Thermal Flow Sensor Strain Compensation via Segmented Resistors
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Solution Overview
Problem
Semiconductor flow rate sensors experience abnormal outputs due to the piezoresistive effect, which is influenced by strain generated at the diaphragm portion, leading to variations in signal readings.
Innovation Solution
Incorporating strain detecting resistors on both sides of the heat generating resistor, allowing for the detection and compensation of strain effects, thereby reducing signal variations caused by strain on the bridge circuit connected to temperature sensing resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If semiconductor materials such as polysilicon are used for the resistor in a thermal type flow rate sensor, then the sensing element can be mass-produced and downsized with low power consumption, but the piezoresistive effect causes abnormal outputs due to strain generated at the diaphragm portion
Solution Approach 1:
The patent divides the sensing element into functionally distinct segments: temperature sensing resistors for flow rate detection and strain detecting resistors for strain measurement. This segmentation allows independent optimization of each function and enables the strain detection system to compensate for piezoresistive effects on temperature sensing resistors, thereby maintaining output accuracy while using semiconductor materials for mass production
Solution Approach 2:
The patent implements a feedback mechanism where strain detecting resistors mounted on the diaphragm measure strain in real-time, and this strain information is used to compensate for the piezoresistive effects on the temperature sensing resistors. The control unit calculates corrected temperature values by subtracting the strain-induced resistance changes from the raw measurements, thereby eliminating abnormal outputs and ensuring reliable flow rate detection
2Reliability
If strain detecting resistors are added to detect and compensate for strain effects, then abnormal outputs are prevented, but the device complexity increases
Solution Approach 1:
The patent makes the diaphragm serve multiple functions: it acts as both the sensing element for temperature-based flow rate detection and as the mounting substrate for strain detecting resistors. By utilizing the diaphragm's structural role in both temperature sensing and strain detection, the patent avoids adding separate strain detection structures, thereby limiting the increase in device complexity while achieving reliable compensation for piezoresistive effects
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 approach effectively minimizes the impact of strain on the flow rate signal, preventing abnormal outputs and ensuring accurate measurements by compensating for strain-induced effects.
Implementation Method 1
a flow rate sensor which measures a flow rate by using a heat generating resistor
Implementation Method 2
temperature sensing resistors are formed on an upstream side and on a downstream side of an air flow by interposing the heat generating resistor, and a flow rate and a direction are detected based on a difference between temperatures of the temperature sensing resistors
Implementation Method 3
A semiconductor material such as polysilicon has a piezoresistive effect in which a resistance value of the material is changed owing to a strain that is generated by deforming a shape of the material
Data Source
AI summary
To reduce a signal variation of a bridge circuit connected with a temperature sensing resistor that is caused by a strain even when the strain is generated at a diaphragm portion of a substrate installed with a heater resistor and the temperature sensing resistor. In a thermal type flow rate resistor including a substrate, a diaphragm 13 formed at the substrate, and a heat generating resistor 2 and temperature detecting resistors 7 through 10 formed on the diaphragm for detecting a flow rate of a measured fluid by heating the heat generating resistor, strain detecting resistors 11 and 12 are formed on an upstream side and on a downstream side of a flow of the measured fluid relative to the heat generating resistor on the diaphragm, an amount of a strain generated on the diaphragm is detected by the strain detecting resistors, and a flow rate signal detected by the heat generating resistor and the temperature detecting resistors is compensated for the strain based on the detected amount of the strain.