Compact Variable ${rm TE}$-${rm TM}$ Polarization Splitter Based on Simplified Coherent Coupling in Lithium Niobate

A compact-sized electrically tunable ${rm TE}$- ${rm TM}$ mode splitter composed of a mode converter and an asymmetric Y-branch structure is presented. The asymmetric Y-branch consists of a straight and a bent waveguides to split two polarization modes based on the mode-sorting effect. To shorten the device length, a simplified coherently coupled-bending structure is utilized for the bent waveguide. Experimental results show that the device length is reduced about 52%, extinction ratios of both ${rm TE}$ and ${rm TM}$ modes are higher than 25 dB, yet the applied voltage is not significantly increased.      

Near-Stoichiometric Ti : LiNbO$_{3}$ Strip Waveguides Fabricated by Standard Ti Diffusion and Post-VTE

We report near-stoichiometric (NS) Ti : LiNbO$_{3}$ waveguides fabricated by indiffusion of 4-, 5-, 6-, 7- $mu{hbox {m}}$-wide 120-nm-thick Ti-strips at 1060 $^{circ}hbox{C}$ for 10 h into a congruent $hbox{LiNbO}_{3}$ (i.e., standard Ti diffusion procedure) and post-vapour-transport-equilibration (VTE) treatment at 1100 $^{circ}hbox{C}$ for 5 h. These waveguides are NS and single-mode at 1.5 $mu{hbox {m}}$, and have a loss of 1.0/0.8 dB/cm for the TM/TE mode. In the width/depth direction of the waveguide, the mode field follows a Gauss/Hermite–Gauss profile, and the Ti profile follows a sum of two error functions/a Gauss function. The post-VTE resulted in increase of diffusion width/depth by 2.0/1.0 $mu{hbox {m}}$. A two-dimensional refractive index profile in the guiding layer is suggested.      

A Two-Port Single-Mode Fiber–Silicon Wire Waveguide Coupler Module Using Spot-Size Converters

In this paper, the performance of a two-port single-mode fiber–silicon wire waveguide coupler module which utilizes an identical spot-size converter (SSC) at the input and output ports is reported. Each of the silicon (Si)-based SSCs comprised cascaded horizontal linear and vertical nonlinear up-tapers measured 300 and 200 $mu$ m in length, respectively, in a common silicon-on-insulator (SOI) substrate. The structural parameters of the tapers were designed for compactness and relaxed tolerance to fabrication errors. The total length of the two-port coupler module was 1000 $mu$ m plus the variable length of the wire waveguide connecting the two SSCs. The mode-field diameter (MFD) of the Si-wire waveguide, 0.32$,times,$0.46 $mu$m $^{2}$, was transformed to the diameter of 2.8$,times,$ 8.0 $mu$ m$^{2}$ at the wavelength of 1.55 $mu$ m (corresponding to an area expansion of about 150 times) and vice versa by the SSCs with a net transmission loss of 4.1 dB/port. The field-mismatch loss between the SSC and the single-mode fiber with the MFD of 5.2 $mu$m was 2.1 dB/port.      

Characterization and Modeling of RF-Performance $(f_{T})$ Fluctuation in MOSFETs

The fluctuation of RF performance (particularly for $f_{T}$ : cutoff frequency) in the transistors fabricated by 90-nm CMOS technology has been investigated. The modeling for $f_{T}$ fluctuation is well fitted with the measurement data within approximately 1% error. Low-$V_{t}$ transistors (fabricated by lower doping concentration in the channel) show higher $f_{T}$ fluctuation than normal transistors. Such a higher $f_{T}$ fluctuation results from $C_{rm gg}$ (total gate capacitance) variation rather than $g_{m}$ variation. More detailed analysis shows that $C_{rm gs} + C_{rm gb}$ (charges in the channel and the bulk) are predominant factors over $C_{rm gd}$ (charges in LDD/halo region) to determine $C_{rm gg}$ fluctuation.      

