Microwave Characterization of Partially Magnetized Ferrites

In order to assist the microwave engineer in predicting the performance of partially magnetized devices, we have characterized the microwave permeability of partially magnetized materials. The real part of the tensor permeability elements, /spl mu/, /spl kappa/, and /spl mu//sub z/, depends primarily on the parameters /spl gamma/4/spl pi/M//spl omega/ and /spl gamma/4/spl pi/M/sub s/ / /spl omega/. Empirical formulas have been developed which show the dependence. At frequencies sufficiently below /spl omega/ = /spl pi/4/spl pi/M/sub s/, the loss can be characterized by the value of /spl mu/' at 4/spl pi/M = 0./spl mu/, /spl kappa/, and /spl mu//sub z/ depend weakly on composition, whereas /spl mu/' (4/spl pi/M = 0) does depend upon the chemical composition.     

Microwave Properties of Lithium Ferrites (Short Papers)

Low-power loss and high-power threshold properties have been measured between 3.0 and 17.2 GHz on three Li-Ti ferrite compositions of magnetizations 1250, 2250, and 3600 G. In each composition the use of cobalt resulted in a linear increase in mu/sub 0/ and h/sub crit/. Temperature measurements were performed at 9.2 GHz on the 2250-G material. An illustration of how the data might be applied is given.     

Dissipative Parameters in Ferrites and Insertion Losses in Waveguide Y-Circulators Below Resonance

Extensive microwave loss measurements have been performed at frequencies from 1.3 to 11 GHz on below-resonance waveguide Y circulators loaded with a wide variety of ferrite and garnet compositions. Dissipative internal and external magnetic parameters have been measured on the same compositions. Also, dielectric loss measurements have been carried out. Two classes have been distinguished, defined by the following conditions: /spl omega//sub M/ / /spl omega/ /spl les/0.8 and 0.85 /spl les//spl omega//sub M/ / /spl omega/ /spl les/1.05. It is inferred that the (insertion loss) IL of such devices is independent of /spl Delta/H and mainly depends on the internal dissipative susceptibility x/sub i/" and on the dielectric loss tan /spl delta/. The relation of the IL versus x/sub i/" and tan /spl delta/ in the case /spl omega//sub M/ / /spl omega/ /spl les/0.8 is independent of frequency and given by the semiempirical equation IL= 10 log/sub 10/ (1-2.85 x/sub i/" - 1.60 tan /spl delta/ - 0.017)/sup -1/.     

Measurements of effective dielectric permittivity of microstrip-line-type liquid crystal devices using inductive coupled ring resonator

The effective dielectric permittivity of microstrip-line-type liquid crystal devices was determined in the 3-33 GHz frequency range by using a newly developed inductive coupled ring resonator. The frequency performance of /spl epsiv/'/sub /spl par// and /spl epsiv/'/sub /spl perp// can be obtained from the measured and simulated resonant frequencies of an inductive coupled ring resonator with or without a DC electric field E/sub 0/.     

Peripheral-coupled-waveguide MQW electroabsorption modulator for near transparency and high spurious free dynamic range RF fiber-optic link

Peripheral coupled waveguide (PCW) design has been deployed in InGaAsP multiple quantum-well (MQW) electroabsorption modulator (EAM) at 1.55-/spl mu/m wavelength. PCW enhances the optical saturation power and reduces the optical insertion loss and the equivalent V/sub /spl pi// simultaneously. A radio-frequency link using a 1.3-mm-long lumped-element PCW EAM has achieved experimentally a link gain of -3 dB, at 500 MHz and at input optical power of 80 mW. The corresponding two-tone multioctave spurious-free dynamic range (SFDR) at the same bias is measured at 118 dB/spl middot/Hz/sup 2/3/. The single-octave SFDR at the third-order null bias is 132 dB/spl middot/Hz/sup 4/5/.     

