Stacked Silicon-Germanium Image Sensor for IR Sensitivity and Low Cross-Talk
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Solution Overview
Problem
Three-dimensional integrated chips (3DICs) with CMOS image sensors face challenges in maintaining high sensitivity for both infrared (IR) and visible light due to material and thickness limitations, leading to reduced quantum efficiency and increased cross-talk between image sensor elements.
Innovation Solution
A stacked image sensor device is designed with a first image sensor element made of germanium and a second image sensor element made of silicon, where the germanium element is thin and the silicon element is thick, allowing for high sensitivity to IR and visible light while minimizing cross-talk, achieved through specific thickness and material selection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the image sensor element thickness is increased, then quantum efficiency for visible light is improved, but cross-talk between adjacent sensor elements increases
Solution Approach 1:
The patent implements local quality differentiation by using a thin germanium layer specifically positioned to detect infrared light while the thicker silicon substrate handles visible light detection. This localized functional differentiation allows the sensor to achieve high quantum efficiency for visible light through the thick silicon substrate while the thin germanium layer minimizes cross-talk between adjacent elements. The selective material placement ensures that each region of the sensor optimizes for its specific wavelength range, reducing unwanted optical interference between neighboring pixels.
2Ease of manufacture
If a single material is used for the image sensor element, then manufacturing simplicity is maintained, but performance for both IR and visible light detection deteriorates
Solution Approach 1:
The patent utilizes a composite material system consisting of silicon and germanium layers deposited on a substrate. This composite structure enables the sensor to detect both infrared and visible light with high efficiency, overcoming the limitations of single-material sensors. The silicon layer optimizes visible light detection while the germanium layer enhances infrared sensitivity, creating a multi-functional sensor that maintains relatively straightforward manufacturing processes through established semiconductor fabrication techniques for layered structures.
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 solution enhances IR and visible light sensitivity with reduced cross-talk, improving design flexibility and image formation accuracy by optimizing the thickness and material of the image sensor elements.
Implementation Method 1
a first image sensor element configured to generate electrical signals from an electromagnetic radiation within a first range of wavelengths
Implementation Method 2
a second image sensor element over the first image sensor configured to generate electrical signals from the electromagnetic radiation within a second range of wavelengths
Data Source
AI summary
A method of forming an image sensor includes forming a first image sensor element within a substrate. The first image sensor element and the substrate respectively comprise a first material. A second image sensor element is formed within the substrate. Forming the second image sensor element includes forming an isolation layer over the first image sensor element. Further, a buffer layer is formed over the isolation layer and an active layer is formed over the buffer layer. The active layer comprises a second material different from the first material.