Ferroelectric Memory Effect Research Articles

Bottom Contact 100nm Channel-Length α-In2 Se3 In-Plane Ferroelectric Memory.

Owing to the emerging trend of non-volatile memory and data-centric computing, the demand for more functional materials and efficient device architecture at the nanoscale is becoming stringent. To date, 2D ferroelectrics are cultivated as channel materials in field-effect transistors for their retentive and switchable dipoles and flexibility to be compacted into diverse structures and integration for intensive production. This study demonstrates the in-plane (IP) ferroelectric memory effect of a 100nm channel-length 2D ferroelectric semiconductor α-In2 Se3 stamped onto nanogap electrodes on Si/SiO2 under a lateral electric field. As α-In2 Se3 forms the bottom contact of the nanogap electrodes, a large memory window of 13V at drain voltage between ±6.5V and the on/off ratio reaching 103 can be explained by controlled IP polarization. Furthermore, the memory effect is modulated by the bottom gate voltage of the Si substrate due to the intercorrelation between IP and out-of-plane (OOP) polarization. The non-volatile memory characteristics including stable retention lasting 17 h, and endurance over 1200 cycles suggest a wide range of memory applications utilizing the lateral bottom contact structure.

Tristate ferroelectric memory effect attained by tailoring the ferroelectric behavior in Bi1/2(Na0.8K0.2)1/2TiO3 with Eu doping.

The ferroelectric behavior of Bi1/2(Na0.8K0.2)1/2TiO3 has been tailored by Eu3+ doping and the intermediate relaxor state is utilized for tristate ferroelectric memory effect. As Eu3+ content increases, the local structural disorder tends to get enhanced and the stability of ferroelectric order gets weakened. The disruption effect of Eu3+ is manifested structurally in XRD and PL spectra, and electrically in the ferroelectric, dielectric and piezoelectric properties. We found that the BNKT:3.0%Eu which owns a relaxor state under electrical cycle would be suitable for tristate ferroelectric memory, where two ferroelectric states and the relaxor state are respectively served as the "±1" and "0" memory states. We designed the verification experiments, and the results show good feasibility and stability. Moreover, it is innovative using PL spectra of Eu3+ to understand the structural changes related to different memory states, owning to its sensitivity to local structural symmetry. It also implies the possibility for non-destructive optical readout.

Ultrathin Piezoelectric Resonators Based on Graphene and Free-Standing Single-Crystal BaTiO3.

Suspended piezoelectric thin films are key elements enabling high-frequency filtering in telecommunication devices. To meet the requirements of next-generation electronics, it is essential to reduce device thickness for reaching higher resonance frequencies. Here, the high-quality mechanical and electrical properties of graphene electrodes are combined with the strong piezoelectric performance of the free-standing complex oxide, BaTiO3 (BTO), to create ultrathin piezoelectric resonators. It is demonstrated that the device can be brought into mechanical resonance by piezoelectric actuation. By sweeping the DC bias voltage on the top graphene electrode, the BTO membrane is switched between the two poled ferroelectric states. Remarkably, ferroelectric hysteresis is also observed in the resonance frequency, magnitude and Q-factor of the first membrane mode. In the bulk acoustic mode, the device vibrates at 233 GHz. This work demonstrates the potential of combining van der Waals materials with complex oxides for next-generation electronics, which not only opens up opportunities for increasing filter frequencies, but also enables reconfiguration by poling, via ferroelectric memory effect.

Tristate Ferroelectric Memory Effect Attained by Tailoring the Ferroelectric Behavior in Bi1/2(Na0.8k0.2)Tio3 with EU Doping

Tristate Ferroelectric Memory Effect Attained by Tailoring the Ferroelectric Behavior in Bi1/2(Na0.8k0.2)Tio3 with EU Doping

PEDOT-PSS nanoribbon and cast film field effect transistors with ferroelectric gating

Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) – PEDOT-PSS was electro-spun to produce high aspect ratio nano-ribbons. Individual nano-ribbons and cast films of varying thicknesses were electrically characterized in a field effect transistor configuration with ferroelectric poly(vinylidene fluoride-trifluoroethylene)-PVDF-TrFE as the gate insulator. The devices showed p-type behavior consistent with hole transport, and a ferroelectric memory effect. Thinner films exhibited stronger field effect compared to thicker films. As the thicknesses increased, relative changes in the gate induced currents decreased, while the threshold voltage and memory window width increased. The mobility was ∼0.5 cm2/V-s and the induced charge density was 2.3 x 1018/cm2 for the 10nm film device. A simple application of non-volatile charge storage was demonstrated via the use of ± 50V erase/write pulses applied to the gate. The device operated successfully with no degradation in the write/erase functionality, and is the first demonstrating a ferroelectric field effect in PEDOT-PSS thin films.

Tristate ferroelectric memory and strain memory in Bi1/2Na1/2TiO3-based relaxor ferroelectrics

Tristate ferroelectric memory and strain memory of Bi1/2Na1/2TiO3 (BNT)-based relaxor ferroelectrics are proposed. These memory effects can be realized in BNT-based materials with double-like P-E hysteresis loops and obvious non-zero remanent polarization. An underlying triple-well free-energy landscape, in which the relaxor state serves as an intermediate stable state between two ferroelectric remanent states, is thought to be responsible for such a ferroelectric behavior and provides the basis for the tristate ferroelectric memory effect. Besides, the strain memory effect utilizes the inherent strain difference between relaxor and ferroelectric states. Experimental verifications on Bi1/2(Na0.8K0.2)1/2(Ti0.955Fe0.030Nb0.015)O3 ceramics show that the tristate ferroelectric memory and the strain memory can be operated as proposed, and the programmability and the retention ability of both effects are fairly good. The present study provides a facile approach to the multistate ferroelectric memory and shape memory piezoelectric actuator applications.

