Miniaturization of implantable neural recording systems to micron-scale volumes will enable minimally invasive implantation and alleviate cortical scarring, gliosis, and resulting signal degradation. Ultrasound (US) power transmission has been demonstrated to have high efficiency and low tissue attenuation for mm-scale implants at depth in tissue [1, 2, 3], but has not been demonstrated with precision recording circuitry. We present an US implantable wireless neural recording system scaled to 0.8mm3, verified to safely operate at 5cm depth with state of the art neural recording performance an average circuit power dissipation of 13μW, and 28.8μW including power conversion efficiency. Sub-mm scale is achieved through single-link power and communication on a single piezocrystal (Lead Zirconate Titanate, PZT) utilizing linear analog backscattering, small die area, and eliminating all other off-chip components.

Neural stimulation is a powerful technique for modulating physiological functions and for writing information into the nervous system as part of brain-machine interfaces. Current clinically approved neural stimulators require batteries and are many cubic centimetres in size -- typically much larger than their intended targets. We present a complete wireless neural stimulation system consisting of a 1.7 mm3 wireless, batteryless, leadless implantable stimulator (the "mote"), an ultrasonic wireless link for power and bi-directional communication, and a hand-held external transceiver. The mote consists of a piezoceramic transducer, an energy storage capacitor, and a stimulator integrated circuit (IC). The IC harvests ultrasonic power with high efficiency, decodes stimulation parameter downlink data, and generates current-controlled stimulation pulses. Stimulation parameters are time-encoded on the fly through the wireless link rather than being programmed and stored on the mote, reducing power consumption and on-chip memory requirements and enabling complex stimulation protocols with high-temporal resolution and low-latency feedback for use in closed-loop stimulation. Uplink data indicates whether the mote is currently stimulating; it is encoded by the mote via backscatter modulation and is demodulated at the external transceiver. We show that the mote operates at an acoustic intensity that is 7.8% of the FDA limit for diagnostic ultrasound and characterize the acoustic wireless link's robustness to expected real-world misalignment. We demonstrate the in vivo performance of the system with motes acutely implanted with a cuff on the sciatic nerve of anesthetized rats and show highly repeatable stimulation across a wide range of physiological responses.