Series impedance of GaAs planar Schottky diodes operated to 500 GHz

The author discusses the impact of ohmic contacts on the series impedance of a GaAs cylindrical planar Schottky diode. The expression for the high-frequency impedance of an annular ohmic contact is developed using a novel transmission line model. This formulation is used to ascertain the contribution of the ohmic contact impedance to the overall device series impedance at both DC and 500 GHz. Diode impedance characterization indicates that the ohmic contact impedance makes a small contribution to the series impedance in comparison to that of the other components, both at DC and submillimeter wavelengths. Hence, the dimensions of the contact pads can be scaled down significantly without any appreciable increase in series impedance but with a decrease in the parasitic pad-to-pad capacitance. Finally, this modeling establishes theoretical guidelines regarding the allowable limits for specific contact resistance in small geometry diodes, so that the device I -V characteristics are not significantly altered as a result of the ohmic contact impedance     

Diamond transistor performance and fabrication

The author reviews some of the device properties of diamonds, as well as recently developed diamond device fabrication techniques for high-frequency, high-power transistors. Two advantages of diamond over other semiconductors used for high-frequency, high power devices are its high thermal conductivity and high electric-field breakdown. Homoepitaxial diamond has been grown by both plasma and hot-filament techniques. The device properties of homoepitaxial diamond produced by the hot-filament technique are reviewed. Much of the development necessary for the production of diamond devices already exists. Doping by homoepitaxy, diamond etching, device quality SiO₂-diamond interface, and ohmic contact technology are reviewed. The remaining problems are the development of large area single crystal diamond substrates, improvement of doping techniques, and refinement in ohmic contact technology     

Circular-pad via model based on cavity field analysis

An equivalent circuit model of a circular-pad grounding via is proposed based on cavity modal analysis. The modes of the via are derived analytically. Each mode is represented by an equivalent circuit taking into account ohmic losses, as well as losses due to spatial and surface wave radiation. It is shown that the degradation of grounding via characteristics at high frequencies is caused by the multimode effects and radiation. The accuracy of the proposed semi-analytical via model is comparable with that of full-wave analysis up to 75 GHz. It is fast and is easily incorporated in high-frequency circuit simulators.     

A Transmission-Line Model for Full-Wave Analysis of Mixed-Mode Propagation

The paper presents a generalized transmission line model able to describe the high-frequency mixed-mode propagation along electrical interconnects. The model is derived from a full-wave formulation and extends the validity of the standard transmission line (TL) model to frequency ranges where the propagation is no longer of transmission electron microscopy (TEM)-type. This generalized TL model describes the high-frequency differential and common mode propagation and the mode conversion. Within its validity limits, the proposed model provides solutions in good agreement with those obtained through full-wave models. Case studies are carried out to evaluate the high-frequency mode conversion in asymmetric interconnects.     

The Propagation Constants of Higher-Order Modes in Coaxial Waveguides With Finite Conductivity

Overmoded coaxial waveguides have been used in coaxial gyrotrons as a key interaction structure. To achieve the required mode selectivity, the resistivity of the center conductor is properly chosen to damp unwanted modes. Considering attenuation due to conductor loss, this study employs the perturbational method to determine the propagation constants of higher-order modes in the coaxial waveguide. The validity of the theoretical model is confirmed by comparison with results obtained using the high-frequency structure simulator (HFSS). Moreover, the method proposed herein is applied to analyze the ohmic mode selection of the coaxial waveguide.     

An Analysis of the Diode Mixer Consisting of Nonlinear Capacitance and Conductance and Ohmic Spreading Resistance

A method is presented for calculating the mixer admittance matrix Y' which results when an ohmic impedance is connected in series with a diode mixer described by an admittance matrix Y. There are no restrictions on the frequency dependence of the ohmic impedance nor on the number of harmonic sidebands considered. The equations are worked out in detail for the "low Q" case in which signal, image, and intermediate frequencies are considered, and it is shown that Y' in this case is "nearly low Q." As a result of this analysis the usual criterion for good high-frequency mixing, i.e., that the product of the spreading resistance and the barrier capacitance be small compared with unity, is criticized and a new figure of merit is proposed. Explicit formulas have been derived for calculating the elements of Y' when Y represents the parallel combination of a nonlinear conductance and capacitance. In general, these formulas are cumbersome, but three special cases have been considered in detail.     

