Modal characteristics of ferrimagnetic tridisk-coupled resonator

The eigenvalue characteristics of a ferrimagnetic tridisk-coupled (TDC) resonator are described first. A TDC resonator is made of three AlYIG ferrite disks partially scraped and mutually attached on a center conductor. The EM field is treated with a consistent theory. The eigenvalue characteristics computed with stress on the mode of ν=1 are represented by the Z₁₀ versus Z₀ and Z₁ versus κ/μ relationships, where Z₁₀ is a degenerate eigenvalue, Z₀ is a wavenumber-eccentric radius product, and Z₁ is a continuously varying eigenvalue dependent on κ/μ with a given value of Z₀. Z₁₀ is distinguished by either a single- or double-value region as a function of Z₀. The computed Z₁ versus κ/μ graph belonging to the double-value region demonstrates a contradiction to the physical reality, which is resolved by introducing an equivalent circular resonant mode. The equivalent resonant mode is definitely identified by a degenerate eigenvalue and its modal curve with large modal separation. Experiments were carried out with various center conductors. The experimental results support the equivalent resonant mode. Finally, discussions are presented     

Enhancement of breakdown voltage in AlGaN/GaN high electronmobility transistors using a field plate

We investigate the breakdown (V_br) enhancement potential of the field plate (FP) technique in the context of AlGaN/GaN power HEMTs. A comprehensive account of the critical geometrical and material variables controlling the field distribution under the FP is provided. A systematic procedure is given for designing a FP device, using two-dimensional (2-D) simulation, to obtain the maximum V_br , with minimum degradation in on-resistance and frequency response. It is found that significantly higher V_br can be achieved by raising the dielectric constant (ε_i) of the insulator beneath the FP. Simulation gave the following estimates. The FP can improve the V_br by a factor of 2.8-5.1, depending on the 2-DEG concentration (n_s) and ε_i. For n _s=1×10¹³/cm², the V_br can be raised from 123 V to 630 V, using a 2.2 μm FP on a 0.8 μm silicon nitride, and 4.7 μm gate-drain separation. The methodology of this paper can be extended to the design of FP structures in other lateral FETs, such as MESFETs and LD-MOSFETs     

A simple yet comprehensive unified physical model of the 2Delectron gas in delta-doped and uniformly doped high electron mobilitytransistors

This paper presents a new approach to model the 2DEG concentration (n_s) versus gate voltage (V_G) behavior and the equilibrium 2DEG concentration (n_s0) in a HEMT. The approach results in a model which is “comprehensive” in the following sense. It is valid for both delta-doped and uniformly doped HEMTs. It captures all the three n_s-V_G nonlinearities (subthreshold, gradual pinchoff, and gradual saturation), and the effects of all the device parameters including temperature, in relation expressing n_s as an explicit closed-form integrable function of V_G having continuous first derivatives; thus, the function readily yields a device current-voltage/capacitance-voltage (I-V/C-V) model which can be incorporated in software meant for simulation of circuits, particularly of the analog variety. The simple model is shown to predict the results of complex numerical calculations and experiments. The closed-form n_s0 expression of the model is the first of its kind reported for delta-doped HEMT's, and reveals an interesting feature unexposed by earlier n_s0 models: the reciprocal of n_s0 in both delta-doped and uniformly doped devices decreases linearly with reduction in spacer width, and saturates at low spacer widths in some delta-doped devices. It is shown that the measured n_s0 in delta-doped devices is predicted correctly if the electrons in the V-shaped well are assumed to be trapped at the donor sites rather than to be filling the conduction subbands     

A new approach to determine the effective channel length and thedrain-and-source series resistance of miniaturized MOSFET's

A new decoupled C-V method is proposed to determine the intrinsic (effective) channel region and extrinsic overlap region for miniaturized MOSFET's. In this approach, a unique channel-length-independent extrinsic overlap region is extracted at a critical gate bias, so bias-independent effective channel lengths (L_eff) are achieved. Furthermore, the two-dimensional (2D) charge sharing effect is separated from the effective channel region. Based on this L_eff and the associated bias-dependent channel mobility, μ_eff , the drain-and-source series resistance (R_DS) can be derived from the I-V characteristics for each device individually. For the first time, the assumption or approximation for R_DS and μ_eff can be avoided, thus the difficulties and controversy encountered in the conventional I-V method can be solved. The 2D charge sharing effect is incorporated into the bias-dependent R_DS. This bias dependence is closely related to the drain/source doping profile and the channel dopant concentration. The proposed L_eff and R_DS extraction method has been verified by an analytical I-V model which shows excellent agreements with the measured I-V characteristics     

