CN114938214A - Acoustic energy excitation SAW resonator and high-order symmetrical trapezoid SAW filter - Google Patents
Acoustic energy excitation SAW resonator and high-order symmetrical trapezoid SAW filter Download PDFInfo
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- CN114938214A CN114938214A CN202210714602.8A CN202210714602A CN114938214A CN 114938214 A CN114938214 A CN 114938214A CN 202210714602 A CN202210714602 A CN 202210714602A CN 114938214 A CN114938214 A CN 114938214A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/02—Details
- H03H9/02535—Details of surface acoustic wave devices
- H03H9/02637—Details concerning reflective or coupling arrays
- H03H9/02685—Grating lines having particular arrangements
- H03H9/02724—Comb like grating lines
- H03H9/02732—Bilateral comb like grating lines
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H9/00—Networks comprising electromechanical or electro-acoustic devices; Electromechanical resonators
- H03H9/46—Filters
- H03H9/64—Filters using surface acoustic waves
- H03H9/6423—Means for obtaining a particular transfer characteristic
- H03H9/6433—Coupled resonator filters
- H03H9/6483—Ladder SAW filters
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Abstract
The invention provides a thin LiNbO 3 A multilayer waveguide SAW resonator structure composed of thin films and SiC and a ladder type circuit optimization scheme. The SAW resonator structure sequentially comprises a SiC high-speed substrate and 64-degree Y-X LiNbO from bottom to top 3 The acoustic wave is guided to spread in a low acoustic velocity region, so that the excitation of the main mode acoustic wave is strengthened, clutter influence is eliminated, insertion loss is reduced, and finally the resonators used for series connection and the resonators used for parallel connection are manufactured into the SAW filter by adopting a ladder circuit optimization scheme. The SAW filter adopting the structure has large bandwidth and low insertion loss, and can have better performance when in work.
Description
Technical Field
The invention relates to the technical field of surface acoustic wave electronic devices, in particular to a sound energy excitation SAW resonator and a high-order symmetrical trapezoid SAW filter.
Background
With the rise of global satellite navigation and positioning systems and the vigorous construction of Beidou systems in China, supporting products such as related antennas, chips, board cards and receivers and the like are developed rapidly, and the market demand on high-performance surface acoustic wave filters for receiving and transmitting is huge.
With the wide application of the L-band and the rapid development of the related technologies, higher and higher requirements are put forward on the performance indexes of the surface acoustic wave filter, such as frequency, bandwidth, frequency temperature coefficient, passband ripple, insertion loss, stopband rejection, volume and the like. The high-performance surface acoustic wave filter with large bandwidth, low fluctuation, low loss, high suppression, high temperature stability and small volume has urgent application requirements in L-band related electronic equipment, and also becomes one of the important research directions of the current surface acoustic wave filter. Although the traditional crystal filter can well realize the signal filtering function, due to the influence of the process machining precision, the bandwidth is small, the insertion loss is large, and the application requirements of high frequency and small volume cannot be met.
SAW filters are typically composed of a cascade of series resonators and parallel resonators. In general, a SAW resonator (surface acoustic wave resonator) has a uniform interdigital single-ended resonator structure, as shown in fig. 1, an interdigital transducer is arranged in the middle, and a metal short-circuit grating array (reflection grating) is arranged on two sides. The bandwidth and insertion loss of the SAW resonator and the SAW filter are mainly dependent on the electromechanical coupling coefficient of the piezoelectric substrate and the influence of the non-main mode noise. Conventional SAW resonators are primarily on lithium niobate (LiNbO) 3 ) The interdigital electrode of the transducer is manufactured on the piezoelectric substrate made of single crystal materials, the electromechanical coupling coefficient of the interdigital electrode is generally lower than 10%, the relative bandwidth is small, the interdigital electrode is easily affected by non-main mode noise, the insertion loss is increased, and the performance of the SAW filter is reduced. In order to meet the requirements of a SAW filter on a large-bandwidth working range and excellent working performance, the technical problem of urgent need for developing a high-performance SAW resonator with a large-bandwidth working range and good clutter suppression is solved.
Disclosure of Invention
Aiming at the defects in the prior art, the technical problems to be solved by the invention are as follows:
1. how to meet the requirement of the SAW filter on the large bandwidth working range;
2. how to enhance the main mode excitation effect in the large bandwidth working range and reduce the influence of non-main mode clutter;
3. how to improve the performance of the SAW filter by optimizing the ladder circuit structure.
