Magnetic properties of PLD‐fabricated ND‐Fe‐B film magnets and their applications to millimeter‐size motors

We succeeded in depositing 200‐ to 300‐µm‐thick Nd‐Fe‐B film magnets with (BH)_max of approximately 55 kJ/m³ on Fe substrates by the PLD method. In addition, we confirmed that a millimeter‐size motor, which was prepared from the obtained film, rotates at 15,160 rpm under a no‐load test. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 159(2): 1–6, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20215     

Nd–Fe–B thick films prepared at the high deposition rate of 90 µm/h

After a postannealing process, the magnetic properties of pulsed laser deposition (PLD)‐made Nd–Fe–B film magnets prepared at the deposition rate of 20–90 µm/h showed constant values, and the average values of H_c, B_r and (BH)_max were 1050 kA/m, 0.6 T, and 60 kJ/m³, respectively. The obtained results were comparable to those previously reported. In conclusion, it was found that a maximum deposition rate of 90 µm/h could be achieved without deterioration of magnetic and mechanical properties. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Magnetic properties of Pr‐Fe‐Co‐V‐W‐Si‐B system exchange spring magnets

The melt‐spun ribbons of Pr‐Fe‐Co‐V‐W‐Si‐B system alloys were prepared by single roller rapid‐quenching method. The effects of composition, surface velocity, and heat treatment on the magnetic properties were investigated. The P₉sFe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy ribbons prepared at a surface velocity of 12.5 m/s were crystallized by heat treatment, and the optimum heat‐treatment condition was found to be at 575°C for 3 min, for which the magnetic properties were (BH)_max = 136.1 kJ/m³, J_r = 0.93 T, H_cJ = 652.2 kA/m, and H_cB = 528.3 kA/m. The temperature coefficients of J_r and H_cJ for the ribbons crystallized from melt‐spun ribbons of Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 alloy were α(J_r)_ave = ?0.057%/°C and α(H_cJ) = ?0.450%/°C. The value of (B)_max for the compression molding Pr₉Fe₇₁Co₈V_0.5W_0.5Si_0.5B_10.5 isotropic bonded magnet prepared by using the ribbons annealed at 575°C for 3 min is 80.0 kJ/m³, and the density is 6.24 Mg/m³. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(3): 10–16, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20211 Copyright © 2006 Wiley Periodicals, Inc.     

Electron‐beam‐pumped light sources using graphite nanoneedle field emitters and Si electron‐transparent films

Sputter‐induced carbon nanoneedle field emitters and Si electron‐transparent films have been developed for electron‐beam‐pumped light sources. The sputter‐induced carbon nanoneedle field emitters exhibited a stable electron emission of 0.1 mA at an average field of 13 V/µm. The 1.5‐µm thick Si electron‐transparent films achieved an electron transmittance of about 60% at an acceleration voltage of 27 kV. An electron‐beam‐pumped light source was demonstrated from the excitation of N₂ gas, and a N₂ gas spectrum was clearly observed. The increase of the beam current is important for increasing the light intensity. Copyright © 2007 Institute of Electrical Engineers of Japan© 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A low‐voltage band‐gap reference circuit with second‐order analyses

A new band‐gap reference (BGR) circuit employing sub‐threshold current is proposed for low‐voltage operations. By employing the fraction of V_BE and the sub‐threshold current source, the proposed BGR circuit with chip area of 0.029mm² was fabricated in the standard 0.18µm CMOS triple‐well technology. It generates reference voltage of 170 mV with power consumption of 2.4µW at supply voltage of 1 V. The agreement between simulation and measurement shows that the variations of reference voltage are 1.3 mV for temperatures from ?20 to 100^°C, and 1.1 mV per volt for supply voltage from 0.95 to 2.5 V, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

Growth of thick and low‐doped 4H‐SiC epitaxial layers in a vertical radiant‐heating VPE reactor