Compact Microracetrack Resonator Devices Based on Small SU-8 Polymer Strip Waveguides

Compact microracetrack resonator (MRR) devices are presented with small SU-8 polymer strip waveguides. The SU-8 strip waveguide has an SU-8 polymer core $(n {sim} 1.573)$ , a SiO$_{2}$ buffer $(n {sim} 1.445)$, and an air cladding. The fabricated straight waveguide has a low propagation loss of about 0.1 dB/mm. With such a high index-contrast optical waveguide, a compact MRR with a small bending radius ( $sim$150 $mu$m) are designed and fabricated. The measured spectral responses of the through/drop ports show a $Q$-factor of 8000.      

$hbox{TiN/ZrO}_{2}$/Ti/Al Metal–Insulator–Metal Capacitors With Subnanometer CET Using ALD-Deposited $hbox{ZrO}_{2}$ for DRAM Applications

We provide the first report of the structural and electrical properties of $hbox{TiN/ZrO}_{2}$/Ti/Al metal–insulator–metal capacitor structures, where the $hbox{ZrO}_{2}$ thin film (7–8 nm) is deposited by ALD using the new zirconium precursor ZrD-04, also known as Bis(methylcyclopentadienyl) methoxymethyl. Measured capacitance–voltage ($C$– $V$) and current–voltage ( $I$–$V$) characteristics are reported for premetallization rapid thermal annealing (RTP) in $hbox{N}_{2}$ for 60 s at 400 $^{circ}hbox{C}$, 500 $^{circ}hbox{C}$, or 600 $^{ circ}hbox{C}$. For the RTP at 400 $^{circ}hbox{C}$ , we find very low leakage current densities on the order of nanoamperes per square centimeter at a gate voltage of 1 V and low capacitance equivalent thickness values of $sim$ 0.9 nm at a gate voltage of 0 V. The dielectric constant of $ hbox{ZrO}_{2}$ is 31 $pm$ 2 after RTP treatment at 400 $^{circ}hbox{C}$.      

10-GHz and 20-GHz Channel Spacing High-Resolution AWGs on InP

This letter reports on 10-GHz and 20-GHz channel-spacing arrayed waveguide gratings (AWGs) based on InP technology. The dimensions of the AWGs are 6.8$,times,$8.2 mm$^{2}$ and 5.0$,times,$6.0 mm$^{2}$, respectively, and the devices show crosstalk levels of $-$12 dB for the 10-GHz and $-$17 dB for the 20-GHz AWG without any compensation for the phase errors in the arrayed waveguides. The root-mean-square phase errors for the center arrayed waveguides were characterized by using an optical vector network analyzer, and are 18 $^{circ}$ for the 10-GHz AWG and 28$^{circ}$ for the 10-GHz AWG.      

An Analytical Method to Extract the Physical Parameters of a Solar Cell From Four Points on the Illuminated $J{-}V$ Curve

For a variety of solar cells, it is shown that the single exponential $J{-}V$ model parameters, namely—ideality factor $eta$ , parasitic series resistance $R_{s}$, parasitic shunt resistance $R_{rm sh}$, dark current $J_{0}$, and photogenerated current $J_{rm ph}$ can be extracted simultaneously from just four simple measurements of the bias points corresponding to $V_{rm oc}$, $sim!hbox{0.6}V_{rm oc}$, $J_{rm sc}$, and $sim! hbox{0.6}J_{rm sc}$ on the illuminated $J{-}V$ curve, using closed-form expressions. The extraction method avoids the measurements of the peak power point and any $dJ/dV$ (i.e., slope). The method is based on the power law $J{-}V$ model proposed recently by us.      

