Germanium-on-Silicon Image Sensor Structure for 1550 Nm NIR Detection
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Solution Overview
Problem
Silicon-based single photon avalanche diodes (SPADs) have limited sensitivity and higher power consumption when detecting Near-Infrared (NIR) wavelengths, particularly around 1550 nm, due to lower absorption coefficients and inefficiencies in converting NIR radiation into electrical signals.
Innovation Solution
The use of a semiconductor device with a germanium absorption layer formed in a recessed area of a silicon substrate, which enhances sensitivity and reduces power consumption by alleviating lattice mismatch issues and improving crystalline stress, allowing operation at lower voltages (e.g., <10V) and extending the operable wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon-based SPAD is used for NIR wavelength detection, then the device structure is simple and compatible with traditional CMOS, but the sensitivity is limited and power consumption is high
Solution Approach 1:
The patent employs a composite material structure consisting of a silicon substrate combined with a germanium absorption layer. The germanium layer is specifically designed to absorb NIR wavelengths while the silicon substrate provides the avalanche multiplication function. This composite approach leverages the complementary strengths of both materials: germanium's superior NIR absorption coefficient and silicon's established CMOS compatibility and avalanche diode performance, thereby resolving the contradiction between detection sensitivity and power consumption.
Solution Approach 2:
The patent applies local quality by creating a germanium absorption layer only in the specific region where NIR photon absorption is needed, rather than making the entire device from germanium. The germanium layer is positioned at the surface of the silicon substrate, forming a localized absorption region that optimizes NIR detection while maintaining the benefits of silicon-based avalanche multiplication. This localized approach improves sensitivity without proportionally increasing power consumption across the entire device.
2Reliability
If a germanium absorption layer is formed in a recessed area of silicon substrate, then sensitivity and efficiency of NIR detection is improved, but device structure becomes more complex
Solution Approach 1:
The patent segments the device structure by creating a recessed area in the silicon substrate and filling it with germanium material. This segmentation separates the absorption function (germanium layer in recess) from the avalanche multiplication function (silicon substrate), allowing each material to perform its optimal function. The recessed structure enables better optical coupling and reduces reflection losses, improving sensitivity while keeping the overall device architecture manageable through functional segmentation.
3Reliability
If silicon-based SPAD operates at higher voltages to compensate for low absorption, then detection capability is maintained, but power consumption increases
Solution Approach 1:
The composite germanium-silicon structure resolves the voltage-power contradiction by assigning different functions to different materials: the germanium absorption layer efficiently captures NIR photons at lower voltages due to its high absorption coefficient, while the silicon substrate performs avalanche multiplication. This functional division eliminates the need to operate the entire device at high voltages, thereby reducing power consumption while maintaining detection capability.
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 significantly improves the sensitivity and efficiency of NIR wavelength detection while reducing power consumption and operational voltage, addressing the limitations of silicon-based SPADs.
Implementation Method 1
Silicon-based single photon avalanche diodes (SPADs) have limited sensitivity... when detecting Near-Infrared (NIR) wavelengths, particularly around 1550 nm, due to lower absorption coefficients
Implementation Method 2
Image sensors convert optical images to digital data... Pixel sensors often manifest as charge-coupled devices (CCDs) or complementary metal oxide semiconductor (CMOS) devices
Implementation Method 3
An avalanche process can be triggered when a reverse biased p-n junction receives additional carriers, such as carriers generated by incident radiation... the p-n junction is biased above its breakdown voltage, thereby allowing a single photon-generated carrier to trigger an avalanche current
Data Source
AI summary
The present disclosure provides a semiconductor structure, including a substrate including a first material, wherein the first material generates electrical signals from radiation within a first range of wavelengths, an image sensor element including a second material, wherein the second material generates electrical signals from radiation within a second range of wavelengths, the second range is different from first range, a transparent layer proximal to a light receiving surface of the image sensor element, wherein the transparent layer is transparent to radiation within the second range of wavelength, and an interconnect structure connected to a signal transmitting surface of the image sensor element.