Strain Sensor With Wheatstone Bridge Circuit
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Solution Overview
Problem
Conventional strain measurement methods using metal-foil or semiconductor strain gauges face issues with thermal stress, grain boundary-related strength reduction, and inadequate temperature compensation, leading to low reliability and precision in measuring strain, especially when integrated with a Wheatstone bridge circuit.
Innovation Solution
A mechanical-quantity measuring device is developed using a semiconductor single crystal substrate with impurity-diffused layers and a Wheatstone bridge circuit integrated within the strain sensor, featuring a metal thin film or polysilicon thin film active resistor combined with dummy resistors to enhance temperature compensation and precision in strain measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a metal foil strain gauge or semiconductor strain gauge with thin film is used for strain measurement, then strain can be measured, but thermal stress occurs at the interface between the thin film and resin substrate due to different linear expansion coefficients, causing the thin film to peel off or break
Solution Approach 1:
The patent changes the material parameter (linear expansion coefficient) by selecting a ceramic substrate with a linear expansion coefficient that closely matches that of the metal foil or polysilicon thin film. This parameter matching eliminates thermal stress at the interface during temperature changes, preventing peeling or breaking of the thin film while maintaining strain measurement capability
Solution Approach 2:
The patent uses a composite structure consisting of a ceramic substrate (such as aluminum oxide or aluminum nitride) combined with metal foil or polysilicon thin film. This composite material system resolves the thermal expansion mismatch problem by choosing a ceramic material whose expansion characteristics are compatible with the thin film, thereby ensuring both mechanical strength and measurement precision
2Reliability
If impurity-diffused layers are formed in a single crystal semiconductor substrate to create a strain sensor, then grain boundary-related strength reduction is eliminated, but the resistors cannot detect strain in a particular direction because they respond to multidirectional strains
Solution Approach 1:
The patent applies local quality by creating dummy resistors with specific geometric configurations (such as grid patterns or cross shapes) that have different strain sensitivity characteristics than the active resistor. These locally differentiated resistor structures enable the Wheatstone bridge to selectively measure strain in a particular direction while eliminating grain boundary issues through the use of single crystal material
Solution Approach 2:
The patent changes the geometric parameters of the dummy resistors to create anisotropic strain response. By adjusting the orientation, shape, and arrangement of the dummy resistors in the Wheatstone bridge circuit, the system achieves directional strain measurement capability while maintaining the mechanical strength benefits of single crystal material
3Measurement precision
If the Wheatstone bridge circuit is integrated within the strain sensor to enhance temperature compensation, then temperature compensation performance is improved, but all resistors including dummy resistors are subjected to strain and cannot function properly
Solution Approach 1:
The patent segments the Wheatstone bridge circuit into functional components: active resistors that respond to strain and dummy resistors with specific geometric configurations that are insensitive to strain in the measurement direction. This segmentation allows the bridge circuit to operate correctly with temperature compensation while maintaining proper function under strain conditions
Solution Approach 2:
The patent creates local quality differences in the resistor structures by designing dummy resistors with geometric configurations (such as grid patterns, cross shapes, or specific orientations) that make them insensitive to strain in the measurement direction. This local differentiation enables the integrated Wheatstone bridge to achieve both temperature compensation and proper strain measurement function
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 solution reduces thermal stress, improves mechanical strength, and enables precise strain measurement in a particular direction by minimizing the effects of grain boundaries and optimizing temperature compensation, allowing for high-precision strain measurement across a wide range of temperatures.
Implementation Method 1
the semiconductor has the piezoresistance effect that the resistance is changed with an applied strain, the impurity-diffused resistors can be used as the strain sensor to measure the strain
Implementation Method 2
since the linear expansion coefficient of the metal foil or polysilicon thin film used for the strain gauge is different about one digit, or ten times from that of the resin, a temperature change at the time of strain measurement will cause a thermal stress in the interface between the thin film and the resin
Data Source
AI summary
A mechanical-quantity measuring device capable of measuring a strain component of structure deformation for an object to be measured in a particular desired direction with long life, high reliability and high precision. A strain sensor is formed on a semiconductor substrate. Impurity-diffused layers considering the crystal orientation of the semiconductor single crystalline substrate are used to form a Wheatstone bridge circuit on the substrate. The Wheatstone bridge circuit can operate on one substrate since the semiconductor single crystal has the anisotropy of piezoresistance effect.