CMOS Image Sensor Pixel With Finger Gate Photogate Design

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Solution Overview

Problem

Conventional CMOS image sensors experience image lag due to charges not transferred to the floating diffusion region, affecting image quality and depth information accuracy.

Innovation Solution

A unit pixel design with a first and second photogate, each having finger gates and a transfer gate, along with a bridging diffusion region and channel stop region, to improve charge transfer efficiency to the floating diffusion region, using transparent conducting oxide and a semiconductor substrate with epitaxial layers for enhanced charge collection and transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional CIS structure is used, then manufacturing is simpler, but image lag occurs due to incomplete charge transfer

Engineering Contradiction:

Improvecharge transfer efficiencyVSAvoidpixel structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The photogate is divided into multiple finger gates that extend in perpendicular direction, segmenting the charge collection region to improve charge transfer efficiency to floating diffusion region while maintaining manageable structural complexity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A bridging diffusion region is introduced as an intermediary structure between the photogate and floating diffusion region to facilitate more efficient charge transfer, acting as a mediator that reduces image lag without requiring complete redesign of the conventional pixel structure

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If larger photodetector area is used, then charge collection is improved, but pixel density decreases

Engineering Contradiction:

Improvecharge collection efficiencyVSAvoidpixel array fill factor

Core Design Contradiction:

Measurement precisionVSArea of moving object

Solution Approach 1:

The finger gates extend in a direction substantially perpendicular to the junction gate, utilizing a second dimension to increase the effective charge collection area without proportionally increasing the footprint area, thereby improving pixel density while maintaining charge collection efficiency

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 design enhances image quality and depth information accuracy by improving charge transfer efficiency, reducing noise and data errors, and increasing the fill factor of the pixel array.

Implementation Method 1

Each pixel of the CIS includes a photo detecting region where charges corresponding to the intensity of incident light are generated

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

The first photogate may be formed of transparent conducting oxide. The transparent conducting oxide may be selected from the group consisting of indium tin oxide, indium zinc oxide, zinc oxide, and titanium dioxide.

Methodology Applied

Scientific EffectTransparency and electrical conductivity:

Data Source

PatentUS8513709B2Photo detecting apparatus and unit pixel thereof

Publication Date: 2013.08.20 SAMSUNG ELECTRONICS CO LTD

AI summary

A unit pixel of a photo detecting apparatus includes a photogate, a transfer gate and a floating diffusion region. The photogate includes a junction gate extending in a first direction and a plurality of finger gates extending from the junction gate in a second direction substantially perpendicular to the first direction. The transfer gate is formed adjacent to the junction gate. The floating diffusion region is formed adjacent to the first transfer gate.