Shallow Trench Texturing for Thin-Silicon Infrared Imagers
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Solution Overview
Problem
Traditional silicon-based photodetecting imagers have limited light absorption properties, particularly for infrared light, as silicon is an indirect bandgap semiconductor with low absorption of electromagnetic radiation with wavelengths greater than 1100 nm, requiring thick silicon layers for detection, which increases the thickness of the imager and reduces response speed.
Innovation Solution
The use of optoelectronic devices with a semiconductor layer coupled to a support substrate and an array of shallow trench isolation surface features, which increase the effective optical path length for longer wavelengths by redirecting and absorbing light multiple times within a thinner silicon material, enhancing light absorption and response speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon layer thickness is increased to improve infrared light absorption, then absorption efficiency improves, but device complexity and material usage increase
Solution Approach 1:
The patent applies surface texturing with curved features (pyramids, domes, or random curvature) to the silicon layer. These curved surface structures increase the optical path length of incident light through multiple internal reflections, enhancing absorption efficiency without requiring increased silicon thickness. The curvature causes light to traverse a longer effective path within the same physical thickness, resolving the contradiction between absorption efficiency and device complexity.
Solution Approach 2:
The patent introduces surface texturing that adds dimensional complexity to the silicon layer surface. By creating three-dimensional surface features (protrusions, trenches, or curved structures), the patent increases the effective absorption path length in the optical dimension without increasing the physical thickness of the silicon layer. This dimensional transformation allows enhanced infrared absorption while maintaining thin-layer device simplicity.
2Adaptability or versatility
If silicon layer thickness is increased to detect longer wavelengths, then detection capability improves, but manufacturing cost and material usage increase
Solution Approach 1:
The curved surface texturing creates multiple internal reflections that extend the optical path length within the silicon layer. This allows photons of longer wavelengths to undergo multiple bounce reflections, increasing their probability of absorption without requiring a thicker silicon layer. The curvature geometry traps light more effectively, enabling extended wavelength detection with reduced material consumption.
Solution Approach 2:
The surface texturing creates continuous internal reflection paths that keep photons circulating within the silicon layer for extended periods. This continuous optical interaction increases the effective absorption opportunity for longer wavelength photons without requiring increased material thickness. The textured surface maintains continuous light-matter interaction, improving detection capability while minimizing silicon usage.
3Reliability
If traditional flat silicon surface is used, then manufacturing is simple, but light absorption efficiency is limited
Solution Approach 1:
The patent employs curved surface features (pyramids, domes, or random curvature patterns) that can be formed through standard semiconductor processing techniques such as chemical etching or deposition. These curved structures enhance light absorption through increased optical path length and multiple internal reflections, while being compatible with existing manufacturing workflows. The curvature geometry provides superior absorption compared to flat surfaces without requiring fundamentally new manufacturing processes.
Solution Approach 2:
The patent modifies the surface geometry parameters of the silicon layer by introducing controlled curvature and roughness. By changing the surface topology from flat to textured with specific curvature radii and feature sizes, the patent enhances absorption efficiency. These parameter changes can be achieved through controlled etching or deposition processes, balancing manufacturing simplicity with improved optical 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
The devices achieve increased light absorption of longer wavelengths in thinner silicon layers, reducing the absorption depth and increasing response speed, while maintaining similar dark current levels to standard devices, and can be configured for both front-side and back-side illumination.
Implementation Method 1
the surface features positioned to interact with electromagnetic radiation that passes through the semiconductor layer
Implementation Method 2
redirecting and diffusing light through textured regions
Implementation Method 3
CMOS sensors are typically manufactured from silicon and can covert visible incident light into a photocurrent
Data Source
AI summary
Photosensitive devices and associated methods are provided. In one aspect, for example, a photosensitive imager device can include a semiconductor layer having multiple doped regions forming a least one junction, a textured region coupled to the semiconductor layer and positioned to interact with electromagnetic radiation. The textured region can be formed from a series of shallow trench isolation features.