Double Pass Back Side Image Sensor Pixel Reflectors
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Solution Overview
Problem
Conventional image sensors require separate fabrication plants for CMOS and color filter array processing, leading to increased complexity and cost, and are prone to contamination, which affects efficiency and reliability.
Innovation Solution
A monochrome-color double pass back side image sensor is fabricated entirely at a single CMOS plant, using pixel reflectors to determine color levels without color filters over the photodiodes, allowing for improved light capture and reduced contamination risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional image sensors use separate fabrication plants for CMOS and color filter array processing, then color filtering functionality is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the color filtering function into the CMOS substrate itself by forming color filter regions directly in the semiconductor material during the CMOS fabrication process. This eliminates the need for separate CFA plant processing and combining two separately manufactured components, thereby reducing manufacturing complexity while maintaining color filtering functionality.
Solution Approach 2:
The CMOS substrate is designed to perform multiple functions: photodetector operation, color filtering, and signal processing. By integrating color filter regions directly into the CMOS structure, the substrate becomes a multi-functional component that eliminates the need for separate dedicated color filter components and their associated fabrication processes.
2Reliability
If color filter arrays are deposited on CMOS substrates, then color filtering is achieved, but contamination from dyes reduces efficiency and reliability
Solution Approach 1:
The patent replaces the chemical dye-based color filtering system with a semiconductor-based optical filtering system. Instead of using organic dyes that can contaminate and degrade, the invention uses doped semiconductor regions with inherent optical absorption properties, eliminating the source of contamination while maintaining color filtering functionality.
Solution Approach 2:
The invention changes the fundamental parameter of color filtering from chemical absorption (dyes) to semiconductor bandgap absorption. By utilizing the inherent optical properties of doped silicon regions, the system achieves color filtering without introducing contaminating organic materials, thereby improving reliability and efficiency.
3Loss of energy
If color filter arrays with microlenses are used, then color filtering and light focusing are achieved, but light loss occurs reducing quantum efficiency
Solution Approach 1:
The patent extracts the color filtering function from the optical path components (removing it from separate CFA layers with microlenses) and integrates it directly into the photodetector structure. This eliminates the need for light to pass through multiple interfaces and filtering layers, reducing light loss and improving quantum efficiency while maintaining color filtering capability.
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 simplifies the manufacturing process, reduces contamination, and enhances quantum efficiency by allowing more light to enter the photodiodes, resulting in improved image sensor performance and cost savings.
Implementation Method 1
Image sensors convert optical light to electrical signals. Conventional image sensors are formed from an array of photodetectors, each of which converts received light into an electrical signal.
Data Source
AI summary
Double pass back side image (BSI) sensor systems and methods are disclosed. The BSI sensor may include a substrate, pixel reflectors formed on the substrate, and pixel photodiodes fabricated in the substrate, each pixel photodiode positioned over a respective one of the pixel reflectors. Micro-lenses may be formed over each photodiode and an image filter may be formed between the photodiodes and the micro-lenses. The pixels reflectors, photodiodes, micro-lenses, and filter may be formed using CMOS fabrication.