TEM observations of magnetic domains and grain boundaries on spin‐sprayed ferrite films exhibiting high permeability usable for gigahertz noise suppressors

Lorentz TEM observations of magnetic domain wall motion, as well as TEM observations of grain boundaries, were performed on spin‐sprayed ferrite films #1 (Ni_0.17Zn_0.22Fe_2.61O₄) and #2 (Ni_0.19Zn_0.20Co_0.03Fe_2.58O₄), both 0.5 µm in thickness. They exhibit much higher natural resonance frequencies than the bulk ferrite and thus have been applied to gigahertz noise suppressors. Films #1 and #2 exhibit prominent and weak in‐plane uniaxial magnetic anisotropy, respectively, which is induced along the liquid flow direction during spin‐spraying. Both films have columnar crystallites with 100‐200 nm widths aligned perpendicular to the film plane, and the boundaries of the crystallites have no pores or impurity phases. Therefore, the crystallites are magnetically exchange‐coupled, which is responsible for the unusually high permeability and high natural resonance frequencies of the films. Under zero bias magnetic field, film #1 exhibits mosaic‐shaped magnetic domains, whereas film #2 exhibits magnetic domains elongated along the easy magnetization axis, both several hundred nanometers in width. For both films the domain structure remains unchanged when an in‐plane bias DC magnetic field,H_dc, of up to 10 Oe is applied along the hard axis. Under a stronger H_dc, the domain structure prominently changes, and the domain walls disappear when H_dc exceeds ∼100 Oe. This confirms our previous finding that the initial permeability is ascribed only to magnetization rotation, with no contribution from domain wall motion [J. Magn. Magn. Mater., 278 , 256 (2004)]. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Improvement of heating characteristics of molybdenum silicide thin film electric heaters

Molybdenum silicide (MoSi₂) has an electrical conductivity as high as that of a metal, and greater chemical stability than that of, for example, SiC, in various atmospheres. Therefore, many kinds of MoSi₂ bulk‐type heaters are used in practical operations up to 1800^°C, which is higher than the temperature of SiC heaters. However, MoSi₂ is fragile at room temperature and has low creep resistance at high temperature. The purpose of this study is to fabricate heaters using thin films of MoSi₂ deposited on alumina substrates and crucibles by RF magnetron sputtering and to evaluate their characteristics. MoSi₂ thin film was deposited on the outside of an alumina crucible without heating the substrate and then Pt wire was attached using a Pt paste with sintering in a vacuum. This MoSi₂ thin film heater showed almost linear resistance–temperature (R–T) characteristics and a uniform heating state. It also showed good controllability of voltage and stability in the power–T characteristics for operations up to 1000^°C. However, at a heating temperature of 1300^°C, the heating area of MoSi₂ thin film decreased because of the reaction between Pt and MoSi₂ in the case of long‐term heating. Thus, Mo thin film was deposited as a buffer layer between Pt and MoSi₂ thin film to prevent such a reaction. This thin film heater showed good linear R–T characteristics up to 1200^°C. However, the temperature coefficient of resistance changed with repeated heating operation as a result of the diffusion of Mo atoms into MoSi₂. Thus, a thin film heater was fabricated with Mo₃Si, having a higher Mo content than MoSi₂. This heater showed a low degree of diffusion of Mo or Pt atoms into the thin film and had excellent practical characteristics up to 1000^°C. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 168(2): 11–19, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20806     

Concentration‐dependent minority carrier lifetime in an In0.53Ga0.47As interdigitated lateral PIN photodiode model based on spin‐on chemical fabrication methodology

The fitted parameters for the analytic function used to specify the doping dependence of minority carrier lifetimes for In_0.53Ga_0.47As (InGaAs) is described in this paper. This model together with other carrier models was used to develop an interdigitated lateral PIN photodiode utilizing InGaAs as the absorbing layer. We propose the usage of spin‐on chemicals such as spin‐on dopants and spin‐on glass to form the p+ wells, n+ wells and the surface passivation layer of the device hence providing a cheap and easy solution versus the conventional epitaxial growth methodology. The modeled device achieved dark currents of 0.21 nA and capacitance of 2.87 nF at an operating voltage of 5 V. Optical illumination at a wavelength of 1550 nm and power of 10 W/cm² enabled the device to achieve responsivity of 0.56 A/W and external quantum efficiency of 44%. The −3 dB frequency response of the device was at 8.93 GHz and signal‐to‐noise ratio is 36 dB. The developed device shows close correlation with experimentally developed devices developed using other fabrication methodologies. The results of this work would be useful in the thorough development of InGaAs‐based devices based on spin‐on chemical fabrication methodology using commercial device simulation packages. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

