Semiconductor Pressure Sensor with Segmented Piezo-Resistive Compensation
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Solution Overview
Problem
Semiconductor pressure sensors face inaccuracies due to temperature fluctuations, residual package stress, and non-uniform electric fields, which affect their accuracy and linearity.
Innovation Solution
A semiconductor pressure sensor design featuring a membrane with resistor pairs oriented in perpendicular directions, connected to current sources to produce differential voltage signals, minimizing temperature influence and enhancing sensitivity and linearity, while separate resistor pairs outside the membrane measure packaging stress to compensate for uniform stress effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional Wheatstone bridge configuration is used with piezo-resistive strips, then the pressure sensor can detect pressure changes, but the measurement accuracy deteriorates under temperature fluctuations and package stress
Solution Approach 1:
The sensor is divided into two functionally independent parts: a first resistor pair located on the membrane for pressure measurement, and a second resistor pair located outside the membrane for stress/temperature compensation. This segmentation allows each part to perform its specific function independently, improving overall measurement accuracy by compensating for environmental factors.
Solution Approach 2:
The second resistor pair acts as an intermediary compensation mechanism. It measures package stress and temperature effects separately, and these measurements are used to compensate for the readings from the first resistor pair, thereby eliminating the harmful effects of environmental factors on pressure measurement.
2Measurement precision
If piezo-resistive strips are arranged to measure deformation, then pressure sensitivity is achieved, but linearity deteriorates under non-uniform stress and temperature conditions
Solution Approach 1:
The first resistor pair is specifically positioned on the membrane where it experiences uniform deformation under pressure, while the second resistor pair is positioned outside the membrane where it experiences only environmental stress and temperature effects. This local quality differentiation ensures that each resistor pair measures only the intended parameter, improving linearity.
Solution Approach 2:
The second resistor pair serves as a mediator that captures environmental variations (temperature and package stress) that would otherwise non-uniformly affect the first resistor pair. By measuring these variations separately and applying compensation, the linearity of pressure measurement is improved.
3Measurement precision
If resistor pairs are located close together on the membrane, then temperature compensation is improved, but sensitivity to package stress increases
Solution Approach 1:
The first resistor pair is located on the membrane to maximize pressure sensitivity, while the second resistor pair is located outside the membrane to minimize pressure sensitivity and maximize stress/temperature compensation capability. This spatial differentiation of local quality allows simultaneous optimization of both functions.
Solution Approach 2:
The sensor is segmented into two distinct locations: on-membrane for pressure measurement and off-membrane for compensation. This segmentation ensures that the compensation resistors are exposed to environmental factors but shielded from pressure-induced deformation, resolving the contradiction between temperature compensation and stress sensitivity.
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 improved accuracy and linearity by isolating temperature and stress effects, increasing sensitivity by 80-95% and reducing sensitivity to temperature gradients and package stress, thereby enhancing overall measurement precision.
Implementation Method 1
The first resistor comprising one or more first elongated piezo-resistive strips arranged in a first direction for measuring deformation of the membrane due to the external pressure
Data Source
AI summary
A semiconductor pressure sensor for measuring an external pressure exerted on the sensor, including: a membrane; a first resistor connected between a first bias node and a first output node; a second resistor connected between the first bias node and a second output node; a first and second current source connected to the first resp. second output node for generating a differential voltage signal indicative of the external pressure to be measured. The resistors including piezo-resistive strips arranged in particular crystallographic directions. The circuit may have a third and four resistor pair for compensating package stress. The Piezo-resistive strips may be formed as p-doped regions within an n-well, the biasing node being electrically connected to the n-well.