Junxiong Gao

Stress analysis and ferroelectric properties of Pb(Zr0.52Ti0.48)0.96Nb0.04O3 thin film grown on different thickness of BaPbO3 electrodes

Pb(Zr0.52Ti0.48)0.96Nb0.04O3 (PZTN) thin films were deposited on BaPbO3 (BPO) electrodes by rf-magnetron sputtering. 34, 68, 135, and 270 nm thick BPOs were adopted in this study. The preferred orientation changes from slightly (100)/(001) to slightly (101)/(110) as the BPO thickness increased. The mean grain sizes obtained by Williamson–Hall plots are 81 nm, 120 nm, 146 nm, and 90 nm, respectively. The same tendency was observed by atomic force microscopy method. In residual stress analysis, tensile stress was observed in every film. The stress magnitude is the maximum in the film with 135 nm thick BPO. Through a simple calculation, we suggest that the tensile stress in our films mainly originates from the phase transformation stresses. We also note that the ferroelectric and dielectrics properties are improved with the raise of tensile stresses. A possible reason is that the tensile stress benefits the tetragonal–monoclinic phase transition in the PZTN films with composition near morphotropic phase boun...

Modeling ferroelectric capacitors based on the dipole switching theory

In this paper, we derived a compact model for the description of the P–E hysteresis behavior based on the dipole switching theory. Simulation results show good agreement with the experiment for various hysteresis loops, and the mathematical description can be easily combined with an electronic design automation software for circuit simulation. Therefore, the model can be used for both circuit simulation and providing better intuition for the ferroelectric material behavior.

Ferroelectric properties of Pt∕PbTiO3∕PbZr0.3Ti0.7O3∕PbTiO3∕Pt integrated capacitors etched in noncrystalline phase

Uniformly patterned Pt∕PbTiO3∕PbZr0.3Ti0.7O3∕PbTiO3∕Pt capacitor arrays were etched in noncrystalline phase. The ferroelectric layer was well crystallized and contains uniform grains. The capacitors exhibit well-saturated hysteresis loop and excellent fatigue properties in terms of larger saturation polarization Pmax of 53.2μC∕cm2 at an applied voltage of 12V, higher remnant polarization Pr of 30.5μC∕cm2 for a coercive field of 58kV∕cm, remnant polarization of about 81.2% at 1010 switching cycles, and a low leakage current density of 10−8A∕cm2 at an applied voltage of 3V. The etching effects on the properties of capacitor were reduced to minimal values, confirmed by scanning electron microscope, energy-dispersive x-ray microanalysis, and piezoresponse force microscopy results. The reliable electric properties and fine profile of the patterns indicate that the capacitors are suitable for ferroelectric random access memories and other integrated ferroelectric devices.

THE OPTIMIZATION OF EXCESS Pb CONTENT IN SOL-GEL DEPOSITED SANDWICH STRUCTURE PbTiO3/PbZr0.3Ti0.7O3/PbTiO3 THIN FILMS

ABSTRACT The PbTiO3/PbZr0.3Ti0.7O3/PbTiO3 (PT/PZT/PT) and PbZr0.3Ti0.7O3 (PZT) thin films were prepared by sol-gel method. In order to optimize the excess Pb content in PT layers, different excess Pb content (x = 0, 0.05, 0.10, 0.15, 0.20) were added to the PT precursor to prepare the PT/PZT/PT films, and the films were annealed at 550∼700 °C for 20 min in O2 atmosphere. The X-ray diffraction (XRD) results show that the pure perovskite structure PT/PZT/PT films can be obtained from the proper Pb/Ti ratio precursor solution (excess Pb content x = 0.10 and 0.15 in PT layers) and annealing temperature of 600∼700 °C. The results of the P–E hysteresis loops indicate that the most proper annealing temperature is 650 °C. Well-saturated hysteresis loops with higher remnant polarization (Pr) and lower conceive field (Ec) are obtained for the film with excess Pb content x = 0.15 in PT layers. The fatigue and leakage current properties indicate that the PT/PZT/PT thin film with excess Pb content x = 0.10 has the lowest fatigue rate and less leakage current density than other films. Considering the results of XRD, ferroelectric, fatigue and leakage current properties, the optimized excess Pb content (x) in PT layers and annealing temperature should be x = 0.10∼0.15 and 650 °C, respectively.

EFFECT OF EXCESS Pb IN PT LAYERS ON MICROSTRUCTURE AND DIELECTRIC CHARACTERISTIC OF PT/PZT/PT THIN FILMS

ABSTRACT The Pb1 + xTiO3/PbZr0.3Ti0.7O3/Pb1 + xTiO3(PT/PZT/PT) sandwich structure thin films with different excess Pb content (x = 0, 0.05, 0.10, 0.15, 0.20) in PT precursor were prepared by sol-gel method. The XRD results show that the crystalline behave of PT/PZT/PT films is quite different to the PZT films, it is greatly affected by temperature and excess Pb content (x) in PT layers. The excess Pb content (x) in PT layers effects the crystallization of the formation of perovskite-phase of PZT layers through the effect of perovskite-phase formation of the PT layers. The SEM results showed that the dense and uniform of grain size surface morphology of PT/PZT/PT thin films annealed at 650°C appeared when the excess Pb cintent x = 0.05, 0.10 and 0.15. The results of ferroelectric, dielectric constant and dielectric loss characteristic of the films correlated obviously to the crystalline behaviors and excess Pb content(x) in PT layers. A higher remnant polarization and better dielectric constant and dielectric loss characteristic were obtained for the films of excess Pb content x = 0.10 and 0.15 in PT layers.

