Micro-Coils for MR Spectroscopy by Deep Silicon Etching

A process for batch fabrication of low-cost microcoils for magnetic resonance spectroscopy is demonstrated. Conductors are fabricated on oxidised silicon substrates by electroplating metals inside a deep photoresist mould, and passivated using an epoxy-based resist. Through-wafer deep reactive ion etching is used to define sample volumes and stencil cuts around each die, and dies are separated by snap-out. Single-coil and multiple-coil sensors are constructed by stacking parts on baseplates fabricated on the same wafer. Single-turn coils have a Q-factor of ≈ 15 at 63.6 MHz, and Helmholtz coils a Q-factor of ≈ 13. Magnetic resonance imaging and spectroscopy are performed, and a SNR of 900 is achieved.