Epitaxial structure SrBi2Ta2O9<116> /SrTiO3<011> /Ce0.12Zr0.88O2<001> /Si<001> for ferroelectric-gate FET memory

Abstract

Epitaxial thin film growth of SrBi₂Ta₂O₉/SrTiO₃/Ce_0.12Zr_0.88O₂ on Si was studied, and this epitaxial layer structure was applied to fabrication of ferroelectric-gate field effect transistors (FETs). The films were prepared by a pulsed laser deposition technique and epitaxial growth was identified by x-ray diffraction. The devices exhibited excellent electrical performances: Capacitance-voltage characteristic of a metal-ferroelectric-insulator-semiconductor (MFIS) diode showed a retention longer than 10 days and I_d-V_g characteristic of an MFIS-FET showed 1 day retention. It is proved that the crystalline quality of ferroelectric thin films is of great importance to develop integrated devices with high performance.     

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.     

Low Temperature Process for Synthesis of (100) Textured Pb(Zr0.48Ti0.52)O3 Thin Films on Si Substrate by Laser Lift-Off Transferring Technique

(100) textured Pb(Zr_0.48Ti_0.52)O₃ (PZT) films were prepared on silicon substrates by MOD process and laser lift-off technique. Textured PZT films were first grown on (001) Sapphire substrate, using Ba(Mg_1/3Ta_2/3)O₃ (BMT) materials as buffer layer. The (100) textured PZT/BMT/Sapphire films were attached to Si substrate using a transient-liquid-phase Pd-In bonding process, and then were separated from Sapphire substrates by a laser lift-off process, in which, a 38 ns pulse from excimer laser (248 nm) at 600 mJ/cm² fluence melted BMT buffer layer, expelling the Sapphire. The crystallinity of the surface of films was further improved by laser annealing. X-ray diffraction analysis of the PZT films showed that the crystallographic structure of films is maintained during laser lift-off process. Electrical testing of the films after laser lift-off process followed by laser annealing demonstrated that the ferroelectric properties are retained for the transferred films (P_r = 9μ C/cm² and E_c = 74 kV/cm).     

Characterization of the CeO2 thin films for insulation layer and Pt/SrBi2Ta2O9/CeO2/Si MFISFET structure

Abstract

CeO₂ and SrBi₂Ta₂O₉ (SBT) thin films for MFISFET (metal-fcrroelectrics-insulator-semiconductor field effect transistor) were deposited by rf sputtering and pulsed laser deposition method, respectively. The effects of oxygen partial pressure during deposition for CeO₂ films were investigated. The oxygen partial pressure significantly affected the preferred orientation, grain size and electrical properties of CeO₂ films. The CeO₂ thin films with a (200) preferred orientation were deposited on Si(100) substrates at 600°C. The films deposited under the oxygen partial pressure of 50 % showed the best C-V characteristics among those under various conditions. The leakage current density of films showed order of the 10^?7～10^?8 A/cm² at 100 kV/cm. The SBT thin films on CeO₂/Si substrate showed dense microstructure of polycrystalline phase. From the C-V characteristics of MFIS structure composed of the SBT film annealed at 800°C, the memory window width was 0.9 V at ±5 V. The leakage current density of Pt/SBT/CeO₂/Si structure annealed at 800°C was 4×10^?7 A/cm² at 5 V.     

Preparation of Textured Growth Pb(Zr,Ti)O3 Thin Films on Si Substrate Using SrTiO3 as Buffer Layers

PZT thin films are deposited on SiO₂/Si substrate by metallo-organic decomposition (MOD) process, using SrTiO₃ (STO) as buffer layer for textured growth. The STO layers deposited on SiO₂/Si substrate by pulsed laser deposition process show (100)/(200) preferred orientation, whereas the STO buffer layer deposited on silica substrate using spin-coating technique show random orientation behavior. The use of STO as buffer layers enhanced the crystallization and the preferred orientations of the PZT films. The PZT on STO buffered SiO₂/Si substrates thus obtained possess high refractive index, (n)_PZT/STO = 2.1159, and are of good enough quality for optical waveguide applications.     

