Bipolar Square Research Articles

9.3: MgxBa1−xAl2S4: Eu Blue Phosphor in Thick Dielectric EL

AbstractA high luminance inorganic electroluminescent (iEL) blue phosphor, europium doped MgxBa1−xAl2S4, has been developed on iFire substrates using dual source electron beam evaporation. The color performance is L60 >200 cd/m2 with CIE x, y‐coordinates 0.135 and 0.105, respectively, using a 120Hz bipolar pulsed square wave form. Partial substitution of magnesium for barium lowers the annealing temperature of BaAl2S4 phosphor for crystallization, which is an important parameter for fabricating large size inorganic EL devices for such applications as large screen television.

터널링 자기저항 소자의 접합면 정전용량에 따른 전기적 응답특성

In this research, the effects of capacitance to the access time were studied at the junction area of tunneling magnetoresistance when these were used as memory devices. These results were obtained by applying electric signal input and magnetic field was not used. We applied bipolar square waves of 1MHz to the MTJ samples to obtain the results and time constant () calculated by observing wave responses utilizing an oscilloscope. And time constant was compared with junction area. Each part of MTJ sample, such as electrical pad, lead and contact area, was modeled as an electrical equivalent circuit based on experimental results. For the 200㎛200㎛ cell, junction capacitance was 90 pF. Also, measurement and simulation results were compared, which showed those similarity.

Polarization Switching Studies in Ferroelectric Glycine Phosphite Single Crystals

Glycine Phosphite [NH 3 CH 2 COOH 3 PO 3 ], abbreviated as GPI, undergoes a para-ferroelectric phase transition from the monoclinic symmetry P2 1 /a to P2 1 at 224.7 K. We report here a systematic study of the polarization switching process in this crystal. Growth of these crystals from aqueous solution has been undertaken employing both solvent evaporation and slow cooling methods. Hysteresis loop measurements along the polar b -axis yielded a spontaneous polarization value of 0.5 w C/cm 2 and a coercive field of 2.5 kV/cm. Conventional Merz technique was employed for polarization switching studies, wherein bipolar square pulses were applied to the sample to induce domain reversal. The transient switching pulse that flows through the sample on application of the field was recorded. The maximum switching time required for domain switching was measured both as a function of electric field and temperature. The experimentally observed switching curves were fitted with the model based on the Pulvari-Kuebler theory of nucleation and growth of domains. From the experimental data, the values of mobility and activation field were obtained. It was observed that switching process in this crystal is predominantly governed by the forward growth of domain walls in the high field region. However, switching process in GPI crystal was found to be slower than that found in other glycine based ferroelectric crystals.

The post annealing effects on ferroelectric properties of SrBi2Ta2O9 thin films prepared by R.F. magnetron sputtering

SrBi2Ta2O9(SBT) films were prepared on Pt/Ti/SiO2/Si substrates by conventional r.f. magnetron sputtering. The ferroelectric and dielectric properties of bismuth layer structured ferroelectrics are studied for the purpose of examining the effects of oxygen flow rate during annealing. Oxygen flow rate influenced the shape of hysteresis loop, polarization value and current voltage characteristics. The remanent polarization (2Pr) and the coercive field (2Ec) obtained from a 240 nm thick SBT films annealed at 760Torr were 4.4uC/cm2 and 72kV/cm at an applied voltage of 5 V, respectively. The films annealed at oxygen flowing condition showed leakage current density of ∼10−7 A/cm2 at 150kV/cm. The films showed fatigue-free characteristics independent of annealing condition up to 1011 cycles under 5 V bipolar square pulse.

Vibration control of a flexible beam with integrated actuators andsensors

The use of system identification to determine linear Auto Regressive MovingAverage eXogenous inputs (ARMAX) models for smart structures has been scarcelyreported in the literature. However, these models can be used as a basis for alinear discrete-time controller design. This work presents a smart structurevibration control scheme developed using an ARMAX model of the structure andcompares its performance to an empirically designed velocity feedbackcontroller. The smart structure is comprised of piezoceramic (such as PZT) actuatorsand strain gauge sensors attached to a cantilever beam and interfaced to a PC,which provides the control software platform. System identification is carriedout in three phases: data collection, model characterization and parameterestimation. Input-output data are collected by stimulating the piezoactuatorswith a bipolar square wave signal and monitoring the strain gauge response.The model is characterized with second-order plant dynamics and a least-squares estimationalgorithm calculates the model parameters. Thecontroller is designed using pole placement to achieve the desired closed-loopresponse. The ARMAX model is used to calculate the pole placement controllersby solution of the Diophantine equation for the prescribed closed-loop polepositions. Results show that the pole placement controller can match theperformance of a velocity feedback controller and maintain this performancewhen the sampling rate is greatly reduced.