Possible coexistence of cycloidal phases, magnetic field reversal of polarization, and memory effect in multiferroic R0.5Dy0.5MnO3 (R = Eu and Gd)

We report the occurrence of both ab and bc cycloidal ordering of Mn-spins at different temperatures and their possible coexistence at low temperatures in the polycrystalline mixed rare-earth compounds, R0.5Dy0.5MnO3 (R = Eu and Gd), which exhibit extraordinary magnetoelectric properties. While the polarization of Gd0.5Dy0.5MnO3 is comparable to TbMnO3, the compound Eu0.5Dy0.5MnO3 shows high value of polarization. However, both of them show giant magnetic tunability and exhibit large magnetocapacitance whose sign changes across the two cycloidal ordering temperatures. Intriguingly, the electric polarization can be reversed upon ramping up or ramping down the magnetic field, which has not been observed for any of the RMnO3 system. Most strikingly, these compounds show non-volatile ferroelectric memory effect even in the paraelectric and paramagnetic region (TC ≤ T ≤ 80 K). We attribute these remarkable properties to the coexistence of ab and bc cycloidal ordered phases.

Effects of Chemical Treatments on the Electrical Behaviors of Ferroelectric Poly(vinylidene fluoride-trifluoroethylene) Copolymer for Nonvolatile Memory Device Applications

Ensuring the sound ferroelectric behaviors of the ferroelectric copolymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] after various fabrication processes routinely performed for the device integration is very important for the practical nonvolatile memory applications using P(VDF-TrFE). In this work, the changes in the electrical and physical properties of the P(VDF-TrFE) thin film were investigated, assuming that some chemical treatments are involved in the fabrication processes for P(VDF-TrFE)-based memory devices. Although the treatments in the conventional developer and acids fortunately caused no critical damage to the film, it was found that the use of some resist strippers provides harsh conditions to the film. They caused the degradation in the crystallinity and surface roughness, and hence large increases in coercive field and leakage current were observed. Among the chemicals tested in this work, we proposed 1-methoxy-2-propanol as the best resist stripper. Metal–ferroelectric–metal capacitors and metal–ferroelectric–insulator–semiconductor diodes were also fabricated using the proposed patterning methods, in which no critical degradation in ferroelectric memory effects was observed when the size of capacitor decreased to 30 ×30 µm2. We conclude that these experimental studies can give us a useful solution to realizing memory arrays and related integrated circuits by exploiting P(VDF-TrFE)-based nonvolatile memory devices.

Microstructure and electrical properties of Ln 2Ti 2O 7 (Ln=La, Nd)

The effects of microstructure on the electrical properties of Ln 2Ti 2O 7 (Ln=La, Nd) films were investigated by depositing on Pt/Ti/Si and Y 2O 3/Si substrates using the sol–gel and spin-coating method. The films were crystallized at 800 °C in O 2 for 30 min in a tube furnace by direct insertion. According to the A-site cation, the different tendencies in ferroelectric properties between films and single crystals were observed. The ferroelectric parameters are: Pr=4.4 μC/cm 2, Ec=131 kV/cm for Nd 2Ti 2O 7 film; and Pr=1.8 μC/cm 2, Ec=75.28 kV/cm for La 2Ti 2O 7 film, respectively. C-V characteristics of Ln 2Ti 2O 7/Y 2O 3/Si structure were measured to investigate the ferroelectric memory effects at 1 MHz with a bias sweep rate of 0.18 V/s. The values of the memory window were 2.7 and 2.3 V for Nd 2Ti 2O 7 and La 2Ti 2O 7 films with 7 V of applied voltage, respectively.

Ferroelectric-gate field effect transistors using Nd 2Ti 2O 7/Y 2O 3/Si structures

Ferroelectric field effect devices offer the possibility of non-volatile active memory elements. In the metal–ferroelectric–semiconductor field effect transistor, it is important for a ferroelectric material to have a low dielectric constant to enable the application of sufficient electric field to a ferroelectric film. In this work, we report the fabrication and characterization of a ferroelectric-gate field effect transistor using Nd 2Ti 2O 7(NTO)/Y 2O 3/Si structures. The crystalline property of the film as a function of annealing temperature was characterized by X-ray diffraction. C– V characteristics were measured to investigate the ferroelectric memory effects at 1 MHz with a bias sweep rate of 0.18 V/s. As a result, the memory windows were in the range of 0.98–3.31 V when the applied voltage varied from 3 to 9 V. Specifically, we confirmed the ferroelectricity of crystallized NTO films.

Fabrication and characterization of Nd2Ti2O7 for ferroelectric field effect transistor

Ferroelectric field effect devices offer the possibility of nonvolatile active memory elements. In the metal-ferroelectric-insulator-semiconductor field effect transistor, it is important for a ferroelectric material to have a low dielectric constant to enable the application of sufficient electric field to a ferroelectric film. In this work, Nd2Ti2O? (NTO) films on CeO2/Si (100) were attained by sol-gel process. The crystalline property of the film according to annealing temperature was characterized by X-ray diffraction. C-V characteristics were measured to investigate the ferroelectric memory effects by HP4284A LCR meter at 1MHz with a bias sweep rate of 0.18V/s. As a result, the crystalline of NTO thin film on CeO2/Si(100) was developed from 700°C and perfect crystalline phase was obtained at 1000 °C. The memory windows were in the range of 0.2 to 2.5 V when the applied voltage varied from 3 to 9 V. And, the fact that C-V loops were caused by the ferroelectricity of NTO was confirmed by P-E characterization of Au/NTO/Pt structure.