Negative Well Voltage for Complete Charge Transfer in Solid-State Imaging

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Solution Overview

Problem

Solid-state imaging devices face challenges in completely transferring signal charge from the optoelectronic conversion section to the floating diffusion section during intense light exposure, leading to afterimages and degraded image quality, while also struggling to increase dynamic range and signal-to-noise ratio simultaneously.

Innovation Solution

The voltage of the well of the charge-voltage conversion section is set to be negative to enhance the potential difference between the optoelectronic conversion section and the charge-voltage conversion section, ensuring complete signal charge transfer even with a large amount of incoming light, and is set higher than the reset voltage when the amplifier transistor outputs the signal to achieve a high amplification ratio.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the floating diffusion section is reduced in capacity to increase conversion efficiency and SN ratio, then signal-to-noise ratio is improved, but signal charge transfer completeness deteriorates causing afterimages

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidsignal charge transfer completeness

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent changes the potential parameter of the well underlying the charge-voltage conversion section from a conventional positive or zero potential to a negative potential. This parameter change creates a potential difference that drives complete signal charge transfer to the floating diffusion section, resolving the contradiction between transfer completeness and conversion efficiency by enabling both small floating diffusion capacity (for high SN ratio) and complete charge transfer (for high reliability).

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the potential difference between optoelectronic conversion section and charge-voltage conversion section is increased to ensure complete charge transfer, then dynamic range is improved, but power consumption increases

Engineering Contradiction:

Improvedynamic rangeVSAvoidpower consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The negative potential applied to the well serves a dual function: it creates the potential difference needed for complete charge transfer (improving dynamic range) and simultaneously enables the use of a small floating diffusion section (improving conversion efficiency). This self-service approach means the same mechanism achieves multiple goals without requiring additional power-consuming components or processes.

Inventive Principle:

Principle #25Self-service

3Measurement precision

If the floating diffusion section capacity is reduced to increase conversion efficiency, then amplification capability is improved, but the voltage for amplifier transistor gate becomes excessively low

Engineering Contradiction:

Improveconversion efficiencyVSAvoidamplifier transistor operating voltage

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent introduces a well with negative potential as an intermediary element between the optoelectronic conversion section and the charge-voltage conversion section. This intermediary creates a potential gradient that ensures complete charge transfer while maintaining adequate voltage levels for amplifier transistor operation, resolving the contradiction between high conversion efficiency and sufficient amplification voltage.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 approach effectively increases the dynamic range and signal-to-noise ratio by ensuring complete signal charge transfer and outputting signals with a high amplification ratio, resulting in improved image quality.

Implementation Method 1

an optoelectronic conversion section that subjects an incoming light to optoelectronic conversion and stores therein a signal charge

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

the voltage of a well of the charge-voltage conversion section is set to be negative... enhancing the potential difference between the optoelectronic conversion section and the charge-voltage conversion section, ensuring complete signal charge transfer

Methodology Applied

Scientific EffectElectric field: Electric Field

Data Source

PatentUS8823069B2Solid-state imaging device, drive method of solid-state imaging device, and imaging apparatus

Publication Date: 2014.09.02 SONY SEMICON SOLUTIONS CORP

AI summary

A solid-state imaging device that includes: a pixel array section configured by an array of a unit pixel, including an optoelectronic conversion section that subjects an incoming light to optoelectronic conversion and stores therein a signal charge, a transfer transistor that transfers the signal charge stored in the optoelectronic conversion section, a charge-voltage conversion section that converts the signal charge provided by the transfer transistor into a signal voltage, and a reset transistor that resets a potential of the charge-voltage conversion section; and voltage setting means for setting a voltage of a well of the charge-voltage conversion section to be negative.