Automatic VT extractors based on ann×n2 MOS transistor array and theirapplication

The development of incremental and decremental V_T extractors based on the square-law characteristic and an n ×n² transistor array is described. Different implementations have been discussed and the effect of nonidealities such as mobility reduction, channel-length modulation, mismatch, and body effect has been analyzed. Besides automatic V_T extraction, parameter K of an MOS transistor can also be extracted automatically using the V_T extractor, without any need of calculation and delay, and the extracted V_T and K are, respectively, in voltage and current. Experimental results are presented and indicate that the differences between extracted values using the V_T extractor and the most popular numerical method are as small as 0.15% and 0.064%. Additional applications, such as in level shifting, temperature compensation, and temperature measurement, where the V_T extractor can be used either as a PTAT sensor or as a centigrade sensor, are presented     

An RKHS approach to robust L2 estimation andsignal detection

The application of RKHS (reproducing kernel Hilbert space) theory to the problems of robust signal detection and estimation is investigated. It is shown that this approach provides a general and unified framework in which to analyze the problems of L² estimation, matched filtering, and quadratic detection in the presence of uncertainties regarding the second-order structure of the random processes involved     

On the number of points on shells for shiftedZ4n lattices

A conjecture is proven on the number of points on shells for the shifted Z⁴ and the shifted Z⁸ lattices. Furthermore, the results are extended to any shifted Z⁴ⁿ lattice (n=0, 1, . . .). These results provide an easy way to compute the number of points on shells for the type of lattices used in the design of multidimensional signal sets or in vector coding     

Proton-exchanged optical waveguides in Z-cut LiNbO3 using phosphoric acid

Proton-exchanged Z-cut LiNbO₃ planar waveguides formed using phosphoric acid were characterized optically. The refractive index profile and the diffusion parameters were studied systematically. These waveguides have propagation losses of less than 1 dB/cm and exhibit properties that are different from those obtained using benzoic acid. The index profile is not a simple step function and can be modeled accurately by a polynomial expression. A maximum surface index increase of 0.145 was measured at a 0.633-μm wavelength. The diffusion constant D₀ and the activation energy Q for the proton-exchange process using this acid were found to be 6.43×10⁸ μm²/h and 82.91 kJ/mol, respectively. The annealing properties of these waveguides were also established, and the effects of annealing on surface index change and waveguide depth increase were found to follow a power-law relationship     

Public-key cryptosystem over ring Z[√-3]/(2m)

The author improves the public-key cryptosystem presented recently (see IEE Proc. E, vol.134, no.5, p.254-6, 1987) and designs a new method of compressing the data expansion     

Efficient N×N star coupler based on Fourieroptics

A technique for constructing an efficient N×N star coupler suitable for mass production in integrated form for large N at optical frequencies is discussed. The coupler can be realised using Si technology by means of two arrays of strip waveguides and a dielectric slab formed on a glass substrate. Power transfer between the two arrays is accomplished through radiation in the dielectric slab with theoretical efficiency exceeding 30% under optimised conditions     

The ZπM algorithm: a method for interferometric imagereconstruction in SAR/SAS

This paper presents an effective algorithm for absolute phase (not simply modulo-2-pi) estimation from incomplete, noisy and modulo-2pi observations in interferometric aperture radar and sonar (InSAR/InSAS). The adopted framework is also representative of other applications such as optical interferometry, magnetic resonance imaging and diffraction tomography. The Bayesian viewpoint is adopted; the observation density is 2-pi-periodic and accounts for the interferometric pair decorrelation and system noise; the a priori probability of the absolute phase is modeled by a compound Gauss-Markov random field (CGMRF) tailored to piecewise smooth absolute phase images. We propose an iterative scheme for the computation of the maximum a posteriori probability (MAP) absolute phase estimate. Each iteration embodies a discrete optimization step (Z-step), implemented by network programming techniques and an iterative conditional modes (ICM) step (pi-step). Accordingly, the algorithm is termed ZpiM, where the letter M stands for maximization. An important contribution of the paper is the simultaneous implementation of phase unwrapping (inference of the 2pi-multiples) and smoothing (denoising of the observations). This improves considerably the accuracy of the absolute phase estimates compared to methods in which the data is low-pass filtered prior to unwrapping. A set of experimental results, comparing the proposed algorithm with alternative methods, illustrates the effectiveness of our approach.     

