FEM Design and Modeling of $chi^{(2)} $ Second-Harmonic Enhancement in Circular Photonic Crystal

In this paper, we analyze the enhancement of $chi^{(2)} $ nonlinear process in membrane-type circular photonic crystal (PhC) based on GaAs. This unconventional kind of PhC is well suited for the generation of whispering gallery modes (WGMs) due to the circular symmetric periodic pattern. By using a laser Gaussian beam at 1.55 $ mu{hbox {m}}$ as pump signal, a WGM at 1.55 $ mu{hbox {m}}$ and a second-harmonic (SH) mode at 0.775 $ mu{hbox {m}}$ are obtained. The SH will be generated in the center of the missing-hole microcavity. The periodic pattern and the microcavity are tailored and optimized providing an SH efficiency conversion as high as 50%. We predict the resonances by an accurate 2-D time-domain model including $chi^{(2)}$ nonlinearity and by a 3-D finite-element method. Finally, by using a 3-D membrane configuration, we found a total quality factor of the SH mode of the order of 35 000.      

On Parallelepiped-Shaped Passbands for Multidimensional Nonseparable ${bf M}$th-Band Low-Pass Filters

The “shape” of the desired frequency passband is an important consideration in the design of nonseparable multidimensional ($M$ -D) filters in $M$-D multirate systems. For $M$-D ${bf M}$th-band filters, the passband shape should be chosen such that the ${bf M}$th-band constraint is satisfied. The most commonly used shape of the passband for $M$-D ${bf M}$ th-band low-pass filters is the so-called symmetric parallelepiped (SPD) ${rm SPD}(pi {bf M}^{- {rm T}})$ . In this paper, we consider the more general parallelepiped passband ${rm SPD}(pi {bf L} ^{rm T})$, and derive conditions on $ {bf L} $ such that the ${bf M}$ th-band constraint is satisfied. This result gives some flexibility in designing $M$-D ${bf M}$th-band filters with parallelepiped shapes other than the commonly used case of $ {bf L} = {bf M}^{- 1}$. We present design examples of 2-D ${bf M}$th-band filters to illustrate this flexibility in the choice of $ {bf L} $.      

Active Matrix OTFT Display With Anodized Gate Dielectric

A complete process for an active-matrix (AM) organic thin-film transistor (OTFT) polymer dispersed liquid crystal (PDLC) display is presented. Evaporated pentacene is used as semiconductor. The display comprises 64$times$64 pixel, each with a pixel pitch of $({hbox{312.5}} times {hbox{312.5}}) mu{hbox{m}}^2$. The AM display is fabricated with standard photolithographic processes. Since all process temperatures are below 180$^{circ}$C the processes for the AM backplane can be easily transferred to plastic substrates like PEN or PET. Due to the thin anodically oxidized ${hbox{Al}}_2$ ${hbox{O}}_3$ gate dielectric with a thickness of 60 nm and $varepsilon_{rm r}=9$, driving voltages between 10 and 12 V are sufficient. To protect the pentacene against the PDLC, it is encapsulated with sputtered ${hbox{Ta}}_2 {hbox{O}}_5$ layer. After the passivation a field effect mobility of 0.2 ${hbox{cm}}^{2}/{hbox{V}}cdot{hbox{s}}$ is obtained for the OTFTs.      

Experimental Examination and Physical Understanding of the Coulomb Scattering Mobility in Strained-Si nMOSFETs

In this paper, the impact of biaxial tensile strain on the electron mobility limited by Coulomb scattering in inversion layers is experimentally examined. It includes the study of both interface state $(N_{rm it})$ and substrate impurity $(N_{rm sub})$ Coulomb scatterings. Compared with unstrained-Si devices, the mobility limited by $N_{rm sub}$ is enhanced in strained-Si nMOSFETs, whereas the mobility limited by $N_{rm it}$ is degraded. These new findings are investigated through extensive mobility measurements at various temperatures (50 K–300 K) and surface electric fields. It is found that two key parameters exist for explaining the opposite strain dependence of mobility limited by $N_{rm it}$ and $N_{rm sub}$ scatterings: One is the valley population, and the other is the distance between inversion layer electrons and the charged centers.      

