Low Capacitance Photodetector via Segmented InGaAs Pixel
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Solution Overview
Problem
Conventional low-capacitance photo detectors for high-speed applications, such as LIDAR and pulse-tracking, face challenges due to high costs and increased dark noise from complex diode epitaxial structures and contact interfaces, which are not adequately addressed by existing technologies.
Innovation Solution
A photodiode system with a pixel structure featuring an InGaAs absorption layer sensitive to infrared wavelengths, an n-doped InP contact layer, and a high-aspect-ratio contact metal design that reduces capacitance by using alternating oxide and nitride layers and a bump-to-stack contact configuration, which connects to a read-out integrated circuit, thereby minimizing mechanical stress and detector noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional complex diode epitaxial structures are used to achieve low capacitance, then capacitance is reduced, but manufacturing cost increases and dark current increases
Solution Approach 1:
The photodetector structure is segmented into distinct functional layers: a simplified epitaxial structure with separate absorption layer, cap layer, and contact layer, each optimized for its specific function. This segmentation allows reduction of overall complexity while maintaining low capacitance performance through standardized layer configurations rather than complex integrated epitaxial designs.
2Ease of manufacture
If conventional contact interfaces are used, then manufacturing is simpler, but dark noise increases due to increased dark current
Solution Approach 1:
A specifically designed contact layer serves as an intermediary between the absorption layer and external contacts. This intermediate layer is engineered to provide low-resistance electrical contact while maintaining low dark current characteristics, thereby reducing dark noise without complicating the manufacturing process.
3Shape
If thicker passivation layers are used to reduce capacitance, then capacitance decreases, but mechanical stress increases
Solution Approach 1:
The passivation structure uses composite material design with alternating oxide and nitride layers. Each layer material is selected for its specific mechanical and electrical properties, creating a composite structure that reduces overall capacitance while distributing and managing mechanical stress through the layered configuration rather than using a single thick layer.
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 reduces detector capacitance and noise, enhancing signal detection, imaging sensitivity, and manufacturing efficiency while maintaining mechanical stability, thus improving the performance and cost-effectiveness of high-speed photodetectors.
Implementation Method 1
an absorption layer operatively connected to an illumination side of the diffusion layer. The absorption layer can include InGaAs, wherein the pixel is sensitive to illumination in infrared wavelengths
Data Source
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AI summary
A system includes a pixel having a diffusion layer within a cap layer. The diffusion layer defines a front side and an illumination side opposite the front side with an absorption layer operatively connected to the illumination side as well as the diffusion and cap layers. A set of alternating oxide and nitride layers are deposited on the front side of the cap and diffusion layers.