High Density Integrated Capacitors for Smart Catheters and Implants

Abstract

The Flex-to-Rigid (F2R) technology platform is an interconnect platform to integrate heterogeneous electronic systems and devices onto a partially flexible chip for minimally invasive medical instruments. This technology platform allows for the integration of micro electro-mechanical systems (MEMS) and integrated circuits (IC) on a chip in a planar plane, which can later be folded into any arbitrary shape. Downscaling of the technology and the increasing number of integrated components in the F2R platform have a high impact on the power distribution and consequently on the signal integrity. It is widely accepted that one of the most powerful strategies to encounter signal integrity problems is to use decoupling capacitors. However, there is an inherent trade-off between the capacitance and size of a capacitor. This thesis is focused on the development on high density capacitors for the integration in the F2R technology platform. One of the objectives was to increase the capacitance density. Because there is limited space available on the F2R chip, additional area to increase the capacitance is found in the depth of the silicon. By etching multiple trenches into the silicon, a capacitance density increase by a factor of 10 is obtained. To even further increase the capacitance, the use of a silicon dioxide – silicon nitride – silicon dioxide multilayer (ONO) dielectric is reviewed. Moreover, a first step has been made in the fabrication of high breakdown voltage and low breakdown voltage parts in this dielectric layer. A second objective was to deliver the capacitors as a ‘’building block’’ that can be implemented in the F2R process flow. Therefore, the process needs to be compatible with the standard IC and MEMS technologies that are available in the Philips Innovation Service cleanroom. The steps of the fabrication process are verified and where needed optimized, and a dedicated mask set is designed for the fabrication of the capacitors. With this mask set, the so called trench capacitors have been made. These test devices are characterized in terms of breakdown voltage and capacitance. It is found that the capacitance density can be increased by an order of magnitude with the introduction of trenches to the test devices. In addition, the advantage of a multilayer dielectric compared to a single layer dielectric is shown.