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ABSTRACT: A series of NdDyFe 17 Co Si solid solutions with = 2 and 3 and = 0 5 1 0 and 1 5 were prepared by induction melting stoichiometric amounts of high-purity elements. The postannealed samples consist of two phases belonging to the space groups R 3 m and P6 3 mmc . The lattice parameters and the unit cell volumes were calculated from the refinements of the magnetic and structural unit cells using the FULLPROF version of the Rietveld program. For a fixed content of Co, the maximum Curie temperatures (305 C to 405 C) were observed in samples with = 1 and having two phases, a disordered rhombohedral (DR) structure and a disordered hexagonal (DH) structure. An increase in the Curie temperature of 70 C per atom of cobalt is observed in NdDyFe 17 Co Si with = 1 and 3, suggesting that with a suitable choice of rare earths this DR phase may be a promising candidate for high-energy product permanent magnets. The magnetization versus temperature (M versus T) plots of the solid solutions, which consist of two phases, exhibit only a single magnetic ordering transition temperature. Index Terms—Disordered hexagonal (DH), disordered rhombo-herdral (DR).
IEEE Transactions on Magnetics 01/2910; 40. · 1.36 Impact Factor
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ABSTRACT: A V-band wideband variable gain low-noise amplifier (VGLNA) with a 3 dB bandwidth of 14 GHz (58-72 GHz) is developed in a 65 nm RFCMOS technology. The three-stage VGLNA, adopting the current steering method for the gain control, shows a measured peak power gain of 21.8 dB with a 1 dB gain flatness of 10 GHz (60-70 GHz). With tuning voltage adjusted from 0.8 to 2.8 V, the gain and noise figure are varied from 21.8 to 12.8 dB and from 4.2 to 5.7 dB, respectively, at 64 GHz. Input P<sub>-1dB</sub> was measured to be -22.1 dBm. DC power consumption is 36 mW with V<sub>DD</sub> = 1.2 V and the chip size is 0.75 × 0.65 mm.
Electronics Letters 09/2011; · 0.96 Impact Factor
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ABSTRACT: A two-bit reflection-type phase shifter (RTPS) is fabricated using 0.13 μm CMOS process for 60 GHz operation. The reflective loads in the RTPS are designed to achieve minimal loss with use of shunt switches and body-floating resistors. The measurement shows an average insertion loss of 6.4 dB for four phase states with the worst case loss of 7.7 dB at 60 GHz.
Electronics Letters 07/2011; · 0.96 Impact Factor
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ABSTRACT: An MMIC amplifier operating at the highest reported frequency up to date for indium-phosphide double-heterojunction bipolar (DHBT) transistor technology is presented. The amplifier chain consists of seven unit-cell stages that contain differential-pair common-base HBTs and compact inverted microstrip matching networks. Amplifier operation in differential mode generates a virtual RF ground at a convenient location inside the unit cell. The measurements at 325 GHz show a small signal gain of 25 dB and a maximum output power of -1.5 dBm. An amplifier gain of greater than 20 dB is observed over 60 GHz bandwidth extending from 285 to 345 GHz.
IEEE Microwave and Wireless Components Letters 06/2011; · 1.72 Impact Factor
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Yong Su Kim,
J. S. Choi,
J. Kim,
S. J. Moon,
B. H. Park,
J. Yu,
J.-H. Kwon, M. Kim,
J.-S. Chung,
T. W. Noh,
J.-G. Yoon
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ABSTRACT: We investigate room-temperature (RT) ferroelectricity in tensile-strained SrTiO <sub>3</sub> (STO) thin films grown on GdScO <sub>3</sub> (110) substrates. To separate the strain and the defect dipole effect, we apply an electric field to measure the polarization in the direction perpendicular to the elongation axis, and the RT ferroelectric polarization is found to be perpendicular to that axis. These results clearly demonstrate the importance of the contribution of defect dipoles to the RT ferroelectricity observed in STO thin films.
Applied Physics Letters 01/2011; · 3.84 Impact Factor
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ABSTRACT: A 300 GHz amplifier is fabricated using indium-phosphide (InP) double-heterojunction bipolar transistor (DHBT) technology. The cascade chain in the amplifier contains six unit cells each containing a pair of common-base DHBTs in differential configuration. A total of three signal lines run through to the unit-cell to obtain the differential-mode amplifier gain and provide proper dc bias. Measured results show the peak gain of 17.3 dB at 290 GHz with 10-dB gain-bandwidth of 20 GHz.
