MEMS micromirrors for imaging applications

Strathclyde theses - ask staff. Thesis no. : T13478Optical MEMS (microelectromechanical systems) are widely used in various applications. In this thesis, the design, simulation and characterisation of two optical MEMS devices for imaging applications, a varifocal micromirror and a 2D scanning micromirror, are introduced. Both devices have been fabricated using the commercial Silicon-on-Insulator multi-users MEMS processes (SOIMUMPs), in the 10 m thick Silicon-on-Insulator (SOI) wafer. Optical MEMS device with variable focal length is a critical component for imaging system miniaturisation. In this thesis, a thermally-actuated varifocal micromirror (VFM) with 1-mm-diameter aperture is introduced. The electrothermal actuation through Joule heating of the micromirror suspensions and the optothermal actuation using incident laser power absorption have been demonstrated as well as finite element method (FEM) simulation comparisons. Especially, the optical aberrations produced by this VFM have been statistically quantified to be negligible throughout the actuation range. A compact imaging system incorporating this VFM has been demonstrated with high quality imaging results. MEMS 2D scanners, or scanning micromirrors, are another type of optical MEMS which have been widely investigated for applications such as biomedical microscope imaging, projection, retinal display and optical switches for telecommunication network, etc. For large and fast scanning motions, the actuation scheme to scan a micromirror in two axes, the structural connections and arrangement are fundamental. The microscanner introduced utilises two types of actuators, electrothermal actuators and electrostatic comb-drives, to scan a 1.2-mm-diameter gold coated silicon micromirror in two orthogonal axes. With assistance of FEM software, CoventorWare, the structure optimisation of actuators and flexure connections are presented. The maximum optical scan angles in two axes by each type of actuator individually and by actuating the two at the same time have been characterised experimentally. By programming actuation signals, the microscanner has achieved a rectangular scan pattern with 7° 10° angular-scan-field at a line-scan rate of around 1656 Hz.Optical MEMS (microelectromechanical systems) are widely used in various applications. In this thesis, the design, simulation and characterisation of two optical MEMS devices for imaging applications, a varifocal micromirror and a 2D scanning micromirror, are introduced. Both devices have been fabricated using the commercial Silicon-on-Insulator multi-users MEMS processes (SOIMUMPs), in the 10 m thick Silicon-on-Insulator (SOI) wafer. Optical MEMS device with variable focal length is a critical component for imaging system miniaturisation. In this thesis, a thermally-actuated varifocal micromirror (VFM) with 1-mm-diameter aperture is introduced. The electrothermal actuation through Joule heating of the micromirror suspensions and the optothermal actuation using incident laser power absorption have been demonstrated as well as finite element method (FEM) simulation comparisons. Especially, the optical aberrations produced by this VFM have been statistically quantified to be negligible throughout the actuation range. A compact imaging system incorporating this VFM has been demonstrated with high quality imaging results. MEMS 2D scanners, or scanning micromirrors, are another type of optical MEMS which have been widely investigated for applications such as biomedical microscope imaging, projection, retinal display and optical switches for telecommunication network, etc. For large and fast scanning motions, the actuation scheme to scan a micromirror in two axes, the structural connections and arrangement are fundamental. The microscanner introduced utilises two types of actuators, electrothermal actuators and electrostatic comb-drives, to scan a 1.2-mm-diameter gold coated silicon micromirror in two orthogonal axes. With assistance of FEM software, CoventorWare, the structure optimisation of actuators and flexure connections are presented. The maximum optical scan angles in two axes by each type of actuator individually and by actuating the two at the same time have been characterised experimentally. By programming actuation signals, the microscanner has achieved a rectangular scan pattern with 7° 10° angular-scan-field at a line-scan rate of around 1656 Hz