Effect of excess-PB and prenucleation layer on properties of Pb(ZryTi1-y)O3 thin films prepared by mod process

Abstract

A modified metal-organic decomposition process, MOD has been successfully utilized to improve the ferroelectric properties of Pb(Zr_0.52Ti_0.48)O₃, PZT, thin films. Multilayer PZT/Pt(Si) films, which contain 0.12 μm layer of spin coated PbO-excess (10 mol%) precursors on top of 0.12 μm layer of stoichiometric PZT precursors, exhibit superior ferroelectric properties (P_r=14.2 μC/cm²; E_c=62 kV/cm) to the single layer PZT/Pt(Si) films of the same thickness (0.24 μm), which are either stoichiometric or 10 mol% Pb-enriched. The ferroelectric properties are further improved when the PZT films were synthesized using a thin pulsed laser deposited (PLD) prenucleation layer (0.06 μm). The subsequently MOD-prepared PZT films posses high remanent polarization (P_r=23.2–26.6 μC/cm²) and low coercive field (E_c=62.9–69.0 kV/cm).     

Electrical characterizations of MgTiO3 thin films grown on Si

Abstract

We have analyzed MgTiO₃ thin films grown on the Si substrate with/without SiO₂ using pulsed laser deposition (PLD). We find that MgTiO₃ thin films start to crystallize at 600°C, causing electrical instabilities in the MIS capacitors above this temperature. Detailed analysis by XRD technique reveals that structural differences of MgTiO₃ thin films were not obvious below 600°C, whereas the electrical characteristics changes as a function of deposition temperature and the presence of thermally grown SiO₂. We observe that the decrease of deposition temperature results in the increase of leakage current and anomalous positive charge (APC) density. These drawbacks were effectively suppressed by growing 100A SiO₂ layer on the Si substrate prior to the deposition of MgTiO₃ thin films.     

Growth of MgTiO3 thin films by pulsed laser deposition and their electrical properties

Abstract

MgTiO₃ thin films have been grown on various substrates by pulsed laser deposition (PLD) to investigate the application for microwave dielectrics and optical devices. Highly oriented MgTiO₃ thin films were obtained on sapphire (c-plane Al₂O₃). MgTiO₃ thin films deposited on SiO₂/Si and platinized silicon (Pt/Ti/SiO₂/Si) substrates were polycrystalline nature. MgTiO₃thin films grown on sapphire were transparent in the visible and had a sharp absorption edge at 280 nm. These MgTiO₃ thin films had extremely fine feature of surface morphology, i.e., rms roughness of 0.87 nm. Dielectric constant and loss of MgTiO₃ thin films deposited by PLD were about 24 and 1.5% at 1MHz, respectively. These MgTiO₃ thin films also exhibited little dielectric dispersion.     

Deposition of large-area graded (Pb1−xLax)TiO3 thin films by pulsed laser depesition

Abstract

Thin films of the composition (Pb_1?xLa_x)TiO₃, PLT, with x=0.05, 0.10 and 0.15 were sequentially pulsed laser deposited on Pt(Si) substrates at 200°C, followed by post-annealing at 550–600°C in furnace to result in a film with graded composition. The ferroelectric properties of the graded materials are markedly different from those of the uniform thin PLT films. For down graded materials, which contain PLT5 composition (x=0.05) at the top and PLT 15 composition (x=0.15) at the bottom of the films, the hysteresis loops are slim and the width of the P-E curves increases with voltage cycling, attaining an equilibrium polarization states similar to the P-E properties of PLT 15 thin films. By contrast, the ferroelectric hysteresis properties reaches the same value as those of PLT5 thin films when the composition is up-graded.     

Electrical and optical properties of microwave dielectric thin films prepared by pulsed laser deposition

Abstract

Bi₂(Zn_1/3Nb_2/3)₂O₇, BiZN, materials possess high dielectric constant and low loss factor in microwave frequency region. They have good potential for device application, especially in the form of thin films. However, the microwave dielectric properties of a thin film are very difficult to be accurately measured. Evaluation on the dielectric behavior of the films through the performance of the microstrip line devices made of these films involves metallic conduction and stray field losses. A novel measuring technique, which can directly evaluate the microwave dielectric properties of a thin film is thus urgently needed.

In this paper, BiZN thin films were grown on [100] MgO single crystal substrates using pulsed laser deposition process. The high-frequency dielectric properties of thus obtained thin films were determined using optical transmission spectroscopy (OTS). The [100] preferentially oriented films with pyrochlore structure can be obtained for the thin films deposited at 400–600°C substrate temperature under 0.1 mbar oxygen pressure. OTS measurements reveal that the index of refraction (n=1.95–2.35) and absorption coefficient (k=0.28x10^?4-2.25 × 10^?4 nm^?1) of the films vary insignificantly with the crystallinity of the BiZN films.     