Analysis and experimentation of nonlinear adaptive controllers for the series resonant converter

It is the purpose of this paper to explore the problem of regulating the output voltage of a DC-to-DC series resonant power converter (SRC). These converters have highly nonlinear dynamics fed by a bipolar square signal generator whose commuting frequency is the only accessible control variable in the control architecture that the authors study. Therefore, they are confronted with the problem of controlling a nonlinear switched system by means of a modulating frequency signal. Two more complications that make this problem more challenging are that the full state is typically not available for measurement, and that the output load, usually represented by a resistance, is unknown. They show here that-for constant control input-SRCs have a unique globally attractive periodic orbit, which motivates them to consider a first harmonic approximation of the system. They then prove that this reduced model consists of a known static nonlinearity in cascade with a first order system with unknown parameters, for which adaptive output feedback solutions can be derived. They propose two different schemes, first a passivity-based controller which, as usual in these schemes, achieves asymptotically the inversion of the nonlinearity. They prove that, under some practically reasonable considerations, this control law reduces to the dissipative controller recently proposed by Stankovic et al. The second scheme directly inverts the static nonlinearity and applies standard adaptive techniques to the resulting linear system. The three controllers are implemented in an experimental setup and the results are presented as a comparative study.

Electrical fatigue of ferroelectric PbZr 0.5Ti 0.5O 3 and antiferroelectric PbZrO 3 thin films

The electrical fatigue of sol-gel derived ferroelectric lead zirconate titanate (PZT 50/50) and antiferroelectric lead zirconate (PZ) thin films was found to strongly depend on the orientation and morphology. Compared to the PZT films, the PZ thin films showed a much slower degradation of polarization, due to their having less internal stress during 180° domain switching of the antiferroelectric phase. More than 70% of the initial polarization value of PZ thin films was maintained after 10 9 cycles of 15 V bipolar square pulse. The randomly oriented PZT films showed less degradation of polarization, compared to the (111) preferred PZT films. In the PZ thin films, the rosette structure with a large portion of pyrochlore phase caused severe fatigue because of nonuniform distribution of electric field and internal stress.

A novel method for laser-induced periodic domain reversal in LiNbO/sub 3/ [nonlinear optical waveguide

An intense laser light in conjunction with a strong localized field is used to reverse the polarity of the ferroelectric domain at the location of a laser beam. The focus beam from an argon laser raises the temperature of a moving z-cut LiNbO/sub 3/ plate close to the Curie point when a bipolar square wave electric field is applied. This technique has been used to construct a nonlinear periodic optical waveguide structure. This waveguide can be used for quasi-phase-matched second-harmonic generation. The applications of such waveguides are well documented in the literature.

Analysis of the degradation and breakdown of thin SiO/sub 2/ films under static and dynamic tests using a two-step stress procedure

A two-step stress test is used to analyze the degradation and breakdown of thin SiO/sub 2/ films. The procedure directly relates the degradation of the oxide to the breakdown statistics, without the need of any assumption about the microscopic degradation mechanism. It partially overcomes the problems associated with dynamic tests and allows the direct comparison of different tests (static and dynamic). The evolution of the degradation of 8 nm thick oxides subjected to constant-voltage (CVS), constant-current (CCS), and bipolar square voltage stresses is analyzed using the two step stress method. The results are compared with those of conventional breakdown tests to show the feasibility of the procedure. Our test procedure is also used to study the degradation of 4 nm thick oxides when subjected to CCS. The obtained results suggest that the two-step stress test will also be a powerful tool to analyze the degradation of ultra-thin oxides.

