Image Sensor Transfer Gate with Non-Uniform Insulator
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Solution Overview
Problem
As integration density of image sensors increases, pixel size decreases, making photodiodes sensitive to structure variations and external environments, leading to low light sensitivity.
Innovation Solution
The image sensor design includes a substrate with an active region defined by a device isolation layer, a photoelectric conversion layer, a well impurity layer, a floating diffusion region, and a transfer gate with a non-uniform gate insulating layer, where the transfer gate's upper portion is higher than the substrate and has a specific surface configuration to enhance electron transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If integration density is increased, then device area is reduced, but photodiode light sensitivity deteriorates
Solution Approach 1:
The transfer gate extends in the vertical dimension by protruding from the substrate surface, creating a three-dimensional structure that increases the effective transfer area without occupying additional planar space. This allows improved electron transfer capability while maintaining high integration density.
Solution Approach 2:
The transfer gate is positioned and configured in advance to optimize electron transfer before charge accumulation occurs. The pre-configured protruding structure and gate insulating layer arrangement prepare the electron transfer path beforehand, ensuring efficient transfer even in miniaturized pixels.
2Productivity
If pixel size is reduced, then integration density is improved, but photodiode structure stability deteriorates
Solution Approach 1:
The transfer gate is nested within the pixel structure, with the gate insulating layer positioned between the gate and the photoelectric conversion layer. This nested arrangement allows the transfer gate to be integrated into the existing pixel architecture without disrupting the photodiode's structural stability.
Solution Approach 2:
The gate insulating layer is applied locally between the transfer gate and the photoelectric conversion layer, providing targeted electrical isolation only where needed. This localized approach maintains the overall structural stability of the miniaturized photodiode while enabling effective charge transfer.
3Productivity
If transfer gate complexity is increased, then electron transfer efficiency is improved, but device manufacturing complexity deteriorates
Solution Approach 1:
The transfer gate is segmented into distinct components: a gate electrode and a gate insulating layer. This segmentation allows each component to be optimized independently for its specific function while simplifying the overall manufacturing process through modular construction.
Solution Approach 2:
The transfer gate utilizes the vertical dimension by protruding from the substrate surface, which improves electron transfer efficiency through increased effective area without requiring complex lateral structures. This vertical extension achieves enhanced performance while maintaining manufacturing simplicity.
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 enhances the sensitivity of the image sensor by efficiently transferring electrons from the photoelectric conversion layer to the floating diffusion region, improving light sensitivity and reducing noise.
Implementation Method 1
a photodiode (PD) that coverts incident light into an electrical signal
Implementation Method 2
A gate insulating layer may be provided, which may have a non-uniform thickness and may be interposed between the well impurity layer and the transfer gate
Data Source
AI summary
An image sensor and a method of fabricating the same are disclosed. The image sensor may include a substrate including an active region defined by a device isolation layer, a photoelectric conversion layer, a well impurity layer, a floating diffusion region, and a transfer gate. When viewed in a plan view, a lower portion of the transfer gate may include a first surface in contact with the device isolation layer, a second surface substantially perpendicular to the first surface, and a third surface connected to the first and second surfaces. The third surface may face the floating diffusion region. A first portion of a gate insulating layer may be adjacent to the third surface and thinner than a portion adjacent to the first surface or the second surface, and this may facilitate more efficient transfer of an electron from the photoelectric conversion layer to the floating diffusion region.