Transfer Gate Structure for Image Sensor Noise Reduction
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Solution Overview
Problem
Current image sensing devices face challenges in minimizing transmission delay and reducing noise and non-uniformity, particularly in dark environments, due to high voltage application and potential pocket formation.
Innovation Solution
The image sensing device incorporates a transfer gate structure with a horizontal and vertical gate configuration that surrounds both the top and side surfaces of the photoelectric conversion element, enhancing transmission efficiency and reducing the voltage required, while also accumulating holes on the gate insulation film to prevent dark electrons from entering the photoelectric conversion element in low-light conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high voltage is applied to the transfer gate to improve photocharge transfer efficiency, then transmission speed is improved, but noise and non-uniformity increase due to potential pocket formation
Solution Approach 1:
The transfer gate is divided into two separate gates: a first transfer gate connected to the photoelectric conversion element and a second transfer gate connected to the floating diffusion region. This segmentation allows independent control of voltage application at each interface, enabling efficient photocharge transfer while preventing potential pocket formation that causes noise and non-uniformity.
Solution Approach 2:
A pixel electrode is introduced as an intermediary component between the two transfer gates and the photoelectric conversion element. This intermediary structure facilitates controlled voltage application and photocharge transfer while maintaining electrical isolation and preventing harmful potential pockets from forming in the conventional single-gate configuration.
2Device complexity
If a conventional single transfer gate is used, then device structure is simple, but transmission delay is significant
Solution Approach 1:
The transfer path is segmented into two distinct transfer gates positioned at different locations. The first transfer gate is located near the photoelectric conversion element to efficiently collect photocharges, while the second transfer gate is positioned near the floating diffusion region to facilitate efficient charge injection. This dual-gate configuration reduces the distance and time for photocharge transfer compared to a single distant gate.
Solution Approach 2:
The transfer gates are positioned in different spatial dimensions within the pixel structure. The first transfer gate is positioned at the photoelectric conversion element interface while the second transfer gate is positioned at the floating diffusion interface, creating a distributed transfer path that reduces transmission delay through spatial optimization.
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 design improves lag characteristics, reduces noise, and prevents potential pocket formation, leading to better uniformity and performance in both bright and dark environments by optimizing the transfer gate structure and voltage application.
Implementation Method 1
a photoelectric conversion element disposed in a substrate, and configured to generate photocharges in response to incident light
Data Source
AI summary
An image sensing device includes a photoelectric conversion element, a floating diffusion (FD) region, and a transfer gate. The photoelectric conversion element is disposed in a substrate, and generates photocharges in response to incident light. The floating diffusion (FD) region is disposed over the photoelectric conversion element, and stores the photocharges generated by the photoelectric conversion element. The transfer gate transfer the photocharges generated by the photoelectric conversion element to the floating diffusion (FD) region in response to a transmission signal. The transfer gate includes a horizontal gate disposed over the photoelectric conversion element, and a vertical gate coupled to the horizontal gate. The vertical gate is positioned at a side of the photoelectric conversion element, and surrounds the photoelectric conversion element.