MEMS Sensor Stepped Cavity and Segmented Proof Masses
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Solution Overview
Problem
Current MEMS sensors face challenges in accurately detecting acceleration in multiple directions due to limitations in their structural design and manufacturing processes, which affect the sensitivity and reliability of the sensors.
Innovation Solution
The proposed MEMS sensor features a semiconductor chip with a layered structure comprising a first and second semiconductor material, where a cavity is formed with a stepped surface and a movable portion supported by a frame portion, allowing for a cantilever structure and extension portions that enhance detection capabilities by varying thickness and projection features, and a method involving trench formation and sacrifice layer etching for manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional MEMS sensor structure with fixed portion and movable portion is used, then the sensor can detect acceleration, but the sensitivity and reliability are insufficient for accurate multi-directional detection
Solution Approach 1:
The movable portion is segmented into multiple independent proof masses (first, second, third proof masses) that can move independently in different directions. This segmentation allows each mass to respond to specific acceleration components, improving measurement precision while the distributed structure enhances reliability through redundancy
Solution Approach 2:
The sensor structure transitions from planar to three-dimensional by stacking multiple proof masses at different heights (first, second, third levels) within the cavity. This vertical dimensionality enables simultaneous detection of acceleration in multiple directions (X, Y, Z axes) with improved sensitivity through electrostatic capacity changes between oppositely positioned masses
2Measurement precision
If the movable portion consists of a single layer Si electrode, then the structure is simple, but the sensitivity for detecting electrostatic capacity changes is limited
Solution Approach 1:
Different regions of the electrode structure have different properties: the proof masses are made of Si electrode material optimized for electrostatic capacity detection, while the frame portion provides mechanical support. The oppositely positioned proof masses create localized electrostatic fields that enhance sensitivity to acceleration-induced displacement
Solution Approach 2:
The sensor employs a composite structure combining Si electrode layers with metal electrode layers, and insulation layers, creating a multi-material system that optimizes both electrostatic detection sensitivity and mechanical properties. The layered composite structure enables precise measurement of electrostatic capacity changes while maintaining structural integrity
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 design improves the sensitivity and reliability of acceleration detection in multiple directions by enabling precise electrostatic capacity changes to be measured, effectively addressing the limitations of existing MEMS sensors.
Implementation Method 1
detects acceleration in the direction of a Z axis by detecting an amount of change in electrostatic capacity between the Si electrode of the movable portion vibrating upwardly and downwardly
Implementation Method 2
the movable portion that is the same in shape as the Si electrode of the fixed portion and that consists of a single layer of a Si electrode completely facing the Si electrode of the fixed portion
Data Source
AI summary
A MEMS sensor includes a semiconductor chip that has a first principal surface and a second principal surface and that has a cavity, a frame portion that forms a bottom portion and a side portion of the cavity, and a movable portion that is formed on the side of the first principal surface and that is supported by the frame portion in a floating state with respect to the cavity, and, in the MEMS sensor, the frame portion has a stepped surface formed at a height position between the bottom portion of the cavity and the first principal surface, and the movable portion includes a main body portion facing the cavity in a first direction and an extension portion that extends from the main body portion toward an upper region of the stepped surface in a second direction and that faces the stepped surface in the first direction.