The complex LMS algorithm

A least-mean-square (LMS) adaptive algorithm for complex signals is derived. The original Widrow-Hoff LMS algorithm is Wj+l= Wj+ 2µεjXj. The complex form is shown to be Wj+1= Wj+ 2µεjX^-j, where the boldfaced terms represent complex (phasor) signals and the bar above Xjdesignates complex conjugate.     

Optical absorption of thin film on a Lambertian reflector substrate

A formula is derived for calculating the optical absorption of thin films deposited on a Lambertian reflector substrate. It is shown that compared with the case of flat reflecting substrate, the incoherent absorption is enhanced by a factor ofmepsilon_{1}in the weak absorption limit, where ε1is the real part of the film dielectric constant andm simeq 2is a slightly varying function of ε1. For a 0.5-µm a-SiHx(bandgap 1.7 eV) solar cell with a Lambertian reflector substrate, the total absorption in terms of the short-circuit current is calculated to be 18.63 mA/cm².     

Measurement of constitutive parameters using the Mie solution of a scattering sphere

A method of determining the relative constitutive parameters (µr, εr) is given. This method is based on the Mie solution of a scattering sphere. Field components scattered in two orthogonal planes are measured at 6.17 GHz and 7.03 GHz to calculate the desired parameters of four representative specimen spheres each 1.27 cm in diameter. A consistency process has been developed to reduce random errors caused by theoretical approximations and experimental inaccuracies. Only those data which are considered to have given consistent solutions are then used to produce the material parameters. A target support which can be rotated 360° is used to determine whether a specimen sphere can be assumed homogeneous and isotropic. The present method has in practice no difficult problem of specimen fitting and positioning. Semiquantitative assessments on the final results of (µr, εr) are made for the specimens measured. Usefulness of this method for measuring lossy materials is demonstrated by the use of three lossy specimens. Recommendations for evaluating a unique set of parameters and improving their accuracies are made in both theoretical and experimental aspects.     

Measurements of the Photo-Induced Complex Permittivity of Si, Ge, and Te at 9 GHz

The photo-induced complex permittivity Delta epsilon /sub r/(=Delta epsilon'/sub r/--j Delta epsilon"/subr/)of single, crystal silicon, germanium, and tellurium samples was studied using a transmission microwave bridge method at frequencies of about 9 GHz. The measurements were made at temperatures in a range from 100 to 300 K over an optical wavelength range from about 0.6 to 1.4 µm for silicon, 0.8 to 2.0 µm for germanium, and 1.5 to 4.2 µm for tellurium. The incident monochromatic illumination was chopped at about 90 Hz. It was found that the spectral variation of Delta epsilon'/sub r/ was similar to that for Delta epsilon"/sub r/ over the wavelength ranges with the incident monochromatic light intensity in the order of 100 µw/cm²². The spectral peaks (for Si and Ge samples) of both Delta epsilon'/sub r/ and Delta epsilon"/sub r/ were found to shift towards shorter wavelengths as the temperature was decreased. From the photo-induced complex permittivity results, the collision time of the free carriers was derived.     

Tailoring the microwave permittivity and permeability of composite materials

The microwave permittivity (?_r) and permeability (µ_r) of composite materials are tailored by adding various loading agents to a host plastic and are subsequently modeled using the Maxwell Garnett theory and second order polynomials. With the addition of manganese zinc ferrite, strontium ferrite, nickel zinc ferrite, barium tetratitanate and graphite powders, materials with values of ?′, e″, µ′, µ″ as high as 22, 5, 2.5 and 1.7 have been obtained. Permittivity and permeability data are calculated at 2.0245 GHz from reflection and transmission measurements performed in a 7 mm coaxial test line. The Maxwell Garnett (MG) theory successfully models ?_r if the filling factor is less than 0.30 and ratio |?₁| (host)/ |?₂| (powder) is greater than 0.04. As this ratio decreases, the MG theory is shown to be independent of ?₂ and second order polynomials are used to effectively model the dielectric constant. Polynomials are also used for the ferrite composites because it was determined that the MG theory was unable to model µ_r. This deficiency is attributed to the difference of domain structures that exist in powdered and sintered ferrites.     

