Per-Pixel Dark Reference Bolometer for Thermal Noise Correction
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Solution Overview
Problem
Uncooled microbolometer arrays face significant challenges in non-uniformity correction, leading to noise in thermal imaging due to self-heating effects, which conventional methods fail to adequately address, especially in applications requiring improved noise performance.
Innovation Solution
Incorporating both an imaging microbolometer and a shielded reference microbolometer with a reference resistor made of thermally sensitive material into each detector element, allowing for per-pixel non-uniformity correction by subtracting thermal noise from the image signal, thereby improving image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional non-uniformity correction methods using reference pixels at row or column ends are used, then device complexity is reduced, but measurement precision deteriorates due to inability to correct local noise within rows and columns
Solution Approach 1:
The detector element is segmented into multiple independent components: an imaging microbolometer for capturing thermal signals and a reference microbolometer for measuring local noise. This segmentation allows separate measurement and correction of non-uniformities at the pixel level, improving correction precision without requiring complex external correction systems.
Solution Approach 2:
Both the imaging microbolometer and reference microbolometer are merged within a single detector element structure, sharing common support infrastructure including the suspended membrane, thermal isolation legs, and readout circuitry. This merging achieves per-pixel correction capability while maintaining relatively simple device architecture.
2Measurement precision
If per-pixel non-uniformity correction is implemented, then measurement precision improves, but device complexity increases due to additional reference microbolometer in each detector element
Solution Approach 1:
Each detector element is equipped with its own reference microbolometer that measures local thermal noise specific to that pixel's location. This local quality approach ensures that non-uniformity correction is tailored to each pixel's specific characteristics, maximizing signal-to-noise ratio improvement while keeping the reference structure simple and localized.
Solution Approach 2:
The reference microbolometer is designed as a copy of the imaging microbolometer structure, with identical thermally sensitive material, membrane, and thermal isolation characteristics. This copying ensures that the reference pixel accurately replicates the thermal behavior of the imaging pixel, enabling precise noise measurement and subtraction while using the same fabrication process.
3Device complexity
If reference pixels are placed on sides of rows or columns, then device complexity is minimized, but measurement precision deteriorates due to inability to capture local noise variations within rows and columns
Solution Approach 1:
The reference microbolometer is positioned within the same two-dimensional array grid as the imaging pixels, rather than placing reference pixels only at row or column ends. This dimensional integration allows the reference measurement to be spatially correlated with the imaging pixel, capturing local noise variations accurately while maintaining a simple regular array structure.
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 enables effective per-pixel noise mitigation, enhancing the signal-to-noise ratio and reducing local noise impacts, offering improved imaging performance compared to conventional methods that correct noise only on a row or column basis.
Implementation Method 1
a reference microbolometer shielded from receiving the electromagnetic radiation and configured to produce a reference signal indicative of the thermal noise
Implementation Method 2
The membrane includes a thermally sensitive material, such as amorphous silicon (a-Si) or vanadium oxide (VOx). As the temperature of the thermally sensitive material varies, the resistance of the thermally sensitive material also varies
Implementation Method 3
an imaging microbolometer configured to receive electromagnetic radiation from a viewed scene and to produce an image signal in response to receiving the electromagnetic radiation
Implementation Method 4
Each pixel includes a membrane which is suspended at a location spaced above the top surface of the substrate, in order to facilitate thermal isolation
Data Source
AI summary
Microbolometer arrays incorporating per-pixel dark reference structures for non-uniformity correction. In one example a thermal imager includes a device substrate, a microbolometer array disposed on the device substrate and including a plurality of detector elements arranged in a two-dimensional array, each detector element including an imaging microbolometer and a reference microbolometer, the imaging microbolometer being configured to receive electromagnetic radiation from a viewed scene and to produce an image signal in response to receiving the electromagnetic radiation, the image signal including a component produced due to thermal noise in the respective detector element, and the reference microbolometer being shielded from receiving the electromagnetic radiation and configured to produce a reference signal indicative of the thermal noise, wherein the thermal imaging device is configured to produce an image of the viewed scene based on a combination of the image signals and the reference signals from the plurality of detector elements.