Integration Technologies for Smart Catheters

Abstract

Around 10% of the population will have to go through a catheterization procedure for the treatment of a cardiovascular disease at a certain stage of their lives. During such a procedure, smart catheters will be the "eyes and ears" of the surgeons, significantly improving the diagnosis and treatment. However, there have been very limited improvements and innovations in smart catheters over the past decade, as most smart catheters are manufactured with technical point solutions, and therefore cannot sustain themselves with enough production volume for continuous innovation. Consequently, Flexto- Rigid (F2R) was developed as an interconnect platformfor heterogeneous integration of electronic components in submillimeter formfactors. F2R is an open technology platformthat can serve many smart catheter applications from a variety of manufactures. It consists of multiple small and thin silicon islands connected by thin flexible interconnects, which allows devices and components to be mounted with standard assembly techniques or directly fabricated onto the F2R platform. This thesis presents innovations in F2R-based applications, integration, and process optimization for smart catheters. The first part of the thesis is an example of applying F2R for making a miniaturized device, a submillimeter optical data link module (ODLM). With smart catheters migrating from analog to digital instruments, an optical interposer is needed to realize highspeed optical data transmission. The biggest challenge is the form factor of the optical interposer, as it needs to fit into a catheter tip that is inserted inside human veins. This challenge falls exactly in the scope of F2R. The ODLM was fabricated, assembled, and integrated into an ICE catheter demo system. The second part of the thesis presents high-density embedded trench capacitor integration in the F2R platform. Compared to assembling discrete capacitors on F2R, embedded capacitors in the F2R substrate save space in the catheter tip and bring the decoupling capacitors directly underneath the ASICs, resulting in better performance. The work involved the trench capacitor process development, especially the high-aspect ratio (HAR) DRIE trench etching process. More importantly, the trench capacitor process was optimized to be compatible with the standard F2R process. The last part of the thesis presents the work on improving the fabrication process of the F2R platform. The largest bottleneck and most critical step of F2R is the "buried trench" process, which creates separated thin silicon islands. The buried trenches consist of thin oxide membranes, that are very sensitive to thin-film stress and other mechanical forces, resulting in reduced production yield. Cavity-BOX SOI eleminates the "buried trench" process by introducing a patterned buried oxide layer. The patterned buried oxide mask allows an intact wafer surface during the process until the final DRIE process, which separates the wafer in one go using this oxide mask. The production yield can be significantly improved using the cavity-BOX SOI for the F2R process. A deep brain stimulation (DBS) probe test structure was fabricated with the cavity-BOX SOI based F2R process to demonstrate the technology concept. A method to align the patterns on the wafer to the patterned buried oxide mask was developed.