Backside-Illuminated Imager Textured Region Infrared Response
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Solution Overview
Problem
Traditional silicon-based photodetecting imagers have limited light absorption and detection properties, particularly for infrared light, due to silicon's indirect bandgap and low absorption of wavelengths greater than 1100 nm, requiring substantial path lengths for detection and resulting in poor absorptance and response speed.
Innovation Solution
The development of backside-illuminated photosensitive imager devices with textured regions and dielectric isolation, where surface features are sized and positioned to enhance light absorption at specific wavelengths, increasing the propagation path length for longer wavelengths and reducing effective absorption depth, thereby improving absorptance and response speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based photodetecting imagers are used with traditional front-side illumination, then the device structure is simple and manufacturing is easier, but light absorption is limited particularly for infrared wavelengths greater than 1100 nm due to silicon's indirect bandgap
Solution Approach 1:
The patent inverts the traditional front-side illumination architecture by implementing backside illumination, where light enters through the substrate opposite to the photodetector active region. This inversion allows light to traverse the entire substrate thickness before reaching the active region, significantly increasing absorption path length for infrared wavelengths greater than 1100 nm where silicon has low absorption coefficient
2Reliability
If the semiconductor substrate thickness is increased to improve light absorption for longer wavelengths, then absorptance increases, but response speed decreases due to longer carrier collection paths
Solution Approach 1:
The patent applies local quality by creating a non-uniform substrate structure with a textured region having different optical properties from the bulk substrate. The textured region with increased surface area and modified refractive index enhances light trapping and absorption locally, allowing thin substrate regions to achieve high absorptance without requiring increased overall thickness that would slow carrier collection
Solution Approach 2:
The patent replaces the mechanical approach of increasing substrate thickness to improve absorption with an optical approach using textured surfaces and anti-reflective coatings. This substitution enables enhanced light absorption through optical path manipulation rather than physical path length extension, maintaining fast carrier collection speeds
3Reliability
If a textured region with surface features is added to enhance light absorption at specific wavelengths, then quantum efficiency improves, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent employs curved surface features including hemispherical domes and rounded pillars in the textured region. These curved structures are formed using standard semiconductor processing techniques such as spin-coating photoresist and reflow processing, avoiding the need for complex nanofabrication while achieving effective light trapping and enhanced quantum efficiency
4Speed
If the semiconductor substrate is thinned to reduce absorption path length and improve response speed, then response speed increases, but absorptance decreases particularly for infrared light
Solution Approach 1:
The patent introduces a textured intermediate layer between the incident light and the photodetector active region. This textured layer acts as an optical mediator that scatters and traps light, increasing the effective absorption path length without increasing the physical substrate thickness, thereby maintaining fast response speeds while improving infrared absorptance
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
These devices enhance infrared light detection and quantum efficiency, allowing for the absorption of longer wavelengths within thinner semiconductor materials, increasing responsivity and reducing the thickness of semiconductor substrates required, while maintaining or improving response speed.
Implementation Method 1
the textured region includes surface features sized and positioned to facilitate tuning to a preselected wavelength of light
Implementation Method 2
increasing the propagation path length for longer wavelengths
Implementation Method 3
The dielectric region is positioned to isolate to the at least one junction from the textured region
Implementation Method 4
CMOS sensors are typically manufactured from silicon and can covert visible incident light into a photocurrent
Data Source
AI summary
Backside illuminated photosensitive devices and associated methods are provided. In one aspect, for example, a backside-illuminated photosensitive imager device can include a semiconductor substrate having multiple doped regions forming a least one junction, a textured region coupled to the semiconductor substrate and positioned to interact with electromagnetic radiation where the textured region includes surface features sized and positioned to facilitate tuning to a preselected wavelength of light, and a dielectric region positioned between the textured region and the at least one junction. The dielectric region is positioned to isolate the at least one junction from the textured region, and the semiconductor substrate and the textured region are positioned such that incoming electromagnetic radiation passes through the semiconductor substrate before contacting the textured region. Additionally, the device includes an electrical transfer element coupled to the semiconductor substrate to transfer an electrical signal from the at least one junction.