Papers

AVS2001 Session MM+BI+NS+EL+SS-FrM: New Frontiers in MEMS: NEMS and BioMEMS

Friday, November 2, 2001 8:20 AM in Room 130

Friday Morning

Start	Invited?	Item
8:20 AM		MM+BI+NS+EL+SS-FrM-1 Optomechanical Effects in and Properties of Nanomechanical Resonant Structures L. Sekaric, M. Zalalutdinov, S.W.P. Turner, A.T. Zehnder, J.M. Parpia, H.G. Craighead (Cornell University) Recently we reported optical excitation and parametric amplification¹ of single-crystal silicon MEMS oscillators with resonant frequencies up to 1MHz. Utilizing the interferometric pattern of a laser beam in a Fabry-Pérot cavity formed by the oscillator, we demonstrated a mechanism which can be used both as a driving/amplification scheme and a detection scheme. Here we report observation of this phenomena in single-crystal silicon nanomechanical oscillators with frequencies up to 25MHz and with dimensions up to 2um. High mechanical quality factors (Qs) of these structures were instrumental in enabling us to observe these phenomena. Qs of micron-scale and sub micron structures have been observed to have been relatively low (~ 10³) as measured in vacuum and at room temperature. We succeeded in improving the Qs of these devices (~ 10⁴) at room temperature and high vacuum. We will describe the bulk and surface treatments used to achieve high Q. In addition, these structures act as passive modulators of the laser light at their resonant frequencies. The sensitivity of the measurement technique and the inherent amplification of the motion via the optical drive presents us with a very efficient interferometer/modulator easily integrable on chip. Our initial modeling shows that the laser power needed to set these devices into oscillation is only up to few tens of microwatts. Our long-standing interest in nanomechanical structures fabricated in different materials, presents us with a natural extension for our current and future work - clearly being at an advantage of using this driving scheme even with electrically insulating device layers and with no theoretical frequency limit. ¹ M. Zalalutdinov, A. Olkhovets, A. Zehnder, B. Ilic, D. Czaplewski, H. G. Craighead, and J. M. Parpia, "Optically pumped paramagnetic amplification for micromechanical oscillators" , Appl. Phys. Lett., Vol. 17 (16) 181 (2001)).
8:40 AM		MM+BI+NS+EL+SS-FrM-2 Micromechanical Cantilever Magnetometers with Integrated Quantum Dots M. Wilde, M. Schwarz, D. Grundler, C. Heyn, D. Heitmann (University of Hamburg, Germany) We have prepared highly sensitive micromechanical cantilever magnetometers with integrated semiconductor quantum dots. They allow us to study, for the first time, the very tiny magnetic moment of the quantum dots which contain only a few 100 electrons. We have used GaAs-AlAs-molecular beam epitaxy with its inherent atomic precision, both, for the optimization of the mechanical properties of the cantilever and for the monolithic integration of the investigated electronic nanostructures.¹ Using laser-interference lithography, tailored periodic arrays of quantum dots have been prepared on the beam. Experiments have been performed down to a temperature of 250 mK in a magnetic field up to 16 T. Field-induced magnetic oscillations have been observed on the quantum dots. The magnetization is significantly different from that of the two-dimensional reference sample and exhibits several new features. Our results suggest that, both, the quantum confinement and the effect of electron-electron interaction have an important effect on the magnetic moment of the quantum dots. Support by the Deutsche Forschungsgemeinschaft Gemeinschaft via Sonderforschungsbereich SFB 508 is gratefully acknowledged. ¹ M. Schwarz, D. Grundler, I. Meinel, Ch. Heyn, and D. Heitmann, Appl. Phys. Lett. 76, 3564 (2000).
9:00 AM		MM+BI+NS+EL+SS-FrM-3 Nano-Electromechanical Systems: Physics and Applications R.H. Blick (Ludwig Maximilians University, Munich, Germany) Mechanical devices in combination with modern semiconductor electronics offer great advantages as for example their robustness against electrical shocks and ionization due to radiation. The main disadvantage of mechanical devices so far is the low speed of operation. This has been overcome with the realization of nanomechanical systems (NEMS), which allow operation at frequencies up to 500 MHz. I will discuss recent work on such nanomechanical resonators focussing on nonlinear dynamics, mechanical mixing, parametric resonance, and possible uses in quantum squeezing experiments. Furthermore, I will present record mechanical quality factors of Q > 10000. Finally, I will outline an approach to using NEMS for applications in biology (Bio-NEMS).