Gain measurements on the KrF(B→X), XeF(B→X), and XeF(C→A) lasertransitions in an XeF(C→A) laser gas mixture

Optimum energy extraction from an electron-beam-pumped XeF(C →A) laser is achieved with a five-component rare gas halide mixture. The characterization and modeling of laser action in such a gas mixture requires a knowledge of small-signal gain and absorption coefficients not only on the blue-green XeF(C→ A) transition, but also in the ultraviolet (UV) region for the competing XeF(B→X) and KrF(B→X ) transitions. The authors report gain measurements on the XeF(C→A) transition and small-signal gain and absorption coefficients at or near both the XeF(B→X ) (351 and 353 nm) and KrF(B→X) (248 nm) transitions. A study of the gain for the UV and visible transitions as a function of Kr and Xe partial pressure is reported, and its impact on the XeF(C→A) kinetics is discussed     

Integrated TE-TM mode converter on Y-cutZ-propagating LiNbO3 with an electrooptic phasematching for coherence multiplexing

The use of an integrated TE-TM mode converter as a coherence multiplexer is described. The component is based on a buried waveguide obtained by proton exchange and postannealing. The electrode structure consists of three electrodes. Two are used to achieve TE-TM conversion, and the third is used to perform phase matching to ensure a high conversion efficiency     

A proposed chemically pumped laser based on theb→X transition in O2

Simple kinetics calculations demonstrate that the well-known electronic energy pooling reaction involving O₂(a ¹Δ) is capable of producing an effective population inversion in O₂(b¹Σ). The densities of O₂(a¹Δ) which are potentially achievable suggest that the extractable energy storage density of an O ₂(b→X) chemical laser might exceed 0.5 MJ/m³. The b→X emission lifetime measurements conducted under conditions of high relative O₂( b¹Σ) density reveal no evidence of rapid self-quenching effects which would be potentially detrimental to laser performance. The relatively long energy storage times predicted, together with freedom from reagent mixing requirements, make such a laser an attractive alternative to other existing and proposed short wavelength chemical lasers     

Analysis of N×N passive optical starcoupler based on the normal modes of N input waveguides

An integrated passive N×N optical star coupler on silicon wafer is described. Antiresonant reflecting optical waveguides (ARROWs) are analyzed and utilized as the input and output waveguides of the N×N coupler. Combining the exact solutions of the slab ARROW waveguide with the effective index method, a 5×5 coupler is analyzed. In the slab waveguide analysis, the input waveguides are coupled to their neighbors. The interaction of the waveguides is described in terms of the normal modes of propagation. The resultant field distribution is then diffracted into the free space region which separates the input and output sections. The radiation illuminates the receiving aperture from which the receiving N waveguides branch out, each output element obtaining equal power levels. Different types of loss such as spillover loss and mismatch loss were analyzed and estimated for N=5. A 5×5 star coupler with a transmission efficiency of 56% at a wavelength of 1.3 μm is achievable     

Low-frequency noise characteristics of lattice-matched(x=0.53) and strained (x>0.53) In0.52Al0.48As/InxGa1-xAs HEMT's

Extensive bias-dependent and temperature-dependent low-frequency (LF) noise measurements were performed on lattice-matched and strained In_0.52Al_0.48As/In_xGa_1-x As(0.53<x<0.70) HEMTs. The input-noise voltage spectra density is insensitive to V_DS bias and shows a minimum at V_GS corresponding to the peak g_m condition. The corresponding output-noise voltage spectral density, which depends strongly on the gain of the devices, increases with V_DS. The input noise was rather insensitive to indium (In) content. Temperature-dependent low-frequency noise measurements on these devices reveal shallow traps with energies of 0.11, 0.15, and 0.18 eV for 60%, 65%, and 70% In HEMTs. Noise transition frequencies for these devices were on the order of 200-300 MHz and remain almost the same for different channel In content and V_DS bias     