DYNAMIC ATOMIC FORCE MICROSCOPY RESOLVED BY WAVELET TRANSFORM

Atomic Force Microscopy (AFM) is perhaps the most significant member of the scanning probe microscopes family and, because of its capability of working in air and liquid environments with virtually no limitations on imaging conditions and types of samples, it is definitely one of the most widely used. It has become an indispensable tool to measure mechanical properties at the nanoscale in various research contexts. Scanning probes used in AFM are micromechanical oscillators (typically cantilevers) and the theory of AFM dynamics is based on the analysis of the oscillating modes of beam resonators or the simpler spring-mass model. Cantilevers can be driven by the thermal excitation and/or an external driver. Usually cantilevers are driven near resonances corresponding to flexural eigenmodes that can be described as damped harmonic oscillators. Advanced techniques consider multifrequency excitation or band excitation to broaden the measurable events in tip-sample interactions, thus expanding the variety of sample properties that can be accessed. Multifrequency methods imply excitation and/or detection of several frequencies of the cantilever oscillations and concern the associated nonlinear cantilever dynamics. Such excitation/detection schemes provide higher resolution and sensitivity to materials properties such as the elastic constants and the sample chemical environment with lateral resolution in the nanometer range. In order to measure these parameters, information on peak force of interaction, energy dissipation and contact dynamics is required. Techniques to measure the parameters of the cantilever in the stationary regime are well established. In dynamics methods the external driver (thermal noise, piezoelectric driver, etc.) excites the cantilever and a number of techniques have been implemented to gain information from the tip-sample interactions, but usually the interaction of the tip with the surface is revealed by the modification of the average value of the amplitude, frequency or phase shift over many oscillation cycles. Reconstruction of the complete evolution of the interaction force between the tip and the sample surface during a single interaction event is not even considered. As an alternative to these well established techniques and to push further the AFM possibilities, it is important to examine the possibility of analyzing single-event or impulsive interactions. This opens the possibility to capture the information conveyed by the sensing tip in a single interaction, in contrast to the cycle average used in many dynamic techniques. The single-event interactions are basically of the impact kind, with the simultaneous excitation of many cantilever eigenmodes and/or harmonics. The averaging techniques provide superior sensibility, allowing to probe the details of force interactions down to the molecular level, but to study single-event interactions it is mandatory to provide analysis techniques that are able to characterize all excited cantilever oscillation modes at once without averaging. The temporal evolution of the amplitude, phase and frequency during few oscillation cycles of the cantilever provides information that cannot be obtained with standard methods. In the present thesis a data analysis method allowing to retrieve these quantities during an impulsive cantilever excitation is proposed. This thesis concentrates on the dynamics of the flexural modes of the thermally driven cantilever in air when its tip is excited by a single impact on the sample surface. The signal analysis is based on the combination of wavelet and Fourier transforms that can be applied to a broad class of AFM impulsive measurements. To exemplify the method, a short time interval around the jump-to-contact (JTC) transition in ambient conditions is investigated, with the aim to characterize the transient excitation of the cantilever eigenmodes before and after the impact. The experimental evidences that high-order flexural modes are excited in air upon a single impact tip\u2013sample interaction induced by the JTC transition are presented. The way to retrieve information about the instantaneous total force act ing on the cantilever tip, contact dynamics and energy dissipation at all frequencies simultaneously, without averaging or interruption, is developed. The exploration of these transient conditions of the cantilever is not possible with dynamic techniques based on the resonant driving or using Fourier transform analysis alone. The analysis presented in this work is useful to deal with nonrepeatable experiments and to determine the exact single interaction dynamics in terms of the full cantilever spectral excitations, features that are not normally considered in dynamical AFM techniques

