A Catalog of Low Power Loss Parameters and High Power Thresholds for Partially Magnetized Ferrites

The low power loss and high power threshold properties have been measured on a number of candidate ferrite phase-shifting materials. The low power loss is characterized by /spl mu//sub 0/', the imaginary part of the diagonal component of the permeability tensor for the completely demagnetized state. /spl mu/sub 0/' was measured from 3.0 to 16.8 GHz. The high power properties are characterized by the parallel pump threshold at a bias field correspontig to H/sub i/ /spl equiv/ 0 and to 4/spl pi/M /spl equiv/ 4/spl pi/M/sub s/. The threshold was measured between 3.0 and 16.8 GHz. For the purposes of computer calculation /spl mu//sub 0/' and h/sub crit/ were fit to an equation of the form A (/spl gamma/4/spl pi/M/sub s/ / /spl omega/)/sup N/. Translating /spl mu//sub 0/' and h/sub crit/ to /spl Delta/H/sub eff/ and /spl Delta/H/sub k/ gives the YIG plus Al as the lowest loss and lowest threshold materials followed by the Gd garnets and MgMn spinels. The Ni spinels are very Iossy.     

Entropy and the law of small numbers

Two new information-theoretic methods are introduced for establishing Poisson approximation inequalities. First, using only elementary information-theoretic techniques it is shown that, when S/sub n/=/spl Sigma//sub i=1//sup n/X/sub i/ is the sum of the (possibly dependent) binary random variables X/sub 1/,X/sub 2/,...,X/sub n/, with E(X/sub i/)=p/sub i/ and E(S/sub n/)=/spl lambda/, then D(P(S/sub n/)/spl par/Po(/spl lambda/)) /spl les//spl Sigma//sub i=1//sup n/p/sub i//sup 2/+[/spl Sigma//sub i=1//sup n/H(X/sub i/)-H(X/sub 1/,X/sub 2/,...,X/sub n/)] where D(P(S/sub n/)/spl par/Po(/spl lambda/)) is the relative entropy between the distribution of S/sub n/ and the Poisson (/spl lambda/) distribution. The first term in this bound measures the individual smallness of the X/sub i/ and the second term measures their dependence. A general method is outlined for obtaining corresponding bounds when approximating the distribution of a sum of general discrete random variables by an infinitely divisible distribution. Second, in the particular case when the X/sub i/ are independent, the following sharper bound is established: D(P(S/sub n/)/spl par/Po(/spl lambda/))/spl les/1//spl lambda/ /spl Sigma//sub i=1//sup n/ ((p/sub i//sup 3/)/(1-p/sub i/)) and it is also generalized to the case when the X/sub i/ are general integer-valued random variables. Its proof is based on the derivation of a subadditivity property for a new discrete version of the Fisher information, and uses a recent logarithmic Sobolev inequality for the Poisson distribution.     

On the filtering problem for stationary random /spl Zopf//sup 2/-fields

It is shown that whenever a stationary random field (Z/sub n,m/)/sub n,m/spl isin/z/ is given by a Borel function f:/spl Ropf//sup z/ /spl times/ /spl Ropf//sup z/ /spl rarr/ /spl Ropf/ of two stationary processes (X/sub n/)/sub n/spl isin/z/ and (Y/sub m/)/sub m/spl isin/z/ i.e., then (Z/sub n, m/) = (f((X/sub n+k/)/sub k/spl epsi/z/, (Y/sub m + /spl lscr// )/sub /spl lscr/ /spl epsi/z/)) under a mild first coordinate univalence assumption on f, the process (X/sub n/)/sub n/spl isin/z/ is measurable with respect to (Z/sub n,m/)/sub n,m/spl epsi/z/ whenever the process (Y/sub m/)/sub m/spl isin/z/ is ergodic. The notion of universal filtering property of an ergodic stationary process is introduced, and then using ergodic theory methods it is shown that an ergodic stationary process has this property if and only if the centralizer of the dynamical system canonically associated with the process does not contain a nontrivial compact subgroup.     

