Effective negative-/spl epsiv/ stopband microstrip lines based on complementary split ring resonators

In this letter a super-compact stopband microstrip structure is proposed. The frequency gap is produced by an array of complementary split ring resonators (CSRRs)-a concept proposed here for the first time-etched on the ground plane. This behavior is interpreted as due to the presence of a negative effective dielectric permittivity in the vicinity of resonance. The resulting device produces a deep rejection frequency band with sharp cutoff, and a pass band that exhibits very low losses and good matching. Due to the sub-lambda operation of CSRRs, the electrical size of the device is very small.     

Extraction of /spl epsiv//sub r/(f) and tan/spl delta/(f) for printed circuit board insulators up to 30 GHz using the short-pulse propagation technique

In this paper, the self-consistent, frequency-dependent dielectric constant epsiv_r(f) and dielectric loss tandelta(f) of several materials are determined over the range 2 to 30 GHz using a short-pulse propagation technique and an iterative extraction based on a rational function expansion. The simple measurement technique is performed in the time domain on representative printed circuit board wiring. Broadband, fully causal transmission-line models based on these results are generated up to 50 GHz for card wiring using low loss materials including BT, Nelco N4000-13, and Nelco N4000-13SI. Simulation and modeling results highlight the need for the accurate frequency-dependent dielectric loss extraction. Signal propagation based on these results shows very good agreement with measured step and pulse time-domain excitations and provides validation of the measurement and model generation technique     

Robust speed control of an induction motor: an /spl Hscr//sub /spl infin// control theory approach with field orientation and /spl mu/-analysis

In this paper we present a robust speed control strategy for an induction motor under field orientation. The control framework employed properly represents the induction motor state-space model and its inherent variations, which are treated as structured uncertainties. Applying an /spl Hscr//sub /spl infin//, optimization methodology on this framework we derive a stabilizing controller to meet design objectives and then robust stability and performance against such variations are checked by using /spl mu/-analysis. No on-line tuning is required for the parameters of the derived controller, which is the dynamic system responsible to keep the rotor flux orientation as well as the speed regulation at design levels, irrespective of the motor operating points. A general methodology arose from the usage of the proposed strategy and simulated experiments showed satisfactory results for the robust speed control of an induction motor.     

BC high-/spl kappa//metal gate Ge/C alloy pMOSFETs fabricated directly on Si (100) substrates

Buried-channel (BC) high-/spl kappa//metal gate pMOSFETs were fabricated on Ge/sub 1-x/C/sub x/ layers for the first time. Ge/sub 1-x/C/sub x/ was grown directly on Si (100) by ultrahigh-vacuum chemical vapor deposition using methylgermane (CH/sub 3/GeH/sub 3/) and germane (GeH/sub 4/) precursors at 450/spl deg/C and 5 mtorr. High-quality films were achieved with a very low root-mean-square roughness of 3 /spl Aring/ measured by atomic force microscopy. The carbon (C) content in the Ge/sub 1-x/C/sub x/ layer was approximately 1 at.% as measured by secondary ion mass spectrometry. Ge/sub 1-x/C/sub x/ BC pMOSFETs with an effective oxide thickness of 1.9 nm and a gate length of 10 /spl mu/m exhibited high saturation drain current of 10.8 /spl mu/A//spl mu/m for a gate voltage overdrive of -1.0 V. Compared to Si control devices, the BC pMOSFETs showed 2/spl times/ enhancement in the saturation drain current and 1.6/spl times/ enhancement in the transconductance. The I/sub on//I/sub off/ ratio was greater than 5/spl times/10/sup 4/. The improved drain current represented an effective hole mobility enhancement of 1.5/spl times/ over the universal mobility curve for Si.     

Characteristics of MOSFET Prepared on Si/MgO /spl dot/ Al/sub 2/O/sub 3//SiO/sub 2//Si Structure

A new silicon on insulator (SOI) wafer with epitaxial-Si/ epitaxial-MgO/spl dot/Al/sub 2/O/sub 3/ (0.1 /spl mu/m)/SiO/sub 2/(0.5 /spl mu/m)/     

Limitation of DC currents by YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//-Au superconducting films

The limitation of dc fault currents is one of the issues for the development of dc networks or links. This paper shows for the first time the high potential of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//-Au bilayers for the design of dc current limiters. Such devices are based on the transition into the normal state of the superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films above a current I/sup */>I/sub c/, where I/sub c/ is the critical current at the onset of dissipation. The study of the transition under current pulses shows that a thermally driven transition into the normal state can occur after a delay t/sub trans/. This duration is defined by the amplitude of the current pulse. For I/sup *//spl ap/3I/sub c/, this delay is less than 10 /spl mu/s. The abrupt transition into the normal state allows an efficient current limitation. A recovery of the superconducting state can also occur under current. This property can be extremely interesting for autonomous operation of a current limiter in an electrical network in case of transient over-currents coming from the starting of high-power devices.     

