Our lab develops new electrode materials and geometries for mapping cortical activity from the surface and the depth of the human brain. These devices are currently being used under authorizations from institutional review boards at UC San Diego, Massachusetts General Hospital, and Oregon Health & Science University. These devices are compliant and conformal to the brain, are electrochemically stable and sensitive, and have currently a thousand of functional channels for coverages from a few millimeters to a few centimeters. We are implementing novel monolithic integration schemes to scale the technology to multiple thousands of channels. We are currently extending the use of the technology based on platinum nanorods for utility in clinical trials for diagnostic and therapeutic purposes. We have ongoing institutional, national, and international collaborations for cortical and spinal cord recording and stimulation across a variety of species. (Students: Jihwan Lee, Andrew Bourhis, Samantha Russman, Ritwik Vatsyayan, Dr. Youngbin Tchoe, Dr. Daniel Cleary (MD), Dr. Joel Martin (MD), Dr. Ronald Sahyouni (MD), Dr. Mickey Abraham (MD), Dr. Karen Tonsfeldt). 

High-fidelity cortical and spinal implants:

Nanowire-Neuron interfaces for brain-on-chip drug screening applications:

We are interested in understanding the spontaneous and stimulated local potential fluctuations and activity in extended networks of neurons in 2D and 3D configurations. The lab developed technologies that can be capable of intracellular intervention for long durations of time and at high spatio-temporal resolution for mapping and stimulation of neuronal activity from primary and human induced pluripotent stem cell neurons and cardiomyocytes. Our technology is based on vertical and individual electrically addressable nanowire arrays and the resultant devices are projected to have the capacity of targeted and programmable drug delivery and are scalable for fab-compatible processing to serve as the next generation drug screening platform for applications in and beyond precision medicine. (Student: Jihwan Lee, Dr. Youngbin Tchoe, Dr. Karen Tonsfeldt) 

In GaN, we developed new approaches for strain engineering to dilate and deflect stresses due to thermal mismatches that resulted in new milestones for the GaN on Si technology including (1) Over 19 micron thick crack-free GaN on Si, 4-5 times thicker than what has been achieved before, (2) threading dislocation densities of 10^7 /cm2, which is about two orders of magnitude lower than that previously achieved on Si, and (3) the first vertical GaN MISFETs on Si with performance similar to that of GaN-on-GaN devices.

We have recently developed the world’s best intrinsic linear transistor by synthesizing linearity achieving a 16dB linearity figure of merit (OIP3/PDC) at 5GHz. We’re extending our achievement to the mm-wave regime. Our devices are built on Si or other scalable technologies that are capable of market penetration.

(Students: Po Chun Chen, Tianhai Wu, Dr. Woojin Choi) 

GaN epitaxy and transistors:  ​​​​

ZnO TFTs for closed-loop normal and shear pressure sensing for robotics and neuroprosthetics:

We developed a scalable dual-gate ZnO thin-film transistor technology on polyimide substrates that can measure (by the piezoelectric effect) and amplify (by the transistor gain mechanism) normal and shear force using the same TFT (sense, amplify, and multiplex). Our sensors can be applied to flat and curved robotic fingers and demonstrate gripping and holding of fragile objects such as raw egg or fruits without visual input or human intervention. Significantly, we demonstrated adjustment of the grip force due to slip of objects for both flat and curved surfaces, providing the first closed-loop robotic feedback for slip using direct sensation of pressure. (Ritwik Vatsyayan, Dr. Hongseok Oh)