An In Vivo Biostability Evaluation of ALD and Parylene‐ALD Multilayers as Micro‐Packaging Solutions for Small Single‐Chip Implants

Abstract Miniaturization of next‐generation active neural implants requires novel micro‐packaging solutions that can maintain their long‐term coating performance in the body. This work presents two thin‐film coatings and evaluates their biostability and in vivo performance over a 7‐month animal study. To evaluate the coatings on representative surfaces, two silicon microchips with different surface microtopography are used. Microchips are coated with either a ≈100 nm thick inorganic hafnium‐based multilayer deposited via atomic layer deposition (ALD‐ML), or a ≈6 µm thick hybrid organic–inorganic Parylene C and titanium‐based ALD multilayer stack (ParC‐ALD‐ML). After 7 months of direct exposure to the body environment, the multilayer coatings are evaluated using optical and cross‐sectional scanning electron microscopy. Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) is also used to evaluate the chemical stability and barrier performance of the layers after long‐term exposure to body media. Results showed the excellent biostability of the 100 nm ALD‐ML coating with no ionic penetration within the layer. For the ParC‐ALD‐ML, concurrent surface degradation and ion ingress are detected within the top ≈70 nm of the outer Parylene C layer. The results and evaluation techniques presented here can enable future material selection, packaging, and analysis, enhancing the functional stability of future chip‐embedded neural implants.