Image Sensor Shield Electrode Carrier Cross-Talk

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Solution Overview

Problem

Hydrogenated amorphous silicon (α-Si:H) based image sensors suffer from carrier cross-talk, image lag, and dark leakage issues due to deep traps and field emission mechanisms, leading to resolution degradation, color fidelity problems, and cosmic noise in dark scenes.

Innovation Solution

Incorporating a shield electrode between adjacent pixel electrodes in the image sensor structure, along with a thickened intrinsic layer and α-SiC:H based n-layer, to create a high potential barrier and prevent carrier cross-talk, while using a transparent conductive layer and insulating layer to manage electric fields and reduce tunneling effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a thick intrinsic layer is used to enhance quantum efficiency, then photo sensing capability is improved, but carrier cross-talk between adjacent pixels increases

Engineering Contradiction:

Improvequantum efficiencyVSAvoidcarrier cross-talk

Core Design Contradiction:

Measurement precisionVSObject-generated harmful factors

Solution Approach 1:

A shield electrode is introduced as an intermediary structure positioned between adjacent pixel electrodes. This shield electrode acts as a barrier that blocks the lateral movement of carriers between pixels, thereby preventing cross-talk while allowing the intrinsic layer to be sufficiently thick for high quantum efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The electrode structure is segmented by introducing shield electrodes that divide the continuous space between pixels into isolated regions. This segmentation creates electrical boundaries that prevent carrier diffusion across pixel boundaries, enabling each pixel to maintain its signal integrity independently.

Inventive Principle:

Principle #1Segmentation

2Area of stationary object

If hydrogenated amorphous silicon material is used to achieve high fill factor, then photo sensing area is improved, but image lag and dark leakage problems occur

Engineering Contradiction:

Improvefill factorVSAvoidimage lag and dark leakage

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

Different regions of the device are assigned different material properties: the intrinsic layer uses hydrogenated amorphous silicon for high photo sensitivity and fill factor, while the shield electrode and n-layer use materials with lower trap density to minimize image lag and dark leakage. This local differentiation allows each region to optimize its specific function.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The device employs a composite structure combining hydrogenated amorphous silicon (α-Si:H) for the photo-sensitive intrinsic layer with hydrogenated amorphous silicon carbide (α-SiC:H) for the n-layer and shield electrode. This composite material approach leverages the high quantum efficiency of α-Si:H while utilizing the lower trap density of α-SiC:H to reduce image lag and dark leakage.

Inventive Principle:

Principle #40Composite materials

3Power

If metal electrodes are used to collect carriers, then electrical connection is improved, but tunneling effects cause dark leakage current

Engineering Contradiction:

Improvecarrier collection efficiencyVSAvoiddark leakage current

Core Design Contradiction:

PowerVSObject-generated harmful factors

Solution Approach 1:

An n-layer made of hydrogenated amorphous silicon carbide is introduced as an intermediary between the metal pixel electrode and the intrinsic layer. This intermediate layer provides a controlled interface that maintains good electrical contact for carrier collection while suppressing tunneling-induced dark leakage current through its specific material properties.

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

The shield electrode effectively prevents carrier cross-talk, allows for thicker intrinsic layers enhancing quantum efficiency, and reduces image lag and dark leakage, resulting in improved sensitivity and color balance without sacrificing electrical specifications.

Implementation Method 1

the shield electrode effectively prevents carrier cross-talk

Methodology Applied

Scientific EffectElectrostatic field: Electric Field

Implementation Method 2

capture photons (light) and convert them into electrons

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 3

reduce tunneling effects

Methodology Applied

Scientific EffectTunneling:

Data Source

PatentUS8334164B2Image sensor and fabrication method thereof

Publication Date: 2012.12.18 POWERCHIP SEMICON MFG CORP

AI summary

An image sensor has a substrate, a dielectric layer positioned on the substrate, a pixel array including a plurality of pixels defined on the substrate, a shield electrode positioned between any two adjacent pixel electrodes of the pixels, a photo conductive layer positioned on the shield electrode and the pixel electrodes, and a transparent conductive layer covering the photo conductive layer.