Read Pulse Research Articles

Bi-stable State for WORM Application Based on Carbazole-containing Polymer

ABSTRACTRecently, several studies have been done by various groups to understand the memory effects behind organic materials, which include understanding in terms of conformation changes, conjugation modification and oxidation-reduction process. In this paper, a WORM (write-once read-many times) memory device using a new polymer material 2-(9H-carbazol-9-yl)ethyl methacrylate (PCz) containing carbazole donor group has been demonstrated. The device uses a MIM (metal-insulator-metal) structure with ITO coated glass as bottom electrode, the synthesized polymer material PCz as the active layer and Al as the top electrode. The toluene solution of PCz was spin-coated on the ITO, followed by solvent removal in a vacuum chamber. Finally, Al was thermally evaporated through shadow mask onto the PCz film.The memory effect of PCz was observed in the I-V characteristic of the MIM structure. The as-fabricated device is found to be in its OFF state, and can be programmed to ON state which is not reversible. The WORM device exhibits a high ON/OFF current ratio of up to 106, and shows a good retention time for both the ON and OFF states which can be sustained within a 24 h timeframe, and extrapolated to sustain for another 10 years. The effect of continuous read pulse on the ON and OFF states was evaluated and no resistance degradation is observed for read cycles up to 107 times. By comparing the electrical characteristics of PCz and PVK as well as their optimized geometry simulation corresponding to their minimized energy states, the memory effect or bi-stable states of PCz can be attributed to the long linker between the carbazole groups and backbone present in PCz which play a part in the conduction mechanism.

Multiple beam splitter for single photons

We propose a method using ``light storage'' and fractional stimulated Raman adiabatic passage (F-STIRAP) to get entangled multiple Fock states from a single photon. A light storage technique is used to store the quantum information of a single-photon pulse in atoms. F-STIRAP pulses then split the stored coherence, such that reading pulses retrieve the quantum information from this new coherence. Since each reading pulse only retrieves part of the total coherence, we can obtain entangled multiple Fock states with arbitrary relative amplitude. This method to create entanglement is versatile for obtaining frequency, time, and∕or spatial entanglement. Indeed, we obtain a multiple beam splitter with easily adjustable parameters.

Enhancement of the switched phase conjugate reflectivity in a BaTiO3 crystal

Abstract We experimentally investigated the response of the photorefractive phase conjugation to a pulsed reading beam in an undoped BaTiO 3 crystal with a four-wave mixing geometry. A single longitudinal-mode Ar + laser was used as a light source. The reading beam with a pulse width of ∼1 s was switched on after writing a steady-state grating in the crystal by two recording beams under a suitable condition and the generated phase conjugation was measured. The phase conjugate output was found to be increased by some factors of magnitude over the initial value for a given peak power and period of the reading pulses. A maximum of the enhanced reflectivity can be controlled by adjusting the interacting beam powers. An increase in the diffraction efficiency was also found with the same read-out process, which plays a key role to increase the phase conjugation as our knowledge.

Sensitivity-enhanced quantitative 13C NMR spectroscopy via cancellation of 1J(CH) dependence in DEPT polarization transfers.

A scheme has been developed to eliminate virtually all signal intensity dependence on 1JCH in polarization transfers between 1H and 13C nuclei, reducing differences in signal intensity to only 1.5% over the entire natural 1JCH range. The scheme relies on the summation of time-domain data acquired with four suitably selected Delta delays so that the J dependence is essentially canceled in the final, signal-averaged free-induction decay. These Delta delays have been incorporated into the DEPT pulse sequence to create sensitivity-enhanced experiments for collecting quantitative 13C{1H} spectra. Four experiments, each with unique read pulse angles, give quantitative spectra with 200-300% more sensitivity than conventional 13C spectra acquired with inverse-gated 1H decoupling. The experiments are ideal for recording spectra with improved quantitative information or for substantially reducing the long acquisition times indicative of quantitative 13C experiments. The ability of the experiments to provide quantitative spectra was demonstrated with a simple ethylbenzene solution, however, they can easily be adapted to various applications for analysis of complex mixtures.

In vivo GABA detection with improved selectivity and sensitivity by localized double quantum filter technique at 4.1T.

