Nanoscale Protuberances for CMOS Image Sensor Anti-Reflection

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Solution Overview

Problem

CMOS image sensors face significant light reflection losses in the optical path, limiting their efficiency due to the presence of unnecessary optical interfaces, which degrades process control and reliability.

Innovation Solution

The implementation of anti-reflection structures with 'moth eye type' nanoscale protuberances at optical interfaces, formed using self-assembling block copolymers or conventional lithography, creates a graded refractive index region, reducing reflection and enhancing light transmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If conventional flat optical interfaces are used in CMOS image sensors, then manufacturing process is simpler, but light reflection losses are significant

Engineering Contradiction:

Improvelight reflection lossVSAvoidoptical interface structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The optical interface is segmented into multiple nanoscale protuberances arranged in arrays, transforming a single flat interface into multiple discrete optical paths. This segmentation reduces reflection by creating gradual refractive index transitions at each protuberance interface, thereby reducing overall light reflection loss while managing the structural complexity through systematic arrangement.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The optical interface is modified locally by forming nanoscale protuberances only in specific regions where light transmission is critical. The local geometry is changed from flat to curved with controlled height and spacing, creating graded refractive index regions that reduce reflection. This local modification approach addresses reflection losses without requiring complete structural redesign of the entire optical path.

Inventive Principle:

Principle #3Local quality

2Loss of energy

If nanoscale protuberances are formed using self-assembling block copolymers, then light transmission is enhanced, but manufacturing process complexity increases

Engineering Contradiction:

Improvelight transmission efficiencyVSAvoidfabrication process

Core Design Contradiction:

Loss of energyVSEase of manufacture

Solution Approach 1:

The manufacturing process utilizes self-assembling block copolymers that automatically organize into nanoscale protuberance structures without requiring complex lithographic patterning. The block copolymers self-organize through thermodynamic processes, forming the desired nanoscale geometry autonomously. This self-service approach enhances light transmission through the resulting structures while reducing the complexity of the fabrication process by eliminating multiple lithography and etching steps.

Inventive Principle:

Principle #25Self-service

3Loss of energy

If optical interfaces are eliminated to maximize light transmission, then light transmission is improved, but process control and reliability degrade

Engineering Contradiction:

Improvelight transmissionVSAvoidprocess control

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

Nanoscale protuberances are introduced as intermediary structures between the air/glass interface and the photodiode. These protuberances act as intermediate optical elements that gradually transition the refractive index from air through the protuberance material to the underlying optical layers. This intermediary structure maximizes light transmission by reducing reflection at each interface while maintaining process control and reliability through well-defined geometric parameters that can be precisely manufactured.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 significantly increases light transmission to photodiodes, thereby enhancing the overall efficiency of CMOS image sensor pixel structures by minimizing reflection losses.

Implementation Method 1

Methodology Applied

Scientific EffectGraded refractive index: Refraction

Data Source

PatentUS8409904B2Methods for forming anti-reflection structures for CMOS image sensors

Publication Date: 2013.04.02 SMARTSENS TECH (HK) CO LTD

AI summary

Protuberances, having vertical and lateral dimensions less than the wavelength range of lights detectable by a photodiode, are formed at an optical interface between two layers having different refractive indices. The protuberances may be formed by employing self-assembling block copolymers that form an array of sublithographic features of a first polymeric block component within a matrix of a second polymeric block component. The pattern of the polymeric block component is transferred into a first optical layer to form an array of nanoscale protuberances. Alternately, conventional lithography may be employed to form protuberances having dimensions less than the wavelength of light. A second optical layer is formed directly on the protuberances of the first optical layer. The interface between the first and second optical layers has a graded refractive index, and provides high transmission of light with little reflection.