Microcoils on Structured Silicon Substrates for Magnetic Resonance Detection

The design and performance of a silicon-based RF detector coil for use in magnetic resonance (MR) spectroscopy applications is described. The coil is fabricated using microelectromechanical systems (MEMS) technology by deep reactive ion etching (DRIE) of an oxidized silicon substrate carrying electroplated conductors. The DRIE step simultaneously forms a sample trough and creates a trepan cut around the coil so that it may be detached from the substrate by cleaving short sections of sprue. A single-turn coil with Q-factor ~16 at 63.6 MHz is demonstrated and MR spectroscopy experiments are described. An accurate numerical model based on the time-domain finite integration technique is used to investigate the effect on the Q-factor of deliberately structuring the substrate to limit the volume of silicon exposed to RF energy. The model is compared with known analytic approximations, and good agreement is obtained.