Modeling study of the impact of surface roughness on silicon and Germanium UTB MOSFETs

We outlined a simple model to account for the surface roughness (SR)-induced enhanced threshold voltage (V/sub TH/) shifts that were recently observed in ultrathin-body MOSFETs fabricated on <100> Si surface. The phenomena of enhanced V/sub TH/ shifts can be modeled by accounting for the fluctuation of quantization energy in the ultrathin body (UTB) MOSFETs due to SR up to a second-order approximation. Our model is then used to examine the enhanced V/sub TH/ shift phenomena in other novel surface orientations for Si and Ge and its impact on gate workfunction design. We also performed a calculation of the SR-limited hole mobility (/spl mu//sub H,SR/) of p-MOSFETs with an ultrathin Si and Ge active layer thickness, T/sub Body/<10 nm. Calculation of the electronic band structures is done within the effective mass framework via the Luttinger Kohn Hamiltonian, and the mobility is calculated using an isotropic approximation for the relaxation time calculation, while retaining the full anisotropy of the valence subband structure. For both Si and Ge, the dependence of /spl mu//sub H,SR/ on the surface orientation, channel orientation, and T/sub Body/ are explored. It was found that a <110> surface yields the highest /spl mu//sub H,SR/. The increasing quantization mass m/sub z/ for <110> surface renders its /spl mu//sub H,SR/ less susceptible with the decrease of T/sub Body/. In contrast, <100> surface exhibits smallest /spl mu//sub H,SR/ due to its smallest m/sub z/. The SR parameters, i.e. autocorrelation length (L) and root-mean-square (/spl Delta//sub rms/) used in this paper is obtained from the available experimental result of Si<100> UTB MOSFETs, by adjusting these SR parameters to obtain a theoretical fit with experimental data on SR-limited mobility and V/sub TH/ shifts. This set of SR parameters is then employed for all orientations of both Si and Ge devices.     

Substrate current based avalanche multiplication measurement in 120 GHz SiGe HBTs

A new substrate current-based technique for measuring the avalanche multiplication factor (M - 1) in high-speed SiGe heterojunction bipolar transistors (HBTs) is proposed. The technique enables M - 1 measurement at high operating current densities required for high-speed operation, where conventional techniques fail because of self-heating. Using the proposed technique, M - 1 was measured up to 10 mA//spl mu/m/sup 2/ on SiGe HBTs featuring 120 GHz peak f/sub T/ which occurs at J/sub C/ about 7 mA//spl mu/m/sup 2/. Implications for circuit applications are also discussed.     

A 2-GHz analog-to-digital delta-sigma modulator for CDMA receivers with 79-dB signal-to-noise ratio in 1.23-MHz bandwidth

This paper presents the design of a second-order single-bit analog-to-digital continuous-time delta-sigma modulator (CT-/spl Delta//spl Sigma/M) that can be used in wireless CDMA receivers. The CT-/spl Delta//spl Sigma/M samples at 2 GHz, consumes 18 mW at 1.8 V and has a 79-dB signal-to-noise ratio (SNR) over a 1.23-MHz bandwidth. The CT-/spl Delta//spl Sigma/M was fabricated in a 0.18-/spl mu/m 1-poly 6-metal, CMOS technology and has an active area of approximately 0.892 mm/sup 2/. The /spl Delta//spl Sigma/M's critical performance specifications are derived from the CDMA receiver specifications.     

Correlating drain-current with strain-induced mobility in nanoscale strained CMOSFETs

The correlation between channel mobility gain (/spl Delta//spl mu/), linear drain-current gain (/spl Delta/I/sub dlin/), and saturation drain-current gain (/spl Delta/Idsat) of nanoscale strained CMOSFETs are reported. From the plots of /spl Delta/I/sub dlin/ versus /spl Delta/I/sub dsat/ and ballistic efficiency (Bsat,PSS), the ratio of source/drain parasitic resistance (R/sub SD,PSS/) to channel resistance (R/sub CH,PSS/) of strained CMOSFETs can be extracted. By plotting /spl Delta//spl mu/ versus /spl Delta/I/sub dlin/, the efficiency of /spl Delta//spl mu/ translated to /spl Delta/I/sub dlin/ is higher for strained pMOSFETs than strained nMOSFETs due to smaller RSD,PSS-to-RCH,PSS ratio of strained pMOSFETs. It suggests that to exploit strain benefits fully, the RSD,PSS reduction for strained nMOSFETs is vital, while for strained pMOSFETs the /spl Delta/I/sub dlin/-to-/spl Delta//spl mu/ sensitivity is maintained until R/sub SD,PSS/ becomes comparable to/or higher than R/sub CH,PSS/.     