A new vertical radiant‐heating reactor has been designed and constructed for thick SiC vapor‐phase epitaxy (VPE). Growth of 4H‐SiC epitaxial layers is performed under a reduced pressure as low as 6.7 × 10³ Pa. A high growth rate exceeding 16 µm/h has been achieved in the reactor. Smooth surface is obtained by controlling the input C/Si ratio of source gases, and we have demonstrated growth of very thick layers over 160 µm with a mirrorlike morphology. Low‐background doping in the 10¹³ cm^?3 range (n‐type) and intentional n‐type doping in a range from low 10¹⁵ to low 10¹⁹ cm^?3 have also been demonstrated. We have performed photoluminescence spectroscopy and deep level transient spectroscopy to check impurities and intrinsic defects in the epitaxial layers, and the spectra show that the layers have a good purity and quality. © 2002 Scripta Technica, Electr Eng Jpn, 138(4): 18–25, 2002; DOI 10.1002/eej.1134     

Influence of Gas Flow Ratio in PE‐CVD Process on Mechanical Properties of Silicon Nitride Film

This paper investigates the influence of gas flow ratio in the preparation of submicron‐thick silicon nitride (SiN_x) films on their elastic properties. SiN_x films with a thickness ranging from 0.14 to 0.69 µm were deposited by plasma‐enhanced chemical vapor deposition (PE‐CVD) onto 10‐µm‐thick single‐crystal silicon (SCS) specimens by changing the gas flow ratio of monosilane (SiH₄) to ammonia (NH₃) to nitrogen (N₂). A uniaxial tensile tester operated under an atomic force microscope (AFM) characterized the Young's modulus of SiN_x films and the fracture strength of SiN_x/SCS laminated specimens. The Young's modulus of SiN_x films ranged from 99.5 to 144.3 GPa, which increased with the gas flow ratio but was independent of the film thickness. Nano‐indentation tests were also carried out to examine the Poisson's ratio of SiN_x films in addition to the tensile tests. The Poisson's ratio was found to be 0.19 to 0.27, on average. Auger spectroscopy revealed that an increase of the atomic content ratio of nitrogen (N) to silicon (Si) in SiN_x films yielded higher elastic constants of the films. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Fabrication and characterization of β−FeSi2 thin films prepared by PLD method using Nd:YAG laser

β?FeSi₂ thin films were grown on Si(111) substrates by pulsed laser deposition (PLD) method using a Nd:YAG laser (λ=1064nm, laser energy=50mJ, laser energy density=1.65J/cm², repetition frequency=10Hz). In the fabrication process, three targets of (a) Fe(5N), (b) FeSi₂(3N), and (c) Fe(5N)+FeSi₂(3N) were used. The β?FeSi₂ thin films having the best properties of crystallinity were obtained in the case of (c), in which the first layer as the template was formed with the target of Fe(5N) and then, on top of that, the second layer was deposited with the target of FeSi₂(3N). At this time, it was found that by XRD measurement, the degree of crystallinity of the films of case (c) in which the first layer was introduced as the template improved 1.4 times as much compared with case (a), and that by SEM and AFM observations, surface morphologies also improved. Moreover, it was found that by TEM observation, the β?FeSi₂ thin films grew uniformly along the direction of (220) or (202) from the interface of the Si substrate and the film to the free surface and that by EDS analysis, the compositions of Fe and Si were uniformly distributed. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 39–45, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20238     

Mode‐matching analysis of a spit‐circular cavity resonator for measurement of the dielectric constant for film on a substrate

