News and events of | Interdisciplinary Microsystems Group

Flexible Microelectrode Array for Neural Recording

Technological advances in microelectrode neural probes have great potential to benefit patients with neurological diseases and injuries because they allow for direct interfacing and intervention with neurons of the nervous system. The interface design involves chronically collecting neural activity directly from the cortex of the brain, interpreting its information, and delivering therapy via an electronic interface. Such Brain-Machine Interface (BMI) systems that are capable of recording and processing the activity of large ensembles of cortical neurons have the potential to allow paralyzed individuals to communicate with the external world via computer control or direct control of prosthetic limbs and wheelchairs.We design, fabricate, and test flexible microelectrode array that can be hybrid-packaged with custom electronics in a fully implantable form factor to realize a self sustained BMI system. Also the flexible cable will provide strain relief to the implanted electrode and potentially improve long term viability.

This project aims at designing novel micromachining techniques for polymer-based flexible substrate microelectrodes as well as defining requirements for recording amplification, signal processing, and wireless telemetry systems. Much effort is going into the design and fabrication of highly compliant 2D electrodes which will potentially increase the possibilities of achieving reliable neural recordings over a chronic period . All efforts are in attempt to further the field of chronic neural recording for neuroprosthetic therapies.

IMG Seminar: Spatially Controlled Electrospun Solid Gradient Aligned Nanofiber Tissue Scaffold for Guided Spiral Ganglion Neuron Culture

Submitted by John Griffin on Mon, 09/13/2010 - 10:27am

Event date:

Wed, 09/15/2010 - 7:00pm to 7:30pm

Speaker: PitFee Jao

The direction of cell growth is associated with chemical, structural and/or mechanical properties of the substrate. Structurally, electrospun nanofibers provide a suitable environment for cell attachment and proliferation due to their similar physical dimension to that of the extracellular matrix. Furthermore, by modulating the topographical features of nanofibers, which include fiber diameter and orientation, cell growth and its related functions can be modified. Here, we demonstrate a solid gradient scaffold for directional growth of spiral ganglion neurons (SGNs).

IMG Welcomes New Faculty Member, YK Yoon

Submitted by PitFee Jao on Thu, 08/19/2010 - 2:40pm

IMG welcomes Professor YK Yoon as new faculty in the Department of Electrical and Computer Engineering. Prof. Yoon joins IMG from the University of Buffalo, The State University of New York. He has achieved numerous awards for excellence including the NSF CAREER Award and the UB's Exceptional Scholar Young Investigator Award. His research interests include MEMS and nanotechnology, RF/Microwave, millimeter wave and terahertz system, Micro/nano-biomedical devices and bio molecule (drug/vaccine/gene) delivery, µ-TAS, lab-on-a-chip, wireless/wired sensors and actuators and Metamaterial and its RF application. Prof. Yoon is also the Director of the Multidisplinary Nano and Microsystems Laboratory at UF.

Effect of Mechanical Stress on AlGaN/GaN High Electron Mobility Transistor (HEMT) Device Characteristics and Reliability

AlGaN/GaN HEMTs are regarded as promising candidate for RF and high power electronics applications due to unique material properties of GaN, such as, wide band gap, high breakdown field, high carrier mobility, and large saturation velocity. Other advantageous characteristics, such as, piezoelectricity and spontaneous polarization within AlGaN and GaN layers result in high 2D electron gas densities. However the wide deployment of the AlGaN/GaN HEMT technology is currently hindered due to its limited electrical reliability. Achieving high-level of reliability concurrently with high power operation remains an important challenge for this technology. Improvements in the reliability of these devices require a thorough understanding of the failure mechanisms that degrade the device performance.

Studies show that AlGaN/GaN HEMTs degrade significantly under typical device operation. Degradation in these devices has been hypothesized to occur due to charge trapping, hot electron effects, and crystallographic defect formation due to inverse-piezoelectric effect. GaN HEMTs have high internal stresses resulting from lattice mismatch between GaN and AlGaN layers and generated during device operation due to inverse piezoelectric effect. Mechanical stress impacts the device performance by affecting the carrier mobility, polarization, band-gap, trap energy levels and trap generation and hence influences the reliability of these devices. The goal of this project is to investigate the effect of stress, bias and temperature on device characteristics and understand the fundamental physics governing the device operation; and hence the failure mechanisms that degrade the device performance. Four-point mechanical wafer bending is used to study the effect of stress on AlGaN/GaN HEMT channel resistance and gate current to provide insight on the role of stress in device reliability.

Capacitive Shear Stress Sensors

This project focuses on the development of a non-intrusive, direct, time-resolved wall shear stress sensor system for low-speed applications. The goals of the project include the fabrication and packaging of a 2-D wall-shear stress sensor with backside wire bond contacts to ensure hydraulic smoothness in flow environments. A differential capacitance transduction scheme is utilized with interdigitated comb fingers on each side of a suspended floating element, allowing for measurements to be made in both the positive and negative x- and y-directions. A synchronous modulation-demodulation circuit is employed to simultaneously capture both mean and fluctuating shear content. Both AC and DC calibrations are performed to determine sensor sensitivity in both directions of transduction. This is the most successful effort of shear sensor development in published literature.