Parylene-based 3D high performance folded multilayer inductors for wireless power transmission in implanted applications

• Parylene-based folded multilayer stacked MEMS inductors with Ni80Fe20 soft magnetic core are fabricated.
• The novel folding and bonding process can use simple single-layer micro fabrication to realize multilayer coils.
• Using the multilayer structure, the performance of MEMS inductors is enhanced significantly.
• Using this MEMS inductor as the receiver, the wireless power transmission system has been set up and tested.
• The WPT system can successfully power implanted MEAs for neural prosthesis as well as commercial LEDs.

This paper presents high performance folded multilayer stacked microelectromechanical systems (MEMS) inductors with Ni80Fe20 soft magnetic core on Parylene substrate for wireless power transmission applications. The novel folding and bonding method successfully solved the crucial process complexity problem for multilayer inductor fabrication, which can realize multilayer coils with simple, fast and low cost process based on one single-layer micro fabrication process and manually folding assembly. Meanwhile, Ni80Fe20 soft magnetic core was introduced to enhance the inductance by electrodeposition techniques. The folded six-layer inductor shows a very high inductance density of 100 nH/mm2 with a quality factor of 10.7 at 4.1 MHz. As the number of layers increases from 1 to 6, the inductance can achieve a 30 times enhancement from 0.427 μH to 12.791 μH. The quality factor of six-layer coil exhibits a 43% increment from 7.48 to 10.68 compared with the three-layer coil. Utilizing this folded multilayer coil as a receiver, a wireless power transmission system was set up, tested and analyzed. At the working frequency of 1.5 MHz, the maximum output power of 19.25 mW is achieved on 30 Ω load with the matching impedance. Effects of the receiver position and direction are investigated, respectively. This system can successfully drive an implanted microelectrode for neural prosthesis as well as commercial light-emitting diodes (LEDs), which shows its promising capability in powering implanted medical systems.