bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anelastic Creep Phenomena in Thin Metal Plated Cantilevers for MEMS
Authors: Vickers-Kirby Deborah J. , Kubena Randall L. , Stratton Frederic P. , Joyce Richard J. , Chang David T. , Kim Jinsoo 
Published: April 2011

ABSTRACTDuring the past several years, we have developed high displacement sensitivity tunneling accelerometers using surface micromachining and metal electroplating techniques. These devices consist of a Au tunneling tip fabricated below a 1-2 μm thick metal cantilever beam of electroplated Ni or Au. A thin film of e-beam evaporated Au on the underside of the cantilever serves as the tunneling counter electrode. In operation, a 100mV bias is applied across the tunneling gap. A larger turn-on voltage is also applied between the cantilever and a control electrode, located on the substrate, to deflect the cantilever and maintain a constant tunneling current of 1 or 10 nA. Typical deflections of the end of 100 μm-long and 250 μm-long cantilevers are 0.5μm during operation. We have observed that the turn-on voltage decreases over time for most devices with a larger drop observed for the Au cantilevers. In all cases, the initial decay of the turn-on voltage was almost completely recoverable after the device was turned off for 24 hrs. This decay was not found to be strongly dependent on the magnitude of the tunneling current, but could be significantly reduced by pre-stressing the cantilever before operation. Finally, a vacuum anneal at 100°C influences the measured temperature dependence of the turn-on voltage. The observed effects appear to be consistent with fatigue and creep phenomena in the cantilevers. These effects are reversible at room temperature and are dependent on the stress and temperature history of the devices. A comparison is made between metal plated and all-Si structures.
Defects and Failure Modes in PZT Films for a MEMS Microengine
Authors: Bahr D.F. , Crozier B.T. , Richards C.D. , Richards R.F. 
Published: April 2011

ABSTRACTPiezoelectric films for a MEMS microengine have been deposited using solution deposition routines onto platinized silicon wafers. These films are used as membranes above a bulk micromachined cavity. A dynamic bulge tester and interferometer were used to characterize the deformation of the films when pressurized. The mechanical strain at failure, as well as the fatigue behavior, have been characterized. Membranes between 300 and 500 nm thick have been shown to sustain mechanical fatigue damage over approximately 10 million cycles at strains of 30% of the monotonic failure strain. Defects in the films due to growth and thermal stresses during processing, and their role in membrane failure, are identified. Crack growth is demonstrated in these films by compliance measurements during fatigue testing, and interfacial failure is identified between the PZT and Pt layers.
Etch Rate and Surface Morphology of Plasma Etched Glass Substrates
Authors: Liu Junting , Nemchuk Nikolay I. , Ast Dieter G. , Couillard J. Gregory 
Published: April 2011

ABSTRACTMicro-machined transparent components are of interest for optical MEMS and miniaturized biological systems. The glass ceramic GC6 developed by Corning is optically transparent, has a softening point in excess of 900°C, and a thermal expansion coefficient matched to silicon. These properties make it useful for the construction of devices that combine thin film silicon electronics with MEMS systems.Both the ceramic precursor (green glass) and the glass ceramic etch at a similar rate, about 1/3 to 1/4 of that of SiO2 etched under the same conditions, indicating that chemistry rather than microstructure control the etch rate. The cleaning steps used to clean the glass precursor profoundly influence the degree of surface roughness that develops during subsequent plasma etching. In glass ceramics, the morphology of plasma etched surface is always very smooth and independent of the cleaning steps used. Assuming that the removal of spinel crystals is the rate limiting step in plasma etching glass ceramics can explain this observation.
Issues in the Flexible Integration of Sputter-Deposited PZT Thin Films with Polysilicon and Ti/Pt Electrode Layers for Use as Sensors and Actuators in Microelectromechanical Systems (MEMS)
Authors: Knollenberg C.F. , Sands T.D. , Nickles A.S. , White R.M. 
Published: April 2011