Electromechanical properties of PMN-PT thin films prepared by pulsed laser deposition technique

Abstract

Ferroelectric relaxor thin films of the composition 0.9Pb(Mg_1/3Nb_2/3)O₃-0.1PbTiO₃ (PMN-PT) were fabricated by pulsed laser deposition technique on Pt/Ti/SiO₂/Si(100) substrates using a La_0.5Sr_0.5CoO₃ film as a template layer. The films were polycrystalline with random orientation of the grains. Electromechanical properties of the films were evaluated by a sensitive interferometric technique as a function of the dc and ac electric fields and frequency. Experimental results show that the effective piezoelectric coefficient d₃₃ can be tuned over a wide range of magnitudes by varying dc bias fields. A small hysteresis and a low remanent d₃₃ were observed, which favor the use of PMN-PT films in electric field-controlled micromechanical devices. The maximum d₃₃ ranged from 50 to 100 pm/V, depending on the thickness of the films and frequency. The piezoelectric properties are explained based on the expression for the electrostriction biased by polarization. At low electric field, strain is proportional to the square of electric field, while at higher fields it can be better described as the polarization squared. The asymmetry of the strain response in PMN-PT films is attributed to the polarization offset appearing due to the different electrode materials.     

SOL-GEL PREPARATION AND CHARACTERIZATION OF MULTIFERROIC BiFeO3 THIN FILMS WITH VARIOUS BI/FE RATIO

ABSTRACT

BiFeO₃ thin films have been prepared on Pt/TiO₂/SiO₂/Si substrates by sol-gel method using precursor solutions of various elemental ratio (Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1). The θ < eqid2 > 2θ scan XRD patterns show all the films consist mainly of polycrystalline perovskite and the crystallinity of Bi:Fe = 1.1:1.0 is better than the others. SEM and AFM images show all BiFeO₃ film have rosette structures, which consist of perovskite phase and matrix phase. The leakage current density measured at the temperature of 80 K is lower than 10^?4 A/cm² in all the films when the electric field reaches 1.6 MV/cm. The leakage mechanism of BiFeO₃ thin film is dominated by Schottky conduction at 80 K. At 80 K, the remanent polarizations at maximum applied voltage of 2.8 MV/cm are 100, 49, and 44 μC/cm² for the ratio of Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1, respectively. The saturated magnetization of BiFeO₃ thin films at 80 K were found to be 14, 22.5, 15 emu/cm³ for the ratio of Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1, respectively. Among these ratio, BiFeO₃ thin film deposited from precursor of Bi:Fe = 1. 1:1.0 gives the best ferroelectric property.     

Laser ablation preparation and property of bismuth-layer-structured SrBi2Ta2Ta2O9 and Bi4Ti3O12 ferroelectric thin films

Abstract

Bismuth-layer-structured ferroelectric thin films, SrBi₂Ta₂O₉ and Bi₄Ti₃O₁₂, have been prepared by laser ablation method on both Pt sheets and Si wafers at low temperatures of 400 ～ 500°C. These thin films have been characterized by XRD, XPS, AFM, C-V, D-E hysteresis and J-V measurement. SrBi₂Ta₂O₉ thin films have a good (105) preferential orientation, and Bi₄Ti₃O₁₂ thin films have (117) and c-axis orientation on these substrates. Ferroelectric film-SiO₂-Si structures show good C-V hysteresis curve owing to Si surface potential controlled by the D-E hysteresis. D-E hysteresis is obtained in Bi₄Ti₃O₁₂ thin film prepared on Pt sheet, and the remnant polarization and the coercive force are 7.5 μC/cm² and 72 kV/cm, respectively.     

Phase evolution and Sn-substitution in LiMn2O4 thin films prepared by pulsed laser deposition

LiMn₂O₄ thin films prepared on a Pt/Ti/SiO₂/Si(100) substrate by pulsed laser deposition were studied with focusing on the effects of different processing conditions and Sn substitution on phase evolvement and surface microstructure. Major experimental parameters include substrate temperature up to 770 °C and working oxygen pressure of 50–250 mTorr. LiMn₂O₄ thin films became highly crystallized with increased grain sizes as the substrate temperature increased. Second phases such as LiMnO₂ and Li₂Mn₂O₄ were found at the temperature of 300 and 770 °C, respectively. As an optimum condition, films grown at 450 °C showed a homogeneous spinel phase with well-defined crystallinity and smooth surface. A high pressure of oxygen tended to promote crystallization and grain growth. Working pressure did not affect significantly the phase formation of the thin films except that unexpected LiMn₃O₄ phase formed at the lowest oxygen pressure of 50 mTorr. Tin-substituted thin films showed lower Mn–O stretching vibrations, which suggests that more Li-ions can be inserted into vacant octahedral sites of the spinel structure.     

