Ferroelectric Diodes Research Articles

Development of a ferroelectric cathode diode

As a promising kind of high current cold cathode, the Ferroelectric Cathode (FEC) has several significant advantages, such as a controllable trigger time, lower vacuum requirement and large emitting area fabricability. The emitting current density of the FEC fabricated at Tsinghua University was more than 200 A/cm2. In order to make the ferroelectric cathode into practical applications, a high current density diode using a ferroelectric cathode was designed, based on the PIC simulation. The performance of the FEC diode was investigated experimentally. When the applied diode voltage was 60 kV, a current density of more than 250 A/cm2 was obtained, and the current density distribution was also measured.

Memristive behaviors of LiNbO3 ferroelectric diodes

Memristive systems are expected to lead to analog computers that process information the way the human brain does. In this work, memristive behaviors have been revealed in ferroelectric diodes employing LiNbO3. The conduction states in such diodes can be continually modulated by the successive voltage sweeps, which is essentially based on electron tunneling through a thin residual barrier. The role of oxygen vacancies in such memristive behaviors is also discussed.

Organic Nonvolatile Memory Devices Based on Ferroelectricity

A memory functionality is a prerequisite for many applications of electronic devices. Organic nonvolatile memory devices based on ferroelectricity are a promising approach toward the development of a low-cost memory technology. In this Review Article we discuss the latest developments in this area with a focus on three of the most important device concepts: ferroelectric capacitors, field-effect transistors, and diodes. Integration of these devices into larger memory arrays is also discussed.

Spin selector by ferroelectric triple barrier resonant tunneling diode

We propose a spin selector of ferroelectric triple barrier resonant tunneling diode with diluted magnetic quantum wells. Spin transport properties of this spin selector are investigated by nonequilibrium Green’s function method. Results show the oscillation of spin polarization of current occurred at low bias voltage due to a transmission resonant peak splitting into subpeaks. By reversing the electric dipole direction of ferroelectric barriers, the spin direction of polarized current is reversed simultaneously at a fixed bias voltage. This implies that the spin direction of injected current can be selected through this spin selector without changing the applied magnetic field.

Spin polarization switched by a ferroelectric resonant tunneling diode

The spin transport through a resonant tunneling diode with a ferroelectric quantum well is studied by nonequilibrium Green’s function method. The results show that the spin polarization can be switched by changing the dipole direction of the ferroelectric quantum well in a resonant tunneling diode. At a special bias, the authors can get highly spin polarized current or evenly spin mixed current depending on the dipole direction.

Shifting intrinsic bistability states in a ferroelectric resonant tunneling diode

The intrinsic bistability state in a resonant tunneling diode (RTD) with a ferroelectric quantum well is investigated by using the nonequilibrium Green's function. The results show that the bistability states can be shifted with switching the polarization direction of ferroelectric quantum well. The electronic properties of the RTD are very sensitive to the ferroelectric polarization. A very small polarization $0.01\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{C}∕{\mathrm{cm}}^{2}$ can produce a predominant peak shift.

Low-voltage operation of ferroelectric poly(vinylidene fluoride-trifluoroethylene) copolymer capacitors and metal-ferroelectric-insulator-semiconductor diodes

Exceptionally low-voltage operation of organic ferroelectric capacitors and diodes was demonstrated. Ferroelectric polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE)] thin films were prepared by the solvent-cast method. Metal-ferroelectric-metal capacitors with 60-nm-thick P(VDF-TrFE) films exhibited well-saturated hysteresis curves whose coercive voltage (Vc) and remanent polarization (Pr) were 2.0V and 11.9μC∕cm2, respectively. The authors also fabricated metal-ferroelectric-insulator-semiconductor diodes with 100-nm-thick P(VDF-TrFE) films. Rectangular-shaped capacitance-voltage (C-V) hysteresis loops were obtained with a voltage sweep range narrower than 5V. The maximum memory window of 4.7V was achieved.

PREPARATION AND ELECTRICAL PROPERTIES OF Pt/ZrO2/Si AND Pt/PLZT/ZrO2/Si STRUCTURES

ABSTRACT Pt/ZrO2/Si and Pt/PLZT/ ZrO2/Si ferroelectric diode structures Using ZrO2 and PLZT(Pb1.05La0.02Zr0.53Ti0.47O3) as dielectric and ferroelectric materials respectively are prepared in this work by CSD method. The P-E curves of PLZT film under different applied voltage are measured which show remnant polarization is about 10 μC/cm2 and coercive voltage is 1.5 V. The I-V curves of Pt/ZrO2/Si structure show low leakage current and moderately high breakdown electric field. The leakage current density under 1 MV/cm electrical field is 2.5 × 10−5 A/cm2 and the breakdown electrical field is about 8.2 MV/cm. The effects of applied voltage and ZrO2 thickness on C-V curves are also investigated. The results indicate 1.5 V memory window under 9 V applied voltage. The I-V characteristic and current difference under “on” and “off” states of Pt/PLZT/ZrO2/Si MFIS structure are also discussed. After applied a writing voltage of +10 V for state “1” and −10 V for state “0,” the read current difference is 0.2 mA under 4 V read voltage.

