Determination of Activation Energies and Electric Dipole Moment of In‐Plane Highly Electrically Conductive Hetero‐C12TCNQ/C20 LB Films Using Thermally Stimulated Current

The activation energies of in‐plane highly electrically conductive 2‐dodecyl‐7,7,8,8‐tetracyanoquinodimethane (C₁₂ TCNQ)/arachidic acid (C₂₀) hetero‐LB films and C₁₂TCNQ homo‐LB films were determined by thermally stimulated current (TSC) measurement. The TSC curves for the upper Al electrode/C₁₂TCNQ/C₂₀/lower Al electrode were nearly of the same shape as those for the upper Al electrode/C₁₂TCNQ/lower Al electrode. The activation energies of the upper Al electrode/C₁₂TCNQ/C₂₀/lower Al electrode and upper Al electrode/C₁₂TCNQ/lower Al electrode were 0.9–1.3 eV at 55–80^°C and 1.6–1.8 eV at 105–120^°C, respectively. The TSC curves for the upper Al electrode/C₁₂TCNQ/C₂₀/lower Al electrode and upper Al electrode/C₁₂TCNQ/lower Al electrode had two peaks at 55–80^°C owing to the depolarization of the electric dipole and two peaks at 105–120^°C owing to the movement of space charges in the C₁₂TCNQ molecule. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

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.     

Interfacial electrostatic phenomena and capacitance–voltage characteristics of ultrathin polyimide Langmuir–Blodgett films

Capacitance–voltage (C–V) characteristic of ultrathin polyimide (PI) Langmuir–Blodgett (LB) films is discussed theoretically and experimentally taking into account the interfacial electrostatic phenomena and interfacial electronic states at the metal/PI LB film interface. It was found that the apparent film thickness decreases due to the charge exchange phenomena at the metal/film interface. It was also found that electrical insulating properties of the Au/PI LB film/Al device depended on the polarity of external voltage, probably due to the formation of the electrostatic interfacial electric field of 10⁸ to 10⁹ V/m. © 2000 Scripta Technica, Electr Eng Jpn 134(3): 9–15, 2001     

Fabrication and characterization of Au/SBT/LZO/Si MFIS structure

Ferroelectric SrBi₂Ta₂O₉ (SBT) films on a p-type Si (100) wafer with a LaZrO _x (LZO) buffer layer have been fabricated to form a metal-ferroelectric-insulator–semiconductor (MFIS) structure. The LZO thin film and SBT films were deposited by using a sol–gel method. The equivalent oxide thickness (EOT) value of the LZO thin film was about 8.83 nm. Also, the leakage current density of the LZO thin film is about 3.3?×?10^?5 A/cm² at bias sweeping voltage of ±5 V. SBT films were crystallized in polycrystalline phase with highly preferred (115) orientation. Also, the intensity of each pick slightly increased as thickness of SBT films increased. The C–V characteristics of Au/SBT/LZO/Si structure showed clockwise hysteresis loop. The memory window width increased as the thickness of SBT films increased. The leakage current density of Au/SBT/LZO/Si structure decreased as thickness of SBT films increased.     

Growth characteristics and film properties of gallium doped zinc oxide prepared by atomic layer deposition

We carried out comprehensive studies on structural, optical, and electrical properties of gallium-doped zinc oxide (Ga:ZnO) films deposited by atomic layer deposition (ALD). The gallium(III) isopropoxide (GTIP) was used as a Ga precursor, which showed pure Ga₂O₃ thin film with high growth rate. Using this precursor, conductive Ga doped ZnO thin film can be successfully deposited. The electrical, structural and optical properties were systematically investigated as functions of the Ga doping contents and deposition temperature. The best carrier concentration and transmittance (7.2?×?10²⁰ cm^?3 and 83.5 %) with low resistivity (≈3.5?×?10^?3?Ωcm) were observed at 5 at.% Ga doping concentration deposited at 250 °C. Also, low correlation of deposition temperature with the carrier concentration and film structure was observed. This can be explained by the almost same atomic radius of Ga and Zn atom.     

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.     

Improvement of the thermal and chemical stability of Al doped ZnO films

To improve the stability of sputter-deposited ZnO:Al (AZO) films at high temperature above 300^∘C, an amorphous Zn-Sn-O (ZTO) film was deposited on the top of AZO films as an protective layer by co-sputtering of pure ZnO and SnO₂ targets. Amorphous ZTO films had resistivity in the range from 10⁻² to 10⁻³ Ωcm and were stable up to temperature of 400^∘C. Heat treatments of bare AZO films in the atmosphere at 400^∘C resulted in a dramatic increase in the resistivity accompanied by substantial decrease in carrier concentration and Hall mobility. The AZO films covered with the ZTO film showed remarkable improvement in thermal stability for subsequent heat treatments in the temperature range from 200 to 400^∘C in the atmosphere as well as chemical stability in weak acidic solution. X-ray photoelectron spectroscopy analysis showed that the improvement was attained by ZTO layer acting as diffusion barrier of oxygens and/or water vapors.     

