Ferroelectric properties of SrBi2Ta2O9 thin films on Si (100) with a LaZrO x buffer layer

To obtain a metal–ferroelectric–insulator–semiconductor (MFIS) structure, we fabricated ferroelectric SrBi₂Ta₂O₉ (SBT) film on a p-type Si (100) wafer with a LaZrO _x (LZO) buffer layer by means of a sol–gel technique. The sol–gel deposited LZO film according to the different annealing temperatures had a good surface morphology even though the crystalline phase was not an amorphous phase. In particular, the root-mean-squared (RMS) surface roughness of the 750-°C-annealed LZO film was about 0.365 nm and its leakage current density was about 8.2?×?10^?7 A/cm² at 10 V. A Au/SBT/LZO/Si structure with different SBT film was fabricated. The C–V characteristics of the Au/SBT/LZO/Si structure showed a clockwise hysteresis loop. The memory window width increased as the SBT film thickness increased. The 600-nm-thick SBT film was crystallized in a polycrystalline phase with a highly preferred (115) orientation. The memory window width of the 600-nm-thick SBT film was about 1.94 V at the bias sweep voltage ±9 V and the leakage current density was about 6.48?×?10^?8 A/cm² at 10 V.     

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.     

Characterization of PT ferroelectric thin films on porous silica for pyroelectric IR detectors

Ferroelectric PbTiO₃ thin films were deposited on Pt/DS/PS/SiO₂/Si substrates by sol–gel technique. Porous silica (PS) thin film was used as thermal-insulation layer and dense silica (DS) thin film was a buffer layer to reduce surface roughness of PS layer. Root mean square surface roughness can be effectively reduced from 9.7 to 3.5 nm after PS buffer layer was prepared. The average grain size of PT thin films decreased slightly with increasing thickness of porous silica. Dielectric constant of PT increased from 107 to 171 at 1 KHz as thickness of PS layer increased from 0 to 2,000 nm. PT thin film prepared on 2,000 nm porous silica exhibited good dielectric property. The leakage current density was less than 1.6?×?10^-6 A/cm² when the applied electrical field was 200 kV/cm. The composite film is suitable for preparing pyroelectric IR detectors.     

Effects of transition metal (Ni, Mn, Cu) doping on ferroelectric properties of Bi0.9Nd0.1FeO3 thin films prepared by chemical solution deposition method

Transition metal (Ni, Mn, Cu) doped Bi_0.9Nd_0.1FeO₃ thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Compared to pure BiFeO₃ (BFO) thin film, improved ferroelectric and leakage current properties were observed in the transition metal doped thin films. The values of remnant polarization (2P _r ) and coercive electric field (2E _c ) of the transition metal doped thin films were 59 μC/cm² and 690 kV/cm at 700 kV/cm for the Ni-doped Bi_0.9Nd_0.1FeO₃ thin film, 57 μC/cm² and 523 kV/cm at 670 kV/cm for the Mn-doped thin film, and 85 μC/cm² and 729 kV/cm at 700 kV/cm for the Cu-doped thin film, respectively. The 2P _r values observed in the transition metal doped thin films were much larger than that of the BFO thin film, 21 μC/cm² at 660 kV/cm. Also the 2E _c values of in the transition metal doped thin films were lower than that of the BFO thin film, 749 kV/cm at 660 kV/cm. The reduced leakage current density was observed in the transition metal doped thin films, which is approximately two orders of magnitude lower than the BFO thin film, 2.6?×?10^?3 A/cm² at 100 kV/cm.     

Effect of seed layers on dielectric properties of Ba(Zr0.3Ti0.7)O3 thin films

The Barium zirconium titanate Ba(Zr_0.3Ti_0.7)O₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates with seed layers at the BZT/Pt interface by sol–gel process. Microstructure and structure of thin films were examined. Dielectric properties of thin films with various seed layers thicknesses were investigated as a function of frequency and direct current electric field. The tunability and dielectric constant of BZT thin films increased with increasing seed layer thickness from 0 to 20 nm, while it decreased with a further increase in thickness above 20 nm, meanwhile, the leakage current showed the similar tendency at applied electric field of 250 kV/cm. The optimized seed layer thickness for BZT thin films plays an important role in maintaining the high tunability and low leakage current, which are suitable for microwave device applications.     