Diffusion-free charge relaxation in a conducting medium

The commonly used two-term relaxation equation can lead to inconsistencies, which researchers have sought to resolve by introducing diffusion and scattering-time effects. It is shown here that the complete equation ∂n^~/∂t + σ/ε n^~+ E^→ċ grad^→(nµ) = 0 is sufficient to account for charge flow, propagation effects and surface-charge induction, as well as instabilities in negative-differential-conductivity materials.     

Fiber-optical transmission between 0.8 and 1.4 µm

The present state of the art and expected development in discrete components for fiber-optic transmission systems are reviewed. Predicted performance of fiber systems in the 0.85, 1.06, and 1.27 µm regions is presented, and the advantages of longer wavelength operation quantified. It is concluded that operation near 1.27 µm is particularly attractive for a) moderate data rate systems employing LED's and multimode fibers whose chromatic dispersion and attenuation are greatly reduced compared with 0.85 and 1.06 µm, and b) high data rate systems employing lasers and monomode fibers. In systems employing lasers and graded index multimode fibers, the advantage of 1.27 µm versus 1.06 µm operation is not as pronounced, although transmission distances at both of these longer wavelengths are significantly increased from those at 0.85 µm.     

Tl3VS4 as an acousto-optic and surface wave material

Single crystals of thallium vanadium sulphide (Tl₃VS₄) up to 2 cm in length were grown from melts using the Stockbarger technique. This material has acoustic velocities as low as 8.73 × 10⁴ cm/sec for bulk shear waves and 8.7 × 10⁴ cm/sec for surface (Rayleigh) waves. In a sample oriented (001)Λ(110), k² was found to be 1.39%, and the temperature coefficient of delay −54 ppm for surface waves. The optical transmission is from 0.75 to 10.5 μm, and the indices of refraction range from 3.156 at 0.749 μm to 2.808 at 5.26 μm. These properties make it an attractive candidate for use in acousto-optic and acoustic surface-wave devices.     

Optical Methods for the Measurement of Complex Dielectric and Magnetic Constants at Centimeter and Millimeter Wavelengths

A method is described which permits the determination of the complex dielectric constant, epsilon* = epsilon/sub o/k/sub e/(l-j tan delta/sub e/), and the complex permeability, µ* = µ/sub o/k/sub m/ (l-j tan delta/sub m/), using free space transmission and reflection from a plane sheet of the sample dielectric. The procedure represents an extension of that used at optical frequencies. Differences arise however, due to the fact that the assumptions of k/sub m/ = 1 and tan delta/sub m/ = 0, which are made in the optical theory, are not always valid at millimeter wavelengths.     

Millimeter-wave measurements of the complex dielectric constant of an advanced thick film UV photoresist

The first measurement of the relative permittivity (ε_r) and loss tangent (tan δ) of EPON™ SU-8 advanced thick film ultraviolet photoresist is reported at frequencies between 75–110 GHz (W-band). The problems associated with such a measurement are discussed, an error analysis given, and values of ε_r=1.725±0.08 and tanδ =0.02±0.001 are determined.     

Gigabit/s Optical Receiver Sensitivity and Zero-Dispersion Single-Mode Fiber Transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 µm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p/sup +/nn/sup -/ Ge APD. The p/sup +/nn/sup -/ Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55 µm and a 10/sup -9/ error rate, which was 4 dB better than the receiving level with a p/sup +/n Ge APD. Detector performance at 1.3 µm was also studied for comparison with performance at 1.55 um. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55 µm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) /spl dot/ km at 1.55 µm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3 µm dispersion free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.     

