Gate‐controlled metal–insulator transition in the LaAlO3/SrTiO3 system with sub‐critical LaAlO3 thickness

We studied the electrical conduction in the LaAlO₃/SrTiO₃ (LAO/STO) interface electron system with a sub‐critical LAO layer thickness of ～3.5 unit cells (uc). It was found that the true dividing point between metallic and insulating behaviour without gating lies near the LAO thickness of 3.5 uc. Our marginally metallic 3.5 uc sample showed a sharp transition to insulating state at temperatures which strongly depended on the applied negative back‐gate voltage. The superior gate‐controllability of the sample was attributed to its sheet carrier density which was an order of magnitude lower than those of conducting LAO/STO samples with 4 uc or more of LAO layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Atomic layer deposition of TiO2 and Al‐doped TiO2 films on Ir substrates for ultralow leakage currents

TiO₂ and Al‐doped TiO₂ (ATO) films were grown on Ir substrates by atomic layer deposition using O₃ as the oxygen source. With increasing O₃ feeding time, the crystalline structure of the TiO₂ films was transformed from anatase to rutile. Above an O₃ feeding time of 35 s, the films crystallized as only rutile due to the formation of IrO₂ layer at the interface. The TiO₂ and ATO films showed higher dielectric constants of 78 and 51, respectively. The films on Ir showed superior leakage properties compared to the films on Ru due to the high work‐function of Ir. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Giant dielectric constant observed in Ba0.96Sr0.04Zrx Y0.005Ti0.995–xO3–δ ceramics

Ba_0.96Sr_0.04Zr_x Y_0.005Ti_0.995–xO_3–δ ceramics were prepared by conventional sintering. The dielectric properties and the Curie temperature of the ceramics were studied. The Ba_0.96Sr_0.04Zr_x Y_0.005Ti_0.995–xO_3–δ ceramics (x = 0.04) exhibit a giant dielectric constant (ε_r ～ 10⁵). The peak value of dielectric constant is ～250,000 at 100 Hz and ～70,000 at 1 MHz for Ba_0.96Sr_0.04Zr_x Y_0.005Ti_0.995–xO_3–δ ceramics (x = 0.04). The results show that Ba_0.96Sr_0.04Zr_x Y_0.005Ti_0.995–xO_3–δ (x = 0.04) ceramics are a promising candidate material for microelectronic applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Local leakage current behaviours of BiFeO3 films

The leakage current behaviours of polycrystalline BiFeO₃ thin films are investigated by using both conductive atomic force microscopy and current-voltage characteristic measurements. The local charge transport pathways are found to be located mainly at the grain boundaries of the films. The leakage current density can be tuned by changing the post-annealing temperature, the annealing time, the bias voltage and the light illumination, which can be used to improve the performances of the ferroelectric devices based on the BiFeO₃ films. A possible leakage mechanism is proposed to interpret the charge transports in the polycrystalline BiFeO₃ films.     

低温原子层沉积氧化铝作为有机电致发光器件的封装薄膜

为了克服传统的原子层深沉积反应温度高于有机材料的玻璃化温度对有机电致发光器件性能产生破坏的缺点,使用低温原子层沉积的方法沉积了Al2O3薄膜,成功地实现了对OLED的薄膜封装。实验中为了抑制环境温度对ALD薄膜均匀性的影响,增加了每个反应周期的抽气时间,从而可以充分地排出反应副产物,抑制了空位的形成,使得薄膜具有较高的均匀性和致密性。微观形貌分析、钙测试以及寿命测试表明,通过增加ALD的PGT,低温制备的薄膜与高温制备的薄膜的均匀性差别较小,且制备过程对OLED器件的光电性能无明显影响。低温制备的薄膜水汽透过率(WVTR)可以达到8.6×10-4g/(m2·d),能够有效地提高有机电致发光器件的寿命。     

Silicon surface passivation by atomic‐layer‐deposited Al2O3 facilitated in situ by the combination of H2O and O3 as reactants

We investigate the effect of O₃ and H₂O oxidant pre‐pulse prior to Al₂O₃ atomic layer deposition for Si surface passivation. Interfacial oxide SiO_x formed by the O₃ pre‐pulse is more beneficial than that by H₂O to a high level of surface passivation. The passivation of thinner H₂O–Al₂O₃ films is more improved by this O₃ pre‐pulse. O₃ pre‐pulse for 10 nm H₂O–Al₂O₃ reduces saturation current density in boron emitter to 18 fA cm^–2 by a factor of 1.7. Capacitance–voltage measurements reveal this interfacial oxide plays a role of decreasing interface trap density without detrimental effect to negative charge density of Al₂O₃. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Low‐thermal budget flash light annealing for Al2O3 surface passivation

This value is achieved due to a very low interface trap density of below 10¹⁰ eV^–1 cm^–2 and a fixed charge density of (2–3) × 10¹² cm^–2. In contrast, plasma ALD‐grown Al₂O₃ layers only reach carrier lifetimes of about 1 ms. This is mainly caused by a more than 10 times higher density of interface traps, and thus, inferior chemical passivation. The strong influence of the deposition parameters is explained by the limitation of hydrogen transport in Al₂O₃ during low‐thermal budget annealing. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Stacked and nanolaminated Al2O3/TiO2 for surface passivation and encapsulation of silicon

