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11 Feb 2013

Volume 102, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 102, 063701 (2013); http://dx.doi.org/10.1063/1.4790115 (5 pages)

In-Tsang Lin, Hong-Chang Yang, and Jyh-Horng Chen
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Origin of variation in switching voltages in threshold-switching phenomena of VO2 thin films

S. B. Lee, K. Kim, J. S. Oh, B. Kahng, and J. S. Lee

Appl. Phys. Lett. 102, 063501 (2013); http://dx.doi.org/10.1063/1.4790842 (5 pages)

Online Publication Date: 11 February 2013

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We investigated the origin of the variation in switching voltages in threshold-switching of VO2 thin films. When a triangular-waveform voltage signal was applied, the current changed abruptly at two switching voltages, i.e., VON (insulator-to-metal) and VOFF (metal-to-insulator). VON and VOFF were measured by changing the period of the voltage signal, the temperature of the environment, and the load resistance. We observed that either VON or VOFF varied significantly and had different dependences with respect to the external parameters. Based on the mechanism of the metal–insulator transition induced by Joule heating, numerical simulations were performed, which quantitatively reproduced all of the experimental results. From the simulation analysis, the variation in the switching voltages for threshold-switching was determined to be thermal in origin.
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71.30.+h Metal-insulator transitions and other electronic transitions
77.55.-g Dielectric thin films

Defect states characterization of non-annealed and annealed ZrO2/InAlN/GaN structures by capacitance measurements

P. Kordoš, R. Stoklas, D. Gregušová, K. Hušeková, J.-F. Carlin, and N. Grandjean

Appl. Phys. Lett. 102, 063502 (2013); http://dx.doi.org/10.1063/1.4792060 (4 pages)

Online Publication Date: 11 February 2013

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InAlN/GaN metal-oxide-semiconductor structures with non-annealed and annealed ZrO2 gate insulators were characterized by capacitance-voltage (C−V) measurements. A significant capacitance hysteresis in both channel depletion and barrier accumulation regions was observed on the non-annealed structures. Fixed positive charge in the gate insulator was identified from the negative shift of the C−V curves. The C−V hysteresis was negligible and the threshold voltage decreased with a corresponding increase of the sheet charge density by 6 × 1012 cm−2 after annealing. The C−V slope in the accumulation region increased and the flat-band voltage decreased with decreased frequency. This confirms a decrease of the oxide/barrier interface trap state density with increased their activation energy. Capacitance saturation in the accumulation region occurs at lower values than it is in the insulator capacitance. Measurements at increased temperature up to 150 °C show a shift of the flat-band voltage to lower values. Both facts support an explanation that leakage current through the gate insulator occurs in the barrier accumulation region. This shows that evaluation of the trap states density from this part of the C−V curves might be difficult.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing
73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Devices with electrically tunable topological insulating phases

Paolo Michetti and Björn Trauzettel

Appl. Phys. Lett. 102, 063503 (2013); http://dx.doi.org/10.1063/1.4792275 (4 pages)

Online Publication Date: 12 February 2013

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Solid-state topological insulating phases, characterized by spin-momentum locked edge modes, provide a powerful route for spin and charge manipulation in electronic devices. We propose to control charge and spin transport in the helical edge modes by electrically switching the topological insulating phase in a HgTe/CdTe double quantum well device. We introduce the concept of a topological field-effect-transistor and analyze possible applications to a spin battery, which also realize a set up for an all-electrical investigation of the spin-polarization dynamics in metallic islands.
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68.65.Fg Quantum wells
72.25.-b Spin polarized transport
73.21.Fg Quantum wells
85.30.Tv Field effect devices
85.75.Hh Spin polarized field effect transistors

Shrink-induced sorting using integrated nanoscale magnetic traps

Dharmakeerthi Nawarathna, Nazila Norouzi, Jolie McLane, Himanshu Sharma, Nicholas Sharac, Ted Grant, Aaron Chen, Scott Strayer, Regina Ragan, and Michelle Khine

Appl. Phys. Lett. 102, 063504 (2013); http://dx.doi.org/10.1063/1.4790191 (5 pages)

Online Publication Date: 13 February 2013

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We present a plastic microfluidic device with integrated nanoscale magnetic traps (NSMTs) that separates magnetic from non-magnetic beads with high purity and throughput, and unprecedented enrichments. Numerical simulations indicate significantly higher localized magnetic field gradients than previously reported. We demonstrated >20 000-fold enrichment for 0.001% magnetic bead mixtures. Since we achieve high purity at all flow-rates tested, this is a robust, rapid, portable, and simple solution to sort target species from small volumes amenable for point-of-care applications. We used the NSMT in a 96 well format to extract DNA from small sample volumes for quantitative polymerase chain reaction (qPCR).
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

High aspect ratio composite structures with 48.5% thermal neutron detection efficiency

Q. Shao, L. F. Voss, A. M. Conway, R. J. Nikolic, M. A. Dar, and C. L. Cheung

Appl. Phys. Lett. 102, 063505 (2013); http://dx.doi.org/10.1063/1.4792703 (4 pages)

Online Publication Date: 13 February 2013

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The pillar structured thermal neutron detector is based on the combination of high aspect ratio silicon p-i-n pillars surrounded by the neutron converter material 10B. By etching high aspect ratio pillar structures into silicon, the result is a device that efficiently absorbs the thermal neutron flux by accommodating a large volume fraction of 10B within the silicon pillar array. Here, we report a thermal neutron detection efficiency of 48.5% using a 50 μm pillar array with an aspect ratio of 25:1.
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29.40.Wk Solid-state detectors

