Non-Linear Imprint Behavior of PZT Thin Films

Development of PZT sputtering method for mass-production

The results of the studies of the features of integrating the elements of nonvolatile ferroelectric random access memory (FRAM) with CMOS technology are presented. The possibility and prospects of using their nanosized layers in the elements of nonvolatile FRAM are demonstrated.

Summary form only given, as follows. Non-volatile ferroelectric random access memories (FRAMs) have widely studied for communication products and smart cards due to low operating voltage, fast switching speed, and nonvolatility. In recent years, high permittivity dielectrics have been studied intensively for ferroelectric random access memories (FRAM) owing to low operating voltage and fast switching speed and nonvolatility Bi-layered Bi/sub 4-x/La/sub x/Ti/sub 3/O/sub 12/ have been intensively studied.

Fabrication of Al0.01Ba0.99TiO3 (Al-BTO) thin films on SrTiO3/MgO/TiO2/SiO2/Si (STO/MgO) and MgO/TiO2/SiO2/Si (MgO) substrates were comparatively prepared using pulsed laser deposition (PLD). The structures of the prepared thin films were studied using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The SrTiO3 buffer layer between Al-BTO thin film and MgO substrate enhanced the ferroelectric, electrical properties. Moreover, the P-E loops showed a dramatic enhancement in the polarization values from 18 μC/cm2 at 600 kV/cm to 52 μC/cm2 at 780 kV/cm for Al-BTO thin films on SrTiO3/MgO and MgO substrates, respectively. In addition, the dielectric SrTiO3 buffer layer decreased the leakage current from 3 × 10−3 to 12 × 10−6 A/cm2 and increased breakdown electric field from 10 to 30 kV/cm. The electric properties revealed that, the dielectric SrTiO3 buffer layer also decreased the conductivity, mobility and carrier concentrations. The data of Al-BTO thin films on SrTiO3/MgO substrate exhibited remarkably adjusted polarization and leakage current indicating a good ferroelectric property for non-volatile ferroelectric random access memory (FERAM) applications.

(104)-oriented Bi4Ti3O12, La-substituted Bi4Ti3O12[(Bi3.44La0.56)Ti3O12] and Nd-substituted Bi4Ti3O12[(Bi3.54Nd0.46)Ti3O12] films were epitaxially grown on (111)SrRuO3//(111)SrTiO3 substrates at 700 °C by metalorganic chemical vapor deposition. All deposited films showed strong (104) orientations. The values of the remanent polarization (Pr) and coercive field (Ec) of the (104)-oriented epitaxial (Bi3.54Nd0.46)Ti3O12 thin film were 25 μC/cm2 and 135 kV/cm, respectively. This Pr value was larger than that of the (104)-oriented (Bi3.44La0.56)Ti3O12 film: Pr and Ec values of the (Bi3.44La0.56)Ti3O12 were 17 μC/cm2 and 145 kV/cm, respectively. These good ferroelectric properties of (Bi3.54Nd0.46)Ti3O12 films can be explained by a large tilting of TiO6 octahedra induced by the substitution of Nd3+, the ionic radius of which is smaller than that of La3+. Moreover, this Pr value is almost equal to that of commercially used lead zirconate titanate (PZT) films for nonvolatile ferroelectric random access memory (FeRAM) applications. These (104)-oriented epitaxial (Bi3.54Nd0.46)Ti3O12 thin films also showed a fatigue-free character. As a result, lead-free Nd-substituted Bi4Ti3O12 films with good ferroelectric properties comparable with those of PZT films are useful candidates for FeRAM applications.

The number of publications and scientific meetings in the field of ferroelectricity has been increasing exponentially in the last 30 years. In addition to the classical fields of phase transitions and critical phenomena four new sub fields have emerged: a) ferroelectric liquid crystals, b) thin films and integrated ferroelectrics which led to the discovery of 2D ferroelectricity and the development of non-volatile ferroelectric random access memory, c) dipolar glasses and relaxors as well as d) incommensurate systems. Quantum effects have been observed as well.

