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21 Jan 2008

Volume 92, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 92, 033101 (2008); http://dx.doi.org/10.1063/1.2830979 (3 pages)

Koichiro Zaitsu, Yosuke Kitamura, Keiji Ono, and Seigo Tarucha
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The balance and noise properties of directly coupled high-Tc superconducting quantum interference device gradiometers with a serial array

Hong-Chang Yang, J. C. Chen, C. H. Wu, K. L. Chen, Herng-Er Horng, Yi-Shou Tsai, and S. Y. Yang

Appl. Phys. Lett. 92, 033501 (2008); http://dx.doi.org/10.1063/1.2835700 (3 pages) | Cited 4 times

Online Publication Date: 22 January 2008

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We characterize the balance and noise properties of directly coupled high-Tc superconducting quantum interference device (SQUID) gradiometers with a series array. The gradiometer consisted of symmetrical pickup loops, in which a series of SQUID was symmetrically configured and directly coupled to pickup loops. We characterize the balance resolution B from the following formula: B = Aeff,uniform field/Aeff,gradient field, where Aeff,uniform field and Aeff,gradient field are the parasitic effective area and the effective area of the gradiometer, respectively. We obtained B = 1.25×10−2 which was comparable to the typical balance resolution of ∼ 10−2 for a gradiometer fabricated onto the 10×10 mm2 substrate. This discrepancy was probably due to the many superconducting pads inside the pickup loops which deteriorated the uniformity of applied uniform magnetic fields. The gradient field sensitivity of ∼ 40 fT/Hz1/2 cm at 1 kHz for two-SQUID gradiometers was demonstrated in a magnetically unshielded environment, which was comparable to the best gradient sensitivity of 30 fT/Hz1/2 cm, with gradiometric flip-chip flux transformer with a length of 24 mm and a base line of 10 mm in shielded environment.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
07.55.Ge Magnetometers for magnetic field measurements

Bias stress stability of indium gallium zinc oxide channel based transparent thin film transistors

A. Suresh and J. F. Muth

Appl. Phys. Lett. 92, 033502 (2008); http://dx.doi.org/10.1063/1.2824758 (3 pages) | Cited 133 times

Online Publication Date: 23 January 2008

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The effects of bias stress on transistor performance are important when considering nontraditional channel materials for thin film transistors. Applying a gate bias stress to indium gallium zinc oxide transparent thin film transistors was found to induce a parallel threshold voltage shift without changing the field effect mobility or the subthreshold gate voltage swing. The threshold voltage change is logarithmically dependent on the duration of the bias stress implying a charge tunneling mechanism resulting in trapped negative charge screening the applied gate voltage.
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85.30.De Semiconductor-device characterization, design, and modeling
85.30.Tv Field effect devices
81.05.Hd Other semiconductors

Mechanism of the flexural resonance frequency shift of a piezoelectric microcantilever sensor in a dc bias electric field

Qing Zhu, Wan Y. Shih, and Wei-Heng Shih

Appl. Phys. Lett. 92, 033503 (2008); http://dx.doi.org/10.1063/1.2827201 (3 pages) | Cited 8 times

Online Publication Date: 23 January 2008

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The flexural resonance frequency of a lead magnesium niobate–lead titanate (PMN-PT)/tin piezoelectric microcantilever sensor (PEMS) was shown to vary in a dc bias electric field, similar to the behavior of width-mode resonance frequency of the PEMS. Both the flexural and the width-mode resonance frequency shifts were attributed to Young’s modulus change in the PMN-PT layer as confirmed by Young’s modulus measurements on a separate PMN-PT strip. Young’s modulus change of the PMN-PT layer in an electric field was a result of the non-180° polarization domain switching as evidenced by the dielectric constant change with the field.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

High quality passivation for heterojunction solar cells by hydrogenated amorphous silicon suboxide films

Thomas Mueller, Stefan Schwertheim, Maximilian Scherff, and Wolfgang R. Fahrner

Appl. Phys. Lett. 92, 033504 (2008); http://dx.doi.org/10.1063/1.2837192 (3 pages) | Cited 9 times

