Publications (37)14.35 Total impact

Conference Paper: 60GHz high isolation SPDT MMIC switches using shunt pHEMT resonator
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ABSTRACT: This paper describes the successful development of a 60 GHz high isolation SPDT MMIC switch for wireless applications. In order to improve the isolation, the shunt pHEMT resonator, which is reduced onstate resistance of FET, is proposed. The developed Vband SPDT switch shows an isolation of over 45 dB and an insertion loss of 1.4 dB at 60 GHz. Input and output return losses are better than 18 dB in ONstate. Moreover, the switch requires no complex offchip bias circuitry and consumes no DC power. These performances of high isolation and low insertion loss presented here are the best among the Vband pHEMT MMIC switches.  [Show abstract] [Hide abstract]
ABSTRACT: We report on a study of 2+1 flavor lattice QCD with the $O(a)$improved Wilson quarks on a $16^3\times 32$ lattice at the lattice spacing $1/a\approx 2$GeV employing Luescher's domaindecomposed HMC(LDDHMC) algorithm. This is dedicated to a preliminary study for the PACSCS project which plans to complete the Wilsonclover $N_f=2+1$ program lowering the updown quark masses close to the physical values as much as possible. We focus on three issues: (i) how light quark masses we can reach with LDDHMC, (ii) efficiency of the algorithm compared with the conventional HMC, (iii) parameter choice for the production runs on PACSCS.  [Show abstract] [Hide abstract]
ABSTRACT: Masses of the eta and etaprime mesons are estimated in Nf=2+1 lattice QCD with the nonperturbatively O(a) improved Wilson quark action and the Iwasaki RGimproved gluon action, using CPPACS/JLQCD configurations on a 16^3 x 32 lattice at beta=1.83 (lattice spacing is 0.122 fm). We apply a stochastic noise estimator technique combined with smearing method to evaluate correlators among flavor SU(2) singlet pseudoscalar operators and strange pseudoscalar operators for 10 combinations of up/down and strange quark masses. The correlator matrix is then diagonalized to identify signals for mass eigenstates. Masses of the ground state and the first excited state extrapolated to the physical point are m_eta= 0.545(16) GeV and m_etaprime= 0.871(46) GeV, being close to the experimental values of the eta and etaprime masses. 
Article: An application of the UVfiltering preconditioner to the Polynomial Hybrid Monte Carlo algorithm
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ABSTRACT: We apply the UVfiltering preconditioner, previously used to improve the MultiBoson algorithm, to the Polynomial Hybrid Monte Carlo (UVPHMC) algorithm. The performance test for the algorithm is given for the plaquette gauge action and the $O(a)$improved Wilson action at $\beta=5.2, c_{\mathrm{sw}}=2.02, M_{\pi}/M_{\rho}\sim 0.8$ and 0.7 on a $16^3\times 48$ lattice. We find that the UVfiltering reduces the magnitude of the molecular dynamics force from the pseudo fermion by a factor 3 by tuning the UVfilter parameter. Combining with the multitime scale molecular dynamics integrator we achieve a factor 2 improvement. Comment: 7 pages, 1 figure, talk presented at Lattice2006 (Algorithm), PoS format; v2 references added  [Show abstract] [Hide abstract]
ABSTRACT: Preliminary study with LDDHMC  mudAWI ≈ 15MeV reached  σ√V/a (2+1 flavor) < σ√V/a (2 flavor) target of PACSCS project  three β values, (3.0fm)3, 104 trajs.  go down to mudAWI = 7MeV or less  current status of production runs: mudAWI = 7, 15, 25MeV at β = 1.9 on 323 × 64 physical results will be presented in next year. 
Article: The PACSCS Project
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ABSTRACT: We describe our plan to develop a largescale cluster system with a peak speed of 14.3Tflops for lattice QCD at the Center for Computational Sciences, University of Tsukuba, as a successor to the current 0.6Tflops CPPACS computer. The system consist of 2560 nodes connected by a 16x16x10 threedimensional hyper crossbar network. Each node has a single lowvoltage 2.8GHz Xeon processor and 2GBytes of memory with 6.4GBytes/sec bandwidth, and 160 GBytes of disk in RAID1 mode. The network link in each of the three directions is made of dual Gigabit Ethernet with the peak throughput of 250MByte/sec. Hence each node has an aggregate network bandwidth of 750MByte/sec. The system will run under Linux and SCore, and an extension of the PM driver is developed for the network. The system will be developed jointly with Hitachi Limited. The installation is scheduled in the first quarter of Japanese Fiscal 2006 (AprilJune 2006) and the start of operation is expected in July 2006.  [Show abstract] [Hide abstract]
ABSTRACT: We consider 2+1 flavor Wilson Chiral Perturbation Theory including the lattice spacing contributions of O($a^{2}$). We adopt a power counting appropriate for the unquenched lattice simulations carried out by the CPPACS/JLQCD collaboration and compute the pseudo scalar meson masses to one loop. These expression are required to perform the chiral extrapolation of the CPPACS/JLQCD lattice data. Comment: 18 pages 
Conference Paper: A Cband AlGaN/GaN HEMT with catCVD SiN passivation developed for an over 100 W operation