ABSTRACTSputter-deposited piezoelectric lead zirconate titanate (PZT) thin films with Ti/Pt and polysilicon electrode layers are being investigated for use in Microelectromechanical Systems (MEMS). Existing research shows the nucleation of the perovskite phase of the PZT is linked to the lattice spacing of the underlying Pt electrode and/or seed layers, and is key in obtaining PZT layers with good piezoelectric/ferroelectric properties. Our research with piezoelectric PZT films on Ti/Pt electrode layers aims at employing these films to generate and receive acoustic waves in flexural plate wave devices (FPWs). Our experiments indicate the formation of a random polycrystalline perovskite phase is linked to the emergence of oriented <100> Pt grains within the dominant <111>-oriented crystal structure during rapid thermal annealing in an oxygen environment. Pt films annealed in nitrogen, in contrast, retained their <111> preferential orientation without the formation of Pt <100> grains. PZT films deposited on these electrodes and annealed in nitrogen were strongly oriented in the <111> direction, but exhibited lossy ferroelectric behavior and were prone to delamination. We are also investigating the feasibility of using doped polysilicon electrode layers with PZT thin films. The multiple layers used with the Pt electrode (Pt, Ti, and SiO2 adhesion layer) have significant interactions with one another, and replacing these layers with a single electrode layer should alleviate these complications. A low-temperature PZT deposition process (300°C) and short annealing cycles (30 sec.), coupled with a TiO2 barrier/seed layer should prevent interdiffusion and reactions between the polysilicon and PZT layers. Our experiments show that PZT films deposited and annealed on doped polysilicon layers develop a random polycrystalline perovskite phase, but are subject to tensile cracking. The use of polysilicon as an electrode layer should also facilitate the integration of piezoelectric PZT layers with polysilicon surface micromachined structures using SiGe sacrificial layers.
Developing a New Material for MEMS: Amorphous Diamond
Authors: Sullivan J. P. , Friedmann T. A. , de Boer M. P. , LaVan D. A. , Hohlfelder R. J. , Ashby C. I. H. , Dugger M. T. , Mitchell M. , Dunn R. G. , Magerkurth A. J. 
Published: April 2011

ABSTRACTAmorphous diamond is a new material for surface-micromachined microelectromechanical systems (MEMS) that offers promise for reducing wear and stiction of MEMS components. The material is an amorphous mixture of 4-fold and 3-fold coordinated carbon with mechanical properties close to that of crystalline diamond. A unique form of structural relaxation permits the residual stress in the material to be reduced from an as-deposited value of 8 GPa compressive down to zero stress or even to slightly tensile values. Irreversible plastic deformation, achieved by heat treating elastically strained structures, is also possible in this material. Several types of amorphous diamond MEMS devices have been fabricated, including electrostatically-actuated comb drives, micro-tensile test structures, and cantilever beams. Measurements using these structures indicate the material has an elastic modulus close to 800 GPa, fracture toughness of 8 MPa.m½, an advancing H2O contact angle of 84° to 94°, and a surface roughness of 0.1 to 0.9 nm R.M.S. on Si and SiO2, respectively.
Preparation of Mesoporous Oxides for Mems Structures
Authors: Paik Jong-Ah , Kitazawa Nobuaki , Fan Shih-Kang , Kim Chang-Jin , Wu Ming C. , Dunn Bruce 
Published: April 2011

ABSTRACTThe high porosity and uniform pore size provided by mesoporous oxide films offer interesting opportunities for MEMS devices that require low density and low thermal conductivity. This paper describes recent efforts at adapting mesoporous films for MEMS fabrication. Mesoporous SiO2 and Al2O3 films were prepared using block copolymers as the structure-directing agents, leading to films which were 70% porous and < 5 nm surface roughness. A number of etchants were investigated and good etch selectivity was observed with both dry and wet systems. Micromachining methods were used to fabricate cantilevers, micro bridges and membranes.
Silicon Germanium Epitaxy: A New Material for MEMS
Authors: Borenstein J.T. , Gerrish N.D. , White R. , Currie M.T. , Fitzgerald E.A. 
Published: April 2011

