Back-Side Illuminated CMOS Sensor Global Shutter via Nested Storage Gates

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Solution Overview

Problem

Standard CMOS image sensors face challenges in achieving global shuttering mode without increasing pixel size, as they require additional charge storage sites that consume valuable area and generate noise, leading to undesirable smearing effects and distortion in moving object images.

Innovation Solution

Implementing a top storage gate structure above the pinned photodiode for charge storage, allowing for efficient global shuttering capability without sacrificing pixel size, and enabling multiple storage sites per pixel for enhanced dynamic range and flexibility.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If additional charge storage sites are added to achieve global shuttering, then global shutter capability is improved, but pixel size increases and noise increases

Engineering Contradiction:

Improveglobal shutter capabilityVSAvoidpixel size

Core Design Contradiction:

Adaptability or versatilityVSArea of moving object

Solution Approach 1:

The patent implements global shutter capability by nesting the charge storage function within the existing pixel structure. The pinned photodiode serves dual purposes: as the primary charge integration node and as the charge storage site for global shutter operation. This eliminates the need for separate storage sites, avoiding pixel size increase while maintaining global shutter functionality.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The pinned photodiode is designed to perform multiple functions: charge integration during exposure, charge storage for global shutter operation, and charge transfer to the floating diffusion. By making the photodiode multi-functional, the patent achieves global shutter capability without adding extra components that would increase pixel size.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Adaptability or versatility

If additional charge storage sites are added to achieve global shuttering, then global shutter capability is improved, but noise and smearing effects increase

Engineering Contradiction:

Improveglobal shutter capabilityVSAvoidnoise and smearing effects

Core Design Contradiction:

Adaptability or versatilityVSObject-generated harmful factors

Solution Approach 1:

By nesting the storage function within the pinned photodiode itself rather than adding separate storage sites, the patent eliminates the interfaces between different charge storage structures that would generate noise and smearing artifacts. The continuous structure reduces charge transfer losses and noise generation.

Inventive Principle:

Principle #7Nested doll (Nesting)

Solution Approach 2:

The patent extracts the charge storage function from separate storage sites and integrates it directly into the pinned photodiode structure. This consolidation removes the harmful interfaces and charge transfer steps between separate storage nodes, thereby reducing noise and smearing effects.

Inventive Principle:

Principle #2Taking out (Extraction)

3Adaptability or versatility

If standard charge storage methods are used, then global shuttering is achieved, but pixel size increases consuming valuable area

Engineering Contradiction:

Improveglobal shutter modeVSAvoidpixel area

Core Design Contradiction:

Adaptability or versatilityVSArea of stationary object

Solution Approach 1:

The pinned photodiode is designed to serve multiple functions simultaneously: charge integration during the exposure phase and charge storage during the readout phase. This multi-functionality eliminates the need for separate storage regions, maintaining compact pixel size while achieving global shutter capability.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent merges the charge integration and charge storage functions into a single pinned photodiode structure. By combining these functions that were traditionally separated in different locations, the patent achieves global shutter operation without increasing pixel area.

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

Enables CMOS image sensors to operate in both rolling and global shutter modes with minimal pixel size increase, reducing noise and smearing artifacts, while allowing for multiple sampling and improved dynamic range for moving target detection.

Implementation Method 1

Typical image sensors sense light by converting impinging photons into electrons that are integrated (collected) in sensor pixels

Methodology Applied

Scientific EffectPhotoelectric Effect: Photoelectric Effect

Data Source

PatentUS8723284B1Back side illuminated CMOS image sensor with global shutter storage gates stacked on top of pinned photodiodes

Publication Date: 2014.05.13 APTINA IMAGING CORP

AI summary

The invention describes a solid-state CMOS image sensor array and in particular describes in detail the image sensor array pixels, with global and rolling shutter capabilities, that utilize charge storage gates located on top of a pinned photodiode. The sensor array is illuminated from the back side and the location of the storage gate on top of the pinned photodiode saves valuable pixel area, which does not compromise the Dynamic Range of the image sensor.