Shared Pixel Transistor Placement for CMOS Image Sensor Sensitivity

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Solution Overview

Problem

Current CMOS image sensors, particularly in the back-surface irradiation type, lack a configuration that can expand the photodiode area and be used in both front-surface and back-surface irradiation types, limiting their versatility and imaging performance.

Innovation Solution

A solid state imaging device with a pixel array unit where color filters of multiple colors are arranged in a 2x2 pixel unit, and shared pixel transistors are intensively arranged in one pixel, allowing for a larger photodiode area and compatibility with both irradiation types by optimizing the placement of shared transistors and color filters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If pixel transistors are miniaturized to increase photodiode area, then the saturation charge amount increases, but the junction capacitance per unit area decreases

Engineering Contradiction:

Improvearea of photodiodeVSAvoidjunction capacitance per unit area

Core Design Contradiction:

Area of stationary objectVSQuantity of substance

Solution Approach 1:

By merging multiple pixel circuits into a shared structure, the total junction capacitance is distributed across a larger photodiode area. The shared floating diffusion region serves multiple pixels, effectively increasing the total junction capacitance while maintaining high capacitance per unit area through optimized sharing arrangements.

Inventive Principle:

Principle #5Merging (Combining)

2Area of stationary object

If shared pixel transistors are arranged only on B pixels in back-surface irradiation type, then the photodiode area is maximized, but the configuration cannot be used in front-surface irradiation type

Engineering Contradiction:

Improvearea of photodiodeVSAvoidcompatibility with irradiation types

Core Design Contradiction:

Area of stationary objectVSAdaptability or versatility

Solution Approach 1:

The shared pixel transistor configuration is designed to be universal and applicable to both front-surface irradiation type and back-surface irradiation type CMOS image sensors. The same structural arrangement of shared transistors and photodiodes can be implemented in both irradiation types, eliminating the need for type-specific designs and maximizing versatility.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 configuration enables the expansion of photodiode area, improving sensitivity and saturation charge amount, and allows for the use of the technology in both front-surface and back-surface irradiation types, enhancing imaging characteristics and versatility.

Implementation Method 1

a photodiode and a floating diffusion region (FD)... a transfer transistor that transfers accumulated charge of the photodiode to the FD

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS11496716B2Solid state imaging device and electronic apparatus

Publication Date: 2022.11.08 SONY SEMICON SOLUTIONS CORP

AI summary

A solid state imaging device includes a pixel array unit in which color filters of a plurality of colors are arrayed with four pixels of vertical 2 pixels×horizontal 2 pixels as a same color unit that receives light of the same color, shared pixel transistors that are commonly used by a plurality of pixels are intensively arranged in one predetermined pixel in a unit of sharing, and a color of the color filter of a pixel where the shared pixel transistors are intensively arranged is a predetermined color among the plurality of colors. The present technology can be applied, for example, to a solid state imaging device such as a back-surface irradiation type CMOS image sensor.