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter for the normal function of mammal and human brain. It is difficult to detect GABA signal with the conventional single quantum technique due to its relatively low concentration and overlapping with other signals from creatine (Cr), glutathione (GSH), as well as macromolecules. Using a high-selective read pulse, DANTE, and at the facility of increased sensitivity and chemical shift resolution at high-field 4.1T, GABA editing by double quantum filter (DQF) with robust suppression of Cr and GSH was achieved. Our editing efficiency of 40-50% was achievable on a GABA phantom (50 mM GABA and 61 mM choline). Furthermore, GABA editing spectra were acquired with echo time TE = 77 ms, and any possible macromolecular contamination to GABA editing spectra was found to be negligible. This high-field DQF setup was applied to 11 healthy volunteers, and the mean GABA level was measured to be 1.12 +/- 0.15 mM in the occipital lobe in reference to 7.1 mM Cr concentration.

Zero-quantum filter offering single-shot lipid suppression and simultaneous detection of lactate, choline, and creatine resonances.

A zero-quantum (ZQ) filter offering single-shot lipid suppression and providing for simultaneous detection of the lactate methyl doublet (1.3 ppm) and nonoverlapping singlets including choline (Cho, 3.2 ppm) and creatine (Cr, 3.0 ppm) is described. Filtering is provided by soft mixing and reading pulses (RF(mix), RF(rd)) that are selective for the lactate methine quartet (4.1 ppm), Cho, and Cr resonances but exclude the 1.3 ppm lactate component and overlapping lipids. Surrounding RF(mix) and RF(rd) are magnetic field gradient pulses of equal magnitude but opposite signs to enable the rephasing of the zero-quantum lactate coherence and the creation of a stimulated echo for singlets within the pulse passbands. The sequence is designed to retain half the original lactate and singlet signal intensities. Theoretical predictions were confirmed experimentally at 1.5T using phantom acquisitions. The lipid suppression factor was measured to be over 10(3).

Nonadiabatic approach to quantum optical information storage

We show that there is no need for adiabatic passage in the storage and retrieval of information in the optically thick vapor of Lambda-type atoms. This information can be mapped into and retrieved out of long-lived atomic coherence with nearly perfect efficiency by strong writing and reading pulses with steep rising and falling edges. We elucidate similarities and differences between the ``adiabatic'' and ``instant'' light storage techniques, and conclude that for any switching time, an almost perfect information storage is possible if the group velocity of the signal pulse is much less than the speed of light in the vacuum c and the bandwidth of the signal pulse is much less then the width of the two-photon resonance. The maximum loss of the information appears in the case of instantaneous switching of the writing and reading fields compared with adiabatic switching, and is determined by the ratio of the initial group velocity of the signal pulse in the medium and speed of light in the vacuum c, which can be very small. Quantum restrictions to the storage efficiency are also discussed.

Improved selectivity of double quantum coherence filtering for the detection of glutathione in the human brain in vivo.

An improved double quantum coherence (DQC) filter for the selective in vivo detection of glutathione (GSH) in the human brain at 1.5 Tesla is presented. The goal was to minimize contamination of the DQC-filtered GSH signal at 2.9 ppm with contributions arising from GABA. The modification consists of tailoring the frequency response of the read pulse, which converts DQC into anti-phase single quantum coherence in such a way that the GABA beta and gamma resonances at 3.0 and 1.9 ppm, respectively, remain unaffected. An implementation incorporating a Dante pulse train is used for in vitro tests as well as for in vivo applications. Magn Reson Med 45:708-710, 2001.

A 0.4-/spl mu/m 3.3-V 1T1C 4-Mb nonvolatile ferroelectric RAM with fixed bitline reference voltage scheme and data protection circuit

A 0.4-/spl mu/m 3.3-V 1T1C 4-Mb nonvolatile ferroelectric random access memory (FRAM) was developed. The FRAM relies on the use of a reference scheme optimally adapted to the entire cell population of an individual device. A simple voltage level detector protects the device against data loss during drops in supply voltage. Finally, a special test mode was implemented to optimize read pulse width. By using these techniques, a high-performance 1T1C 4-Mb FRAM was successfully developed.

A high-resolution (13)C 3D CSA-CSA-CSA correlation experiment by means of magic angle turning.

