Vertically Integrated Global-Shutter Pixel for High Dynamic Range
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Solution Overview
Problem
Existing image sensor pixel arrays struggle to simultaneously provide global-shutter operation, high dynamic range, low read noise, high optical fill factor, and simultaneous exposure and read operations.
Innovation Solution
A vertically integrated pixel design featuring a pinned photodiode, transfer gate, low-gain select transistor, reset transistor, capacitance, and source-follower transistor, which allows for global-shutter operation, low read noise through correlated double sampling, and high optical fill factor via backside illumination and overflow integration capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a global-shutter pixel design is implemented, then simultaneous exposure and read operations are achieved, but device complexity increases
Solution Approach 1:
The patent implements a vertically integrated stacked pixel architecture where different functional layers are stacked in three dimensions. The pinned photodiode, transfer gate, integration capacitor, and read circuitry are arranged in separate vertical layers, allowing global-shutter operation while reducing in-plane complexity and enabling simultaneous exposure and read operations.
Solution Approach 2:
The pixel is divided into distinct functional segments or layers: a pinned photodiode layer for charge generation, a transfer gate layer for charge movement, an integration capacitor layer for signal storage, and a read circuit layer for signal processing. This segmentation allows each component to be optimized independently while working together to achieve global-shutter operation.
2Adaptability or versatility
If high dynamic range is achieved through multiple capacitors, then high-contrast scenes are captured, but device complexity increases
Solution Approach 1:
The integration capacitor is positioned in a separate vertical layer from the photodiode and read circuitry. This three-dimensional stacking allows the capacitor to be added for high dynamic range capability without increasing the in-plane footprint or significantly increasing overall device complexity.
3Area of stationary object
If backside illumination is used to increase optical fill factor, then photosensitive area is maximized, but manufacturing precision requirements increase
Solution Approach 1:
The patent uses backside illumination where light enters the pixel through the back surface of the substrate rather than the front. This inversion allows the active photosensitive area to be maximized by removing front-side metal interconnects and allowing light to pass through the substrate and hit the pinned photodiode directly, achieving high optical fill factor despite increased manufacturing complexity.
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
Enables global-shutter operation with high dynamic range and low read noise, achieving simultaneous exposure and read operations while maintaining a high optical fill factor, effectively capturing high-contrast scenes without distortion.
Implementation Method 1
a pinned photodiode (PPD) which generates a photocurrent Iph
Data Source
AI summary
A pixel comprising a pinned photodiode (PPD) which generates a photocurrent Iph, a transfer gate connected in series between the PPD and a first node, a low-gain select transistor connected between the first node and a second node, a reset transistor connected between the second node and a reset voltage, a capacitance connected between the second node and a first constant potential, and a source-follower transistor whose source, gate and drain are connected to an output node, the first node and a second constant potential, respectively. When properly arranged, a vertically integrated (3D) global-shutter pinned PPD pixel is provided, which uses an overflow integration capacitor and subthreshold conduction of the reset transistor for increased dynamic range. Global shutter operation is achieved by storing the pixel output on sampling capacitors in another semiconductor layer at the end of integration.