Low-Power Programmable Pseudorandom Word Generator and Clock Multiplier Unit for High-Speed SerDes Applications

This paper presents the design of a low-power programmable pseudorandom word generator (PRWG) and a low-noise clock multiplier unit (CMU) for high-speed SerDes applications. The PRWG is capable of producing test patterns with sequence length of $2 ^{7} -1$, $2 ^{10} -1$, $2 ^{15} -1$, $2 ^{23} -1$, and $2 ^{31} -1~hbox{b}$ according to CCITT recommendations, and the random word is 16-bit wide. High-speed and low-power operations of the PRWG are achieved by parallel feedback techniques. The measured jitter of the CMU is only 3.56 ${hbox {ps}}_{rm rms}$, and the data jitter at the PRWG output is mainly determined by the CMU. Implemented in an 0.18-$mu{hbox {m}}$ CMOS process, the power dissipation for the PRWG is only 10.8 mW, and the CMU consumes about 87 mW from a 1.8-V supply. This PRWG can be used as a low-cost substitute for external parallel test pattern generators.      

Two-Dimensional Ferroelectric Photonic Crystal Waveguides: Simulation, Fabrication, and Optical Characterization

The optical properties of two dimensional photonic crystal (PhC) waveguides were investigated using ferroelectric barium titanate (BTO) thin films as the optical medium. The photonic band structure was calculated using a 2-D finite difference time domain (FDTD) method; a broad band gap is observed that results from the high refractive index contrast. The simulated transmission spectra indicate the stop band of PhC is mainly determined by three parameters: lattice constant, refractive index contrast, and waveguide mode order. From transmission measurements the PhC with a lattice constant ${a}=420$ nm shows a strong light dispersion and the other PhC with ${a}=450$ nm shows a 120-nm broad stop band. Strong localization of visible light within the PhC cavities is demonstrated from the light scattering images. The observed strong light confinement and its spatial intensity profile due to resonance agree with the calculated profiles. From polarized optical microscopy we discovered the scattered light wavelength was highly sensitive to magnitude of the lattice constant. The optical scattering properties indicate BTO PhC can potentially serve as micrometer size electro-optically tunable switches and color filters.      

Soil Moisture Retrieval During a Corn Growth Cycle Using L-Band (1.6 GHz) Radar Observations

This paper reports on the retrieval of soil moisture from dual-polarized L-band (1.6 GHz) radar observations acquired at view angles of 15$^{circ}$, 35 $^{circ}$, and 55$^{circ}$ , which were collected during a field campaign covering a corn growth cycle in 2002. The applied soil moisture retrieval algorithm includes a surface roughness and vegetation correction and could potentially be implemented as an operational global soil moisture retrieval algorithm. The surface roughness parameterization is obtained through inversion of the Integral Equation Method (IEM) from dual-polarized (HH and VV) radar observations acquired under nearly bare soil conditions. The vegetation correction is based on the relationship found between the ratio of modeled bare soil scattering contribution and observed backscatter coefficient $(sigma^{rm soil}/sigma^{rm obs})$ and vegetation water content $(W)$. Validation of the retrieval algorithm against ground measurements shows that the top 5-cm soil moisture can be estimated with an accuracy between 0.033 and 0.064 $hbox{cm}^{3}cdothbox{cm}^{-3}$, depending on the view angle and polarization.      

Fast joint reconstruction of dynamic R2* and field maps in functional MRI

Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) is conventionally done by reconstructing ${T}_{2}^{*}$-weighted images. However, since the images are unitless they are nonquantifiable in terms of important physiological parameters. An alternative approach is to reconstruct ${R}_{2}^{*}$ maps which are quantifiable and have comparable BOLD contrast as ${T}_{2}^{*}$-weighted images. However, conventional ${R}_{2}^{*}$ mapping involves long readouts and ignores relaxation during readout. Another problem with fMRI imaging is temporal drift/fluctuations in off-resonance. Conventionally, a field map is collected at the start of the fMRI study to correct for off-resonance, ignoring any temporal changes. Here, we propose a new fast regularized iterative algorithm that jointly reconstructs ${R}_{2}^{*}$ and field maps for all time frames in fMRI data. To accelerate the algorithm we linearize the MR signal model, enabling the use of fast regularized iterative reconstruction methods. The regularizer was designed to account for the different resolution properties of both ${R}_{2}^{*}$ and field maps and provide uniform spatial resolution. For fMRI data with the same temporal frame rate as data collected for ${T}_{2}^{*}$-weighted imaging the resulting ${R}_{2}^{*}$ maps performed comparably to ${T}_{2}^{*}$-weighted images in activation detection while also correcting for spatially global and local temporal changes in off-resonance.      

