Pulse-Extended Excimer Laser Crystallisation of Pb(Zr,Ti)O 3 Thin Films for Integration on Low Thermal Budget Substrates

Excimer laser annealing has been used to convert low temperature (non-ferroelectric) deposited lead zirconate titanate (PZT) to the perovskite phase without significantly heating underlying layers. A pulse-extension technique has been used to lengthen the laser pulse duration from 25 ns to 374 ns, lowering the surface temperature and improving the heat distribution in the PZT, as compared to the non-extended case, but still not significantly heating the substrate. Initial experiments are reported which have shown the technique to be capable of crystallising over half a 500 nm thick PZT film to perovskite although a melting effect limited the converted thickness. The thickness crystallised is however of the order of that used in FeRAM devices and modelled temperature profiles suggest that the technique provides a tractable solution for high temperature processing of ferroelectric thin films of thickness 200-300 nm on low thermal budget substrates.     

Slow Dielectric Relaxation in Pb(Zr,Ti)O3 and (Ba,Sr)TiO3 Ferroelectric Thin Films

An impedance analysis of Ni/Pb(Zr,Ti)O₃/Pt thin-film structures based on measurements at the frequencies from 100 Hz to 100 MHz, along with the data of Grazing Angles XRD, TEM and photo-electric study, is used to obtain electronic structure of the PZT thin films deposited by sol-gel method on silicone substrates. Both slow capacitance relaxation and charging/discharging currents versus time under step-voltage excitation have been studied in (Ba,Sr)TiO₃ thin films between SrRuO₃ electrodes.     

Resistive Switching and Current Conduction Mechanisms in Amorphous LaLuO3 Thin Films Grown by Pulsed Laser Deposition

The unipolar resistive switching characteristics of the amorphous LaLuO₃ thin films deposited by pulsed laser deposition have been studied. Reliable and repeatable nonvolatile switching of the resistance of LaLuO₃ films was obtained between two well defined states of low and high resistance with nearly constant resistance ratio ～10⁷ and non-overlapping switching voltages in the range of 0.66-0.83 V and 1.9-2.7 V respectively. The temperature dependent measurement revealed metallic and semiconducting behavior in low and high resistance states respectively. The switching between low and high resistance states was attributed to the change in the separation between oxygen vacancies in light of the correlated barrier hopping theory. The current conduction mechanism of the device in high-resistance state followed the Poole's law, whereas the conduction in low-resistance state was found to be dominated by percolation. The resistance of low and high resistance states of the film showed no obvious degradation for up to ～10⁴ seconds indicating good retention. The achieved characteristics of the resistive switching in LaLuO₃ thin films seem to be promising for futuristic nonvolatile memory applications.     

Effect of AC&DC Field on the Dielectric Response of (Pb,La)TiO3 Thin Films

Lanthanum doped lead titanate thin films are the potential candidates for the capacitors, actuators and pyroelectric sensor applications due to their excellent dielectric, and ferroelectric properties. Lanthanum doped lead titanate thin films are grown on platinum coated Si substrates by excimer laser ablation technique. A broad diffused phase transition with the maximum dielectric permittivity (?_max) shifting to higher temperatures with the increase of frequency, along with frequency dispersion below T_c, which are the signatures of the relaxor like characteristics were observed. The dielectric properties are investigated from ?60°C to 200°C with an application of different dc fields. With increasing dc field, the dielectric constant is observed to reduce and phase transition temperature shifted to higher temperature. With the increased ac signal amplitude of the applied frequency, the magnitude of the dielectric constant is increasing and the frequency dispersion is observed in ferroelectric phase, whereas in paraelectric phase, there is no dispersion has been observed. The results are correlated with the existing theories.     

Study of Thickness Dependence on Electrical Properties of (Pb,La)TiO 3 Thin Films for Memory Applications

Lead-lanthanum- titanate (Pb 0.72 La 0.28 ) TiO 3 (PLT) is one of the interesting materials for DRAM applications due to its room temperature paraelectric nature and its higher dielectric permittivity. PLT thin films of different thickness ranging from 0.54- 0.9 w m were deposited on Pt coated Si substrates by excimer laser ablation technique. We have measured the voltage (field) dependence, the thickness dependence, temperature dependence of dc leakage currents and analysis is done on these PLT thin films. Current- voltage characteristics were measured at different temperatures for different thick films and the thickness dependence of leakage current has been explained by considering space charge limited conduction mechanism. The charge transport phenomena were studied in detail for films of different thicknesses for dynamic random access memory applications.     