Convergence and loss bounds for Bayesian sequence prediction

The probability of observing x/sub t/ at time t, given past observations x/sub 1/...x/sub t-1/ can be computed if the true generating distribution /spl mu/ of the sequences x/sub 1/x/sub 2/x/sub 3/... is known. If /spl mu/ is unknown, but known to belong to a class /spl Mscr/ one can base one's prediction on the Bayes mix /spl xi/ defined as a weighted sum of distributions /spl nu/ /spl isin/ /spl Mscr/. Various convergence results of the mixture posterior /spl xi//sub t/ to the true posterior /spl mu//sub t/ are presented. In particular, a new (elementary) derivation of the convergence /spl xi//sub t///spl mu//sub t/ /spl rarr/ 1 is provided, which additionally gives the rate of convergence. A general sequence predictor is allowed to choose an action y/sub t/ based on x/sub 1/...x/sub t-1/ and receives loss /spl lscr//sub x(t)y(t)/ if x/sub t/ is the next symbol of the sequence. No assumptions are made on the structure of /spl lscr/ (apart from being bounded) and /spl Mscr/. The Bayes-optimal prediction scheme /spl Lambda//sub /spl xi// based on mixture /spl xi/ and the Bayes-optimal informed prediction scheme /spl Lambda//sub /spl mu// are defined and the total loss L/sub /spl xi// of /spl Lambda//sub /spl xi// is bounded in terms of the total loss L/sub /spl mu// of /spl Lambda//sub /spl mu//. It is shown that L/sub /spl xi// is bounded for bounded L/sub /spl mu// and L/sub /spl xi///L/sub /spl mu// /spl rarr/ 1 for L/sub /spl mu// /spl rarr/ /spl infin/. Convergence of the instantaneous losses is also proven.     

High-power single-mode antiresonant reflecting optical waveguide-type vertical-cavity surface-emitting lasers

Antiresonant reflecting optical waveguide (ARROW) techniques are employed in vertical cavity surface emitting lasers (VCSELs) to achieve high-power single-mode emission. Using the effective-index method and fiber mode approximation, the cold-cavity lateral modal behavior for the circular shaped ARROW VCSEL demonstrates significant reduction of radiation loss from that of a single antiguide, while maintaining strong discrimination against high-order modes. The circular-waveguide is created by selective chemical etching and two-step metal-organic chemical vapor deposition growth, with proton implantation used to confine the current injection to the low-index core region. A single-mode CW power of 7.1 mW has been achieved from an 8 /spl mu/m diameter ARROW device (index step /spl Delta/n = 0.05, emission at /spl lambda//sub 0/ = 980 nm) with a far-field FWHM of 10/spl deg/. Larger aperture (12 /spl mu/m) devices exhibit multimode operation at lower drive currents with a maximum single-mode continuous-wave output power of 4.3 mW.     

On the feasibility of CMOS multiband phase shifters for multiple-antenna transmitters

We present the design of an integrated multiband phase shifter in RF CMOS technology for phased array transmitters. The phase shifter has an embedded classical distributed amplifier for loss compensation. The phase shifter achieves a more than 180/spl deg/ phase tuning range in a 2.4-GHz band and a measured more than 360/spl deg/ phase tuning range in both 3.5-GHz and 5.8-GHz bands. The return loss is less than -10dB at all conditions. The feasibility for transmitter applications is verified through measurements. The output power at a 1-dB compression point (P/sub 1 dB/) is as high as 0.4dBmat 2.4GHz. The relative phase deviation around P/sub 1 dB/ is less than 3/spl deg/. The design is implemented in 0.18-/spl mu/mRF CMOS technology, and the chip size is 1200/spl mu/m /spl times/ 2300 /spl mu/m including pads.     

