Bulk Wave Resonator Structure Without Cavity for High-Frequency Passbands
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Solution Overview
Problem
Existing bulk wave resonators face challenges in achieving higher resonant frequencies due to mechanical instability caused by a thinned piezoelectric layer separated from the support substrate, which is exacerbated by the presence of a cavity, limiting their ability to operate at higher frequencies.
Innovation Solution
A bulk wave resonator design that includes a support substrate, an acoustic multilayer film with alternating dielectric layers, and a piezoelectric layer supported by the multilayer film without a cavity, utilizing thickness shear vibration excited by a parallel electric field, and employing specific cut angles for the piezoelectric layer to enhance mechanical stability and resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the thickness of the piezoelectric layer is reduced to increase resonant frequency, then the resonant frequency increases, but the mechanical stability deteriorates due to the thinned structure being separated from the support substrate by a cavity
Solution Approach 1:
The invention removes the cavity structure from between the piezoelectric layer and support substrate, eliminating the separation that causes mechanical instability. This allows the piezoelectric layer to be directly supported while maintaining reduced thickness for high resonant frequency operation
Solution Approach 2:
Instead of having the piezoelectric layer suspended over a cavity as in conventional FBAR structures, the invention inverts the approach by having the piezoelectric layer directly supported on the support substrate without a cavity, fundamentally changing the structural configuration to achieve both high frequency and mechanical stability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves higher resonance frequencies with improved mechanical stability and reduced energy loss, allowing for the development of bandpass filters with a high-frequency passband and wider bandwidth.
Implementation Method 1
a first electrode and a second electrode that are disposed to face each other with a gap therebetween on a first surface of the piezoelectric layer opposite to the acoustic multilayer film, and that are applied with a voltage for allowing the piezoelectric layer to generate the bulk wave
Implementation Method 2
a bulk wave in the first direction that is generated by a thickness shear vibration in the first direction, which is excited by a parallel electric field when a voltage is applied to the first electrode and the second electrode
Data Source
AI summary
[PROBLEM TO BE SOLVED] To provide a bulk wave resonator having a high frequency passband.[SOLUTION] A bulk wave resonator using a bulk wave, includes a support substrate, an acoustic multilayer film that includes, stacked on the support substrate, a plurality of types of dielectrics having different acoustic impedances, a piezoelectric layer that is stacked on the acoustic multilayer film, a first electrode, and a second electrode. The first and second electrodes are disposed to face each other with a gap therebetween on a first surface of the piezoelectric layer opposite to the acoustic multilayer film, and are applied with a voltage for allowing the piezoelectric layer to generate the bulk wave. A direction that is parallel to the surface of the piezoelectric layer and in which the first electrode and the second electrode face each other is defined as a first direction. The bulk wave resonator uses, as a main mode, a bulk wave in the first direction that is generated by a thickness shear vibration in the first direction, which is excited by a parallel electric field formed in the piezoelectric layer when a voltage applied to the first electrode and the second electrode.