Temperature Dependence of the Electrical Properties of SrBi2Ta2 O 9 Thin Films Deposited by Radio‐Frequency Magnetron Sputtering

Fatigue‐free bilayered (SBT) films were successfully prepared on substrates by radio‐frequency magnetron sputtering. The applied voltage showing the maximum capacitance decreases with increasing temperature. The remanent polarization (2Pr) and the coercive field (2.Ec) obtained for the SBT films were 13 μC/cm2 and 128 kV/cm at an applied voltage of 5 V at 30°C. The films measured at room temperature and 100°C showed fatigue‐free characteristics up to 1011cycles under 5 V bipolar square pulses. SBT films show the retention loss of only 6% after 10 years at 100°C. The leakage current density is less than at an applied voltage of 3 V at 75°C. The dominant transport mechanism of SBT films was an interface limited Schottky emission. The Pt/SBT contacts have a Schottky barrier height of .

Preparation of fatigue-free SrBi2Ta2O9 thin films by r.f. magnetron sputtering and their ferroelectric properties

Fatigue-free bismuth-layered SrBi2Ta2O9 (SBT) films were deposited on Pt/Ti/SiO2/Si substrates by r.f. magnetron sputtering at room temperature. The variation of structure and electrical properties were studied as a function of annealing temperatures from 750–850 °C. The films annealed at 800 °C had a composition ratio of Sr:Br:Ta = 0.7:2.0:2.0. X-ray photoelectron spectroscopy signals of bismuth show an oxygen-deficient state within the SBT films. The films annealed at 800 °C have a thickness of 200 nm and a relatively dense microstructure. The remanent polarization (2P r), and the coercive field (2E c), obtained for the SIBT films, were 9.1 μC cm−2 and 85 kV cm−1 at an applied voltage of 3 V, respectively. The films showed fatigue-free characteristics up to 1010 cycles under 5 V bipolar square pulses. The leakage current density was about 7 × 10−7 A cm−2 at 150 kV cm−1. The SBT films prepared by r.f. magnetron sputtering were attractive for application to non-volatile memories.

Characterization of Ferroelectric SrBi2Ta2 O 9 Thin Films Deposited by a Radio Frequency Magnetron Sputtering Technique

Fatigue‐free Bi‐layer films were deposited on substrates by radio frequency magnetron sputtering. The addition of 30 mole percent (m/o) and 20 m/o into the target was necessary in order to compensate for the lack of Sr and Bi in the films. A 200 nm thick film annealed at 800°C exhibited dense morphology, a dielectric constant of 210, and a dissipation factor of 0.06 at a frequency of 1 MHz. The remnant polarization 2Pr and the coercive field 2Ec of the films were 9.1 μC/cm2 and 85 kV/cm, respectively, at an applied voltage of 5 V. The leakage current density was about at 150 kV/cm. The films showed fatigue‐free characteristics under a ±5 V bipolar square pulse of 1 MHz up to . The films prepared by radio frequency magnetron sputtering are attractive for application to nonvolatile memory devices.

Velocity and Position Control of a Parallel Biwheel Vehicle Driven with a Stepping Motor.

Translational motion control of a parallel biwheel vehicle (PBV), which is driven with a stepping motor operated in an open-loop mode, is described. The posture of the PBV is regulated by a discrete time sliding mode controller. A zero point offset on the inclination angle of the PBV is introduced to trigger and to control the translational motion of the PBV, since a conventional sliding mode servo system is not controllable if the angular velocity of the PBV wheel is selected as the reference input. The velocity and position of the PBV can be regulated through the offset by additional PID and PD controllers. For a bipolar square wave velocity reference, the velocity of the PBV can quickly follow the reference signal and the PBV can run with fairly constant velocity. For a bipolar square wave position reference, the PBV shows a fast step-like response followed by a somewhat slow one bound on a sliding surface. A conflict between the PID and PD motion controllers and the discrete sliding mode posture controller occurs when the position of the PBV settles toward the reference position.

Flux-enhanced growth of multi-source physical vapor deposited SrGa 2S 4:Ce,Cl electroluminescent thin films

The flux-assisted deposition of the active phosphor layer in the highest efficiency, true blue (CIE coordinates of x = 0.14 y = 0.12 ) electroluminescent (EL) devices based on SrGa 2S 4:Ce,Cl is described. Luminances of 78 cd/m 2 luminous efficiencies of 0.017 lm/W at a transferred charge of 1 μC/cm 2 with 1 kHz/50 μs bipolar square wave excitation were achieved. The influence of the coevaporated fluxes LiF and NaF in addition to the elements Sr, Ga, S, and the activator starting material CeCl 3, on film growth is examined. The relation between Ga Sr , S Sr , flux Sr rates, and substrate temperature ( T Sub) on phase homogeneity due to flux, crystal quality, film thickness, and device performance is described.

