n-type Ge/Si antennas for THz sensing.

Area of Science:

• Plasmonics
• Terahertz (THz) technology
• Semiconductor device fabrication

Background:

• Germanium-on-silicon (Ge-on-Si) plasmonics offers a pathway to miniaturized and cost-effective terahertz (THz) radiation manipulation.
• Conventional fabrication methods for THz plasmonic devices can be complex and expensive.
• The integration of plasmonic devices with microfluidics requires robust designs that maintain functionality.

Purpose of the Study:

• To investigate the plasmonic properties of doped Ge bow-tie antennas fabricated using CMOS mainstream technology.
• To explore the effect of surface functionalization on the resonant frequencies of these antennas.
• To assess the feasibility of protecting the plasmonic antennas while maintaining their functionality for microfluidic applications.

Main Methods:

• Fabrication of doped Ge bow-tie antennas using low-cost CMOS mainstream technology.
• Characterization of antenna resonances in the 500–700 GHz range using THz time-domain spectroscopy.
• Surface functionalization with a thin layer of α-lipoic acid to study resonance shifts.
• Investigation of resonance shifts in antennas protected by a silicon nitride cap layer.

Main Results:

• Ge-on-Si bow-tie antennas exhibited resonances between 500 and 700 GHz.
• Surface functionalization with α-lipoic acid resulted in a red-shift of antenna resonances by approximately 20 GHz.
• Silicon nitride-capped antennas showed a comparable red-shift upon biolayer coverage, indicating field extension beyond the cap.

Conclusions:

• Doped Ge-on-Si bow-tie antennas are viable for THz manipulation, leveraging cost-effective CMOS technology.
• Surface functionalization effectively tunes antenna resonances, enabling sensor applications.
• The demonstrated protection strategy with silicon nitride is compatible with microfluidic integration, preserving plasmonic functionality.