Stacked Pixel CMOS Image Sensor Vertical Color Sensing

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Solution Overview

Problem

Conventional CMOS image sensors require light-absorbing color filters to sense colors, which leads to reduced sensitivity and resolution due to light absorption and the need for complex pixel structures with multiple transistors, making it challenging to achieve high-resolution, low-noise imaging without sacrificing sensitivity.

Innovation Solution

The implementation of stacked photo-sites with a potential barrier under the pinned photodiode structure allows for vertical separation of photo-generated carriers, enabling color sensing without conventional light-absorbing filters, thereby reducing noise and maintaining sensitivity, and allowing for higher pixel density and resolution.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If conventional light-absorbing color filters are used to sense colors, then color sensing capability is achieved, but sensitivity and resolution are reduced due to light absorption

Engineering Contradiction:

Improvecolor sensing capabilityVSAvoidsensitivity

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent transitions from planar color filtering to three-dimensional stacked photodiodes, where different wavelengths are detected at different depths vertically. This dimensional change eliminates the need for light-absorbing filters while maintaining color sensing capability through depth-based wavelength discrimination.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The pixel is divided into multiple stacked photodiodes, each detecting different wavelength ranges. This segmentation of the detection function across vertical layers enables color sensing without requiring light-absorbing filters, thereby preserving sensitivity.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If conventional light-absorbing color filters are used to sense colors, then color sensing capability is achieved, but resolution is reduced

Engineering Contradiction:

Improvecolor sensing capabilityVSAvoidresolution

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

By stacking photodiodes vertically at the same pixel location, the patent enables multiple color measurements without requiring spatial separation of color filter pixels. This eliminates the resolution loss inherent in Bayer filter patterns while maintaining full color sensing capability.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Reliability

If multiple transistors are used in pixel structure for noise reduction, then noise performance is improved, but device complexity increases

Engineering Contradiction:

Improvenoise performanceVSAvoidpixel structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the color filtering function from the optical path and relocates it to the vertical stacking architecture of photodiodes. This eliminates the need for complex color filter arrays and associated interpolation circuits, simplifying the overall system while maintaining color sensing capability.

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 approach enables the generation of two or more color-coded signals without light-absorbing filters, improving sensitivity and resolution while simplifying the pixel structure, allowing for high-performance imaging with small pixel sizes and reduced noise.

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

Implementation Method 2

a potential barrier formed between the first region and a second region underneath the first region and diverting the photo-generated carriers from the second region to the second charge storage region

Methodology Applied

Scientific EffectElectrostatic repulsion: Electrostatics

Data Source

PatentUS8686479B2Stacked pixel for high resolution CMOS image sensor

Publication Date: 2014.04.01 INTELLECTUAL VENTURES II LLC

AI summary

Provided is a solid-state CMOS image sensor, specifically a CMOS image sensor pixel that has stacked photo-sites, high sensitivity, and low dark current. In an image sensor including an array of pixels, each pixel includes: a standard photo-sensing and charge storage region formed in a first region under a surface portion of a substrate and collecting photo-generated carriers; a second charge storage region formed adjacent to the surface portion of the substrate and separated from the standard photo-sensing and charge storage region; and a potential barrier formed between the first region and a second region underneath the first region and diverting the photo-generated carriers from the second region to the second charge storage region.