MEMS Gyroscope Test Structure for Spurious Mode Screening
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Solution Overview
Problem
MEMS gyroscopes face performance degradation due to spurious modes caused by manufacturing inaccuracies and environmental changes, which shift in frequency and can be excited by higher harmonics of the driving signal, leading to early failures and increased costs due to laboratory characterization and testing.
Innovation Solution
Incorporating resonance modification test structures with softening and hardening structures that adjust the average gap between electrodes, allowing for variable voltage application to modify the resonance frequency and driving frequency, thereby shifting harmonics away from spurious modes and identifying potential instability during testing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If manufacturing tolerances are relaxed to reduce costs, then manufacturing precision deteriorates, but spurious modes are excited causing reliability to worsen
Solution Approach 1:
The patent applies preliminary action by performing spurious mode testing during the manufacturing process itself, rather than waiting for field failures. The test structure allows manufacturers to identify and filter out components with spurious modes before they reach customers, preventing reliability issues while maintaining relaxed manufacturing tolerances that reduce costs.
Solution Approach 2:
The gyroscope structure includes integrated test structures that allow the device to self-diagnose for spurious modes. The movable mass and electrodes form both the operational gyroscope and the test structure, enabling manufacturers to use the device's own components to identify reliability issues without requiring separate test equipment.
2Reliability
If laboratory characterization and testing are performed to identify spurious modes, then reliability improves, but loss of time and increased costs occur
Solution Approach 1:
The patent merges the operational gyroscope structure with the test structure. The same movable mass, electrodes, and mechanical structure serve dual purposes: as the functional gyroscope and as the spurious mode test structure. This eliminates the need for separate characterization equipment and reduces testing time while maintaining reliability.
Solution Approach 2:
The test structure is designed to be universal, working with any gyroscope device of the type. The same electrode configurations and mechanical structures used in operation are also used for testing, allowing a single device to serve multiple functions and eliminating the need for specialized external testing equipment.
3Ease of manufacture
If spurious modes are not detected early, then manufacturing costs increase due to field failures, but detection requires complex testing
Solution Approach 1:
The patent applies local quality by adding test functionality only to specific locations within the gyroscope structure where spurious modes are most likely to occur. The test electrodes are positioned at strategic locations around the movable mass, providing targeted detection capability without requiring complex testing throughout the entire 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 allows for early identification of components at risk of spurious mode excitation, reducing the likelihood of early failures and costs by verifying stability through softening and hardening ramps, ensuring reliable operation and maintaining gyroscope performance.
Implementation Method 1
the resonance modification test structure is configured to be biased, in a resonance modification test step, to a direct and variable modification voltage such as to cause a modification of the average gap between each modification fixed electrode and a respective modification movable electrode
Implementation Method 2
a movable mass suspended on the substrate and having a resonance frequency
Data Source
AI summary
Test method of a vibrational MEMS structure wherein, a direct, variable modification voltage is applied to a resonance modification test structure having non-rectilinear electrodes, modifying the resonance frequency of the movable mass and the driving frequency. During the test, the movable mass is verified about stability and, if not stable, the vibrational MEMS structure is rejected.