Structural and improved electrical properties of rare earth (Sm, Tb and Ho) doped BiFe0.975Mn0.025O3 thin films

Pure BiFeO₃ (BFO) and rare earth (RE) ion co-doped (Bi_0.9RE_0.1)(Fe_0.975Mn_0.025)O₃ (RE?=?Sm, Tb and Ho, denoted by BSFM, BTFM and BHFM) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of distorted rhombohedral perovskite structure for the thin films were confirmed by using an X-ray diffraction and a Raman scattering analysis. Microstructural features for the thin films were examined by using a scanning electron microscopic analysis. Among the thin films, the lowest leakage current density of 1.22?×?10^?6 A/cm² (at 100 kV/cm), large remnant polarization (2Pr) of 72.4 μC/cm² and low coercive field (2E _c ) of 689 kV/cm (at 980 kV/cm) were measured for the BTFM thin film.     

Effects of Substrate and Annealing Temperatures on the Characteristics of SrBi4Ti4O15 Thin Films

In this study, radio frequency (RF) sputtering was used as the method and the layer-structured bismuth compound of SrBi₄Ti₄O₁₅ + 4 wt% Bi₂O₃ ferroelectric ceramic was used as the target to deposit the SrBi₄Ti₄O₁₅ (SBT) thin films. The addition of excess Bi₂O₃ content in the target ceramic was used to compensate the vaporization of Bi₂O₃ during the sintering and deposition processes. SBT ferroelectric thin films were deposited on Pt/Ti/SiO₂/Si under optimal RF magnetron sputtering parameters with different substrate temperatures for 2 h. After that the SBT thin films were post-heated using rapid temperature annealing (RTA) method. The dielectric and electrical characteristics of the SBT thin films were measured using metal-ferroelectric-metal (MFM) structure. From the physical and electrical measurements of X-ray diffraction pattern, scanning electronic microscope (SEM), I-V curve, and C-V curve, we had found that the substrate temperature and RTA-treated temperature had large influences on the morphology, the crystalline structure, the leakage current density, and the dielectric constant of the SBT thin films.     

Preparation of Si-Added SrBi2Ta2O9 Ferroelectric Thin Films by RF Magnetron Sputtering

Si-added SrBi₂Ta₂O₉ (SBT) ferroelectric films were prepared by RF magnetron sputtering on a Pt/Ti/SiO₂/Si (100) structure. The films were deposited at temperatures below 100°C for surpressing Bi evaporation, and crystallized at 800°C in air. A typical composition was Sr_0.79Bi_2.37Ta_2.00Si_0.2O_x. The remanent polarization value (2Pr) of the Si-added SBT film was 16 μC/cm². The Si atom addition was found to be effective in improvement of the fatigue and leakage current of SBT ferroelectric films. The leakage current density was further improved by annealing in the high-pressure oxygen ambient at 7 atms.     

Effect of crystalline phases on the ferroelectric properties of HoMnO3 thin films

Ferroelectric HoMnO₃ thin films were deposited on the Si (100) substrates at 700°C for 2 h by metal–organic chemical vapor deposition. When the films were post-annealed at 800°C for 1 h in air, the single phase of hexagonal HoMnO₃ was detected, and the remnant polarization (Pr) and coercive field (Ec) were decreased due to the decrease of c-axis orientation. With an increase of annealing time, the crystalline phase of HoMnO₃ was changed from the single hexagonal to the mixtures of the hexagonal and orthorhombic phases of HoMnO₃, and/or HoMn₂O₅. Leakage current density was related with charge valence of Mn ion and surface roughness of thin film. Pr of hexagonal HoMnO₃ thin films with high c-axis orientation was 136 nC/cm² and the leakage current density was 10^?6 A/cm².     

