Xueguang Han

Structural, ferroelectric, dielectric, and magnetic properties of BiFeO3/Bi3.15Nd0.85Ti3O12 multilayer films derived by chemical solution deposition

BiFeO3/Bi3.15Nd0.85Ti3O12 (BFO/BNdT) multilayer films have been grown on Pt-coated silicon substrate by chemical solution deposition. Using Bi3.15Nd0.85Ti3O12 as an inducing layer, ferroelectric properties of BiFeO3 were enhanced significantly. The 2Pr and coercive electric field of the Pt/BFO/BNdT/Pt capacitor were about 22.1 μC/cm2 and 50 kV/cm, respectively. The dielectric constant and the dissipation factor of the multilayer were 373 and 0.05 measured at 105 Hz, respectively. The multilayer capacitors not only exhibited excellent fatigue resistance without polarization reduction after 1010 switching cycles but also showed lower leakage current density (around the order of 10−9–10−7 A/cm2) and negligible data loss due to imprint. The magnetic hysteresis indicated that the multiplayer was antiferromagnetic and the saturated magnetization was about 2.47 emu/cm3.

Characterization of Pt/Bi3.15Nd0.85Ti3O12/HfO2/Si structure using a hafnium oxide as buffer layer for ferroelectric-gate field effect transistors

We have investigated the structural and electrical properties of metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with Bi3.15Nd0.85Ti3O12 (BNdT) thin film deposited on Si and hafnium oxide (HfO2)/Si substrates. Microstructural analysis reveals the formation of well-crystallized BNdT perovskite film and good interface between BNdT film and HfO2 buffer layer. Pt/BNdT/HfO2/Si structure exhibits a memory window of 1.12 V at an operation voltage of 3.5 V. The width of memory window for the MFIS structure varies with increasing thickness of HfO2 layer, and 4-nm-thickness is optimum. The results from the fatigue test indicate a slight degradation of the memory window after 1010 switching cycles. These properties are encouraging for the development of ferroelectric memory transistors.

Characteristics of Pt/BiFeO3/TiO2/Si capacitors with TiO2 layer formed by liquid-delivery metal organic chemical vapor deposition

Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with 250 nm thick BiFeO3 (BFO) ferroelectric film and 150 nm thick TiO2 layer on silicon substrate have been fabricated and characterized. TiO2 was deposited on Si substrate by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD) process. The microstructure and the electrical properties of the Pt/BFO/TiO2/Si capacitors were studied. TiO2 demonstrates excellent insulating properties on Si substrate. The MFIS structure showed clockwise capacitance-voltage hysteresis loops due to the ferroelectric polarization of BFO. The maximum memory window is 3.51 V. When sweeping voltages decreased from ±14 to ±6 V, the memory window width decreased from 3.51 to 1.11 V. The leakage current of the film was of the order of 10−8 A/cm2 at an applied voltage of 4 V.

Comparative Study on Structural and Ferroelectric Properties of Dual-Site Rare-Earth Ions Substituted Multiferroelectric BiFeO3

We report a comparative study of dual-site rare-earth ions substituted BiFeO3 (BFO) crystal for the first time. BFO, Bi0.95Nd0.05Fe0.95Nb0.05O3 (BNFNO), Bi0.95Nd0.05 Fe0.95Mn0.05O3 (BNFMO), and Bi0.95La0.05Fe0.95Nb0.05O3 (BLFNO) thin films are prepared by sol-gel process. X-ray diffraction and Raman scattering analysis reveals a crystal transformation from rhombohedral to tetragonal upon substitution. The mean grain size decreases from 150 (BFO) to 10 nm (BNFNO) with dual-site substitution. Significant leakage current density enhancement from 1.8×10−3 (BFO) to 6.9×10−7 A/cm2 (BNFNO) at an applied electrical field of 0.1 MV/cm is observed, indicating that dual-site substitution is an effective method to modify BFO material.

ATOMIC LAYER DEPOSITION HfO2 FILM USED AS BUFFER LAYER OF THE Pt/(Bi0.95Nd0.05)(Fe0.95Mn0.05)O3/HfO2/Si CAPACITORS FOR FeFET APPLICATION

Neodymium and manganese-doped BiFeO3 — (Bi0.95Nd0.05)(Fe0.95Mn0.05)O3(BNFMO) ferroelectric film and HfO2 layer with different thickness were fabricated using metal-organic decomposition and atomic layer deposition (ALD) method, respectively. Metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with 200 nm thick BNFMO and 5 nm thick HfO2 layer on silicon substrate have been prepared and characterized. It is found that there is no distinct interdiffusion and reaction occurring at the interface between BNFMO/HfO2 and HfO2/Si. The capacitance–voltage (C–V) and leakage current properties of Pt/HfO2/Si capacitors with different HfO2 thickness were studied. The MFIS structure showed clockwise C–V hysteresis loops due to the ferroelectric polarization of BNFMO. The maximum memory window is 5 V. The leakage current of the Pt/BNFMO/HfO2/Si capacitor was about 2.1 × 10-6 A/cm2 at an applied voltage of 4 V.

The Structure and Characterization of ZrO2 Thin Films Prepared by Liquid Delivery-MOCVD

In this study, 50 nm-thick ZrO2 thin films have been prepared on Si substrate by liquid delivery metal-organic chemical vapor deposition(LD-MOCVD) at 650°C. The structural characteristics of the samples were investigated by X-ray diffraction analysis and SEM respectively, showed a tetragonal phase and a high uniformity of ZrO2 films. The electrical properties were studied by C-V and I-V measurements on Au/ZrO2/Si Metal-Insulator-Semiconductor (MIS) structure. The dielectric constant of ZrO2 films was 15. The leakage current-voltage dependence showed 3 different conduction mechanisms, which were Poole-Frenkel conduction mechanism, Schottky emission mechanism or ohmic emission.

FABRICATION AND PROPERTIES OF METAL-PZT-METAL CAPACITORS BY LIQUID DELIVERY MOCVD

ABSTRACT Pb(Zr1−x,Tix)O3(PZT) thin films were prepared on 8-inch and 4-inch Pt or Ir-electroded Si wafers by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD) using cocktail sources of Pb, Zr and Ti. The processing conditions were optimized in order to obtain high-performance PZT films. The thickness uniformity of PZT films on 8-inch substrate was about ± 3.24%. The deposition rate of Pb (15.8 nm/min) and Ti (17.9 nm/min) deposited on Si substrate were faster than that of Zr (2.5 nm/min). The growth temperature of PZT film was adjusted to 570–630°C depending on the substrates used. The properties of metal/PZT/metal capacitors were also studied. The PZT films based on Pt substrate showed no good ferroelectric properties. By contrast, the ferroelectric properties of Ir/IrO2/PZT/IrO2/Ir capacitors were excellent. At an applied voltage of 5 V, the remanent polarization (Pr) and coercive field (Ec) values were about 36 μ C/cm2 and 50 kV/cm, respectively.

Characterization of Pt/BiFeO3/ZrO2/Si Capacitors for Memory Applications

BFO film was fabricated on ZrO2 insulating buffer by sol-gel method. The ZrO2 was deposit on Si substrate by liquid delivery metal-organic chemical vapor deposition (LD-MOCVD) process. The microstructure and the electric properties of the Pt/BFO/ZrO2/Si capacitors were studied. ZrO2 demonstrates excellent insulating properties on Si substrate. The MFIS structure showed clockwise capacitance-voltage hysteresis loops due to the ferroelectric polarization of BFO. The maximum memory window is 2.26V. The leakage current density of the capacitor was of the order of 10−7 A/cm2 at an applied voltage of 8V.