In this paper, we apply the mode‐matching technique (eigenmode expansion) to formulate an analytical model for a split cylindrical cavity resonator with a thick ceramic film layer sandwiched between two‐layer alumina substrates. We then compute the resonant frequencies with the TE₀₁₁ mode with an eigenvalue problem approach using the model formula. The quality factor (Q ‐factor) of the resonator is also calculated by applying the perturbation method to the analytical model. The validity of the proposed analytical technique is confirmed by applying this method to the estimation of permittivity of thick films as an inverse problem. Ceramic films (2 µm thickness) were synthesized using a chemical solution method onto 200‐µm‐thick, 50‐mm‐diameter alumina substrates. The complex permittivity of the films was then determined using the TE₀₁₁ mode split cylindrical cavity resonator in the 10‐GHz band. The extent of the edge effect at a sample insertion space was evaluated by comparing the estimated results through TE wave analysis using the mode‐matching method when the transverse resonance technique and the perturbation method were applied to calculate the resonant frequency and the dielectric Q ‐factor. The results obtained indicate that a difference of 0.153% in the permittivity of the alumina substrate causes differences of 6.10 and 3.75% in the measured permittivity and loss tangent, respectively, of 2‐µm‐thick ceramic film with a permittivity of ∼50. Differences in permittivity and loss tangent were more pronounced with thinner films. It was also confirmed that the estimated results for permittivity and the loss tangent values of these ceramic films were affected by the estimated permittivity value of the alumina substrate. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Grain‐size dependence of absorption characteristics of the electromagnetic wave absorbers of ferrite‐SiO2 composites

Grain‐size dependence of electromagnetic absorbing characteristics for composite materials made of Ni‐Zn ferrite and SiO₂ was investigated using SiO₂ with various grain sizes (29 µm, 30 nm, 12 nm, and 7 nm). The absorption characteristics of ferrite composites using SiO₂ with an average grain size of 30, 12, or 7 nm were improved compared with those of ferrite composites using SiO₂ with an average grain size of 29 µm in the low‐frequency region. Furthermore, the grain size dependence of the absorption characteristics for composite materials of Mn‐Zn ferrite with an average grain size of 130 nm and SiO₂ with an average grain size of 29 µm was investigated. The absorbing center frequency shifted to a higher frequency region than that of Mn‐Zn ferrite. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 146(4): 1–9, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10269     

Vertical‐type organic device using thin‐film ZnO transparent electrode

We propose a double heterojunction organic light‐emitting diode (OLED) using a zinc oxide (ZnO) film, which works as a transparent and electron injection layer. The crystal structure of the ZnO films as a function of Ar/O₂ flow ratio and the basic characteristics of the OLED depending on the ZnO sputtering conditions are investigated. Excellent characteristics of the novel OLED were obtained, as high as 470 cd/m² at 22 V and 7.6 mA/cm². The results obtained here demonstrate that the vertical organic light‐emitting transistor (OLET) using a ZnO layer as an electron injection layer is promising as a key element for flexible sheet displays. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 158(2): 49–55, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20151     

0.3‐V bulk‐driven programmable gain amplifier in 0.18‐µm CMOS

A new solution for an ultra low voltage bulk‐driven programmable gain amplifier (PGA) is described in the paper. While implemented in a standard n‐well 0.18‐µm complementary metal–oxide–semiconductor (CMOS) process, the circuit operates from 0.3 V supply, and its voltage gain can be regulated from 0 to 18 dB with 6‐dB steps. At minimum gain, the PGA offers nearly rail‐to‐rail input/output swing and the input referred thermal noise of 2.37 μV/Hz^1/2, which results in a 63‐dB dynamic range (DR). Besides, the total power consumption is 96 nW, the signal bandwidth is 2.95 kHz at 5‐pF load capacitance and the third‐order input intercept point (IIP₃) is 1.62 V. The circuit performance was simulated with LTspice. Copyright © 2016 John Wiley & Sons, Ltd.     

Low‐resistive and transparent AZO films prepared by PLD in magnetic field

Al₂O₃‐doped ZnO (AZO) thin films have been deposited onto glass substrates using a split target consisting of AZO (1 wt%) and AZO (2 wt%) by pulsed laser deposition with an ArF excimer laser (λ = 193 nm, 15 mJ, 10 Hz, 0.75 J/cm²). By applying a magnetic field perpendicular to the plume, the lowest resistivity of 8.54 × 10^?5Ω·cm and an average transmittance exceeding 91% over the visible range were obtained at a target‐to‐substrate distance of 25 mm for approximately 279‐nm‐thick AZO film (1.8 wt%) grown at a substrate temperature of 230 °C in vacuum. From cross‐sectional TEM observations and the XRD spectrum, a reason why the low resistivity (54 × 10^?5Ω·cm) was reproducibly obtained was considered to be due to the fact that a disorder of crystal growth originating in the vicinity of the interface between the substrate and the film was suppressed by application of the magnetic field and the c‐axis orientation took preference, giving rise to the increase of mobility. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(2): 40–45, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20026     