Influence of the fiber index profile on vectorial fiber modes and application to tapered fiber devices

The correspondence between the scalar modes LP and the nearly degenerate true vectorial modes in circular two-layer fibers is well established. For example, LP/sub 21/ corresponds to a combination of EH/sub 11/ and HE/sub 31/, while LP/sub 02/ is composed only of HE/sub 12/. For the multilayer fibers, inversion of the correspondences for certain modes can occur. We illustrate this inversion for a three-layer fiber. We propose a method permitting to distinguish the hybrid modes HE/sub /spl nu//spl mu// and EH/sub /spl nu//spl mu// in such fibers and we show the possibility of major taper-induced power coupling between these modes in SMF-28 fiber.     

On the /spl theta/-coverage and connectivity of large random networks

Wireless planar networks have been used to model wireless networks in a tradition that dates back to 1961 to the work of E. N. Gilbert. Indeed, the study of connected components in wireless networks was the motivation for his pioneering work that spawned the modern field of continuum percolation theory. Given that node locations in wireless networks are not known, random planar modeling can be used to provide preliminary assessments of important quantities such as range, number of neighbors, power consumption, and connectivity, and issues such as spatial reuse and capacity. In this paper, the problem of connectivity based on nearest neighbors is addressed. The exact threshold function for /spl theta/-coverage is found for wireless networks modeled as n points uniformly distributed in a unit square, with every node connecting to its /spl phi//sub n/ nearest neighbors. A network is called /spl theta/-covered if every node, except those near the boundary, can find one of its /spl phi//sub n/ nearest neighbors in any sector of angle /spl theta/. For all /spl theta//spl isin/(0,2/spl pi/), if /spl phi//sub n/=(1+/spl delta/)log/sub 2/spl pi//2/spl pi/-/spl theta//n, it is shown that the probability of /spl theta/-coverage goes to one as n goes to infinity, for any /spl delta/>0; on the other hand, if /spl phi//sub n/=(1-/spl delta/)log/sub 2/spl pi//2/spl pi/-/spl theta//n, the probability of /spl theta/-coverage goes to zero. This sharp characterization of /spl theta/-coverage is used to show, via further geometric arguments, that the network will be connected with probability approaching one if /spl phi//sub n/=(1+/spl delta/)log/sub 2/n. Connections between these results and the performance analysis of wireless networks, especially for routing and topology control algorithms, are discussed.     

Power gain singularities in transferred-substrate InAlAs-InGaAs-HBTs

Deep submicron transferred-substrate heterojunction bipolar transistors exhibit peaking and singularities in the unilateral power gain (U) at high frequencies. Unbounded U has been observed in some devices over a 20-110 GHz bandwidth. Associated with the effect are a strong decrease in collector-base capacitance with increased bias current, and negative conductance in the common-emitter output conductance G/sub 22/ and positive conductance in the reverse conductance G/sub 12/. Unbounded U is observed in devices operating at current densities as low as 0.56 mA//spl mu/m/sup 2/. A potential explanation of the observed characteristics is dynamic electron velocity modulation in the collector-base junction. A theoretical model for the dynamics of capacitance cancellation by electron velocity modulation is developed, and its correlation with experimental data examined.     

High-performance InGaP/GaAs HBTs with compositionally graded bases grown by solid-source MBE

N-p-n InGaP/GaAs heterojunction bipolar transistors (HBTs) with compositionally graded In/sub x/Ga/sub 1-x/As (Be doped) bases have been successfully grown by solid-source molecular beam Epitaxy (SSMBE) using a gallium phosphide (GaP) decomposition source. In this paper, the dc and RF characteristics of HBTs with different indium mole fractions in the graded In/sub x/Ga/sub 1-x/As base (x:0 /spl rarr/ ;0.1 and x:0 /spl rarr/ 0.05) are measured to investigate optimum-grading profiles. The measured average current gains, /spl beta/s of a control sample, a 10% graded-base sample and a 5% graded-base sample, are 162, 397 and 362, respectively. To our knowledge, these current gains are the highest values ever reported in compositionally graded-base InGaP/GaAs HBTs with a base sheet resistance R/sub sh/ of /spl sim/200 /spl Omega//sq establishing a new benchmark for InGaP/GaAs HBTs. Furthermore, these compositionally graded-base HBTs show higher unity current/gain cutoff frequency, f/sub T/ and maximum oscillation frequency, f/sub max/. Compared to the control sample with the same base thickness, the base transit time /spl tau//sub B/ of the graded sample is reduced by /spl sim/15% to /spl sim/20% by the induced built-in potential, resulting in an increase of f/sub max/ from 16 to 18.5 GHz in a device with an emitter size of 10/spl times/10 /spl mu/m/sup 2/. Additionally, for the 5% graded-base sample, with a 5/spl times/5 /spl mu/m/sup 2/ emitter region, f/sub T/ and f/sub max/ are 16.3 and 33.8 GHz, respectively, under low-level collector current. These results demonstrate that InGaP/GaAs HBTs with In/sub x/Ga/sub 1-x/As graded-base layers (x:0 /spl rarr/ 0.05) have the potential for high-speed analogue to digital converters.     

