Room-Temperature Quantum Cascade Laser: ZnO/Zn1−x Mg x O Versus GaN/Al x Ga1−x N

A ZnO/Zn_1?x Mg _x O-based quantum cascade laser (QCL) is proposed as a candidate for generation of THz radiation at room temperature. The structural and material properties, field dependence of the THz lasing frequency, and generated power are reported for a resonant phonon ZnO/Zn_0.95Mg_0.05O QCL emitting at 5.27 THz. The theoretical results are compared with those from GaN/Al _x Ga_1?x N QCLs of similar geometry. Higher calculated optical output powers [ $ {P}_{\rm{ZnMgO}} $  = 2.89 mW (nonpolar) at 5.27 THz and 2.75 mW (polar) at 4.93 THz] are obtained with the ZnO/Zn_0.95Mg_0.05O structure as compared with GaN/Al_0.05Ga_0.95N QCLs [ $ {P}_{\rm{AlGaN}} $  = 2.37 mW (nonpolar) at 4.67 THz and 2.29 mW (polar) at 4.52 THz]. Furthermore, a higher wall-plug efficiency (WPE) is obtained for ZnO/ZnMgO QCLs [24.61% (nonpolar) and 23.12% (polar)] when compared with GaN/AlGaN structures [14.11% (nonpolar) and 13.87% (polar)]. These results show that ZnO/ZnMgO material is optimally suited for THz QCLs.     

Growth of GaN Crystals by the Na Flux Method Under a Temperature Gradient

The effects of temperature gradients on the growth of GaN crystals by the Na flux method were investigated. Yields of GaN pyramid crystals of up to 70% were obtained by use of temperature gradients of 40–70°C/cm and 7 MPa nitrogen pressure. The crystals were obtained by spontaneous nucleation growth. Introducing a moderately large temperature gradient can suppress formation of a hard polycrystalline surface layer at the gas–liquid interface and aid transfer of heat and solute, resulting in controllable GaN crystal growth and better yield of GaN crystals. The maximum size of GaN crystals with hexagonal pyramidal faces was approximately 3 mm. The full-width at half-maximum of the rocking curve measured for the $ \left( {10\bar 11} \right) $ x-ray diffraction peak was only 36 arcsec. A emission peak at approximately 365 nm was observed at room temperature by photoluminescence spectroscopy. Characterization suggested the GaN crystals were of good crystalline quality.     

A Low-Voltage and Low-Power 3-GHz CMOS LC VCO for S-Band Wireless Applications

A fully integrated 0.18- \(\upmu \hbox {m}\) CMOS LC-tank voltage-controlled oscillator (VCO) suitable for low-voltage and low-power S-band wireless applications is proposed in this paper. In order to meet the requirement of low voltage applications, a differential configuration with two cross-coupled pairs by adopting admittance-transforming technique is employed. By using forward-body-biased metal oxide semiconductor field effect transistors, the proposed VCO can operate at 0.4 V supply voltage. Despite the low power supply near threshold voltage, the VCO achieves wide tuning range by using a voltage-boosting circuit and the standard mode PMOS varactors in the proposed oscillator architecture. The simulation results show that the proposed VCO achieves phase noise of \(-\) 120.1 dBc/Hz at 1 MHz offset and 39.3 % tuning range while consuming only \(594~\upmu \hbox {W}\) in 0.4 V supply. Figure-of-merit with tuning range of the proposed VCO is \(-\) 192.1 dB at 3 GHz.     

Measurement of Thermoelectric Properties of Single Semiconductor Nanowires

We have measured the thermopower and the thermal conductivity of individual silicon and indium arsenide nanowires (NWs). In this study, we evaluate a self-heating method to determine the thermal conductivity λ. Experimental validation of this method was performed on highly n-doped Si NWs with diameters ranging from 20 nm to 80 nm. The Si NWs exhibited electrical resistivity of $\rho = (8\pm4)\, \hbox{m}\Upomega\,\hbox{cm}$ ρ = ( 8 ± 4 ) m Ω cm at room temperature and Seebeck coefficient of ?(250 ± 100) μV/K. The thermal conductivity of Si NWs measured using the proposed method is very similar to previously reported values; e.g., for Si NWs with 50 nm diameter, λ = 23 W/(m K) was obtained. Using the same method, we investigated InAs NWs with diameter of 100 nm and resistivities of $\rho = (25\pm5)\, \hbox{m}\Upomega\,\hbox{cm}$ ρ = ( 25 ± 5 ) m Ω cm at room temperature. Thermal conductivity of λ = 1.8 W/(m K) was obtained, which is about 20 to 30 times smaller than in bulk InAs. We analyzed the accuracy of the self-heating method by means of analytical and numerical solution of the one-dimensional (1-D) heat diffusion equation taking various loss channels into account. For our NWs suspended from the substrate with low-impedance contacts the relative error can be estimated to be ≤25%.     