Robust decoding for timing channels

To transmit information by timing arrivals to a single-server queue, we consider using the exponential server channel's maximum likelihood decoder. For any server with service times that are stationary and ergodic with mean 1/μ seconds, we show that the rate e ^-1μ nats per second (capacity of the exponential server timing channel) is achievable using this decoder. We show that a similar result holds for the timing channel with feedback. We also show that if the server jams communication by adding an arbitrary amount of time to the nominal service time, then the rate e^-1μ₁μ₂/(μ₁+μ ₂) nats per second is achievable with random codes, where the nominal service times are stationary and ergodic with mean 1/μ₁ seconds, and the arithmetic mean of the delays added by the server does not exceed 1/μ₂ seconds. This is a model of an arbitrarily varying channel where the current delay and the current input can affect future outputs. We also show the counterpart of these results for single-server discrete-time queues     

On the weight hierarchy of Preparata codes over Z4

Hammons et al. (see ibid., vol.40, p.301-19, 1994) showed that, when properly defined, the binary nonlinear Preparata code can be considered as the Gray map of a linear code over Z₄, the so called Preparata code over Z₄. We consider the rth generalized Hamming weight d_r(m) of the Preparata code of length 2^m over Z₄. For any m⩾3, d_r(m) is exactly determined for r=0.5, 1, 1.5, 2, 2.5 and 3.0. For a composite m, we give an upper bound on d_r(m) using the lifting technique. For m=3, 4, 5, 6 and 8, the weight hierarchy is completely determined. In the case of m=7, the weight hierarchy is completely determined except for d₄(7)     

A new SPICE MOSFET Level 3-like model of HEMT's for circuitsimulation

A fully analytical model for the current-voltage (I-V) characteristics of HEMT's is presented. It uses a polynomial expression to model the dependence of sheet carrier concentration (n_s) in the two-dimensional electron gas (2-DEG) on gate voltage (V_G ). The resultant I-V relationship incorporates a correction factor α analogous to SPICE MOSFET Level 3 model and is therefore more accurate than models assuming a linear n_s-V_G dependence leading to square law type I-V characteristics. The model shows excellent agreement with experimental data over a wide range of bias. Further, unlike other models using nonlinear n_s-V_G dependence, it neither uses fitting parameters nor does it resort to iterative methods at any stage. It also includes the effects of the extrinsic source and drain resistances. Due to its simplicity and similarity in formulation to the SPICE MOSFET Level 3 model, it is ideally suited for circuit simulation purposes     

A macroscopic model of nonlinear constitutive relations insuperconductors

A macroscopic model is proposed for nonlinear electromagnetic phenomena in superconductors. Nonlinear constitutive relations are derived by modifying the linear London's equations. The superelectron number density as a function of applied macroscopic current density, n _s(J), is derived from a distribution of electron velocities at a certain temperature T. At temperature T≠0 K, the function n_s(J) has a smooth variation near the macroscopic critical current density J_c. Agreement has been found between this n _s(J,T) model and the temperature dependence of n_s in the two-fluid model. The nonlinear conductivities σ_s(J) and σ_n(J) are obtained from the London's equation with the modified n_s(J) function. Nonlinear resistance R(I), kinetic inductance L_k(I) and surface impedance Z_s(I) in thin wire, slab, and strip geometries are calculated     

Real-valued maximum likelihood decoder for quasi-orthogonal space-time block codes

In this letter, we propose a low complexity Maximum Likelihood (ML) decoding algorithm for quasi-orthogonal space-time block codes (QOSTBCs) based on the real-valued lattice representation and QR decomposition. We show that for a system with rate r = n_s/T, where n_s is the number of transmitted symbols per T time slots; the proposed algorithm decomposes the original complex-valued system into a parallel system with n_s 2 × 2 real-valued components, thus allowing for a simple joint decoding of two real symbols. For a square QAM constellation with L points (L-QAM), this algorithm achieves full diversity by properly incorporating two-dimensional rotation using the optimal rotation angle and the same rotating matrix for any number of transmit antennas (N ⩾4). We show that the complexity gain becomes greater when N or L becomes larger. The complexity of the proposed algorithm is shown to be linear with the number of transmitted symbols n_s.     

