoelectric layer, substituting the thickness of the ideal piezoelectric layer into a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR, and obtaining the parallel resonance frequency of the FBAR;
obtaining an electromechanical coupling coefficient of a material used by the piezoelectric layer, substituting the obtained electromechanical coupling coefficient of the material used by the piezoelectric layer and the FBAR parallel resonance frequency into a correlation model of the electromechanical coupling coefficient and the FBAR resonance frequency, and obtaining an FBAR series resonance frequency;
the method for establishing the thickness relation of each layer of the corresponding oscillation film according to the known FBAR resonance frequency comprises the following steps:
establishing a correlation model of the parallel resonance frequency of the ideal piezoelectric layer and the FBAR according to the resonance condition of the ideal piezoelectric layer of the FBAR;
establishing a correlation model of the electromechanical coupling coefficient and the FBAR resonant frequency according to the corresponding relation of the electromechanical coupling coefficient and the FBAR resonant frequency;
acquiring the working frequency of the FBAR filter, determining the working frequency band of the FBAR filter according to the working frequency of the FBAR filter, and determining the parallel resonance frequency and the series resonance frequency of each FBAR in the FBAR filter according to the working frequency band and the FBAR cascade construction principle;
substituting the obtained FBAR parallel resonance frequency and FBAR series resonance frequency into an association model of the ideal piezoelectric layer and the FBAR parallel resonance frequency to obtain the thickness of the ideal piezoelectric layer;
determining the actual piezoelectric layer thickness according to the actual piezoelectric layer thickness proportion;
substituting the obtained FBAR parallel resonance frequency and FBAR series resonance frequency into a correlation model of an electromechanical coupling coefficient and the FBAR resonance frequency to obtain an electromechanical coupling coefficient of the piezoelectric material, and determining the piezoelectric material according to the electromechanical coupling coefficient;
obtaining the equivalent piezoelectric layer thickness through the ideal piezoelectric layer thickness and the determined actual piezoelectric layer thickness; i.e. the ideal piezoelectric layer thickness minus the determined piezoelectric layer thickness, the remaining thickness being the equivalent piezoelectric layer thickness of the electrodes and other material layers;
obtaining the thickness of each layer of materials except the piezoelectric layer by combining the equivalent thickness of the piezoelectric layer with the materials selected by each layer except the piezoelectric layer, wherein each layer except the piezoelectric layer at least comprises an upper electrode layer and a lower electrode layer;
wherein, the relation between the resonant frequency and the thickness of each layer material is established through the relation between the thickness of each layer structure and the thickness of an ideal piezoelectric layer:
or
Wherein
2Ha＝2ha+2h1+2h2+......+2hn (6)
Wherein, 2hn(n-1, 2,3 … …) are layers other than the piezoelectric layerThickness of the material, vn(n is 1,2,3 … …) is the longitudinal sound velocity of the material represented, 2haIs the actual thickness of the piezoelectric layer.
2. The method of claim 1, wherein after acquiring the FBAR parallel resonance frequency and the FBAR series resonance frequency, the method further comprises the steps of: and acquiring the working frequency of the FBAR filter.
3. The method of claim 1, wherein establishing a correlation model of the ideal piezoelectric layer and the FBAR parallel resonance frequency according to the FBAR ideal piezoelectric layer resonance condition comprises:
from the ideal piezoelectric layer resonance condition formula:
obtaining the ideal piezoelectric layer thickness:
where θ is the phase shift angle, k is the wave number, 2HaIs an ideal piezoelectric layer thickness, vaIs the longitudinal wave velocity f of piezoelectric materialpIs the FBAR parallel resonance frequency.
4. The method of claim 1, wherein a correlation model of the electromechanical coupling coefficient and the FBAR resonant frequency is established according to a corresponding relationship between the electromechanical coupling coefficient and the FBAR parallel resonant frequency and the FBAR series resonant frequency, specifically:
kt 2is an electromechanical coupling coefficient, fsThe FBAR series resonance frequency.
5. The method of claim 1, wherein each FBAR parallel resonance frequency and FBAR series resonance frequency is determined according to the following method:
determining the difference of the resonant frequencies of the FBARs according to the working frequency of the FBAR filter and the difference of the maximum two times of the resonant frequencies of the FBARs in the working frequency band of the FBAR filter;
for series FBAR, parallel resonant frequency fpIs the highest frequency of the FBAR filter passband, series resonance frequency fsThe intermediate frequency of the passband of the FBAR filter; for parallel FBAR, parallel resonant frequency fpFor the intermediate frequency of the passband of the FBAR filter, the series resonance frequency fsDetermining the FBAR parallel resonance frequency f for the lowest frequency of the FBAR filter passbandpAnd series resonant frequency fs。
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