Experimental implementation of spatial H/sub /spl infin// control on a piezoelectric-laminate beam

This paper is aimed to develop a feedback controller that suppresses vibration of flexible structures. The controller is designed to minimize the spatial H/sub /spl infin// norm of the closed-loop system. This technique guarantees average reduction of vibration throughout the entire structure. A feedthrough term is incorporated into the truncated flexible-structure model to compensate for the neglected dynamics in the finite-dimensional model. Adding the feedthrough term reduces the uncertainty associated with the truncated model, which is instrumental in ensuring the robustness of the closed-loop system. The controller is applied to a simply-supported piezoelectric-laminate beam and is validated experimentally to show the effectiveness of the proposed controller in suppressing structural vibration. It is shown that the spatial H/sub /spl infin//. control has an advantage over the pointwise H/sub /spl infin// control in minimizing the vibration of the entire structure. This spatial H/sub /spl infin// control methodology can also be applied to more general structural vibration suppression problems.     

MOS characteristics of substituted Al gate on high-/spl kappa/ dielectric

Substituted aluminum (SA) metal gate on high-/spl kappa/ gate dielectric is successfully demonstrated. Full substitution of polysilicon with Al is achieved for a Ti-Al-polysilicon-HfAlON gate structure by a low-temperature annealing at 450/spl deg/C. The SA gate on HfAlON dielectric shows a very low work function of 4.25eV, which is well suitable for bulk nMOSFETs. The SA process is fully free from the Fermi-level pinning problem. In addition, the SA process also shows improved uniformity in leakage current distribution compared to fully silicided metal gate.     

Microstructures of epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thick films grown by photoassisted metal-organic chemical vapor deposition

Epitaxial, high-quality YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films were grown by a photoassisted metal-organic chemical vapor deposition technique with a single liquid precursor delivery system, and characterized by X-ray diffraction (XRD), scanning electron microscopy, and low-high-resolution transmission electron microscopy techniques. Very dense and single-crystal-like film structure was observed in all of these YBCO thick films. Large precipitates on these thick films were identified as BaCu/sub 3/O/sub 4/, sprinkled only at surface of these YBCO thick films. YBCO thick films with high crystalline and superconductive quality were confirmed by data of XRD analyses and superconductivity measurements. At the same time, the reason why epitaxial YBCO thick films with high-quality single-crystal-like structure can be grown up to about 4.5 /spl mu/m thick is illustrated from the point of view of photoactivation. It is also found that these thick films were optimally oxygenated with their superconductive properties in concern.     

Effect of Mg doping on the superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta//

Superconducting properties of Cu/sub 1-x/Tl/sub x/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta// (Cu/sub 1-x/Tl/sub x/Mg/sub y/-1234) material have been studied in the composition range y=0,1.5,2.25. The zero resistivity critical temperature [T/sub c/(R=0)] was found to increase with the increased concentration of Mg in the unit cell; for y=1.5 [T/sub c/(R=0)]=131 K was achieved which is hitherto highest in Cu/sub 1-x/Tl/sub x/-based superconductors. The X-ray diffraction analyses have shown the formation of a predominant single phase of Cu/sub 0.5/Tl/sub 0.5/Ba/sub 2/Ca/sub 3-y/Mg/sub y/Cu/sub 4/O/sub 12-/spl delta// superconductor with an inclusion of impurity phase. It is observed from the convex shape of the resistivity versus temperature measurements that our as-prepared material was in the region of carrier over-doping, and the number of carriers was optimized by postannealing experiments in air at 400/spl deg/C, 500/spl deg/C, and 600/spl deg/C. The T/sub c/(R=0) was found to increase with postannealing and the best postannealing temperature was found to be 600/spl deg/C. The mechanism of increased T/sub c/(R=0) is understood by carrying out infrared absorption measurements. It was observed through softening of Cu(2)-O/sub A/-Tl apical oxygen mode that improved interplane coupling was a possible source of enhancement of T/sub c/(R=0) to 131 K.     

