Research
Our multidisciplinary research focuses on providing theoretical foundations and engineering platforms for creating electrical, mechanical and optical devices and systems that can seamlessly integrate into the human body. Such devices and systems will enable a better understanding of the living systems and a wealth of patient data that can revolutionize scientific discovery and treatment paradigms. To build these miniature devices and systems, we focus on all the crucial areas of integrated biomedical system design, including integrated circuits, microfabrication, system-level modeling and integration, and hardware-software integration. The principle of our integrated system approach is based on combining concepts from physics (such as optics and ultrasonics) and engineering (such as integrated circuits and micro/nanofabrication) to bring new functional capabilities to biomedical devices and systems that can open the door to novel monitoring, diagnostics, and therapeutics. Specific areas of interest include health monitoring applications, implantable neural interfaces, and closed-loop therapeutics.
Research Highlights
Wireless Microelectronic Systems for Monitoring Physiological Signals
Continuous real-time monitoring of physiological biomarkers can yield insights into the underlying aspects of a wide range of diseases and guide diagnostic and therapeutic decisions for critical care patients and in surgeries. Tissue oxygenation, one of the key physiological biomarkers, is a critical determinant of organ function. Existing systems for monitoring tissue oxygenation are limited by a few factors: i) the need for wired connections, ii) the inability to provide real-time data, and iii) operation restricted to surface tissues. We demonstrated the first minimally invasive wireless system to monitor deep-tissue oxygenation that reports continuous real-time data from centimeter-scale depths in sheep, avoiding the drawbacks of the current O2-sensing technologies. The system is composed of a wireless, mm-sized, ultrasound-powered O2 sensor implant that communicates bidirectionally with a transceiver outside the body. The implant incorporates a single piezoelectric crystal and a luminescence sensor that consists of a µLED, an O2-sensing film, an optical filter, and a custom mixed-signal integrated circuit (IC). This work, demonstrating various aspects of system performance, has been published in Nature Biotechnology (2021).
Berkeley News: Tiny wireless implant detects oxygen deep within the body
Microfabricated Optical Devices for Biomedical Applications
Continuous monitoring of voltages is of great interest in several applications. As an example, we recently demonstrated the first millimeter-scale, low-Q optical voltage sensor capable of transducing electrical signals into an optical readout using standard microfabrication techniques for grid applications [Optics Express (2021)]. We then demonstrated a high-Q, CMOS-compatible piezoelectric-based optical modulator that enables establishing an optical data uplink to wireless implants [Optics Express (2022)]. The modulator acts as a pF-scale capacitor, requires no bias voltage, and operates at CMOS voltages of down to 0.5V, avoiding the drawbacks of existing devices used for optical communication with implants. We believe this technology would provide a path toward the realization of sub-mm scale wireless implants for use in bio-sensing applications.
Low-power Integrated Circuits
Building minimally invasive wireless implant systems requires ultra-miniaturization of the implant to minimize tissue damage and hence enable chronic use of the implant. This mainly imposes limits on the antenna size and thereby the amount of power harvested by the implant, which in turn limits the power consumption of the implant integrated circuit (IC). To overcome this problem, we develop low-power mixed-signal ICs through innovations in circuit design and architecture for ultra-small, mm- or sub-mm scale, implants. Recently, we developed a state-of-the-art mixed-signal IC fabricated in a TSMC 65 nm LP CMOS process to build an oxygen sensor implant. The sensor implant operates on the same readout principle as most wired luminescent sensors, but with competitive or better resolution and the lowest power consumption of any system ever demonstrated by a wide margin. The implant IC details were presented at the ISSCC Conference (2020).
Ultra-low-power Microsystems via an Integrated CMOS-MEMS Platform
We demonstrated near-zero power monolithic CMOS-MEMS piezoelectric devices [Transducers (2017)]. The integrated devices were fabricated by wafer-level eutectic bonding of MEMS to CMOS. The close integration of CMOS electronics with MEMS sensors enabled minimizing the package size and provided lower electrical parasitics, improving the device sensitivity. Such monolithic integration can be used to develop ultra-low-power, ultraminiature, implantable medical sensors and devices. This can enable the development of high-performance microsystems with capabilities for use with minimal tissue damage.
Wireless Power and Data Transfer for Ultraminiature Implantable Medical Devices
Acoustic links for implantable medical devices (implants) have gained attention primarily because they provide a route to wireless deep-tissue systems. The miniaturization of the implants is a key research goal in these efforts because smaller implants result in less acute tissue damage. Implant size in most ultrasonic systems is limited by the piezoelectric bulk crystal used for power harvesting and data communication. Further miniaturization of the piezocrystal degrades system power transfer efficiency (PTE) and data transfer reliability. We developed a new method for packaging the implant piezocrystal. The method maximizes PTE and information transfer across the acoustic link, enabling the design of ultra-efficient acoustic links for ultrasonic implants; this provides a path toward the further miniaturization of these implants to sub-mm scales [IEEE T-UFFC (2021)].