Soft X-ray Absorption and Photoemission Spectroscopy Study of Cobalt-Based Thermoelectric Oxides: \hbox{Ca}_3\hbox{Co}_4\hbox{O}_9, \hbox{Ca}_3\hbox{Co}_2\hbox{O}_6, and \hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}

The electronic structures of Co-based potential thermoelectric (TE) oxides, including $\hbox{Ca}_3\hbox{Co}_4\hbox{O}_9$ and $\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}$ (y = 8 + δ) single crystals and polycrystalline $\hbox{Ca}_3\hbox{Co}_2\hbox{O}_6$ , have been investigated by employing soft x-ray absorption spectroscopy (XAS) and photoemission spectroscopy (PES). Co 2p XAS measurements show that Co ions are nearly trivalent ( $\hbox{Co}^{3+}$ ) in all of these Co-based TE oxides with a small mixture of $\hbox{Co}^{4+}$ ions in $\hbox{Bi}_{2}\hbox{Sr}_{2}\hbox{Co}_2\hbox{O}_{y}$ . Valence-band PES and O 1s XAS measurements show that the occupied Co 3d states are located at the top of the valence bands and that the lowest unoccupied states have the primarily Co 3d character, respectively. These findings suggest the importance of the Co 3d electronic structures in determining TE properties of these Co-based oxides.     

A 97 dB 400 MHz rail to rail fully differential opamp based on split length FGMOS-MOS cell

Recently introduced MOS-FGMOS split length cell has been used to increase the DC gain of a fully differential op amp. Resultant proposed opamp structure exhibits gain of 97 dB and unity gain bandwidth of 400 MHz with power consumption of 1.2 mW. An opamp design has been verified with Cadence Spectre using a 130 nm technology at 1.2 V and has a slew rate of \(53\,\hbox {V}/\mu \hbox {s}\) with a phase margin of \(78^{\circ }\) .     

A High Gain and Low Flicker Noise CMOS Mixer with Low Flicker Noise Corner Frequency Using Tunable Differential Active Inductor

This paper presents the design of a high conversion gain and low flicker noise down conversion CMOS double balanced Gilbert cell mixer using \(0.18\,\upmu \hbox {m}\) CMOS technology. The high conversion gain and low flicker noise mixer is implemented by using a differential active inductor (DAI) circuit and cross-coupled current injection technique within the conventional double-balanced Gilbert cell mixer. A cross-coupled current bleeding circuit is used to inject the current to the switching stage to decrease the flicker noise. Instead of spiral inductor, a DAI with high tunability of the inductor and quality factor is used to tune out the parasitic capacitance effect and decrease the leakage current that has a harmonic component and produce the flicker noise. By tuning the DAI, the flicker noise corner frequency is reduced to 150 Hz. The proposed circuit is simulated with Cadence Spectra and the simulation results shows the NF of 11.2 dB, conversion gain of 23.7 dB and IIP3 of \(-6\)  dB for an RF frequency of 2.4 GHz. The excellent LO-RF, LO-IF, RF-LO and RF-IF isolations of \(-60, -110, -52\) and \(-64\)  dB are achieved respectively. The total power consumption is 10.5 mW from a 1.8 V DC power supply.     

The First Year Nursing Students’ Achievement and Critical Thinking in Local Wisdom Course Using Problem Based Learning Process