ABSTRACTA wide array of materials have been investigated as candidate fabrication templates for precision microelectromechanical structures, including boron-diffused silicon, boron-doped epitaxial silicon, polysilicon, silicon-on-insulator, and wafer-thick bulk structures. Here we present the latest fabrication results for epitaxial silicon-germanium alloys, a new class of materials which possess excellent crystalline structure, are compatible with non-toxic etchants in bulk micromachining, and are capable of on-chip integration with electronics. For MEMS applications, silicon-germanium alloy layers are grown using a graded buffer approach, resulting in very high quality micromachined structures. Very low defect densities are obtained through the use of these relaxed buffers. Original etch-stop studies determined that Ge doping provided a very weak selectivity in anisotropic etchants such as KOH and EDP. However, by extending the range of Ge concentration to over 20%, we have found extremely high etch selectivities in a variety of etchants. Unlike boron-doped layers, SiGe exhibits etch stop characteristics in the non-toxic, process compatible solution TMAH. The combination of independence from boron doping concentration and etchant compatibility make SiGe a material which is ideal for integration with on-chip electronics.In this work we present the latest fabrication data on comb-drive resonators built using SiGe epitaxial layers. Process compatibility issues related to wafer curvature, surface finish and reactive-ion-etching chemistries are addressed. An unexpected result of the fabrication process, curvature of released structures, is resolved by annealing wafers after the SiGe deposition. Changes in Young's modulus arising from the high atomic fraction of Ge in the device can be determined by simple beam analysis based on observed resonant frequencies. Overall, build precision for these devices is excellent. We conclude by addressing the remaining challenges for wide-scale implementation of silicon-germanium epitaxial MEMS.
Recrystallization of Nickel and Ni Alloy Substrates for YBCO Coated Conductors
Authors: Nast Rainer , Obst Bernhard , Goldacker Wilfried , Schauer Wolfgang 
Published: April 2011

ABSTRACTTo avoid grain boundary grooving and abnormal grain growth during recrystallization of nickel and Ni alloy substrate tapes, the commonly used high recrystallization temperatures must be lowered.The development of the cube orientation is a nucleation-growth process. So the kinetics of the cube recristallization is strongly temperature dependent, and there is a very marked effect of the stacking fault energy (SFE) of the specific alloy on the activation energy. Concurrently with measurements of the formation kinetics of the cube orientation, the recrystallization texture of Ni (+99,99 wt.%), NiCr10 wt.% and NiMn10 wt.% tapes in dependence on the deformation history, the annealing temperature and time was investigated. Profile rolling to a rectangular rod, without further high temperature annealing, leads to a worse cube texture compared to round swaged rods with an in-plane 200 peak splitting. The increase of the recrystallization temperature and time sharpens the texture due to grain growth, limited by the occurrence of secondary recrystallization when a sample specific temperature is exceeded.In binary Ni alloys the commonly used alloying elements reduce the SFE. This favors the formation of recrystallization twins {122}<212> obstructing the oriented coating. In Mn alloyed tapes this effect is strongly pronounced. The tapes show a good cube texture, but also a high volume fraction of twins due to the low SFE. To suppress the twin formation we investigated ternary Ni based alloys with respect to possibly increased SFE and report first results.
Superconducting Thallium Oxide and Mercury Oxide Films
Authors: Bhattacharya Raghu N. , Yan S. L. , Xing Zhongwen , Xie Yiyuan , Wu Judy Z. , Feldmann Matt , Chen Jun , Xiong Qihua , Ren Z. F. , Blaugher Richard D. 
Published: April 2011

ABSTRACTPreviously we reported on a two-layer electrodeposition process of thallium oxide superconductors that showed transport critical current density above 106 A/cm2 at 77 K in zero field. In this article, we report our effort to convert an electrodeposited thick film of (Tl,Bi,Pb)2(Sr,Ba)2Ca1Cu2Ox to (Hg,Bi,Pb)2(Sr,Ba)2Ca1Cu2Ox by the cation-exchange process. We are also reporting magneto-optical imaging data on Tl oxide superconductor films, which are compared with YBCO. Magneto-optical imaging provides insight into the nature of current flow in the Tl oxide superconductor, and thus, will help us to improve the critical current density in bulk high-temperature superconductor wire or tape.
Phase Relations of the Bi-2201–CuO Pseudobinary Join as a Function of Oxygen Pressure
Authors: Meen James K. , Müller Karoline , Salmeron Celia , Elthon Don 
Published: April 2011

