3D Image Sensor Pixel Transfer Gate Structure
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Solution Overview
Problem
The challenge is to develop an image sensor with improved performance that can integrate a large number of unit pixels in a limited area without degrading their characteristics, which is essential for high-pixel image generation, while maintaining efficient transfer efficiency of photocharge from the photoelectric conversion element to the floating diffusion.
Innovation Solution
The image sensor incorporates a 3D pixel structure with a transfer transistor having first and second transistors coupled in series, each with different threshold voltages, and a boosting capacitor to enhance the on/off characteristics and transfer efficiency, including a channel layer with different conductivity types and a parasitic capacitor for improved capacitance without additional processing or area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of unit pixels is increased in a limited area, then high-pixel image generation is enabled, but the transfer efficiency of photocharge deteriorates
Solution Approach 1:
The patent transitions from a planar transfer gate structure to a three-dimensional structure where the transfer gate extends vertically into the photoelectric conversion element. This dimensional change allows the transfer gate to make contact with photodiodes at multiple depths, effectively increasing the collection area without expanding the lateral pixel density, thus maintaining transfer efficiency while enabling higher pixel counts in limited area.
Solution Approach 2:
The transfer gate is nested within the photoelectric conversion element by extending into its interior space. This nesting approach allows the transfer gate to access photodiodes at different depth levels without occupying additional lateral space, enabling efficient photocharge collection from multiple photodiodes while maintaining compact pixel structure for high-density integration.
2Ease of manufacture
If a conventional transfer gate structure is used, then fabrication is simple, but transfer efficiency is insufficient for high-pixel images
Solution Approach 1:
The transfer gate structure extends vertically into the photoelectric conversion element, creating a three-dimensional configuration. This dimensional enhancement improves transfer efficiency by enabling contact with photodiodes at multiple depths while maintaining compatibility with standard semiconductor fabrication processes, thus achieving high performance without significantly complicating manufacturing.
3Device complexity
If the transfer gate contacts only one photodiode, then the structure is simple, but photocharge transfer from multiple photodiodes is inefficient
Solution Approach 1:
The transfer gate extends vertically into the photoelectric conversion element, creating multiple contact points with photodiodes at different depth levels. This three-dimensional configuration enables efficient photocharge collection from multiple photodiodes simultaneously while maintaining a relatively simple single-gate structure, thus improving transfer efficiency without proportionally increasing device complexity.
Solution Approach 2:
The single transfer gate structure performs multiple functions by contacting multiple photodiodes through its vertical extension. This multi-functional design allows one transfer gate to efficiently collect photocharge from several photodiodes, reducing the need for additional transfer gates and maintaining structural simplicity while achieving high transfer efficiency.
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 increases the transfer efficiency of the image sensor, leading to improved unit pixel characteristics and image quality by effectively transferring photocharge, thus enabling high-pixel image generation within a limited area.
Implementation Method 1
a photoelectric conversion element suitable for generating photocharge in response to incident light
Data Source
AI summary
An image sensor may include: a photoelectric conversion element including a second conductive layer formed over a first conductive layer; an insulating layer and a third conductive layer which are sequentially formed over the second conductive layer; an opening exposing the second conductive layer through the third conductive layer and the insulating layer; a channel layer formed along the surface of the opening, and including first and second channel layers which are coupled to each other while having different conductivity types; and a transfer gate formed over the channel layer to fill the opening, and partially formed over the third conductive layer.