P on N Image Sensor Structure Reducing Crosstalk
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
CMOS image sensor devices suffer from electrical cross-talk due to electron diffusion between photodiodes, leading to degraded spatial resolution and reduced optical sensitivity, particularly in applications requiring high-performance imaging like digital still cameras.
Innovation Solution
A semiconductor device with a substrate doped with a first type of dopant and a semiconductor layer doped with a second type of dopant, where the semiconductor layer has a reverse type of dopant to reduce minority diffusion, and shallow trench isolation features are used to isolate image sensor elements, along with a voltage bias to prevent electron diffusion and reduce cross-talk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photodiodes and MOS transistors are formed in a P- silicon layer on a P+ silicon substrate, then image sensing function is achieved, but electrical cross-talk occurs due to electron diffusion into neighboring photodiodes
Solution Approach 1:
The invention introduces intermediate P+ isolation regions between adjacent N-type photodiodes to segment the semiconductor structure. These isolation regions act as barriers that prevent electron diffusion from one photodiode to another, thereby eliminating electrical cross-talk while preserving the image sensing function of each photodiode element.
Solution Approach 2:
The P+ isolation regions serve as intermediary structures between the N-type photodiodes. These intermediate regions with opposite doping type create potential barriers that block the diffusion of minority carriers (electrons) between adjacent photodiodes, thus preventing cross-talk without affecting the primary sensing function.
2Object-generated harmful factors
If the semiconductor layer is made thinner to reduce electron diffusion, then cross-talk is reduced, but optical sensitivity and light absorption are degraded
Solution Approach 1:
The invention applies different doping characteristics to different regions: the N-type photodiode regions maintain sufficient thickness for optimal light absorption and optical sensitivity, while the P+ isolation regions are positioned specifically at interfaces to block electron diffusion. This localized differentiation allows each region to optimize its function without compromising the other.
3Object-generated harmful factors
If deeper isolation structures are used to prevent electron diffusion, then cross-talk is reduced, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The invention changes the doping parameter (introducing P+ regions with high dopant concentration) rather than changing the geometric parameters (depth or complexity of isolation structures). By modifying the electrical parameters through doping, effective electron diffusion barriers are created without requiring complex deep isolation structures, thus reducing manufacturing difficulty while maintaining cross-talk suppression.
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
The solution effectively reduces electrical cross-talk, enhancing spatial resolution and optical sensitivity by preventing electron diffusion between image sensor elements, thereby improving the overall performance of CMOS image sensors.
Implementation Method 1
The generated electrons outside depletion region will diffuse into neighboring photodiode and causes electrical cross-talk
Implementation Method 2
a voltage bias to prevent electron diffusion and reduce cross-talk
Implementation Method 3
an incident light generates electron-hole pairs in the P- silicon layer
Data Source
AI summary
The present disclosure provides an image sensor semiconductor device. The semiconductor device includes a semiconductor substrate having a first type of dopant; a semiconductor layer having a second type of dopant different from the first type of dopant and disposed on the semiconductor substrate; a photo-sensitive structure formed in the semiconductor layer; a multi-layer interconnect (MLI) structure disposed on the semiconductor layer; a color filter disposed on the MLI structure and disposed above the photo-sensitive structure; and a microlens disposed over the color filter and disposed above the photo-sensitive structure.