Piezoresistive Surface Stress Sensor with Full Bridge Configuration
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Solution Overview
Problem
Piezoresistive cantilever array sensors have low sensitivity for detecting uniformly distributed surface stress due to the uniform distribution of stress across the cantilever surface, which limits their effectiveness in detecting small amounts of objects in medical and environmental research.
Innovation Solution
A surface stress sensor with a full bridge configuration using anisotropic high piezoresistance factor of single-crystal silicon, which concentrates stress on the piezoresistive part, enhancing sensitivity by triple digits compared to traditional cantilever sensors, and allowing for larger adsorption cantilevers to increase sensitivity further.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a piezoresistive cantilever array sensor is used, then the sensor can be manufactured using CMOS process and integrated into semiconductor devices, but the sensitivity is low due to uniform stress distribution across the cantilever surface
Solution Approach 1:
The sensor surface is divided into multiple independent piezoresistive elements arranged in a matrix configuration. Each element independently detects stress at its location, and the collective signal from all elements provides high-sensitivity detection of uniformly distributed surface stress while maintaining CMOS manufacturing compatibility
Solution Approach 2:
Multiple piezoresistive elements are combined into a matrix array where their individual stress detection signals are summed together. This merging of detection capabilities transforms the uniform low-level stress signal across the surface into a high-level collective signal that achieves triple-digit sensitivity improvement
2Measurement precision
If the cantilever size is increased to improve sensitivity, then more surface stress can be detected, but the cantilever becomes more susceptible to mechanical noise such as vibration and liquid movement
Solution Approach 1:
The large sensing area is segmented into multiple small piezoresistive elements rather than using one large cantilever. This segmentation maintains high sensitivity through signal summation while each small element remains mechanically stable and resistant to vibration and liquid movement effects
Solution Approach 2:
The sensor combines multiple small stable piezoresistive elements into a unified detection system that achieves the sensitivity of a large sensor. The collective signal from all elements provides high sensitivity while each individual element maintains mechanical stability
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 surface stress sensor achieves high sensitivity and stability, with a signal-to-noise ratio exceeding 100 times that of traditional piezoresistive cantilever sensors, enabling detection of small amounts of objects with high accuracy and applicability in medical and environmental research.
Implementation Method 1
the upward/downward deflection of the cantilever due to stress on the surface of the cantilever causes compression/elongation strain in the piezoresistive member, which changes the resistance of the piezoresistive member
Data Source
Figure 1~2
Figure 3a~3d
Figure 4a~4d
AI summary
Deflection of a free end of one plate-like member, that is caused by uniform stress, is transmitted to the other plate-like member by moving a free end of the other plate-like member. According to this configuration, the uniform stress applied to the one plate-like member is converted into stress induced by a point force in the other plate-like member, and then, the induced stress is concentrated on a fixed end side narrow portion in which a piezoresistor is provided. Thus, a novel structure for a piezoresistive surface stress sensor having high sensitivity to uniform stress applied to the surface of the sensor is provided.