Medical implants today are often rigid & bulky causing discomfort and infections with prolonged usage. Hence there is a need for implants made using elastomeric packaging materials that closely match the flexibility of human tissue so as to conform to any surface inside the body with relative ease. Ideally, such implants should also be operated wirelessly so as to avoid bulky wires for signal & power or periodic surgeries for battery replacements. Conventional approaches to flexible electronics which rely on sheet- level roll-roll processing and printed interconnects cannot face up to this task as the integration densities achieved is very poor on the account of coarse interconnect pitches and use of packaged chips. To overcome these limitations, we developed a novel flexible device integration technology based on Fan-Out Wafer-Level Packaging (FOWLP) called FlexTrate TM . This wafer level packaging scheme uses standard Si BEOL techniques to interconnect dies embedded in Poly Di-Methyl Siloxane (PDMS) at interconnect pitches < 40 μm. In this work, we demonstrate a fully functional implantable system powered wirelessly using 2-coil resonant magnetic coupling at 13.56 MHz for applications in Optogenetics. The system is composed of a Schottky diode, five Si DT capacitor dies, an active voltage regulator and an AlGaInP μLED seamlessly integrated with an NFC coil with two metallization layers, at 40 μm interconnect pitch, on FlexTrate TM . The system supplies a regulated DC voltage to the μLED at a link Power Transfer Efficiency (PTE) > 15% in a human tissue phantom. System design, fabrication and characterization is discussed.