CN-122001332-A - Elastic wave filter and multiplexer

CN122001332ACN 122001332 ACN122001332 ACN 122001332ACN-122001332-A

Abstract

The invention discloses an elastic wave filter and a multiplexer, and belongs to the technical field of radio frequency. The elastic wave filter of the invention comprises a plurality of series arm and parallel arm resonators, each resonator comprising a piezoelectric substrate and an interdigital transducer thereon. The improvement of the invention is that in at least one resonator the piezoelectric layer of the piezoelectric substrate is locally etched and filled with a dielectric layer, on which the interdigital transducer is directly arranged. The electromechanical coupling coefficient of the corresponding resonator can be independently regulated by controlling the ratio of the thickness h2 of the dielectric layer to the thickness h1 of the piezoelectric layer to be less than or equal to 0.09, so that the rectangle degree of one side or two sides of the passband of the filter is pertinently improved, and the out-of-band rejection characteristic is improved. The structure realizes fine regulation and control of frequency response characteristics while maintaining basic performance of the filter, and has simple structure and good process compatibility.

Inventors

LIU PING
YU ZHENYI
FU SULEI
XU ZHIBIN
WANG WEIBIAO

Assignees

无锡市好达电子股份有限公司

Dates

Publication Date: 20260508
Application Date: 20251229

Claims (10)

1. An elastic wave filter, comprising: a resonator including a plurality of series-arm resonators and a plurality of parallel-arm resonators, and a plurality of sections of conductive traces, input terminals, and output terminals for achieving electrical connection between the resonators; At least one of the series arm resonators includes a piezoelectric substrate, and an interdigital transducer; the piezoelectric substrate comprises a piezoelectric layer; the piezoelectric layer of the series arm resonator is etched and filled with a dielectric layer on which the interdigital transducer is placed.
2. The elastic wave filter according to claim 1, wherein, At least one of the parallel arm resonators includes a piezoelectric substrate, and an interdigital transducer; the piezoelectric substrate comprises a piezoelectric layer; The piezoelectric layer of the parallel arm resonator is etched and filled with a dielectric layer on which the interdigital transducer is placed.
3. An elastic wave filter according to claim 2, wherein, The thickness of the piezoelectric layer in the z direction is h1, the thickness of the dielectric layer in the z direction is h2, and h2/h1 satisfies that h2/h1 is less than or equal to 0.09.
4. An elastic wave filter according to claim 3, wherein, The admittance ratio of the resonator satisfying h2/h1 is less than or equal to 0.09 is more than 60 dB.
5. The elastic wave filter according to claim 1, wherein, The piezoelectric substrate includes: the piezoelectric layer, or The piezoelectric layer and a support substrate disposed directly below the piezoelectric layer, or The piezoelectric layer, a low acoustic velocity layer disposed directly below the piezoelectric layer, and the support substrate disposed directly below the low acoustic velocity layer, or The piezoelectric layer, the low acoustic velocity layer disposed directly below the piezoelectric layer, a trapping material layer disposed directly below the low acoustic velocity layer, and the support substrate disposed directly below the trapping material layer.
6. The elastic wave filter according to claim 5, wherein, The trapping material layer is formed by one or more of amorphous silicon, polycrystalline silicon, amorphous germanium and polycrystalline germanium.
7. The elastic wave filter according to claim 1, wherein, The dielectric layer is made of a material with dielectric properties, such as silicon dioxide, silicon nitride, aluminum oxide, etc. .
8. The elastic wave filter according to claim 1, wherein, The piezoelectric layer is a film made of one or more materials with piezoelectric characteristics, such as lithium tantalate, lithium niobate, aluminum nitride, zinc oxide and the like.
9. The elastic wave filter according to claim 1, wherein, The interdigital transducer also comprises a false finger electrode.
10. A multiplexer comprising at least two filter branches, wherein at least one of said filter branches is an elastic wave filter according to any one of claims 1 to 9.

Description

Elastic wave filter and multiplexer Technical Field The present invention relates to the field of radio frequency technologies, and in particular, to an elastic wave filter and a multiplexer. Background With rapid development of wireless communication technology, especially wide application of high-frequency broadband communication systems such as 5G, internet of things and satellite communication, performance requirements on radio frequency front-end devices are increasingly improved. The filter is used as a key component for realizing frequency selection and signal isolation in a radio frequency system, and the performance of the filter directly influences the channel capacity, anti-interference capability and signal integrity of the communication system. In the prior art, elastic wave filters typically achieve resonance and filtering functions by constructing interdigital transducers on a piezoelectric substrate. Although such structures are well established in terms of basic performance, there are significant shortcomings in squareness and out-of-band rejection. The degree of squareness is a key indicator for measuring the steepness of transition between the pass band and the stop band of the filter, and a high degree of squareness means better out-of-band rejection capability and lower signal distortion. Out-of-band rejection refers to the degree of attenuation of a signal by a filter outside the passband of the elastic wave filter. In particular, it describes the rejection capability of a filter for signal components whose frequencies are outside of its passband. However, conventional designs tend to have difficulty achieving desirable squareness and strong out-of-band rejection characteristics while ensuring low insertion loss and high selectivity. Especially in a multi-band and high-density integrated system, the problems of adjacent channel interference, signal crosstalk and the like are easily caused by poor rectangularity and weak out-of-band inhibition, so that the overall performance of the system is affected. To improve the rectangularity, the prior art attempts various methods such as optimizing the filter topology, adjusting resonator parameters, introducing impedance matching networks, etc. However, these methods tend to improve the rectangularity while sacrificing other performance metrics, such as increased insertion loss, reduced passband flatness, degraded out-of-band rejection, increased structural complexity, etc., and thus make it difficult to achieve overall optimization of performance. Therefore, how to effectively improve the rectangle degree and out-of-band rejection of the elastic wave filter on the basis of maintaining the original advantages of the elastic wave filter is a technical problem to be solved in the field. Particularly in the application scenarios of high frequency, high suppression and small size, there is a need for an elastic wave filter design method with simple structure, controllable performance and easy manufacture, so as to realize good balance of filtering performance, rectangularity and out-of-band suppression. Disclosure of Invention The invention provides an elastic wave filter and a multiplexer, which aim to solve the technical problems of the steepness (i.e. rectangle) of the passband edge and insufficient out-of-band rejection of the traditional elastic wave filter when the traditional elastic wave filter pursues high frequency selectivity. The invention has the core technical scheme that the dielectric layer is locally introduced to accurately regulate and control the electromechanical coupling characteristic of the resonator, so that the rectangular degree of the filter and the elastic wave filter and multiplexer with out-of-band rejection are improved. The specific scheme of the invention is as follows: an elastic wave filter comprising: a resonator including a plurality of series-arm resonators and a plurality of parallel-arm resonators, and a plurality of sections of conductive traces, input terminals, and output terminals for achieving electrical connection between the resonators; At least one of the series arm resonators includes a piezoelectric substrate, and an interdigital transducer; the piezoelectric substrate comprises a piezoelectric layer; the piezoelectric layer of the series arm resonator is etched and filled with a dielectric layer on which the interdigital transducer is placed. Further, at least one of the parallel arm resonators includes a piezoelectric substrate, and an interdigital transducer; the piezoelectric substrate comprises a piezoelectric layer; The piezoelectric layer of the parallel arm resonator is etched and filled with a dielectric layer on which the interdigital transducer is placed. Further, the thickness of the piezoelectric layer in the z direction is h1, the thickness of the dielectric layer in the z direction is h2, and h2/h1 satisfies that h2/h1 is less than or equal to 0.09. Further, the admittance ratio of t