MIM capacitors using atomic-layer-deposited high-/spl kappa/ (HfO/sub 2/)/sub 1-x/(Al/sub 2/O/sub 3/)/sub x/ dielectrics

Metal-insulator-metal (MIM) capacitors with (HfO/sub 2/)/sub 1-x/(Al/sub 2/O/sub 3/)/sub x/ high-/spl kappa/ dielectric films were investigated for the first time. The results show that both the capacitance density and voltage/temperature coefficients of capacitance (VCC/TCC) values decrease with increasing Al/sub 2/O/sub 3/ mole fraction. It was demonstrated that the (HfO/sub 2/)/sub 1-x/(Al/sub 2/O/sub 3/)/sub x/ MIM capacitor with an Al/sub 2/O/sub 3/ mole fraction of 0.14 is optimized. It provides a high capacitance density (3.5 fF//spl mu/m/sup 2/) and low VCC values (/spl sim/140 ppm/V/sup 2/) at the same time. In addition, small frequency dependence, low loss tangent, and low leakage current are obtained. Also, no electrical degradation was observed for (HfO/sub 2/)/sub 1-x/(Al/sub 2/O/sub 3/)/sub x/ MIM capacitors after N/sub 2/ annealing at 400/spl deg/C. These results show that the (HfO/sub 2/)/sub 0.86/(Al/sub 2/O/sub 3/)/sub 0.14/ MIM capacitor is very suitable for capacitor applications within the thermal budget of the back end of line process.     

Mode Propagation in a Nonuniform Cylindrical Medium (Correspondence)

A simplified form of the coupling coefficient C(/spl beta//sub p/, /spl beta//sub q/) resulting from a coupled mode theory analysis of wave propagation in a nonuniform medium is derived. It is found for most situations of interest that C(/spl beta//sub p/, /spl beta//sub q/) is proportional to 1/(/spl beta//sub p/-/spl beta//sub q/) and the power transfer between two modes is proportional to 1/(/spl beta//sub p/ - /spl beta//sub q/)/sup 4/. /spl beta//sub p/ and /spl beta//sub q/ are the two different modal propagation constants. For a dielectric rod C(/spl beta//sub p/, /spl beta//sub q/) is a simple line integral around the rod boundary. Approximate forms are presented for optical waveguides.     

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.     

Dependence of the neodymium random laser threshold on the diameter of the pumped spot

We experimentally studied the dependence of the threshold energy density E/sub th//S in Nd/sub 0.5/La/sub 0.5/Al/sub 3/(BO/sub 3/)/sub 4/ random laser on the diameter of the pumped spot d and found that at d/spl ges/130/spl mu/m, E/sub th//S is proportional to 1/d+const. This functional dependence is different from the one commonly expected in the case of diffusion, /spl prop/1/d/sup 2/+const. However, the obtained experimental dependence does not mean the failure of the diffusion model. Calculating the mean photon's residence time /spl tau//sub res//sup p/ (which photons, making their diffusion-like random walks, spend inside the gain volume) as the function of d and further assuming that E/sub th//S/spl prop/(/spl tau//sup p//sub res/)/sup -1/, we predicted the experimentally obtained functional dependence, /spl prop/1/d+const. The major difference between our model and that of and was in the boundary conditions.     

Long-wavelength In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As large-area avalanche photodiodes and arrays

Large-area (500-/spl mu/m diameter) mesa-structure In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiodes (APDs) are reported. The dark current density was /spl sim/2.5/spl times/10/sup -2/ nA//spl mu/m/sup 2/ at 90% of breakdown; low surface leakage current density (/spl sim/4.2 pA//spl mu/m) was achieved with wet chemical etching and SiO/sub 2/ passivation. An 18 /spl times/ 18 APD array with uniform distributions of breakdown voltage, dark current, and multiplication gain has also been demonstrated. The APDs in the array achieved 3-dB bandwidth of /spl sim/8 GHz at low gain and a gain-bandwidth product of /spl sim/120 GHz.     

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.     

Impact of poly-gate depletion on MOS RF linearity

The distortion behavior for thin oxide MOS transistors can be degraded due to polysilicon-gate depletion effects. The nonlinear, bias-dependent gate capacitance for thin oxide MOSFET's results in significant 2nd-order derivatives in gate capacitance, (/spl part//sup 2/C(V/sub gs/)//spl part/V/sub gs//sup 2/), which in turn results in substantial 3rd-order derivative contributions to drain current, (/spl part//sup 3/I/sub ds///spl part/V/sub gs//sup 3/). This may restrict the use of very-thin oxide MOSFET's in RF applications.     

A Micropower CMOS-Instrumentation Amplifier

A CMOS switched capacitor instrumentation amplifier is presented. Offset is reduced by an auto-zero technique and effects due to charge injection are attenuated by a special amplifier configuration. The circuit which is realized in a 4-/spl mu/m double poly process has an offset (/spl tau/) of 370 /spl mu/V, an rms input referred integrated noise (0.5 -f/sub c//2) of 79 /spl mu/V, and consumes only 21 /spl mu/W (f/sub c/ = 8 kHz, V/sub DD/ = 3 V).     