Semi-empirical model of the ensemble-averaged differential Mueller matrix for microwave backscattering from bare soil surfaces

A semi-empirical model of the ensemble-averaged differential Mueller matrix for microwave backscattering from bare soil surfaces is presented. Based on existing scattering models and data sets measured by polarimetric scatterometers and the JPL AirSAR, the parameters of the co-polarized phase-difference probability density function, namely the degree of correlation /spl alpha/ and the co-polarized phase-difference /spl sigmav/, in addition to the backscattering coefficients /spl sigma//sub /spl nu//spl nu///sup 0/,/spl sigma//sub hh//sup 0/ and /spl sigma//sub /spl nu/h//sup 0/, are modeled empirically in terms of the volumetric soil moisture content m/sub /spl nu// and the surface roughness parameters ks and kl, where k=2/spl pi/f/c, s is the rms height and l is the correlation length. Consequently, the ensemble-averaged differential Mueller matrix (or the differential Stokes scattering operator) is specified completely by /spl sigma//sub /spl nu//spl nu///sup 0/,/spl sigma//sub hh//sup 0/,/spl sigma//sub /spl nu/h//sup 0/,/spl alpha/, and /spl zeta/.     

5.8-GHz CMOS T/R switches with high and low substrate resistances in a 0.18-/spl mu/m CMOS process

Two single-pole, double-throw transmit/receive switches were designed and fabricated with different substrate resistances using a 0.18-/spl mu/m p/sup $/substrate CMOS process. The switch with low substrate resistances exhibits 0.8-dB insertion loss and 17-dBm P/sub 1dB/ at 5.825 GHz, whereas the switch with high substrate resistances has 1-dB insertion loss and 18-dBm P/sub 1dB/. These results suggest that the optimal insertion loss can be achieved with low substrate resistances and 5.8-GHz T/R switches with excellent insertion loss and reasonable power handling capability can be implemented in a 0.18-/spl mu/m CMOS process.     

Graded base type-II InP/GaAsSb DHBT with f/sub T/=475 GHz

The first demonstration of a type-II InP/GaAsSb double heterojunction bipolar transistor (DHBT) with a compositionally graded InGaAsSb to GaAsSb base layer is presented. A device with a 0.4/spl times/6 /spl mu/m/sup 2/ emitter dimensions achieves peak f/sub T/ of 475 GHz (f/sub MAX/=265 GHz) with current density at peak f/sub T/ exceeding 12 mA//spl mu/m/sup 2/. The structure consists of a 25-nm InGaAsSb/GaAsSb graded base layer and 65-nm InP collector grown by MBE with breakdown voltage /spl sim/4 V which demonstrates the vertical scaling versus breakdown advantage over type-I DHBTs.     

Wideband DHBTs using a graded carbon-doped InGaAs base

We report an InP/InGaAs/InP double heterojunction bipolar transistor (DHBT), fabricated using a mesa structure, exhibiting 282 GHz f/sub /spl tau// and 400 GHz f/sub max/. The DHBT employs a 30 nm InGaAs base with carbon doping graded from 8/spl middot/10/sup 19//cm/sup 3/ to 5/spl middot/10/sup 19//cm/sup 3/, an InP collector, and an InGaAs/InAlAs base-collector superlattice grade, with a total 217 nm collector depletion layer thickness. The low base sheet (580 /spl Omega/) and contact (<10 /spl Omega/-/spl mu/m/sup 2/) resistivities are in part responsible for the high f/sub max/ observed.