Hybrid Isolation Structure for Image Sensor Noise Reduction

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Solution Overview

Problem

Existing photoelectric conversion apparatuses face issues with light intrusion into charge storing portions due to diffuse reflection in isolation regions, affecting image quality and electrical characteristics such as pressure resistance and parasitic MOS effects.

Innovation Solution

A photoelectric conversion apparatus is designed with a first isolation portion having a PN junction and a second isolation portion with an insulator, arranged between the charge storing portion and transistors, to reduce light intrusion and maintain electrical isolation and pressure resistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a single isolation structure (LOCOS or gap) is used, then manufacturing is simple, but light intrusion occurs causing noise and dark current in charge storing portions

Engineering Contradiction:

Improvelight intrusion into charge storing portionVSAvoidisolation structure complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The isolation structure is divided into two distinct portions: a first isolation portion (LOCOS structure) and a second isolation portion (gap structure). This segmentation allows each portion to perform a specific function - the first portion provides primary isolation while the second portion blocks light intrusion paths, thereby reducing noise and dark current without requiring complete structural redesign

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different isolation structures are applied in different locations based on local requirements. The first isolation portion using LOCOS is applied in areas where electrical isolation is primary, while the second isolation portion using gaps is applied where light blocking is critical. This local differentiation optimizes performance for each specific region's needs

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If isolation regions are made larger to reduce light intrusion, then noise and dark current decrease, but pressure resistance and electrical characteristics deteriorate

Engineering Contradiction:

Improvenoise and dark currentVSAvoidpressure resistance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The isolation function is segmented between two portions with different characteristics. The first isolation portion maintains electrical connectivity and pressure resistance, while the second isolation portion provides light blocking. This segmentation allows the system to achieve noise reduction without sacrificing pressure resistance, as each portion is optimized for its specific function

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first isolation portion acts as an intermediary between the charge storing portion and the external environment, providing electrical isolation while maintaining pressure resistance. The second isolation portion then provides additional light blocking. This intermediary structure allows the system to achieve multiple functions without requiring any single isolation structure to be overly large

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If a PN junction isolation structure is used, then electrical isolation is improved, but manufacturing precision requirements increase

Engineering Contradiction:

Improveelectrical isolationVSAvoidisolation structure fabrication

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent merges two established isolation techniques (LOCOS and gap structures) into a single hybrid structure. This merging allows the system to benefit from the electrical isolation properties of LOCOS while incorporating the light-blocking advantages of gap structures, achieving improved electrical isolation without requiring new or highly complex manufacturing processes

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 effectively reduces the intrusion of charges from isolation regions into charge storing portions, enhancing image quality by minimizing noise and dark current while maintaining sufficient pressure resistance.

Implementation Method 1

an isolation area for electrically isolating the charge storing portion, wherein the isolation area includes a first isolation portion having a PN junction

Methodology Applied

Scientific EffectPN junction: Diode

Implementation Method 2

a second isolation portion having an insulator and arranged between the first charge storage element and at least a part of the plurality of transistors

Methodology Applied

Scientific EffectLight blocking by insulator: Absorption (EM radiation)

Data Source

PatentUS11600650B2Photoelectric conversion apparatus and imaging system using the same

Publication Date: 2023.03.07 CANON KK

AI summary

In a photoelectric conversion apparatus including charge storing portions in its imaging region, isolation regions for the charge storing portions include first isolation portion each having a PN junction, and second isolation portions each having an insulator. A second isolation portion is arranged between a charge storing portion and at least a part of a plurality of transistors.