IN SITU INVESTIGATION OF RETENTION PROPERTIES OF POLYDOMAIN FERROELECTRIC THIN FILMS BY MULTIMODE SCANNING FORCE MICROSCOPY

ABSTRACT The domain structures and retention properties of the sandwich structure PT/PZT/PT thin films with pure perovskite structure, strong (111)-preferred orientation and excellent ferroelectric properties were investigated in situ by piezoresponse force microscope (PFM) and electrostatic force microscope (EFM) synchronously. The piezoresponse domain images and the profiles of piezoresponse with various times exhibit that the forward backswitching and the sidewise motion of the domain walls occurred synchronously in the backswitching of the written domain. The time-dependent surface potential images and line potential profiles show that the potential decay with time. The tendency of decay becomes slower as time goes on, and the highest decay rate is within the first 15 min.

AN INNOVATED PROCESS OF Pt/PbTiO3/PbZr0.3Ti0.7O3/PbTiO3/Pt INTEGRATED FERROELECTRIC CAPACITORS FOR FeRAM

ABSTRACT An innovated and the typical one-mask-patterned integrated ferroelectric capacitors process with Sol-Gel deposited technique are investigated. The key improvement for the innovated route is that the ferroelectric film was etched in non-crystalline phase. Due to the etching damage, the ferroelectric and fatigue properties of the typical integrated capacitor were degradation, and the desquamation of top electrode was also existed. The uniformly Pt/PbTiO3/PbZr0.3Ti0.7O3/PbTiO3/Pt (Pt/PT/PZT/PT/Pt) integrated ferroelectric capacitor arrays with explicit and smooth side-wall were obtained by the innovated integrated process. The XRD results exhibit that the innovated integrated ferroelectric capacitor was well crystallized, and the ferroelectric film belongs to the perovskite phase. The etching degradation on the properties of the innovated integrated ferroelectric capacitor was reduced to minimize, confirmed by SEM, EDX results, the ferroelectic and fatigue properties. The innovated process can be compatible with standard complementary metal oxide semiconductor (CMOS) technique. The reliable electric properties and fine profile of patterns indicate that it can be applied in the ferroelectric random access memories and other integrated ferroelectric devices.

THE DOMAIN STRUCTURE AND ELECTRIC PROPERTIES OF DOUBLE-SIDE SEED LAYERS PT/PZT/PT THIN FILMS

ABSTRACT The multilayer PbTiO3/PbZr0.3Ti0.7O3/PbTiO3(PT/PZT/PT) thin films were prepared by a Sol-Gel method on the Pt(111)/Ti/SiO2/Si(100) substrate for FeRAM application. The XRD patterns exhibits a perfect perovskite-phase with strong (111)-preferred orientation. The domain structures were investigated by scanning force microscopy. The out-of-plane polarization (OPP), in-plane polarization (IPP), the OPP amplitude and OPP phase images were obtained. The domain of the films has a complex structure with c-domain and deviated—c-domain which direction deviated from the vertical direction of surface of the film. The complex domain structure is related to the orientation of the crystal grains in the film. The results of ferroelectric, fatigue, dielectric and leakage current density indicate that the thin film has a better property. It has larger saturation polarization P max of 57.6 μ C/cm2 at an applied voltage of 10 V, higher remnant polarization P r of 32.3 μ C/cm2 for a the conceive voltage (Vc) of 2.5 V. After 1010 cycles, it still has more than 80% remnant polarization. The dielectric constants decreased with the frequency increased, and the decrease became slightly up to 1 MHz. The dielectric loss increased with the frequency increased, and there are no abrupt changes in the scan region. The leakage current mechanism of the thin film can be modeled in terms of SCLC theory.

A COMPACT MODEL FOR THE SIMULATION OF FERROELECTRIC CAPACITOR

ABSTRACT A compact model for description of the ferroelectric hysteresis loop behavior based on the dipole switching theory was derived. A cell of ferroelectric crystal is just as an equivalent dipole, so the hysteresis loop characteristic of ferroelecticity is the polarization characteristic of dipole in the electric field. The simulation results show good agreement with the experiment data for various hystersis loops. Therefore the model can be used for both circuit simulation and provide better intuition into the ferroelectric material behavior.

Fabrication and Characterization of Metal/Ferroelectric/Semiconductor Field Effect Transistor with the Ag/Bi4Ti3O12/p-Si(100) Structure

Metal-ferroelectric-semiconductor field-effect-transistors (MFS-FETs) with the Ag/Bi4Ti3O12/p-Si (100) structures were fabricated. The I-ds-V-g hysteresis curve of the FET shows the counter-clockwise direction, which demonstrates the charge of channel conductivity due to the ferroelectric polarization of Bi4Ti3O12 and the memory window with a gate voltage of +/-6V was 1.2 V. The current ratio of I-ds(on) to I-ds(off) was over two orders in magnitude at zero gate voltage which indicates the MFS-FET can be used in nondestructive readout (NDRO) applications.