Photosensitive Capacitor Pixel for CMOS Image Sensor Fabrication
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Solution Overview
Problem
Existing CMOS image sensor fabrication processes are costly and time-consuming due to additional steps required for image sensor production, differing from standard CMOS fabrication, and often necessitate deep implants and special isolation processes, which are not compatible with standard logic and DRAM fabrication.
Innovation Solution
The integration of a photosensitive capacitor within each pixel, comprising a conductive layer wrapped coaxially around an electrode, a dielectric layer, and a photosensitive semiconductor material, coupled with a transistor network for signal readout, which allows for frontside illumination and reduces the need for deep implants and special isolation processes, making the fabrication more compatible with standard CMOS processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If standard CMOS fabrication processes are used for image sensor production, then manufacturing cost and time are reduced, but image sensor performance and quality are compromised due to lack of specialized processes
Solution Approach 1:
The photosensitive capacitor structure is designed to serve multiple functions: it acts as both the light-sensitive element and the charge storage element, eliminating the need for separate photodiode and capacitor structures. This multi-functional design allows standard CMOS processes to achieve image sensor functionality without requiring specialized deep implant and isolation processes, thus resolving the contradiction between manufacturing efficiency and sensor performance
2Reliability
If deep implants and special isolation processes are used, then image sensor performance is improved, but fabrication complexity and cost increase
Solution Approach 1:
The invention extracts the essential image sensing function from the complex deep implant and isolation process sequence by using a photosensitive capacitor that can be fabricated with standard CMOS processes. This extraction removes the problematic deep implant and isolation steps while retaining the core light-detection capability, thereby reducing fabrication complexity without sacrificing performance
3Reliability
If deep implants and special isolation processes are used, then image sensor performance is improved, but manufacturing time and cost increase
Solution Approach 1:
The photosensitive capacitor is designed to be formed during the standard CMOS fabrication sequence before final assembly, utilizing existing process steps such as oxide deposition and patterning. This preliminary formation of the light-sensitive element during routine fabrication eliminates the need for separate, time-consuming deep implant and isolation processes, thereby reducing total manufacturing time while maintaining performance
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 approach reduces the complexity and cost of image sensor production, increases the area for photosensitive material, and enhances image sensor performance by eliminating the need for wafer thinning and special isolation processes, while maintaining compatibility with standard logic and DRAM fabrication.
Implementation Method 1
a photosensitive semiconductor material for generating an image signal in response to image light
Implementation Method 2
the dielectric layer includes a negative charge layer to induce a depletion zone at an interface of the dielectric layer and the photosensitive semiconductor material
Implementation Method 3
the conductive layer is reflective to the image light
Data Source
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Figure 3A
AI summary
An image sensor pixel, and image sensor, and a method of fabricating the same is disclosed. The image pixel includes a photosensitive capacitor and a transistor network. The photosensitive capacitor includes an electrode, a conductive layer, a dielectric layer, and a photosensitive semiconductor material. The conductive layer is disposed around the electrode and the dielectric layer is formed between the conductive layer and the electrode. The photosensitive semiconductor material is for generating an image signal in response to image light and is disposed between the dielectric layer and the electrode. The transistor network is coupled to readout the image signal from the electrode of the photosensitive capacitor.