Improved noise model for MESFETs and HEMTs in lower gigahertz frequency range

A noise model based on an equivalent circuit is applied to an HEMT. Besides the frequency dependence of the most important noise parameters (F/sub min/, R/sub opt/, X/sub opt/, R/sub N/) two apparent experimental facts are explained: the limited R/sub opt/, X/sub opt/ and the increase of R/sub N/ with decreasing frequency.<>     

Temperature dependence of 1/f noise in polysilicon-emitter bipolar transistors

1/f noise was measured on polysilicon-emitter bipolar n-p-n and p-n-p transistors over a temperature range of 173K相似文献   

Design optimization of AlInAs-GalnAs HEMTs for low-noise applications

In order to optimize the low-noise performance of 50-nm-gate AlInAs-GalnAs high-electron mobility transistors (HEMTs), by using an ensemble Monte Carlo simulation we study the influence of three important technological parameters on their noise level: the doping of the /spl delta/-doped layer, the width of the devices and the length of the recess. The noise behavior of the devices is firstly analyzed in terms of the physics-based P, R, and C parameters, and then characterized from a practical (circuit oriented) point of view through their four noise parameters: minimum noise figure, F/sub min/, noise resistance, R/sub n/, and complex input admittance, Y/sub opt/ (or reflection coefficient, /spl Gamma//sub opt/). We have observed an enhancement of the noise when the /spl delta/-doping or the device width are increased (a deterioration parallel to that of f/sub max/). Thus, the optimum noise operation is obtained for the lowest possible values of the /spl delta/-doping and device width. However, for small width the effect of the offset parasitic capacitances makes F/sub min/ increase, thus, imposing a limit for the reduction of the noise. Moreover, the increase of R/sub n/ for small W makes the noise tuning condition critical to reach the optimum low-noise operation. We have also confirmed that when shortening the recess length from 100 to 20 nm at each side of the gate F/sub min/ is reduced, with a slight deterioration of f/sub max/, while the static characteristics are not modified.     

Fabrication of niobium titanium nitride thin films with high superconducting transition temperatures and short penetration lengths

We report a systematic study of the superconducting and normal state properties of reactively sputtered Nb/sub 0.62/Ti/sub 0.38/N thin films deposited on thermally oxidized Si wafers. The superconducting transition temperature (T/sub c/) was found to increase from 12 K for films prepared on unheated substrates to over 16 K for films prepared on substrates maintained at 450/spl deg/C. A Nb buffer layer was found to improve T/sub c/ by /spl sim/0.5 K for growths at lower substrate temperatures. The films fabricated at 450/spl deg/C have an amply smooth surface (1.5/spl plusmn/0.25 nm root mean square roughness), a sufficiently high T/sub c/, and sufficiently small penetration depth (200/spl plusmn/20 nm at 10 K) to be useful as ground planes and electrodes for current-generation 10 K rapid single-flux quantum circuit technology.     

High sensitivity Si-based backward diodes for zero-biased square-law detection and the effect of post-growth annealing on performance

High-sensitivity Si-based backward diodes were realized that are monolithically integratable with transistor circuitry. Potential applications include large area focal plane arrays. The Si-based backward diodes exhibit a high zero-biased curvature coefficient, /spl gamma/, of 31 V/sup -1/ and a low zero biased junction capacitance, C/sub j/, of 9 fF//spl mu/m/sup 2/, all at room temperature. The predicted low frequency voltage sensitivity, /spl beta//sub V/, for a 50 /spl Omega/ source is 3100 V/W. The high sensitivity, low junction capacitance, and Si/SiGe heterojunction bipolar transistor compatibility of the Si-based backward diodes make them very attractive for zero-bias square-law detector applications.     

Characterization of GaAs FET's in Terms of Noise, Gain, and Scattering Parameters through a Noise Parameter Test Set

A method for the complete characterization of GaAs FET's in terms of noise parameters (F/sub o/,Gamma/sub on/, R/sub n/), gain parameters (G/sub ao/, Gamma /sub og/, R/sub g/), and of those scattering parameters ( S/sub11/, S/sub22/|,S/sub12/| S/sub21|, /spl angle/S/sub 12/S/sub 21/ ) that are needed for low-noise microwave amplifier design is presented. The instrumentation employed, i.e., a noise-figure measuring system equipped with a vectorial reflectometer, as well as the time consumption, are the same required for the determination of noise parameters only through conventional methods. The measuring setup and the experimental procedure are described in detail. Considerations about the computer-aided data processing technique are also provided. As an experimental result, the characterization of a sample device versus frequency (4-12 GHz) and drain current is reported. A comparison between the scattering parameters provided by the method and those measured by means of a network analyzer is also included.     