ABSTRACTPhase relations on the join Bi-2201–CuO have been determined as a function of P(O2). Most of the major changes that occur between P(O2) of 1 and 0.01 atm occur in the most oxidizing part of the range. Stoichiometric Bi-2201 occurs only at the most oxidizing conditions and in a narrow temperature range near the solidus. In the Bi-2201–CuO system, the ternary phase that forms has higher Bi:Sr and Cu:Sr than Bi-2201. That phase, Sr14Cu24Oy, and CuO occur in the subsolidus and the invariant point at which they coexist with liquid is a ternary eutectic. The liquid is more Sr-rich than the Bi-2201–CuO join. Decrease in P(O2) produces a change in the Bi- 2201 solid solution so that stoichiometric Bi-2201 does not occur. At P(O2) ≤0.5 atm, all Bi- 2201 solid solutions have Bi:Cu<2 but Bi:Sr near unity and Sr14Cu24Oy does not form. Small amounts of a phase believed to be Bi9Sr11Cu5Ox form under these conditions and the primary phase field of that phase crosses the pseudobinary join and minimum melting is at a ternary tributary reaction point. The liquid there is more Bi-rich than the join. Further decrease in P(O2) causes a continued freezing point depression and enlargement of the CuO primary phase field so that the compositions of multiply-saturated liquids move away from the CuO apex.
Microstructural analysis of the compatibility of solution deposited buffer layers with the TFA process for YBCO
Authors: Salama K. , Sathyamurthy S. , Mironova M. 
Published: April 2011

ABSTRACTIn this paper, the feasibility of applying solution deposition processes for the fabrication of coated conductors has been explored. The crystal and chemical compatibility of the buffer layers processed using metalorganic decomposition with the Y123 deposition using the trifluoroacetate process has been studied. Two buffer layer materials have been used, namely, barium zirconate and strontium titanate. The measured superconducting properties of these conductors were correlated with the microstructure observed on these samples using SEM and cross-sectional TEM. In case of barium zirconate buffer layers, though there exists a very good structural and chemical compatibility between the buffer layer and the Y123, the presence of surface defects in the buffer layer causes compositional heterogeneity and randomly oriented grains in the Y123 film. This leads to poor superconducting properties. In case of strontium titanate buffer layers, due to the excellent crystal and chemical compatibility, and the absence of surface defects, high critical current densities (of the order of 106A/cm2 at 77K and self field) were obtained. However, TEM cross section studies reveals the presence of a significant portions of a-oriented Y123 crystallites which could lead to lower critical current densities. Further studies of the TFA process is required to eliminate the occurrence of a-oriented Y123 in the microstructure. This could lead to further improvements in the properties.
Growth Mechanism of RE-Ba-Cu-O Crystal by Liquid Phase Epitaxy Process
Authors: Nomura K. , Hoshi S. , Yao X. , Nakamura Y. , Izumi T. , Shiohara Y. 
Published: April 2011

ABSTRACTGrowth of YBa2Cu3Oy (YBCO) crystals both on the MgO and the YBCO substrates has been investigated in order to clarify the growth mechanism of the liquid phase epitaxy (LPE) process for the coated conductor. It was found that the slope angle of the growth grain varied with growing in the initial stage of the LPE growth. In the case of the MgO substrate, the slope angle increased with laterally growing the crystal. On the other hand, the slope angle decreased with growing the crystal in the case of the YBCO substrate. This phenomenon with the opposite tendency could be explained by considering the difference in the step-advancing rates between on the MgO and the YBCO surfaces. It was found that the deep and steep valley of the LPE grains due to the slow step-advancing rate on the MgO is the origin of the flux trapping inclusions. It is necessary that the seed films should cover the entire MgO surface without undesired orientation grains and impurity particles in order to obtain the high quality LPE layer.
Texture Formation and Superconducting Properties of YBa2Cu3Ox Thin Films Prepared by Solution Process on LaAlO3 Single Crystals
Authors: Jee Y.-A , Ma B. , Li M. , Fisher B. L. , Balachandran U. 
Published: April 2011