The invention relates to a multilayer waveguide high-performance SAW resonator, which is realized by adopting the following technical scheme: the SAW resonator is sequentially provided with a SiC high-speed substrate and 64-degree Y-X LiNbO from bottom to top 3 Piezoelectric film, interdigital electrode of the energy converter; the thickness of the piezoelectric film layer is 0.15-0.4 lambda, the thickness of the interdigital electrode of the transducer is 0.01-0.4 lambda, and lambda represents an interdigital period.
The resonator structure guides the sound waves to propagate in a low sound velocity area, strengthens and excites the sound waves of the main mode, eliminates clutter influence and reduces insertion loss. The low acoustic velocity region refers to a piezoelectric film, namely LiNbO 3 (ii) a The piezoelectric substrate, i.e., SiC, is a high acoustic velocity region.
The small lattice mismatch of the materials between the resonator multilayer waveguide structures is beneficial to reducing the insertion loss in the SAW device, and the electromechanical coupling coefficient (K) 2 ) The effective increase in (1) is mainly due to more effective excitation of SAW in the piezoelectric film, thereby reducing the influence of noise waves and reducing loss. The specific reasons are as follows: by optimizing the thickness of the piezoelectric film and the electrode, the mode-guiding wave is realized in the multilayer waveguide structure by utilizing the high-speed substrate, and the sound energy is limited in the piezoelectric film, so that the excitation of the main mode sound wave is strengthened.
The high-order symmetrical trapezoid SAW filter is realized by adopting the following technical scheme: the multistage cascade ladder type circuit is adopted, each stage ladder type circuit comprises an SAW resonator used for series connection and two SAW resonators used for parallel connection, the two SAW resonators used for parallel connection are symmetrically distributed on two sides of the series SAW resonator to form a shunt branch of the stage ladder type circuit, and two ends of each SAW resonator used for parallel connection are connected with an inductor in parallel; the SAW resonator employs an acoustic energy to excite the SAW resonator.
The working principle of the multilayer waveguide SAW filter structure is as follows:
1. the SAW resonator structure comprises a SiC high-speed substrate and 64-degree Y-X LiNbO from bottom to top in sequence 3 Piezoelectric film, transducer interdigital electrode. The method is characterized in that propagation characteristics of all guided wave modes in a multilayer waveguide structure are researched, acoustic waves are guided to be propagated in a low-acoustic-speed area, the effect of enhancing the acoustic wave of a main mode is strengthened, the influence of a non-main mode clutter mode is restrained by optimizing the thickness of a piezoelectric film and the thickness of an interdigital electrode, the bandwidth of an SAW resonator and a filter made of the SAW resonator is increased, the insertion loss of the SAW resonator is reduced, and the SAW resonator and the filter are good in working performance.
2. Inductors are connected in parallel with the resonators in the ladder-shaped circuit of the SAW filter, and the insertion loss and the in-band fluctuation of the filter pass band after the inductors are connected in parallel are obviously improved.
3. The SAW filter adopts a multistage cascade ladder circuit, and increases the external inhibition of the stop band.
Compared with the prior art, the invention has the following beneficial technical effects:
1. the SAW resonator and the SAW filter structure can obtain larger bandwidth and stronger main mode excitation effect, are beneficial to realizing large bandwidth working range of the SAW filter, and improve the insertion loss of the SAW filter and the working performance of the SAW filter due to the stronger main mode effect and the strong inhibition to non-main mode clutter.
2. The scheme of optimizing the symmetrical ladder circuit for the parallel inductance of the parallel resonator circuit is adopted, the insertion loss of a pass band and the in-band fluctuation of the parallel resonator circuit are obviously improved, and the multi-stage cascade ladder circuit is adopted, so that the out-of-stop-band inhibition of the parallel resonator circuit is increased.
The SAW filter structure of the invention can realize the following indexes:
nominal frequency f 0 ：1650MHz；
1dB relative bandwidth: > 5%;
-3dB relative bandwidth: > 12%;
insertion loss: <0.8 dB;
out-of-band rejection:>25dB（f 0 - 250MHz~f 0 - 110MHz，f 0 +110MHz~f 0 + 250MHz）。
drawings
Fig. 1 is a schematic diagram of a uniform interdigital single-ended resonator structure.
Fig. 2 is a schematic diagram of an interdigital electrode transducer structure.
Fig. 3 is a schematic diagram of the SAW resonator structure of the present invention.
FIG. 4 shows a multilayer waveguide structure and a conventional LiNbO 3 The dominant mode of the structure excites the admittance contrast diagram.
FIG. 5 shows a multilayer waveguide structure and conventional LiNbO 3 Admittance of the structure is compared with the figure.