A dual-polarized broadband planar antenna and channelizing filter bank for millimeter wavelengths

Roger O'Brient, Peter Ade, Kam Arnold, Jennifer Edwards, Greg Engargiola, William L. Holzapfel, Adrian T. Lee, Michael J. Myers, Erin Quealy, Gabriel Rebeiz, Paul Richards, and Aritoki Suzuki

Appl. Phys. Lett. 102, 063506 (2013); http://dx.doi.org/10.1063/1.4791692 (4 pages)

Online Publication Date: 13 February 2013

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We describe the design, fabrication, and testing of a broadband log-periodic antenna coupled to multiple cryogenic bolometers. This detector architecture, optimized here for astrophysical observations, simultaneously receives two linear polarizations with two octaves of bandwidth at millimeter wavelengths. The broad bandwidth signal received by the antenna is divided into sub-bands with integrated in-line frequency-selective filters. We demonstrate two such filter banks: a diplexer with two sub-bands and a log-periodic channelizer with seven contiguous sub-bands. These detectors have receiver efficiencies of 20%–40% and percent level polarization isolation. Superconducting transition-edge sensor bolometers detect the power in each sub-band and polarization. We demonstrate circularly symmetric beam patterns, high polarization isolation, accurately positioned bands, and high optical efficiency. The pixel design is applicable to astronomical observations of intensity and polarization at millimeter through sub-millimeter wavelengths. As compared with an imaging array of pixels measuring only one band, simultaneous measurements of multiple bands in each pixel has the potential to result in a higher signal-to-noise measurement while also providing spectral information. This development facilitates compact systems with high mapping speeds for observations that require information in multiple frequency bands.
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84.40.Ba Antennas: theory, components and accessories
89.20.Kk Engineering

Fast switching protocol for ferroelectric random access memory based on poly(vinylidene fluoride-trifluoroethylene) copolymer ultrathin films

Ying Hou, Zhaoyue Lü, Tiansong Pu, Yuan Zhang, Guoqiang Xu, and Haisheng Xu

Appl. Phys. Lett. 102, 063507 (2013); http://dx.doi.org/10.1063/1.4792689 (5 pages)

Online Publication Date: 14 February 2013

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The polarization switching behaviors with different pulse processes for ferroelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer ultrathin films have been studied. The faster switching speed with imprint time is observed for the films with the certain switching and imprint directions. The internal electric fields for these processes are well analyzed, and it is found that the effective fields as well as charge trap states in ferroelectric layers are strongly responsible for the switching behaviors. This result provides an effective route to design the optimum protocol for ferroelectric random access memory based on P(VDF-TrFE) copolymer ultrathin film.
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85.50.Gk Non-volatile ferroelectric memories
77.80.Fm Switching phenomena

Green-tea modified multiwalled carbon nanotubes for efficient poly(3,4-ethylenedioxythiophene):poly(stylenesulfonate)/n-silicon hybrid solar cell

Ishwor Khatri, Zeguo Tang, Qiming Liu, Ryo Ishikawa, Keiji Ueno, and Hajime Shirai

Appl. Phys. Lett. 102, 063508 (2013); http://dx.doi.org/10.1063/1.4792691 (5 pages)

Online Publication Date: 14 February 2013

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Poly(3,4-ethylenedioxythiophene):poly(stylenesulfonate) (PEDOT:PSS)/n-Si hybrid solar cells were studied with and without embedding green-tea modify multiwalled carbon nanotubes (MWCNTs) at interface. Devices fabricated with embedding green-tea modified MWCNTs show much better performance than that of a device without MWCNTs with short circuit current density (Jsc), open circuit voltage (Voc), fill factor, and power conversion efficiency (η) as 30.31 mA/cm2, 0.54 V, 0.66, and 10.93%, respectively. Here, we believe that green-tea disperse MWCNTs bundles to individual and its incorporation improved built-in potential (Vb) of the device for better hole transport, easy exciton splitting, and suppression of charge recombination, thereby improving photovoltaic response.
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88.40.H- Solar cells (photovoltaics)

Pulsed-laser deposited Pb(Zr0.52,Ti0.48)O3-on-silicon resonators with high-stopband rejection using feed-through cancellation

H. Yagubizade, M. Darvishi, Y.-Y. Chen, M. D. Nguyen, J. M. Dekkers, R. J. Wiegerink, M. C. Elwenspoek, and N. R. Tas

Appl. Phys. Lett. 102, 063509 (2013); http://dx.doi.org/10.1063/1.4792739 (4 pages)

Online Publication Date: 14 February 2013

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A length extensional mode lead zirconate titanate (PZT)-on-Si resonator is presented using 50 Ω termination with high-stopband rejection exploiting feed-through cancellation. A 250-nm-thick (100)-dominant oriented PZT thin-film deposited on top of 3 μm Si using pulsed laser deposition has been used. The resonator is presented with the length of 40 μm (half-wavelength), which corresponds to a resonance frequency of about 83 MHz. The effect of feed-through cancellation has been studied to obtain high-stopband rejection using bottom electrode patterning in the presence of a specific grounding resistance. Using this technique, the stopband rejection can be improved by more than 20 dB.
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84.40.Az Waveguides, transmission lines, striplines
81.15.Fg Pulsed laser ablation deposition
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