Cryogenic characteristics of wide-band pseudomorphic HEMT MMIClow-noise amplifiers

Two wideband (8-18-GHz) single-stage MMIC (monolithic microwave integrated circuit) low-noise amplifiers (LNAs) using 0.2-μm T-gate InGaAs pseudomorphic HEMT (high-electron-mobility transistor) technology, designed and fabricated for room temperature operation, were evaluated and compared at cryogenic temperatures below 20 K. One is a balanced design using 3-dB Lange couplers, and the other is a feedback design using a series RLC parallel feedback network. The gain flatness over the 8-18-GHz frequency band was maintained for both amplifiers at room and cyrogenic temperatures, indicating that the topology for wideband designs is insensitive to temperature of operation. As the physical temperature decreased from 297 K to below 20 K, the balanced LNA exhibited an average gain increase of 2 dB and as much as an eightfold reduction of noise temperature to 20 K, while the feedback LNA exhibited an average gain increase of less than 1 dB and an average foufold reduction of noise temperature to 50 K. The negative feedback network of the feedback LNA resulted in less gain increase and less noise temperature reduction at cryogenic temperatures     

Effects of spacer thickness on noise performance of bipolar transistors

The effects of spacer thickness on noise performance of a bipolar junction transistor with different emitter widths and operation frequencies are examined. The minimum noise figure (NF/sub min/) derived from the Y-parameters as well as the base (r/sub B/) and emitter resistance (r/sub E/) obtained from the device simulation is used as a measure of noise characteristics. Furthermore, the noise resistance (R/sub n/), optimum source admittance (Y/sub sop/), and the associated gain (G/sub A,assc/) are also given in this brief. To achieve the minimum value of NF/sub min/, the spacer thickness should be targeted to an optimal value, and its value is frequency and geometry dependent.     

Cryogenic operation of third-generation, 200-GHz peak-f/sub T/, silicon-germanium heterojunction bipolar transistors

We present a comprehensive investigation of the cryogenic performance of third-generation silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) technology. Measurements of the current-voltage (dc), small-signal ac, and broad-band noise characteristics of a 200-GHz SiGe HBT were made at 85 K, 120 K, 150 K, 200 K, and 300 K. These devices show excellent behavior down to 85 K, maintaining reasonable dc ideality, with a peak current gain of 3800, a peak cut-off frequency (f/sub T/) of 260 GHz, a peak f/sub max/ of 310 GHz, and a minimum noise figure (NF/sub min/) of approximately 0.30 dB at a frequency of 14 GHz, in all cases representing significant improvements over their corresponding values at 300 K. These results demonstrate that aggressively scaled SiGe HBTs are inherently well suited for cryogenic electronics applications requiring extreme levels of transistor performance.     

Optimal capacity of p-persistent CSMA protocols

We deal with the characterization and computation of the p value, say p/sub opt/, corresponding to the maximum protocol capacity in p-persistent carrier-sense multiaccess (CSMA) protocols. The contribution of this paper is twofold. First, we give an analytical justification, and a numerical validation of a heuristic formula widely used in the literature to characterize the p/sub opt/. Second, we provide closed formulas for the p/sub opt/, and we show that the optimal capacity state, given the message length distribution, is characterized by an invariant figure: the Mp/sub opt/ product.     

Design of Cryogenic SiGe Low-Noise Amplifiers

This paper describes a method for designing cryogenic silicon-germanium (SiGe) transistor low-noise amplifiers and reports record microwave noise temperature, i.e., 2 K, measured at the module connector interface with a 50-Omega generator. A theory for the relevant noise sources in the transistor is derived from first principles to give the minimum possible noise temperature and optimum generator impedance in terms of dc measured current gain and transconductance. These measured dc quantities are then reported for an IBM SiGe BiCMOS-8HP transistor at temperatures from 295 to 15 K. The measured and modeled noise and gain for both a single-and two-transistor cascode amplifier in the 0.2-3-GHz range are then presented. The noise model is then combined with the transistor equivalent-circuit elements in a circuit simulator and the noise in the frequency range up to 20 GHz is compared with that of a typical InP HEMT.     

