Fabrication and Reliability Study of Parylene-Ceramic Based Flexible Interconnects For Implantable Devices

Abstract

The Flex-to-Rigid (F2R) platform is a generic IC-based technology platform that allows flexible sensors and electronics to be fabricated and integrated onto the catheters or guidewires of minimally invasive medical instruments. In this thesis, a process flow was developed for the fabrication of flexible metal interconnects based on the F2R platform using materials that are biocompatible for neural implants, namely parylene and titanium nitride. A “parylene last” process flow was developed that allows a higher temperature budget of up to 400°C for IC fabrication, and enabled the addition of a ceramic encapsulation layer beneath the parylene encapsulation for improved adhesion and decreased permeability to moisture. For this process flow, two new technology modules were developed: the titanium buried mask and the aluminium etch stop layer. A device with working flexible interconnects connected to bond pads on a rigid silicon island was fabricated. Evaluation testing showed that the interconnects were able to function after four weeks at accelerated aging conditions corresponding to four months in human body conditions, and were able to be bent to a diameter of less than 0.25 mm before device failure.