The purpose of this one group—pre test post test design classroom research was to examine learning achievement, critical thinking and satisfaction of first year nurse students at school of nursing during academic year 2011. In the research activity, 94 students participated in three weeks for each scenario in Local Wisdom and Health Care which composed of 4 scenarios. Problem based learning process were included the preparation of facilitators, preparation of learners, and problem/scenario based assignments. The instruments composed of 1) 135 items, 4 multiple choices test which were covered behavioral objectives and blue print of test and validated by course lecturers 2) opinion evaluation form, open ended questionnaire and 3) the critical thinking questionnaire, 80 items in five domains which are Inference, Recognition of Assumption, Deduction, Interpretation, and Evaluation of Argument with internal consistency of .73. Data were analyzed using frequency, percentage, mean, standard deviation, percentile, t test and $\chi ^{2}$ test. It was found that the highest score of learning achievement was 88.79 % while the lowest score was 70.33 %, average learning achievement score was 80.60 $(\pm 3.47)\%$ . The highest grade levels were B+ and B equally (41.49 %). Students demonstrated higher overall critical thinking $(49.62 \pm 5.78)$ after undergone problem based learning process than before the problem based learning process $(46.69 \pm 6.00)$ statistically significance $(\text{ t}\,=\,4.443, p\,<\,.05)$ . Inference and Recognition of Assumption domain after PBL process were better than their own thoughts before PBL process significantly (t = 2.288, $p\,<\,.05$ ; t = 6.287, $p\,<\,.05$ , respectively). The ability of critical thinking was found that the high, moderate and low level (percentile $>75, 25-75$ and $<25$ ) after PBL were difference from the ability before the process significantly $(\chi ^{2}=12.219, p\,<\,.05)$ .     

A Novel 2.5–3.1 GHz Wide-Band Low-Noise Amplifier in 0.18 \upmu \hbox {m} CMOS

Aiming for the simultaneous realization of constant gain, accurate input and output impedance matching and minimum noise figure (NF) over a wide frequency range, the circuit topology and detailed design of wide broadband low noise amplifier (LNA) are presented in this paper. A novel 2.5–3.1 GHz wide-band LNA with unique characteristics has been presented. Its design and layout are done by TSMC 0.18  \(\upmu \hbox {m}\) technology. Common gate stage has been used to improve input matching. In order to enhance output matching and reduce the noise as well, a buffer stage is utilized. Mid-stages which tend to improve the gain and reverse isolation are exploited. The proposed LNA achieves a power gain of 15.9 dB, a NF of 3.5 dB with an input return loss less than \(-\) 11.6, output return loss of \(-\) 19.2 to \(-\) 19 and reverse isolation of \(-\) 38 dB. The LNA consumes 54.6 mW under a supply voltage of 2 V while having some acceptable characteristics.     

Ultra-Low Power Read-Decoupled SRAMs with Ultra-Low Write-Bitline Voltage Swing

We propose an ultra-low power memory design method based on the ultra-low ( \(\sim \) 0.2 V) write-bitline voltage swing to reduce the write power dissipation for read-decoupled SRAM (RD-SRAM) cells. By keeping the write bitlines at ground level (0 V) during standby and charging them to a low voltage \(V_\mathrm{L}\) ( \(\sim \) 0.2 V) during write operations, the power dissipation for the write bitlines is greatly reduced (0.2 V/ \(V_\mathrm{DD})^{ 2 }\,\times \) 100 %) due to reduced voltage swing (from \(V_\mathrm{DD }\)  = 1.2 to 0.2 V) on the write bitlines. The proposed method is applicable to both dual-voltage and single-voltage operations. We analyze the proposed ultra-low write-bitline voltage swing method and investigate its reliability based on 10K Monte-Carlo simulations. We further verify the functionality and performance of our proposed design through measurements on the fabricated prototypes based on the 65 nm CMOS process. By means of a \(256 \times 64\) bit RD-SRAM memory implementation, we show that our proposed method reduces 87 % write power dissipation when compared to a conventional design.     

Six Order Cascaded Power Line Notch Filter for ECG Detection Systems with Noise Shaping

This paper presents the design of an operational transconductance amplifier-C (OTA-C) notch filter for a portable Electrocardiogram (ECG) detection system. A six order cascaded filter is utilized to reduce the effect of the power line interference at (50/60 Hz). The proposed filter is based on a programmable balanced OTA circuit. Based on this, PSPICE post layout simulation results for the extracted filter using 0.25  \(\upmu \) m technology and operating under \(\pm \) 0.8 V voltage supply are also given. The six order notch filter provides a notch depth of 65 dB (43 dB for 4th order), input referred noise spectral density with noise shaping of 9  \(\upmu \) Vrms/ \(\surd \) Hz at the pass band frequencies and 9 mVrms/ \(\surd \) Hz at the notch (zero) frequency which provide noise shaping for the ECG signal. These results demonstrate the ability of the filter to be used for ECG signal filtering which is located within 150 Hz.     