Low-Threshold Strained Quantum-Well GaSb-Based Lasers Emitting in the 2.5- to 2.7-$mu$ m Wavelength Range

GaInAsSb–GaSb strained quantum-well (QW) ridge waveguide diode lasers emitting in the wavelength range from 2.51 to 2.72 $ mu{hbox {m}}$ have been grown by molecular beam epitaxy. The devices show ultralow threshold current densities of 44 $hbox{A}/{hbox {cm}}^{2}$ (${L}rightarrow infty $) for a single QW device at 2.51 $ mu{hbox {m}}$, which is the lowest reported value in continuous-wave operation near room temperature (15 $^{circ}hbox{C}$) at this wavelength. The devices have an internal loss of 3 ${hbox {cm}}^{-1}$ and a characteristic temperature of 42 K. By using broader QWs, wavelengths up to 2.72 $mu{hbox {m}}$ could be achieved.      

Negative Bias Temperature Instability Dominated Degradation of Metal-Induced Laterally Crystallized p-Type Polycrystalline Silicon Thin-Film Transistors

Device degradation of solution-based metal-induced laterally crystallized p-type polycrystalline silicon (poly-Si) thin-film transistors (TFTs) is studied under dc bias stresses. While typical negative bias temperature instability (NBTI) or electron injection (EI) is observed under $-V_{g}$ or $-V_{d}$ only stress, respectively, no typical hot carrier (HC) degradation can be identified under high $-V_{d}$ stress combined with either low or high $-V_{g}$ stress. Instead, mixed NBTI and EI degradation is observed under combined low $-V_{g}$ and $-V_{d}$ stresses; and combined degradation of NBTI and HC occurs under high $-V_{d}$ and moderate $-V_{g}$ stresses. NBTI is the dominant mechanism in both cases. Grain boundary (GB) trap generation is found to correlate with the NBTI degradation with the same time exponent, suggesting the key role of GB trap generation in poly-Si TFTs' degradation.      

Performance Improvement of N-Type $hbox{TiO}_{x}$ Active-Channel TFTs Grown by Low-Temperature Plasma-Enhanced ALD

We report on performance improvement of $n$-type oxide–semiconductor thin-film transistors (TFTs) based on $hbox{TiO}_{x}$ active channels grown at 250 $^{circ}hbox{C}$ by plasma-enhanced atomic layer deposition. TFTs with as-grown $hbox{TiO}_{x}$ films exhibited the saturation mobility $(mu_{rm sat})$ as high as 3.2 $hbox{cm}^{2}/hbox{V}cdothbox{s}$ but suffered from the low on–off ratio $(I_{rm ON}/I_{rm OFF})$ of $hbox{2.0} times hbox{10}^{2}$. $hbox{N}_{2}hbox{O}$ plasma treatment was then attempted to improve $I_{rm ON}/I_{rm OFF}$. Upon treatment, the $hbox{TiO}_{x}$ TFTs exhibited $I_{rm ON}/I_{rm OFF}$ of $hbox{4.7} times hbox{10}^{5}$ and $mu_{rm sat}$ of 1.64 $hbox{cm}^{2}/hbox{V}cdothbox{s}$, showing a much improved performance balance and, thus, demonstrating their potentials for a wide variety of applications such as backplane technology in active-matrix displays and radio-frequency identification tags.      

High-Temperature Microwave Performance of Submicron AlGaN/GaN HEMTs on SiC

The effect of temperature on the small-signal radio-frequency (RF) performance of submicron AlGaN/GaN high-electron-mobility transistors on SiC has been studied from room temperature (RT) up to 600 K. A relation between ambient and channel temperatures has been established by means of finite-element simulations. The thermal behavior of the intrinsic parameters $C_{rm gs}$, $C_{rm gd}$, $g_{m, {rm int}}$, and $g_{rm ds}$ has been extracted accurately from RF measurements by means of the small-signal equivalent circuit. Main dc parameters $(I_{D}, g_{m, {rm ext}})$ show reductions close to 50% between RT and 600 K, mainly due to the decrease in the electron mobility and drift velocity. In the same range, $f_{T}$ and $f_{max}$ suffer a 60% decrease due to the reduction in $g_{m, {rm ext}}$ and a slight increase of $C_{rm gs}$ and $C_{rm gd}$. An anomalous thermal evolution of $C_{rm gd}$ at low $I_{D}$ has been identified, which is indicative of the presence of traps.      

