Uncooled Microbolometer Terahertz Detection via Patterned Resonant Absorber
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Solution Overview
Problem
Current uncooled microbolometer detectors face challenges in extending their absorption spectrum beyond 30 μm, particularly in the terahertz and far-infrared regions, due to material absorption limitations and diffraction effects, making it difficult to efficiently detect terahertz radiation while maintaining the advantages of infrared detector technology such as cost-effectiveness and ease of fabrication.
Innovation Solution
An uncooled microbolometer detector design featuring an optical absorber with patterned electrically conductive layers forming a resonant structure, capable of absorbing electromagnetic radiation in the terahertz region, and optionally including a spectral filter to pre-filter radiation, allowing for tailored absorption spectra and improved radiation detection in the terahertz range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional infrared microbolometer detectors include a reflector deposited on the underlying substrate to form a quarter-wavelength Fabry-Perot optical resonant cavity, then radiation absorption is maximized in the infrared spectral band, but forming such a quarter-wavelength resonant cavity is not practical for surface micromachining techniques used in the microfabrication of uncooled microbolometer detectors
Solution Approach 1:
The patent changes the resonant structure parameters from a quarter-wavelength Fabry-Perot cavity (requiring precise thickness control) to a half-wavelength resonant cavity formed by patterned electrically conductive layers. This parameter change allows the same absorption enhancement function to be achieved with a structurally simpler design that is compatible with standard surface micromachining techniques and does not require precise thickness control of dielectric layers.
Solution Approach 2:
The patent replaces the mechanical/optical resonant cavity structure (Fabry-Perot) with an electrical resonant structure formed by patterned conductive layers. This substitution allows the resonant absorption function to be achieved through electrical conductivity patterns rather than through precise mechanical thickness control of dielectric layers, simplifying the fabrication process.
2Object-affected harmful factors
If the pitch of terahertz-sensitive pixels is increased to avoid diffraction effects, then diffraction is reduced, but the pixel pitch becomes larger than that of infrared-sensitive pixels
Solution Approach 1:
The patent makes the pixel pitch dynamic or adjustable by using patterned electrically conductive layers that can be configured in different geometries. By changing the pattern geometry (e.g., spacing, shape, orientation of conductive elements), the effective optical pitch can be adjusted to match the physical pitch, allowing terahertz detection with smaller pixel pitches without suffering from diffraction effects.
Solution Approach 2:
The patent addresses the pitch problem by adding another dimension to the solution - using vertically stacked patterned conductive layers instead of relying solely on horizontal spacing. This multi-layer approach allows the optical response to be controlled by the vertical stacking configuration, enabling terahertz sensitivity with smaller in-plane pixel pitches while avoiding diffraction through proper geometric patterning in the vertical dimension.
3Measurement precision
If materials with high temperature coefficient of resistance are used for the thermistor, then temperature-dependent electrical resistance is enhanced, but the absorption spectrum extension beyond 30 μm is limited by material absorption characteristics
Solution Approach 1:
The patent segments the radiation absorption function from the temperature sensing function. The patterned electrically conductive layers serve as the radiation-absorbing resonant structure, while the thermistor materials (with their high TCR) remain responsible for temperature sensing. This segmentation allows each component to be optimized for its specific function - the conductive layers for spectral range extension and the thermistor for temperature sensitivity - without compromising either performance.
Solution Approach 2:
The patent introduces patterned electrically conductive layers as an intermediary between the incident terahertz radiation and the thermistor. These conductive layers act as a resonant absorber that converts terahertz radiation into localized heating, which then transfers to the thermistor. This intermediary structure enables the thermistor to detect terahertz radiation indirectly, extending the spectral range beyond the direct absorption capabilities of traditional thermistor materials while maintaining high temperature 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 solution enables effective absorption of terahertz radiation within the uncooled microbolometer detectors, extending their spectral range while maintaining the advantages of infrared detector technology, such as cost-effectiveness and ease of fabrication, by optimizing the geometric and material properties of the electrically conductive layers and incorporating a spectral filter to enhance radiation detection efficiency.
Implementation Method 1
an optical absorber including at least one electrically conductive layer extending on the platform over and in thermal contact with the at least one thermistor and patterned to form a resonant structure defining an absorption spectrum of the uncooled microbolometer detector, the optical absorber being exposed to electromagnetic radiation and absorbing the electromagnetic radiation according to the absorption spectrum
Implementation Method 2
patterned to form a resonant structure defining an absorption spectrum of the uncooled microbolometer detector
Implementation Method 3
a material having a temperature-dependent electrical resistance... a thermistor, which is the resistive element whose electrical resistance changes in response to temperature variations caused by the absorbed radiation
Implementation Method 4
The platform is generally held above and thermally insulated from a substrate by a support structure
Data Source
AI summary
An uncooled microbolometer detector that includes a substrate, a platform held above the substrate by a support structure, at least one thermistor provided on the platform, and an optical absorber. The optical absorber includes at least one electrically conductive layer extending on the platform over and in thermal contact with the at least one thermistor and patterned to form a resonant structure defining an absorption spectrum of the uncooled microbolometer detector. The optical absorber is exposed to electromagnetic radiation and absorbs the electromagnetic radiation according to the absorption spectrum. A microbolometer array including a plurality of uncooled microbolometer detectors arranged in a two-dimensional array is also provided. Advantageously, these embodiments allow extending the absorption spectrum of conventional infrared uncooled microbolometer detectors to the terahertz region of the electromagnetic spectrum.