Ring Transfer Transistor Pixel Circuit for Radiation Hardening

Solution Overview

Problem

CMOS image sensors face challenges in achieving low dark current and radiation hardness, particularly in low light conditions and space environments where they are exposed to protons and gamma rays, which degrade their performance.

Innovation Solution

The implementation of low leakage pinned photodiodes using ring transfer transistors, where the transfer transistor is surrounded by a photo diode and a floating diffusion, along with a poly silicon ring to reduce leakage and enhance charge transfer efficiency, is proposed. This design includes a pixel sensing circuit with a charge storage element surrounded by a photo diode and a transfer transistor with an enclosed geometry MOSFET, optimizing the layout to minimize leakage and maximize radiation tolerance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional photodiode and transistor layout is used, then manufacturing is simpler, but dark current increases and radiation hardness decreases

Engineering Contradiction:

Improvedark current performanceVSAvoidpixel circuit layout

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The transfer transistor is positioned inside the photodiode region, creating a nested configuration where the transistor is surrounded by the photodiode. This nesting reduces the distance between the photodiode and transistor, minimizing leakage current paths while maintaining a compact pixel layout that does not significantly increase overall device complexity

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The photodiode and transfer transistor are merged into a single integrated structure where the transistor is fully surrounded by the photodiode region. This merging eliminates separate isolation structures and reduces the number of manufacturing steps, while simultaneously reducing dark current by minimizing interface leakage between separate components

Inventive Principle:

Principle #5Merging (Combining)

2Reliability

If conventional photodiode and transistor layout is used, then manufacturing is simpler, but radiation hardness decreases

Engineering Contradiction:

Improveradiation hardnessVSAvoidpixel circuit layout

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The transfer transistor is positioned inside the photodiode region, creating a nested configuration where the transistor is surrounded by the photodiode. This nesting reduces the distance between the photodiode and transistor, minimizing leakage current paths while maintaining a compact pixel layout that does not significantly increase overall device complexity

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The photodiode and transfer transistor are merged into a single integrated structure where the transistor is fully surrounded by the photodiode region. This merging eliminates separate isolation structures and reduces the number of manufacturing steps, while simultaneously reducing dark current by minimizing interface leakage between separate components

Inventive Principle:

Principle #5Merging (Combining)

3Reliability

If leakage is not minimized, then manufacturing is easier, but low light performance deteriorates

Engineering Contradiction:

Improvelow light performanceVSAvoidpixel circuit fabrication

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The transfer transistor is positioned inside the photodiode region, creating a nested configuration where the transistor is surrounded by the photodiode. This nesting reduces the distance between the photodiode and transistor, minimizing leakage current paths while maintaining a compact pixel layout that does not significantly increase overall device complexity

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The photodiode and transfer transistor are merged into a single integrated structure where the transistor is fully surrounded by the photodiode region. This merging eliminates separate isolation structures and reduces the number of manufacturing steps, while simultaneously reducing dark current by minimizing interface leakage between separate components

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 solution results in a radiation-tolerant image sensor with low dark current, enabling improved low light performance, faster operation, and increased frame rates, while maintaining compatibility with existing semiconductor manufacturing processes.

Implementation Method 1

a pixel sensing circuit includes a charge storage element surrounded by and functionally coupled to a photo diode

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS8138535B2Method for manufacturing a pixel sensing circuit

Publication Date: 2012.03.20 SEMICON COMPONENTS IND LLC

AI summary

Systems and methods of pixel sensing circuits. In accordance with a first embodiment of the present invention, a pixel sensing circuit includes a floating diffusion functionally coupled to and surrounded by a ring transfer transistor. The ring transfer transistor is functionally coupled to and surrounded by a photo diode. The photo diode may be surrounded by a region of poly silicon. The disclosed structure provides radiation hardening and low light performance.