A low-power transmission-gate-based 16-bit multiplier for digital hearing aids

The most widespread 16-bit multiplier architectures are compared in terms of area occupation, dissipated energy, and EDP (Energy-Delay Product) in view of low-power low-voltage signal processing for digital hearing aids and similar applications. Transistor-level simulations including back-annotated wire parasitics confirm that the propagation of glitches along uneven and re-convergent paths results in large unproductive node activity. Because of their shorter full-adder chains, Wallace-tree multipliers indeed dissipate less energy than the carry-save (CSM) and other traditional array multipliers (6.0 µW/MHz versus 10.9 µW/MHz and more for 0.25 µm CMOS technology at 0.75 V). By combining the Wallace-tree architecture with transmission gates (TGs), a new approach is proposed to improve the energy efficiency further (3.1 µW/MHz), beyond recently published low-power architectures. Besides the reduction of the overall capacitance, minimum-sized transmission gate full-adders act as RC-low-pass filters that attenuate undesired switching. Finally, minimum size TGs increase the V _dd to ground resistance, hence decreasing leakage dissipation (0.55 nW versus 0.84 nW in CSM and 0.94 nW in Wallace).     

Growth and characterization of InGaAs/InP p-quantum-well infrared photodetectors with extremely thin quantum wells

High-quality InGaAs/InP quantum wells with ultra-narrow well widths (∼10?) and peak response at 4.55 μm were grown by gas source molecular beam epitaxy. These structures were characterized by cross-sectional tunneling microscopy (XSTM), double-crystal x-ray diffraction (DCXRD), and cross-sectional transmission electron microscopy (XTEM). Based on the structural parameters determined by XTEM, XSTM, and DCXRD, the field dependent photocurrent spectra were simulated using a six-band effective bond-orbital model. The theoretical calculations are in excellent agreement with experimental data. When used to fabricate p-type InGaAs/InP quantum-well infrared photodetectors (QWIPs), and combined with the high responsivity of 8.93 μm n-type InGaAs/InP QWIPs, these structures offer the possibility of dual band monolithically integrated QWIPs.     

Mark detection technology in electron-beam direct writing

Monte Carlo (MC) simulation and experimental results are used to investigate mark detection technology in electron-beam (e-beam) direct writing for a 10-kV acceleration voltage. The simulation is based on a single scattering and a continuously slowing down approximation model, and also takes into account the Gaussian profile of the e-beam in order to calculate the backscattered electrons from the mark edges in detail. The simulation results for the alignment signals from a 66° tapered pedestal mark with a 1.1-µm-thickness resist are in good agreement with the experimental results. For the 10-keV e-beam, a location accuracy of about 0.15 µm (3 σ) is obtained by an alignment mark 2.3 µm high and 3.8 µm wide under the same conditions as the simulation. In this study, it is revealed that the simulation for the mark signal makes it possible to evaluate the accuracy of mark detection.     

Design and applications of two-port SAW resonators on YZ-lithium niobate

The fundamental design criteria for two-port SAW resonators are discussed. The distributed reflective arrays are modeled as lossy repetitively mismatched transmission lines with impedance mismatch ε and expressions for the reflection magnitude and phase are given. An experimental technique is described to directly determine both ε and the proper placement of the input/output transducers. Experimental two-port resonator filters have been realized having Q's of 2000-5000, 5-7 dB insertion loss, and ∼35-dB sidelobe suppression. By electrically cascading three resonators, sidelobe suppression of ∼80 dB has been achieved. Resonator structures have been developed in which continuous frequency tuning up to 0.18 percent has been obtained by electronic means.     

GaAs microlens arrays grown by shadow masked MOVPE

This paper describes the fabrication of high quality GaAs microlenses and microlens arrays using shadow masked metalorganic vapor phase epitaxial (MOVPE) growth (SMMG). Microlenses with apertures as small as 30 μm were fabricated and focal lengths down to 40 μm were measured. The smaller lenses closely fit the theoretical behavior of ideal spherical lenses while larger lenses (focal length >80 μm) showed a more complex physical shape and could not be modeled as spherical. This deviation from a spherical shape is expected from simulation of SMMG. The full width at half maximum of the beam waist was <2 μm for all sizes of microlens indicating that these lenses are compatible with coupling to single mode fibers.     