Microwave Symposium Digest (MTT), 2010 IEEE MTT-S International; 06/2010
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ABSTRACT: A fully integrated Q-band 4-bit MMIC phase shifter with InGaAs pin diodes has been designed and fabricated. To achieve low insertion loss and good phase shifting characteristics at Q-band frequencies, topology based on a switched transmission line is employed using a thin-film microstrip line structure implemented in the MMIC fabrication process. The fabricated phase shifter has demonstrated good performance such as an insertion loss of less than 6.1 dB in the frequency range 46 49 GHz with a small intrinsic chip size of 2.48 0.87 mm. The results show the best insertion loss characteristic among the switched transmission-line type phase shifters reported at Ka- and Q-band frequencies.
Electronics Letters 03/2010; · 0.96 Impact Factor
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ABSTRACT: The light extraction efficiency of an organic light-emitting diode (OLED) was significantly enhanced upon incorporating a photonic-crystal (PC) pattern consisting of ZnS pillars residing on top of the transparent anode-glass substrate. The luminance efficiency of the PC-OLED is enhanced by a factor of 2.1 to 2.4 depending on the periodicity of the PC structure, when compared to that of a control OLED operating under the same conditions.
Journal of Applied Physics 01/2010; · 2.17 Impact Factor
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ABSTRACT: We report interband cascade lasers operating in a single spectral mode (λ≈3.6 μ m ) at -5–30 ° C . A corrugated pattern etched into both sidewalls of the 6- and 9-μ m -wide ridges serves to suppress higher-order lateral modes by increasing their loss, and also provides a fourth-order distributed-feedback grating for longitudinal mode selection. Despite the grating’s weak coupling strength, the 9 μ m ridge produced up to 12 mW per facet of single-mode cw output power at 25 ° C , with a side-mode suppression ratio of ≫30 dB .
Applied Physics Letters 01/2010; · 3.84 Impact Factor
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J.H. Park,
S. Nam,
G. Garipov,
J.A. Jeon,
J.Y. Jin,
B. Khrenov,
J.E. Kim, M. Kim,
Y.K. Kim,
J. Lee,
G.W. Na,
I.H. Park,
Y.-S. Park,
B.W. Yoo
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ABSTRACT: A novel type of telescope, a pinhole-like camera with a micromirror array, is introduced for space observation of transient luminous events (TLEs) like gigantic lightning occurring at upper atmosphere currently under question or investigation. The presented telescope has a unique feature of wide field of view (FOV) of surveillance, fast zoom-in and tracking. A high-fill factor, two-axis rotational micromirror array is proposed for the key component of the telescope. To obtain a large static deflection of a mirror, the self-aligned vertical comb-drive actuator is used. Multi-layered structures of a micromirror are fabricated using bulk micromachining techniques, such as deep reactive ion etching and wafer bonding on the full wafer-scale.
Micro Electro Mechanical Systems, 2009. MEMS 2009. IEEE 22nd International Conference on; 03/2009
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ABSTRACT: Presented is a closed-loop feedback control of an electrostatically actuated micromirror to track a moving light source and to stabilise fast the tilting angle. The micromirror has been designed and fabricated with single crystalline silicon. Tracking and tilt-angle stabilisation has been tested using a position-sensing detector and analogue feedback control circuit. Successful tracking of a moving light source was achieved. The feedback control has been also verified to improve the tilt-angle stabilisation time of the micromirror significantly.
Electronics Letters 11/2008; · 0.96 Impact Factor
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ABSTRACT: We report a five-stage interband cascade laser that operates at λ=3.75 μ m in cw mode up to a maximum temperature of 319 K . With gold electroplating, epitaxial-side-up mounting, and one facet coated for high reflectivity, a 3 mm ×9.2 μ m ridge emits over 10 mW of cw power at 300 K .
Applied Physics Letters 06/2008; · 3.84 Impact Factor
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ABSTRACT: We have demonstrated an electrically pumped photonic-crystal distributed-feedback laser with an interband cascade active region emitting at 3.3 μm. At 78 K, the stripe of width 400 μm emits up to 67 mW of cw power into a single spectral mode with side-mode suppression ratio ≈ 27 dB. The full width at half maximum of the far-field divergence angle is ≈ 0.5°, which combined with the near-field profile yields an effective M2 of 1.7–2.0.
Applied Physics Letters 02/2008; 92(7):071110-071110-3. · 3.84 Impact Factor
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ABSTRACT: We employ a cavity-length study to determine the temperature variation of the internal loss and gain per unit current density in a ten-stage interband cascade laser that operated cw up to 269 K with an emission wavelength of 4.05 μm. The characteristic temperature for the gain per unit current density is 39 K, which is slightly lower than T0 of the threshold current and is consistent with dominance by Auger recombination. The internal loss for the 150-μm-wide mesa devices increased from 11 cm−1 at 78 K to 28 cm−1 at 275 K.