Endurance Reliability of Multilevel-Cell Flash Memory Using a $ hbox{ZrO}_{2}/hbox{Si}_{3}hbox{N}_{4}$ Dual Charge Storage Layer

The mechanisms of programming/erasing (P/E) and endurance degradation have been investigated for multilevel-cell (MLC) Flash memories using a $hbox{Si}_{3}hbox{N}_{4}$ (NROM) or a $hbox{ZrO}_{2}/hbox{Si}_{3}hbox{N}_{4}$ dual charge storage layer (DCSL). Threshold-voltage $(V_{rm th})$ -level disturbance is found to be the major endurance degradation factor of NROM-type MLCs, whereas separated charge storage and step-up potential wells give rise to a superior $V_{rm th}$ -level controllability for DCSL MLCs. The programmed $V_{rm th}$ levels of DCSL MLCs are controlled by the spatial charge distribution, as well as the charge storage capacity of each storage layer, rather than the charge injection. As a result, DCSL MLCs show negligible $V_{rm th}$-level offsets ($ ≪ $ 0.2 V) that are maintained throughout the $hbox{10}^{5}$ P/E cycles, demonstrating significantly improved endurance reliability compared to NROM-type MLCs.      

High-Speed High-Isolation 2$, times ,$2 Fiber-Optic Switch for Wideband Radar Photonic Beamforming Controls

A new high-performance 2$, times ,$2 fiber-optic switch is designed and demonstrated for wideband radar photonic beamforming controls. The switch deploys two bulk acoustooptic deflectors (AODs) in an imaging free-space symmetric optical design that exploits image inversion control via a Dove prism to form a 2$, times ,$2 fully reversible low crosstalk noise high-speed switching structure. Experiments at the 1550-nm test wavelength show the switch to handle 0.5-W level optical input powers, $≪ {hbox{2.2-}}mu$s switching time, $≪ $2.6-dB fiber-to-fiber optical loss, better than 56-dB optical crosstalk levels, and $≪$0.2-dB polarization-dependent loss (PDL).      

A Heterogeneous 16-Bit DAC Using a Replica Compensation

A highly monotonic very low power 16-bit 2-MS/s digital-to-analog converter (DAC) for high-resolution control loop systems is proposed and demonstrated. Replica compensation is used in improving the monotonicity of a heterogeneous DAC composed of a coarse current steering DAC and a fine resistor-ladder DAC. A complete DAC, including an on-chip bandgap reference and an output buffer, consumes only 0.6 mA with a 2.7-V supply. The 2.19-mm $^{2}$ DAC with 10-I/O bonding pads implemented in 0.18- $mu$m Bi-CMOS process achieves ${pm} 0.8$ least significant bit (LSB) differential nonlinearity, ${pm} 4$ LSB integral nonlinearity, and ${pm} $ 3-mV offset error at 2-MS/s sample rate.      

A Scalable Digitalized Buffer for Gigabit I/O

A serial input–output (I/O) composed of inverters and transmission gates only is proposed to achieve high supply voltage scalability and low area overhead. The inverter with an inductive biasing circuit can extend bandwidth, and reduce the simultaneous switching noise simultaneously. With a TSMC 0.18-$mu{hbox {m}}$ CMOS process, the I/O occupies an area of 0.014 ${hbox {mm}}^{2}$ and operates from 4 Gbps@1.9 V to 1.5 Gbps@1.1 V.      

