3D Image Sensor Stacked Architecture Reducing Dark Current
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Solution Overview
Problem
The reduction in photodiode size for increased pixel density leads to reduced image quality due to decreased light reception area and photon incidence, causing charge sharing phenomena, dark current generation, and sensitivity reduction in image sensors.
Innovation Solution
The implementation of a 3D image sensor structure with a photodiode connected to readout circuitry through a metal interconnection, featuring a P0/N−/P− junction and a first conduction type connection region for swift photo charge movement, minimizing dark current and maintaining sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If photodiode size is reduced to increase pixel density, then pixel density increases, but light receiving area decreases and image quality deteriorates
Solution Approach 1:
The patent transitions from a planar 2D pixel arrangement to a 3D stacked architecture where photodiodes are positioned vertically over readout circuitry. This dimensional change allows photodiodes to maintain larger light receiving areas while achieving higher effective pixel density through vertical stacking, directly resolving the contradiction between pixel density and light receiving area.
2Productivity
If photodiode size is reduced, then pixel density increases, but photon incidence decreases and sensitivity reduces
Solution Approach 1:
By stacking photodiodes vertically over readout circuitry in the third dimension, the patent enables each photodiode to maintain a larger effective light receiving area, thereby increasing photon incidence and sensitivity while still achieving high pixel density through the vertical stacking arrangement.
3Speed
If transfer transistor source and drain are heavily doped to improve charge transfer, then charge transfer improves, but charge sharing phenomenon occurs and image error increases
Solution Approach 1:
The patent implements asymmetric doping where only the drain region of the transfer transistor is heavily doped while the source region maintains lighter doping. This local differentiation allows efficient charge transfer to the floating diffusion node while preventing charge sharing between adjacent pixels, as the lightly-doped source does not create strong electric fields that would cause charge to leak to neighboring pixels.
4Area of stationary object
If 3D stacked structure is implemented to increase fill factor, then fill factor increases, but dark current generation increases due to poor charge movement
Solution Approach 1:
The patent applies localized heavy doping specifically to the drain region of transfer transistors in the 3D stacked structure. This creates strong electric fields at critical charge transfer nodes to ensure swift charge movement and prevent charge accumulation that would generate dark current, while maintaining the high fill factor benefits of the stacked architecture.
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 prevents charge sharing, reduces dark current, and maintains image sensitivity by ensuring full photo charge dumping and efficient charge transfer between the photodiode and readout circuitry, enhancing image quality.
Implementation Method 1
an electrical junction region in the first substrate, the electrical junction region being electrically connected to the readout circuitry
Implementation Method 2
An image sensor is a semiconductor device for converting an optical image into an electrical signal
Data Source
AI summary
An image sensor includes a first substrate, readout circuitry, an electrical junction region, a metal interconnection and an image sensing device. The readout circuitry is formed on and/or over the first substrate and the electrical junction region is formed in the first substrate and electrically connected to the readout circuitry. The metal interconnection is electrically connected to the electrical junction region. The image sensing device is formed on and/or over the metal interconnection.