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.

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.

Cellular stiffness plays an important role for several diseases such as atherosclerosis, malaria and cancer. Cellular stiffness can be derived by the velocity of a cell that is squeezed through a constriction channel. For example, a rigid cell will move slowly through the constriction channel and vice versa. In this research a microfluidic device with integrated electrodes was fabricated to detect the cell within the constriction channel. The velocity of the cell can be measured if the cell is detected at two different location. In this thesis the fabrication process of the device based on standard IC process is presented and electrically characterized.