Piezoresistive Sensor Impurity Segmentation for Stability
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Solution Overview
Problem
Existing piezoresistive sensors face challenges in achieving stable operating characteristics due to difficulties in covering the piezoresistive region with a protection region, leading to instability and a narrowed use temperature range, especially when the concentration of p-type impurities is reduced for increased sensitivity.
Innovation Solution
A piezoresistive sensor structure is implemented with a piezoresistive region having a first conductivity type impurity, a protection region with a second conductivity type impurity covering the top, and contact regions with a higher impurity concentration than the protection region, ensuring the inequality: impurity concentration of the piezoresistive region < impurity concentration of the protection region < impurity concentration of the contact regions, allowing for stable ohmic connections and reduced contaminant effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the concentration of p-type impurities in the piezoresistive region is reduced to improve sensitivity, then the sensitivity of the piezoresistive region is improved, but electrical connection between the piezoresistive region and electrodes becomes difficult
Solution Approach 1:
The contact region is divided into two distinct zones: a first contact region with high p-type impurity concentration for ensuring ohmic connection with electrodes, and a second contact region with lower p-type impurity concentration for maintaining sensitivity. This segmentation allows each zone to fulfill its specific function independently, resolving the contradiction between electrical connection reliability and sensitivity.
Solution Approach 2:
Different impurity concentrations are applied to different spatial locations within the contact region. The first contact region (near electrodes) has high impurity concentration for low resistance connection, while the second contact region (near piezoresistive region) has lower impurity concentration for high sensitivity. This local differentiation resolves the contradiction by optimizing each location for its specific function.
2Object-affected harmful factors
If an n-type impurity region (protection region) is formed on the surface of the piezoresistive region to cover it, then protection against contaminants is improved, but it is very difficult to reverse the surfaces of contact regions including high concentration p-type impurity regions
Solution Approach 1:
The contact regions with high p-type impurity concentration are formed first, extending to the surface before the n-type protection region is formed. This preliminary action ensures that the contact regions are established and protected from being converted to n-type during subsequent processing, simplifying the manufacturing process while maintaining both protection and electrical connection functionality.
Solution Approach 2:
Instead of forming the protection region first and then trying to create contact regions through complex reversal processes, the invention inverts the sequence: contact regions are formed first with high impurity concentration, and then the protection region is formed over them. This inversion eliminates the need for difficult reversal processes while achieving the same protective effect.
3Object-affected harmful factors
If the concentration of n-type impurities in the protection region is increased to ensure complete coverage, then protection effectiveness is improved, but a pn junction is formed between the protection region and high concentration p-type impurity region, reducing breakdown voltage and losing practicality
Solution Approach 1:
The protection region is designed with spatially varying n-type impurity concentration: higher concentration in regions away from contact regions for effective contaminant protection, and lower concentration in regions adjacent to high p-type impurity contact regions to avoid pn junction formation. This local differentiation maintains protection effectiveness while preventing breakdown voltage reduction.
Solution Approach 2:
The lower n-type impurity concentration region acts as an intermediary zone between the high p-type impurity contact region and the high n-type impurity protection region. This intermediary prevents direct pn junction formation between high concentration regions, thereby maintaining breakdown voltage while still providing protection functionality.
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 the stability and sensitivity of the piezoresistive sensor by minimizing the impact of contaminants and maintaining high sensitivity, enabling broader operational temperature ranges and improved accuracy.
Implementation Method 1
a piezoresistive sensor that detects the displacement of a diaphragm as a stress using piezoresistive effects
Data Source
AI summary
A piezoresistive sensor includes a piezoresistive region to which first conductivity type impurity has been introduced, the piezoresistive region being formed in a semiconductor layer; a protection region to which second conductivity type impurity has been introduced, the protection region covering a top of a region in which the piezoresistive region is formed, the protection region being formed in the semiconductor layer; and contact regions to which the first conductivity type impurities have been introduced, the contact regions being connected to the piezoresistive region, the contact regions being formed so as to reach a surface of the semiconductor layer except a region in which the protection region is formed, in which the following inequality holds: impurity concentration of the piezoresistive region<impurity concentration of the protection region<impurity concentrations of the contact regions.