AlGaAs/GaAs HBTs for 10-Gb/s ICs using a new base ohmic contactfabrication process

A new basic ohmic contact technology for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is presented. The effect of the device parameters on the high-frequency performance of HBT ICs for 10-Gb/s systems is analyzed, and it is shown that, at a cutoff frequency (f_T) of 40 GHz or more, reducing base resistance or collector capacitance is more effective than increasing f_T for obtaining high-frequency performance. A process is developed for fabricating base electrodes with a very low ohmic contact resistivity, ~10^-7 Ω-cm², by using a AuZn/Mo/Au alloy, which provides the required high performance. Self-aligned AlGaAs/GaAs HBTs, with a 2.5-μm×5-μm emitter, using a AuZn/Mo/Au alloy base metal and an undoped GaAs collector, are shown to have an f_T and a maximum oscillation frequency of about 45 and 70 GHz, respectively, at 3.5 mA. An AGC amplifier with a 20-dB gain and a bandwidth of 13.7 GHz demonstrates stable performance     

Analytical treatment of MOSFET source—Drain resistance

Series resistance in the metal-oxide-semiconductor field-effect transistor becomes increasingly important as design rules shrink. Material properties associated with the interconnect metal, the semiconductor, and the interface separating the two regions thus assume greater importance. An analytical formulation of the resistance in terms of these material properties is thus quite desirable. We formulate and solve a two-dimensional model of current flow by the method of matched asymptotic expansions. The major utility of this solution is provided by higher order corrections to the standard transmission line model of current flow in the ohmic contact region. We find that present methods for the extraction of material properties from experimental measurements with a transmission line model analysis would be enhanced by the inclusion of higher order terms we present here.     

A generalized dynamic circuit model of magnetic cores for low- andhigh-frequency applications. II. Circuit model formulation andimplementation

This paper describes the formulation and implementation of a generalized dynamic magnetic core circuit model suitable for both low- and high-frequency applications. The behavior of magnetic cores with any arbitrary flux waveforms is modeled by a simple ladder network consisting of nonlinear inductors and resistors. The nonlinear B-H loop and the hysteresis loss are incorporated in distributed nonideal inductors and calculated by the Preisach scalar model of magnetic hysteresis. The eddy current and anomalous losses are accounted for by the generalized nonlinear equivalent resistors reported in Part I of the paper. The transmission line modeling method is employed to solve the nonlinear state equations. Numerical aspects and software implementation of the model are discussed. The generalized model has been verified by simulations and measurements at both low- and high-frequency operations     

Lateral space-charge effects on ballistic electron transport across graded heterojunctions

Hot electron transport across graded compound semiconductor heterojunctions has been explored using a two-dimensional formulation of the self-consistent ensemble Monte Carlo method. The Al_xGa_1-xAs/GaAs heterojunction imbedded into a vertical field effect transistor with two ohmic contacts (source, drain) and two lateral Schottky gates has been used as an example. Lateral space charges modulated by the gates are shown to control ballistic injection of electrons over the heterojunction under steady state conditions. The transient response to a gate pulse is found to be determined by carrier transit from the heavily doped source contact region into the channel. A conceptual one-dimensional section model is used to explain the Monte Carlo results.     

Noise Loading Analysis in FDM Systems

This paper investigates the characterization of nonlinear distortion produced in FDM systems under high-frequency operation, by using noise loading techniques. By employing a general Volterra-based model, the paper develops an appropriate noise loading technique for the assessment of nonlinear distortion in such wide-band transmission systems. The advantage of using Volterra series representation is that it takes account of system nonlinear-memory behavior in a combined formulation.     

Theoretical and experimental investigation of the fast- andslow-scale instabilities of a DC-DC converter

We use an exact formulation based on nonlinear maps to investigate both the fast-scale and slow-scale instabilities of a voltage-mode buck converter operating in the continuous conduction mode and its interaction with a filter. Comparing the results of the exact model with those of the averaged model shows the shortcomings of the latter in predicting fast-scale instabilities. We show the impact of parasitics on the onset of chaos using a high-frequency model. The experimentally validated theoretical results of this paper provide an improved understanding of the dynamics of the converter beyond the linear regime and this may lead to less conservative control design and newer applications     

Ni基n型SiC材料的欧姆接触机理及模型研究

研究了Ni基n型SiC材料的欧姆接触的形成机理,认为合金化退火过程中形成的C空位(Vc)而导致的高载流子浓度层对欧姆接触的形成起了关键作用。给出了欧姆接触的能带结构图,提出比接触电阻ρC由ρC1和ρC2两部分构成。ρC1是Ni硅化物与其下在合金化退火过程中形成的高载流子浓度层间的比接触电阻,ρC2则由高载流子浓度层与原来SiC有源层之间载流子浓度差形成的势垒引入。该模型较好地解释了n型SiC欧姆接触的实验结果,并从衬底的掺杂水平、接触金属的选择、合金化退火的温度、时间、氛围等方面给出了工艺条件的改进建议。     

Effect of annealing temperature on Ti/Al/Ni/Au ohmic contacts on undoped AlN films

The Ti/Al/Ni/Au metals were deposited on undoped AlN films by electron beam evaporation. The influence of annealing temperature on the properties of contacts was investigated. When the annealing temperatures were between 800 and 950℃, the AlN-Ti/Al/Ni/Au contacts became ohmic contacts and the resistance decreased with the increase of annealing temperature. A lowest specific contacts resistance of 0.379 Ω·cm² was obtained for the sample annealed at 950℃. In this work, we confirmed that the formation mechanism of ohmic contacts on AlN was due to the formation of Al-Au, Au-Ti and Al-Ni alloys, and reduction of the specific contacts resistance could originate from the formation of Au₂Ti and AlAu₂ alloys. This result provided a possibility for the preparation of AlN-based high-frequency, high-power devices and deep ultraviolet devices.     