FIG. 6 is a conventional ladder circuit diagram.
FIG. 7 is a circuit diagram of an improved high order symmetrical ladder SAW filter of the present invention.
FIG. 8 is a frequency response curve diagram of a ladder circuit of a SAW filter employing a first-order conventional series and parallel resonator structure.
FIG. 9 is a frequency response curve diagram of a first-order series and parallel resonator structure of a ladder circuit of a SAW filter using parallel resonators and parallel inductors.
FIG. 10 is a graph of the frequency response of a multi-stage optimized ladder circuit used in the present invention.
Detailed Description
The principle of interdigital electrode transducers (IDT) is explained in connection with fig. 2: in the conventional metal interdigital transverse filter, an alternating voltage V is directly applied to the input transducer via the bus bar, and an electric field distribution with a period of a pair of interdigital intervals 2p (λ) is generated, and due to the inverse piezoelectric effect of the piezoelectric substrate, the vicinity of the surface of the piezoelectric medium causes a corresponding elastic deformation, thereby causing vibration of solid particles, and rapidly propagates from the end of the IDT in the form of an elastic wave accompanied by a periodic electric field distribution. The surface wave can be rapidly transmitted to the other end of the piezoelectric medium where the output transducer is located, and the output transducer induces charges at two ends of the metal electrode due to the piezoelectric effect of the piezoelectric substrate, so that the output transducer is directly utilized to output an alternating electrical signal. This is the basic principle of metal interdigital transducers mainly used for exciting and detecting surface acoustic wave signals.
When the electric signal wavelength corresponding to the frequency of the electric signal is the same as the period of the uniform IDT, the excited surface acoustic wave signal is strongest, and when the electric signal wavelength corresponding to other frequencies is different from the period of the uniform IDT, the phases of the acoustic wave signals excited by each pair of interdigital electrodes are mutually counteracted, and the amplitude is reduced. Another result is that the uniform IDT device has a reinforcing effect on a given frequency signal and an attenuating effect on other signals than the frequency signal, i.e., IDT has frequency selectivity. Because the input voltage signal is transmitted to the output end in the form of surface acoustic wave and then converted into an electric signal to be output, the surface acoustic wave conversion device realizes the conversion functions of filtering, delaying, encoding and the like in the process of bidirectional conversion of the input electric signal-acoustic signal-electric signal. A surface acoustic wave signal excited by a uniform IDT device propagates in two directions simultaneously, and thus is also referred to as a bidirectional transducer.
The invention is further described below with reference to the following figures and examples.
Example 1
As shown in FIG. 3, the SAW resonator comprises a SiC high-speed substrate and 64-degree Y-X LiNbO from bottom to top in sequence 3 Piezoelectric film, transducer interdigital electrode; the thickness of the piezoelectric film layer is 0.15-0.4 lambda, the thickness of the interdigital electrode of the transducer is 0.01-0.4 lambda, and lambda represents an interdigital period.
Example 2
Based on example 1, 64 ℃ Y-X LiNbO 3 And the upper surface of the piezoelectric film is also provided with reflecting grids positioned at two sides of the interdigital electrode of the transducer.
Y-X LiNbO 3 The electrode pair in the middle of the upper surface of the piezoelectric film is called an IDT, and the electrode pairs on both sides are called reflection gratings. The surface wave excited by the middle IDT is reflected back under the action of the reflecting gratings at the two sides, the distance between the two reflecting gratings is called a resonant cavity, finally, the surface acoustic wave forms standing wave with certain frequency between the resonant cavities, when the frequency of the standing wave is equal to the frequency of external excitation, the sound wave emitted by the IDT is strongest, the frequency is called resonant frequency, and the basic principle of single-end surface acoustic wave resonator resonance is adopted.
Example 3
A multilayer waveguide high-performance SAW resonator is prepared by the following method: s1) polishing and cleaning the SiC substrate;
s2) growing 64-degree Y-X LiNbO on the SiC substrate by using a chemical vapor deposition method or a pulse laser deposition method 3 A piezoelectric thin film layer of a material;
s3) growing an electrode layer on the piezoelectric thin film layer, arranging a photoresist mask on the surface of the electrode layer according to the gap position of the interdigital electrode of the transducer, and etching the electrode layer to form the interdigital electrode of the transducer, thereby obtaining the SAW resonator structure.
