Backside Illumination Global Shutter Pixel Light Leakage

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Solution Overview

Problem

Backside illumination global shutter image sensors face challenges with light leakage into storage nodes, leading to reduced shutter efficiency due to the exposure of photoelectrons over time, which affects the accuracy of signal capture after exposure is stopped.

Innovation Solution

The implementation of a backside illumination global shutter pixel with a deep trench isolation pattern, a storage node, and an extending photoelectric conversion portion that blocks light leakage by absorbing any scattered or leaking light before it reaches the storage node, using a combination of metal grid and reflector layers for effective shielding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a light-shielding pattern is disposed above the storage diode to block light, then light blocking is improved, but light leakage from other directions still occurs reducing shutter efficiency

Engineering Contradiction:

Improvelight blockingVSAvoidshutter efficiency

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The patent extends the photoelectric conversion element in the depth direction (third dimension) to form an extending photoelectric conversion portion that reaches into the second region above the storage node. This dimensional extension allows the photoelectric conversion element to occupy space that would otherwise be available for light propagation, thereby blocking light leakage paths without adding lateral complexity to the light-shielding pattern.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The extending photoelectric conversion portion is nested within the deep trench isolation structure, utilizing the vertical space within the trench to position the extended photoelectric conversion element. This nesting approach allows the photoelectric conversion element to extend into the region above the storage node while maintaining integration with the existing isolation structure.

Inventive Principle:

Principle #7Nested doll (Nesting)

2Manufacturing precision

If the pixel pitch is reduced to increase resolution, then image quality is improved, but the amount of light entering the pixel is further reduced

Engineering Contradiction:

Improvepixel pitchVSAvoidamount of light entering pixel

Core Design Contradiction:

Manufacturing precisionVSIllumination intensity

Solution Approach 1:

The patent utilizes the vertical dimension to extend the photoelectric conversion element into the second region, effectively increasing the light-sensitive area in the depth direction. This allows smaller lateral pixel dimensions while maintaining adequate light capture capability, as the extended portion captures light that would otherwise pass through the reduced lateral opening.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Duration of action of stationary object

If photoelectrons are stored in storage nodes for an extended period, then global shutter functionality is achieved, but light leakage produces additional photoelectrons changing the stored signals

Engineering Contradiction:

Improvephotoelectron storage durationVSAvoidsignal accuracy

Core Design Contradiction:

Duration of action of stationary objectVSMeasurement precision

Solution Approach 1:

The patent extracts or removes the light leakage problem by extending the photoelectric conversion element to occupy the space above the storage node. This extension creates a physical barrier that prevents stray light from reaching the storage node, thereby eliminating the source of additional unwanted photoelectrons during the storage period.

Inventive Principle:

Principle #2Taking out (Extraction)

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 design enhances shutter efficiency by preventing light from reaching the storage node, ensuring that photoelectrons remain unchanged after exposure, thereby improving the accuracy and reliability of signal capture in global shutter mode.

Implementation Method 1

the photo diodes of all of the pixels are exposed at the same time to produce photoelectrons

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

the extending photoelectric conversion portion is disposed between the second surface and the storage node... absorbing any scattered or leaking light before it reaches the storage node

Methodology Applied

Scientific EffectLight absorption: Absorption (EM radiation)

Data Source

PatentUS10134791B1Backside illumination global shutter sensor and pixel thereof

Publication Date: 2018.11.20 NOVATEK MICROELECTRONICS CORP

AI summary

A backside illumination global shutter pixel is disposed in a substrate having a first surface and a second surface and includes an isolation structure having a deep trench isolation pattern, a storage node, and a photoelectric conversion element. The deep trench isolation pattern has a channel and defines a first region and a second region connected with each other by the channel. The storage node is disposed in the second region. The photoelectric conversion element has a main photoelectric conversion portion disposed in the first region and an extending photoelectric conversion portion extended from the main photoelectric conversion portion through the channel to the second region. The extending photoelectric conversion portion is disposed between the second surface and the storage node. A backside illumination global shutter sensor including a plurality of backside illumination global shutter pixels is also provided.