CMOS Image Sensor Charge Transfer via Central Conversion Unit

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Solution Overview

Problem

Conventional CMOS image sensors face inefficiencies in charge transfer due to long transfer distances between the charge accumulation unit and the charge voltage conversion unit, leading to deteriorated transfer characteristics and reduced saturation electrons, requiring increased masks and implantation steps which complicate the process and reduce electron saturation.

Innovation Solution

The solution involves a solid-state imaging element where the charge voltage conversion unit is connected to the center of the charge accumulation unit, with a configuration of electrodes forming a transfer gradient, including recessed electrodes to minimize transfer distance and enhance saturation electron count, allowing for parallel arrangement of photoelectric conversion and voltage conversion units, thereby improving charge transfer efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the charge voltage conversion unit is connected to a position other than the center of the charge accumulation unit, then the pixel layout flexibility is improved, but the transfer distance becomes long and charge transfer efficiency deteriorates

Engineering Contradiction:

Improvepixel layout flexibilityVSAvoidcharge transfer efficiency

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent applies asymmetry by positioning the charge voltage conversion unit at the center of the charge accumulation unit, creating a symmetric radial electrode arrangement. This central positioning ensures that all electrodes are equidistant from the conversion unit, optimizing charge transfer paths and eliminating the transfer efficiency deterioration that would occur with asymmetric/off-center positioning.

Inventive Principle:

Principle #4Asymmetry

2Area of stationary object

If the transfer distance is increased, then the pixel area can be reduced, but the number of masks and implantation steps must be increased and transfer characteristics deteriorate

Engineering Contradiction:

Improvepixel areaVSAvoidnumber of masks and implantation steps

Core Design Contradiction:

Area of stationary objectVSDevice complexity

Solution Approach 1:

The patent segments the charge accumulation unit into multiple regions with multiple electrodes arranged radially around the central charge voltage conversion unit. This segmentation allows for optimized charge collection from different regions simultaneously, maintaining efficient transfer characteristics while enabling compact pixel area without requiring additional masks or implantation steps.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements a nested structure where multiple electrodes are arranged concentrically around the central charge voltage conversion unit, with each electrode positioned at a specific radius. This nested radial arrangement allows compact integration of multiple charge collection paths within a small pixel area, avoiding the need for increased manufacturing complexity while maintaining optimal transfer characteristics.

Inventive Principle:

Principle #7Nested doll (Nesting)

3Adaptability or versatility

If the transfer distance is increased, then the pixel layout flexibility is improved, but the number of saturation electrons in unit area decreases

Engineering Contradiction:

Improvepixel layout flexibilityVSAvoidnumber of saturation electrons

Core Design Contradiction:

Adaptability or versatilityVSQuantity of substance

Solution Approach 1:

The patent applies local quality by creating a non-uniform electrode arrangement where electrodes are positioned at different radial distances from the central charge voltage conversion unit. This allows different regions of the charge accumulation unit to have optimized local electric field characteristics, maximizing charge collection efficiency and saturation electron density in each local region while maintaining overall compact pixel area.

Inventive Principle:

Principle #3Local quality

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 improves charge transfer efficiency and increases the number of saturation electrons, simplifying the pixel layout and reducing noise by minimizing transfer distance and allowing for parallel arrangement of units, thus enhancing imaging performance.

Implementation Method 1

a photoelectric conversion unit that generates a charge by photoelectric conversion according to an amount of incident light

Methodology Applied

Scientific EffectPhotoelectric conversion: Photoelectric Effect

Implementation Method 2

A plurality of electrodes that forms a transfer gradient to transfer the charge accumulated in the charge accumulation unit

Methodology Applied

Scientific EffectTransfer gradient: Electric Field

Data Source

PatentUS10497740B2Solid-state imaging element, imaging device, and electronic device

Publication Date: 2019.12.03 SONY GROUP CORP

AI summary

The present technology relates to a solid-state imaging element, an imaging device, and an electronic device that can improve transfer efficiency of a charge accumulation unit (MEM) and can increase the number of saturation electrons Qs. In a case where a charge voltage conversion unit (FD) is connected to a center of a charge accumulation unit (MEM) in each pixel and pixels are arrayed in an array, a column in which photoelectric conversion units (PD) are arrayed and a column including charge voltage conversion units (FD) and pixel transistors are arrayed in parallel. The present technology can be applied to a CMOS image sensor.