BSI CMOS Pixel Array Barrier Layer Design

Solution Overview

Problem

Conventional Back Side Illumination (BSI) CMOS image sensors face challenges in maximizing photon collection efficiency due to electron absorption by well regions, which reduces the number of electrons collected by photodiodes and increases interference between adjacent pixels.

Innovation Solution

The implementation of a thick epitaxial layer with high resistivity and a barrier layer to prevent electron absorption by well regions, combined with a collection area that directs electrons to the photodiode, enhances the collection efficiency and quantum efficiency of the pixel array.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional BSI CMOS pixel array is used, then the structure is simple and manufacturing is easier, but electron absorption by well regions reduces collection efficiency and quantum efficiency

Engineering Contradiction:

Improvecollection efficiencyVSAvoidpixel structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The pixel array is divided into distinct functional regions: a first region containing photodiodes for photon detection and a second region containing well regions for charge storage. This segmentation prevents electrons generated in the first region from being absorbed by well regions, thereby improving collection efficiency while maintaining a manageable structural complexity through clear functional zoning.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An epitaxial layer is introduced as an intermediary structure between the photodiodes and well regions. This epitaxial layer acts as a mediator that directs electron flow from the first region to the photodiodes while preventing electron absorption by the well regions in the second region, thus improving quantum efficiency without significantly complicating the manufacturing process.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If a thick epitaxial layer with high resistivity is implemented, then quantum efficiency improves, but manufacturing complexity increases

Engineering Contradiction:

Improvequantum efficiencyVSAvoidfabrication difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The epitaxial layer is designed with specific parameter optimizations: increased thickness and high resistivity. These parameter changes enhance the layer's ability to direct electron flow and prevent electron absorption, thereby improving quantum efficiency. The parameters are carefully selected to balance performance improvement with manufacturing feasibility.

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If well regions are present in the pixel array, then charge storage capability is provided, but electron absorption increases and reduces the number of electrons collected by photodiodes

Engineering Contradiction:

Improveelectron collection quantityVSAvoidelectron absorption by well regions

Core Design Contradiction:

Quantity of substanceVSObject-generated harmful factors

Solution Approach 1:

The pixel array is divided into distinct functional regions: a first region containing photodiodes for photon detection and a second region containing well regions for charge storage. This segmentation prevents electrons generated in the first region from being absorbed by well regions, thereby improving collection efficiency while maintaining a manageable structural complexity through clear functional zoning.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An epitaxial layer is introduced as an intermediary structure between the photodiodes and well regions. This epitaxial layer acts as a mediator that directs electron flow from the first region to the photodiodes while preventing electron absorption by the well regions in the second region, thus improving quantum efficiency without significantly complicating the manufacturing process.

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 configuration significantly increases the collection efficiency of photodiodes and reduces electron absorption by well regions, thereby improving the quantum efficiency and minimizing interference between pixels.

Implementation Method 1

an absorption area to absorb incoming photons and to generate electrons responsive to absorbed photons

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS9356169B2Apparatus, system and method of back side illumination (BSI) complementary metal-oxide-semiconductor (CMOS) pixel array

Publication Date: 2016.05.31 KEYSTONE INTPROP MANAGEMENT LTD

AI summary

Some demonstrative embodiments include devices and/or methods of Back Side Illumination (BSI) Complementary Metal-Oxide-Semiconductor (CMOS) pixel array. For example, a BSI CMOS pixel array may include a plurality of pixels, a pixel of the plurality of pixels may include one or more Metal-Oxide-Semiconductor (MOS) transistors comprising one or more well regions, a well region of the one or more well regions comprising an N-Well (NW) region or a P-well (PW) region; a photodiode; an epitaxial (epi) layer comprising an absorption area and a collection area, the absorption area to absorb incoming photons and to generate electrons responsive to absorbed photons, and the collection area connecting the absorption area to the photodiode to provide the electrons from the absorption area to the photodiode; and a barrier layer separating the absorption area from the one or more well regions.