Journal of Applied Physics 01/2008; 103(1):013114-013114-4. · 2.17 Impact Factor
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ABSTRACT: The authors report the operating characteristics of ten-stage interband cascade lasers from two wafers with room-temperature wavelengths of 4.1 and 4.3 μ m . For 150-μ m -wide stripes, the threshold current densities are as low as 4.8 A / cm <sup>2</sup> at 78 K (cw) and 1.15 kA / cm <sup>2</sup> at room temperature (pulsed). At 78 K , the cw wall-plug efficiency for an 11-μ m -wide ridge with 0.5- mm -long cavity and coated facets is 27%, while a 3- mm -long cavity emits a maximum cw power of 200 mW . Devices from the two wafers have maximum cw operating temperatures of 261 K (λ≈4.0 μ m ) and 243 K (λ≈4.2 μ m ) .
Applied Physics Letters 05/2007; · 3.84 Impact Factor
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ABSTRACT: In this paper, we propose the antenna which has a wideband operation (GSM850, EGSM, DCS1800, USPCS, WCDMA). This antenna is designed by using a meander branch structure which has via and lines on FR-4(epsiv<sub>r</sub>=4.4) PCB. The antenna was designed by the commercial software HFSS 3-D EM simulator. The designed antennas are manufactured by PCB processing, and measured by using the network analyzer and test chamber. The antennas with the dimension of 8 mm width, 20 mm height and 3.2 mm thickness, are applied on the internal antenna for wideband cell phones. Its size was minimized so that it can be mounted inside of a cellphone.
Microwave Conference, 2006. APMC 2006. Asia-Pacific; 01/2007
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Geoscience and Remote Sensing Symposium, 2006. IGARSS 2006. IEEE International Conference on; 09/2006
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ABSTRACT: We demonstrate a surface-emitting photonic-crystal distributed-feedback laser, emitting at λ≈3.7 μ m from an antimonide type-II “W” active region. While single-mode operation was not achieved, the spectral emission linewidth for cw optical pumping was only 1.3 Å . For pulsed operation with a pump-spot diameter of 0.8 mm , 60% of the nearly circular output beam was transmitted through an aperture with an angular diameter approximately five times that of a Gaussian emitted beam, assuming that the emission area and pump area are the same.
Applied Physics Letters 06/2006; · 3.84 Impact Factor
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P.D. Kirsch,
M.A. Quevedo,
G. Pant,
S. Krishnan,
S.C. Song,
H.J. Li,
J.J. Peterson,
B.H. Lee,
R.W. Wallace, M. Kim,
B.H. Gnade
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ABSTRACT: We report on the relationship between the materials science of a HfO<sub>2</sub>/TiN stack and transistor performance. Atomic layer deposited (ALD) HfO<sub>2</sub> can be scaled to a physical thickness of 1.2 nm resulting in EOT 1.0 nm. In scaling HfO<sub>2</sub> the interfacial SiO<sub>2</sub> layer (IL) is also scaled and the extent of HfO<sub>2</sub> crystallization is reduced. Reduced HfO<sub>2</sub> crystallinity is coincident with reduced threshold voltage instability (10 mV) and increased electron mobility (82% Univ. SiO <sub>2</sub>). For these stable, high mobility devices, we find that HfO<sub>2</sub> can coordinate N as Hf-N without excessive nitridation of the IL
VLSI Technology, Systems, and Applications, 2006 International Symposium on; 05/2006
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ABSTRACT: Electronic, structural, and magnetic properties of Mn-doped lanthanum ferrites were studied by neutron diffraction, superconducting quantum interference device, and impedance spectroscopy. Neutron diffraction refinements were performed with the constraint of full La occupancy, which showed the presence of excess oxygen when x≪0.4 . Mixed valent Mn cations and cation vacancies, therefore, exist in all the samples. The samples with x≫0.7 are magnetically ordered at room temperature with orthorhombic symmetry (Pbnm) . When x≪0.3 the structure is rhombohedral and magnetically disordered above 16 K . The majority carriers, electron holes, correspond to high oxidation states of Mn. The carrier concentration is determined from the Seebeck coefficients, and is a function of temperature and Fe concentration. The measurements of conductivity and Seebeck coefficients show polaron hopping at elevated temperatures.
Journal of Applied Physics 05/2006; · 2.17 Impact Factor
