Nanoscale Bolometer Minimized Thermal Conductance

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Solution Overview

Problem

State-of-the-art microbolometers are limited by thermal conductance, preventing them from reaching the thermodynamic limit of detectivity due to their mechanical design, which sets a lower bound on thermal conductance and restricts their ability to operate at the radiation-dominated fundamental limit.

Innovation Solution

A nanobolometer with a thin suspended membrane structure and subwavelength antenna, tethered by thin support beams, optimized using silicon-based MEMS technology to minimize thermal conductance and enhance radiation absorption, allowing operation near the thermodynamic limit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the support legs are made with the same SiN thickness as the absorber plate to ensure structural integrity, then the thermal conductance is reduced, but it still sets a lower bound that prevents reaching the thermodynamic limit

Engineering Contradiction:

Improvestructural integrityVSAvoiddetectivity

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent changes the thickness parameter of the support legs from being equal to the absorber plate thickness (500 nm) to being significantly thinner (nanoscale dimensions). This parameter change reduces the thermal conductance of the support legs below the previous lower bound, enabling the bolometer to operate near the thermodynamic limit while maintaining sufficient structural integrity through careful design of the nanoscale support structure.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If the absorber area is increased to reduce thermal conductance and reach the radiation-dominated limit, then detectivity improves, but pixel size and resolution are sacrificed

Engineering Contradiction:

ImprovedetectivityVSAvoidpixel size

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

The patent changes the dimensional parameters of the support legs from micrometer scale to nanometer scale. This drastic reduction in support leg dimensions reduces their thermal conductance without requiring an increase in absorber area, thus improving detectivity while maintaining compact pixel size and high resolution.

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If thinner support beams are used to reduce thermal conductance, then detectivity approaches the thermodynamic limit, but structural stability becomes more difficult to maintain

Engineering Contradiction:

Improvespecific detectivityVSAvoidstructural stability

Core Design Contradiction:

Measurement precisionVSStrength

Solution Approach 1:

The patent employs nanoscale support beams that function as flexible, ultra-thin structural elements. These nanoscale beams provide sufficient structural stability despite their minimal thickness by utilizing appropriate material selection and geometric design, enabling thermal conductance reduction while maintaining the mechanical integrity required for device operation.

Inventive Principle:

Principle #30Flexible shells and thin films

Solution Approach 2:

The patent optimizes multiple parameters of the support beams including thickness, width, length, and material composition to achieve the desired balance between thermal conductance and structural stability. By carefully tuning these parameters at the nanoscale, the support beams provide adequate mechanical support while minimizing thermal leakage to approach the thermodynamic detectivity limit.

Inventive Principle:

Principle #35Parameter changes

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 nanobolometer achieves a significant increase in specific detectivity, approaching the ideal bolometer limit, with improved thermal response time and pixel size, making it competitive with cooled IR imaging technologies.

Implementation Method 1

a subwavelength antenna on the front surface of the suspended membrane plate patterned to absorb infrared light incident on the front surface of the suspended membrane plate

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Implementation Method 2

A nanobolometer with a thin suspended membrane structure and subwavelength antenna, tethered by thin support beams, optimized using silicon-based MEMS technology to minimize thermal conductance

Methodology Applied

Scientific EffectThermal insulation: Thermal Insulation

Implementation Method 3

a reflecting metallic backplane spaced approximately one-quarter wavelength from the front surface of suspended membrane plate, thereby providing a Salisbury screen to enable greater absorbance of the incident infrared light

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 4

a thermometer disposed on the suspended membrane plate to measure the temperature thereof

Methodology Applied

Scientific EffectThermal radiation: Thermal Radiation

Data Source

PatentUS11788893B1Nanoscale bolometer operating near the thermodynamic limit

Publication Date: 2023.10.17 NATIONAL TECHNOLOGY & ENGINEERING SOLUTIONS OF SANDIA LLC

AI summary

A nanoscale bolometer for infrared (IR) thermal imaging comprises a subwavelength antenna that provides a specific detectivity approaching a fundamental, thermodynamic limit. The uncooled nanobolometer achieves performance comparable to cooled, high-performance, semiconductor photodetectors, but with significantly reduced size, weight, power, and cost.