Estimation of fractional changes in peak gNa,g¯Na, ENa, andh∞ (V) of cardiac cells from V˙max of the propagating action potential

Fractional changes in the peak sodium conductances of the cardiac cell membrane during the action potential are often estimated from fractional changes in Vmax. The present model study shows, in reasonable accord with experimental evidence, that this approach is valid for propagating action potentials provided that the membrane capacitance does not change and that the nonsodium current is small at the time of Vmax. When the maximum conductance of the sodium channel (gNa) and the sodium equilibrium potential (ENa) are varied independently of one another, fractional changes in either of them can be predicted from fractional changes in Vmax if a reasonable estimate of the initial value of ENa is available. Manipulations which modify the resting membrane potential without changing gNa allow to calculate fractional changes in the steady-state Na+ inactivation [h infinity (V)] when ENa is known. Simulation runs were carried out for a continuous cable and a discontinuous cable with either a low (1 omega.cm2) or a high (10 omega.cm2) junctional resistance. The predictions of the model are valid in the discontinuous cable provided that the recording point remains strictly the same throughout the series of measurements. Because the high-resistance discontinuous cable provides conditions which reduce further the nonsodium current at the time of Vmax, the accuracy of the predictions are better in this case. It is concluded that properly designed experimental approaches based on Vmax measurements can yield important information on manipulations affecting gNa, ENa, and h infinity (V) during propagation, and that a better accuracy is possible in cardiac muscle when measurements are made during transverse propagation.     

Ga1-yInyAs/InAsxP1-1 (y>0.53, x>0) pin photodiodes for long wavelengthregions (λ>2 μm) grown by hydride vapour phase epitaxy

pin photodiodes with a 2.3 μm absorption edge are presented, using hydride vapour phase epitaxy. A Ga₁-_yIn_yAs (y=0.72) absorption layer, lattice-mismatched to the InP substrate, was grown on an InAs_xP_1-x (x=0-0.33) graded composition buffer layer. Typical dark current was 5 μA (0.03 A/cm²) at -6 V. Effective carrier lifetime of 0.05 μs was estimated from I/V characteristics     

An analysis of P-SixOyN(1-y)Hz film (y=0~1) quality affectingaluminum slit-like open metallization

A study of the P-Si_xO_y N_(1-y)H _z (y=0~1) passivation film quality causing aluminum slitlike open metallization is reported. Slitlike open metallization after 150°C, 1000-h aging with various P-Si_xO_y N_(1-y)H_z compositions revealed that the higher the deposition temperature and the closer the composition to the oxide (y=1), the more the open failure took place. These results can be explained satisfactorily on the basis of the stress-temperature relation of the two extremes, P-Si_xO and P-Si_xN _yH_z     

Direct epitaxial growth of InP based heterostructures on SrTiO3/Si(0 0 1) crystalline templates

A study of the structural and optical properties of an InAsP/InP quantum well heterostructure grown on a crystalline SrTiO₃ (STO)/Si(0 0 1) template is presented. The mismatch between InP and STO is fully accommodated by an array of geometric dislocations confined at the heterointerface. As a consequence, InP takes its bulk lattice parameter as soon as growth begins, and does not contain threading dislocations related to plastic relaxation. It contains twins related to the initially three-dimensional growth. Despite these twins, photoluminescence from the quantum well is detected at room temperature, showing that STO/Si(0 0 1) templates have an interesting potential for the monolithic integration of III-V semiconductors on silicon.     