9:40 AM		MM+BI+NS+EL+SS-FrM-5 Zeptonewton Force Detection at Millikelvin Temperatures H.J. Mamin, D. Rugar (IBM Almaden Research Center) Scanning force microscopes routinely operate with forces in the piconewton range, but new applications such as cantilever-based magnetometry and magnetic resonance force microscopy demand force resolutions that can be a million times smaller. The minimum detectable force is ultimately limited by the dissipation in the cantilever and its temperature. We have pushed this limit by cooling a single-crystal silicon cantilever in vacuum to a temperature below 100 mK. To sense the sub-angstrom thermal-mechanical motion with minimal heating of the cantilever, an improved optical fiber interferometer was developed that could be operated at optical powers as low as 2 nW. The cantilever mean square amplitude of vibration showed the expected linear dependence on temperature down to 400 mK, at which point other noise sources became significant. At the lowest temperature, the cantilever achieved a noise temperature of 220 mK, with a corresponding force noise of 820 zeptonewtons in a 1 Hz bandwidth.
10:00 AM		MM+BI+NS+EL+SS-FrM-6 Chemical Detection Based on Nanostructured MEMS Sensors P.G. Datkos (Oak Ridge National Laboratory); M.S. Sepaniak, N. Lavrik, C.A. Tipple (University of Tennessee) The recent advent of MEMS devices has opened-up new possibilities for chemical detection. Microcantilevers respond to chemical stimuli by undergoing changes in their bending when molecules adsorb on their surface. Increased effective surface area is important in such systems because it results in increased total energy of interfacial interactions. In fact, in nanostructured surfaces (quasi 3-D interfaces) the effective surface stresses can significantly exceed true surface stresses. We used electron beam lithography to fabricate ordered nanofeatures on the surfaces of a microcantilever, We then functionalized the nanostructured surface with a beta-cyclodextrine coating (to impart chemical selectivity) using self-assembled monolayer techniques. We found an increase of two orders of magnitude when nanostructured coatings have been used. We present and discuss our findings on the interactions of functionalized microcantilevers with tetrachloroethylene molecules.
10:20 AM		MM+BI+NS+EL+SS-FrM-7 Biomedical Microsystems for Minimally Invasive Medical Procedures S. Roy (The Cleveland Clinic Foundation) Traditional surgery for many medical problems, including gallstones, endometriosis, and various cancers, usually requires long, deep incisions and a lengthy recovery period. Minimally invasive surgery, also known as "keyhole" or "band-aid" surgery, has been used for several years as an alternative to traditional "open" surgery. Minimally invasive procedures for both diagnostics and therapeutics have generated much attention from clinicians, patients, and healthcare administrators for their ability to reduce patient pain, scarring, and hospital stays. Current tools for minimally invasive procedures typically tend to operate as mechanical appendages of the clinician, but with absence to touch-and-feel sensations and only limited vision. The ability of MEMS technology to develop miniature, low-cost, and sophisticated transducers is particularly attractive for the development of smart surgical tools that enhance clinical efficacy. The talk will present an overview of current and upcoming applications of MEMS technology in cardiology, neurology, and orthopedics that are under development at The Cleveland Clinic Foundation and other institutions. Device examples will include pressure sensors, accelerometers, strain gauges, flow meters, valves, pumps, imaging transducers, drug delivery systems, and cutting tools.
11:00 AM		MM+BI+NS+EL+SS-FrM-9 Fabrication Process and Resulting Structures for a Micron-Scale Force-Detected Nuclear Magnetic Resonance (NMR) Spectrometer L.A. Madsen, G.M. Leskowitz, D.P. Weitekamp (California Institute of Technology); W. Tang, T. George, K. Son (NASA Jet Propulsion Laboratory) NMR is the most widely used method of analysis of chemical structure and dynamics at the millimeter length scale. In order to overcome the inherent poor sensitivity of traditional inductively detected NMR for small samples, we are developing the novel BOOMERANG¹ method of force-detected NMR in a homogeneous magnetic field. Our experimental NMR results on liquid and solid 3 mm samples with a prototype spectrometer motivate the scaling of our detectors to observe samples < 100 microns in diameter. Achieving micron-scale detectors will bring about inexpensive NMR spectrometers with superior sensitivity for in-situ analysis, sub-monolayer surface NMR, and massively parallel studies on sample libraries. Ultimately, scaling of these detectors to the nano-scale may allow single-molecule NMR spectroscopy and imaging. We present a microfabrication process for BOOMERANG NMR detectors. This double-sided process utilizes deep RIE to define a Si beam fixed at both ends with a stress buttress at its center. High-aspect ratio NiFe or CoNiFe magnet structures are electrodeposited onto the backside of this beam. A combination of photoresist and oxide sacrificial layers allows ~1 micron spacing between a field compensation magnet and the moving detector magnet, and between the compensation magnet and the Si beam. Initial results of the 6-mask process are promising. We present patterned, electrodeposited magnets on the micro-oscillator substrate, as well as our efforts to characterize the micro-detectors and improve device yield. ¹ Sol. St. Nucl. Magn. Reson. 11, 73 (1998).