Pb(Zr,Ti)O3 thin film growth on yttrium-treated Si(100)

Abstract

Pulsed laser ablation has been used to deposit ferroelectric Pb(Zr, Ti)O₃ (PZT) thin films on Si(100) and on yttrium-treated Si(100) substrates. The yttrium (Y) treatment of a Si surface followed by oxidation resulted in formation of a very thin, Y-enhanced SiO₂ antidiffusion barrier layer, thereby suppressing the undesirable PZT/Si interdiffusion. The best PZT film grown on Y-treated Si(100) had a breakdown voltage of 0.6 MV/cm, a coercive field of 71 KV/cm, and a remanent polarization of 18 μC/cm².     

Microwave Tunable Properties of Ni-Doped (Ba0.5Sr0.5)TiO3 Thin Films Grown by Pulsed Laser Deposition

(Ba_0.5Sr_0.5)TiO₃ (BST) thin films were deposited by pulsed laser deposition (PLD) and investigated as a function of Ni dopant concentration in low and high frequency regions. In low frequency region (<10 MHz), the Ni-dopant concentration in BST films has a strong influence on the material properties including dielectric and tunable properties. Ni-doped (≤3 mol%) BST films showed denser, smoother morphologies and smaller grain sizes than those with 6 and 12 mol% Ni. Dielectric constant and loss of 3 mol% Ni-doped BST films were about 980 and 0.3%, respectively. In addition, tunability and figure of merit of 3 mol% doped BST films showed maximum values of approximately 39% and 108, respectively. In high frequency region (>1 GHz), the frequency tunability range at center frequency of undoped BST and 3 mol% Ni-doped BST coplanar waveguide (CPW) resonators showed 102 and 152 MHz, respectively at 30 V dc bias. The Ni-doped BST thin films are possible in applications of microwave tunable capacitors.     

Pulsed Laser Deposition of Ba0.6Sr0.4TiO3 Thin Films and Their Optical Properties

ABSTRACT

Barium strontium titanate [Ba_0.6Sr_0.4TiO₃ or BST (60/40)] thin films were deposited on MgO (100) substrates using pulsed laser deposition. X-ray diffraction (XRD) measurements revealed that the BST thin films had epitaxially grown on the MgO (100) substrates. The surface morphology of the thin films was observed using an atomic force microscope and the grain size was found to be about 100–150 nm. The surface roughness was around 4.9 nm for a 250 nm thick film. The optical transmittance of the BST thin film was measured using a transmission mode ellipsometer. The BST/MgO configuration was highly transparent in the visible region. The optical band gap energy of the BST film, calculated by applying the Tauc relation, was 3.56 eV. Optical waveguide characteristics of the BST (60/40) thin film were determined using a prism coupler. The electro-optic (E-O) properties were measured at 632.8 nm wavelength using a phase modulation detection method. The BST film exhibited a predominately quadratic E-O behavior and the quadratic E-O coefficient was found to be 0.58 × 10^{? 17} m²/V².     

Pulsed Laser Deposited Ba(Mg1/3Ta2/3)O3 Microwave Dielectric Thin Films

Ba(Mg_1/3Ta_2/3)O₃ (BMT) microwave dielectric thin films were successfully synthesized by a modified pulsed laser deposition (PLD) process, which includes low temperature (200°C) deposition and high temperature (>500°C) annealing. Crystalline structured BMT thin films were obtained when the PLD-deposited films were post-annealed at a temperature higher than 500°C in oxygen atmosphere. The characteristics of BMT thin film, including crystallinity, grain size, film roughness, and dielectric properties were improved with annealing temperature, achieving dielectric constant K = 23.5 and dissipation factor tan δ = 0.015 (at 1 MHz) for the 800°C-annealed films.     

Growth,Microwave Properties and Microstructure of Ba0.05Sr0.95TiO3 Thin Films

Charged defects were found to have a significant influence over the microwave properties of Ba_0.05Sr_0.95TiO₃ thin films.     

Structure and properties of sol-gel processed (Pb,La)TiO3 ferroelectric thin films

Abstract

The influence of heat treatment and substrate materials on PLT thin films by sol-gel processing has been researched. Epitaxial growth PLT thin films with perovskite-type structure on sapphire, SrTiO₃ and MgO single crystal substrates have been prepared. The epitaxial relations are (100)PLT28/(100)SrTiO₃, (111)PLT28//(0001)sapphire and (100)PLT14//(100)MgO. The PLT polycrystal thin films with perovskite-type structure on Si single crystal and quartz glass substrates have been prepared. The remanent polarization Pr and the coercive field Ec of PLT15 ceramic thin films are 7.7 μc/cm² and 34 kv/cm at 4 KHz respectively. The optical transmittance of PLT28 ceramic thin films within the wavelength range of λ = 500–1000 nm is approximately 80%.     

