Suspended MEMS Resonator Fabrication on Planar Cavity Surfaces
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Solution Overview
Problem
Existing MEMS resonators face challenges in achieving stable and reproducible operation due to thermal and mechanical fluctuations, leading to inconsistent fabrication and defects, primarily because features are formed on surfaces that are not planar when a cavity is present, causing stress and undulations.
Innovation Solution
The fabrication method involves forming the features of the MEMS resonator before creating the cavity, using a multilayer substrate with dielectric materials to form a cavity with rectilinear corners and planar surfaces, ensuring the resonator is suspended in a dielectric cavity with precise dimensions, eliminating etch-time variations and allowing for stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the cavity is formed first and then features are formed on its surface, then the cavity can be created early in the process, but the features will be formed on non-planar surfaces causing stress and undulations that reduce manufacturing precision
Solution Approach 1:
The patent applies preliminary action by forming the resonator features on a planar surface before creating the cavity underneath. This sequence ensures that all critical features are defined on a flat, stress-free surface, eliminating the problems of non-planar formation. The cavity is then formed by removing sacrificial material after the features are already in place, maintaining both manufacturing precision and process efficiency.
2Adaptability or versatility
If features are formed on non-planar surfaces, then the cavity structure can be accommodated, but thermal and mechanical fluctuations cause inconsistent fabrication and defects
Solution Approach 1:
The patent resolves this contradiction by performing all feature formation operations before cavity creation. The resonator, electrodes, and other critical features are fabricated on a planar sacrificial layer, ensuring uniform stress distribution and thermal characteristics. Only after these features are complete is the cavity formed by selective removal of the sacrificial material, thereby maintaining reliability while accommodating the cavity structure.
3Ease of manufacture
If etch-time variations are present during cavity formation, then process flexibility is maintained, but dimensional control of the cavity becomes inconsistent
Solution Approach 1:
The patent replaces time-based etch control with a mechanical/physical reference system. Instead of relying on etch duration to define cavity dimensions, the cavity boundaries are determined by pre-formed etch stop layers and sacrificial material interfaces. These physical references provide consistent dimensional control regardless of etch-rate variations or timing differences, while still allowing process flexibility in the etching step itself.
Data Source
AI summary
A microelectromechanical system (MEMS) device is provided that includes a substrate having a dielectric cavity formed therein and a movable electromechanical device suspended in the dielectric cavity. The dielectric cavity includes a substantially planar bottom surface and at least one sidewall surface extending substantially perpendicularly from the bottom surface. The movable electromechanical device is suspended in the dielectric cavity such that the movable electromechanical device is spaced apart from the bottom surface and the at least one sidewall surface of the dielectric cavity. The bottom surface of the cavity and each of the at least one sidewall surface of the cavity meet at a rectilinear corner.