Fabrication and Characterization of High-Current-Gain 4H-SiC Bipolar Junction Transistors

This paper reports on newly developed high-performance 4H-SiC bipolar junction transistors (BJT) with improved current gain and power handling capabilities based on an intentionally designed continuously grown 4H-SiC BJT wafer. The measured dc common-emitter current gain is as high as 70, the specific on -state resistance $(R_{{rm SP}hbox{-}{rm ON}})$ is as low as 3.0 $hbox{m}Omegacdothbox{cm}^{2}$, and the open-base breakdown voltage $(V_{rm CEO})$ reaches 1750 V. Large-area 4H-SiC BJTs with a footprint of 4.1 $times$ 4.1 mm have been successfully packaged into a high-gain $(beta = hbox{50.8})$ high-power (80 A $times$ 700 V) all-SiC copack and evaluated at high temperature up to 250 $^{circ}hbox{C}$. Small 4H-SiC BJTs have been stress tested under a continuous collector current density of 100 $hbox{A}/hbox{cm}^{2}$ for 24 h and, for the first time, have shown no obvious forward voltage drift and no current gain degradation. Numerical simulations and experimental results have confirmed that simultaneous high current gain and high open-base breakdown voltage could be achieved in 4H-SiC BJTs.      

Photonic Crystal Slab Waveguides Based on Antiresonant Reflecting Optical Waveguide Structures

A novel two-dimensional photonic crystal slab waveguide based on an antiresonant reflecting optical waveguide (ARROW) structure is proposed and designed. Lightwaves propagating in this waveguide are confined by antiresonance reflection vertically and the photonic band gap laterally. In order to obtain the characteristics of the ARROW-based photonic crystal waveguides, the three-dimensional finite-difference time-domain simulations are performed. With a lateral adiabatic taper, a coupling efficiency of 80.3% from a single-mode fiber to the ARROW-based photonic crystal waveguide of a single-line defect is obtained. In addition, propagation losses less than 10 dB/mm and bend losses of 0.23 and 0.39 dB/bend for the designed 60$^{circ}$ and 120$^{circ}$ bends are achieved at an operating wavelength of $1.55~mu{hbox {m}}$.      

Interface Electronics for a CMOS Electrothermal Frequency-Locked-Loop

This paper describes a new implementation of a CMOS electrothermal frequency-locked-loop (FLL), whose output frequency is determined by the temperature-dependent phase shift of an electrothermal filter (ETF). The FLL maintains a constant phase shift in the ETF, and as a result drives it with a signal whose frequency is a well-defined function of temperature. Compared to a previous implementation, the FLL described here has significantly more loop gain, less electrical phase-spread, and is more suitable for full integration. Measurements on 16 samples (from one batch) show that the temperature dependence of the FLL's output frequency agrees very well with the known thermal properties of bulk silicon. The untrimmed spread of this frequency is less than $pm $0.45% ($3sigma $ ) from $-{hbox{40}}^{circ}{hbox{C}}$ to 100$^{circ} {hbox {C}}$, which corresponds to a temperature-sensing inaccuracy of less than $pm {hbox{0.7}},^{circ}{hbox{C}}$ ( $3sigma$).      

Fabrication and Characterization of Temperature Insensitive 660-nm Resonant-Cavity LEDs

InGaP/AlGaInP 660-nm resonant-cavity light-emitting diodes (RCLEDs) with stable temperature characteristics have been achieved by extending the resonant cavity length from one optical wavelength $(1lambda)$ to three optical wavelengths $(3lambda)$ and tripling the number of quantum wells. When the operation temperature increases from 25 $^{circ}$C to 95 $^{circ}$ C, the degree of power variation at 20 mA is reduced from ${-}$2.1 dB to ${-}$0.6 dB for the conventional 1- $lambda$ cavity RCLEDs and 3- $lambda$ cavity RCLEDs, respectively. In order to interpret the temperature-dependent experimental results, advanced device simulation is applied to model the RCLEDs with different cavity designs. According to the numerical simulation results, we deduce that the stable temperature-dependent output performance should originate from the reduction of electron leakage current and thermally enhanced hole transport for the 3- $lambda$ cavity AlGaInP RCLEDs.      

