Ceramic Packages for Acoustically Coupled Neural Implants

Recently, ultrasound has emerged as an energy modality for powering and communicating with very small implantable devices. In the academic literature, demonstrated ultrasonically-powered devices have been packaged in polymer encapsulants of various types. Traditional polymeric insulation materials such as parylene and silicone are known to crack, delaminate, or allow water vapor diffusion after implantation. Materials such as ceramics and metals, are much more robust to the biological environment and have significantly lower water vapor permeabilities than polymers. Although ceramics and metals are routinely used in medical implants, it remains to be shown whether packages suitable for efficient acoustic energy transfer and backscatter communication are possible. In this work, we present a hybrid ceramic-metal packaging method for the encapsulation of ultrasonic implants intended for neural applications. Alumina packages are joined to platinum electrodes with an active-braze alloy and laser microwelding is used to seal the package cavity. We show acoustic windows can be engineered into the implant, enabling ultrasonic backscatter communication and opening the possibility of chronically implanted, wireless, leadless, and battery-less, neural interfaces.