The Characteristics of Magnesium Titanate Thin Film as Buffer Layer by Electron Beam Evaporation

We have studied the application of magnesium titanate thin films as buffer layer for the improvement of adhesion of Pt films to Si substrate. Magnesium titanate films were successfully prepared on Si(100) substrate by electron beam evaporation. The crystal phase of MgTi₂O₅ and MgTiO₃ films on Si substrate were observed. These films had a very smooth and densely packed surface morphology and showed a good characteristic as the adhesion layer for Pt. Also, AES analysis showed the excellent properties as the reaction barrier layer between Pt and Si.     

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.     

(111)-Oriented BaTiO3 thin films hydrothermally formed on TiO2/Si substrate

Abstract

Barium titanate (BaTiO₃) thin films with high (111)-orientation were successfully grown on TiO₂-covered Si(111) substrate using hydrothermal method, where the TiO₂ layer was previously fabricated at room temperature by means of ion-beam-assisted deposition. This processing method provides a simple mild-chemical route for directly producing the analogous crystalline films on different substrates. The BaTiO₃ films did not reach the TiO₂/Si interface even if the hydrothermal treatment was prolonged to 24 hours. Both Rutherford backscattering and spread-resistance profiling characterizations confirmed the diffusion nature of the formed Ba-TiO₃/TiO₂/Si system.     

Characterization of Ni/Ce Co-Doped BST Thin Film Grown on LSCO/Pt Electrodes Prepared by Pulsed Laser Deposition

Perovskite (Ba_0.6Sr_0.4)TiO₃ (BST) thin films doped with Ni, Ce and Ni/Ce codopants were prepared on LSCO/Pt/SiO₂/Si substrates by pulsed laser deposition method. In this study, La_0.5Sr_0.5CoO₃ (LSCO) bottom electrodes were used to improve the crystallinity and dielectric properties of BST films. Single ion doped(1 mol%Ni doped,1 mol%Ce doped) BST films showed more improved crystallinity, smoother surface, and smaller grain size than that with 1 mol%Ni/1 mol%Ce. The dielectric constant and loss of Ni/Ce co-doped BST films were about 298 and 1.8%, respectively. In addition, tunability and figure of merit of co-doped BST films showed minimum values of approximately 9.3% and 5, respectively. With 1% Ni-doped BST thin films, results gave a tunability of 54.2% and a loss tangent of 1.8% while a figure of merit was 30. Correlation of the material properties with dielectric and tunable properties suggests the 1 mol%Ni-doped BST films are effective potential candidate for tunable device applications.     

Effect of seed layer on electrical properties of Pb(Zr,Ti)O3 films grown by metalorganic chemical vapor deposition

Abstract

Pb(Zr_xTi_1?x)O₃ (PZT) ferroelectric thin films were prepared by metalorganic chemical vapor deposition (MOCVD) on Pt/Ti/SiO₂/Si substrate. Very thin PZT films, which were deposited at a lower temperature and post-annealed at higher temperature for crystallization, were used as a seed layer. PZT films grown on the seed layer exhibited superior characteristics in the crystalline structure and electrical properties, compared to those deposited without seed layer. Depending on the deposition conditions of PZT seed layer, a wide variation of surface morphology and stoichiometry was found between samples, whereas chemical composition was found to be very similar.     

Effect of Buffer Layer on the Properties of Laser Ablated PZT Thin Films

Lead zirconate titanate (PbZr _x Ti_1?x O₃) or PZT ceramics are a class of piezoelectric materials that are currently experiencing widespread use in industry as electromechanical devices. PtSi/ZnO/PZT thin films were deposited by pulsed laser deposition at relatively low substrate temperature. The PZT thin films on PtSi substrates and on ZnO buffer layer were deposited at substrate temperature 300°C. The composition analysis shows that the film deposited at low temperature is stoichiometric. The films exhibit ferroelectric nature with coercive field of 19.6 kV/cm for 800 nm thick film. The leakage current density of the films shows a good insulating behavior.