A linear-sweep MOS-C technique for determining minority carrier lifetimes

A nonpulse MOS-C τ0measurement procedure, based upon the capacitance-voltage characteristics derived in response to a linear voltage sweep initiated and maintained under inversion biases, is described, analyzed, and illustrated. The most significant advantages of the procedure are interpretational and instrumentational simplicity. For typical dopings and oxide thicknesses, the conveniently measured lifetime range covers 0.1 µs ≲ τ0≲ 10 µs. About a decade improvement in the limits on the conveniently measured lifetime range can be achieved by employing relatively thin (0.1 µ) or relatively thick (1 µ) oxides.     

Submicrometer electron-beam direct writing technology for 1-Mbit DRAM fabrication

A 1-Mbit DRAM with 0.5-µm minimum linewidth is fabricated using variable shaped e-beam direct writing technology. A simple linewidth control technique using newly developed submicrometer resists is developed to achieve high resolution and better linewidth accuracy. In addition, a highly accurate registration technique is developed to ensure required overlay. These techniques are successfully used to achieve overlay accuracy of 0.04 µm(σ) and linewidth deviation of 0.018 µm(σ) in the fabrication.     

Precise time and frequency dissemination via the Loran-C system

The Loran-C Navigation System is described in terms of its characteristics as a precise time and frequency dissemination system. The technique employed in timing a Loran-C chain is described, and user techniques are addressed including economic considerations. The accuracy available for both ground-wave and sky-wave transmission modes is shown to be a function of the low-frequency propagation factors and equipment delays involved. Phase and amplitude perturbations due to irregular terrain effects are shown to produce time difference discrepancies in inland service areas. Using broad assumptions, both ground-wave and sky-wave coverages are estimated. Experience shows that Loran-C provides an excellent medium for the dissemination of precise time and frequency on a continuous basis in both the ground-wave and sky-wave modes. The stability of the ground wave provides a submicrosecond precision capability, but the accuracy of the system is limited by propagation effects to about ± 1 µs. Loran-C sky-wave synchronization appears to be capable of ± 1 µs precision for one-hop daytime transmissions and an estimated ± 8 µs for one-hop nighttime transmissions. As distance is increased and more sky-wave hops are involved, nighttime synchronization precision is degraded to about ± 20 µs. Accuracy of sky-wave synchronization is limited to about ± 50 µs for both daytime and nighttime.     

Using Preformed Meisenheimer Complexes as Dopants for n-Type Organic Thermoelectrics with High Seebeck Coefficients and Power Factors

A pre-formed Meisenheimer complex of a naphthalenediimide (NDI) with tetrabutylammonium fluoride (TBAF) is obtained in a simple way by mixing dibrominated 4,9-dibromo-2,7-bis(2-octyldodecyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone and TBAF in solution and used as a dopant for n-type organic thermoelectrics. Two n-type polymers PNDIClTVT and PBDOPVTT are synthesized, n-doped, and characterized as conductive and thermoelectric materials. PNDIClTVT doped with NDI-TBAF presents a high σ value of 0.20 S cm^–1, a Seebeck coefficient (S) of −1854 µV K^–1, and a power factor (PF) of 67 µW m^–1 K^–2, among the highest reported PF in solution-processed conjugated n-type polymer thermoelectrics. Using 4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine and NDI-TBAF as co-dopants, PNDIClTVT has a PF > 35 µW m^–1 K^–2; while for PBDOPVTT σ = 0.75 S cm^–1 and PF = 58 µW m^–1 K^–2. In this study it is found that an ionic adduct together with a neutral dopant improves the performance of n-type organic thermoelectrics leading to an enhanced power factor, and more generally, the role of such an adduct in polymer doping is also elucidated.