Ferroelectric field effect in (La,Sr)CoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 heterostructures

Abstract

Epitaxial LaCoO₃/Pb(Zr,Ti)O₃/(La,Sr)CoO₃ (LSCO) heterostructures have been grown on LaAlO₃ by pulsed laser deposition for investigating ferroelectric field effect. In the heterostructure, semiconducting LaCoO₃ was used as a conducting channel layer, instead Si. The resistivity of the LaCoO₃ (LCO) channel layer was found to be dependent on an oxygen ambient, primarily the ambient oxygen pressure during deposition. The resistivity of the LCO layer varied in the range of 0.1 – 100 Ω cm. Ferroelectric field effect induced in LaCoO₃ layer was observed by measuring the resistance modulation of the LCO layer with respect to the polarized state of the PZT layer. The resistance modulation of 9% was obtained in the 680 Å thick LCO layer. Further the resistance modulation was improved up to 45% after applying dc bias. It is suggested that the LCO/PZT/LSCO heterostructure can be used as a ferroelectric field effect transistor.     

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.     

Effect of discharge power density on the properties of Al and F co-doped ZnO thin films prepared at room temperature

ZnO transparent conducting thin films co-doped with aluminium and fluorine (AZO:F) were prepared on glass substrates by RF magnetron sputtering at room temperature. The effect of discharge power density on the microstructure, surface morphology, electrical and optical properties was investigated. From XRD analysis, it was revealed that the intensity of (002) favoured orientation of ZnO films increased with power density from 2.6 to 6.1?W/cm² and then turned to a randomly orientated structure as power density continuously increased to 7.8?W/cm². The film prepared at 6.1?W/cm² showed a better crystallization and microstructure with larger, pyramid-like grains that were approximately 180?nm long and 90?nm wide. As a result, the electrical resistivity of the AZO:F films had a minimum of 4.1?×?10^?4???cm. The improvement in the electrical resistivity of AZO:F films was due to the increase in carrier concentration from 8.8?×?10²⁰ to 1.38?×?10²¹?cm^?3 and the mobility from 5.8 to 11.8?cm² V^?1 s^?1. The increase in carrier concentration with power density was also found to affect the optical property of the films due to the Moss-Burstein shift.     

Effects of the Ga-doping concentration on the characteristics of Zn<Subscript>0.7</Subscript>Mg<Subscript>0.3</Subscript>O thin films deposited by metal-organic chemical vapor deposition using an ultrasonic nebulization

Ga-doped Zn_0.7-xMg_0.3O thin films were deposited on glass substrates at 350 °C by metal-organic chemical vapor deposition using an ultrasonic nebulization technique to transport the source precursors, and the effects of the Ga-doping concentration were investigated. The films with Ga-doping concentrations less than 5 mol% grew with [001] preferred orientation perpendicular to the substrate surface and were composed of large crystallites. At Ga content greater than 5 mol%, the films grew with random orientation and very small crystallite size. The charge carrier concentration in the films increased rapidly up to 4 mol% Ga and then decreased gradually with further increases in the Ga-content. The film resistivity decreased with increasing Ga-content up to 4 mol% due mainly to the increase in charge carrier concentration. Then, the resistivity increased gradually with increasing Ga-content due to the decrease in mobility. The lowest resistivity of the Ga-doped Zn_0.7-xMg_0.3O thin film was 3.8?×?10^?1 Ωcm at the Ga doping concentration of 4 mol%. The mean transmittance in the visible range was more than 85% in all films. The optical band gap of the films increased with increasing Ga-doping concentration up to 5 mol% due to the Burstein-Moss effect.     

Microstrip Band Pass Filter of GHz Region Employing Aerosol-Deposited Alumina Thick Films

The miniaturized 10 GHz microstrip band-pass filter was successfully fabricated on the alumina thick films grown on Cu substrates at room temperature by aerosol deposition method and using the newly developed pattern electroplating procedure and electromagnetic analysis. The relative dielectric permittivity and loss tangent of the aerosol-deposited alumina thick films on Cu were 9.9 and 0.089, respectively. The resistivity of the electroplated Cu line was determined to be 2 × 10^{? 8} Ω m. The very good agreement was shown between results simulated using a 3-dimensional electromagnetic analysis and the actual measured data.     