E-TCAM: An Efficient SRAM-Based Architecture for TCAM

Ternary content addressable memories (TCAMs) perform high-speed search operation in a deterministic time. However, when compared with static random access memories (SRAMs), TCAMs suffer from certain limitations such as low-storage density, relatively slow access time, low scalability, complex circuitry, and higher cost. One fundamental question is that can we utilize SRAM to combine it with additional logic to achieve the TCAM functionality? This paper proposes an efficient memory architecture, called E-TCAM, which emulates the TCAM functionality with SRAM. E-TCAM logically divides the classical TCAM table along columns and rows into hybrid TCAM subtables and then maps them to their corresponding memory blocks. During search operation, the memory blocks are accessed by their corresponding subwords of the input word and a match address is produced. An example design of \(512\times 36\) of E-TCAM has been successfully implemented on Xilinx Virtex- \(5\) , Virtex- \(6\) , and Virtex- \(7\) field-programmable gate arrays (FPGAs). FPGA implementation results show that E-TCAM obtains \(33.33\)  % reduction in block-RAMs, \(71.07\)  % in slice registers, \(77.16\)  % in lookup tables, \(53.54\)  % in energy/bit/search, and offers \(63.03\)  % improvement in speed, compared with the best available SRAM-based TCAM designs.     

A Wide Tuning Range Voltage Controlled Oscillator with a High Tunable Active Inductor

This paper presents a wide tuning range CMOS voltage controlled oscillator (VCO) with a high-tunable active inductor circuit. In this VCO circuit, the coarse frequency is achieved by tuning the integrated active inductor circuit. The VCO circuit is designed in 0.18  \(\upmu \hbox {m}\) CMOS process and simulated with Cadence Spectra. The simulation results show the frequency tuning range from 120 MHz to 2 GHz resulting in a tuning range of 94 %. The phase noise variation is from \(-\) 80 to \(-\) 90 dBc/Hz at a 1 MHz frequency offset, and output power variation is from \(-\) 4.7 to \(+\) 11.5 dBm. The active inductor power consumption is 2.2 mW and the total power dissipation is 7 mW from a 1.8 V DC power supply. By comparing the proposed VCO circuit with the general VCO topology, the results show that this VCO architecture by using the novel, high-tunable and low power active inductor circuit, presents a better performance regarding low chip size, low power consumption, high tuning range and high output power.     

Low Voltage Low Cost Quadrature Oscillator Based on Active Inductor

This paper presents a new low voltage low cost quadrature oscillator, which consists of two LC negative oscillators based on active inductor. In this quadrature oscillator, the back-gates of the core transistors are used as coupling terminals to provide the quadrature outputs. The proposed floating active inductor has a two layer transistor structure. The quadrature oscillator has been implemented with the chart 0.18  \(\upmu \) m CMOS technology. At the supply voltage of 1.2 V, the total power consumption is 16 mW. The phase noise at 1 MHz frequency offset is \(-\) 111.8 dBc/Hz at the oscillation frequency of 3.946 Hz.     

Performance Analysis of Microwave Radio Refractivity on Radio Field Strength and Radio Horizon Distance Over Akure,Nigeria

Surface radio refractivity studies are being carried out in Akure, \((7.15^{\circ }\hbox {N}, 5.12^{\circ }\hbox {E})\) South-Western Nigeria, by in-situ measurement of atmospheric pressure, temperature, and relative humidity using Wireless Weather Station (Integrated Sensor Suit, ISS). Five years of measurement (January, 2007–December, 2011) were used to compute the surface radio refractivity and its diurnal, daily, seasonal and yearly variations are analyzed. The results were then used to compute radio horizon distance \((\hbox {R}_\mathrm{DH})\) and examine the field strength (FSV) variability. Results obtained show that the surface radio refractivity, \(\hbox {N}_\mathrm{s}\) , varies with the time of the day as well as the seasons of the year. High values of \(\hbox {N}_\mathrm{s}\) were recorded in the morning and evening hours while the values were minima around 1,500 h local time. An average value of surface radio refractivity of 364.74 N-units was obtained for this location. The annual maximum mean of FSV is 15.24 dB and the minimum is 2.20 dB. This implies that the output of a receiving antenna in Akure may generally be subject to variations not less than 2 dB in a year, but can be as high as 15 dB.     

Influence of the carrier Gas, trimethylgallium flow, and growth time on the character of the selective epitaxy of GaN

The influence of the carrier gas, trimethylgallium flow, and growth time on the character of the selective epitaxy of GaN in stripe windows oriented along the crystallographic direction 〈 $\bar 1$ 100〉 GaN for various widths of the mask between the stripes is studied. It is shown that the addition of nitrogen in the reactor atmosphere leads to changes in the form of the stripes in the case of wide (40 μm) mask from a rectangular form restricted by a {1 $\bar 1$ 20} lateral face to a trapezoidal form restricted by a {1 $\bar 1$ 22} lateral face. It is also shown that during growth in the nitrogen-hydrogen mixture, the gallium flow starts to considerably affect the form of the growing stripes. It is shown that the process is significantly unstable, which leads to a noticeable variation in the form type as the transverse section of the stripe increases.     

