Non-linear tethers for piezoelectric device suspension
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for suspending piezoelectric devices over cavities in substrates often result in mechanical stress and damage due to etching processes like XeF2, which can be incompatible with certain materials and cause physical stress, leading to inefficient device performance and increased manufacturing costs.
Innovation Solution
The use of non-linear tethers with non-collinear centerlines to suspend devices over cavities, allowing for etching with less stressful materials like TMAH or KOH, reducing mechanical isolation issues and manufacturing expenses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If XeF2 etching is used to release devices from substrate, then device release is achieved, but physical stress and damage to tethers and devices occur
Solution Approach 1:
A sacrificial layer is introduced as an intermediary between the device and substrate. This sacrificial layer is selectively etched away to release the device, while the device and substrate remain intact. The sacrificial layer absorbs the etching process, preventing direct stress and damage to the device and substrate structures.
Solution Approach 2:
The sacrificial layer is designed as a temporary, disposable structure that is removed after serving its release function. Using a sacrificial material that can be easily and completely removed (such as through selective etching) eliminates the need for complex release mechanisms and avoids long-term structural complications.
2Reliability
If XeF2 etching is used, then device release is achieved, but incompatibility with certain materials requires additional encapsulation layers
Solution Approach 1:
The etching chemistry is changed from XeF2 to a selective etchant that is compatible with the device materials. By changing the etching parameters (chemistry and selectivity), the process becomes compatible with metals and other materials used in piezoelectric devices, eliminating the need for additional protective encapsulation layers.
Solution Approach 2:
The sacrificial layer serves as a mediator that enables device release without requiring the device itself to be exposed to harsh etching chemicals. The sacrificial layer is removed instead, allowing the device to remain protected and compatible with standard materials.
3Strength
If straight tethers are used to suspend devices, then mechanical connection is achieved, but etching stress concentrates and causes damage
Solution Approach 1:
The tether geometry is changed from straight to curved or meandering. This curvature distributes etching stress along the tether length rather than concentrating it at single points. The curved path allows stress to be gradually distributed, reducing the likelihood of tether failure during the etching process.
4Reliability
If devices are suspended over cavities, then mechanical isolation is improved, but etching processes cause stress to tethers and devices
Solution Approach 1:
The sacrificial layer acts as an intermediary that enables cavity formation without exposing the suspended device and tether structures to harsh etching conditions. The sacrificial material is removed to create the cavity, while the device remains protected, maintaining both mechanical isolation and structural integrity.
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. A device structure can comprise a device over a sacrificial portion or cavity and a tether with a tether opening extending to the sacrificial portion or cavity. The tether or tether opening can have a T shape. The tether can have a tether length at least one third as large as a device length and the device can have a device length at least twice as large as a device width.