Z4×(F2+uF2)上的一类循环码

定义了Z₄×（F₂+uF₂）上的循环码,明确了一类循环码的生成元结构,给出了该类循环码的极小生成元集.利用Gray映射,构造了一些二元非线性码.     

The inaccuracy of Kubicek's one-cylinder model in thoracicimpedance cardiography

The validity of a one- and a two-cylinder model, underlying thoracic impedance cardiography (TIC), was investigated by studying the length dependence of the impedance parameters Z₀, (dZ/dt)_min, and stroke volume (SV). It can be shown that, within a one-cylinder model, all parameters are directly proportional to the length, whereas, if the volume conduction of the thorax and the neck are modeled separately, Z₀ and (dZ/dt)_min are expected to be linear dependent and SV will he nonlinear dependent upon the length. The expectations were compared to results from in vivo measurements. Two electrode arrays were studied, in which the caudal recording electrode position was varied; SV was calculated using Kubicek's equation. Except for small distances, the results showed a nearly linear relation between the parameters and the length. Regression analysis of the linear part revealed statistically significant intercepts (p<0.05). Neither the intercept nor the nonlinear part can be explained by a one-cylinder model, whereas a model consisting of two cylinders serially connected describes the experimental results accurately. Thus SV estimation based on a one-cylinder model is biased due to the invalid one-cylinder model. Corrections for the Kubicek-equation need to be developed in future research using this two-cylinder model     

A new technique for measuring MOSFET inversion layer mobility

An experimental technique for accurately determining both the inversion charge and the channel mobility μ of a MOSFET is presented. With this new technique, the inversion charge is measured as a function of the gate and drain voltages. This improvement allows the channel mobility to be extracted independent of drain voltage V_DS over a wide range of voltages (V_DS=20-100 mV). The resulting μ(V_GS) curves for different V_DS show no drastic mobility roll-off at V _GS near V_TH. This suggests that the roll-off seen in the mobility data extracted using the split C- V method is probably due to inaccurate inversion charge measurements instead of Coulombic scattering     

Dispersive subband-resonant nonlinearity in amorphous Si/SiO2 quantum well structures

Dispersive nonlinearity in amorphous Si/SiO₂ quantum well structures (QW's) has been investigated. The refractive index changes obtained from the intensity-dependent reflection spectra are nonlinearly dependent on the excitation intensity and can be described by the model of the saturating nonlinearity at low pump intensities. The nonlinear refractive index reveals resonant behavior associated with the subband structure of the QW's. The saturated nonlinear index and the saturation intensity have been obtained as Δn_s=-0.11 and I_s=1.9 MW/cm² at the transitions between the lowest subbands, and Δn_s~0.3 and I_s~0.5 MW/cm² at the transitions between the second subbands of the valence and conduction bands. The nonlinearity for the second subband transitions has been found high enough to provide potentially bistable operation, but the bistability is not expected at the transitions between the ground subbands. Carrier lifetime less than 1 ps restricting the switching time of the nonlinearity has been estimated from the saturation intensity     

Algebraic construction of cyclic codes over Z8 with agood Euclidean minimum distance

Let S(8) denote the set of the eight admissible signals of an 8PSK communication system. The alphabet S(8) is endowed with the structure of Z₈, the set of integers taken modulo 8, and codes are defined to be Z₈-submodules of Z₈ⁿ. Three cyclic codes over Z₈ are then constructed. Their length is equal to 6, 8, and 7, and they, respectively, contain 64, 64, and 512 codewords. The square of their Euclidean minimum distance is equal to 8, 16-4√2 and 10-2√2, respectively. The size of the codes of length 6 and 7 can be doubled while the Euclidean minimum distance remains the same     

High channel mobility in inversion layers of 4H-SiC MOSFETs byutilizing (112¯0) face

A dramatic improvement of inversion channel mobility in 4H-SiC MOSFETs was successfully achieved by utilizing the (112¯0) face: 17 times higher (95.9 cm²/Vs) than that on the conventional (0001) Si-face (5.59 cm²/Vs). A low threshold voltage of MOSFETs on the (112¯0) face indicates that the (112¯0) MOS interface has fewer negative charges than the (0001) MOS interface. Small anisotropy of channel mobility in 4H-SiC MOSFETs (μ_(11¯00)/μ₍₀₀₀₁₎=0.85) reflects the small anisotropy in bulk electron mobility     