Raman scattering has proven to be extremely useful for studies of phase transitions in ferroelectric materials and, in particular, as a tool to characterize soft modes [1] and features related to order-disorder phenomena [2]. The dynamical behavior of phase transitions and their sensitivity to temperature and doping can be easily elucidated by Raman scattering measurements [3–5]. The perovskite (ABO3) ferroelectric materials in thin-film form are of considerable interest, particularly for non-volatile ferroelectric random access memory and microwave devices. The ferroelectric properties depend strongly on film preparation, chemical composition and microstructures (crystal structures, orientation, grain size, domain structure, and surface roughness). Micro-Raman scattering from ferroelectric thin films provides a useful link between the phonon spectrum and the microstructure of the film.

With the significant innovation and rapid development of the nonvolatile ferroelectric random access memory devices (FeRAMs), many efforts have been done to research and develop the ferroelectric films. Bismuth layer-structured ferroelectrics, such as lanthanum-doped bismuth titanate, have been paid a lot of attentions for their super properties. Temperature and ultraviolet irradiation, two of the important factors which can affect the properties of films, have been attracted much attention. In this paper, we mainly investigated the annealing temperature and the ultraviolet irradiation effect on the ferroelectric properties of Bi3.25La0.75Ti3O12 (BLT) thin films.

New electrode materials (Ir and IrO/sub 2/) are proposed for high-density nonvolatile ferroelectric random access memories (NVFERAMs). These electrodes are used in order to integrate ferroelectric (SrBi/sub 2/Ta/sub 2/O/sub 9/) capacitors with standard CMOS technology. Excellent electrical characteristics (e.g. low leakage and high polarization), good fatigue resistance and good mechanical properties (i.e. excellent adhesion to SiO/sub 2/ without using a glue layer) were obtained for the new capacitor structures.

Robust in-plane polarization switching in epitaxial BiFeO3 films

Effects of annealing atmosphere on microstructure and ferroelectric properties of praseodymium-doped Bi 4Ti 3O 12 thin films prepared by sol–gel method

A facile synthesis of Al-doped BaTiO3 thin films by a hydrothermal-galvanic couple method on TiAlN film electrodes

The integration of thin film ferroelectrics with silicon processing is being implemented for various types of devices. The technology is based on the sputtering or chemical deposition of lead-based perovskites such as lead zirconate titanate. Factors concerned with the integration of ferroelectric films with semiconductor processing are described. Major interests in Canada include nonvolatile ferroelectric random access memories for high-speed digital or long-term analog memory applications, high-density capacitors, electro-optic switches, and a wide range of sensors and actuators integrated into silicon.

Ferroelectric Ce-doped Bi₄Ti₃O₁₂ (BCT) thin films were deposited by liquid delivery metal organic chemical vapor deposition (MOCVD) onto a Pt(111)/Ti/SiO₂/Si(100) substrate. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the crystal structure, the surface, and the cross-section morphology of the deposited ferroelectric films. After annealing above 640℃, the BCT films exhibited a polycrystalline structure with preferred (00l) and (117) orientations. The BCT film capacitor with a top Pt electrode showed a large remnant polarization (2P r ) of 44.56 μC/㎠ at an applied voltage of 5 V and exhibited fatigue-free behavior up to 1.0×10¹¹ switching cycles at a frequency of 1 ㎒. This study clearly reveals that BCT thin film has potential for application in non-volatile ferroelectric random access memories and dynamic random access memories.

Ferroelectric (PBZ) thin films with different ratio were fabricated by a sol-gel process. Electrical properties of PBZ films on substrates (metal/ferroelectric/metal structure) and on substrates metal/ferroelectric/insulator/semiconductor (MFIS) structure were investigated. The dielectric and ferroelectric properties depend greatly on the ratio of the PBZ films. For the MFIS structure, the film shows the best memory property with memory window of when it was scanned at . Experimental results demonstrate that ferroelectric PBZ films with -buffered MFIS structure is suitable for non-volatile field effect transistor-type ferroelectric random access memory applications.