XBAR Fabrication Using Polysilicon Pillars for Air Cavity Control
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Solution Overview
Problem
Current RF filters, particularly those using acoustic wave resonators, are not well-suited for higher frequencies and wider bandwidths required in future communication networks, such as the 5G NR standard, which necessitates the development of more effective bandpass filters capable of handling higher transmit power and wider communication channel bandwidths.
Innovation Solution
The use of Transversely-Excited Film Bulk Acoustic Resonators (XBARs) with polysilicon pillars for improved fabrication techniques, specifically employing a front-side membrane release process to create air cavities, which reduces etching time and complexity, and enhances control over cavity shape, allowing for the production of high-frequency capable RF filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional acoustic wave resonators are used, then existing manufacturing processes can be maintained, but high-frequency performance and bandwidth capabilities are insufficient
Solution Approach 1:
The patent changes the physical parameters of the resonator structure by introducing air cavities and polysilicon pillars, which modifies the acoustic wave propagation characteristics to achieve high-frequency operation with improved bandwidth capability
Solution Approach 2:
The resonator structure is segmented into distinct regions with air cavities and polysilicon pillars, creating a multi-component structure that enables independent optimization of different functional zones for enhanced frequency performance
2Ease of manufacture
If traditional cavity formation methods are used, then existing fabrication processes can be maintained, but etching time and process complexity increase
Solution Approach 1:
Polysilicon pillars are formed in advance as sacrificial structures before the final cavity formation step. These pre-formed pillars guide the subsequent release process, enabling more efficient air cavity creation with reduced etching time and simplified process steps
3Manufacturing precision
If polysilicon pillars with air cavities are introduced, then control over cavity shape is improved, but device structure complexity increases
Solution Approach 1:
Polysilicon pillars serve as intermediary sacrificial structures that simplify the overall fabrication process. By using these temporary structures, the patent achieves precise cavity shape control while the pillars themselves are eventually removed, so they do not remain as permanent complexity in the final device
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 enables the creation of RF filters with improved high-frequency performance and bandwidth capabilities, addressing the limitations of existing technologies by providing better control over cavity formation and reducing manufacturing time and costs, thus supporting the demands of advanced communication systems.
Implementation Method 1
a thin floating layer or diaphragm of a single-crystal piezoelectric material
Implementation Method 2
A microwave signal applied to the IDT excites a shear primary acoustic wave in the piezoelectric diaphragm, such that the acoustic energy flows substantially normal to the surfaces of the layer
Data Source
AI summary
An acoustic resonator device is formed using sacrificial polysilicon pillar by forming a polysilicon pillar on a substrate and depositing a dielectric layer to bury the polysilicon pillar and planarizing the surface of the dielectric layer. A piezoelectric plate is bonded to the planarized surface of the dielectric layer and thinned to a target piezoelectric membrane thickness. At least one conductor pattern is formed on the thinned piezoelectric plate and the polysilicon pillar is then removed using an etchant introduced through holes in the piezoelectric plate to form an air cavity where the pillar was removed.