Flexible parylene-platinum based electrodes and interconnects

Abstract

F2R is a generic IC fabrication based platform that allows for the fabrication of miniature and flexible sensing functionalities for minimally invasive medical instruments. Examples of these minimally invasive medical instruments are catheters and guidewires. By introducing more materials to the F2R technology, it can be extended to more applications. An example of such an application is neural brain probes.

This thesis focuses on the introduction of parylene and platinum to the F2R technology. This is a challenging task, as many different technologies have to be introduced and modified. Therefore, the main objective of this thesis was to develop a fabrication process that allows for the electrical and mechanical evaluation of flexible parylene-platinum based electrodes and interconnects.

In order to electrically and mechanically evaluate the devices, test structures were designed. These test structures make the electrical and mechanical evaluation possible and can be used for further evaluation of future developments. Furthermore, several fabrication technology modules have been developed. The effect of particles on the stability of the device has been reduced by investigating their origin. The step coverage of platinum was improved by optimizing the dry etching of parylene. This was done by introducing CF4 to the etching process, which resulted in a desired 45° slope of sidewall of the parylene structures. Also, the patterning of platinum was improved by separating the etching process into two steps. This resulted in fenceless and clean metallization.

Since the adhesion of the layers is of major importance for in-body applications, the adhesion of parylene and platinum was investigated. By exploring several adhesion promoting techniques, the overall adhesion of the devices was found to be good, and therefore sufficient for electrochemical characterization.

All the previous technology modules were integrated where possible, and have led to the fabrication of flexible parylene-platinum based devices. These test devices consist of a silicon island with bond pads and flexible part with electrodes and a comb-meander structure. Rolling tests have shown that the devices can be rolled to an inner diameter of <1 mm without damaging the interconnects. This flexibility is required for the assembling of a 3D brain probe using a flexible microelectrode array.