Pixel Sensor Nanoscale Hole Arrays for Higher Blue-Green QE
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Solution Overview
Problem
CMOS image sensors face challenges in achieving high quantum efficiency across various wavelengths of light, particularly for visible light, green light, and blue light, due to limitations in the design of photodiode structures and light absorption mechanisms.
Innovation Solution
The implementation of high absorption (HA) structures with angled walls and nanoscale structures over photodiodes in a pixel array, which modify the refractive interface to direct wider angles of incident light towards photodiodes, improving quantum efficiency for longer wavelengths like red and NIR light, while nanoscale structures enhance efficiency for shorter wavelengths like green and blue light by refracting visible light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional photodiode structures are used, then the device complexity is low, but the quantum efficiency for various wavelengths of light is insufficient
Solution Approach 1:
The photodiode structure is segmented into multiple functional regions including a first region with a first doped region and a second region with a second doped region. This segmentation allows different portions of the photodiode to handle different wavelengths of light efficiently, with each region optimized for specific spectral ranges, thereby improving overall quantum efficiency without excessive complexity
Solution Approach 2:
Different regions of the photodiode are assigned different local properties through selective doping. The first doped region and second doped region have different doping concentrations and types, creating local quality variations that optimize light absorption for different wavelengths in different spatial locations, resolving the contradiction between simple structure and high quantum efficiency
2Measurement precision
If filters are placed over light-sensitive CMOS circuitry to determine colors, then color detection capability is improved, but the light absorption efficiency for certain wavelengths decreases
Solution Approach 1:
The patent extracts the wavelength-selective function from traditional filters and integrates it directly into the photodiode structure through selectively doped regions. This eliminates the need for separate filter layers, maintaining color detection precision while improving light absorption efficiency by reducing interface losses and enhancing direct photon-to-charge conversion
Solution Approach 2:
The filtering function and light detection function are merged into a single integrated photodiode structure. The selectively doped regions perform both wavelength selection and charge generation simultaneously, eliminating the need for separate filter components and improving overall system efficiency while maintaining color accuracy
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 significantly enhances quantum efficiency for both longer and shorter wavelengths, improving the overall light absorption capabilities of CMOS image sensors, particularly for red, green, and blue light, by strategically designing the refractive interfaces and structures within the pixel array.
Implementation Method 1
nanoscale structures over photodiodes in a pixel array, which modify the refractive interface to direct wider angles of incident light towards photodiodes
Implementation Method 2
high absorption (HA) structures with angled walls and nanoscale structures over photodiodes in a pixel array, which modify the refractive interface to direct wider angles of incident light towards photodiodes
Implementation Method 3
Complementary metal oxide semiconductor (CMOS) image sensors utilize light-sensitive CMOS circuitry to convert light energy into electrical energy. The light-sensitive CMOS circuitry may include a photodiode formed in a silicon substrate. As the photodiode is exposed to light, an electrical charge is induced in the photodiode (referred to as a photocurrent)
Data Source
AI summary
An array of nanoscale structures over photodiodes of a pixel array improves quantum efficiency (QE) for shorter wavelengths of light, such as green light and blue light. The nanoscale structures may be used without high absorption (HA) structures (e.g., when the pixel array is configured only for visible light) or may at least partially surround HA structures (e.g., when the pixel array is configured both for visible light and near infrared light). Additionally, the array of nanoscale structures may be formed using photolithography such that the nanoscale structures are approximately spaced at regular intervals. Therefore, QE for the pixel array is improved more than if the array of nanoscale structures were to be formed using a random (or quasi-random) process.