Infrared Detector Responsivity Stabilization via Reference Pixel Feedback
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Solution Overview
Problem
Infrared sensors face challenges in maintaining sensitivity and stability due to changes in heat conduction through the gas surrounding the absorber, leading to errors in output signals over time, particularly caused by outgassing, hermeticity leaks, or pressure changes within the sensor cavity.
Innovation Solution
A semiconductor device with a sensor pixel and a reference pixel, both thermally and electrically matched, where the reference pixel is heated to maintain equal temperature with the sensor pixel, allowing for the calculation of responsivity by measuring the difference in output signals, which is then used to generate an accurate IR radiation measurement, compensating for changes in heat conduction and pressure within the cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensor uses a thermally isolated absorber structure suspended in a cavity, then the sensitivity of the pixel is improved, but the heat conduction through the surrounding gas becomes unstable over time
Solution Approach 1:
The patent introduces a reference pixel as an intermediary element that experiences the same environmental changes (pressure, temperature, gas composition) as the sensor pixel but is shielded from IR radiation. By comparing the sensor pixel output with the reference pixel output, the system can distinguish between signal changes due to IR radiation and changes due to environmental factors, thereby stabilizing measurements despite unstable heat conduction through the gas.
Solution Approach 2:
The patent implements a feedback mechanism where the reference pixel continuously monitors environmental changes and this information is used to compensate for drift in the sensor pixel. The system measures the output of both pixels and uses the reference pixel's data to correct the sensor pixel's measurements, maintaining accuracy over time despite changes in heat conduction properties.
2Stability of the object's composition
If the sensor operates in a hermetically sealed cavity, then the stability of the measurement environment is improved, but pressure changes due to outgassing or leaks still occur over time
Solution Approach 1:
The reference pixel serves as a mediator that experiences the same pressure changes and environmental drift as the sensor pixel. By comparing both pixels, the system can identify and compensate for pressure-related drift, maintaining measurement reliability even in the hermetically sealed cavity where gradual pressure changes occur due to outgassing or minor leaks.
3Measurement precision
If the sensor pixel and reference pixel are thermally matched, then the accuracy of differential measurement is improved, but the complexity of the device increases
Solution Approach 1:
The patent merges the sensor pixel and reference pixel into a single integrated device structure, sharing common components such as the hermetically sealed cavity, suspension structures, and readout circuitry. This integration approach reduces overall device complexity compared to using separate independent sensors, while maintaining the thermal matching necessary for accurate differential measurements.
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 stabilizes the responsivity of the sensor, reducing errors and maintaining accuracy over time by regularly updating the responsivity measurement and compensating for changes in the cavity conditions, ensuring precise detection of IR radiation.
Implementation Method 1
The absorber is typically a so called membrane or diaphragm suspended in a sealed cavity by means of a suspension structure... The more IR-power the isolated structure receives, the higher the temperature of the absorber will be
Implementation Method 2
a heater for increasing the temperature of the second absorber by applying a power to that heater
Implementation Method 3
The temperature increase of the absorber is thus an indication of the amount of incident IR radiation, and is typically measured by means of a resistor with a high temperature dependence (bolometer)
Implementation Method 4
measured by means of a resistor with a high temperature dependence (bolometer) or by means of a series of thermocouples (thermopile)
Implementation Method 5
For each amount of IR radiation, there is an equilibrium temperature at which the heating-up due to the incident IR power equals the heat loss from the absorber to the surrounding substrate and cap via heat conduction, heat convection and heat radiation
Implementation Method 6
heat loss from the absorber to the surrounding substrate and cap via heat conduction, heat convection and heat radiation
Implementation Method 7
heat loss from the absorber to the surrounding substrate and cap via heat conduction, heat convection and heat radiation
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
A semiconductor device (100) for measuring IR radiation comprising: at least one sensor pixel (10); at least one reference pixel (20) shielded from said IR radiation comprising a heater (23); a controller (50) adapted for: measuring a responsivity by applying power to the heater, while not heating the sensor pixel; measuring a first output signal of an unheated pixel and a first reference output signal of the heated pixel, obtaining the responsivity as a function of a measure of the applied power to the heater and of the difference between the first output signal and the first reference output signal; applying a period of cooling down until the temperature of the reference pixel and the sensor pixel are substantially the same; generating the output signal indicative of the IR radiation, based on the difference between the sensor and the reference output signal, by converting this difference using the responsivity.