Semiconductor Diaphragm Pressure Sensor Micro-Stress Reduction
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Solution Overview
Problem
Existing pressure sensors face issues with micro-stress susceptibility from wiring and poor environmental durability due to differences in linear expansion coefficients between metal wiring and semiconductor materials, leading to shifted zero points and noise in sensor output.
Innovation Solution
A pressure sensor configuration is developed where sensor gauges are formed on the (100) face of a silicon substrate, aligned to maximize pressure sensitivity, and semiconductor resistors are covered with an insulating oxide film, reducing the number of contact holes and areas with different expansion coefficients, thereby minimizing micro-stress effects and enhancing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum or metal wiring is used in the pressure sensor structure, then electrical connectivity is achieved, but thermal stress is generated due to different coefficients of linear expansion among the aluminum wiring, insulating film and semiconductor resistances, causing the zero point of the sensor output to shift
Solution Approach 1:
The patent removes aluminum or metal wiring from the sensor structure entirely. Instead, it uses semiconductor resistors configured in a bridge circuit that are directly formed on the semiconductor substrate, eliminating the source of thermal stress caused by differential expansion between metal wiring and other components.
Solution Approach 2:
The patent uses semiconductor materials throughout the sensing structure, including semiconductor resistors and semiconductor substrate, rather than combining dissimilar materials like aluminum wiring with semiconductor components. This material homogeneity ensures uniform thermal expansion characteristics and eliminates thermal stress.
2Reliability
If the semiconductor resistance is not protected by an insulating film, then manufacturing is simpler, but environmental durability is extremely poor and high precision is not achieved due to large affect of noise components and drift in the sensor output
Solution Approach 1:
The patent integrates the insulating film formation into the overall semiconductor fabrication process, where the insulating film is deposited over the semiconductor resistors as part of the standard manufacturing sequence. This merging of protection function into the fabrication process achieves durability without significantly increasing complexity.
3Measurement precision
If wiring is provided with pressure sensitivity to improve sensitivity, then pressure sensitivity is enhanced, but the sensor becomes susceptible to micro-stress from the wiring and other stresses on the sensor
Solution Approach 1:
The patent removes the problematic pressure-sensitive wiring entirely from the structure. Instead of using wiring that responds to pressure (and thus introduces micro-stress), it employs a bridge circuit configuration of semiconductor resistors where the sensing function is distributed across multiple resistive elements rather than concentrated in pressure-sensitive wiring.
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 results in a pressure sensor with high sensitivity, insusceptibility to micro-stress, and improved environmental durability, as evidenced by stable output characteristics under thermal cycling tests.
Implementation Method 1
pressure on a medium to be measured is sensed by converting the displacement of the diaphragm, corresponding to the pressure on the medium to be measured, into a change in resistance of the piezoresistive element
Implementation Method 2
a piezo element is formed by the thermal dispersion of boron
Implementation Method 3
an aluminum layer is formed on the (110) face of the silicon substrate by means of an electron beam evaporation method
Implementation Method 4
anisotropic etching with potassium hydroxide is performed on the rear surface side of the (110) face of the silicon substrate to form a diaphragm
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
A diaphragm is formed at a predetermined location of a sensor chip made of semiconductor material, and a sensor gauge for differential pressure or pressure sensing-use is provided on the sensor chip that includes at least the diaphragm. The sensor gauge has a plurality of sensor gauges (210) synergistically forming a bridge circuit, and are connected to one another with semiconductor resistors (220), the semiconductor resistors and the sensor gauges are covered with an insulating film, and the number of contact holes (240), passing through a portion of the insulating film, for electrode line-out use for forming contacts electrically connected to the semiconductor resistors does not exceed the number of sensor gauges.