Thermal Infrared Sensor Sub-Wavelength Antireflection Structure

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Solution Overview

Problem

Thermal infrared sensors that receive infrared rays from the back surface of a substrate face reduced sensitivity due to reflection issues at interfaces between the substrate and the infrared ray absorbing film, as antireflection structures cannot be effectively formed at these locations.

Innovation Solution

A thermal infrared sensor with an infrared ray antireflection structure featuring a sub wavelength structure on the surface of the infrared ray absorbing film facing the semiconductor substrate, formed using photoengraving and etching technologies, along with a thermal oxidation process, to reduce reflection and enhance sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the infrared ray absorbing film is thermally separated from the substrate by etching to increase sensitivity, then the sensitivity of the thermal infrared sensor is improved, but reflection of infrared rays occurs at the interfaces between the substrate and the infrared ray absorbing film, degrading the sensitivity

Engineering Contradiction:

Improvesensor sensitivityVSAvoidinfrared ray reflection

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

The patent applies preliminary action by forming the antireflection film on the infrared ray absorbing film surface before the etching process that creates the hollow space. This sequence ensures that the antireflection coating is in place before thermal separation occurs, preventing reflection at the interfaces while maintaining the sensitivity benefits of thermal isolation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces an antireflection film as an intermediary layer between the infrared ray absorbing film and the external environment. This intermediate layer reduces the reflection of infrared rays at the interfaces caused by thermal separation, allowing the sensor to maintain high sensitivity while minimizing harmful reflective losses.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-generated harmful factors

If antireflection films are formed on the substrate back surface to prevent reflection, then reflection at the substrate back surface is reduced, but it is difficult to form antireflection films at the interfaces between the substrate and hollow space after the hollow space is formed by etching

Engineering Contradiction:

Improveinfrared ray reflectionVSAvoidmanufacturing process complexity

Core Design Contradiction:

Object-generated harmful factorsVSEase of manufacture

Solution Approach 1:

The patent resolves the manufacturing difficulty by performing the antireflection film formation step before the etching process that creates the hollow space. This preliminary action allows the antireflection coating to be applied to the complete surface of the infrared ray absorbing film, including areas that will later become interfaces with the hollow space, eliminating the need for complex post-etch coating processes.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent inverts the conventional sequence by forming the antireflection film on the infrared ray absorbing film surface before creating the hollow space through etching, rather than attempting to form it after. This inversion simplifies the manufacturing process by allowing a single, straightforward coating step that covers all surfaces that will later be exposed to infrared rays.

Inventive Principle:

Principle #13The other way round (Inversion)

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 implementation of a sub wavelength structure on the infrared ray absorbing film surface facing the semiconductor substrate effectively reduces infrared ray reflection, thereby increasing the sensitivity of the thermal infrared sensor.

Implementation Method 1

an infrared ray antireflection structure configured with a sub wavelength structure, the infrared ray antireflection structure being provided on a surface of the infrared ray absorbing film facing the semiconductor substrate

Methodology Applied

Scientific EffectSub wavelength structure interference: Interference

Implementation Method 2

the infrared ray absorbing film 105 is facing the substrate 103. This thermal infrared sensor detects infrared rays as the temperature sensor 106 captures temperature changes that occur when infrared rays entering from the substrate 103 are absorbed at the infrared ray absorbing film 105

Methodology Applied

Scientific EffectInfrared absorption: Absorption (EM radiation)

Implementation Method 3

a temperature sensor configured to detect temperature changes of the infrared ray absorbing film

Methodology Applied

Scientific EffectThermal radiation detection: Thermal Radiation

Data Source

PatentUS8927934B2Thermal infrared sensor and manufacturing method thereof

Publication Date: 2015.01.06 RICOH CO LTD

AI summary

A thermal infrared sensor includes an infrared ray absorbing film that is thermally separated from a semiconductor substrate by a hollow part; and a temperature sensor configured to detect temperature changes of the infrared ray absorbing film. The infrared ray absorbing film includes an infrared ray antireflection structure configured with a sub wavelength structure, the infrared ray antireflection structure being provided on a surface of the infrared ray absorbing film facing the semiconductor substrate.