Lognormal selection with applications to lifetime data

We consider selection problems on k lognormal (/spl mu//sub i/,/spl sigma//sub i//sup 2/) populations when the /spl sigma//sub i//sup 2/ are unequal, under both known & unknown cases. Selection based on linear functions of /spl mu/ & /spl sigma//sup 2/ are considered. For the unequal & unknown /spl sigma//sub i//sup 2/ case, a two-stage Rinott-type asymptotic procedure is proposed. In consideration to reliability & survival analysis applications, an asymptotic procedure is also proposed for the parametric selection based on the /spl alpha/-quantiles. Simulation studies to evaluate the procedures & to compare the latter procedure to the nonparametric procedure based on the /spl alpha/-quantiles are presented. The procedures are demonstrated using examples from reliability & quality control.     

The empirical distribution of rate-constrained source codes

Let X = (X/sub 1/,...) be a stationary ergodic finite-alphabet source, X/sup n/ denote its first n symbols, and Y/sup n/ be the codeword assigned to X/sup n/ by a lossy source code. The empirical kth-order joint distribution Q/spl circ//sup k/[X/sup n/,Y/sup n//spl rceil/(x/sup k/,y/sup k/) is defined as the frequency of appearances of pairs of k-strings (x/sup k/,y/sup k/) along the pair (X/sup n/,Y/sup n/). Our main interest is in the sample behavior of this (random) distribution. Letting I(Q/sup k/) denote the mutual information I(X/sup k/;Y/sup k/) when (X/sup k/,Y/sup k/)/spl sim/Q/sup k/ we show that for any (sequence of) lossy source code(s) of rate /spl les/R lim sup/sub n/spl rarr//spl infin//(1/k)I(Q/spl circ//sup k/[X/sup n/,Y/sup n//spl rfloor/) /spl les/R+(1/k)H (X/sub 1//sup k/)-H~(X) a.s. where H~(X) denotes the entropy rate of X. This is shown to imply, for a large class of sources including all independent and identically distributed (i.i.d.). sources and all sources satisfying the Shannon lower bound with equality, that for any sequence of codes which is good in the sense of asymptotically attaining a point on the rate distortion curve Q/spl circ//sup k/[X/sup n/,Y/sup n//spl rfloor//spl rArr//sup d/P(X/sup k/,Y~/sup k/) a.s. whenever P(/sub X//sup k//sub ,Y//sup k/) is the unique distribution attaining the minimum in the definition of the kth-order rate distortion function. Consequences of these results include a new proof of Kieffer's sample converse to lossy source coding, as well as performance bounds for compression-based denoisers.     

Asymptotic properties on codeword lengths of an optimal FV code for general sources

This correspondence is concerned with asymptotic properties on the codeword length of a fixed-to-variable length code (FV code) for a general source {X/sup n/}/sub n=1//sup /spl infin// with a finite or countably infinite alphabet. Suppose that for each n /spl ges/ 1 X/sup n/ is encoded to a binary codeword /spl phi//sub n/(X/sup n/) of length l(/spl phi//sub n/(X/sup n/)). Letting /spl epsiv//sub n/ denote the decoding error probability, we consider the following two criteria on FV codes: i) /spl epsiv//sub n/ = 0 for all n /spl ges/ 1 and ii) lim sup/sub n/spl rarr//spl infin///spl epsiv//sub n/ /spl les/ /spl epsiv/ for an arbitrarily given /spl epsiv/ /spl isin/ [0,1). Under criterion i), we show that, if X/sup n/ is encoded by an arbitrary prefix-free FV code asymptotically achieving the entropy, 1/nl(/spl phi//sub n/(X/sup n/)) - 1/nlog/sub 2/ 1/PX/sup n/(X/sup n/) /spl rarr/ 0 in probability as n /spl rarr/ /spl infin/ under a certain condition, where P/sub X//sup n/ denotes the probability distribution of X/sup n/. Under criterion ii), we first determine the minimum rate achieved by FV codes. Next, we show that 1/nl(/spl phi//sub n/(X/sup n/)) of an arbitrary FV code achieving the minimum rate in a certain sense has a property similar to the lossless case.     

Room-temperature self-organised In/sub 0.5/Ga/sub 0.5/As quantum dot laser on silicon

The first room-temperature operation of In/sub 0.5/Ga/sub 0.5/As quantum dot lasers grown directly on Si substrates with a thin (/spl les/2 /spl mu/m) GaAs buffer layer is reported. The devices are characterised by J/sub th//spl sim/1500 A/cm/sup 2/, output power >50 mW, and large T/sub 0/ (244 K) and constant output slope efficiency (/spl ges/0.3 W/A) in the temperature range 5-95/spl deg/C.     