DC conduction behavior of Bi3.15Nd0.85Ti3O12 thin films grown by RF-magnetron sputtering

The Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were deposited on Pt(111)/Ti/SiO₂/Si substrates by using RF-magnetron sputtering method and studied the ferroelectric and leakage current charateristics. The polarization – electric field (P-E) hysteresis loops of BNT film was well saturated with the remnant polarization (2P _r ) of 29.8 μC/cm² and a coercive field (2E _c ) of 121 kV/cm. The leakage current density – electric field (J-E) characteristics of the Pt/BNT/Pt capacitor reveals the presence of two conduction region, having Ohmic behavior at low electric field (below 50 kV/cm) and Schottky-emission or Poole-Frenkel emission at high electric field (above 60 kV/cm). The barrier height and trapped level of BNT films are estimated to be 1.11 eV and 0.90 eV, respectively.     

Enhancement of ferroelectricity in gadolinium (Gd) and transition metal (Ni, Co, Cr) Co-doped BiFeO3 thin films via a chemical solution deposition technique

The BiFeO₃ (BFO) and the gadolinium and transition metal ions co-doped (Bi_0.9Gd_0.1)(Fe_0.975 TM _0.025)O_3-δ (TM?=?Ni, Co and Cr, BGFNi, BGFCo and BGFCr) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Compared to the pure BFO, improved electrical and ferroelectric properties were observed in the co-doped (Bi_0.9Gd_0.1)(Fe_0.975 TM _0.025)O_3-δ thin films. Among the thin films, the BGFCr thin film exhibited large remnant polarization (2P _r ), low coercive field (2E _c ), and reduced leakage current density, which are 136 μC/cm², 1360 kV/cm at 1470 kV/cm, and 5.14?×?10^-6 A/cm² at 100 kV/cm, respectively.     

Preparation and properties of Pb(Zr, Ti)O3 ferroelectric thin films and compositionally graded thin films on LaNiO3/Si substrates

LaNiO₃ (LNO) thin films were prepared on Si (100) wafer by MOD method. Pb(Zr, Ti)O₃ ferroelectric thin films and their compositionally graded thin films were prepared on LNO/Si (100) substrates by a modified sol–gel method. The composition depth profile of a graded film was determined by using a combination of Auger electron spectroscopy and Ar ion etching. The results confirmed that the processing method produces graded composition change. XRD analysis showed that the graded thin film possessed a composite structure of tetragonal and rhombohedral. The dielectric constant of the graded thin films was higher than that of each thin film unit, but the loss tangent was near to each other at 10 kHz. The temperature characteristics of the dielectric constant of the graded thin films at different frequencies showed three peaks and ferroelectric relaxor feature to some extent. Hysteresis loops showed that graded thin film had higher remanent polarization, smaller coercive field than each thin film unit. The pyroelectric coefficient of the graded thin films increased gradually with temperature, and was higher than that of each thin film unit.     

Dielectric properties for Tantalum-doped strontium barium titanate thin films prepared by sol-gel method

In this work, Sr_0.5Ba_0.5Ti_1-zTa_zO₃ (SBT) thin films were prepared on a Pt/SiO₂/Si substrate by sol-gel process. The microstructures of SBT thin films were examined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). The influences of Ta on the microstructure and dielectric properties of SBT thin films were studied. It is found that tetragonal perovskite crystal grains existed in SBT thin films. Ta⁵⁺ doping fines the grain of SBT thin films. It is found that Ta⁵⁺ doping decreases dielectric loss for SBT thin films.     