Design and Application of Multimode Substrate Integrated Waveguides in Parallel Multichannel Signaling Systems

Multimode signal transmission concept is employed in this paper to increase the channel capacity of a substrate integrated waveguide (SIW) interconnect. In order to generate two uncoupled channels without adding an additional physical link, ${rm TE}_{10}$ and ${rm TE}_{20}$ modes of an SIW interconnect are harnessed as signal carriers. To excite these two orthogonal modes simultaneously, a multimode double launcher is proposed and characterized. It is shown that the performance of the launcher is limited by the coupling between the two mode launchers (transitions). Therefore, a method for improving port isolation is suggested, which results in increasing the channel bandwidths. A balun structure based on an SIW is presented and included in the multimode waveguide in order to efficiently excite the ${rm TE}_{20}$ mode. Ultimately, the multimode waveguide with the optimized transitions is used in a parallel data transmission system demonstrating excellent transmission quality for the data rate of a 1-Gb/s/channel.      

Positive Bias Temperature Instability (PBTI) Characteristics of Contact-Etch-Stop-Layer-Induced Local-Tensile-Strained $hbox{HfO}_{2}$ nMOSFET

The positive bias temperature instability (PBTI) characteristics of contact-etch-stop-layer (CESL)-strained $hbox{HfO}_{2}$ nMOSFET are thoroughly investigated. For the first time, the effects of CESL on an $hbox{HfO}_{2}$ dielectric are investigated for PBTI characteristics. A roughly 50% reduction of $V_{rm TH}$ shift can be achieved for the 300-nm CESL $hbox{HfO}_{2}$ nMOSFET after 1000-s PBTI stressing without obvious $ hbox{HfO}_{2}/hbox{Si}$ interface degradation, as demonstrated by the negligible charge pumping current increase ($≪$ 4%). In addition, the $hbox{HfO}_{2}$ film of CESL devices has a deeper trapping level (0.83 eV), indicating that most of the shallow traps (0.75 eV) in as-deposited $ hbox{HfO}_{2}$ film can be eliminated for CESL devices.      

Design Principles for Higher (Prime) Order Composite Directional Couplers

The theoretical construction of ideal (lossless) 3 $,times,$3, 4 $,times,$4, and 5 $,times,$5 dimensional directional couplers from 2$,times,$ 2 directional couplers is demonstrated. Such devices could be fabricated as planar waveguide circuit elements.      

Impacts of $hbox{N}_{2}$ and $hbox{NH}_{3}$ Plasma Surface Treatments on High-Performance LTPS-TFT With High-$kappa$ Gate Dielectric

Low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) with high- $kappa$ gate dielectrics and plasma surface treatments are demonstrated for the first time. Significant field-effect mobility $mu_{rm FE}$ improvements of $sim$86.0% and 112.5% are observed for LTPS-TFTs with $hbox{HfO}_{2}$ gate dielectric after $hbox{N}_{2}$ and $ hbox{NH}_{3}$ plasma surface treatments, respectively. In addition, the $hbox{N}_{2}$ and $ hbox{NH}_{3}$ plasma surface treatments can also reduce surface roughness scattering to enhance the field-effect mobility $mu_{rm FE}$ at high gate bias voltage $V_{G}$, resulting in 217.0% and 219.6% improvements in driving current, respectively. As a result, high-performance LTPS-TFT with low threshold voltage $V_{rm TH} sim hbox{0.33} hbox{V}$, excellent subthreshold swing S.S. $sim$0.156 V/decade, and high field-effect mobility $mu_{rm FE} sim hbox{62.02} hbox{cm}^{2}/hbox{V} cdot hbox{s}$ would be suitable for the application of system-on-panel.      

