A. Erbil

High-Q single crystal silicon HARPSS capacitive beam resonators with self-aligned sub-100-nm transduction gaps

This paper reports on the fabrication and characterization of high-quality factor (Q) single crystal silicon (SCS) in-plane capacitive beam resonators with sub-100 nm to submicron transduction gaps using the HARPSS process. The resonating element is made of single crystal silicon while the drive and sense electrodes are made of trench-refilled polysilicon, yielding an all-silicon capacitive microresonator. The fabricated SCS resonators are 20-40 /spl mu/m thick and have self-aligned capacitive gaps. Vertical gaps as small as 80 nm in between 20 /spl mu/m thick silicon structures have been demonstrated in this work. A large number of clamped-free and clamped-clamped beam resonators were fabricated. Quality factors as high as 177000 for a 19 kHz clamped-free beam and 74000 for an 80 kHz clamped-clamped beam were measured under 1 mtorr vacuum. Clamped-clamped beam resonators were operated at their higher resonance modes (up to the fifth mode); a resonance frequency of 12 MHz was observed for the fifth mode of a clamped-clamped beam with the fundamental mode frequency of 0.91 MHz. Electrostatic tuning characteristics of the resonators have been measured and compared to the theoretical values. The measured Q values of the clamped-clamped beam resonators are within 20% of the fundamental thermoelastic damping limits (Q/sub TED/) obtained from finite element analysis.

Metalorganic chemical vapor deposition of PbTiO3 thin films

PbTiO3 thin films have been grown successfully for the first time by using purely metalorganic precursors, namely, titanium isopropoxide and tetraethyllead. A scanning electron micrograph showed dense and noncolumnar growth with good surface morphology. Temperature‐dependent x‐ray diffraction studies provide evidences for a reversible tetragonal to cubic phase transition around 540 °C. At room temperature, the dielectric constant is about 180.

Metalorganic chemical vapor deposition of BaTiO3 thin films

We report the results of a recent study on the {ital in} {ital situ} deposition of single phase BaTiO{sub 3} thin films by using the metalorganic chemical vapor deposition technique. The effects of growth parameters on the characteristics of the thin films were investigated in the substrate temperature range of 550--800 {degree}C. Barium {beta}-diketonate and titanium isopropoxide were used as the metal sources. Growth rates ranging from submicron to several microns per hour have been deposited on various substrates in an inverted vertical warm-wall reactor. X-ray diffraction data and Rutherford backscattering spectra provided the evidence for single BaTiO{sub 3} phase. Scanning electron microscopy was used to study the surface and the cross-sectional morphology of the films. Dielectric constant of the as-deposited film was around 250 at room temperature. The resistivity of the films were greater than 10{sup 9} {Omega} cm.

Quality factor in trench-refilled polysilicon beam resonators

In this paper, thermoelastic damping (TED) in trench-refilled (TR) polysilicon microelectromechanical beam resonators is studied as a mechanism for limiting quality factor (Q) at low frequencies. An approximate model based on Zeners theory is developed and verified by numerical simulations in FEMLAB. According to the proposed model a double-dip characteristic is expected for the quality factor versus frequency curve of TR beam resonators. To verify the model experimentally, equal-width TR micro-resonators are fabricated in different length to cover a broad range of frequencies. Frequency response of these devices agrees well with our model. By using the theoretical and numerical models developed in this paper, an upper bound for the quality factor in TR beam resonators or any similar structure such as TR polysilicon gyros can be predicted.

