This PDF file contains the front matter associated with SPIE Proceedings Volume 6464, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We present the application of Drosophila fruit flies as an unconventional substrate for microfabrication. Drosophila by itself represents a complex system capable of many functions not attainable with current microfabrication technology. By using Drosophila as a substrate, we are able to capitalize on these natural functions while incorporating additional functionality into a superior hybrid system. In the following, development of microfabrication processes for Drosophila substrates is discussed. In particular, results of a study on Drosophila tolerance to vacuum pressure during multiple stages of development are given. A remarkable finding that adult Drosophila may withstand up to 3 hours of exposure to vacuum with measurable survival is noted. This finding opens a number of new opportunities for performing fabrication processes, similar to the ones performed on a silicon wafer, on a fruit fly as a live substrate. As a model microfabrication process, it is shown how a collection of Drosophila can be made to self-assemble into an array of microfabricated recesses on a silicon wafer and how a shadow mask can be used to thermally evaporate 100 nm of indium on flies. The procedure resulted in the production of a number of live flies with a pre-designed metal micropattern on their wings. This demonstration of vacuum microfabrication on a live organism provides the first step towards the development of a hybrid biological/solid-state manufacturing process for complex microsystems.

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 report the design and fabrication of a micromachined quartz crystal balance (QCM) array for self assembled monolayers (SAMs) and protein adsorption studies. The microQCM was fabricated using recently developed inductively coupled plasma etching process for quartz to realize resonators with 60 &mgr;m thickness and electrode diameters of 0.5 mm. The reduction in the thickness and lateral pixel size has resulted in a sensitivity improvement by factor of 1700 over a commercially available macro-sized QCM. Adsorption of hexadecanethiol on the gold electrode of the QCM in ethanol at a concentration of 1 mM was recorded in real time and a frequency shift of 3650 Hz was obtained. Modeling the SAMs layer as an ideal, rigid mass layer the expected frequency shift was calculated to be 1031 Hz. This was followed by a study of the adsorption of human serum albumin (HSA) protein on the SAMs layer. For 1.5×10^-10 moles/ml concentration of protein solution in phosphate buffer solution (PBS) we obtained a frequency change of 13.28 kHz. Modeling the protein layer as a viscoelastic layer in a viscous Newtonian fluid, for saturation protein surface coverage, the frequency change was calculated to be 17.27 kHz whereas the experimentally obtained frequency change was 51.82 kHz. In both rigid and viscoelastic film adsorption experiments, we find the microQCM to exhibit three times greater sensitivity than the predicted value when operated at the third overtone. These results show that the micromachined QCM in array format is a very sensitive gravimetric sensor capable of mass resolutions into the femtograms range.

A new non-volatile memory technology for embedded memory applications is described. The technology uses one cantilever per cell with two stable states to store information. The two stable states are either stuck down to a landing electrode or not. Because the cantilever and landing electrodes are conducting, each cantilever can be read easily by measuring the contact resistance between the two. The cantilever stays in the 'on' state due to short range attractive forces at the contact including metal-to-metal bonding and Van der Waals forces. Using standard CMOS processing equipment and materials the cantilevers are designed to switch at the native voltages found in micro-controllers, making this technology an attractive alternative to other forms of embedded non-volatile memory as it reduces the memory block area by eliminating the requirement for charge pumps. With scaling of the cantilever geometries, the switching speed drops to below 100ns making it very much faster to program and erase than FLASH and SONOS devices. The high activation energies associated with adhesion ensure that the technology is reliable over a wide temperature range. In this paper we discuss how the cantilevers are encapsulated in a wafer scale CMOS process and how the resulting microcavities are qualified. We will discuss how the contact adhesion forces are modeled to give controllable erasure of the cantilever into the 'off' state.

We measured field emission from a silicon nanopillar mechanically oscillating between two electrodes. The pillar has a height of about 200 nm and a diameter of 50 nm, allowing resonant mechanical excitations at radio frequencies. The tunneling barriers for field emission are mechanically modulated via displacement of the gold island on top of the pillar. We present a rich frequency-dependent response of the emission current in the frequency range of 300 ~ 400 MHz at room temperature. Modified Fowler-Nordheim field emission is observed and attributed to the mechanical oscillations of the nanopillar.