Properties of anisotropic Ba‐Zn‐Cu system W‐type hexagonal ferrite magnets

Experiments were carried out to investigate the magnetic and physical properties of Ba‐Zn‐Cu W‐type hexagonal ferrites sintered without atmosphere control. Compositions were chosen according to the formula BaZn_2–xCu_xFe₁₆O₂₇, where x was varied 0 ˜ 0.5 and 1.0. The effect of BaO addition after semisintering treatment on magnetic properties of Ba‐Zn‐Cu compounds was examined. It was found that BaO addition for Ba‐Zn‐Cu compounds was very useful in stabilizing the W‐type hexagon. The optimum condition of making magnets and some properties of typical specimens are as follows: composition—BaZn_1.7Cu_0.3Fe₁₆O₂₇ with 4 wt% Ba added; semisintering conditions—1275 °C for 1.0 h in air; sintering conditions—1175°C for 0.5 h in air; magnetic properties and lattice constant are J_m = 0.405 T, J_r = 0.370 T, H_cJ = 88.15 kA/m, (BH)_max = 19.12 kJ/m³, T_c = 356 °C, H_A = 994.7 kA/m, K_A = 2.01 × 10⁵ J/m³, c = 32.928 × 10^–10 m, a = 5.927 × 10^–10 m, c/a = 5.556. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 36–42, 2001     

High‐tuning‐range CMOS band‐pass IF filter based on a low‐Q cascaded biquad optimization technique

A design procedure for high‐order continuous‐time intermediate‐frequency band‐pass filters based on the cascade of low‐Q biquadratic cells is presented. The approach is well suited for integrated‐circuit fabrication, as it takes into account the maximum capacitance spread dictated by the available technology and maximum acceptable sensitivity to component variations. A trade‐off between noise and maximum linear range is also met. A novel, wide‐tuning‐range transconductor topology is also described. Based on these results, a 10‐pole band‐pass filter for a code division multiple‐access satellite receiver has been designed and tested. The filter provides tunable center frequency (f₀) from 10 to 70 MHz and exhibits a 28‐MHz bandwidth around f₀ = 70 MHz with more than 39‐dB attenuation at f₀/2 and 2f₀. Third‐order harmonic rejection is higher than 60 dB for a 1‐Vpp 70‐MHz input, and equivalent output noise is lower than 1 mV_rms. The circuit is fabricated in a 0.25‐µm complementary metal oxide semiconductor process, and the core consumes 12 mA from a 2.5‐V supply, offering the best current/pole ratio figure. The die area resulted to be 0.9 × 1.1 mm². Copyright © 2014 John Wiley & Sons, Ltd.     

A fully integrated,highly linear CMOS T/R switch for X‐Band phased array radars

This paper presents the design and implementation of a single‐pole, double‐throw transmit/receive (T/R) switch for X‐Band (8–12 GHz) phased array radar applications. The T/R switch was fabricated in a 0.25‐µm SiGe BiCMOS process and occupies 0.44‐mm² chip area, including pads. The design focuses on the techniques, primarily, to achieve higher power handling capability (P_1dB), along with higher isolation and better insertion loss (IL) of the T/R switch. These techniques include resistive‐body floating, using on‐chip impedance transformation networks and DC biasing of all terminals of the T/R switch. In addition, optimization of transistor widths and parallel resonance technique are used to improve IL and isolation, respectively. All these design techniques resulted in a measured IL of 3.6 dB, isolation of 34.8 dB and IP_1dB of 28.2 dBm at 10 GHz. The return losses at both input and output ports are better than 16 dB from 8 to 12 GHz. To our knowledge, this paper presents the single‐ended CMOS T/R switch with the highest IP_1dB, competitive isolation and comparable IL at X‐Band, compared to other reported works in the literature and attributed to the unique design methodologies and techniques. Copyright © 2012 John Wiley & Sons, Ltd.     