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ABSTRACT: We applied a CatCVD (catalytic chemical vapor deposition) passivation film to AlGaN/GaN HEMTs, to resolve the tradeoff between their drain current transient time and gatedrain break down voltage. We did not employ any field plate because it degrades high frequency operation over Cband. The SiN passivation film, deposited after a NH<sub>3</sub> treatment, resulted in less transient time and less gate leakage current than conventional PECVD passivation. A Tshaped gate HEMT fabricated by this technique, with Lg = 0.4 μm and Wg = 50.4 mm, delivered an output power over 140 W (2.79 W/mm), which was a record power at Cband. 
Conference Paper: A high efficiency, high voltage, balanced cascode FET
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ABSTRACT: A high efficiency, high operating voltage GaAs HFET is presented. A balanced cascode circuit without RF feedback, which achieves the high PAE of 78.2% at 2.1GHz, is proposed. The optimization of a balance capacitor is analyzed theoretically and proved experimentally. This result contributes to the design of high voltage power amplifiers with low breakdown voltage transistors. 
Conference Paper: A high power density TaN/Au Tgate pHEMT with high humidity resistance for KaBand applications
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ABSTRACT: A 0.8 W/mm high power pHEMT with high humidity resistance is reported. By using tantalum nitride as the refractory gate metal and a silicon nitride layer prepared by a catalytic chemical vapor deposition technique for passivation of this transistor, tough moisture resistance was obtained showing no Id degradation even after 500 hours at 130 degrees centigrade and 85% humidity. Moreover, the Schottky breakdown voltage of the TaN gate is higher than that of a WSiN gate. A onestage prematched amplifier with the new pHEMT has achieved 0.83 W/mm output power at Vds = 8 V, with 8.5 dB gain and 40% power added efficiency in the Kaband. These are some of the highest power figures ever reported.  [Show abstract] [Hide abstract]
ABSTRACT: CPPACS and JLQCD Collaborations are carrying out a joint project of the 2+1 flavor full QCD with the RGimproved gauge action and the nonperturbatively O(a)improved Wilson quark action. This simulation removes quenching effects of all three light quarks, which is the last major uncertainty in lattice QCD. In this report we present our results for the light meson spectrum and quark masses on a 203×40 lattice at the lattice spacing a≃0.10 fm. 
Conference Paper: A high reliability GaN HEMT with SiN passivation by CatCVD
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ABSTRACT: This is the first report of catalytic vapor deposition (CatCVD) passivated AlGaN/GaN HEMT. We have found out that the CatCVD passivation film with NH3 treatment greatly enhances the reliability of the AlGaN/GaN HEMT. It is rationalized, through the low frequency capacitancevoltage measurement, that the NH3 treatment in the CatCVD reactor before the SiN film deposition minimizes the damage at the SiN/AlGaN interface, leading to reducing the surface trap density. The AlGaN/GaN HEMT passivated by the CatCVD SiN film suppresses the degradation of an output power to less than 0.4 dB under the RF operation of Vd = 30 V, f = 5 GHz after 200 h. 
Conference Paper: Intermodulation distortion analysis of class F and inverse class F amplifiers at low quiescent currents
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ABSTRACT: The thirdorder intermodulation distortions (IM3) of classF and inverse classF HBT amplifiers were experimentally compared at low quiescent currents (Iq). It has been revealed that the IM3 of inverse classF is lower than that of classF. This is due to lower gain increase at low input power (Pin) and lower gain decrease at high Pin. When the load impedances are tuned to obtain the same IM3 at the same output power (P out) of 16.5 dBm, the efficiency of inverse classF is almost same at a Pout of less than 15.5 dBm and higher than that of classF at a Pout of more than 15.5 dBm.  [Show abstract] [Hide abstract]
ABSTRACT: Renormalization constants (Zfactors ) of vector and axialvector currents are determined nonperturbatively in quenched QCD for a renormalization group improved gauge action and a tadpoleimproved clover quark action using the Schrödinger functional method. Nonperturbative values of Zfactors turn out to be smaller than 1loop perturbative values by O(15%) at a lattice spacing of a1[approximate] 1 GeV. The pseudoscalar and vector meson decay constants calculated with the nonperturbative Zfactors show a much better scaling behavior compared to previous results obtained with tadpoleimproved oneloop Zfactors. In particular, the nonperturbative Zfactors normalized at infinite physical volume show that the scaling violations of the decay constants are within about 10% up to the lattice spacing a1~1 GeV. The continuum estimates obtained from data in the range a1~ 1–2 GeV agree with those determined from finer lattices (a1~24 GeV) with the standard action. 