Structure and dielectric properties of Ca-doped (Ba0.7Sr0.3) TiO3 thin films fabricated by sol–gel method

A wide range of Ca-doped (Ba_0.7Sr_0.3)TiO₃ (BST) thin films (from 0 to 20 mol%) have been prepared on Pt/Ti/SiO₂/Si (100) substrates by sol–gel technique. The structural and dielectric properties of BST thin films were investigated as a function of Ca dopant concentration. The results showed that the microstructure and dielectric properties of the BST films were strongly dependent on the Ca contents. With the Ca dopant concentration increasing, the grain size, dielectric constant and dielectric loss of the BST thin films decreased. As the content of Ca dopant reaches 10 mol%, the dielectric constant, dielectric loss, tunability, the value of FOM and the leakage current density are 281, 0.0136, 16.7%, 12.3 and 5.5?×?10^?6 A/cm², respectively.     

Fundamental characteristics of DRAM capacitor application of PLZT ultrathin films prepared by MOCVD

Lanthanum-modified lead zirconate titanate (PLZT) thin films (50 nm to 200 nm) were deposited on Pt/SiO₂/Si substrate by metal-organic chemical vapor deposition (MOCVD). The electrical properties of the films were investigated as a function of the La content or the substrate temperature. Ferroelectric PZT(0/50/50) films were obtained at substrate temperatures as low as 500 °C; their electrical characteristics improved with increasing substrate temperature. La exhibited adequate solid solution in the PZT above 650 °C. PLZT(15/45/55) films with a thickness of 100 nm were found to have good properties for application to the capacitors of dynamic random access memory (DRAM), namely, an effective charge density of 80 fF/μm², a permittivity of 1000, an SiO₂ equivalent thickness of 0.4 nm, and a leakage current density of 5 × 10⁻⁸ A/cm. Addition of La to PZT was effective in reducing the leakage current with an increase in the registration rate. RuO₂ and/or IrO₂ bottom electrodes for ferroelectric PLZT films were also investigated. The RuO₂ films were found effective as diffusion barriers for PLZT and MgO. Significant interdiffusion at RuO₂/Si and RuO₂/SiO₂ interfaces occurred during the deposition of PLZT films. Annealing of the RuO₂ film considerably depressed interface reactions. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 25–36, 1998     

CHARACTERISTICS OF METAL-FERROELECTRIC-INSULATOR-SILICON DEVICES USING HFSION BUFFER LAYERS

ABSTRACT

In this work, metal-ferroelectric-insulator-silicon (MFIS) devices were fabricated using HfSiON as buffer layers and their electrical properties were studied. Ultra-thin HfSiON films were fabricated by electron-beam evaporation at room temperature and post-annealed using different parameters such as temperature, time in O₂. By annealing a 2 nm-thick HfSiON film at 800°C for 60s in O₂, a negligible hysteresis loop and small equivalent oxide thickness of 2.3 nm were obtained with a corresponding leakage current density of 6.8 × 10^{? 5} A/cm² at a voltage shifted from the flat band voltage by 1 V. In the fabrication of MFIS diodes, Sr_0.8Bi_2.2Ta₂O₉ (SBT) films with 400 nm thickness were formed by chemical solution deposition. For Pt/SBT (400 nm)/HfSiON(2 nm)/Si diodes, a memory window of 0.8 V in width was observed during double capacitance-voltage sweep between +5 and –5 V. At the same time, excellent data retention properties were observed. The high and low capacitances in the hysteresis loop were well distinguishable even after 24 h had elapsed.     

Dielectric characteristics investigation of (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 ferroelectric thin films

By the radio frequency (RF) magnetron sputtering methods, (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ (BSTZ) ferroelectric thin films were deposited on the Pt/Ti/SiO₂/Si(100) substrates. The crystal structural and microstructure of these thin films were analyzed by means of the XRD, SEM, and AFM. Moreover, the dielectric characteristics were also investigated by the C-V and J-E analyses. The optimal deposition parameters for these BSTZ thin films were: RF power is 160 W, oxygen concentration is 25%, substrate temperature is 580°C, and chamber pressure is 0.075 mPa. Under these optimal deposition conditions, the (111) and (110) oriented polycrystalline of the BSTZ thin films grow easily. And under a bias voltage of 0.5 MV/cm, the dielectric constant and leakage current density of the BSTZ thin films are 191 and 3×10^?8 A/cm², respectively. In addition, under various measured temperatures (0 ～ 80°C) and frequencies (100 kHz ～ 1 MHz), all the dielectric constants remain almost unchanged. Compared to BSTZ thin films reported previously, in this study, the deposited thin films have the advantage of lower leakage current and hence are suitable for the applications of dynamic random access memory.     

