High-Density μLED-Based Optical Cochlear Implant With Improved Thermomechanical Behavior.

Area of Science:

• Biomedical Engineering
• Materials Science
• Neuroscience

Background:

• Traditional cochlear implants stimulate the auditory nerve electrically.
• Optogenetics offers a more precise method for neural stimulation but requires light delivery.
• Previous optical cochlear implant (oCI) designs faced challenges with thermomechanical bending.

Purpose of the Study:

• To realize an optical cochlear implant (oCI) with optimized thermomechanical properties.
• To improve probe stability and reduce bending for effective optogenetic stimulation.
• To enhance material integration and adhesion for long-term device reliability.

Main Methods:

• Fabrication of a 144-micro-light-emitting diode (μLED) oCI probe using a single, transparent epoxy material.
• Development of a spin-coating process for precise epoxy layer deposition (down to 5 μm).
• Investigation of metallization and adhesion layers, identifying SiC/Ti for superior epoxy adhesion.
• Implementation of a stress-free release method using sacrificial aluminum layer dissolution.

Main Results:

• The single-epoxy oCI probe exhibited significantly reduced thermomechanical bending and negligible hysteresis compared to previous designs.
• Optimized spin-coating achieved thin epoxy layers (<7% thickness variation).
• Silicon carbide with titanium metallization improved epoxy adhesion by a factor of two.
• The oCI probe demonstrated a temperature increase limited to 1 K at 10 mA μLED current.
• Optical output power reached 0.82 mW (462 nm wavelength) with a radiant emittance of 407 mW/mm², suitable for optogenetics.

Conclusions:

• A novel oCI probe utilizing a single epoxy material overcomes thermomechanical instability issues.
• The optimized fabrication process and material selection ensure high performance and reliability.
• This advanced oCI is well-suited for future optogenetic experiments in auditory research.