Piezoresistive Stress Sensor Shielding for Leakage-Free Sensing
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Solution Overview
Problem
Existing semiconductor stress sensors face challenges with leakage currents due to modulation caused by external electrical fields, leading to reduced sensitivity and potential breakdown, particularly when using metallic shields or shallow diffusion methods.
Innovation Solution
A piezo-resistor based sensor design featuring a conductive shield and guard ring structure, where the conductive shield covers the piezo-diffusion region between contacts, and the guard ring bridges any gaps between the shield and interconnect structures, preventing inversion and leakage currents while maintaining sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a metallic shield layer is placed over the piezo-resistor to prevent modulation, then protection against external electrical fields is improved, but the piezo-resistor moves further from the surface causing significant loss of sensitivity
Solution Approach 1:
A shallow diffusion shield of opposite conductivity type is introduced as an intermediary layer between the piezo-resistor and the external electrical fields. This shield prevents direct interaction between external fields and the piezo-resistor while maintaining close proximity to the sensing element, thus protecting against modulation without sacrificing sensitivity.
2Object-affected harmful factors
If a shallow diffusion shield is used to prevent modulation, then protection against external electrical fields is improved, but the doping must be limited to avoid inversion causing breakdown between piezo-resistor and shield
Solution Approach 1:
The doping concentration and depth of the shield diffusion are precisely controlled within specific parameter ranges. By optimizing these parameters, the shield provides sufficient protection against external fields while preventing inversion that would lead to breakdown, thus maintaining reliability.
3Object-affected harmful factors
If highly doped sections are placed between piezo-resistor and interconnect to avoid stress modulation, then protection against stress modulation is improved, but leakage paths still exist between shield and highly doped p-diffusions
Solution Approach 1:
The leakage path between the shield and highly doped p-diffusions is eliminated by extending the shield diffusion to completely cover and overlap these regions. This extraction of the leakage path prevents charge accumulation and eliminates the source of leakage currents.
4Object-affected harmful factors
If the entire piezo-resistor is covered with metal including contacts to interconnect, then protection against modulation and leakage is improved, but extra processing effort is required for a second metallic shield layer
Solution Approach 1:
The shallow diffusion shield serves multiple functions simultaneously: it acts as a protective shield against external electrical fields, prevents stress modulation from interconnects, and eliminates leakage paths. This multi-functionality eliminates the need for additional metallic shield layers, reducing processing complexity.
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 design effectively prevents leakage currents and modulation, enhancing the sensitivity and reliability of semiconductor stress sensors by isolating the piezo-diffusion regions and maintaining stable voltage connections, thus reducing the risk of breakdown.
Implementation Method 1
piezo-resistor based sensor
Data Source
Figure 1~2B
Figure 3
Figure 4~5B
AI summary
A piezo-resistor sensor (100) comprising: a diffusion (104) of a first conductivity type in a well (118) of an opposite second type, contacts (114) with islands (110) in the diffusion, interconnects (112) with the contacts, a shield (108) covers the diffusion between the contacts and extends over side walls of the diffusion between the contacts, each interconnect covers the diffusion at the corresponding contact and extends over edges of the diffusion, each island is at a side covered by its interconnect, a guard ring (102) of the second type around the diffusion, the shield covers the well between the diffusion and the ring, and the edge of the ring facing the diffusion, if a gap between the shield and the interconnect is present, the ring bridges this gap, and/or the edges of the diffusion are completely covered by the combination of the shield and the interconnects.