Non-Linear Tethers for Piezoelectric Cavity Suspension
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Solution Overview
Problem
Existing methods for suspending piezoelectric devices over cavities in substrates, such as XeF2 dry etching, can be incompatible with metal electrodes and cause physical stress, leading to device damage and inefficiencies in mechanical isolation.
Innovation Solution
The use of non-linear tethers with non-collinear centerlines to connect devices to substrates, allowing for improved etching processes using wet etchants like TMAH or KOH, reducing damage and enhancing mechanical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If XeF2 dry etching is used to form cavities under suspended devices, then the etching process can be performed, but the process causes physical stress to devices and is incompatible with metal electrodes, leading to device damage
Solution Approach 1:
The patent changes the etching chemistry parameter from XeF2 dry etching to wet etchants (TMAH or KOH), which are compatible with metal electrodes and cause less physical stress to devices. This parameter change resolves the contradiction by making the etching process both manufacturable and device-friendly
Solution Approach 2:
The patent introduces an intermediary tether structure with non-linear geometry that mediates between the device and substrate during etching. The tether's non-collinear configuration allows etchant access while protecting the device from stress, enabling use of gentler wet etching processes
2Reliability
If devices are suspended over cavities to improve mechanical isolation, then acoustic wave resonance is enhanced, but the etching process to form cavities causes damage to devices
Solution Approach 1:
The patent applies curvature to the tether centerline, creating a non-linear path between device and substrate. This curved configuration allows etchant to access the cavity while distributing mechanical stress, enabling cavity formation that improves mechanical isolation without damaging devices
Solution Approach 2:
The tether is segmented into non-collinear portions that can independently flex and absorb stress during etching. This segmentation allows the structure to maintain mechanical isolation benefits while protecting the device from etching-induced damage
3Device complexity
If straight tethers are used to suspend devices, then the structure is simple, but the etching process cannot access all areas and causes stress concentration
Solution Approach 1:
The tether centerline is designed with curvature rather than being straight, creating a non-linear path that allows etchant access from multiple angles. This curved geometry enables complete cavity formation while distributing stress, accepting increased structural complexity for improved reliability
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
Non-linear tethers facilitate the suspension of piezoelectric devices over cavities with reduced damage and improved mechanical isolation, enhancing device performance and manufacturing yields by using less stressful etching processes.
Implementation Method 1
etching processes using wet etchants like TMAH or KOH
Implementation Method 2
a device comprising a piezoelectric material
Data Source
AI summary
A suspended device structure comprises a substrate, a cavity disposed in a surface of the substrate, and a device suspended entirely over a bottom of the cavity. The device is a piezoelectric device and is suspended at least by a tether that physically connects the device to the substrate. The tether has a non-linear centerline. A wafer can comprise a plurality of suspended device structures.