Quantitative retrieval of soil moisture content and surface roughness from multipolarized radar observations of bare soil surfaces

A semiempirical polarimetric backscattering model for bare soil surfaces is inverted directly to retrieve both the volumetric soil moisture content M/sub v/ and the rms surface height s from multipolarized radar observations. The rms surface height s and the moisture content M/sub v/ can be read from inversion diagrams using the measurements of the cross-polarized backscattering coefficient /spl sigma//sub vh//sup 0/ and the copolarized ratio p(=/spl sigma//sub hh//sup 0///spl sigma//sub vv//sup 0/). Otherwise, the surface parameters can be estimated simply by solving two equations (/spl sigma//sub vh//sup 0/ and p) in two unknowns (M/sub v/ and s). The inversion technique has been applied to the polarimetric backscattering coefficients measured by ground-based polarimetric scatterometers and the Jet Propulsion Laboratory airborne synthetic aperture radar. A good agreement was observed between the values of surface parameters (the rms height s, roughness parameter ks, and the volumetric soil moisture content M/sub v/) estimated by the inversion technique and those measured in situ.     

On the theory of 1/f noise of semi-insulating materials

The 1/f noise phenomena associated with devices involving semi-insulating materials, for instance GaAs MESFET's on semi-insulating GaAs, has long been a perplexing problem. In this particular case the 1/f noise corner frequency can be up to 100 MHz before the mean square noise current at the drain is dominated by the Nyquist noise associated with the channel conductance. No reasonable explanation has ever been given, although there are many different theories. 1/f noise is a common phenomena in nature and other devices involving semi-insulating materials. We propose here that this 1/f noise is a bulk phenomena associated with localized high frequency variations and long range low frequency fluctuations, the lowest frequency being limited only by the volume of the material. Specifically the proposal here is that injection of a current I into a semi-insulating material will result in a mean square noise voltage at the point of injection given by v/sub n//sup 2/~=2(kT/q)q/spl Delta/fR(/spl omega//sub c///spl omega/) Volts/sup 2/ where /spl omega//sub c/=1/t/sub t/, for the radian frequencies, /spl omega/, larger than /spl omega//sub c/ which is the reciprocal of the transit time of the carriers. For a long sample and long transit times then this 1/f noise voltage due to current injection will be larger than the Nyquist mean square noise of the sample alone as long as the DC voltage developed across the semi-insulating sample exceeds ((2kT/q)l/sup 2/(/spl omega///spl mu/))/sup 1/2/. This theory then gives the 1/f or 1//spl omega/ frequency dependence. The dc current I might be injected for instance by the substrate current in a GaAs MESFET being injected into the semi-insulating substrate, or gate current in an IGET being injected into the gate insulator.<>     

Cyclic codes over GR(4/sup m/) which are also cyclic over /spl Zopf//sub 4/

Let GR(4/sup m/) be the Galois ring of characteristic 4 and cardinality 4/sup m/, and /spl alpha/_={/spl alpha//sub 0/,/spl alpha//sub 1/,...,/spl alpha//sub m-1/} be a basis of GR(4/sup m/) over /spl Zopf//sub 4/ when we regard GR(4/sup m/) as a free /spl Zopf//sub 4/-module of rank m. Define the map d/sub /spl alpha/_/ from GR(4/sup m/)[z]/(z/sup n/-1) into /spl Zopf//sub 4/[z]/(z/sup mn/-1) by d/spl alpha/_(a(z))=/spl Sigma//sub i=0//sup m-1//spl Sigma//sub j=0//sup n-1/a/sub ij/z/sup mj+i/ where a(z)=/spl Sigma//sub j=0//sup n-1/a/sub j/z/sup j/ and a/sub j/=/spl Sigma//sub i=0//sup m-1/a/sub ij//spl alpha//sub i/, a/sub ij//spl isin//spl Zopf//sub 4/. Then, for any linear code C of length n over GR(4/sup m/), its image d/sub /spl alpha/_/(C) is a /spl Zopf//sub 4/-linear code of length mn. In this article, for n and m being odd integers, it is determined all pairs (/spl alpha/_,C) such that d/sub /spl alpha/_/(C) is /spl Zopf//sub 4/-cyclic, where /spl alpha/_ is a basis of GR(4/sup m/) over /spl Zopf//sub 4/, and C is a cyclic code of length n over GR(4/sup m/).