GeSi Photodiode Array for Near-Infrared Time-of-Flight Sensing
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Solution Overview
Problem
Conventional silicon-based photodiodes have low optical absorption efficiency for near-infrared wavelengths, limiting their sensitivity and dynamic range, especially in time-of-flight applications where efficient absorption is crucial for depth resolution and power management.
Innovation Solution
Integrating germanium or germanium-silicon photodiodes with silicon photodiodes on a common substrate to create a photodiode array that absorbs visible and near-infrared wavelengths, enhancing the device's bandwidth and absorption efficiency, and using multi-gate structures to control carrier collection and improve signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based photodiodes are used, then the device structure is simple and manufacturing is easy, but the optical absorption efficiency for near-infrared wavelengths is low
Solution Approach 1:
The patent employs a composite material structure consisting of a silicon substrate with a germanium-silicon (GeSi) layer deposited on top. The GeSi layer has higher optical absorption efficiency for near-infrared wavelengths compared to pure silicon, while the silicon substrate provides mechanical support and electrical conductivity. This composite structure resolves the contradiction by combining materials with complementary properties to achieve both good optical absorption and structural integrity.
Solution Approach 2:
The patent modifies the compositional parameter of the photodiode material by creating a graded GeSi layer where the germanium concentration varies through the thickness of the layer. This parameter change allows optimization of optical absorption at different depths while maintaining lattice matching with the silicon substrate, thereby improving near-infrared absorption efficiency without compromising the overall device manufacturability.
2Reliability
If germanium or germanium-silicon photodiodes are integrated with silicon photodiodes, then the sensitivity and dynamic range increase, but the device complexity increases
Solution Approach 1:
The patent divides the photodiode structure into distinct functional segments: a silicon-based photodiode for visible light detection and a germanium-silicon photodiode for near-infrared detection. Each segment is optimized for its specific wavelength range, and they are integrated on the same substrate. This segmentation allows the system to achieve high sensitivity across a broad spectrum while maintaining relatively simple individual device structures that can be manufactured using standard processes.
Solution Approach 2:
The integrated photodiode array achieves multi-functionality by combining different material systems (silicon and germanium-silicon) that respond to different wavelength ranges. A single device structure performs both visible and near-infrared detection, eliminating the need for separate devices and reducing overall system complexity despite the enhanced functionality.
3Measurement precision
If higher modulation frequencies are used in time-of-flight systems, then the depth resolution improves, but the power consumption increases
Solution Approach 1:
The patent replaces the traditional approach of increasing power consumption to achieve higher modulation frequencies with a material-based solution. The germanium-silicon photodiode's superior optical absorption efficiency enables effective detection at higher modulation frequencies because more photons are absorbed per unit time, generating sufficient signal even at reduced optical power levels. This substitutes the mechanical/electrical approach (increasing power) with an optical/material approach (improving absorption).
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 integration of germanium or germanium-silicon photodiodes with silicon increases the photodiode array's sensitivity and dynamic range, allowing for higher modulation frequencies and improved depth resolution in time-of-flight systems while maintaining power efficiency.
Implementation Method 1
the second photodiode comprises a germanium-silicon region fabricated on the semiconductor layer, the germanium-silicon region configured to absorb photons at infrared or near-infrared wavelengths and to generate photo-carriers from the absorbed photons
Implementation Method 2
the first photodiode includes a semiconductor layer configured to absorb photons at visible wavelengths and to generate photo-carriers from the absorbed photons
Data Source
AI summary
A method for fabricating an image sensor array having a first group of photodiodes for detecting light at visible wavelengths a second group of photodiodes for detecting light at infrared or near-infrared wavelengths, the method including growing a germanium-silicon layer on a semiconductor donor wafer; defining pixels of the image sensor array on the germanium-silicon layer; defining a first interconnect layer on the germanium-silicon layer, wherein the interconnect layer includes a plurality of interconnects coupled to the first group of photodiodes and the second group of photodiodes; defining integrated circuitry for controlling the pixels of the image sensor array on a semiconductor carrier wafer; defining a second interconnect layer on the semiconductor carrier wafer, wherein the second interconnect layer includes a plurality of interconnects coupled to the integrated circuitry; and bonding the first interconnect layer with the second interconnect layer.