Recessed Floating Diffusion Layout for Image Sensor Charge Transfer
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Solution Overview
Problem
Current image sensors face challenges in enhancing charge transfer efficiency from the photodiode to the floating diffusion region, which affects their electrical characteristics.
Innovation Solution
The image sensor design includes a photodiode with a transfer gate structure partially buried in the substrate, a recessed floating diffusion region, and a p-type impurity region positioned between the transfer gate and recess, optimizing the distance and doping concentrations to improve charge transfer efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the distance between the photodiode and floating diffusion region is reduced to enhance charge transfer efficiency, then charge transfer efficiency is improved, but device complexity increases due to the need for recess structures and additional impurity regions
Solution Approach 1:
The patent introduces a vertical recess structure in the substrate to position the floating diffusion region closer to the photodiode. This dimensional change (creating a downward凹陷 structure) allows the floating diffusion region to be placed at a lower depth, reducing the vertical distance for charge transfer without increasing horizontal footprint or overall device complexity
Solution Approach 2:
The patent applies localized p-type impurity regions specifically at the boundaries between the photodiode and floating diffusion region, and between the floating diffusion region and substrate. This localized doping creates optimal charge transfer conditions only where needed, rather than uniformly doping the entire structure, thus improving charge transfer efficiency without requiring complex global structural changes
2Reliability
If additional impurity regions are added to optimize charge transfer, then charge transfer efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent combines multiple impurity region functions into integrated doping steps. The p-type impurity regions are formed in conjunction with the floating diffusion region doping process, merging the creation of charge transfer optimization regions with the standard floating diffusion formation process. This integration reduces the number of separate manufacturing steps while achieving the desired charge transfer 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 configuration reduces the distance between the light sensing element and the floating diffusion region, enhancing charge transfer efficiency and improving the electrical characteristics of the image sensor.
Implementation Method 1
a photodiode disposed in a substrate and including an n-type impurity region
Implementation Method 2
an impurity region disposed at a portion of the substrate between the TG structure and the recess and doped with p-type impurities
Implementation Method 3
a second n-type impurity region in the substrate, wherein the second n-type impurity region is disposed over and is spaced apart from the first n-type impurity region
Data Source
AI summary
An image sensor includes a photodiode disposed in a substrate and including an n-type impurity region, wherein the n-type impurity region is doped with n-type impurities, a transfer gate (TG) structure partially buried in the substrate and disposed on the n-type impurity region, a recess disposed at an upper surface of the substrate and being spaced apart from the TG structure, a floating diffusion (FD) region disposed under the recess and doped with n-type impurities, and an impurity region disposed at a portion of the substrate between the TG structure and the recess and doped with p-type impurities. An upper surface of the FD region is lower than an upper surface of the impurity region.