An ultra‐thin oxide sub‐1 V CMOS bandgap voltage reference

This paper presents a sub‐1 V CMOS bandgap voltage reference that accounts for the presence of direct tunneling‐induced gate current. This current increases exponentially with decreasing oxide thickness and is especially prevalent in traditional (non‐high‐κ/metal gate) ultra‐thin oxide CMOS technologies (t_ox < 3 nm), where it invalidates the simplifying design assumption of infinite gate resistance. The developed reference (average temperature coefficient, T_{C_AVG}, of 22.5 ppm/°C) overcomes direct tunneling by employing circuit techniques that minimize, balance, and cancel its effects. It is compared to a thick‐oxide voltage reference (T_{C_AVG} = 14.0 ppm/°C) as a means of demonstrating that ultra‐thin oxide MOSFETs can achieve performance similar to that of more expensive thick(er) oxide MOSFETs and that they can be used to design the analog component of a mixed‐signal system. The reference was investigated in a 65 nm CMOS technology with a nominal V_DD of 1 V and a physical oxide thickness of 1.25 nm. Copyright © 2013 John Wiley & Sons, Ltd.     

Electrical characteristics of Pt-SBT-Polysilicon (MFIP) capacitors with yttrium oxide as the buffer layer

Abstract

MFIS structures with Strontium Bismuth Tantalate (SBT) as the ferroelectric thin film and yttrium oxide as the buffer layer have been fabricated on polysilicon layer as well single crystal silicon. Yttrium oxide film was deposited by electron beam evaporation and SBT was deposited by spin on MOD technique. Preliminary analysis of capacitance vs voltage (C-V) curve shows hysteresis and the direction of hysteresis corresponds to ferroelectric polarization. For an applied DC bias of ± 5 V, the C-V curve shows a memory window of ± 2 V.     

Numerical simulation on novel FinFETs: asymmetric poly-silicon gate FinFETs and TiN gate FinFETs

We report our numerical study on the device performance of an asymmetric poly-silicon gate FinFET and FinFET with TiN metal gate structure. Our numerical simulation revealed that the asymmetric poly-silicon FinFET structure and TiN gate FinFET structures exhibit superior V _T tolerance over the conventional FinFET structure with respect to the variation of fin thickness. For instance, the V _T tolerance of the asymmetric poly-Si FinFET were 0.02 V while TiN gate FinFET exhibited 0.015 V tolerance for the variation of the fin thickness of 5 nm (from 30 to 35 nm) while the conventional FinFET demonstrates 0.12 V fluctuation for the same variation of the fin thickness. Our numerical simulation further revealed that the threshold voltage (V _T) can be controlled within the range of −0.1∼+0.5 V through varying the doping concentration of the asymmetric poly-silicon gate region from 1.0×10¹⁸ to 1.0×10²⁰ cm⁻³.     

富FeCo晶粒对非晶TbFeCo薄膜磁特性的影响

用磁控溅射法分别在玻璃基底和硅片上沉积Tbx(Fe85Co15)100-x(x=24.7, 40.8, 厚～20nm)薄膜和Fe51Pt49(8 nm)/ Tbx(Fe85Co15) 100-x (～70 nm)双层薄膜,研究了非晶TbFeCo薄膜中富FeCo晶粒的存在对薄膜磁特性的影响.使用磁光克尔效应(MOKE)和振动样品磁强计(VSM)测量样品的磁滞回线,观察到单层TbFeCo薄膜及FePt/TbFeCo双层薄膜中由于富FeCo晶粒的存在导致的磁化反转相分离的特征,并通过测量FePt/TbFeCo双层薄膜的小回线进一步得到了分离后的磁化反转回线,证实了本文的解释.通过改变Tb靶的溅射功率,也观察到Tb含量不同的样品中都存在磁化反转相分离的特征.     

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.     

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.     

CMOS Non‐tailed differential pair

A continuous‐time complementary metal–oxide–semiconductor differential pair that does not require the traditional tail current source as a way to control the direct current and common‐mode current is presented. Compared with a p‐channel long‐tailed pair, the proposed non‐tailed solution operates under a higher maximum input common‐mode voltage that includes (V_DD + V_SS)/2 even under low supply voltages. Experimental measurements on a prototype fabricated in a 0.35‐µm technology (with metal – oxide – semiconductor thresholds greater than 0.6 V) confirm this behavior for supply voltages as low as 1.2 V, whereas the long‐tailed pair with the same technology offers the same capability only for supplies higher than 1.6 V. Copyright © 2015 John Wiley & Sons, Ltd.     

