Global Shutter Pixel Layout for Lower Parasitic Light Sensitivity

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Solution Overview

Problem

Conventional solid-state imaging elements face challenges in achieving global shutter functionality due to parasitic light sensitivity (PLS) issues, where light leakage from the photoelectric conversion element to the charge holding unit causes unwanted image artifacts, making it difficult to prevent light leakage effectively.

Innovation Solution

The implementation of a solid-state imaging element with a dual charge holding region structure, including a front-stage and rear-stage charge holding region of different capacities, along with transfer transistors and a light-shielding wall, to prevent charge leakage from the photoelectric conversion element, and a signal processing circuit to compare and select pixel signals based on charge amounts, thereby reducing PLS.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If a single charge holding unit is added next to the photoelectric conversion element to enable global shutter method, then simultaneous exposure of all pixels is achieved, but light leakage from the photoelectric conversion element to the charge holding unit causes parasitic light sensitivity (PLS) artifacts

Engineering Contradiction:

Improveglobal shutter functionalityVSAvoidparasitic light sensitivity

Core Design Contradiction:

Extent of automationVSObject-affected harmful factors

Solution Approach 1:

The charge holding unit is divided into two separate regions: a first charge holding region and a second charge holding region. This segmentation allows the first region to be positioned close to the photoelectric conversion element for efficient charge transfer, while the second region is positioned farther away and shielded from light leakage, thus resolving the contradiction between achieving global shutter functionality and preventing parasitic light sensitivity.

Inventive Principle:

Principle #1Segmentation

2Productivity

If the charge holding unit is disposed next to the photoelectric conversion element to facilitate charge transfer, then transfer efficiency is improved, but light leakage prevention becomes difficult

Engineering Contradiction:

Improvecharge transfer efficiencyVSAvoidlight leakage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The charge holding unit is segmented into two regions with different positions relative to the photoelectric conversion element. The first charge holding region is disposed next to the photoelectric conversion element to ensure efficient charge transfer, while the second charge holding region is disposed at a position where light leakage can be effectively prevented, thus resolving the contradiction between charge transfer efficiency and light leakage prevention.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A light-shielding wall is introduced as an intermediary element between the photoelectric conversion element and the charge holding regions. This light-shielding wall blocks light leakage paths while allowing charge transfer to proceed efficiently to the first charge holding region, thus resolving the contradiction between maintaining charge transfer efficiency and preventing light leakage.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If a light-shielding wall is added to prevent light leakage to the charge holding unit, then PLS resistance is improved, but device complexity increases

Engineering Contradiction:

Improveparasitic light sensitivityVSAvoidstructure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The charge holding unit is divided into two regions, which inherently creates structural complexity. However, this segmentation is achieved within the existing pixel structure without adding external components, thus improving PLS resistance while minimizing the increase in device complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The light-shielding function is merged with the charge holding structure itself by creating two charge holding regions at different positions. This eliminates the need for separate external light-shielding components, thus improving PLS resistance while keeping the device complexity increase minimal.

Inventive Principle:

Principle #5Merging (Combining)

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 enhances PLS resistance and improves image quality by effectively preventing light leakage and accurately processing pixel signals, especially in low illuminance conditions, while maintaining image quality in high illuminance scenarios.

Implementation Method 1

a photoelectric conversion element

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Data Source

PatentUS12192659B2Solid-state imaging element, imaging device, and method for controlling solid-state imaging element

Publication Date: 2025.01.07 SONY SEMICON SOLUTIONS CORP

AI summary

PLS resistance is improved in a solid-state imaging element in which all pixels are simultaneously exposed. A front-stage transfer transistor transfers a charge from a photoelectric conversion element to a front-stage charge holding region and a rear-stage charge holding region which have different capacities. A rear-stage transfer transistor transfers the charge from the rear-stage charge holding region to a floating diffusion region. An intermediate transfer transistor transfers a charge, which remains in the front-stage charge holding region after the charge has been transferred from the rear-stage charge holding region to the floating diffusion region, to the floating diffusion region via the front-stage charge holding region.