MEMS-based Fiber-optic Two-photon Microscopy Probe for Real Time In vivo 3D Neural Imaging in Freely Behaving Animals

The goal of this project is to develop a miniature two-photon microscopy probe with light weight and use it on freely behaving mice for in vivo 3D neural imaging. Both 2-axis MEMS scanning mirror and z-axis tunable microlens will be developed. Double-cladding photonic crystal fibers will be used to accommodate the excitation laser and the frequency-doubled two-photon signals. 

A MEMS-based Fast-response Five-hole Probe with Optical Pressure Transducers

The goal of this research is to develop a MEMS-based Five-hole Probe(5HP) that is able to measure the localized velocity vector (both the velocity magnitude and direction) and the static and dynamic pressure, in steady and/or unsteady flow fields. Five optical pressure sensors located on the hemisphere tip of the 5HP provide all information that is needed to resolve the flow. This 5HP is expected to be able to provide high spatial resolution, high frequency response and is compatible with elevated temperature environments. A primary focus of this research is on the microfabrication and micromachining of a die that incorporates five optical transducers and its successive packaging process. The completed sensors will be tested in flow cells and wind tunnels at UF for the final calibration.

Non-Bragg Resonance and Its Applications

This project studies on wave propagation in waveguide with periodical boundaries, in such a case, a new kind of resonance occurs. This new kind of resonance is very different from the traditional Bragg resonance.

In Non-Bragg resonance, the resonance frequency and bandwidth strongly depends on the geometric configuration of the waveguide, and, the resonance is tunable. Theoretical and experimental results show good agreements.

Spatially controlled electrospun solid gradient nanofibers for guided spiral ganglion neuron culture

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). Spatial nanofiber alignment is controlled using a custom directional electrospinning setup. The electric field to spatially control the confinement of nanofibers was simulated with COMSOL Multiphysics simulation tool and experimentally verified. To promote neurite outgrowth and impart directionality to SGN cells, a spatial gradient of neurotrophin (NT) is introduced. By sequentially electrospinning solutions of increasing concentrations of NT in the biodegradable polymer and collecting sections of these aligned fibers along a uniaxial direction, we achieved uniform sectional nanofibers of increasing gradient concentrations. Initial tests with SGNs show improved cell adhesion and decreased morbidity to microfabricated PLGA scaffolds. Our solid gradient nanofiber membrane is versatile, obviates the need for the complex microfluidic mixer system to generate an NT gradient, is potentially implantable, and can be used in other nerve regeneration studies in peripheral nerve system and central nerve system.

Fabrication of Nanoporous membrane and its non-lithographic patterning using Electrospinning and Stamp-thru-Mold (ESTM)

The Electrospinning and Stamp-thru-mold (ESTM) technique, an integrated fabrication process which incorporates the versatility of the electrospinning process for nanofiber fabrication with
the non-lithographic patterning ability of the stamp-thru-mold process is introduced. In-situ multilayer stacking of orthogonally aligned nanofibers, ultimately resulting in a nanoporous membrane, has been demonstrated using orthogonally placed collector electrode pairs and an alternating bias scheme. The pore size of the nanoporousmembrane can be controlled by the number of layers and the deposition time of each layer. Non-lithographic patterning of the fabricated nanoporousmembrane is then performed by mechanical shearing using a pair of pre-fabricated micromolds. This patterning process is contamination free compared to other photo lithographical patterning approaches. The ability to pattern on different substrates has been tested with and without oxygen plasma surface treatment. In vitro tests of ESTM poly-lactic-coglycolic acid (PLGA) nanofibers verify the biocompatibility of this process. Simulation by the COMSOL Multiphysics tool has been conducted for the analysis of electrospun nanofiber alignment.

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. 

Investigation of Stress Effects on Thin-Film PZT Ferroelectric Capacitors for FRAM Enhancement

The combined application of stress, temperature, and bias has the potential to enhance FRAM (ferroelectric random access memory) performance at the 130-nm technology node and possibly extend the technology to the 90-nm node and beyond.  While temperature and bias have been traditionally used to pole ferroelectric thin-films, applied stress has also been shown to enhance ferroelectric properties. This can lead to an improved FRAM signal margin, which is a key metric for FRAM reliability and performance.  We propose to comprehensively study the effects of stress, temperature, and bias on the ferroelectric properties of fully integrated thin-film PZT ferroelectric capacitors.  These effects will be investigated experimentally.  We will then develop SPICE simulation models and simulate the stress in ferroelectric films based on TI’s 130-nm process. Our goal is to gain a deep understanding of the underlying physics of stress effects at bias and temperature on ferroelectric capacitors, and use this knowledge to develop accurate models that can simulate these effects and be used in FRAM design.  We will then recommend strain-engineering methods for enhancing FRAM performance at the 130-nm node and beyond. 

Advancing FRAM technology beyond the 130-nm node can increase storage density and reduce cost, leading to new potential markets and applications.  However, further scaling of ferroelectric PZT films can diminish FRAM performance.  It has been suggested that scaling beyond the 130-nm technology node will require different FRAM structure and materials, which can lead to increased costs and development time.  We propose that stress engineering may be a solution to enhance current FRAM technology and extend it to the 90-nm node and beyond.