We present a novel approach for the fabrication of lithium-ion microbattery electrodes which deliver high energy and high power density. The key enabling technology is the use of self-assembled Tobacco mosaic virus (TMV) nanoforests as a template for active battery materials. The self-assembling TMV is a genetically modified biological nanorod with increased metal binding properties for enhanced manufacturability. High energy density is achieved due to the active surface area increase within a given footprint by combining TMV with three-dimensional (3D) microfabricated structures. The TMV nanostructure enables high power density through larger electrode/electrolyte contact area and faster charge transport. The electrodes consist of an array of electroplated gold micropillars. The pillars are coated with the self-assembled nanoscale TMV template and subsequently metalized in-place. Active battery material (V2O5) is conformally deposited using atomic layer deposition (ALD) on the hierarchical micro/nano network. Electrochemical testing of these electrodes indicates a 3-5 fold increase in energy density, compared to the TMV-templated electrodes without micropillars, without increasing footprint area or reducing rate performance. Further increase in energy density can be achieved by increasing surface area of 3D microelements as demonstrated by fabrication and electrochemical testing of the electrodes with hollow gold micropillars. Scaling up energy density by increasing active material thickness beyond 100 nm revealed some loss in surface area which highlighted the importance of nanoscale engineering for achieving maximum energy and power density in energy storage systems.
We present the use of the polysaccharide chitosan for immobilizing biomolecules on microfabricated
device surfaces. The main advantages of chitosan are its abundance of primary amine groups and its ability
to be electrodeposited. Biomolecules are easily attached to chitosan's amines by standard glutaraldehyde
chemistry. The electrodeposition of chitosan allows accurate spatial and temporal control of biomolecule
placement. We have used this biofunctionalization approach to develop a biophotonic hybridization sensor.
Here we present for the first time probe DNA functionalization of the chitosan interface and hybridization
detection using fluorescently labeled target DNA and integrated optical waveguides.
We have demonstrated a planar waveguide-based tunable integrated optical filter in indium phosphide (InP) with on-chip micro-electro-mechanical (MEMS) actuation. An air-gap Fabry-Perot resonant microcavity is formed between two waveguides, whose facets have monolithically integrated high-reflectivity multilayer InP/air Distributed Bragg Reflector (DBR) mirrors. A suspended beam electrostatic microactuator attached to one of the DBR mirrors modulates the microcavity length, resulting in a tunable filter. The DBR mirrors provide a broad high-reflectivity spectrum, within which the transmission wavelength can be tuned. The in-plane configuration of the filter enables easy integration with other active and passive waveguide-based optoelectronic devices on a chip and simplifies fiber alignment. Experimental results from the first generation of tunable optical filters are presented. The microfabricated filter exhibited a resonant wavelength shift of 12nm (1513-1525nm) at a low operating voltage of 7V. A full-width-half-maximum (FWHM) of 33 nm was experimentally observed, and the quality factor was calculated to be 46. Several improvements of the MEMS actuator, waveguide, and optical cavity design for the future devices are discussed.
We report, for the first time, the design and simulation of electrostatic MEMS comb-drive actuators incorporating gray-scale technology to tailor actuator properties. Specifically, 3-dimensional comb-fingers and suspensions enable customized displacement characteristics and lower driving voltages without increasing the device footprint. The local height of each comb-finger is varied using gray-scale technology to modify the change in capacitance with position, thereby altering the generated force. The displacement characteristics of various comb-finger geometries were simulated using analytical approximations and finite element analysis (FEMLAB). Simulations show that variable height comb-finger designs may reduce the local change in capacitance (or force) by up to 75%, resulting in increased displacement resolution. We also show that gray-scale technology is capable of simultaneously reducing the height of comb-drive suspensions, causing a corresponding reduction in spring constant for lower driving voltages. The design and simulation of variable height comb-drives is presented along with experimental confirmation of the simulated performance.
We present a new platform for the optical analysis of biomolecules based upon the polysaccharide chitosan. The versatile, stable, and compatible nature of chitosan makes it an ideal material for integrating biological materials in microfabricated systems. Chitosan’s pH-responsive solubility allows electrochemical deposition, while its chemical reactivity enables facile coupling of proteins, oligonucleotides, and other biomolecules by covalent bonds. This work demonstrates the spatially selective assembly of a fluorescent molecule on chitosan and its applicability to microscale optical transducers. We define multimode waveguides and fluidic channels on a Pyrex wafer using a single layer of SU-8. Our implementation of sidewall patterning of transparent electrodes (indium tin oxide) on SU-8 structures is demonstrated and can be highly beneficial to fluorescent signal transduction. In this optical configuration, normally incident excitation light illuminates a chitosan surface on the vertical face of a collector waveguide intersected by a microfluidic channel. We demonstrate the collection of the optical signal in the integrated waveguide and analyze the signal by coupling the waveguide to a grating spectrometer.
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