A High Gain,Low-Power Low-Noise Amplifier for Ultra-Wideband Wireless Systems

This paper presents a high gain, low-power common-gate ultra-wideband low-noise amplifier employing a simple configuration for wideband input matching. In our design, a series resistance-inductance network at the source combines with the parasitic capacitance of a transistor to form a parallel RLC input matching configuration in the common-gate input stage. Because of the additional resistance, this matching configuration partially alleviates the restriction of transconductance of the input transistor and also provides wideband matching. The low-noise amplifier was fabricated using the TSMC 0.18  \(\mu \) m technology with an average noise figure of 3.75 dB, a power gain of 18.68 dB with a ripple of \(\pm \)  0.8 dB, an input return loss less than \(-10\)  dB from 3 to 7.6 GHz, and DC power consumption of 8.56 mW, including the output buffer with a 1.8 V supply voltage.     

Electronic Structure and Thermoelectric Properties of Pseudoquaternary \hbox{Mg}_{2}\hbox{Si}_{1-x-y}\hbox{Sn}_{x}\hbox{Ge}_{y}-Based Materials

A theoretical study is presented on complex pseudoternary Bi-doped \(\hbox{Mg}_{2}\hbox{Si}_{1-x-y}\hbox{Sn}_{x}\hbox{Ge}_{y}\) materials, which have recently been revealed to reach high thermoelectric figures of merit (ZT) of ～1.4. Morphological characterization by scanning electron microscopy and energy-dispersive x-ray spectroscopy indicated that the investigated samples were multiphase and that the alloy with nominal composition \(\hbox{Mg}_{2}\hbox{Si}_{0.55}\hbox{Sn}_{0.4}\hbox{Ge}_{0.05}\) contained three phases: \(\hbox{Mg}_{2}\hbox{Si}_{0.35}\hbox{Sn}_{0.6}\hbox{Ge}_{0.05}\) (Sn-rich phase), \(\hbox{Mg}_{2}\hbox{Si}_{0.65}\hbox{Sn}_{0.3}\hbox{Ge}_{0.05}\) (Si-rich phase), and \(\hbox{Mg}_{2}\hbox{Si}_{0.15}\hbox{Sn}_{0.5}\hbox{Ge}_{0.35}\) (Ge-rich phase). The electronic structure of all these phases was calculated in the framework of the fully charge self-consistent Korringa–Kohn–Rostoker method with the coherent potential approximation (KKR-CPA) to treat chemical disorder. Electron transport coefficients such as the electrical conductivity, thermopower, and the electronic part of the thermal conductivity were studied by combining the KKR-CPA technique with Boltzmann transport theory. The two-dimensional (2D) plots (as a function of electron carrier concentration and temperature), computed for the thermopower and power factor, well support the large thermoelectric efficiency detected experimentally. Finally, employing the experimental value of the lattice thermal conductivity as an adjustable parameter, it is shown that ZT ≈ 1.4 can be reached for an optimized Bi content near T ≈ 900 K in case of the nominal composition as well as the Sn-rich phase. The question of the effect of disorder on the convergence of the conduction bands and thus the electron transport properties is addressed through detailed examination of the Fermi surfaces.     

Asymptotic throughput for large-scale wireless networks with general node density

We study the asymptotic throughput for a large-scale wireless ad hoc network consisting of n nodes under the generalized physical model. We directly compute the throughput of multicast sessions to unify the unicast and broadcast throughputs. We design two multicast schemes based on the so-called ordinary arterial road system and parallel arterial road system, respectively. Correspondingly, we derive the achievable multicast throughput by taking account of all possible cases of n _s  = ω(1) and 1 ≤ n _d  ≤ n ? 1, rather than only the cases of $n_s=\Uptheta(n)$ as in most related works, where n _s and n _d denote the number of sessions and the number of destinations of each session, respectively. Furthermore, we consider the network with a general node density $\lambda \in [1,n]$ , while the models in most related works are either random dense network (RDN) or random extended network (REN) where the density is λ = n and λ = 1, respectively, which further enhances the generality of this work. Particularly, for the special case of our results by letting λ = 1 and $n_s=\Uptheta(n)$ , we show that for some regimes of n _d , the multicast throughputs achieved by our schemes are better than those derived by the well-known percolation-based schemes.