This paper presents a unique solution to the inaccuracies produced when thermally scanning various micro and nano systems with thermistor tip scanning thermal microscopy (SThM). Under dc measurement conditions, thermistor tip heating induces perturbations in the measured system that change with sample properties like material and geometry. As a result, normal SThM scans are affected by errors that make it difficult to interpret the 2D-temperature scans of such systems. By coating the SThM tips with a thermally resistive material (100nm of Si₃N₄) we demonstrate that the temperature dependence on sample material and geometry can be minimized and the tip heating problem can be mitigated to that of a constant temperature offset problem. Included are the first images of coated scanning thermal microscopy (C-SThM) as well as a lumped model that describes the basis of the improvement seen in the thermal images.

We present results of room temperature studies of the electrical characteristics of back-gated ultrathin graphite films prepared by mechanical transfer of thin sections of Highly Oriented Pyrolytic Graphite (HOPG) to a Si/SiO₂ substrate. The films studied were quite thin, exhibiting only a few graphene layers (n). Films with thickness in the range 1 < n < 20 were studied, where n has been deduced by Atomic Force Microscopy (AFM) z-scans. The n value deduced by AFM z-scan data was correlated with the n value deduced by Raman scattering data. We discuss at some length, the issue of whether or not Raman scattering can provide a standalone measure of n. Electrical contacts were made to a few of the low n (n = 1,2,3) graphene films. Most graphene films exhibited a nearly symmetric resistance (R) anomaly vs. gate voltage (V_G) in the range 25 < V_G < 110 V; some films exhibited as much as a factor of ~50 decrease in R (relative to the maximum R) with changing VG. An interesting low bias shoulder on the negative side of the resistance peak anomaly was also observed. The devices were fabricated with a lithography free process.

Transmission electron microscopy (TEM) and micro-Raman spectroscopy are key techniques in the structural characterization of carbon nanotubes. For device applications, carbon nanotubes are typically grown by chemical vapor deposition (CVD) on silicon substrates. However, TEM requires very thin samples, which are electron transparent. Therefore, for TEM analysis, CVD grown nanotubes are typically deposited on commercial TEM grids by post-processing. This procedure has two problems: It can damage the nanotubes, and it does not work reliably if the nanotube density is too low. The ability to do TEM directly on as-grown nanotubes lying on the silicon substrate would solve these two problems. In this talk, for this purpose, we fabricate micromachined TEM grids from silicon substrates. Subsequently, we grow nanotubes on these micromachined TEM grids by CVD, and characterize the nanotubes by TEM, micro-Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). We show that these substrates provide a low cost, mass producible, efficient, and reliable platform for direct TEM, Raman, AFM, and SEM analysis of as-grown nanotubes or other nanomaterials on the same substrate, eliminating the need for any post-processing after CVD growth.

Semiconductor nanowires such as zinc oxide nanowires are projected to be the next generation materials for nanoscale sensors and actuators. They also serve as ideal systems for studying material behavior at the small scale. In this paper, we report experimental results on the mechanical properties of zinc oxide nanowires. We have designed a MEMS (microelectromechanical systems) test-bed for mechanical characterization of nanowires and use a microscale version of pick-and-place as a generic specimen preparation and manipulation technique. We performed experiments on zinc oxide nanowires inside a scanning electron microscope (SEM) and estimated the Young's modulus to be approximately 21 GPa and the fracture strain to vary from 5% to 15%. We attribute the difference in mechanical properties of the nanowires from bulk properties to several factors such as lower number of defects, charge redistribution at the atomic scale and surface effects.

We have developed a MEMS-based testing stage that can quantitatively characterize both the electrical and mechanical properties of nanocrystalline metal films. This stage, which is SEM and TEM compatible, is a modified version of an earlier MEMS-based tensile testing stage (M. A. Haque and M. T. A. Saif, Proc. Natl. Acad. Sci., 101(17), 6335-6340 (2004)). This modified stage requires a simpler fabrication procedure, involving fewer lithography and etching steps, and has higher yield compared to the earlier version. It allows for 4-point electrical resistivity measurement, and in-situ tensile testing in SEM and TEM of free-standing nano-scale metal films. The stage was used to perform a tensile test on a 100-nm-thick aluminum film and electrical resistivity measurement on a 110-nm-thick aluminum film, the results of which are described.