Non-volatile memory cells based on ZnxCd1−xS ferroelectric Schottky diodes

Ferroelectric Schottky diodes were fabricated with n-type Zn0.4Cd0.6S. These devices show promising nonvolatile memory properties and the integration into complementary metal-oxide-semiconductor (CMOS) circuits seems feasible. So far, we have demonstrated on-resistances down to 100 Ω, on/off ratios up to 107, switching voltages below 100 mV, operating temperatures up to 180 °C, and switching times below 50 ns. The devices can be deposited at low temperatures (200 °C) by conventional rf-sputtering and survive the 30-min anneal at 400 °C in forming gas, which is mandatory in CMOS processing.

Reliability of Au/PZT/BIT/p-Si ferroelectric diode

A ferroelectric memory diode that consisted of Au/PZT/BIT/p-Si multilayer configuration was fabricated by pulsed laser deposition (PLD) technique. The reliability issues (I–V characteristics, capacitance retention, fatigue and imprint) were investigated. The I–V curve showed the conventional Schottky diode characteristics with a small current density of −5.3×10−10 A/cm2 at a voltage of −4 V and 6.7×10−8 A/cm2 at a voltage of +4 V, and this characteristic can be maintained below 50°C. The capacitance variety of the ferroelectric diode was only 5% in 10 hours after withdrawing the applied bias of +5 V or −5 V, indicating the diode had good capacitance retention. By applying 100 kHz bipolar pulses of 5 V amplitude, the decay in remanent polarization was only 10% after 109 switching cycles, and meanwhile the increase in coercive field was 12%. After being irradiated for 20 min with a 200 W ultraviolet ray lamp, the remanent polarization and coercive field had both varied, and a voltage shift was observed, but the figure of merit FOM was about 0.2 and the diode had no imprint invalidation.

Current Pulse Shaping in Electron Gun Using Ferroelectric Cathode

We have operated an electron gun using a ferroelectric cathode at a diode voltage of 450 kV. The beam current and its waveform have been studied under various triggering conditions. Adjusting the amplitude and applied timing of the trigger pulse has led to a unique method of current pulse shaping for the ferroelectric diode. The method is convenient and the beam current with a reasonable pulse shape is achievable even with a relatively poor condition of the voltage pulse. Optimum conditions for applying the trigger pulse have been determined and the beam current with the required shape is obtained.

Memory characteristics of Au/PZT/BIT/p-Si ferroelectric diode

A ferroelectric memory diode consisting of Au/PZT/BIT/p-Si multilayer configuration has been fabricated by pulsed laser deposition (PLD) technique. The ferroelectric properties and the memory characteristics are investigated. The P-E curve of the PZT/BIT/p-Si films system had an asymmetry saturated hysteresis loop withP t=15 μC/cm2 andE c=48 kV/cm, and the decay in remanent polarization was only 10% after 109 switching cycles, meanwhile the increase in coercive field was 12%. The C-V hysteresis loop and the I-V curve showed a memory effect derived from the ferroelectric polarization of PZT/BIT films, and the current density was 6.7×10−8 A/cm2 at a voltage of +4V. Our diode had nonvolatile and nondestructive memory readout operation. There was a read current disparity of 0.05 μA for logic “1” and logic “0” at a read voltage of +2V, and the stored logical value (“1” or “0”) could be read out in 30 min.

Fabrication and characteristics of Au/PZT/BIT/p-Si ferroelectric memory diode

A ferroelectric memory diode that consisted of Au/PZT/BIT/p-Si multilayer configuration was fabricated. The Pb(Zr 0.52Ti 0.48)O 3 (PZT) ferroelectric films with a c-axis oriented Bi 4Ti 3O 12 (BIT) buffer layer were deposited on a p-Si(1 0 0) substrate by pulsed laser deposition technique. The ferroelectric characteristics and the electrical characteristics were measured respectively. The results suggested that the growth of the BIT ferroelectric layer was helpful to increase the memory window and to reduce the current density by impairing the serious interaction and interdiffusion at the ferroelectric/Si interface. The C–V hysteresis loop showed a memory effect due to the ferroelectric polarization of PZT/BIT films. The I–V curve was Schottky-diode-like and had a hysteresis loop due to the ferroelectric remanent polarization. We confirmed our diode had nonvolatile and nondestructive memory readout operation. After applied a writing voltage of +5 V for logic “1” and −5 V for logic “0” respectively, the reading currents were 0.1 and 0.05 μA at a reading voltage of +2 V correspondingly.