Example 4
Fig. 7 is a topological structure of a high-order ladder filter, which is a high-order symmetrical ladder SAW filter, and a multistage cascaded ladder circuit is adopted, in order to make the filter package compact and symmetrical, each stage of ladder circuit includes one SAW resonator for series connection and two SAW resonators for parallel connection, and the two SAW resonators for parallel connection are symmetrically distributed on two sides of the series SAW resonator to form a shunt branch of the stage ladder circuit, which is helpful for improving the performance of the SAW filter, and two ends of each SAW resonator for parallel connection are connected in parallel with an inductor, which is helpful for increasing out-of-band rejection; the SAW resonator employs an acoustic energy to excite the SAW resonator.
The technical effects of the present invention will be further described below with reference to the drawings attached to the specification.
FIG. 4 shows a multilayer waveguide structure and a conventional LiNbO 3 The contrast diagram of the main mode excitation admittance of the structure shows that the admittance impedance ratio of the optimized multilayer waveguide structure is the traditional LiNbO 3 About ten times higher.
FIG. 5 shows a multilayer waveguide structure and a conventional LiNbO 3 Compared with the admittance graph of the structure, the optimized multilayer waveguide structure not only has increased bandwidth, but also has no clutter interference in the band.
Fig. 9 is a frequency response curve diagram of a first-order series and parallel resonator structure of a ladder circuit of the SAW filter adopting a parallel resonator parallel capacitor, and fig. 9 is compared with fig. 8, so that the out-of-band rejection of the improved novel ladder circuit structure is obviously improved.
As can be seen from the frequency response curve diagram of the high-order symmetrical topology optimization ladder circuit adopted by the invention shown in FIG. 10, the bandwidth of the SAW filter is increased, and the out-of-band rejection and the passband ripple are obviously improved.
Claims (4)
1. The acoustic energy excited SAW resonator is characterized in that the SAW resonator sequentially comprises a SiC high-speed substrate and 64-degree Y-X LiNbO from bottom to top 3 Piezoelectric film, transducer interdigital electrode; the thickness of the piezoelectric film layer is 0.15-0.4 lambda, the thickness of the interdigital electrode of the transducer is 0.01-0.4 lambda, and lambda represents an interdigital period.
2. The acoustic energy excited SAW resonator of claim 1, wherein 64 ° Y-X LiNbO 3 And the upper surface of the piezoelectric film is also provided with reflecting grids positioned at two sides of the interdigital electrode of the transducer.
3. An acoustic energy excited SAW resonator as claimed in claim 1, prepared by: s1) polishing and cleaning the SiC substrate;
s2) growing 64-degree Y-X LiNbO on the SiC substrate by using a chemical vapor deposition method or a pulse laser deposition method 3 A piezoelectric thin film layer of a material;
s3) growing an electrode layer on the piezoelectric film layer, arranging a photoresist mask on the surface of the electrode layer according to the gap position of the interdigital electrode of the transducer, and etching the electrode layer to form the interdigital electrode of the transducer, thereby obtaining the SAW resonator structure.
4. A high-order symmetrical trapezoid SAW filter adopts a multistage cascade ladder circuit, and is characterized in that each stage ladder circuit comprises a SAW resonator used for series connection and two SAW resonators used for parallel connection, the two SAW resonators used for parallel connection are symmetrically distributed on two sides of the series SAW resonator to form a shunt branch of the stage ladder circuit, and two ends of each SAW resonator used for parallel connection are connected with an inductor in parallel; the SAW resonator employs an acoustic energy as claimed in any one of claims 1 to 3 to excite the SAW resonator.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202210714602.8A CN114938214A (en) | 2022-06-23 | 2022-06-23 | Acoustic energy excitation SAW resonator and high-order symmetrical trapezoid SAW filter |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115882813A (en) * | 2023-03-08 | 2023-03-31 | 成都频岢微电子有限公司 | Based on surface acoustic wave-lumped element combination syntonizer and band-pass filter |
| CN116944006A (en) * | 2023-09-19 | 2023-10-27 | 中北大学 | D, d 11 PMUT unit driven by working mode and preparation method thereof |
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2022
- 2022-06-23 CN CN202210714602.8A patent/CN114938214A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115882813A (en) * | 2023-03-08 | 2023-03-31 | 成都频岢微电子有限公司 | Based on surface acoustic wave-lumped element combination syntonizer and band-pass filter |
| CN116944006A (en) * | 2023-09-19 | 2023-10-27 | 中北大学 | D, d 11 PMUT unit driven by working mode and preparation method thereof |
| CN116944006B (en) * | 2023-09-19 | 2023-12-15 | 中北大学 | D, d 11 PMUT unit driven by working mode and preparation method thereof |
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