Silicon nanorods‐based all‐dielectric waveguides with long decay‐length at the telecommunication band

We investigate subwavelength waveguides composed of silicon nanorods array in straight and nonstraight regimes deposited on a silica (SiO₂) substrate. It is shown that using all‐dielectric nanorods with high permittivity to design an all‐dielectric optical waveguide provides several advantages such as low‐dissipation coefficient and long decay length for the distributed fields. Exploiting silicon arrays in touching and nontouching arrangements, we examined the optical response of the structure to the guiding of magnetic and electric fields with transverse and longitudinal polarization modes. We studied the decay length for all propagated modes in both nanochain orientations numerically. Simulation results for straight arrays showed that the averaged decay length for the structure with dielectric particles in touching regime is 1.6 µm (for the waveguide with the length of 2.2 µm), and for the nontouching array is 2.2 µm (for the array with the length of 3.1 µm). Calculating transmission loss factors and considering decay length of the proposed waveguide, we verified the strong potential of the proposed structure to design all‐dielectric photonic devices to operate at telecommunication spectra (λ~1310 nm and 1550 nm). Also, we computed bending losses [dB] for the examined structures based on the bends degree. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrostatic fluctuation measurements in the periphery of reversed field pinch plasma

In this paper, the authors study the magnetic and electric properties of ferromagnetic substance/semimetal (Fe/Bi) system multilayered thin films prepared by ion beam sputtering. The multilayered thin film was prepared with 99.6% Fe and 99.99% Bi. The experimental results are summarized as follows. From XRD in the small‐degree region (2θ = 2 to 4^°), Fe/Bi system thin films for N = 3,4, and 5 Fe layers have formed multilayer structures. Coercive force H_c increased with increasing number of Fe layers. The maximum value was 4.522 kA/m at N = 6 Fe layers. The coercive force then decreased and its value was constant at more than 15 layers. Electrical resistivity, ρ, of Fe/Bi system multilayered thin films changed from conductivity to semiconductivity at temperatures in the range for T = 380 to 400 K. Magneto‐resistance (MR) ratio decreased with increasing applied field H when the current was parallel to an applied magnetic field (I‖H). MR ratio reached a maximum of 0.154% at N = 4 Fe layers at room temperature. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(1): 1–8, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20068     

A low‐power,area‐efficient multichannel receiver for micro MRI

A new integrated, low‐noise, low‐power, and area‐efficient multichannel receiver for magnetic resonance imaging (MRI) is described. The proposed receiver presents an alternative technique to overcome the use of multiple receiver front‐ends in parallel MRI. The receiver consists of three main stages: low‐noise pre‐amplifier, quadrature down‐converter, and a band pass filter (BPF). These components are used to receive the nuclear magnetic resonance signals from a 3 × 3 array of micro coils. These signals are combined using frequency domain multiplexing (FDM) method in the pre‐amplifier and BPF stages, then amplified and filtered to remove any out‐of‐band noise before providing it to an analog‐to‐digital converter at the low intermediate frequency stage. The receiver is designed using a 90 nm CMOS technology to operate at the main B₀ magnetic field of 9.4 T, which corresponds to 400 MHz. The receiver has an input referred noise voltage of 1.1 nV/√Hz, a total voltage gain of 87 dB, a power consumption of 69 mA from a 1 V supply voltage, and an area of 305 µm × 530 µm including the reference current and bias voltage circuits. Copyright © 2013 John Wiley & Sons, Ltd.     

Electrodeposited Co‐Pt thin films with high coercivity

Co‐Pt alloy film magnets were prepared by electrodeposition. After annealing as‐deposited films with face‐centered‐cubic (fcc) crystal structure, the structure of films with 24 to 50 at.% Co content transformed from disordered fcc phase to ordered face‐centered‐tetragonal (fct) L1₀ phase. It was clarified that Co‐Pt film magnets with a Co content of 43 at.% have high coercivity of approximately 880 kA/m. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 7–12, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20216