An In Vivo Biostability Evaluation of ALD and Parylene-ALD Multilayers as Micro-Packaging Solutions for Small...

Area of Science:

• Biomaterials science
• Neurotechnology
• Materials engineering

Background:

• Advancing active neural implants necessitates robust micro-packaging to ensure long-term functional stability within the body.
• Thin-film coatings are critical for protecting implantable electronics from the corrosive biological environment.

Purpose of the Study:

• To evaluate the biostability and in vivo performance of two distinct thin-film micro-packaging coatings over a 7-month period.
• To assess the suitability of these coatings for next-generation neural implant applications.

Main Methods:

• Two silicon microchips with varying microtopography were coated with either a hafnium-based multilayer (ALD-ML) or a hybrid Parylene C/titanium multilayer stack (ParC-ALD-ML).
• Coated microchips underwent a 7-month in vivo animal study.
• Post-exposure analysis included optical microscopy, cross-sectional scanning electron microscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS).

Main Results:

• The ≈100 nm inorganic hafnium-based multilayer (ALD-ML) exhibited excellent biostability, showing no signs of ionic penetration after 7 months.
• The ≈6 µm hybrid Parylene C and titanium-based multilayer stack (ParC-ALD-ML) displayed surface degradation and ion ingress within the outer Parylene C layer.

Conclusions:

• The hafnium-based multilayer coating offers superior long-term biostability for neural implant micro-packaging.
• These findings provide critical data for material selection and design to enhance the reliability of future chip-embedded neural implants.