On-Chip IR Sensor Calibration via Resistive Heater and Thermopile Junctions
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Solution Overview
Problem
Existing infrared (IR) radiation sensors are large, expensive, fragile, and require complex calibration procedures, making them difficult to calibrate accurately in the field and prone to false measurements due to ambient visible light interference.
Innovation Solution
A compact IR radiation sensor design featuring thermopile junctions with a resistive heater and internal calibration circuitry, allowing for robust, economical, and easy field calibration by heating the thermopile junctions to determine responsivity, and using a CMOS semiconductor process dielectric stack with a silicon substrate to block visible light while passing IR radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a silicon substrate with etched cavity is used to thermally isolate the thermopile junction, then the sensor becomes more robust and less fragile, but the manufacturing process becomes more complex
Solution Approach 1:
The device is segmented into distinct functional layers: a robust silicon substrate providing mechanical support, a suspended dielectric membrane containing the thermopile junctions for sensing, and separate calibration heater structures. This segmentation allows the silicon substrate to provide robustness while the suspended membrane provides thermal isolation, resolving the contradiction between strength and manufacturing complexity.
Solution Approach 2:
The thermopile junctions are moved from a planar configuration on the silicon substrate to a suspended three-dimensional structure above the substrate. This dimensional change allows thermal isolation through the vertical cavity while maintaining mechanical robustness through the solid silicon substrate, eliminating the need for complex back-side etching processes.
2Ease of operation
If an internal calibration heater and circuitry are integrated on-chip, then field calibration becomes easier and more accurate, but the device complexity increases
Solution Approach 1:
The calibration heater is merged with the thermopile junction structure, using the same suspended dielectric membrane and support beams. This integration allows the calibration function to be performed using the existing thermal isolation infrastructure, providing easy field calibration without adding separate complex calibration subsystems.
Solution Approach 2:
The suspended dielectric membrane structure serves multiple functions: it provides thermal isolation for the thermopile junctions during normal operation, and simultaneously serves as the heating element and thermal path for calibration operations. This multi-functionality enables easy field calibration while minimizing additional device complexity.
3Measurement precision
If the thermopile junction is thermally isolated from the substrate, then the sensor accuracy improves by blocking ambient heat, but the device becomes more fragile
Solution Approach 1:
A robust silicon substrate acts as an intermediary between the external environment and the suspended thermopile junction. The substrate provides mechanical strength and durability, while the suspended membrane structure provides thermal isolation. This intermediary approach allows the thermopile to be thermally isolated for accurate measurements without directly exposing the fragile sensing elements to mechanical stress.
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 provides a more robust, cost-effective, and easily calibrated IR radiation sensor that minimizes the impact of ambient light and simplifies the calibration process, enhancing accuracy and reliability for temperature measurement and gas concentration detection.
Implementation Method 1
A resistive heater (6) in the dielectric stack for heating the first thermopile junction
Implementation Method 2
The first and second thermopile junctions are connected in series and form a single 'thermopile'. Incoming IR radiation indicated by arrows 5 causes the temperature of the thermopile junction supported on the floating portion of dielectric membrane to be greater than the temperature of the second thermopile junction
Implementation Method 3
using a CMOS semiconductor process dielectric stack with a silicon substrate to block visible light while passing IR radiation
Data Source
AI summary
A radiation sensor includes an integrated circuit radiation sensor chip (1A) including first (7) and second (8) thermopile junctions connected in series to form a thermopile (7,8) within a dielectric stack (3). The first thermopile junction (7) is insulated from a substrate (2) of the chip. A resistive heater (6) in the dielectric stack for heating the first thermopile junction is coupled to a calibration circuit (67) for calibrating responsivity of the thermopile (7,8). The calibration circuit causes a current flow in the heater and multiplies the current by a resulting voltage across the heater to determine power dissipation. A resulting thermoelectric voltage (Vout) of the thermopile (7,8) is divided by the power to provide the responsivity of the sensor.