Ultrasonically Powered Compact Implantable Dust for Optogenetics

This paper presents an ultrasonically powered microsystem for deep tissue optogenetic stimulation. All the phases in developing the prototype starting from modelling the piezoelectric crystal used for energy harvesting, design, simulation and measurement of the chip, and finally testing the whole system in a mimicking setup are explained. The developed system is composed of a piezoelectric harvesting cube, a rectifier chip, and a micro-scale custom-designed light-emitting-diode (LED), and envisioned to be used for freely moving animal studies. The proposed rectifier chip with a silicon area of 300 mu m x 300 mu m is implemented in standard TSMC 0.18 mu m CMOS technology, for interfacing the piezoelectric cube and the microLED. Experimental results show that the proposed microsystem produces an available electrical power of 2.2 mW while loaded by a microLED, out of an acoustic intensity of 7.2 mW/mm(2) using a (1 mm)(3) crystal as the receiver. The whole system including the tested rectifier chip, a piezoelectric cube with the dimensions of (500 mu m)(3), and a mu LED of 300 mu m x 130 mu m have been integrated on a 3 mm x 1.5 mm glass substrate, encapsulated inside a bio-compatible PDMS layer and tested successfully for final prototyping. The total volume of the fully-packaged device is estimated around 2.85 mm(3).