Acoustic Wave Cavity Structure for Uniform Piezoelectric Thickness
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Solution Overview
Problem
The existing acoustic wave devices face challenges in achieving accurate film thickness of piezoelectric layers due to uneven boundaries between sacrificial and intermediate layers, leading to variations in film thickness and performance.
Innovation Solution
The acoustic wave device incorporates an intermediate layer with distinct portions, where one portion is more soluble in an etchant than the other, allowing for precise control and formation of a cavity without a sacrificial layer, thereby improving the film thickness accuracy of the piezoelectric layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a sacrificial layer is etched via a through hole to form a cavity, then the cavity can be formed in the intermediate layer, but the boundary between the sacrificial layer and intermediate layer becomes uneven causing film thickness variation
Solution Approach 1:
The intermediate layer is divided into two portions with different etch resistance: a first portion closer to the cavity that is more soluble in etchant, and a second portion farther from the cavity that is less soluble. This segmentation allows the first portion to be selectively removed to form a clean cavity boundary while the second portion remains intact to support the piezoelectric layer, preventing boundary unevenness and film thickness variation.
Solution Approach 2:
Different regions of the intermediate layer are given different local properties regarding etch resistance. The first portion has higher solubility in the prescribed etchant compared to the second portion, allowing selective removal of material in the cavity region while maintaining structural integrity in the support region, thus achieving both cavity formation and uniform film thickness.
2Device complexity
If the intermediate layer has uniform etch resistance, then the structure is simpler, but the cavity cannot be formed without a sacrificial layer
Solution Approach 1:
The etch resistance parameter of the intermediate layer is varied spatially to enable cavity formation. By making the first portion more soluble than the second portion, the material properties change locally, allowing the cavity to be formed through selective etching without requiring a separate sacrificial layer, thus maintaining structural simplicity while achieving precise cavity formation.
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
This approach enhances the accuracy and consistency of the piezoelectric layer thickness, reducing variations and improving the overall performance and resonance characteristics of the acoustic wave device.
Implementation Method 1
The first portion is more soluble in a prescribed etchant than the second portion
Data Source
AI summary
An acoustic wave device includes a support substrate with a thickness in a first direction, an intermediate layer on the support substrate, a piezoelectric layer adjacent to the support substrate in the first direction, and a functional electrode on the piezoelectric layer. A cavity is provided in the intermediate layer. The intermediate layer includes a first portion and a second portion. The first portion is closer to the cavity than the second portion. The first portion or the second portion is modified.