Magnetorefractive Effect for Co/Ru Multilayer Film with Antiferromagnetic Interlayer Exchange Coupling

The spin‐dependent scattering of conduction electron in metallic magnetic multilayers was investigated to reveal the optical properties which corresponded to the magnetization state. From the measurement of magnetorefractive effect in antiferro‐magnetically exchange coupled Co/Ru multilayers, it was found that (1) the transmittance varied around 1% at wavelength of 1550 nm during the parallel/antiparallel spin alignment changes, (2) as a result of number of repetition and Co thickness for the multilayers, transmittance difference between the parallel and antiparallel spin alignment states had trade‐off relationship with the magnitude of transmittance, and (3) asymmetric Co/Ru/Co stacking structure brought different interlayer exchange coupling fields in each layer, which resulted in magnetic field sensitive transmittance.     

Propagation characteristics of a positive surface streamer

The potential distribution of a developing positive surface streamer was measured by the Pockels effect. The transient potential distribution along a linear path was measured at minimum resolutions of 20 µm and 2 ns. Additionally, velocity of a streamer, average electric field along a streamer, and the developing length were measured while changing the insulator thickness from 0.8 to 5.0 mm. The potential along a positive surface streamer decreases linearly with the distance from the high‐potential electrode, and its gradient is about 500–650 V/mm, which is independent of the inception voltage and the insulator thickness. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Theoretical studies of the capacitance‐voltage characteristics of metal‐ferroelectric‐GaN structures

We have simulated the capacitance versus voltage characteristics (C‐V) of metal‐ferroelectric‐gallium nitride (GaN metal‐ferroelectric‐semiconductor) structures and found useful design rules for improving the devices' performance. The thickness effects of ferroelectric film on the C‐V are studied. When the ferroelectric Pb(Zr, Ti)O3 thickness is no more than 100 nm, the GaN metal‐ferroelectric‐semiconductor structures can approach inversion just under 5 V, which is the generally applied voltage used in semiconductor‐based integrated circuits. This marked improvement of C‐V behaviors is mainly due to the high dielectric constant and large polarization of the ferroelectric gate oxide. Copyright © 2011 John Wiley & Sons, Ltd.     

An integrated microelectromechanical microwave switch based on piezoelectric actuation

In the field of microwave applications, microelectromechanical systems (MEMS) are attractive devices in order to force miniaturization by on chip integration. Here, we describe the design, fabrication and testing of a silicon based micromachined switch using piezo-electrically actuated elements. The microwave circuit consists of a coplanar waveguide (CPW) design with two piezoelectric activated beams integrated between the middle line and the ground planes. During operation the beams short the CPW by two overhanging bridge contacts and therefore the transmission characteristics of the microwave circuit change. The CPW is realized by 3 µm thick electroplated copper to yield good transmission characteristics, whereas the clamped—clamped beams benefit from a 250 nm thin PZT film between 100 nm thin Pt electrodes on top of a SiO₂ layer. By the use of double side clamped beams awkward stress compensation of the piezoelectric stack is omitted. Instead the system relies on some initial mechanical stress. Measurements prove deflections of more than 13 µm for a 1400 µm long beam with operation voltages below 10 V. This is in good agreement with finite element simulations. The novel RF-MEMS is predicted to reach an isolation (in “on” state) of more than 20 dB up to 15 GHz.     

Fundamental characteristics of a MEMS‐diaphragm actuator using a thermal expansion drive composed of a conductive polymer

Performance of a MEMS actuator using a thermal expansion drive of a conductive polymer (CP) is investigated by applying electricity to it. The actuator consists of a thin polymer diaphragm (5 mm diameter) and a thin CP (ion‐doped polythiophene) layer coated on the diaphragm surface. Polyimide (10 μm thickness) and PET (110 μm thickness) sheets were chosen as the diaphragm materials. The diaphragm is deflected by the thermal expansion of the CP by applying electricity to it. Merits of using the CP instead of metal are realizing flexible actuators and the applicability to a low‐heat‐resistant material diaphragm. The relationship between thickness of the CP layer (10–50 μm thickness) and electrical resistance (30–600 Ω) and the relationship between the input voltage (1–8 V) and the generated diaphragm displacement (several tens of micrometers) were investigated experimentally. These relationships were compared with those in the case of using the thermal expansion of a vapor‐deposited aluminum layer (0.1 μm thickness). The results of the investigation indicate that the diaphragm based on CP can produce the required displacement. In the case the CP‐layer‐based thermal expansion, however, larger input voltage than in the case of the aluminum‐layer‐based thermal expansion is needed to obtain the same displacement amplitudes. Therefore, the main problem concerning use of the CP‐based diaphragm is considered to be enhancing the electrical conductance of the CP layer. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

