Inductive Links With Integrated Receiving Coils for Mems and Implantable Applications

Microelectromechanical systems (MEMS) is a burgeoning field, and the next stage of development is predicted to be the integration of micro- sensors, actuators and circuits on a single silicon chip. Such microsystems will bring about revolutionary advancement in many fields, especially for implantable, autonomous applications. However, when freeing the chip from wire tethering, one major obstacle is the powering needs of MEMS devices, mainly microactuators, which are dramatically different from those of CMOS integrated circuit (IC) chips. Here we demonstrate that inductive links with integrated receiving coils can provide sufficient voltage or power to many MEMS devices. To further improve the performance of the inductive link, an inlaid electroplating procedure is developed to reduce the internal resistance of integrated receiving coils. Trenches into Si substrates by deep reactive ion etching (DRIE) are used as electroplating molds, and copper coils of centimeter side length and up to 100 µm in height and 10 µm in width are electroplated. Enhanced outputs are obtained for inductive links with micromachined microcoils. Another application involves transmission of long-duration pulse trains onto an implantable receiving coil. Some medical conditions, such as ParkinsonåÁå_s disease, already benefit from such pulse trains for deep brain stimulation (DBS) generated by a wired link. Wireless transmission of the pulses is challenging due to the small time constant of the inductive link. Using amplitude modulation, we successfully retrieve pulse trains from a receiving coil with a passive envelope detector, and electroplated coils provide improved performance. For either application, the output from the integrated coil is enhanced at a resonant frequency intrinsic to the inductive link. Selective driving and signal transmission are demonstrated for multiple receiving coils with frequency-multiplexed input. A dual-coil fabrication process with electroplated through-wafer vias is developed for future monolithic integration of coils with electronics. Combining dual coils with discrete demodulation and switching transistors, biphasic signals are generated across a resistor representing body tissue. The above results offer possibilities to replace pulse generators with an external unit in coordination with implanted receiving coils and circuit components.