Silicon solar cells passivated with Al₂O₃ require a capping layer that protects the passivation layer from humidity because of sensitivity of Al₂O₃ to moisture. Al₂O₃/TiO₂ stacks obtained by atomic layer deposition have been known to provide a high level of passivation layers because of their excellent field‐effect passivation. In this work, degradation of this Al₂O₃/TiO₂ stack, when exposed to humidity, is examined, and an attempt is made for a humidity‐resistant encapsulation layer by adding Al₂O₃/TiO₂ nanolaminates that can be deposited in‐situ without breaking vacuum. Placing the nanolaminate on top of the TiO₂ and Al₂O₃ stack is found to lead to almost no degradation even after 10 days of humidity exposure. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Buffers for high temperature superconductor coatings. Low temperature growth of CeO2 films by metal–organic chemical vapor deposition and their implementation as buffers

Smooth, epitaxial cerium dioxide thin films have been grown in-situ in the 450–650°C temperature range on (001) yttria-stabilized zirconia (YSZ) substrates by metal–organic chemical vapor deposition (MOCVD) using a new fluorine-free liquid Ce precursor. As assessed by X-ray diffraction, transmission electron microscopy (TEM), and high-resolution electron microscopy (HREM), the epitaxial films exhibit a columnar microstructure with atomically abrupt film-substrate interfaces and with only minor bending of the crystal plane parallel to the substrate surface near the interface and at the column boundaries. With fixed precursor temperature and gas flow rate, the CeO₂ growth rate decreases from 10 Å/min at 450°C to 6.5 Å/min at 540°C. The root-mean-square roughness of the films also decreases from 15.5 Å at 450°C to 4.3 Å at 540°C. High-quality, epitaxial YBa₂C₃O_7−x films have been successfully deposited on these MOCVD-derived CeO₂ films grown at temperatures as low as 540°C. They exhibit T_c=86.5 K and J_c=1.08×10⁶ A/cm² at 77.4 K.     

溶胶-凝胶法制备MgO/(Ba0.8Sr0.2)TiO3多层薄膜及其介电和漏电特性研究

采用改进的溶胶-凝胶方法在LaNiO₃/Si(100)衬底上制备了MgO/(Ba_{0.8Sr0.2)TiO3多层薄膜.实验结果表明，MgO层的引入改变了(Ba0.8}Sr_0.2)TiO₃的介电特性和漏电流行为，使薄膜的漏电 流降低了3个数量级，但介电常数也有相应降低.漏电流的显著降低是由MgO子层的高阻特性 以及微量Mg向(Ba_0.8关键词： 0.8Sr_0.2)TiO₃多层薄膜')" href="#">MgO/(Ba_0.8Sr_0.2)TiO₃多层薄膜 漏电流 介电常 数     

The electrical properties of dielectric stacks of SiO2 and Al2O3 prepared by atomic layer deposition method

We produced dielectric stacks composed of ALD SiO₂ and ALD Al₂O₃, such as SiO₂/Al₂O₃, Al₂O₃/SiO₂, and SiO₂/Al₂O₃/SiO₂, and measured the leakage currents through the stacks in comparison with those of the single oxide layers. SiO₂/Al₂O₃ shows lowest leakage current for negative bias region below 6.4 V, and Al₂O₃/SiO₂ showed highest current under negative biases below 4.5 V. Two distinct electron conduction regimes are observed for Al₂O₃ and SiO₂/Al₂O₃. Poole-Frenkel emission is dominant at the high-voltage regime for both dielectrics, whereas the direct tunneling through the dielectric is dominant at the low-voltage regime. The calculated transition voltage between two regimes for SiO₂ (6.5 nm)/Al₂O₃ (12.6 nm) is −6.4 V, which agrees well with the experimental observation (−6.1 V). For the same EOT of entire dielectric stack, the transition voltage between two regimes decreases with thinner SiO₂ layer.     

Large scale synthesis of pinhole‐free shell‐isolated nanoparticles (SHINs) using improved atomic layer deposition (ALD) method for practical applications

Shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) as a new member of Raman technique garnered great attention among scientific community. In this work, we used an improved experimental setup to float the bare silver nanoparticles in air with the help of extraneous airflow, and used atomic layer deposition (ALD) method to coat ultra‐thin inert shell without pinholes. Under optimal conditions, we successfully prepared three kinds of SHINERS NPs (Ag@Al₂O₃, Ag@SiO₂ and Ag@TiO₂) in large quantity without pinholes. The ultra‐thin inert shell maintains the SERS activity of silver nanoparticles for long period of time. Transmission electron microscopy (TEM) images confirm the uniform coating of shell material on silver nanoparticles. Finally, the as‐prepared SHINs have been applied to detect various samples to demonstrate the applications. The presented ALD method offers a unique way to coat ultrathin shell (1–10 nm) on metal nanoparticles in large quantity (1–10 g) for practical applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Microwave dielectric properties of (1 − x)(Mg0.95Co0.05)TiO3–x(Na0.5La0.5)TiO3 ceramic system

The microstructures and the microwave dielectric properties of the (1 − x)(Mg_0.95Co_0.05)TiO₃–x(Na_0.5La_0.5)TiO₃ ceramic system were investigated. Two-phase system was confirmed by the XRD patterns and the EDX analysis. A co-existed second phase (Mg_0.95Co_0.05)Ti₂O₅ was also detected. The microwave dielectric properties are strongly related to the density and the matrix of the specimen. A new microwave dielectric material 0.88(Mg_0.95Co_0.05)TiO₃–0.12(Na_0.5La_0.5)TiO₃, possessing an excellent combination of dielectric properties: ε_r  22.36, Q × f  110,000 GHz (at 9 GHz), τ_f  2.9 ppm/°C), is proposed as a candidate dielectric for GPS patch antennas.