Semiconductor Strain Sensor Electrode Placement
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Solution Overview
Problem
Conventional semiconductor strain sensors experience thermal stresses and temperature drift due to the significant difference in thermal expansion coefficients between aluminum electrodes and single-crystalline silicon substrates, leading to thermal hysteresis in output signals.
Innovation Solution
The semiconductor strain sensor is designed with electrodes positioned on the outer frame portion, separated by at least 100 μm from the boundary between the diaphragm and outer frame portions on a silicon-on-insulator substrate, reducing the impact of thermal stresses on the piezoresistive elements and suppressing thermal hysteresis to less than 0.2 percent FS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum electrodes are used on single-crystalline silicon substrate, then electrical signal extraction is achieved, but thermal expansion coefficient difference causes thermal stresses and temperature drift
Solution Approach 1:
The patent divides the substrate into distinct functional regions: a diaphragm portion for pressure sensing and an outer frame portion for electrode placement. This spatial segmentation separates the piezoresistive element formation area from the electrode formation area, preventing thermal stresses from the aluminum electrode from affecting the piezoresistive element on the diaphragm portion.
Solution Approach 2:
The patent extracts the electrode from its conventional position adjacent to the diaphragm boundary and relocates it to the outer frame portion. This extraction removes the harmful thermal stress source from the vicinity of the piezoresistive element, eliminating the root cause of thermal hysteresis while maintaining electrical signal extraction functionality.
2Device complexity
If electrode is positioned close to diaphragm boundary for compact design, then device size is reduced, but thermal stress affects piezoresistive element causing thermal hysteresis
Solution Approach 1:
The substrate is segmented into a diaphragm portion and an outer frame portion, with the electrode specifically positioned on the outer frame. This segmentation creates a natural spatial separation that prevents thermal stress transmission from the electrode to the piezoresistive element, achieving both compact integration and low thermal hysteresis (≤0.2% FS).
Solution Approach 2:
The outer frame portion acts as an intermediary region that decouples the electrode from the diaphragm portion. By placing the electrode on the outer frame at a distance of ≥100 nm from the boundary, the frame serves as a thermal isolation barrier, preventing thermal stresses from reaching the piezoresistive element while maintaining electrical connectivity.
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 configuration enhances temperature stability, ensuring that the semiconductor strain sensor meets the 1 percent FS control system demand even after assembly, and allows for precise pressure measurement applications like intake air pressure monitoring in vehicle engines.
Implementation Method 1
a piezoresistive element that is formed on the diaphragm portion, and that outputs an electrical signal in response to pressure
Implementation Method 2
an electrode that is formed on the outer frame portion, and that extracts the electrical signal from the piezoresistive element
Data Source
AI summary
An SOI substrate includes a thin diaphragm portion that is formed by removing a portion of the substrate from a rear surface side, and a thick outer frame portion that surrounds the diaphragm portion. A piezoresistive element that outputs an electrical signal in response to pressure is formed on the diaphragm portion, and an electrode that extracts the electrical signal from the piezoresistive element is formed on the outer frame portion. The electrode is disposed at a position on the outer frame portion that is separated by greater than or equal to 100 μm from a boundary line between the diaphragm portion and the outer frame portion.