Conference Paper: The efficiency of classF and inverse classF amplifiers
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ABSTRACT: The efficiency of classF and inverse classF amplifiers are studied using measurements and theories. At high quiescent current, inverse classF amplifiers show higher efficiency than that of classF. This phenomenon is experimentally ensured with GaAs pHEMTs and GaAs HBTs. A harmonic balanced simulation also supports this result, and reveals the difference between the classes. An analytic waveform analysis with restricted harmonics explains this dependence on the quiescent currents. 
Conference Paper: Efficiency enhancement of Doherty amplifier with combination of classF and inverse classF schemes for Sband base station application
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ABSTRACT: A new efficiency enhancement technique for the Doherty amplifier for use in Sband base stations is presented. The proposed technique includes a scheme in which the carrier amplifier operates under the classF condition, while the peak amplifier operates under the inverse classF condition. In a conventional Doherty scheme, however, both the carrier and the peak amplifiers operate at the same operational class. Theoretical analysis projects that the backoff power level from the power saturation to obtain the peak efficiency is improved from 6 dB for the conventional scheme to 8.2 dB for the proposed design. The saturation output power is also projected to be improved by 1 dB. The fabricated amplifier being verified exhibits a 45% efficiency at 10 dB backoff. This paper describes the advantages of the proposed design scheme by showing theoretical analyses and a circuit design followed by experimental verification at 2.1 GHz.  [Show abstract] [Hide abstract]
ABSTRACT: We have investigated Franz–Keldysh oscillations (FKOs) from a baseemitter junction in an InGaP/GaAs heterojunction bipolar transistor structure using photoreflectance spectroscopy. The profiles of the FKOs originating from the InGaP emitter are compared with the line shapes calculated with the use of electrooptic functions. It is found that the line shape of the FKOs is remarkably affected by interference of probe light due to the multiple layer structure. Taking account of the interference effect, we have derived a novel analysis method for a convenient linear plot of the extremum positions of FKOs. The bandgap energy estimated with the present method well agrees with the bandgap energy obtained from the photoluminescence measurement of an InGaP/GaAs heterostructure for a reference.  [Show abstract] [Hide abstract]
ABSTRACT: We present a lattice QCD calculation of the parameters \alpha and \beta which are necessary in the theoretical estimation of the proton lifetime in grand unified theories (GUTs) using chiral lagrangian approach. The simulation is carried out using the Wilson quark action at three gauge coupling constants in the quenched approximation. We obtain \alpha(2GeV)=0.0091(08)(^{+10}_{19})GeV^3 and \beta(2GeV)=0.0098(08)(^{+10}_{20})GeV^3 in the continuum limit where the first error is statistical and the second one is due to scale setting.  [Show abstract] [Hide abstract]
ABSTRACT: We report on a calculation of the light hadron spectrum and quark masses in threeflavor dynamical QCD using the nonperturbatively O(a)improved Wilson quark action and a renormalizationgroup improved gauge action. Simulations are carried out on a 163 × 32 lattice at β = 1.9, where a−1 ≅ 2 GeV, with 6 ud quark masses corresponding to and 2 s quark masses close to the physical value. We observe that the inclusion of dynamical strange quark brings the lattice QCD meson spectrum to good agreement with experiment. Dynamical strange quarks also lead to a reduction of the uds quark masses by about 15%.  [Show abstract] [Hide abstract]
ABSTRACT: We propose an analysis method for FranzKeldysh (FK) oscillations appearing in photoreflectance (PR) spectra of heterojunction device structures, which enables precise and simultaneous evaluation of the builtin electric field strength and bandgap energy. Samples for PR measurements were n +GaAs/nAl 0.3Ga 0.7As/iGaAs heterostructures with different Al 0.3Ga 0.7Aslayer thickness. We have found that the phase of the FK oscillations originating from the iGaAs buffer layer depends on the Al 0.3Ga 0.7Aslayer thickness. We have derived a calculation model for FK oscillations that includes the interference of probe light. From the comparison of the calculated spectra with the measured spectra, we conclude that mixing of the real and imaginary parts of a modulated dielectric function, which is caused by the probelight interference, gives rise to the phase shift of the FK oscillations. Our FKoscillation analysis method reduces ambiguity in the estimation of bandgap energy that is considerable in a conventional analysis.
Publication Stats
288  Citations  
14.35  Total Impact Points  
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Institutions

19992008

Mitsubishi Electric Corporation
Edo, Tōkyō, Japan


20032005

University of Tsukuba
 Centre for Computational Sciences
Tsukuba, Ibaraki, Japan


1997

Mitsubishi Corp.
Itan, Hyōgo, Japan