Cyclic codes and self-dual codes over F2+uF2

We introduce linear cyclic codes over the ring F₂+uF ₂={0,1,u,u¯=u+1}, where u²=0 and study them by analogy with the Z₄ case. We give the structure of these codes on this new alphabet. Self-dual codes of odd length exist as in the case of Z₄-codes. Unlike the Z₄ case, here free codes are not interesting. Some nonfree codes give rise to optimal binary linear codes and extremal self-dual codes through a linear Gray map     

The correlation between gate current and substrate current in 0.1μm NMOSFET's

The correlation between gate and substrate currents in NMOSFET's with effective channel length, L_eff, down to 0.1 μm is investigated within the general framework of the lucky-electron model. It Is found that the correlation coefficient, Φb/Φ_i, decreases with decreasing L_eff in the 0.1 μm regime, where Φ_b is the effective Si-SiO₂ barrier height for channel hot-electrons, and Φ_i is the effective threshold potential for impact ionization. Furthermore, this effect becomes stronger in NMOSFET's with shorter L_eff. These experimental results suggest the need for further investigation on specific assumptions in the lucky-electron model to understand hot-electron behavior and impact ionization-mechanisms in 0.1 μm-scale NMOSFET's     

High-linearity high-current-drivabilityGa0.51In0.49P/GaAs MISFET usingGa0.51In0.49P airbridge gate structure grown byGSMBE

A novel structure Ga_0.51In_0.49P/GaAs MISFET with an undoped Ga_0.51In_0.49P layer serving as the airbridge between active region and gate pad was first designed and fabricated. Wide and flat characteristics of g_m and f_max versus drain current or gate voltage were achieved. The device also showed a very high maximum current density (610 mA/mm) and a very high gate-to-drain breakdown voltage (25 V). Parasitic capacitances and leakage currents were minimized by the airbridge gate structure and thus high f_T of 22 GHz and high f_max of 40 GHz for 1 μm gate length devices were attained. To our knowledge, both were the best reported values for 1 μm gate GaAs channel FET's     

High-performance devices for a 0.15-μm CMOS technology

Devices have been designed and fabricated in a CMOS technology with a nominal channel length of 0.15 μm and minimum channel length below 0.1 μm. In order to minimize short-channel effects (SCEs) down to channel lengths below 0.1 μm, highly nonuniform channel dopings (obtained by indium and antimony channel implants) and shallow source-drain extensions/halo (by In and Sb preamorphization and low-energy As and BF₂ implant were used. Maximum high V _DS threshold rolloff was 250 mV at effective channel length of 0.06 μm. For the minimum channel length of 0.1 μm, the loaded (FI=FO=3, C=240 fF) and unloaded delays were 150 and 25 ps, respectively     

MOVPE-grown millimeter-wave InGaAs mixer diode technology andcharacteristics

The merits of InGaAs-based millimeter-wave mixer diodes are explored experimentally and theoretically. Schottky junctions on InGaAs exhibit barriers (φ_b) in the neighborhood of 0.25 eV. The high mobility of InGaAs contributes to the low n⁺ sheet resistances of 1.9-5 Ω/square for 1-μm n⁺ InGaAs layers (n_s=1.5×10¹⁹ cm^-3, μ _n=1800 cm²/V·s) grown with our in-house Metalorganic Vapor Phase Epitaxy (MOVPE) system, The design, material growth, fabrication, and characterization of InGaAs integrated mixer/antennae are reported. Pt plating technology, adapted here for InGaAs Schottky contacts, has improved the ideality factor (η) and yield relative to conventional evaporated Pt. With 810 μW of local oscillator power, applied to the diode, and zero DC bias, an integrated InGaAs mixer/antenna demonstrated an excellent diode performance of 199 K RF input double-sideband noise temperature with a corresponding single-sideband (SSB) conversion loss (L_c) of 5.0 dB at LO, RF, and IF frequencies of 94 GHz, 94 GHz±1.4 GHz, and 1.4 GHz, respectively. Likewise, the diodes in an InGaAs subharmonic integrated mixer/antenna demonstrated an equivalent RF-port double-sideband (DSB) noise temperature (T_mix) of 1058 K and single-sideband conversion loss of 10.2 dB at 180 GHz with a 90-GHz LO power (PLO) of 1.6 mW. Compared to GaAs diodes with RF coupling and IF losses removed, the single-ended InGaAs noise temperature results were within 46-100 K of those for state-of-the-art GaAs mixer diodes while requiring significantly less LO power