Miniaturized, RF-Based, and Battery-Free Stimulators Packaged with Polymer-Metal Flex Circuits for Implant Applications

This paper describes the fabrication, packaging, assembly, and characterization of a very small (~1 mm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>) assemblage of an RF-powered, wireless, and battery-free neuromodulation device that is integrated with a microfabricated thin-film polymer-metal flex circuit. The implantable device consists of a microfabricated polyimide-metal flex circuit that is bonded to an application-specific integrated circuit (ASIC) and a surface-mount inductor (SMI) using a conductive epoxy with a microstamping and aligned-bonding process. The assemblage is encapsulated in silicone to support operation while submerged in saline or while implanted. Wireless power is delivered through an RF link at 439 MHz. Two versions of the device were developed. One version has a pair of 280-um-diameter stimulation electrodes, and the other version has pads for the integration of a chip-scale LED. Both versions were successfully operated in air and saline. This work advances ultraminiature leadless neural interfaces for anatomically constrained environments and sets the foundation for long-term preclinical evaluation.