Anti-Reflection Film Reduces Crosstalk in Image Sensors

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Solution Overview

Problem

Conventional image sensors suffer from color crosstalk and noise issues due to light reflection from the silicon surface and metal wire lines, which reduces light efficiency and increases noise, and the existing anti-reflection films do not effectively prevent light from being incident on adjacent photodiodes, thereby decreasing sensitivity.

Innovation Solution

An image sensor with anti-reflection films formed above and around photodiodes in the interlayer insulating layer, using materials like poly silicon, amorphous silicon, tungsten, and TiN, to absorb light reflections and prevent them from reaching adjacent photodiodes, thereby reducing crosstalk and noise.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a reflection film is formed between the photodiode and metal wiring layer to improve light sensitivity, then light efficiency increases, but color crosstalk and noise are generated due to light reflecting from metal wire lines and incident on adjacent photodiodes

Engineering Contradiction:

Improvelight efficiencyVSAvoidcolor crosstalk and noise

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an anti-reflection film as an intermediary layer between the color filter and the photodiode. This film has a refractive index lower than both the color filter and the photodiode, creating an optical impedance matching layer that reduces reflection at the interfaces. By placing this intermediary material, the patent successfully reduces the harmful reflections that cause color crosstalk while maintaining light efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the optical parameter (refractive index) of the anti-reflection film to be lower than both the color filter and photodiode materials. This parameter change optimizes the optical path and reduces reflection coefficients at the interfaces, thereby minimizing color crosstalk and noise while preserving light sensitivity.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If the reflection film covers a portion of the photodiode to improve light sensitivity, then light efficiency increases, but the effective region of the photodiode is reduced causing sensitivity decrease

Engineering Contradiction:

Improvelight efficiencyVSAvoideffective region of photodiode

Core Design Contradiction:

Use of energy by moving objectVSArea of stationary object

Solution Approach 1:

The patent segments the optical path management by using a separate anti-reflection film layer instead of relying on the photodiode's own surface structure. This segmentation allows the anti-reflection film to handle reflection control while the photodiode maintains its full effective area for light detection, resolving the conflict between light efficiency and active area.

Inventive Principle:

Principle #1Segmentation

3Reliability

If light reflects from the silicon surface and reflects again from the metal wire line to be incident on an adjacent photodiode, then color crosstalk is generated, but the conventional reflection film does not prevent this path

Engineering Contradiction:

Improvelight sensitivityVSAvoidcolor crosstalk

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful reflection effect into a beneficial one by using the anti-reflection film to guide reflected light back toward the original photodiode instead of allowing it to scatter to adjacent photodiodes. The film's low refractive index causes reflected light to refract at angles that redirect it back to the source photodiode, turning potential crosstalk into useful signal reinforcement.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 anti-reflection films effectively reduce color crosstalk and noise, enhancing image quality by ensuring light is focused on the intended photodiode and minimizing interference from adjacent photodiodes, leading to improved light sensitivity and reduced noise.

Implementation Method 1

using materials like poly silicon, amorphous silicon, tungsten, and TiN, to absorb light reflections and prevent them from reaching adjacent photodiodes

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Implementation Method 2

an anti-reflection film formed between a color filter and a photodiode, and having a refractive index smaller than refractive indexes of the color filter and the photodiode

Methodology Applied

Scientific EffectReflection reduction: Anti-Reflective Coating

Data Source

PatentUS7898011B2Image sensor having anti-reflection film for reducing crosstalk

Publication Date: 2011.03.01 SK HYNIX INC

AI summary

An image sensor for reducing crosstalk includes anti-reflection films which are formed between a plurality of metal wire lines of the lowest metal wiring layer and a semiconductor substrate and between one of the metal wiring layers and another metal wiring layer. The image sensor having the anti-reflection films according to the present invention can reduce color crosstalk and noises in comparison with a conventional image sensor by using the anti-reflection films formed above the surroundings of the photodiodes.