Superconducting quantum interference devices: State of the art and applications

Superconducting quantum interference devices (SQUIDs) are sensitive detectors of magnetic flux. A SQUID consists of a superconducting loop interrupted by either one or two Josephson junctions for the RF or dc SQUID, respectively. Low transition temperature (T/sub c/) SQUIDs are fabricated from thin films of niobium. Immersed in liquid helium at 4.2 K, their flux noise is typically 10/sup -6//spl Phi//sub 0/ Hz/sup -1/2/, where /spl Phi//sub 0//spl equiv/h/2e is the flux quantum. High-T/sub c/ SQUIDs are fabricated from thin films of YBa/sub 2/Cu/sub 3/O/sub 7-x/, and are generally operated in liquid nitrogen at 77 K. Inductively coupled to an appropriate input circuit, SQUIDs measure a variety of physical quantities, including magnetic field, magnetic field gradient, voltage, and magnetic susceptibility. Systems are available for detecting magnetic signals from the brain, measuring the magnetic susceptibility of materials and geophysical core samples, magnetocardiography and nondestructive evaluation. SQUID "microscopes" detect magnetic nanoparticles attached to pathogens in an immunoassay technique and locate faults in semiconductor packages. A SQUID amplifier with an integrated resonant microstrip is within a factor of two of the quantum limit at 0.5 GHz and will be used in a search for axions. High-resolution magnetic resonance images are obtained at frequencies of a few kilohertz with a SQUID-based detector.     

Asymmetric broad waveguide diode lasers (/spl lambda/ = 980 nm) of large equivalent transverse spot size and low temperature sensitivity

980-nm InGaAs-InGaAsP diode lasers of asymmetric broad-waveguide (BW) transverse structure are demonstrated. Single-transverse-mode devices have equivalent (transverse) spot sizes of 0.8 /spl mu/m (i.e., significantly larger than for symmetric BW structures), which are obtained at no price in device-parameter temperature sensitivity. Built-in discrimination against the first-order transverse mode allows fundamental-transverse-mode operation in relatively narrow beams (/spl theta//sub /spl perp// = 34/spl deg/). For 2-mm-long 100-/spl mu/m-wide-stripe uncoated devices with double-quantum-well active regions, the threshold-current density is as low as 190 A/cm/sup 2/, while the characteristic temperatures for the threshold-current density T/sub 0/, and the external differential quantum efficiency T/sub 1/ are high: 183 K and 650 K, respectively.     

Influences of sulfur passivation on temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs PHEMT

The influences of (NH/sub 4/)/sub 2/S/sub x/ treatment on an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) are studied and demonstrated. Upon the sulfur passivation, the studied device exhibits better temperature-dependent dc and microwave characteristics. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ gate/dimension PHEMT with sulfur passivation, the higher gate/drain breakdown voltage of 36.4 (21.5) V, higher turn-on voltage of 0.994 (0.69) V, lower gate leakage current of 0.6 (571) /spl mu/A/mm at V/sub GD/=-22 V, improved threshold voltage of -1.62 (-1.71) V, higher maximum transconductance of 240 (211) mS/mm with 348 (242) mA/mm broad operating regime (>0.9g/sub m,max/), and lower output conductance of 0.51 (0.53) mS/mm are obtained, respectively, at 300 (510) K. The corresponding unity current gain cutoff frequency f/sub T/ (maximum oscillation frequency f/sub max/) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (>0.8f/sub T/,f/sub max/) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300/spl sim/510 K) are observed.     

Electron mobility in an AlGaN/GaN two-dimensional electron gas. I. Carrier concentration dependent mobility

The transport properties of two-dimensional electron gas (2-DEG) at the AlGaN/GaN interface were studied by characterizing the 2-DEG mobility dependence on carrier concentration, n/sub s/, and temperature. High-quality AlGaN/GaN heterostructures were grown, and heterostructure field effect transistors (HFETs) using a Fat FET geometry were fabricated. Measurements of 2-DEG mobility were performed by magnetoresistance and capacitance-conductance. In order to understand the dominant transport factors, the mobility was modeled using different scattering mechanisms and compared to our results. It is found that mobility dependence on n/sub s/ shows a bell-shape behavior over the whole temperature range. For low n/sub s/ the mobility is dominated by Coulomb interaction from interface charge, and at high n/sub s/ the mobility is dominated by interface roughness. Using previously reported experimental values of interface charge and interface roughness in our modeling, we show good agreement with mobility measurement results. Scattering from interface states in AlGaN/GaN heterostructures, seems to be related to the high polarization field in the heterointerface. At temperatures higher than 200K polar optical phonon scattering dominates the transport, yet both interface charge and roughness affect the mobility at the low and high n/sub s/, respectively.     

