Optical Black Pixel Light Shielding via Hybrid Ti/TiN and Metal Stubs

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Solution Overview

Problem

Existing image sensor technologies fail to form optical black pixels that accurately mimic the dark signal response of clear pixels, leading to inadequate image quality due to insufficient opacity and light penetration, especially in high-end applications.

Innovation Solution

A hybrid approach combining a 1000 Å thick Ti/TiN layer with in-pixel metal stubs to increase opacity without thickening the Ti/TiN layer, and additional metal layers for enhanced infrared occlusion, allowing for improved light shielding while maintaining dark current performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a light shield is used to form optical black pixels, then light penetration is blocked, but the opacity is insufficient for high-end applications and off-axis light rays still penetrate

Engineering Contradiction:

Improvelight penetrationVSAvoidopacity

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent uses a composite metal stack consisting of alternating layers of titanium (Ti) and titanium nitride (TiN) to create the optical black pixel structure. This composite material approach provides superior light blocking performance compared to single-material shields, particularly for off-axis light rays, while maintaining compatibility with standard CMOS fabrication processes.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent transitions from a single-layer light shield to a multi-layer stacked structure, adding dimensional complexity to the shielding approach. The alternating Ti/TiN layers create multiple interfaces that reflect and absorb light at different angles and wavelengths, effectively blocking off-axis light rays that would penetrate single-layer shields.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Object-affected harmful factors

If Ti/TiN layer thickness is increased to improve opacity, then light blocking performance improves, but manufacturing complexity and process deviations increase

Engineering Contradiction:

Improvelight blocking performanceVSAvoidmanufacturing process complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent divides the optical black layer into multiple thin alternating layers of Ti and TiN, each deposited to controlled thicknesses. This segmentation allows each layer to be deposited within standard process capabilities while the cumulative effect of multiple layers provides superior light blocking. The total equivalent thickness achieves high opacity without requiring any single layer to exceed manufacturing limits.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent optimizes the thickness parameters of individual Ti and TiN layers to achieve the desired optical performance. By carefully controlling the thickness of each alternating layer, the design achieves maximum light blocking at specific wavelengths (particularly infrared) while keeping individual layer thicknesses within standard deposition process capabilities, thus avoiding the need for excessively thick single layers that would create manufacturing difficulties.

Inventive Principle:

Principle #35Parameter changes

3Object-affected harmful factors

If metal stubs are added to increase opacity, then light shielding improves, but dark current levels may be affected

Engineering Contradiction:

Improvelight shieldingVSAvoiddark current

Core Design Contradiction:

Object-affected harmful factorsVSObject-generated harmful factors

Solution Approach 1:

The patent introduces metal stubs that extend the Ti/TiN optical black structure laterally beyond the photodiode area. These stubs are positioned in the inter-level metal layers and provide additional light blocking for oblique rays without directly contacting or shading the photodiode active area. This localized extension of the black structure achieves improved shielding while maintaining dark current characteristics by avoiding direct interference with the photodiode region.

Inventive Principle:

Principle #3Local quality

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 results in a 100× improvement in visible spectrum opacity and 10× improvement in infrared spectrum opacity, effectively enhancing image sensor performance without compromising dark current levels, suitable for high-end applications.

Implementation Method 1

a Ti/TiN layer overlaying the photodiode... 100× improvement in visible spectrum opacity and 10× improvement in infrared spectrum opacity

Methodology Applied

Scientific EffectLight absorption and reflection by metal layers: Absorption (EM radiation)

Implementation Method 2

in-pixel metal stubs that further occlude the focal radius of each pixel's incoming light beam

Methodology Applied

Scientific EffectLight occlusion by metal structures: Absorption (EM radiation)

Data Source

PatentUS7999340B2Apparatus and method for forming optical black pixels with uniformly low dark current

Publication Date: 2011.08.16 SAMSUNG ELECTRONICS CO LTD

AI summary

An apparatus and method for forming optical black pixels having uniformly low dark current. Optical Black opacity is increased without having to increase Ti/TiN layer thickness. A hybrid approach is utilized combining a Ti/TiN OB layer in conjunction with in-pixel metal stubs that further occlude the focal radius of each pixel's incoming light beam. Additional metal layers can be used to increase the opacity into the infrared region.