Atsushi Tsurumaki-Fukuchi

Resistive switching artificially induced in a dielectric/ferroelectric composite diode

Ferroelectric resistive switching was artificially induced in a conductive ferroelectric capacitor by inserting a thin dielectric layer at an electrode/ferroelectric interface. Ferroelectric capacitors consisting of semiconducting Bi-deficient Bi1−δFeO3 layers with SrRuO3 electrodes showed no resistive switching, but resistive switching emerged in these ferroelectric capacitors when a thin LaFeO3 dielectric layer was inserted at one of the SrRuO3/Bi1−δFeO3 interfaces. In addition to resistive switching, SrRuO3/LaFeO3/Bi1−δFeO3/SrRuO3 devices showed rectifying current–voltage characteristics, suggesting an asymmetric potential distribution along the stacking direction in the device. The results shed light upon the mechanism of resistive switching in ferroelectric diodes and demonstrate that interface engineering provides a simple but effective approach toward controlling the ferroelectric resistive switching characteristics.

Multilevel recording in Bi-deficient Pt/BFO/SRO heterostructures based on ferroelectric resistive switching targeting high-density information storage in nonvolatile memories

We demonstrate the feasibility of multilevel recording in Pt/Bi(1-d)FeO3/SrRuO3 capacitors using the ferroelectric resistive switching phenomenon exhibited by the Pt/Bi(1-d)FeO3 interface. A tunable population of up and down ferroelectric domains able to modulate the Schottky barrier height at the Pt/Bi(1-d)FeO3 interface can be achieved by means of either a collection of SET/RESET voltages or current compliances. This programming scheme gives rise to well defined resistance states, which form the basis for a multilevel storage nonvolatile memory.

Modeling of hysteretic Schottky diode-like conduction in Pt/BiFeO3/SrRuO3 switches

The hysteresis current-voltage (I-V) loops in Pt/BiFeO3/SrRuO3 structures are simulated using a Schottky diode-like conduction model with sigmoidally varying parameters, including series resistance correction and barrier lowering. The evolution of the system is represented by a vector in a 3D parameter space describing a closed trajectory with stationary states. It is shown that the hysteretic behavior is not only the result of a Schottky barrier height (SBH) variation arising from the BiFeO3 polarization reversal but also a consequence of the potential drop distribution across the device. The SBH modulation is found to be remarkably lower ( 0.5 eV). It is also shown that the p-type semiconducting nature of BiFeO3 can explain the large ideality factors (>6) required to simulate the I-V curves as well as the highly asymmetric set and reset voltages (4.7 V and −1.9 V) exhibited by our devices.

Resistive switching characteristics in dielectric/ferroelectric composite devices improved by post-thermal annealing at relatively low temperature

We have investigated the effects of post-thermal annealing on the resistive switching characteristics of dielectric/ferroelectric composite devices of SrRuO3/LaFeO3/Bi1−δFeO3/SrRuO3. Annealing of the devices above 85 °C enhanced the hysteresis of the current–voltage characteristics, resulting in an increase in the resistive switching ratio. After post-thermal annealing at 200 °C, devices with a thicker LaFeO3 layer exhibited a larger resistive switching ratio, and the device-to-device variation in the resistive switching ratio decreased as the LaFeO3-layer thickness was increased. The pulsed-voltage-induced resistive switching characteristics, such as the resistive switching ratio and the switching speed, were also improved by post-thermal annealing.

Ca doping dependence of resistive switching characteristics in ferroelectric capacitors comprising Ca-doped BiFeO3

We have investigated the transport and ferroelectric properties of ferroelectric capacitors comprising Ca-doped BiFeO3 (BFO) to elucidate the correlation between resistive switching and ferroelectricity. A capacitor consisting of Ca-doped (3.6 at. %) BFO film exhibited polarization–voltage hysteresis, indicating ferroelectricity of the film. As the Ca-doping ratio was increased, the leakage current increased, and zero-crossing hysteretic current–voltage characteristics, i.e., bipolar resistive switching, were observed in capacitors consisting of Ca-doped BFO films with doping ratios of 6.4–13 at. %. A capacitor consisting of a highly Ca-doped BFO (23 at. %) film showed neither resistive switching nor ferroelectric behavior. Distinct changes in the retention and pulsed-voltage-induced resistive switching characteristics were observed around a Ca-doping ratio of 9.0 at. %. The Ca-doping dependence of the resistive switching appeared to correlate with the ferroelectric phase diagram of the Ca-doped BFO films...

Capacitance evaluation of compact silicon triple quantum dots by simultaneous gate voltage sweeping

We propose a simple method to evaluate the triple quantum dots (TQDs) coupled in series with the compact device structure. Compact coupled quantum dots, each with an attached control gate, offer promising applications as quantum computing and single-electron transfer devices. However, device reduction required in practical applications creates a capacitive cross-talk between a control gate and its neighboring dots making it difficult to determine the charge transition boundaries in each dot. To properly evaluate the electron-transfer characteristics of TQDs, a method is proposed whereby the three gate voltages are simultaneously swept. We studied the charge stability diagram of the compact TQDs using Monte Carlo simulations, and confirmed the effectiveness of the method. Compact Si-TQDs were actually fabricated by the use of pattern-dependent oxidation and additional oxidation method for this study. The method was then applied to the stability diagrams obtained from the devices. The nine measurements of t...

Modeling of the I-V and I-t characteristics of multiferroic BiFeO 3 layers

We have investigated the current-voltage (I-V) and current-time (I-t) characteristics of Pt/BiFeO3/SrRuO3 structures fabricated on SrTiO3 substrates. The devices exhibit resistive switching effect under the application of a single and multiple voltage loops. The I-V curves are simulated using a Schottky-like conduction model with voltage-varying parameters. The model includes series resistance correction and barrier lowering effect. The I-t curves are fitted using a power-law model. It is found that the Schottky barrier height (SBH) modulation arising from the BiFeO3 polarization reversal is remarkably lower (<;0.07 eV) than previously reported (>0.5 eV) and that the ON current decay for a constant applied voltage is low and characterized by very small power exponent (~10-2). This indicates that the ON state is remarkably stable against electrical stress.