Low Temperature ALD Processes for Cardiac Implant Encapsulation

Hermetical sealing of implants is mandatory to provide patients' security and to guarantee a proper functionality of implants over their lifetime in the patient's body. Due to the demand of size reduction in implants' housings, Atomic Layer Deposition (ALD) is getting more and more an established method. ALD can realize compact and hermetic implant encapsulations with a significant lower space requirement compared to metal and silicon housings. For a cardiac implant with a requested operation time of a few weeks, we present a combined encapsulation method based on a stack of Parylene C and ALD layers grown at low temperature. Parylene C is an established biocompatible encapsulation material, which by itself has already good encapsulation properties for a certain period of time. To improve long-term stability, a low-temperature ALD process is being developed to provide the Parylene C with an additional ceramic barrier. For this purpose, Al2O3 and Ta2O5, which are both biocompatible materials, are chosen. To guarantee a compatibility with the temperature sensitive Parylene C layer underneath, ALD processes with deposition temperatures below 150 °C are being developed. It has been shown that Al2O3 and Ta2O5 provide sufficient barrier properties on solid surfaces, but tend to propagate cracks when deposited on soft Parylene C surfaces. Nevertheless, a sufficient barrier layer consisting of Parylene C in combination with Al2O3 and Ta2O5 could be developed for the targeted operating time. All in all, an alternating stacking of both Parylene C and ALD ceramic layers could be an option to achieve a further increase in the maximum operating time of the implant.