Mesa Gauge Force Detection Device Offset Voltage Reduction
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Solution Overview
Problem
Force detection devices utilizing the piezoresistive effect face challenges in reducing offset voltage due to non-coinciding resistance values of mesa gauges, despite symmetry in their dimensions, attributed to differing crystal directions.
Innovation Solution
A force detection device design where all mesa gauges extend along the same direction, ensuring identical crystal directions and equalized resistance values, with a force transmission block having different contact areas with pairs of mesa gauges to function as variable and fixed resistive elements in a bridge circuit, reducing offset voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If mesa gauges are arranged with symmetric dimensions in a bridge circuit, then the structural symmetry is improved, but the resistance values do not coincide due to differing crystal directions, causing offset voltage
Solution Approach 1:
The patent applies asymmetry by deliberately orienting all mesa gauges to extend along the same direction (e.g., the <110> crystal direction in silicon), breaking the conventional symmetric arrangement where gauges are oriented in different crystal directions. This asymmetric orientation strategy ensures that all gauges experience identical piezoresistive effects under the same stress, causing their resistance values to coincide and eliminating offset voltage in the bridge circuit.
2Device complexity
If mesa gauges are oriented in different crystal directions to form a bridge circuit, then the bridge circuit structure is established, but the resistance values become unequal, reducing measurement accuracy
Solution Approach 1:
The patent applies local quality by ensuring that all mesa gauges share the same crystal orientation (e.g., all extending along the <110> direction), while maintaining their different positions and roles in the bridge circuit. This localized uniformity in crystal direction ensures that each gauge responds identically to applied stress, making their resistance values equal and improving measurement accuracy despite their different circuit positions.
3Shape
If the force transmission block contacts all mesa gauges with equal area, then the structural symmetry is maintained, but the sensitivity and linearity of force detection are reduced
Solution Approach 1:
The patent applies asymmetry by designing the force transmission block with different contact areas for different pairs of mesa gauges. Specifically, the contact area with the first pair of mesa gauges differs from the contact area with the second pair, creating an asymmetric force distribution that enhances the differential output of the bridge circuit. This asymmetric contact design improves both sensitivity and linearity by optimizing the stress distribution across the gauges.
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 design achieves reduced offset voltage and improved sensitivity and linearity in force detection by ensuring identical resistance changes across all mesa gauges under stress, enhancing the device's ability to detect pressures accurately.
Implementation Method 1
a force detection device that utilizes a piezo-resistive effect... When the force transmission block presses the mesa gauges, a compressive stress to be applied to the mesa gauges increases, and electric resistance values of the mesa gauges change due to the piezoresistive effect
Data Source
AI summary
A force detection device includes: a substrate that includes a power supply wire, a reference wire, a first output wire, a second output wire and first to fourth mesa gauges extending along a first direction; and a force transmission block connected to the substrate. A pair of the first and second mesa gauges and a pair of the third and fourth mesa gauges are connected in parallel to each other between the power supply wire and the reference wire. The first output wire is connected between the first and second mesa gauges. The second output wire is connected between the third and fourth mesa gauges. A contact area of the force transmission block with a first pair of the first and fourth mesa gauges is different from a contact area of the force transmission block with a second pair of the second and third mesa gauges.