Online Publication Date: 23 January 2008

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In this letter, we report on our investigations of hydrogenated amorphous silicon suboxides (a-SiOx:H) used as a high quality passivation scheme for heterojunction solar cells. The a-SiOx:H films were deposited using high frequency (70 MHz) plasma enhanced chemical vapor deposition by decomposition of carbon dioxide, hydrogen, and silane at a substrate temperature of around 155 °C. High effective lifetimes of outstanding 4 ms on 1 Ω cm n-type float-zone material and a surface recombination velocity of ⩽ 2.6 cm/s have been repeatedly obtained. Optical analysis revealed a distinct decrease of blue light absorption in the a-SiOx:H films compared to commonly used intrinsic amorphous silicon passivation used in heterojunction cells.
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81.65.Rv Passivation
68.55.at Other materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.10.Fq Growth from melts; zone melting and refining
73.25.+i Surface conductivity and carrier phenomena
84.60.Jt Photoelectric conversion

Theoretical and experimental investigation of gigahertz-band, temperature-compensated electromechanical coupling configurations based on AlN films

Cinzia Caliendo

Appl. Phys. Lett. 92, 033505 (2008); http://dx.doi.org/10.1063/1.2837179 (3 pages) | Cited 10 times

Online Publication Date: 24 January 2008

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Highly c-axis oriented piezoelectric AlN films were sputtered on (0001) Al2O3 substrates and four gigahertz-range surface acoustic wave (SAW) electroacoustic coupling configurations were realized by conventional photolithographic process. The thermal sensitivity of each device was experimentally estimated and found in good accordance with the theoretical predictions. Eight gigahertz-range, thermally compensated SAW devices were obtained for specific AlN thickness, SAW propagation direction, and electrical boundary conditions. A theoretical analysis of the acoustic and electrical behavior of the four coupling structures is proposed to match the achievable performances of the SAW devices with the design requirements.
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43.38.-p Transduction; acoustical devices for the generation and reproduction of sound
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Infrared analysis of the bulk silicon-hydrogen bonds as an optimization tool for high-rate deposition of microcrystalline silicon solar cells

A. H. M. Smets, T. Matsui, and M. Kondo

Appl. Phys. Lett. 92, 033506 (2008); http://dx.doi.org/10.1063/1.2837536 (3 pages) | Cited 22 times

Online Publication Date: 24 January 2008

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It is demonstrated that the signature of bulk hydrogen stretching modes in the infrared of microcrystalline silicon (μc-Si:H) deposited at high deposition rates can be used for solar cell optimization in the high pressure depletion regime. A relation between the performance of a p-i-n solar cell and the hydride stretching modes corresponding to hydrogenated crystalline grain boundaries is observed. These crystalline surfaces show postdeposition oxidation and the absence of these surfaces in the μc-Si:H matrix reflects device grade microcrystalline material.
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84.60.Jt Photoelectric conversion
78.30.Am Elemental semiconductors and insulators
81.65.Mq Oxidation

High-performance visible-blind GaN-based p-i-n photodetectors

Bayram Butun, Turgut Tut, Erkin Ulker, Tolga Yelboga, and Ekmel Ozbay

Appl. Phys. Lett. 92, 033507 (2008); http://dx.doi.org/10.1063/1.2837645 (3 pages) | Cited 8 times

Online Publication Date: 24 January 2008

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We report high performance visible-blind GaN-based p-i-n photodetectors grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The dark current of the 200 μm diameter devices was measured to be lower than 20 pA for bias voltages up to 5 V. The breakdown voltages were higher than 120 V. The responsivity of the photodetectors was ∼ 0.23 A/W at 356 nm under 5 V bias. The ultraviolet-visible rejection ratio was 6.7×103 for wavelengths longer than 400 nm.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

Low 1/f noise, full bridge, microcantilever with longitudinal and transverse piezoresistors

J. R. Mallon, Jr., A. J. Rastegar, A. A. Barlian, M. T. Meyer, T. H. Fung, and B. L. Pruitt

Appl. Phys. Lett. 92, 033508 (2008); http://dx.doi.org/10.1063/1.2825466 (3 pages) | Cited 8 times

Online Publication Date: 25 January 2008

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This paper reports on low 1/f noise, low corner-frequency, piezoresistive microcantilevers suitable for static and slowly time varying, force and displacement sensing applications such as chemical and biosensing. We demonstrate a full bridge, piezoresistive cantilever with greater than 140 dB dynamic range, a noise amplitude spectral density floor of 3.7 nV/V √Hz at 0.1 Hz. At 1.0 Hz, the noise spectral density is 1.2 nV/V √Hz equivalent to 10 pN/√Hz or 5 pm/√Hz. The force resolution over the frequency band of 0.1–100 Hz is 100 pN.
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07.10.Cm Micromechanical devices and systems
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