0.5‐V bulk‐driven differential amplifier

A new 0.5‐V fully differential amplifier is proposed in this article. The structure incorporates a differential bulk‐driven voltage follower with conventional gate‐driven amplification stages. The bulk‐driven voltage follower presents differential gain equal to unity while suppressing the input common‐mode voltage. The amplifier operates at a supply voltage of less than 0.5 V, performing input transconductance almost equal to a gate transconductance and relatively high voltage gain without the need for gain boosting. The circuit was designed and simulated using a standard 0.18‐µm CMOS n‐well process. The low‐frequency gain of the amplifier was 56 dB, the unity gain bandwidth was approximately 3.2 MHz, the spot noise was 100 nV/√Hz at 100 kHz and the current consumption was 90 μΑ. Copyright © 2012 John Wiley & Sons, Ltd.     

A 5.25‐V‐tolerant bidirectional I/O circuit in a 28‐nm CMOS process

A 5.25‐V‐tolerant bidirectional I/O circuit has been developed in a 28‐nm standard complementary metal‐oxide‐semiconductor (CMOS) process with only 0.9 and 1.8 V transistors. The transistors of the I/O circuit are protected from over‐voltage stress by cascode transistors whose gate bias level is adaptively controlled according to the voltage level of the I/O pad. The n‐well bias level of the p‐type metal‐oxide‐semiconductor transistors of the I/O circuit is also adapted to the voltage level of the I/O pad to prevent any junction leakage. The 5.25‐V‐tolerant bidirectional I/O circuit occupies 40 µm × 170 µm of silicon area. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation of BST thin films on Pt electrode on Si wafer with down-flow LSMCVD reactor

Abstract

A novel type of down-flow LSMCVD (Liquid Source Mist CVD) reactor was developed to prepare a high dielectric BST thin film on Pt electrode on Si wafer. Barium acetate [Ba (OOCCH₃)₂], strontium acetate [Sr (OOCCH₃)₂], and titanium isoproxide [Ti (OC₃H₇ ⁱ )₄] were used as metal sources. Metal sources were dissolved in acetic acid, 1-butanol, or 2-methoxyethanol. BST [Ba/(Ba + Sr) = 0.7] film annealed on Pt/Ti/SiO₂/Si above 650°C was polycrystalline. BST film has a (110) preferred orientation with increasing temperature. Surface roughness of BST film and grain size increased with increasing temperature. The metal-oxygen bond was formed at 650°C as shown in the spectra of FTIR. The depth profiles of elements of BST thin films indicated a uniform composition throughout the film. BST films annealed at 750°C showed a dielectric constant and a tanδ of 390 (thickness: 150 nm) and 0.06 at a frequency of 100 kHz, respectively. The behavior of capacitance of the BST film with bias voltage showed paraelectric property. BST film annealed at 750°C had the leakage current density of 3.2 (μA/cm²) at a bias voltage of 2V.     

Proposal of flux‐lock‐type fault current limiter with high‐TC superconducting element

This paper proposes a new type of fault current limiter (FCL), which consists of a high‐T_C superconducting (HTS) element and two coils wound on the same core without any leakage magnetic flux. In this FCL, either the limiting impedance or the initial limiting current level can be controlled by adjusting the inductances and the winding direction of the coils. Therefore, this FCL could relax the material restrictions on high‐T_C superconducting FCL. A current‐limiting experiment by a model FCL was carried out, and the limiting performance was observed. The initial limiting current level of the model FCL was 1.7 times higher than the critical current of the HTS element, and the fault current is suppressed to 52% immediately after the short‐circuit in the test. Considering voltage–current characteristics of a high‐T_C superconductor in a computer simulation, the calculated results almost agreed with the experimental results. © 1999 Scripta Technica, Electr Eng Jpn, 127(1): 31–38, 1999