It is shown in this paper that a previously reported 90 degrees sample flipping (13)C 2D CSA-CSA correlation experiment may be carried out alternatively by employing constant slow sample rotation about the magic angle axis and by synchronizing the read pulse to 13 of the rotor cycle. A high-resolution 3D CSA-CSA-CSA correlation experiment based on the magic angle turning technique is reported in which the conventional 90 degrees 2D CSA-CSA powder pattern for each carbon in a system containing a number of inequivalent carbons may be separated according to the isotropic chemical shift value. The technique is demonstrated on 1,2,3-trimethoxybenzene in which all of the overlapping powder patterns that cannot be segregated by the 2D CSA-CSA experiment are resolved successfully by the 3D CSA-CSA-CSA experiment, including even the two methoxy groups (M(1) and M(3)) whose isotropic shifts, confirmed by high-speed MAS, are separated by only 1 ppm. A difference of 4 ppm in the principal value component (delta(33)) between M(1) and M(3) is readily obtained.

Williams-Comstock model with finite-length transition functions

The theory of the third-order-polynomial (TOP) and fifth-order-polynomial (FOP) magnetization transitions is presented. These transitions have a finite length, rather than an asymptotic approach to /spl plusmn/M/sub r/., which is the case with some widely-used transition functions. The Williams-Comstock model is used to obtain the transition parameters, which are equal to half the transition lengths, resulting in quadratic equations and simple expressions. In this analysis, the write-field gradient is maximized with respect to the deep-gap field, as well as with respect to the distance of the transition from gap center, which results in a higher gradient than is obtained with the original Williams-Comstock approach, at the expense of a higher write current. Analytic expressions are obtained for the read pulses of inductive and shielded magnetoresistive heads, and equations for nonlinear transition shift are derived for the arctangent and the TOP transitions. The results are compared with those obtained using arctangent and tanh transitions and with experiment. In addition, certain aspects of the write-process Q function and the optimum deep-gap field are discussed.

Single-Shot Line Scan Imaging Using Stimulated Echoes

A new high-speed MRI method is described for single-shot line scan imaging (LSI) based on stimulated echoes (STE). To allow for multislice imaging, the technique comprises a series of slice-selective preparation pulses (each corresponding to the first RF pulse of a STE sequence), a slab-selective refocusing pulse (second RF pulse), and multiple line-selective read pulses (third RF pulses). An alternative version employs packages of two slice-selective pulses followed by multiple line-selective read pulses. Experimental applications deal with human brain imaging on a clinical MRI system at 2.0 T. The technique offers user-selectable trade-offs between volume coverage (1–15 sections) and in-plane spatial resolution (1–5 mm linear pixel dimension) within total acquisition times of less than 500 ms. Although LSI yields a lower signal-to-noise ratio than Fourier imaging, single-shot LSI with STEs is free from resonance offset effects (e.g., magnetic field inhomogeneities and susceptibility differences) that are typical for echo-planar imaging. Moreover, the technique exhibits considerable robustness against motion and provides access to arbitrary fields-of-view, i.e., localized imaging of inner volumes without aliasing artifacts due to phase wrapping.

Under-keepered media with MR heads

This paper reports on using magneto-resistive heads with soft magnetic "under-keeper" layers below the media. A simple model based on imaging is in agreement with experimental data. The keeper layer screens low spatial frequency media signals, narrowing the read pulse slightly. In addition, the keeper introduces noise at low spatial frequency.

Driving of a-Si:H adjustable threshold three color detectors for video applications

Heterojunction adjustable threshold three color detectors (ATCDs) have been shown to detect the three fundamental colors of the visible spectrum under three different bias conditions. Operation has already been demonstrated under steady-state conditions and has been proven in transient conditions at video rates. We assumed that a large area array was scanned row by row and each pixel was addressed by a reading pulse during each array sweep. Between two reading pulses, the pixel is open circuit, discharging through recombination of excess carriers. The driving waveform is three fold-valued and the correct readout requires more than one sequential sweep of the array for each value of the waveform. The exact number of sequential sweeps required for correct sensing also depends on the time duration of the reading pulses, and under particular conditions, it can be reduced to two.