We describe experimental results from micromechanical resonators coated with chemoselective polymers that detect chemical vapors from volatile organic compounds or explosives using all-optical interrogation. The shift in the resonant frequency of a gold microbeam is read-out using photothermal actuation and microcavity interferometry. For detection of toluene vapor, response times of less than 5 seconds are achieved for vapor concentrations as low as 60 ppm. For detection of TNT vapor, concentrations as low as 10 ppb are detected in 100 seconds. An analysis of the measured frequency noise in these sensors shows that it is dominated by thermal-mechanical fluctuations at the fundamental flexural mode. Our measurements thus indicate that thermal-mechanical frequency noise is the primary intrinsic detection limit for typical resonant-frequency MEMS biosensors or chemical vapor sensors.

A central problem in the development of mechanical devices and systems is accurate and fast motion sensing. We demonstrate an integrated and near-field optical displacement sensing technique based on optical evanescent wave coupling. Exploiting the strong dependence of waveguide-to-waveguide coupling to changes in separation between waveguides we were able to detect in- and out-of-plane mechanical motions of a mechanical resonator. We have studied the sensitivity of the proposed motion detection technique with a 3D full-vectorial mode solver and make predictions on the attainable displacement detection limits based on a noise analysis. This work demonstrates both the feasibility and the effectiveness of integrating nanomechanical devices with photonic circuitry.

This paper reports our effort to develop amorphous hydrogenated silicon carbide (a-SiC:H) films specifically designed for MEMS-based microbridges using methane and silane as the precursor gases. In our work, the a-SiC:H films were deposited in a simple, commercial PECVD system at a fixed temperature of 300°C. Films with thicknesses from 100 nm to 1000 nm, a typical range for many MEMS applications, were deposited. Deposition parameters such as deposition pressure and methane-to-silane ratio were varied in order to obtain films with suitable residual stresses. Average residual stress in the as-deposited films selected for device fabrication was found by wafer curvature measurements to be -658 ± 22 MPa, which could be converted to 177 ± 40 MPa after thermal annealing at 450°C, making them suitable for micromachined bridges, membranes and other anchored structures. Bulk micromachined membranes were constructed to determine the Young's modulus of the annealed films, which was found to be 205 ± 6 GPa. Chemical inertness was tested in aggressive solutions such as KOH and HF. Prototype microbridge actuators were fabricated using a simple surface micromachining process to assess the potential of the a-SiC:H films as structural layers for MEMS applications.

Comb drive microactuators are widely used in MEMS devices. Most of the comb drives reported in MEMS field are made using fabrication technology with silicon as structural material. Recent development in UV lithography of SU-8 has made it possible to fabricate the ultra high aspect ratio microstrucres with excellent sidewall quality. In this paper, we report a low cost alternative to the silicon based comb drive by using cured SU-8 polymer as structural material. To achieve electrical conductivity in cured SU-8, a new approach to selectively electroless plate metal on high aspect ratio cured SU-8 polymer microstructures is also reported. In this approach, UV light source was used to activate surfaces of the cured SU-8 microstructures. Selective electroless plating of metals on cured SU-8 was achieved by controlling the UV exposure dosage. The technologies for fabrication of comb drive microactuators based on SU-8 polymer as main structural material were sucessfully developed. Preliminary experimental results have proved the feasibility of the microactuator and the fabrication technology.

We report on the on-chip integration of a valve and pump for acquiring microfluidic samples and moving them through micro-channels. The valve employs temperature-sensitive hydrogels which are controlled by micro-heaters. The pump is a nickel rotor actuated magnetically by an external rotating magnet. The valve is fabricated as a series of hydrogel rings spaced within microfluidic channels. The expanded state of the hydrogel cylinders at low temperatures blocks liquid flow. Upon application of heat, the hydrogels contract in volume allowing liquid to flow through them. The pump brings about a recirculating movement of the liquid within the microchannel due to the rotation of the nickel rotor. The device is fabricated by combining liquid phase photopolymerization of structural polymers and temperature responsive hydrogels, with nickel electroplating. The valve has a response time of ~45 s and the pump generates a flow rate of ~1 μL/min.

Microbolometers and other thermal detectors have traditionally been limited to seeing objects in a broad wavelength band at a single sensitivity. Recent advances in interface heat transfer and optical cavity design promise to change that. In this paper, we present recent work on thermal infrared detectors with tunable responsivity and wavelength. First, we demonstrate that extended dynamic range in thermal detectors can be achieved by electrostatically bringing a portion of the detector support structure in contact with the substrate. The exact amount of heat transfer can be controlled by adjusting the contact area and pressure. The thermal conductance and responsivity can be switched more than an order of magnitude using this technique. Next, we demonstrate that a wavelength tunable device in the LWIR can be achieved by modifying the structure of a microbolometer to incorporate a modified Gires Tournois optical cavity. The cavity couples light at a single wavelength into the microbolometer while other wavelengths are rejected. We demonstrate that resonance can be tuned from 8.7 to 11.1 &mgr;m with applied voltages from 0 to 42 V. The FWHM of the resonance can be switched between around 1.5 &mgr;m in a narrow-band mode and 2.83 &mgr;m in a broad-band mode.