Characteristics of Bi4Ti3O12 thin films on ITO/glass and Pt/Si substrates prepared by R.F. sputtering and rapid thermal annealing

Bi₄Ti₃O₁₂ thin films are deposited on ITO/glass and Pt/Ti/Si(100) substrates by R.F. magnetron sputtering at room temperature. The films are then heated by a rapid thermal annealing (RTA) process conducted in oxygen atmosphere at temperatures ranging from 550–700^∘C. X-ray diffraction examination reveals that the crystalinity of the films grown on Pt/Ti/Si is better than that of the films grown on ITO/glass under the same fabrication conditions. SEM observation shows that the films grown on Pt/Ti/Si are denser than those grown on ITO/glass substrates. Interactive diffusion between the Bi₄Ti₃O₁₂ film and the ITO film increases with the increase of annealing temperature. The optical transmittance of the thin film annealed at 650^∘C is found to be almost 100% when the effect of the ITO film is excluded. The relative dielectric constants, leakage currents and polarization characteristics of the two films are compared and discussed.     

Ferroelectric SrBi2Ta2O9 thin films deposited by liquid injection MOCVD using novel bimetallic alkoxide precursor

Abstract

The ferroelectric SBT films were deposited on Pt/Ti/SiO₂/Si substrates by liquid injection metalorganic chemical vapor deposition (MOCVD) with single-mixture solution of Sr[Ta(OEt)₅(dmae)]₂ and Bi(C₆H₅)₃. The Sr/Ta and Bi/Ta ratio in SBT films depended on deposition temperature and mol ratio of precursor in the single-mixture solution. At the substrate temperature of 400°C, Sr/Ta and Bi/Ta ratio were close to 0.4 and 1 at precursor mol ratio of 0.5～1.0. As-deposited film was amorphous. However, after annealing at 750°C for 30 min in oxygen atmosphere, the diffraction patterns indicated polycrystalline SBT phase. The remanent polarization (Pr) and coercive field (Ec) of SBT film annealed at 750°C were 4.7 μC/cm²and 115.7 kV/cm at an applied voltage of 5 V, respectively. The SBT films annealed at 750°C showed practically no polarization fatigue up to 10¹⁰ switching cycles.     

Preparation of BST thin films on Pt electrode on Si wafer with down-flow LSMCVD reactor

Abstract

A novel type of down-flow LSMCVD (Liquid Source Mist CVD) reactor was developed to prepare a high dielectric BST thin film on Pt electrode on Si wafer. Barium acetate [Ba (OOCCH₃)₂], strontium acetate [Sr (OOCCH₃)₂], and titanium isoproxide [Ti (OC₃H₇ ⁱ )₄] were used as metal sources. Metal sources were dissolved in acetic acid, 1-butanol, or 2-methoxyethanol. BST [Ba/(Ba + Sr) = 0.7] film annealed on Pt/Ti/SiO₂/Si above 650°C was polycrystalline. BST film has a (110) preferred orientation with increasing temperature. Surface roughness of BST film and grain size increased with increasing temperature. The metal-oxygen bond was formed at 650°C as shown in the spectra of FTIR. The depth profiles of elements of BST thin films indicated a uniform composition throughout the film. BST films annealed at 750°C showed a dielectric constant and a tanδ of 390 (thickness: 150 nm) and 0.06 at a frequency of 100 kHz, respectively. The behavior of capacitance of the BST film with bias voltage showed paraelectric property. BST film annealed at 750°C had the leakage current density of 3.2 (μA/cm²) at a bias voltage of 2V.