Electroplating RF mems resonators and optical characterization

Abstract

Magnetic resonance imaging (MRI) is an advantageous imaging platform for endovascular interventions due to its higher safety and performance comparing with other imaging techniques. Localization of the catheter under MRI requires the employment of external devices. Among the various solutions in literature, electromagnetic tracking systems (EMTS) are advantageous due to their ease of use, safety, small size, and relatively high accuracy. They typically utilize conductive wiring for the transmission of electrical signal. However, under MRI radio frequency (RF) magnetic elds induce heat in conductive materials. This thesis presents fabrication, and characterization of RF MEMS-based electromagnetic resonators designed to be integrated with a MRIcompatible catheter tracking system. The tracking system is designed to communicate with ber optic cables eliminating the use of conductive materials. MEMS resonators act as transducer to convert the electrical signal to displacement using the mechanical force induced by Lorentz force. The devices are designed such that the vibration can be detected either via laser Doppler vibrometry (LDV) and/or via di raction grating interferometry (DGI). The resonance frequencies of a family of devices are investigated by nite element method (FEM) simulation. The range of frequency for the MEMS sensor array is from 145 kHz to 1.48 MHz. Devices are fabricated using electroplating nickel onto a seed layer of copper on a silicon substrate and characterized by LDV. The characterization setup provides a magnetic eld of 0.62 Tesla which is generated by two parallel cubic permanent magnets. The characterization results show that the MEMS resonators are able to resonate by having a 10 dB of signal-to-noise ratio (SNR) at the electrical current of 25 A (RMS). Experimental results prove that the devices are ready to function in the real-world application.