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Normal-Incidence Germanium Photodetectors Integrated with Polymer Microlenses for Optical Fiber Communication
Yu-Hsuan Liu1,2, Chia-Peng Lin2, Po-Wei Chen2
1Institute of Photonics Technologies, National Tsing Hua University, Hsinchu 30013, Taiwan.
Sensors (Basel, Switzerland)
|July 13, 2024
Summary
We developed a new method to add polymer microlenses to germanium photodetectors, improving high-speed photo-receiver performance and fiber alignment tolerance. This advancement eases packaging and maintains reliability for advanced optical communications.
Area of Science:
- Optoelectronics
- Materials Science
- Photonics
Background:
- High-speed photo-receivers are crucial for modern optical communication systems.
- Integrating optical components like microlenses with semiconductor devices presents fabrication challenges.
- Germanium (Ge) p-i-n photodiodes (PDs) offer excellent performance for near-infrared applications.
Purpose of the Study:
- To present a novel photon-acid diffusion method for integrating polymer microlenses (MLs) onto high-speed germanium photodetectors.
- To enhance the performance and packaging tolerance of a four-channel photo-receiver.
- To demonstrate the feasibility of this integration for advanced optical communication applications.
Main Methods:
- Fabrication of normal-incidence Ge p-i-n PDs on a 200 mm Si substrate.
- Integration of polymer microlenses (MLs) using a novel photon-acid diffusion method.
- Characterization of photo-receiver performance including dark current, responsivity, 3 dB bandwidth (BW), effective aperture size, and sensitivity.
Main Results:
- A 54 µm diameter ML on a 29 µm diameter PD resulted in a 21.4 GHz BW and 54 µm effective aperture.
- Optical fiber misalignment tolerance increased from ±5 µm to ±15 µm.
- Photo-receiver sensitivity reached -9.2 dBm at 25.78 Gb/s (NRZ) with a bit error rate of 10⁻¹².
- The integrated devices passed GR-468 reliability tests.
Conclusions:
- The novel integration method successfully enhances photo-receiver performance and packaging ease.
- The demonstrated Ge PDs with polymer MLs offer a cost-effective, high-yield solution compatible with CMOS fabrication.
- This technology holds potential for future high-speed optical communication systems, such as 400 Gb/s PAM4.