Tailoring Dispersion and Confinement Losses of Photonic Crystal Fibers Using Hybrid Cladding

We present a hybrid cladding photonic crystal fiber (PCF) for shaping nearly zero ultraflattened dispersion and low confinement losses in a wide range of wavelengths. The finite difference method with anisotropic perfectly matched boundary layer is used to investigate the guiding properties. It has been shown theoretically that it is possible to obtain nearly zero ultraflattened dispersion of ${hbox{0 }} pm {hbox{0.25}} ~{hbox{ps}}/{hbox{nm}}/{hbox{km}}$ in a wavelength range of 1.44 to 2.0 $ mu{hbox{m}}$ with low confinement losses less than 0.005 dB/km within the entire band of interest from a five-ring hybrid cladding PCF.      

Novel Design of a 2.5-GHz Fully Integrated CMOS Butler Matrix for Smart-Antenna Systems

This paper presents a novel design of monolithic 2.5-GHz 4 $,times,$4 Butler matrix in 0.18- $mu$m CMOS technology. To achieve a full integration of smart antenna system monolithically, the proposed Butler matrix is designed with the phase-compensated transformer-based quadrature couplers and reflection-type phase shifters. The measurements show an accurate phase distribution of ${hbox{45}}{pm}{hbox{3}}^{circ}, ~{hbox{135}} pm {hbox{4}}^{circ}, ~ -{hbox{45}} pm {hbox{3}}^{circ}, ~{hbox{and}}~ -{hbox{135}} pm {hbox{4}}^{circ}$ with amplitude imbalance less than 1.5 dB. The antenna beamforming capability is also demonstrated by integrating the Butler matrix with a 1$,times,$ 4 monopole antenna array. The generated beams are pointing to $-{hbox{45}}^{circ}, ~ -{hbox{15}}^{circ}$ , 15$^{circ}$, and 45$^{circ}$, respectively, with less than 1$^{circ}$ error, which agree very well with the predictions. This Butler matrix consumes no dc power and only occupies the chip area of 1.36 $,times,$1.47 mm$^{2}$ . To our knowledge, this is the first demonstration of the single-chip Butler matrix in CMOS technology.      

Design of Ultrahigh- $Q$ 1-D Photonic Crystal Microcavities

Waveguide based 1-D photonic crystal (PC) microcavities in silicon-on-insulator are investigated by 2-D finite-difference time-domain method. Values up to $6.7times 10 ^{6}$ for the quality factor $(Q)$ are feasible if the cavities are properly designed. The factors that govern $Q$ are analyzed in both real space and momentum space. Etching down into the ${hbox {SiO}}_{2}$ layer is found to give more than 20% improvement in $Q$ compared to the structure in which etching is stopped at the oxide layer. Short air gap mirrors are used to reduce the vertical scattering loss. The addition to the Bragg mirrors of tapered periods optimized to produce a cavity mode with a near Gaussian shaped envelope results in a major reduction in vertical loss. A new tapered structure with varying Si block width demonstrates an ultrahigh- $Q$ and relieves the fabrication constraints compared to the conventional air slots tapered structure.      

Performance Improvement of Organic Thin-Film Transistors by Electrode/Pentacene Interface Treatment Using a Hydrogen Plasma

Pentacene-based organic thin-film transistors (TFTs) have been fabricated with and without treatment by hydrogen $(hbox{H}_{2})$ plasma at the interface between the electrode and the pentacene surface. Processing with a $hbox{H}_{2}$ plasma was carried out in a plasma-enhanced chemical vapor deposition with varying treatment times. The interface treatment by $hbox{H}_{2}$ plasma resulted in improved device electrical properties. Removal of oxygen from the pentacene surface occurs due to slight etching by the plasma. Sufficient flux density of the $hbox{H}_{2}$ plasma leads to full pentacene-surface coverage by rearranging the hydrogen with carbon instead of oxygen. Atomic force microscopy profiles reveal the morphology changes of the pentacene surface after treatment, and secondary ion mass spectrometry shows the change via compositional depth profiles indicating $ hbox{H}_{2}$, $hbox{O}_{2}$, and C–H binding. Hydrogen treatment, therefore, appears to modify the interface by removing the surface oxygen layer, resulting in better performance of the organic TFT.