ABSTRACTYBa2Cu3Ox (YBCO) thin films were fabricated by the trifluoroacetate (TFA) process on LaAlO3 (LAO) single crystal in an argon atmosphere. We focused on lowering the heat treatment temperature by decreasing the oxygen partial pressure to adopt the TFA process to metallic substrates. YBCO phase formation was checked by measuring Tc with the inductive method. In-plane and out-of-plane film textures were evaluated by phi-scan and omega scan, respectively. Raman spectroscopy was used to estimate grain connectivity, in-plane texture, and second-phase formation of the films. Although Raman spectroscopy revealed some evidence of cation disorder, the film prepared at 750°C shows a sharp superconducting transition at 91 K and critical current density of 1.3 MA/cm2 at 77 K. Optimal heat treatment temperature was 750°C in the argon atmosphere, which is consistent with the thermodynamic estimate that heat treatment temperature decreases as oxygen partial pressure decreases.
Pb-doped Bi-2212: Homogeneity Area, Oxidation and Effect on jc
Authors: Veresov A. , Pulkin M. , Knotko A. , Putlayev V. , Salje E. K. H. 
Published: April 2011

ABSTRACTThe most promising way to improve jc in superconductors is likely to be a creation of small precipitates in the material during decomposition of supersaturated solid solution. It was recognised recently that Pb-doping of 2212 could have beneficial effect on jc. Bi2.1−xPbxSr2CaCu2O8+d (x=0.1…0.7) was prepared at different temperatures and oxygen partial pressure (pO2=10−3 – 0.21 atm) via nitrate route. The effect of pO2 and Pb-doping on Bi-2212 phase formation was explored with XRD, SEM/EPMA and TEM/SAED. The limit of Pb solubility in Bi-2212 was found to increase with a decrease in pO2 and corresponded to a decrease in x=0.3 at pO2 = 0.21 atm (850 °C) and x=0.6 at pO2 ∼ 10−3 atm (750 °C). TEM study of the as-synthesized solid solutions revealed significant nanoscale inhomogeneity attributed to Pb-segregation. For the samples with x > 0.3 the inhomogeneity quite often looked like a well- ordered wave with the period of about 10 nm. The samples of (Bi,Pb)-2212 processed under pO2 conditions were oxidized at 600–750°C in air for 0.5–60 h in order to cause precipitation of secondary phases from the supersaturated solid solution. Thermogravimetrical study (TG) of the oxidation gave a strong evidence of two stages composing the process. It was found that jc was enhanced by a factor of 2 after annealing at 650°C (i.e. during the first stage of oxidation).
Preparation and Properties of Exfoliated Graphite/Polystyrene Composite
Authors: Xiao Peng , Sun Luyi , Xiao Min , Gong Kecheng 
Published: April 2011

ABSTRACTA composite based on exfoliated graphite (EG) and polystyrene was prepared by polymerization-filling technique. With the argument of the amount of filled EG, the molecular weight of polystyrene in the resulting composite increased and the molecular weight distribution decreased. The glass transition temperature of the polystyrene was determined by dynamic mechanical analysis (DMA) and showed the glass temperature of polystyrene increasing to 123.74°C. The thermal degradation behavior was studied using thermogravimetry (TG) and showed higher thermal stability of the composite than that of pure polystyrene and polystyrene//EG composite prepared by melt-blending. Four-probe instrument and high resistivity meter were used to measure the volume conductivity of the composites. Composites prepared by both polymerization-filling technique and melt-blending exhibit increased electrical conductivity, while composite prepared by polymerization-filling technique has a conductive percolation threshold lower than 2.5wt%.
Intercalated clay nanocomposites: Morphology, mechanics and fracture behavior
Authors: Zerda Adam S. , Lesser Alan J. 
Published: April 2011

ABSTRACTIntercalated nanocomposites of modified montmorillonite clays in a glassy epoxy were prepared by crosslinking with commercially available aliphatic diamine curing agents. These materials are shown to have improved Young's modulus but corresponding reductions in ultimate strength and strain to failure. These results are consistent with most particulate filled systems, The macroscopic compressive behavior is unchanged, although the failure mechanism in compression varies from the unmodified samples. The fracture toughness of these materials is investigated and improvements in toughness values of 200% over unmodified resis are demonstrated. The fracture surface topology is examined using SEM and tappin-mode AFM and showm to be related to the clay morphology of the system.