Direct measurement of interfacial structure in epitaxial Gd2O3 on GaAs (0 0 1) using scanning tunneling microscopy

The epitaxial growth of Gd₂O₃ on GaAs (0 0 1) has given a low interfacial density of states, resulting in the demonstration of the first inversion-channel GaAs metal-oxide-semiconductor field-effect transistor. Motivated by the significance of this discovery, in this work, cross-sectional scanning tunneling microscopy is employed herein to obtain precise structural and electronic information on these epitaxial films and interfaces. At the interface, the interfacial stacking of Gd₂O₃ films is directly correlated with the stacking sequence of the substrate GaAs. Additionally, from the local electronic states across the gate oxides, the spatial extent of the GaAs wavefunctions into the oxide dielectric may suggest a minimum Gd₂O₃ thickness to be of bulk properties.     

Evaluation of Qbd for electrons tunneling fromthe Si/SiO2 interface compared to electron tunneling from thepoly-Si/SiO2 interface

Electrical time-to-breakdown (TTB) measurements have shown the charge to breakdown Q_bd of gate oxide capacitors fabricated on n-type well (n-well) substrates always to be higher than that of capacitors on p-type well (p-well) substrates on the same wafer when both are biased into accumulation under normal test conditions. Here the authors correlate the higher n-well Q_bd to smooth capacitor oxide/substrate interfaces and minimized grain boundary cusps at the poly-Si gate/oxide interfaces, confirming that Fowler-Nordheim tunneling is the dominant current conduction mechanisms through the oxide. They correlate higher Q_bd to higher barrier height for a given substrate type and observe that the slope of the barrier height versus temperature plot is lower for both p-well and n-well cases with electrons tunneling from the silicon substrate. This is attributed to surface roughness at the poly-Si gate/SiO₂ interface. A poly-Si gate deposition and annealing process with clean, smooth oxide/substrate interfaces will improve the p-well breakdown characteristics and allow higher Q_bd to be achieved     

Stripline resonator measurements of Zs versus Hrf in YBa2Cu3O7-x thin films

A report is presented on measurements of the surface impedance, Z_S, of YBa₂Cu₃O_7-x thin films using a stripline resonator. The films were deposited on LaAlO₃ substrates by off-axis magnetron sputtering. The authors obtained Z_S as a function of frequency from 1.5 to 20 GHz, as a function of temperature from 4 K to the transition temperature (~90 K), and as a function of the RF magnetic field from zero to 300 Oe. At low temperatures the surface resistance, R _S, of the films shows a very weak dependence on the magnetic field up to 225 to 250 Oe. At 77 K, R_S is proportional to the square of the field. The penetration depth shows a much weaker dependence on the field than does R_S. The origins of the magnetic field dependence of Z_S are also discussed     

Density functional theory study of first-layer adsorption of ZrO2 and HfO2 on Ge(1 0 0)

Density functional theory was used to performed a survey of transition metal oxide (MO₂ = ZrO₂, HfO₂) ordered molecular adsorbate bonding configurations on the Ge(1 0 0)-4 × 2 surface. Surface binding geometries of metal-down (O-M-Ge) and oxygen-down (M-O-Ge) were considered, including both adsorbate and displacement geometries of M-O-Ge. Calculated enthalpies of adsorption show that bonding geometries with metal-Ge bonds (O-M-Ge) are essentially degenerate with oxygen-Ge bonding (M-O-Ge). Calculated electronic structures indicate that adsorbate surface bonding geometries of the form O-M-Ge tend to create a metallic interfaces, while M-O-Ge geometries produce, in general, much more favorable electronic structures. Hydrogen passivation of both oxygen and metal dangling bonds was found to improve the electronic structure of both types of MO₂ adsorbate systems, and induced the opening of true semiconducting band gaps for the adsorbate-type M-O-Ge geometries. Shifts observed in the DOS minima for both O-M-Ge and M-O-Ge adsorbate geometries are consistent with surface band bending induced by the adsorbate films, where such band bending extends much further into the Ge substrate than can be modeled by the Ge slabs used in this work.