Vertical Transfer Gate Storage for Global Shutter Image Sensors
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Global shutter image sensors face challenges in capturing fast-moving objects without distortion, as existing technologies struggle to efficiently store image charge and prevent parasitic light and electrical crosstalk, leading to image lag and elongation distortion.
Innovation Solution
The implementation of pixel cells with global shutter storage transistors featuring vertical transfer gate storage structures and deep trench isolation light shields, which enhance charge storage capacity while minimizing the area required, thereby reducing distortion and improving pixel fill factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If storage capacitors or storage transistors are used to temporarily store image charge in global shutter pixel cells, then image charge can be held until readout, but parasitic light and electrical crosstalk contaminate the stored charge leading to image lag
Solution Approach 1:
The patent transitions from planar storage structures to three-dimensional vertically stacked structures. The photodiode, storage node, and readout circuitry are arranged in vertical layers, with the storage node positioned between them. This vertical stacking separates the charge storage region from parasitic light sources and electrical crosstalk paths that exist in conventional planar designs, thereby improving storage purity while maintaining compact pixel area.
Solution Approach 2:
The patent introduces intermediate structures between the photodiode and storage node, including isolation layers and transfer gate mechanisms. These intermediaries prevent direct electrical coupling that would cause crosstalk and block parasitic light paths, allowing clean charge transfer while isolating the storage node from contamination sources during the holding period.
2Quantity of substance
If larger storage nodes are used to increase full well capacity, then more image charge can be stored, but the pixel area increases reducing the fill factor
Solution Approach 1:
The patent exploits the third dimension (vertical depth) to increase storage capacity. By stacking the photodiode, storage node, and readout circuitry vertically, the storage node can be made larger in volume without increasing the lateral pixel footprint. This allows increased full well capacity while maintaining a high fill factor, as the additional storage capacity comes from vertical extension rather than lateral expansion.
3Productivity
If vertical transfer gate storage structures are implemented, then charge storage efficiency and full well capacity improve, but device complexity increases
Solution Approach 1:
The patent combines multiple functions into integrated vertical structures. The transfer gate, storage node, and isolation structures are merged into a single vertically stacked assembly that can be fabricated using standard CMOS processes. This integration reduces the number of separate components and interconnections needed, managing device complexity while achieving high charge storage efficiency and full well capacity through the vertical 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 configuration allows for efficient storage and transfer of image charge, reducing image lag and distortion, and increasing the full well capacity, enabling high-speed image capture without elongation distortion in global shutter image sensors.
Implementation Method 1
storage capacitors or storage transistors can be used to temporarily store the image charge acquired by each pixel cell in the array
Implementation Method 2
image charge is transferred from the photodiode to the storage transistor
Data Source
AI summary
A pixel cell includes a photodiode disposed in a semiconductor material layer to accumulate image charge photogenerated in the photodiode in response to incident light. A storage transistor is coupled to the photodiode to store the image charge photogenerated in the photodiode. The storage transistor includes a storage gate disposed proximate a first surface of the semiconductor material layer. The storage gate includes a pair of vertical transfer gate (VTG) portions. Each one of the pair of VTG portions extends a first distance into the semiconductor material layer through the first surface of the semiconductor material layer. A storage node is disposed below the first surface of the semiconductor material layer and between the pair of VTG portions of the storage gate to store the image charge transferred from the photodiode in response to a storage signal.