Electrical characteristics of 8-/spl Aring/ EOT HfO/sub 2//TaN low thermal-budget n-channel FETs with solid-phase epitaxially regrown junctions

The authors demonstrate high-performing n-channel transistors with a HfO/sub 2//TaN gate stack and a low thermal-budget process using solid-phase epitaxial regrowth of the source and drain junctions. The thinnest devices have an equivalent oxide thickness (EOT) of 8 /spl Aring/, a leakage current of 1.5 A/cm/sup 2/ at V/sub G/=1 V, a peak mobility of 190 cm/sup 2//V/spl middot/s, and a drive-current of 815 /spl mu/A//spl mu/m at an off-state current of 0.1 /spl mu/A//spl mu/m for V/sub DD/=1.2 V. Identical gate stacks processed with a 1000-/spl deg/C spike anneal have a higher peak mobility at 275 cm/sup 2//V/spl middot/s, but a 5-/spl Aring/ higher EOT and a reduced drive current at 610 /spl mu/A//spl mu/m. The observed performance improvement for the low thermal-budget devices is shown to be mostly related to the lower EOT. The time-to-breakdown measurements indicate a maximum operating voltage of 1.6 V (1.2 V at 125 /spl deg/C) for a ten-year lifetime, whereas positive-bias temperature-instability measurements indicate a sufficient lifetime for operating voltages below 0.75 V.     

Effects of interstitial oxygen defects at HfO/sub x/N/sub y//Si interface on electrical characteristics of MOS devices

Effects of the defects at high-/spl kappa/ dielectric/Si interface on the electrical characteristics of MOS devices are important issues. To study these issues, a low defect (denuded zone) at Si surface was formed by a high-temperature annealing in hydrogen atmosphere in this paper. Our results reveal that HfO/sub x/N/sub y/ demonstrates significant improvement on the electrical properties of MOS devices due to its low amount of the interstitial oxygen [O/sub i/] and the crystal-originated particles defects as well as small surface roughness at HfO/sub x/N/sub y//Si interface. The current-conduction mechanism of the HfO/sub x/N/sub y/ film at the low- and high-electrical field and high-temperature (T>100/spl deg/C) is dominated by Schottky emission and Frenkel-Poole (FP) emission, respectively. The trap energy level involved in FP conduction was estimated to be around 0.5eV. Reduced gate leakage current, stress-induced leakage current and defect generation rate, attributable to the reduction of defects at HfO/sub x/N/sub y//Si interface, were observed for devices with denuded zone. The variable rise and fall time bipolar-pulse-induced current technique was used to determine the energy distribution of interface trap density (D/sub it/). The results exhibit that relatively low D/sub it/ can be attributed to the reduction of defects at Si surface. By using denuded zone at the Si surface, HfO/sub x/N/sub y/ has demonstrated significant improvement on electrical properties as compared to SiO/sub x/N/sub y/.     

Effect on ion implanted germanium profile on the characteristics of Si/sub 1-x/Ge/sub x//Si heterojunction bipolar transistors

An optimum profile for Ge ion implantation in SiGe/Si heterojunction bipolar transistors is determined by using a two-dimensional simulator code for advanced semiconductor devices. The simulation code is based on a two-dimensional drift-diffusion model for heterostructure degenerate semiconductors with nonparabolicity included in the energy band structure. The model allows accurate simulations of carrier transport in short base devices. The simulation results indicate that for high current gain the Ge profile maximum must be close to the base-collector junction, and that the unavoidable tail of the implanted germanium in the collector region does not deteriorate the gain.<>     

Simulations of microwave characteristics of high-temperature superconducting microstrip lines by using an empirical two-fluid model

A numerical analysis of the microwave propagation characteristics of a high-temperature superconducting microstrip transmission line is presented. It is based on the transmission line theory and empirical two-fluid model which appropriately incorporates the quasiparticle scattering and residual loss of the superconductor. First, the calculated attenuation constant and phase velocity are compared with those predicted by the conventional two-fluid model for a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// microstrip line with a linear substrate, lanthanum aluminate, LaAlO/sub 3/. Next, we have specifically investigated the effects of nonlinear substrate such as strontium titanate, SrTiO/sub 3/, on the attenuation constant and phase velocity. The tunable feature of such a microwave device owing to the nonlinear dielectric ferroelectric is illustrated and discussed.     

Studies of CW laser oscillation on the 1315-nm transition of atomic iodine pumped by O/sub 2/(a/sup 1//spl Delta/) produced in an electric discharge

In this paper, we report on studies of a continuous-wave laser at 1315 nm on the I(/sup 2/P/sub 1/2/)/spl rarr/I(/sup 2/P/sub 3/2/) transition of atomic iodine where the O/sub 2/(a/sup 1//spl Delta/) used to pump the iodine was produced by a radio frequency excited electric discharge. The electric discharge was sustained in He-O/sub 2/ and Ar-O/sub 2/ gas mixtures upstream of a supersonic cavity which is employed to lower the temperature of the continuous gas flow and shift the equilibrium of atomic iodine in favor of the I(/sup 2/P/sub 1/2/) state. The results of experimental studies for several different flow conditions, discharge arrangements, and mirror sets are presented. The highest laser output power obtained in these experiments was 520 mW in a stable cavity composed of two 99.995% reflective mirrors.     

