MEMS Test Structure for Wafer-Level Spurious Mode Detection
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Solution Overview
Problem
Microelectromechanical devices, particularly gyroscopes, suffer from spurious vibration modes that distort their response due to intrinsic process variabilities and mechanical nonlinearities, leading to rejects during assembly, which are costly and inefficient to detect before final assembly.
Innovation Solution
A test structure and equipment are integrated into the microelectromechanical devices to test spurious vibration modes at the wafer level, using capacitive coupling and electrostatic forces to identify defective devices, allowing their removal before assembly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If microstructure is designed to avoid spurious vibration modes, then device reliability is improved, but device complexity increases and manufacturing precision requirements increase
Solution Approach 1:
The patent applies preliminary action by implementing test structures and testing procedures during the manufacturing process (wafer-level testing) to identify devices with spurious vibration modes before final assembly. This allows defective devices to be detected and eliminated early, preventing reliability issues in the final product without requiring complex design modifications to the microstructure itself.
Solution Approach 2:
The patent replaces complex mechanical design solutions (modifying microstructure to eliminate spurious modes) with an electrical/testing-based approach. By using test structures that apply forces and measure responses electrically, the system identifies spurious vibration modes without requiring mechanical redesign, thus reducing device complexity while maintaining reliability.
2Reliability
If mechanical nonlinearities are reduced, then spurious vibration modes are mitigated, but manufacturing precision requirements increase and device dimensions increase
Solution Approach 1:
The patent applies self-service by using the device's own structure and materials to create test structures that are integrated into the manufacturing process. The test structures use the same semiconductor material and fabrication processes as the device itself, eliminating the need for external testing equipment or additional precision manufacturing steps. This allows spurious vibration mode detection without increasing manufacturing precision requirements.
3Measurement precision
If devices are tested at the end of assembly, then comprehensive testing is possible, but time and resources are wasted on assembling defective devices
Solution Approach 1:
The patent implements preliminary action by performing tests at the wafer level before final device assembly and packaging. The test structures are integrated into the wafer during manufacturing, allowing defective devices to be identified early in the production process. This eliminates the waste of time and resources associated with assembling and packaging defective devices, while maintaining comprehensive testing capability through the integrated test structures.
4Reliability
If sinusoidal forcing is used instead of square-wave, then spurious vibration modes are reduced, but energy consumption increases and architectural complexity increases
Solution Approach 1:
The patent applies the taking out principle by extracting and isolating the forcing function generation to the test equipment rather than the device itself. The test structures provide a controlled environment where forcing functions can be applied and measured without affecting the device's normal operation. This allows the use of optimal forcing waveforms during testing without increasing the device's energy consumption or architectural complexity during actual use.
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
The test structure enables systematic identification and removal of defective devices, reducing waste and saving resources by detecting spurious vibration modes early in the manufacturing process, with minimal impact on device dimensions and sensitivity.
Implementation Method 1
using capacitive coupling and electrostatic forces to identify defective devices
Implementation Method 2
using capacitive coupling and electrostatic forces to identify defective devices
Implementation Method 3
elastically constrained to the support body so as to be able to oscillate along one or more axes
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
A microelectromechanical device includes: a support body (8, 10-13); at least one movable mass (15) of semiconductor material, elastically constrained to the support body (8, 10-13) so as to be able to oscillate; fixed detection electrodes (22, 23) rigidly connected to the support body (8, 10-13) and capacitively coupled to the at least one movable mass (15); and at least one test structure (17) of semiconductor material, rigidly connected to the support body (8, 10-13) and distinct from the fixed detection electrodes (22, 23). The test structure (17) is capacitively coupled to the at least one movable mass (15) and is configured to apply electrostatic forces (FX, FY, FZ) to the at least one movable mass (15) in response to a voltage between the test structure (17) and the at least one movable mass (15).