Dual Transfer Gate Image Sensor Charge Transmission
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Solution Overview
Problem
Current image sensing devices face challenges in efficiently transferring photocharges from the photodiode to the floating diffusion region, particularly as the depth of the photodiode increases, leading to reduced Full Well Capacity and increased dark current noise.
Innovation Solution
The implementation of an image sensing device with two transfer gates, where the second transfer gate is buried in the substrate and receives a negative voltage, while the first transfer gate is positioned over the substrate and receives a positive voltage, optimizing the overlap and voltage application to enhance photocharge transmission efficiency and reduce dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the photodiode depth is increased to improve light capture efficiency, then the light sensitivity is improved, but the Full Well Capacity is reduced and dark current noise increases
Solution Approach 1:
The transfer path is segmented into two distinct transfer gates (first and second transfer gates) positioned at different depths. The second transfer gate is located deeper in the substrate to efficiently collect photocharges from the deep photodiode, while the first transfer gate is positioned higher to transfer charges to the floating diffusion region, thereby maintaining both deep photodiode benefits and adequate Full Well Capacity
Solution Approach 2:
The solution introduces a vertical dimension to the charge transfer mechanism by placing transfer gates at different depth levels within the substrate. This multi-level vertical arrangement allows efficient charge collection from deep photodiodes while maintaining sufficient charge storage capacity, resolving the contradiction between depth and Full Well Capacity
2Illumination intensity
If the photodiode depth is increased to improve light capture efficiency, then the light sensitivity is improved, but the dark current noise increases
Solution Approach 1:
The transfer path is segmented into two distinct transfer gates (first and second transfer gates) positioned at different depths. The second transfer gate is located deeper in the substrate to efficiently collect photocharges from the deep photodiode, while the first transfer gate is positioned higher to transfer charges to the floating diffusion region, thereby maintaining both deep photodiode benefits and adequate Full Well Capacity
Solution Approach 2:
The two transfer gates act as intermediary structures that facilitate efficient charge collection and transfer from the deep photodiode to the floating diffusion region. This intermediary charge transfer mechanism reduces charge loss and minimizes dark current noise generation, allowing the photodiode to operate at optimal depth
3Device complexity
If a single transfer gate is used to simplify the device structure, then the device complexity is reduced, but the photocharge transmission efficiency is reduced
Solution Approach 1:
The transfer path is segmented into two distinct transfer gates (first and second transfer gates) positioned at different depths. The second transfer gate is located deeper in the substrate to efficiently collect photocharges from the deep photodiode, while the first transfer gate is positioned higher to transfer charges to the floating diffusion region, thereby maintaining both deep photodiode benefits and adequate Full Well Capacity
Solution Approach 2:
The solution introduces a vertical dimension to the charge transfer mechanism by placing transfer gates at different depth levels within the substrate. This multi-level vertical arrangement allows efficient charge collection from deep photodiodes while maintaining sufficient charge storage capacity, resolving the contradiction between depth and Full Well Capacity
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 improves the transmission efficiency of photocharges and reduces dark current noise, ensuring higher Full Well Capacity and better image quality in high-performance image sensors.
Implementation Method 1
a photoelectric conversion region disposed in the substrate and configured to generate photocharges in response to incident light
Implementation Method 2
first and second transfer gates having portions disposed to overlap each other and configured to transmit the photocharges from the photoelectric conversion region to the floating diffusion (FD) region
Data Source
AI summary
An image sensing device is provided to include a substrate, a photoelectric conversion region disposed in the substrate and configured to generate photocharges in response to incident light, a floating diffusion (FD) region disposed in the substrate and configured to store the photocharges generated in the photoelectric conversion region, and first and second transfer gates having portions disposed to overlap each other and configured to transmit the photocharges from the photoelectric conversion region to the floating diffusion (FD) region.