MEM Resonators for RF Applications and Chemical Sensing

In this thesis modelling, design, fabrication and characterization of MEM (MicroElectroMechanical) resonators for RF applications and chemical sensing are discussed. MEM resonators allow to obtain integrated highly selective filters and low phase noise oscillators for RF applications, as well as sensors of chemical and biological species, which can be used to obtain a sensor array on a chip, leading to the possibility of very complex analysis in a very small space. Specifically, a novel RF device, namely a free-free resonator on the third mode, is presented and its basic working is demonstrated. Effect of temperature and axial stress on this device and on other flexural resonators is discussed and an equivalent circuit for free-free resonator is proposed. Furthermore, the optimized design of a bulk-mode disk resonator is presented. The goal of this optimization is the achievement of the maximum quality factor (i.e. maximizing selectivity in filter architecture or minimizing the phase noise in resonator-based oscillators) at a target resonance frequency. The maximization is based on an original strategy of estimation of the quality factor of the device through FEM simulations. Finally, the design of an innovative microbalance is presented. The main features of this device are the actuation and the sensing, which are both magnetic. The device has been fabricated with a CMOS-compatible process. The frequency response of the device was measured, showing the basic working of the device

NASA Tech Briefs, June 2000

Topics include: Computer-Aided Design and Engineering; Electronic Components and Circuits; Electronic Systems; Test and Measurement; Physical Sciences; Materials; Computer Programs; Computers and Peripherals

Program for Technical Sessions Third International Conference on Mars Polar Science and Exploration

Contains the contents, program, abstracts, and indexes for the Third International Conference on Mars Polar Science and Exploration. The purpose of the conference is to assess the current state of Mars polar and climate research; discuss what might be learned from investigations of terrestrial analogs and the data returned from upcoming missions; and identify the potential science objectives, platform options, and instrument suites for robotic missions to the martian poles within the next decade.Lunar and Planetary Institute; National Aeronautics and Space Administration; Canadian Space Agency; International Glaciological Society; Geological Survey of Canada; University of Alberta, Department of Earth and Atmospheric Sciences; NASA Mars Program OfficeConveners, Stephen Clifford, Lunar and Planetary Institute, Peter Doran, University of Illinois at Chicago, David Fisher, Geological Survey of Canada, Christopher Herd, University of Albert

Electro-Hydrodynamic Spot-Spray Application of Food-Grade Oil & Emulsifier Blends As a Release Agent in Baking

In industrial baking, vegetable oil is used as a release agent for bread depanning. The conventional process of applying oil uses pressure and shear to atomize the oil. This works but generates over-spray and, thus, creates a sanitation problem and a potential food safety risk. The objective of this research project is to determine if the four major commercially available vegetable oils (Palm oil, Soybean Oil, Rapeseed oil, Sunflower Oil) can be made, by the introduction of an emulsifier/surfactant, to carry an electrical charge greater than the Rayleigh point so that they can be electro-hydrodynamically (EHD) atomized. Coulombic attraction pulls the atomized liquid to the target without the problem of over-spray. To accomplish this, each base oil was blended with a surfactant (Lecithin, Polysorbate, Propylene Glycol) at concentrations of 5% and 10%. The solution was sprayed through a capillary tube (19ga, 22ga) in a spot spray mode onto oil sensitive paper at 25kV and 50kV at varying temperatures and pressures. An ANOVA of the DOE structured experiment was performed to analyze the inputs (concentration, voltage, temperature, and pressure) relative to the outputs (droplet count, droplet size, coverage area, and sample weight) to determine the performance of the experiment at different interaction points.Twenty-four separate experiments involving 865 individual tests provided the data to determine EHD viability for each oil and emulsifier blend. The criteria of average droplet count >200/in2, average droplet size <1mm2, average coverage area between 15%-60%, and average sample weight <0.2g was used as a minimum target for success. Every experimental group tested with a 22ga capillary tube met or exceeded the target. Tests using the 19ga capillary produced generally poor results. From this, it was determined that energy density relative to mass flow was a determining factor in successful EHD atomization. Energy density relative to mass flow, at the given input 2.5 and 5 Joules followed the exponential regression of respectively Ed=6ṁ(-1.004)·102 and Ed=6ṁ(-1.004)·104 respectively. Based on the success of all four base oils with all three emulsifiers, it is reasonable to assume that other oils/emulsifiers might follow the same energy density curve.Biosystems and Agricultural Engineerin