Near-Infrared Sensor Grating Structure for Thin CMOS Coupling
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Solution Overview
Problem
Integrating near infrared light sensors with CMOS image sensors is challenging due to low absorption of near infrared light by silicon-based materials, leading to low quantum efficiency, and existing solutions like thickening the silicon base or adding germanium increase complexity and thickness.
Innovation Solution
Incorporating a surface plasmon polariton structure at the light-receiving surface of near infrared light detectors using existing CMOS manufacturing steps, with embedded and metal gratings tuned to resonate at the infrared wavelength, enhancing optical coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the silicon base is thickened to improve near infrared light absorption, then quantum efficiency is improved, but device thickness and complexity increase
Solution Approach 1:
The patent changes the optical parameters of the silicon surface by introducing a periodic grating structure with specific pitch and depth parameters. This grating structure modifies the optical coupling conditions to enhance near infrared light absorption without requiring increased silicon thickness, thereby resolving the contradiction between quantum efficiency and device thickness.
Solution Approach 2:
Instead of solving the absorption problem by increasing thickness in one dimension, the patent introduces a periodic structure that adds spatial frequency dimensions to the light-silicon interaction. The grating's periodic modulation creates multiple diffraction orders that increase the effective optical path length without increasing physical thickness.
2Reliability
If germanium is added to improve near infrared light absorption, then quantum efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent achieves enhanced near infrared absorption by modifying the geometric parameters of the silicon grating structure rather than changing the material composition. This approach maintains compatibility with existing CMOS manufacturing processes that are optimized for silicon, avoiding the need for germanium integration and associated process complexity.
Solution Approach 2:
The patent uses standard CMOS fabrication techniques to create the grating structure, essentially copying existing manufacturing capabilities rather than introducing new material deposition or processing steps. The grating is formed using conventional photolithography and etching processes already present in CMOS lines.
3Reliability
If a surface plasmon polariton structure is incorporated to improve optical coupling, then near infrared light absorption is improved, but manufacturing complexity increases
Solution Approach 1:
The patent implements surface plasmon polariton effects through a two-dimensional periodic grating pattern on the silicon surface. This planar periodic structure excites surface plasmons that enhance optical coupling, achieving the desired effect without requiring three-dimensional metallic nanostructures or complex multilayer stacks.
Solution Approach 2:
The patent merges the grating structure with the existing CMOS sensor surface, combining the optical enhancement function with the detector substrate. The grating is directly formed on or in the silicon detector layer, eliminating the need for separate optical coupling components or additional fabrication stages.
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
Improves near infrared light absorption by a factor of five or more, maintaining sensor thickness and reducing complexity by using existing manufacturing processes.
Implementation Method 1
The metal grating and aligned embedded grating of each respective infrared light sensor form a surface plasmon polariton structure configured to couple with light at the design-basis infrared wavelength to form a surface plasmon at the light-receiving surface of the respective infrared light sensor
Implementation Method 2
with embedded and metal gratings tuned to resonate at the infrared wavelength, enhancing optical coupling
Data Source
AI summary
A near infrared sensing device includes a near infrared light sensor configured to detect infrared light at least at a design-basis infrared wavelength, and a surface plasmon polariton structure including at least an embedded grating that is embedded in a light-receiving surface of the near infrared light sensor. The surface plasmon polariton structure is configured to couple with light at the design-basis infrared wavelength to form a surface plasmon polariton at the light-receiving surface of the near infrared light sensor. The surface plasmon polariton structure may further include a metal grating disposed on the light-receiving surface of the near infrared light sensor and aligned with the embedded grating. The embedded grating may comprise an embedded metal grating that is embedded in the light-receiving surface of the near infrared light sensor, or trenches formed in the light-receiving surface of the near infrared light sensor and at least partially filled with air.