Metalorganic chemical vapor deposition of [100] textured MgO thin films

We report on the results of a recent study on the deposition of [100] textured MgO films on fused quartz substrates by using the metalorganic chemical vapor deposition technique. Magnesium β‐diketonate was used as the metal source and the growth rate of the film was about 0.4 μm/h at 740 °C in a horizontal warm wall reactor. X‐ray diffraction experiments provided evidence that the MgO films on fused quartz were fully textured with [100] orientation perpendicular to the substrate surface. The films had a very smooth surface morphology and optical transparency with an index of refraction of 1.71.

c‐axis oriented YBa2Cu3O7−x superconducting films by metalorganic chemical vapor deposition

Highly textured single phase superconducting YBa2Cu3O7−x films have been successfully grown on the yttria‐stabilized zirconia (100) substrates by using the metalorganic chemical vapor deposition technique. The as‐deposited films grown at 650 °C were homogeneous mixtures of the related metal oxides and carbonates. Subsequent thermal annealing under oxygen flow yielded single phase superconducting films whose thickness corresponded to the deposition rates of approximately 10 μm/h. After the post‐annealing the films deposited on the yttria‐stabilized zirconia substrates exhibited a highly textured x‐ray pattern with c axis perpendicular to the substrate surface. These films show an onset superconducting transition temperature of 93 K with the resistance becoming zero at 84 K.

Metalorganic chemical vapor deposition of Tl2CaBa2Cu2Oy superconducting thin films on sapphire

Superconducting Tl2CaBa2Cu2Oy thin films have been successfully grown on the single‐crystal sapphire (1102) substrate by using the metalorganic chemical vapor deposition technique. The growth rate of the films was about 5 μm/h. The as‐deposited film was post‐annealed in a partially sealed ceramic crucible in the presence of a Tl2Ca2Ba2Cu3Oy pellet to achieve the superconducting phase. The x‐ray data show strong diffraction from the Tl2CaBa2Cu2Oy superconducting phase in addition to the trace amounts of Ca2CuO3 and BaCO3. Superconducting transition temperatures with onset above 100 K and zero resistance at 94 K can be obtained by further heat treatment at 500 °C in oxygen.

Thermoelastic damping in trench-refilled polysilicon resonators

This paper presents quality factor measurement results for trench-refilled (TR) polysilicon beam resonators which demonstrate an increase in Q as their resonant frequency increases, a trend opposite to what is expected from solid beams of the same dimensions. This phenomenon is believed to be due to a multi-path thermoelastic damping characteristic. The frequency-dependant behavior of Q/sub TED/ in trench-refilled resonators with voids is analyzed, for which the measurement data is agreeable. A multiphysics FEMLAB simulation was also performed to illustrate the thermal gradients in a resonating TR beam. We show that in a particular frequency range, trench-refilled polysilicon beams can have a higher Q than their silicon counterpart and the thickness of the resonator can be tuned to produce a desired quality factor behavior.

Metalorganic chemical vapor deposition of Tl sub 2 CaBa sub 2 Cu sub 2 O sub y superconducting thin films on sapphire

Superconducting Tl2CaBa2Cu2Oy thin films have been successfully grown on the single‐crystal sapphire (1102) substrate by using the metalorganic chemical vapor deposition technique. The growth rate of the films was about 5 μm/h. The as‐deposited film was post‐annealed in a partially sealed ceramic crucible in the presence of a Tl2Ca2Ba2Cu3Oy pellet to achieve the superconducting phase. The x‐ray data show strong diffraction from the Tl2CaBa2Cu2Oy superconducting phase in addition to the trace amounts of Ca2CuO3 and BaCO3. Superconducting transition temperatures with onset above 100 K and zero resistance at 94 K can be obtained by further heat treatment at 500 °C in oxygen.

Effect of growth parameters on TiO2 thin films deposited using MOCVD

The goal of this paper is to characterize the performance of an inverted vertical MOCVD reactor used for the deposition of titanium dioxide thin films. Utilizing two- and three-dimensional numerical simulation to gain a more complete understanding of the fundamental relationships underlying the epitaxial growth process, we develop a model to predict gas velocity, temperature distribution, concentration of reactant gas, and deposition rate. A 3D model is used to explain experimentally observed off-axis deposition of grown films. The model is also used to find the control mechanism for different process conditions. Simulations are compared to experimental results, and excellent agreement is obtained.