A superconductive magnetoresistive memory element using controlled exchange interaction

A memory device that can be switched between the normal state and superconducting state by an external magnetic field is proposed. The device consists of a superconducting/double magnetic (SM1M2) trilayer and is switched in a manner analogous to giant magnetoresistive memory devices. Using Usadel equations it is shown that the superconducting transition temperature of the device changes when the magnetic configurations of magnetizations of the two lower layers are switched between parallel and antiparallel. Appropriate design parameters are discussed and the materials issues analyzed.

Depolarization characteristics of ferroelectric Pb(Zr0.4Ti0.6)O3 and SrBi2Ta2O9 thin films

Abstract We evaluated depolarization characteristics of ferroelectric sol-gel Pb(Zr0.4Ti0.6)O3 and MOD (Metallo-Organic-Decomposition) Bi-layered SrBi2Ta2O9 thin-film capacitors derived by spin-on techniques with Pt electrodes. The evaluations were carried out for the extended experimental conditions, e. g., pulse height, pulse width, temperature, excess lead. Consequently, we found that the depolarization characteristics depended strongly on the capacitance of load capacitor. The newly obtained hysteresis loop during the pulse response indicates that sufficient field with opposite direction was generated on the ferroelectric capacitor at the moment the read pulse becomes zero. We experimentally found that the mechanism of depolarization is based on depoling (or partial switching) by an opposite-direction field arisen from accumulated switching charge on a load capacitor. This mechanism can be easily extended to the internal depolarization field due to the interfacial linear capacitor between the ferroelectric region and electrode.

Mode-locked pulse operation of GaAs/AlGaAs field effect transistor self-electro-optic effect device smart pixels and saturation considerations

The input/output ports of Smart Pixels are the optical signal receivers and transmitters. We have tested the simplest, lowest power dissipating, receiver-transmitter pair circuit with mode-locked (ML) laser pulses and find switching times as short as 200 ps. We also observe that the product of the set optical energy and switching time is a constant. In addition we present a comparison of the saturation properties of quantum well modulators when operated with short ML pulses, versus bit-period length pulses (quasi-continuous wave operation). Although the read pulse energy requirements of smart pixel optical signal transmitters are near saturation conditions, we conclude that with careful design, operation with short pulses, which gives the minimum switching time, should be possible.

Imprint testing of ferroelectric capacitors used for non-volatile memories

Abstract A set of criteria is presented, based on the polarization versus electric field hysteresis characteristics, which can be used to reveal a tendency towards imprint failure in ferroelectric capacitors. A series of pulsed voltage waveforms, generated by the RT66A ferroelectric tester, are utilized to validate our established criteria for the tendency towards imprinting. The tests have been performed on hetero-structure Pb(ZrxTi1−x)O3(PZT)-based capacitors produced by a pulsed laser ablation depositon technique (PLAD). The loss of retained charge in the ferroelectric capacitors is considered in light of the imprint test methodology. Rates of retention loss and imprint are extracted from the experimental data and treated as separate processes that lead to device failure. The rate of approach towards imprint failure is found to be influenced by the magnitude of the read pulse.

Ferroelectric Space Charge Non-Destructive Read-Out memory

Abstract The Ferroelectric Space Charge (FESC) Memory is a technique to achieve Non-Destructive Read-Out (NDRO) of a ferroelectric memory that employs standard metal-ferroelectric-metal memory capacitors. The NDRO technique allows the polarization state of the capacitor to be read without altering the polarization. This provides the advantage that the memory capacitor is not subjected to the destructive read/rewrite cycle commonly employed in ferroelectric memories, so the lifetime of the device is limited only by the number of times the memory is written. In addition, the NDRO avoids the period of data volatility in the time interval between the read pulse and the subsequent rewrite of the data. The FESC NDRO approach utilizes changes in the dielectric response of the ferroelectric due to interactions between the internal space charges, the spontaneous polarization, and internal and external electrical potentials. The NDRO is implemented entirely in circuitry and does not require specialized ferroelectri...

Detecting Proton Magnetization via 13C-Coupled Relaxation Studies

Abstract Two new pulse sequences are described for perturbing and observing previously neglected magnetization modes Via 13C- coupled relaxation experiments. These pulse sequences are used to study the AX2 spin system of [2-13C]glycine. Improved nonlinear least-squares fits of experimental data and additional insights into the relaxation of the spin system are realized by measuring the time evolution of the newly detected magnetizations via new read pulse sequences.