Silicon Piezoresistor Slab Layout for High-Sensitivity Force Sensing
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Solution Overview
Problem
Existing force sensors face damage from overforces due to operating beyond their designed ranges, and traditional piezoresistive element placement results in lower sensitivity and higher costs.
Innovation Solution
Positioning piezoresistive elements closer to the center of the die, where the load-bearing actuation element makes contact, utilizing a slab die without anisotropic etching, which enhances localized stress detection and reduces sensor size and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If piezoresistive elements are positioned at traditional locations on the die, then the sensor structure is simpler, but the sensitivity is lower
Solution Approach 1:
The patent applies local quality by positioning piezoresistive elements at specific high-stress locations on the die (such as near the center or at corners depending on the embodiment) rather than uniformly distributing them. This localized placement optimizes the sensitivity at critical stress points while maintaining overall structural simplicity. The selective positioning ensures that the sensing elements are where the stress concentration is highest, maximizing measurement precision without requiring complex structural modifications.
2Ease of manufacture
If a slab die without anisotropic etching is used, then manufacturing cost and complexity are reduced, but traditionally this would lower stress detection capability
Solution Approach 1:
The patent changes the geometric parameters of the slab die and the positioning of piezoresistive elements to optimize stress detection without requiring anisotropic etching. By adjusting the slab thickness, dimensions, and the specific locations where piezoresistive elements are placed (such as at corners or center), the design achieves adequate stress concentration and detection capability while using simpler, more cost-effective manufacturing processes that avoid complex etching steps.
3Ease of manufacture
If the die size is reduced, then cost is lowered, but the ability to withstand proof loads may be compromised
Solution Approach 1:
The patent employs segmentation by strategically placing multiple piezoresistive elements at different locations on the reduced-size die (such as at corners and/or center) rather than relying on a single large sensing area. This segmented approach allows the smaller die to distribute stress measurement points effectively, maintaining proof load capacity despite the reduced overall size. Each segmented sensing point contributes to the overall measurement capability and structural integrity.
4Measurement precision
If piezoresistive elements are placed closer to the center contact point, then sensitivity increases up to 100 times, but the risk of damage from overforce increases
Solution Approach 1:
The patent implements beforehand cushioning by positioning piezoresistive elements close to the center contact point to maximize sensitivity, while simultaneously incorporating a structural frame surrounding the slab die. This frame acts as a protective element that absorbs and distributes excessive forces before they can damage the sensitive piezoresistive elements. The frame serves as a mechanical cushion that protects the high-sensitivity sensing elements during overforce events.
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 achieves up to 100 times higher sensitivity and significantly higher proof loads with reduced costs by eliminating the need for diaphragm etching and using a smaller die.
Implementation Method 1
Positioning piezoresistive elements closer to the center of the die, where the load-bearing actuation element makes contact, utilizing a slab die without anisotropic etching, which enhances localized stress detection
Data Source
AI summary
A method for sensing force using a sense die is disclosed. The method may include providing a sense die comprising a chip having a slab formed thereon; applying a force to the slab of the sense die; and determining the magnitude of the force applied to the slab via one or more sense elements attached to the slab. In some examples, the ratio of the width of the slab to the distance between the sense elements is greater than 2/1.