Ge-Si Photodiode Readout Circuit for Near-Infrared 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, and are inefficient for applications requiring broader wavelength detection.
Innovation Solution
The use of germanium or germanium-silicon materials in photodiodes, integrated with silicon on a common substrate, enhances the operating wavelength range, sensitivity, and dynamic range, allowing for efficient detection of both visible and near-infrared light by forming a hybrid photodiode array with multiple gates for improved phase information collection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon-based photodiodes are used, then manufacturing is simple and cost-effective, but optical absorption efficiency for near-infrared wavelengths is low
Solution Approach 1:
The patent employs a heterojunction structure combining silicon and germanium materials. The silicon substrate provides mechanical support and electrical functionality, while the germanium layer enhances near-infrared optical absorption. This composite material approach resolves the contradiction by integrating the manufacturing advantages of silicon with the superior NIR absorption properties of germanium, achieving both ease of manufacture and high optical absorption efficiency simultaneously.
2Device complexity
If conventional silicon photodiodes are used, then device structure is simple, but operating wavelength range is limited
Solution Approach 1:
By forming a heterojunction between silicon and germanium layers, the patent extends the operating wavelength range from visible light (silicon only) to include near-infrared wavelengths. The germanium layer with its narrower bandgap enables detection of longer wavelengths while the silicon layer maintains visibility detection, thus achieving broad spectral coverage without significantly complicating the device structure.
Solution Approach 2:
The patent applies different materials to different functional regions: silicon for visible light detection and germanium for near-infrared detection. This local differentiation of material properties within the photodiode structure enables multi-wavelength operation while maintaining overall structural simplicity and facilitating targeted optimization for specific wavelength ranges.
3Ease of manufacture
If silicon photodiodes are used, then manufacturing processes are成熟, but sensitivity and dynamic range are limited
Solution Approach 1:
The heterojunction structure combines the manufacturing maturity of silicon processes with the enhanced sensitivity of germanium for near-infrared wavelengths. The germanium layer increases the quantum efficiency and sensitivity in the NIR range where pure silicon performs poorly, while maintaining compatibility with established silicon fabrication techniques for overall device manufacturing.
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
This configuration increases the device bandwidth, enabling higher modulation frequencies and improved depth resolution in time-of-flight imaging, while reducing pixel sizes and crosstalk, and supports simultaneous visible and near-infrared image sensing.
Implementation Method 1
an absorption region configured to absorb photons and to generate photo-carriers from the absorbed photons
Data Source
AI summary
A circuit that includes: a photodiode configured to absorb photons and to generate photo-carriers from the absorbed photons; a first MOSFET transistor that includes: a first channel terminal coupled to a first terminal of the photodiode and configured to collect a portion of the photo-carriers generated by the photodiode; a second channel terminal; and a gate terminal coupled to a first control voltage source; a first readout circuit configured to output a first readout voltage; a second readout circuit configured to output a second readout voltage; and a current-steering circuit configured to steer the photo-carriers generated by the photodiode to one or both of the first readout circuit and the second readout circuit.