A translationally-scanning mirror is always desired for the axial scanning in optical coherence tomography (OCT), but conventional scanners are bulky and have relatively slow scanning speed. This paper reports a micromirror that has the potential to achieve both the scanning speed and range required by OCT. The large piston motion of the micromirror is obtained using a large-vertical-displacement (LVD) microactuator. The device is fabricated using a deep-reactive-ion-etch (DRIE) CMOS-MEMS process. A pair of electrothermal bimorph actuators is employed to achieve tilt-free mirror plate and large piston motion. A linear voltage divider with a voltage ratio of 1:2.3 between the two electrothermal actuators has been used to obtain static displacements up to 200 &mgr;m. The frequency response of this device was obtained using a laser Doppler vibrometer, and resonant peaks were observed at 1.18 and 2.62 kHz. AC signals at 50 Hz with a voltage ratio of 1:1.2 were supplied to the actuators, and the maximum dynamic piston motion was measured to be 26 &mgr;m. The decreasing amplitude over increasing frequency was caused by the heat-sink effect of the mirror plate. A phase delay between the two actuators was also observed.

Micromachined waveguide Fabry-Perot cavities are demonstrated. The devices are fabricated in silicon-on-insulator using a cryogenic dry-etch process, enabling large aspect ratios with high verticality and low surface roughness (⩽10 nm). Details of the process development are presented with emphasis on our specific device application. The Fabry-Perot cavities consist of shallow-etched rib waveguides and deep-etched silicon/air distributed Bragg reflector (DBR) mirrors. The high-index-contrast mirrors enable large reflectance with only a few mirror periods. High Q-factor (Q≈27,000) and large finesse (F≈500) were measured. We demonstrate thermo-optic tuning over &Dgr;&lgr;=6.7 nm and also examine modulation of the cavity (f=150 kHz). Future improvements and application areas of this device are discussed.

Porous Silicon (PS) has many interesting and unique properties that make it a viable material in the field of MEMS. In this paper we investigate the application of PS in improving the sensitivity of bulk micromachined piezoresistive pressure sensors. A part of the silicon membrane thickness has been converted into PS by electrochemical etching in HF based electrolyte. The property of low Young's modulus of PS and its dependence on porosity have been exploited in obtaining higher sensitivity compared to pressure sensors with single crystalline silicon membranes. The sensitivity is found to increase with the porosity and thickness of PS layer and these can be easily controlled by varying the PS formation parameters.

This paper focuses on the design and development of a novel MEMS based force sensor for use in a smart electrical switch which can be used to sense forces applied during the disconnection/connection of the switch. Sensed forces will permit the power to the switch to be turned on/off electronically to prevent arcing at 42 Volts, which would otherwise damage the switch electrical contacts. This paper focuses on the design of a packaging cover for the switch incorporated with a meso-structure, for input force reduction, using a Stereolithography fabrication process. This packaging cover will be installed on a standard ceramic pin grid array (PGA) package to which a MEMS force sensor will be wire-bonded. The complete sensor is proposed for use in smart electrical connectors within automobiles. The purpose of the packaging cover is to transform the macroscopic input force imparted by a technician during disconnection or connection of the switch into a grasping action on the sensor. The macroscopic input force is estimated to be 60N at maximum. To prevent potential damage on the MEMS sensor, the cover converts the applied force to a smaller force in the milli-Newton scale. Since the sensor is to be operated under the harsh environment of the automobile, transverse comb-drive capacitors are selected as the force sensing technique. The capacitive MEMS sensor will be fabricated using PolyMUMPs surface micromachining. To ensure linearity, the displacement of the comb drive is limited to 1 &mgr;m for a net capacitance change of 0.013 pF. Principles of strain energy and Castigliano's Theorem are used to model the proposed cover design. It is found that for a 60 N input force, the design is capable of converting that force to a lateral displacement of 30.86 &mgr;m, which is equivalent to a 0.01 N force onto the sensor. Design analysis, and results from Finite Element Method (FEM) simulation of the cover design will be presented in this paper.