Improved Growth Of Srga2s4 Thin Film Electroluminescence Phosphors

AbstractCerium activated ternary strontium thiogallate phosphor thin films have been deposited by multi-source evaporation of elemental strontium, gallium and sulfur as source materials. Cerium chloride (CeCI3) has been used as activator starting material. In order to avoid SrS as well as Ga phase segregations elemental In as well as compounds, such as LiF, NaF, LiCl, and SrCI2, have been investigated as possible growth enhancing agents.Coevaporation of indium resulted in an improved crystallization with the drawback of an increased reabsorption of the cerium emission. The other additives lead to improved crystal quality combined with true-blue cathodoluminescence (CL) performance (C.I.E. color coordinates of up to 0. 14/0.12) which proves phosphor layers without any SrS phase segregations.Thin film electroluminescent (TFEL) devices with SrGa2S4:CeCl3 phosphor layers prepared with LiF as additive exhibit highest ever reported L40 luminances of 78 cd/m2 and luminous efficiencies of 0.017 lm/W at a transferred charge of 1 μ;C/cm2 with 1 kHz / 50 μs bipolar square wave excitation.

Exposure of domestic quail embryos to extremely low frequency magnetic fields.

Four hundred domestic quail eggs (Coturnix coturnix japonica) were used to study the possible teratogenic effects of extremely low frequency magnetic fields (ELF-MFs) on early embryonic development. Ten females were selected from a flock on the basis of their high fertility rate and low number of spontaneous abnormalities and they were selectivity maintained in nesting-boxes in a room where feeding and environmental conditions were carefully controlled. All the eggs used in the experiments were filiated by their progemtor, and were handled in the same way from the time they were laid until the point at which they were placed in a specially designed incubator, which dramatically reduces the stray magnetic fields produced by the heating system. Twenty eggs per experiment (10 control and 10 exposure) were placed in two different areas within the incubator. For each experiment two eggs from each of the 10 females were used. These were placed pairwise in the same position in the incubation areas (one in the control area and one in the exposure area). The first 12 experiments (240 eggs in total) were sham (ELF-MFs source turned off) in order to identify the variability of test quantities. The last eight experiments (160 eggs in total) involved magnetic fields (continuous bipolar square signal, rise and fall time 4 microseconds, in Helmholtz' coils) and they were divided into two exposure groups: the first four experiments at 50-Hz frequency and the last four at 100-Hz frequency. The magnetic flux density was different for each experiment within each frequency group, but the same sequence was always used: 0.2, 1.2, 2.2, 3.2 microtesla. The number of abnormal embryos found in the area exposed to 100 Hz was significantly higher than for their controls (Chi-square test, p = 0.048) but this difference was not significant for the 50-Hz group (p = 0.232). An ANOVA test was significant for the magnetic field variable (p < 0.05). A higher number of dead embryos was observed in the two groups of exposed eggs. Finally, a gross examination of the external morphology of the abnormal exposed embryos showed a high percentage of abnormalities of the nervous system, particularly at the cephalic level.

Theory of electroporation of planar bilayer membranes: predictions of the aqueous area, change in capacitance, and pore-pore separation

A large increase in the transmembrane voltage, U(t), of a fluid bilayer membrane is believed to result in the occurrence of temporary aqueous pathways ("pores") across the membrane. The number, size, and evolution dynamics of these pores are expected to be crucial to the transport of water-soluble species ranging from small ions to macromolecules such as proteins and nucleic acids. In this paper we use a transient aqueous pore theory to estimate the fraction of the membrane area, Fw(t), which is temporarily occupied by water-filled pores for short square, exponential, and bipolar square pulses. For short pulses, "reversible electrical breakdown" occurs when the transmembrane voltage reaches about 1 V, and Fw(t) is predicted to rise rapidly, but always to be less than 10(-3). The conductance of a large number of pores causes reversible electrical breakdown and prevents a significantly larger U from being reached. Despite the large dielectric constant of water, for reversible electroporation the associated change in membrane capacitance, delta C, due to the pores is predicted to be small. Moreover, for a flat membrane the minimum value of the mean pore-pore separation is large, about 60 times the minimum pore radius. In flat membranes, pores are predicted to repel, but the opposite is expected for curved cell membranes, allowing the possibility of coalescence in cell membranes. For some moderate values of U, rupture (irreversible electrical breakdown) occurs, as one or more supracritical pores expand to the membrane boundary and the entire membrane area becomes aqueous. In all cases it is found that a quantitative description of electroporation requires that a pore size distribution, rather than a single size pore.