Microwave and noise performance of SiGe BiCMOS HBT under cryogenic temperatures

In this letter, the microwave and noise performance of SiGe heterojunction bipolar transistors (HBTs) has been characterized when cooling down the temperature. It was found that SiGe HBTs (fabricated in the framework of BiCMOS process) exhibit a maximum oscillation frequency f/sub max/ of about 292 GHz at 78 K, which represents an increase of about 30% with the value measured at room temperature. The noise performance has also been characterized at cryogenic temperatures, using an original de-embedding approach. Then, using the Hawkin's noise model in conjunction with an accurate small signal equivalent extraction, the four noise parameters have been estimated. The noise figure with a 50 /spl Omega/ source impedance was measured to be equal to 1.5 dB at 40 GHz at 78 K, which is one of the lowest value reported for BiCMOS SiGe HBT in the millimeter-wave range.     

An analysis of small-signal source-body resistance effect on RF MOSFETs for low-cost system-on-chip (SoC) applications

In this paper, we demonstrate a comprehensive analysis of small-signal source-body resistance (R/sub sb/) effect on the RF performances of RF MOSFETs for low-cost system-on-chip (SoC) applications for the first time. Our results show that for RF MOSFETs, both the kink phenomena of S/sub 11/ and S/sub 22/ become more obscure as reverse body bias (V/sub B/) increases due to the decrease of transconductance (g/sub m/). In addition, an increase of source-body spacing enhances both the kink phenomena of S/sub 11/ and S/sub 22/, but deteriorates the current-gain cut-off frequency (f/sub T/), maximum oscillation frequency (f/sub MAX/), and RF noise and power performances due to the increase of R/sub sb/ of the devices. Analytical formulas are derived to explain the kink phenomena of S/sub 11/ and S/sub 22/, and to explain why increasing R/sub sb/ leads to a reduction of equivalent substrate resistance R/sub sub/, or worse f/sub T/, f/sub MAX/, and RF noise performances of the devices. The present analyzes enable RF engineers to understand the S-parameters, noise parameters, and power performances of RF MOSFETs more deeply, and hence are helpful for them to optimize the layout of MOSFETs and to create a fully scalable RF CMOS model for SoC applications.     

Design of Microwave GaAs MESFET's for Broad-Band Low-Noise Amplifiers

As a basis for designing GaAs MESFET's for broad-band low-noise amplifiers, the fundamental relationships between basic device parameters, and two-port noise parameters are investigated in a semiempirical manner. A set of four noise parameters are shown as simple functions of equivalent circuit elements of a GaAs MESFET. Each element is then expressed in a simple analytical form with the geometrical and material parameters of this device. Thus practical expressions for the four noise parameters are developed in terms of the geometrical and material parameters. Among the four noise parameters, the minimum noise figure F/sub min/, and equivalent noise resistance R/sub n/, are considered crucial for broad-band Iow-noise amplifiers. A low R/sub n/ corresponds to less sensitivity to input rnismatch, and can be obtained with a short heavily doped thin active channel. Such a high channel doping-to-thickness (N/a) ratio has a potential of producing high power gain, but is contradictory to obtaining a low F/min/. Therefore, a compromise in choosing N and a is necessary for best overall amplifier performance. Four numerical examples are given to show optimization processes.     

Free-space electrooptic sampling of terahertz radiation from optically excited superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films

The characteristics of photogenerated terahertz radiation from a current-biased superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) bow-tie antenna were investigated using a free-space electrooptic sampling technique. Picosecond electromagnetic pulses about 450 fs wide were obtained. The frequency spectrum derived by Fourier transforming the picosecond pulses spans over 0.1-4 THz. The dynamics of the quasi-particles optically induced by the ultrafast laser pulse primarily determines the performances of the transient terahertz radiation generated under different operating parameters. The results indicate a characteristic quasi-particle relaxation time of about 2.5 ps close to the critical temperature T/sub c/, and a faster time at lower temperatures.     

Design of Stable, Very Low Noise, Cavity-Stabilized IMPATT Oscillators for C Band

Two types of C-band IMPATT oscillators, which easily meet the noise and stability requirements for use as local oscillators in microwave FM communications equipment, are described. Both types use a transmission cavity-stabilization circuit as proposed by Kurokawa. In one of them a TE/sub 103/ mode rectangular invar cavity is used for stabilization, while in the other the coupling is made via a high-Q cylindrical TE/sub 011/, mode cavity. Although the Si IMPATT diode is inherently noisy, it is shown that a proper choice of circuit parameters and diode characteristics leads to measured FM noise levels of less than 0.2 Hz in a 100-Hz band. With respect to frequency stability, special attention is paid to hysteresis-free compensation of temperature effects and to the influence of changes with time and ambient temperature of the diode and of the internal atmosphere of the cavity. By careful processing and sealing, an average temperature stability of better than -0.4 ppm//spl deg/C was realized with temperature cycling between 26 and 51/spl deg/C over a period of 450 h.