Design of Ferroelectric Diode for High-Current Matched Electron-Beam Generation

An electron gun using a ferroelectric cathode with a two-stage compression system has been designed. The performance of the beam generated by the gun has been investigated by simulation and experiment. When the applied diode voltage is 440 kV, a beam current of 230 A is obtained. The waveform of the beam current follows the diode voltage reasonably well, and their flat top overlaps for about 200 ns. Faraday cup measurement shows that the beam radius is 4.1 mm after second-stage compression, and the axial variation of the beam radius has been minimized.

Properties of Au/Pb(Zr0.52Ti0.48)O3/ Bi4Ti3O12/p-Si Ferroelectric Memory Diodes

AbstractA ferroelectric memory diodes that consists of Au/Pb(Zr0.52Ti0.48)O3/Bi4Ti3O12/p-Si multilayer configuration was fabricated by pulsed laser deposition (PLD) technique. The ferroelectric properties and the electrical characteristics of the ferroelectric film system were investigated. The polarization-voltage curve of Pb(Zr0.52Ti0.48)O3/Bi4Ti3O12 thin films system had an asymmetry hysteresis loop with Pr=20μC/cm2 and Ec=48 kV/cm, and the decay in remnant polarization was only 10% after 109 switching cycles. The C-V curve and the I-V curve showed memory effects derived from the ferroelectric polarization of PZT/BIT films. The current density was 6.7×10−8A/cm2 at a voltage of +4V, and the conductivity behavior is discussed. The results suggested that the growth of the BIT ferroelectric layer is helpful to good ferroelectric properties, fatigue and capacitance retention characteristics.

New Optical Logic Gates using Liquid Crystal Optical Diodes

New optical logic gates have been fabricated by stacking two ferroelectric liquid crystal optical diodes (LC-ODs) fabricated by polymer stabilization. The device exhibits a strong asymmetric electrooptic performance; for this reason, the device is referred to as a liquid crystal optical diode. The liquid crystal logic gates fabricated by stacking two LC-ODs are shown to enable the performance of logic calculations, such as AND, NAND, OR, XOR, and XNOR.

Electron emission from lead–zirconate–titanate ceramics

We report extensive experimental data on electron emission from lead–zirconate–titanate ferroelectric ceramics. A 1–2 MV/m pulse is applied to a gridded ferroelectric cathode and diode currents of up to 120 A/cm2 are measured across an A–K gap of 5×10−2 m, with the anode at 35 kV. Both the current and the anode voltage pulse duration may extend to several microseconds. The measurements extend previously reported data by nearly two orders of magnitude in the diode voltage and by a factor of more than 3 in the diode spacing. Two major regimes of operation were identified. In the first ∼1 μs the ferroelectric cathode controls the electron flow through the diode. Beyond this time plasma effects dominate the current flow. The results are of importance to the development of novel cathodes for high current electron beam generation.

High dielectric permittivity ionic materials for dram's designed by computer simulation

By a simulated annealing Monte Carlo (MC) method the relative dielectric permittivity as a function of applied external electric field is determined for the cubic perovskite structure NaCaF3 at 475K and 300K. In this work, particular attention is focused on designing ionics with exceptionally high zero-field dielectric constants for maximizing storage capacity in ferroelectric memories. Dielectric permittivity vs. applied electric field data are in qualitative agreement with those obtained experimentally for a ferroelectric Schottky diode.

Memory effects in ferroelectric/perovskite-semiconductor hetero-structures

Abstract Epitaxial ferroelectric heterostructures are proposed which used parent phase of the cuprate high-T c superconductors and the related perovskite semiconductors. Properties of prototy8pe field effect transistor (FET) and diodes employing this structures are presented. The FETs markedly improved the memory retention time over the conventional ferroelectric FETs. It retained one-half of the initial modulation after 10 months. Additionally, they exhibited switching time of 10–100 μs at 7 V despite their large feature sizes (100 μm). A new memory effects was found in ferroelectric diodes consisted of several combinations of ferroelectric and perovskite semiconductors. Their conductivity in the forward bias was reproducibly switched between high and low values by positive and negative biases.

Ferroelectric Schottky diode.

A Schottky contact consisting of a semiconducting ferroelectric material and a high work function metal shows a bistable conduction characteristic. An on/off ratio of about 2 orders of magnitude was obtained in a structure consisting of a 0.2 \ensuremath{\mu}m ferroelectric PbTi${\mathrm{O}}_{3}$ film, a Au Schottky contact, and a ${\mathrm{La}}_{0.5}$${\mathrm{Sr}}_{0.5}$Co${\mathrm{O}}_{3}$ Ohmic bottom electrode. The observations are explained by a model in which the depletion width of the ferroelectric Schottky diode is determined by the polarization dependence of the internal electric field at the metal-ferroelectric interface.