Enhanced Transmission in a Fiber-Coupled Au Stripe Waveguide System

We experimentally demonstrated the enhanced transmission in a fiber-coupled Au stripe waveguide system using a linearly tapered (LT) structure at a telecommunication wavelength of 1.55 $mu{hbox {m}}$. The LT structure consists of two 100- $mu{hbox {m}}$-long tapered regions connecting various widths of input and output waveguides with a waist region. The lowest insertion loss of the 1-cm-long LT-Au stripe waveguide is $sim$4.3 dB, when it has 6-$mu{hbox {m}}$ -wide input and output waveguides and a 4- $mu{hbox {m}}$-wide waist waveguide. The insertion loss is reduced by $sim$ 2 dB compared to the 4-$mu{hbox {m}}$-wide and 1-cm-long straight Au stripe waveguide, which is achieved by decreasing the coupling loss. The losses of the LT region, which has a tapered angle of less than 0.3$^{circ}$ between the input–output waveguides and the waist waveguide, are smaller than 0.4 dB. We showed that the insertion loss of the Au stripe waveguide can be reduced by introducing the LT structure, which can also provide efficient mode conversion.      

Temperature-Insensitive Dual-Comb Filter Based on Multimode Interference Ti : LiNbO $_{3}$ Waveguide

A temperature-insensitive dual-comb filter has been demonstrated for the first time by multimode interference based on a Ti : LiNbO$_{3}$ channel waveguide. The phase difference between comb filters was about 180 $^{circ}$. We only observed less than ${pm}$0.125-nm variation of the center wavelength of the filter during temperature change from 20 $^{circ}$C to 50 $^{circ}$C. The measured extinction ratio and channel spacing of the comb filter were about ${-}$25 dB and 3.2 THz, respectively.      

Improved Microwave Noise Performance by SiN Passivation in AlGaN/GaN HEMTs on Si

Effects of silicon nitride (SiN) surface passivation by plasma enhanced chemical vapor deposition (PECVD) on microwave noise characteristics of AlGaN/GaN HEMTs on high-resistivity silicon (HR-Si) substrate have been investigated. About 25% improvement in the minimum noise figure $(NF_{min})$ (0.52 dB, from 2.03 dB to 1.51 dB) and 10% in the associate gain $(G_{rm a})$ (1.0 dB, from 10.3 dB to 11.3 dB) were observed after passivation. The equivalent circuit parameters and noise source parameters (including channel noise coefficient $(P)$, gate noise coefficient $(R)$, and their correlation coefficient $(C)$ ) were extracted. $P$ , $R$ and $C$ all increased after passivation and the increase of C contributes to the decrease of the noise figure. It was found that the improved microwave small signal and noise performance is mainly due to the increase of the intrinsic transconductance $(g_{{rm m}0})$ and the decrease of the extrinsic source resistance $(R_{rm s})$.      

Linear Systems, Sparse Solutions, and Sudoku

In this paper, we show that Sudoku puzzles can be formulated and solved as a sparse linear system of equations. We begin by showing that the Sudoku ruleset can be expressed as an underdetermined linear system: ${mmb{Ax}}={mmb b}$, where ${mmb A}$ is of size $mtimes n$ and $n>m$. We then prove that the Sudoku solution is the sparsest solution of ${mmb{Ax}}={mmb b}$, which can be obtained by $l_{0}$ norm minimization, i.e. $minlimits_{mmb x}Vert{mmb x}Vert_{0}$ s.t. ${mmb{Ax}}={mmb b}$. Instead of this minimization problem, inspired by the sparse representation literature, we solve the much simpler linear programming problem of minimizing the $l_{1}$ norm of ${mmb x}$, i.e. $minlimits_{mmb x}Vert{mmb x}Vert_{1}$ s.t. ${mmb{Ax}}={mmb b}$, and show numerically that this approach solves representative Sudoku puzzles.