Buried Conductor Pixel Gate Stack for CMOS Image Sensors
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Solution Overview
Problem
Conventional CMOS image sensors experience increased dark current due to the use of highly conductive materials in the gate stacks of pixel cells, which affects the performance of the image sensors.
Innovation Solution
The implementation of low resistance conductors, specifically polysilicon and silicide or refractory metal layers, in the pixel cells, which are formed after the initial insulating layers to minimize dark current and maintain the functionality of the photodiode without increasing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If highly conductive materials are used in gate stacks, then electrical conductivity is improved, but dark current increases
Solution Approach 1:
The gate electrode is divided into multiple segments with different materials (polysilicon, silicide, refractory metal) stacked in layers, allowing each segment to contribute differently to conductivity while controlling dark current generation
Solution Approach 2:
The gate stack uses composite materials combining polysilicon with silicide or refractory metal layers, achieving high electrical conductivity in the conductive layers while the insulating layers prevent dark current generation at the photodiode interface
2Productivity
If low resistance conductors are implemented, then signal transmission efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The conductive layers (silicide or refractory metal) are formed during the gate stack fabrication process before final patterning, pre-establishing low resistance paths that simplify subsequent manufacturing steps
Solution Approach 2:
The silicide or refractory metal layers act as intermediary conductive elements between the polysilicon gate electrode and the photodiode, providing low resistance connection without requiring additional complex interconnection structures
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 use of low resistance conductors effectively reduces dark current in CMOS image sensors, enhancing their performance by maintaining the integrity of the photodiode while allowing for efficient routing of charge and signals without increasing noise.
Implementation Method 1
each one of the pixel cells 10 includes a photo-conversion device 21... The photodiode 21 includes an n-type photodiode charge accumulation region 22... functions by receiving photons of light and converting those photons into charge carried by electrons
Implementation Method 2
The conductive layers 271, 272 are formed through the second and third insulating layers 234, 250... low resistance conductors, specifically polysilicon and silicide or refractory metal layers... efficiently routing of charge and signals
Data Source
Figure 1A~1B
Figure 1C
Figure 2~3A
AI summary
A pixel cell having (200) a photo-conversion device (21) at a surface of a substrate (11) and at least one contact area (277) from which charge or a signal is output or received. A first insulating layer (233) is located over the photo-conversion device and the at least one contact area. The pixel cell further includes at least one conductor in contact with the at least one contact area. The conductor includes a polysilicon material (271) extending through the first insulating layer and in contact with the at least one contact area. Further, a conductive material (272) , which includes at least one of a suicide and a refractory metal, can be over and in contact with the polysilicon material.