Investigation of some aspects of the liquid crystal optical voltage contrast technique for integrated circuit physical analysis

This paper presents results of the optical voltage contrast mechanism using nematic liquid crystal on an operational amplifier integrated circuit (op-amp IC) connected up as a unity-gain inverting amplifier. The dependence of the intensity of the contrast mechanism on the peak-to-peak voltage (V pk-pk), duty cycle (d) and frequency (f) was investigated for an input symmetrical, bipolar square waveform. It was found that the optical voltage contrast intensity varies as the square of V pk-pk for a constant duty cycle square wave. For a constant V pk-pk, the intensity dependence on duty cycle d is proportional to d for d < 50% and (1−d) for d > 50%. The low-frequency cutoff of the intensity response occurs at tens of hertz. This correlates well to the response time of the liquid crystal molecules which is in the region of tenths of seconds. The high-frequency falloff of the intensity response, at tens of kilohertz, to a 9–11 V peak-to-peak voltage is due to the finite slew rate of the op-amp test specimen which is typically around 0.5 V/μs. The slewing of the output waveform is equivalent to a deviation of the duty cycle from that of 50% which gives rise to the maximum intensity signal. This was confirmed by investigating the amount of slew of the output waveform for different input frequencies, fitting an increased duty cycle waveform to the slewed waveform and calculating the theoretical intensity response. The theoretical falloff in intensity correlates well with the experimental high-frequency rolloff.

Characteristics of Y2O3:Eu/ZnS/Y2O3:Eu Red Light Emitting Electroluminescent Devices

Hot-carrier-injection-type electroluminescent (HCI-EL) devices of Y2O3:Eu/ZnS/Y2O3:Eu structure were fabricated by the electron beam deposition technique and red light emission of about 10 cd/m2 intensity was observed from Eu3+ ions. Brightness at relatively high applied voltage was proportional to the applied frequency, as has been reported, while it was decreased above several hundred Hz at relatively low applied voltage. It is considered that the resistance part of the Y2O3:Eu layer becomes dominant at relatively low applied voltage and the capacitance part becomes dominant at higher applied voltage. Red light emission from Eu3+ ions was observed for both half cycles of bipolar square wave applied to the Y2O3:Eu/ZnS/Y2O3-structure EL device, of which only one side of Y2O3 layers was doped with Eu. It is considered that light emission may occur by impact ionization of holes generated in the ZnS layer.

Electroporation by using bipolar oscillating electric field: an improved method for DNA transfection of NIH 3T3 cells.

Using the plasmid DNA pSV2-neo (which, when integrated into the cellular genome confers resistance to the antibiotic G418 for selection), we examined and compared the transfection efficiency on NIH 3T3 cells electropermeabilized by applying a sequence of high-frequency unipolar or bipolar square waves or a single square pulse. Results show that a bipolar square wave is, at least, 1.7- and 5.5-fold more efficient than the unipolar square wave and single square pulse, respectively. In the range of electric field strength used for optimum transfection, the survivability of electropermeabilized cells was comparable between the unipolar and bipolar square waves but fell considerably with the single square pulse. Qualitative comparison of cell permeabilization induced by the three types of wave forms and monitored by ethidium bromide uptake revealed that only the bipolar square wave permeabilizes the cell membrane symmetrically at the two hemispheres facing the electrodes. With unipolar square wave or single square pulse, the membrane is permeabilized either on one side or asymmetrically. Taken together, our result suggests that permeabilization of the membrane at multiple sites without affecting cell survivability may account for the improvements in transfection efficiency observed with bipolar oscillating electric fields.