Z-axis MEMS Accelerometer Wafer Bending Compensation
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Solution Overview
Problem
MEMS accelerometers face offset errors in differential capacitance measurements due to wafer bending, which complicates the measurement process and requires additional wiring for compensation.
Innovation Solution
The implementation of two pairs of z-axis seesaws suspended from a central anchor point, where the capacitances are summed to reduce offset errors induced by wafer bending in the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wafer bending occurs during manufacturing or operation, then structural changes and tilting of the device wafer occur, but offset errors are introduced in differential capacitance measurements
Solution Approach 1:
The accelerometer is divided into multiple identical sensor elements (first accelerometer element and second accelerometer element) that are arranged symmetrically. Each element independently measures acceleration, and their outputs are combined through differential processing to eliminate common-mode errors from wafer bending.
Solution Approach 2:
The patent employs a symmetric arrangement of accelerometer elements positioned at opposite sides of the device wafer. This symmetric configuration ensures that wafer bending affects both elements equally but in opposite directions, allowing differential measurement to cancel out the bending-induced offset errors.
2Measurement precision
If additional wiring or complex compensation systems are implemented to correct wafer bending effects, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The accelerometer structure itself provides the compensation mechanism through its symmetric dual-element design. The differential measurement approach allows the system to self-correct for wafer bending effects without requiring external compensation circuits, additional wiring, or complex control algorithms.
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 arrangement effectively reduces offset errors in differential output signals, enhancing the robustness of the accelerometer against wafer bending and maintaining accurate measurements without the need for additional wiring or complex compensation systems.
Implementation Method 1
MEMS accelerometers may comprise capacitors for detecting the movement of partly mobile device structures
Implementation Method 2
A first piezoelectric element and a second piezoelectric element are arranged in a device plane of an accelerometer
Data Source
Figure 1a~1b
Figure 2a
Figure 2b
AI summary
A capacitive micromechanical accelerometer comprising a first proof mass, a second proof mass, a third proof mass and a fourth proof mass. Each proof mass is configured as a seesaw which undergoes rotation out of the xy-plane in response to z-axis acceleration. The four proof masses are suspended from the same central anchor point with torsionally flexible suspension arrangements. Errors introduced into the output signal by wafer bending can be automatically compensated in a differential capacitive measurement.