Improved analysis of low frequency noise in dynamic threshold MOS/SOI transistors

In this paper, low-frequency noise (LFN) in N- and P-channel dynamic-threshold (DT) MOSFETs on Unibond substrate (SOI) is thoroughly investigated and, especially, an improved formulation of classical McWhorter’s noise model is proposed. In order to confirm our approach, an experimental comparison between body tied and DTMOS on SOI substrate has been achieved in terms of LFN behaviour. Furthermore, two different types of DTMOS transistors have been used: with and without current limiter. The LFN in DTMOS is analysed in ohmic and saturation regimes and the impact of the use of a current limiter (clamping transistor) is thoroughly analysed. An explanation based on floating body effect inducing excess noise is also proposed.     

基于有限元法的高频开关电源变压器绕组损耗分析

应用有限元法对高频开关电源变压器绕组损耗进行分析,分别对单股粗导线构成的绕组和由多股细导线并绕构成的绕组进行仿真,得到其绝缘损耗、磁滞损耗、欧姆损耗以及能量分布等参数。仿真结果表明,虽然单股粗导线构成的绕组绝缘损耗较小,但是其磁滞损耗和欧姆损耗比由多股细导线并绕构成的绕组要大得多,导致整体绕组损耗要大于由多股细导线并绕构成的绕组。所以用多股细导线并绕来代替单股的粗导线,可以有效地减小高频变压器绕组损耗。     

$f_{T}$ and $f_{rm MAX}$ of 47 and 81 GHz , Respectively, on N-Polar GaN/AlN MIS-HEMT

In this letter, we demonstrate the record small-signal performance from N-polar GaN-based metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) by using a GaN spacer structure with an AlN barrier to reduce alloy scattering. High Si doping in GaN without excessive surface roughening has been achieved using a digital doping scheme. A low ohmic contact resistance of 0.16 $Omega cdot hbox{mm}$ was measured. Submicrometer gates were fabricated by electron-beam lithography using a triple-layer resist process. $f_{T}$ and $f_{rm MAX}$ of 47 and 81 GHz, respectively, were obtained for the 150-nm-gate-length device. Further analysis has been done to understand the effect of access resistance on the high-frequency performance, defining a pathway for getting a higher gain and thus achieving a better high-frequency performance from N-polar GaN-based HEMTs.      

High-frequency power transformer model for circuit simulation

A model for the circuit simulation of transformers used in high-frequency power processing is proposed. Many important transformer effects are combined in a single formulation. An Atherton-Jiles model with improved minor-loop handling ability is employed to simulate the hysteresis effect in the magnetic core. Eddy currents and skin and proximity effects are simulated by dynamically approximating the field and flux distributions in the entire structure. Leakage fluxes, capacitive couplings and the influence of temperature on electric and magnetic materials are also included. The parameters needed for simulation are magnetic material characteristics, available in data sheets, core geometry and winding geometry. The model was implemented (built) in the source code of SPICE3     

Study of the actuation speed,bounces occurrences,and contact reliability of ohmic RF-MEMS switches

The influence of the bias signal waveform on the electromechanical dynamic response of ohmic RF-MEMS switches is here investigated by means of electromechanical characterizations and modelling procedures. The actuation transient of ohmic RF-MEMS switches was studied in this work developing a fast to compute, but comprehensive electromechanical model, using electromechanical parameters from experimental results. The developed model was then used to investigate how different bias waveforms influence the switch dynamic, in terms of actuation time, and bounces occurrences, and a practical solution to limit bounces, without compromising the actuation time was presented. Furthermore, it was demonstrated how it is possible to improve the reliability to cycling stress using ad hoc shaped bias signals.     

AlInN/AlN/GaN HEMT Technology on SiC With 10-W/mm and 50% PAE at 10 GHz

High-frequency high-electron-mobility transistors (HEMTs) were fabricated on AlInN/AlN/GaN heterostructures grown by low-pressure metal-organic chemical vapor deposition on a SiC substrate. The results presented in this letter confirm the high performance that is reachable by AlInN-based technology with an output power of 10.3 W/mm and a power-added efficiency of 51% at 10 GHz with a gate length of 0.25 ?m. A good extrinsic transconductance value that is greater than 450 mS/mm and exceeding AlGaN/GaN HEMT results was also measured on these transistors. To our knowledge, these results are the best power results published on AlInN/GaN HEMTs. These good results were attributed to optimized heterostructure properties associated with low-resistance ohmic contacts and an effective passivation layer minimizing drain current slump in high-frequency operations.