Fabrication of MOD-derived YBCO films on [001]LaAlO/sub 3/ and their application to /spl lambda//4 CPW SIR BPFs

Chemically derived epitaxial thin films of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) are fabricated on [001]LaAlO/sub 3/ substrates by the metalorganic-deposition (MOD) process, which has advantages of high quality, nonvacuum, low-cost, and large-scale production of high-T/sub c/ superconducting films. The MOD-derived YBCO films have a sharp transition at the critical temperature (90.4 K) and a high-quality film with a surface resistance of 0.13 m/spl Omega/ (30 K, 9.98 GHz) is obtained. As a microwave application, simple and compact bandpass filters (BPFs) using /spl lambda//4 coplanar-waveguide. stepped-impedance resonators are demonstrated on the YBCO films. A two-stage Chebyshev BPF of center frequency of 5.731 GHz, bandwidth of 135 MHz, and insertion loss of 0.29 dB with little input power dependency in a power range less than 10 dBm is realized on the film.     

Electrical and reliability characteristics of an ultrathin TaO/sub x/N/sub y/ gate dielectric prepared by ND/sub 3/ annealing of Ta/sub 2/O/sub 5/

This letter describes a unique process for the preparation of high quality tantalum oxynitride (TaO/sub x/N/sub y/) via the ND/sub 3/ annealing of Ta/sub 2/O/sub 5/, for use in gate dielectric applications. Compared with tantalum oxide (Ta/sub 2/O/sub 5/), a significant improvement in the dielectric constant was obtained by the ammonia treatment followed by light reoxidation in a wet ambient. We were able to confirm nitrogen incorporation in the tantalum oxynitride (TaO/sub x/N/sub y/) by Auger electron spectroscopy. Compared with NH/sub 3/ nitridation, tantalum oxynitride prepared by nitridation in ND/sub 3/ shows less charge trapping and larger charge-to-breakdown characteristics.     

Path to the measurement of positive gain on the 1315-nm transition of atomic iodine pumped by O/sub 2/(a/sup 1//spl Delta/) produced in an electric discharge

Laser action at 1315 nm on the I(/sup 2/P/sub 1/2/)/spl rarr/I(/sup 2/P/sub 3/2/) transition of atomic iodine is conventionally obtained by a near-resonant energy transfer from O/sub 2/(a/sup 1//spl Delta/) which is produced using wet-solution chemistry. The system difficulties of chemically producing O/sub 2/(a/sup 1//spl Delta/) have motivated investigations into gas phase methods to produce O/sub 2/(a/sup 1//spl Delta/) using low-pressure electric discharges. We report on the path that led to the measurement of positive gain on the 1315-nm transition of atomic iodine where the O/sub 2/(a/sup 1//spl Delta/) was produced in a flowing electric discharge. Atomic oxygen was found to play both positive and deleterious roles in this system, and as such the excess atomic oxygen was scavenged by NO/sub 2/ to minimize the deleterious effects. The discharge production of O/sub 2/(a/sup 1//spl Delta/) was enhanced by the addition of a small proportion of NO to lower the ionization threshold of the gas mixture. The electric discharge was upstream of a continuously flowing supersonic cavity, which was employed to lower the temperature of the flow and shift the equilibrium of atomic iodine more in favor of the I(/sup 2/P/sub 1/2/) state. A tunable diode laser system capable of scanning the entire line shape of the (3,4) hyperfine transition of iodine provided the gain measurements.     

Design optimization of high breakdown voltage AlGaN-GaN power HEMT on an insulating substrate for R/sub ON/A-V/sub B/ tradeoff characteristics

High breakdown voltage AlGaN-GaN power high-electron mobility transistors (HEMTs) on an insulating substrate were designed for the power electronics application. The field plate structure was employed for high breakdown voltage. The field plate length, the insulator thickness and AlGaN layer doping concentration were design parameters for the breakdown voltage. The optimization of the contact length and contact resistivity reduction were effective to reduce the specific on-resistance. The tradeoff characteristics between the on-resistance and the breakdown voltage can be improved by the optimization of the above design parameters, and the on-resistance can be estimated to be about 0.6 m/spl Omega//spl middot/cm/sup 2/ for the breakdown voltage of 600 V. This on-resistance is almost the same as that for the device on a conductive substrate.