Interface Structures and Epitaxial Behavior of Ferroelectric (Ba,Sr)TiO 3 Thin Films

Perovskite Ba 0.6 Sr 0.4 TiO 3 thin films were epitaxially grown on (001) LaAlO 3 and (001) MgO by using pulsed laser ablation. The films are single crystal cubic structure with interface relationship of (001) BST // (001) MgO and <100> BST // <100> MgO for the films on (001) MgO and (001) BST // (001) LAO and <100> BST // <100> LAO . High-resolution transmission electron microscopy studies indicated that the initially grown layer of the film on both (001) MgO and (001) LAO is TiO 2 monolayer. Equally spaced misfit dislocations were found to form at the interface to release the lattice mismatch energy. Physical property measurements show that the films exhibit excellent room temperature dielectric behavior with very low dielectric loss of 0.007 and very large tenability of 45% at 1 MHz. The figure of merit of 60°/dB has been achieved for the microwave phase shifter operated at 24 GHz and room temperature.     

Optical Waveguiding Properties of (Pb,La)TiO3/Al2O3 Planar Structures

Thin films of lead lanthanum titanate (Pb,La)TiO₃ have been grown by radio-frequency magnetron sputtering on (0001) Al₂O₃ substrates. The structure, the microstructure and the optical properties of the films have been investigated as a function of the postdeposition annealing. Films deposited at low temperatures crystallize to a perovskite phase after the annealing treatment from 500°C to 650°C. X-ray (–2) diffraction studies have shown that films are crystallized with a strong (111) orientation and the best crystalline structure is reported at 600°C. The optical properties were both demonstrated by spectrophotometry and prism coupling. PLT thin films with a transparency of 80% in the wavelength range 300–2000nm have exhibited a refractive index of 2.38 @ 632.8nm representing 97% of the bulk corresponding material. Investigation of optical propagation has been accomplished in a 10mm long planar optical waveguide using a butt-coupling configuration.     

Growth of (Ba,Sr)TiO 3 Thin Films by MOCVD: Stoichiometry Effects

(Ba x Sr 1 m x )TiO 3 thin films were deposited in a planetary multi-wafer MOCVD reactor combined with a liquid delivery system using 0.35 molar solutions of Ba(thd) 2 and Sr(thd) 2 and a 0.4 molar solution of Ti(O-i-Pr) 2 (thd) 2 . The film growth on Pt-(111) was investigated within a wide parameter field, e.g., the deposition temperature was varied between 560C and 650C, which yields films with microstructures ranging from randomly oriented polycrystalline to perfectly (100)-textured columnar structures. Special emphasis is given to film stoichiometry: starting with (Ba 0.7 Sr 0.3 )TiO 3 the Group-II/Ti content was varied from 0.9 to 1.1 and the Ba content was reduced to the limit of pure SrTiO 3 films. The electrical properties of MIM structures were investigated after deposition of Pt top electrodes. The nominal thickness of the films was varied between 5 and 100 nm and permittivity and leakage current both are shown to depend strongly on the film thickness. These dependencies on the film thickness are analyzed within the phenomenological dead layer model. The dependence of the electrical properties on stoichiometry are discussed in detail.     

Structure of Ferroelectric (Ba,Sr)TiO3 Thin Films for Tunable Microwave Devices

Ferroelectric (Ba,Sr)TiO₃ films have been deposited on (001) MgO single crystals by a pulsed laser deposition with oxygen background while heating the substrates. Deposited BST films exhibit epitaxial growth along (001), which are confirmed by x-ray diffraction measurement. Structure of (Ba,Sr)TiO₃ along in-plane and surface normal direction have been investigated and found to have a tetragonal distortion depend on the deposition conditions, such as oxygen pressure. Lattice parameter decreases with increasing oxygen pressure, and tetragonallity (c/a) changes from 1.005 to 0.997 as oxygen pressure increase. Interestingly, energy gap measured by FTIR decreases with decreasing oxygen pressure until it reach a certain oxygen pressure, then increases again with increasing oxygen pressure. Furthermore, microwave properties of devices measured by a HP 8510C vector network analyzer from 0.045–20 GHz suggest that the least distorted films exhibit a larger dielectric constant changes with dc bias field.     

Preparation of Pb(Zr,Ti)O3 Thin Films on Silica Substrate by Metallo-Organic Decomposition

In this study, we report the deposition of crack-free transparent PZT films (up to ～859 nm) by metallo-organic decomposition (MOD) process on amorphous silica substrate. Effect of SrTiO₃ (STO) buffer layer on the growth behavior of PZT thin films deposited on SiO₂-coated silicon substrates was systematically studied. Perovskite phase, which cannot be formed directly on SiO₂/Si substrates, has been obtained when a thin STO film (～150 nm) was used as buffer layer. A SIMS examination indicates that the upward diffusion of Si-species into PZT layer is minimal, although downward diffusion of Pb-species into the SiO₂ layer is still observable.     

Pb(Mg1/3Nb2/3)0.97Ti0.03O3 Ferroelectric Thin Films, Deposited by Laser Ablation on TiN Bottom Electrodes

Pb(Mg_1/3Nb_2/3)_0.97Ti_0.03O₃ (PMNT) polycrystalline thin films were deposited on Titanium Nitride electrode at different temperatures by laser ablation, using a wavelength of 248 nm. The morphology of the films was analyzed by scanning electron microscopy (SEM). The nature of the ferroelectric layer-electrode interface is studied by transmission electron microscopy (TEM) as well as the effect of its characteristics in the performance of the multilayer system. The influence of the annealing temperature on the dielectric properties was studied by hysteresis and fatigue measurements.     

Polarization Switching in (100)/(001) Oriented Epitaxial Pb(Zr, Ti)O3 Thin Films

Thin films made of (100)/(001)-oriented Pb(Zr, Ti)O₃ (PZT) were deposited by liquid-delivery metal-organic chemical vapor deposition on Ir/MgAl₂O₄/SiO₂/Si(100) substrates. For comparison, PZT thin films were also deposited on Ir/MgO(100) substrates. The X-ray scan spectra for the (202) reflections revealed that the PZT films have four-fold symmetry. It indicates that the PZT films were epitaxially grown as a cube-on-cube structure on both substrates. The switchable polarization (Q_sw) of the PZT capacitors on the silicon substrate was only 23 C/cm² at 1.8 V; however, Q_sw of PZT capacitors on MgO was 99 C/cm². In the case of PZT films deposited on silicon, the volume fraction of (001)-oriented domains (which contribute to polarization switching) was 15.1% (calculated from an XRD pattern). This result is due to the lower Q_sw of PZT capacitors on silicon. By piezoresponse-force microscopy, switchable and unswitchable domains could be identified by imaging color contrast, namely, (001) and (100) domains, respectively. Consequently, domain distribution of the PZT film on a silicon substrate indicates that the (001) domain exists in the (100) domain matrix.     

Inverse Capacitance-Voltage Characteristics of Bi3.25La0.75Ti3O12 Thin Film Pulsed Laser Deposited on Thermally Oxidized n-Type Si Substrates

Comparative studies on the electrical properties of a metal-ferroelectric-insulator-semiconductor field effect transistor were conducted using pulsed laser ablated ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films deposited on SiO₂/Si substrates with different SiO₂ thicknesses. The SiO₂ layer was prepared on n-type Si substrates by dry oxidation at a temperature of 800°C. Small angle x-ray reflectivity studies were used to measure the SiO₂ thickness. The capacitance-voltage (C-V) measurements revealed that the films showed good interfacial properties. Shifts in flatband voltages were observable, but were effectively reduced by deposition of the ferroelectric films. Au/BLT/SiO₂/Si diodes with 8 nm SiO₂ layer showed to be stable with relatively large memory window values of about 0.3 V, 2.5 V, 5.0 V, and 7.0 V, at increasing bias voltages of ±5 V, ±7 V, ±10 V, and ±12 V, respectively.     

Microwave Performance of Distributed Analog Phase Shifter Using Ferroelectric (Ba,Sr)TiO3 Thin Films

This work presents the design, fabrication and microwave performance of distributed analog phase shifter (DAPS) fabricated on (Ba,Sr)TiO₃ (BST) thin films for X-band applications. Ferroelectric BST thin films were deposited on MgO substrates by pulsed laser deposition. The DAPS consists of high impedance coplanar waveguide (CPW) and periodically loaded tunable BST interdigitated capacitors (IDC). In order to reduce the insertion loss of DAPS and to remove the alteration of unloaded CPW properties according to an applied dc bias voltage, BST layer under transmission lines were removed by photolithography and RF-ion milling. The measured results are in good agreement with the simulated results at the frequencies of interest. The measured differential phase shift based on BST thin films was 24° and the insertion loss decreased from ?1.1 dB to ?0.7 dB with increasing the bias voltage from 0 to 40 V at 10 GHz.