Effects of sputtering pressure and thickness on properties of ZnO:Al films deposited on polymer substrates

Highly conducting and transparent aluminum doped zinc oxide (ZnO:Al) thin films have been deposited on polyimide substrate by r.f. magnetron sputtering at room temperature. The influence of sputter pressure and thickness on the structural, electrical, and optical properties of ZnO:Al films deposited on polyimide substrate is reported. The crystallinity and degree of orientation was increased by decreasing the sputter pressure. For higher sputtering pressures an increase on the resistivity was observed due to a decrease on the mobility and the carrier concentration. As the film thickness was increased, the crystallite sizes were increased, but the average transmittance in the wavelength range of the visible spectrum was decreased. The electrical performances of the ZnO:Al films deposited on glass substrates are slightly worse than the ones of the films deposited on polyimide substrates with same thickness. The lowest resistivity of 8.6?×?10^?4 Ω cm can be obtained for films deposited on glass substrate with the thickness of 800 nm.     

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.     

Energy-level alignment at model interfaces of organic electroluminescent devices studied by UV photoemission: trend in the deviation from the traditional way of estimating the interfacial electronic structures

The electronic structures of model interfaces of organic electroluminescent (EL) devices were investigated with UV photoemission spectroscopy (UPS). Interfaces of TTN (tetrathianaphthacene) and TCNQ (tetracyanoquinodimethane) were also studied as extreme cases for hole transport and electron transport material, respectively. For all organic/metal interfaces studied, the work function of metal electrode was changed by deposition of organic layer, i.e., the vacuum level was shifted at the interface, indicating the invalidity of the traditional energy level alignment model where a common vacuum level was assumed at organic/metal interface. At TCNQ/Au, DP-NTCI/Al, which are acceptor/metal interfaces, upward shift of the vacuum level of organic layer relative to that of metal was observed, suggesting the formation of interfacial dipole due to electron-transfer from metal to acceptor. At other organic/metal interfaces, TPD(N, N'-diphenyl-N, N'-(3-methylphenyl)-1, 1'-biphenyl-4, 4'-diamine)/Au or ITO (indium tin oxide), ALq/sub 3/ (tris(8-hydroxyquinolino) aluminum)/Al, DP-NTCl(N, N'-diphenyl-1,4,5,8- naphthyltetracarboxylimide)/Al or Au, downward shift of the vacuum level was observed. Such downward shift has been also observed in our previous study for porphyrin/metal interfaces, and seems to be a trend for organic/metal interfaces at which no electron-transfer from metal to organic layer occurs. This trend suggests that the traditional model tends to underestimate (overestimate) the barrier height for hole (electron) injection. On the other hand, the vacuum level shift at ALq/sub 3//TPD interface was less than 0.1 eV, leading to an apparent applicability of the traditional model. However, it is not always the case for organic/organic interfaces: finite shift of 0.2 eV was observed at TTN/TCNQ interface due to electron-transfer from TTN to TCNQ. Possible origins of vacuum level shift at organic/metal interfaces were also discussed.     

Low‐resistive and transparent AZO films prepared by PLD in magnetic field

Al₂O₃‐doped ZnO (AZO) thin films have been deposited onto glass substrates using a split target consisting of AZO (1 wt%) and AZO (2 wt%) by pulsed laser deposition with an ArF excimer laser (λ = 193 nm, 15 mJ, 10 Hz, 0.75 J/cm²). By applying a magnetic field perpendicular to the plume, the lowest resistivity of 8.54 × 10^?5Ω·cm and an average transmittance exceeding 91% over the visible range were obtained at a target‐to‐substrate distance of 25 mm for approximately 279‐nm‐thick AZO film (1.8 wt%) grown at a substrate temperature of 230 °C in vacuum. From cross‐sectional TEM observations and the XRD spectrum, a reason why the low resistivity (54 × 10^?5Ω·cm) was reproducibly obtained was considered to be due to the fact that a disorder of crystal growth originating in the vicinity of the interface between the substrate and the film was suppressed by application of the magnetic field and the c‐axis orientation took preference, giving rise to the increase of mobility. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(2): 40–45, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20026     

Effect of fluorine doping on the properties of ZnO films deposited by radio frequency magnetron sputtering

ZnO films with varying fluorine content were prepared on Corning glass by radio frequency magnetron sputtering of ZnO target containing ZnF₂ at room temperature, and the compositional, electrical, optical, and structural properties of the as-grown films together with the vacuum-annealed films were investigated. The fluorine content in the fluorine doped ZnO (FZO) films increased almost linearly with increasing ZnF₂ content in sputter target, and the highest atomic concentration was 7.3%. Vacuum-annealing caused a slight reduction of fluorine content in the films. The resistivity of the as-grown FZO films deposited showed a typical valley-like behavior with respect to the fluorine content in film, i.e. having minimum resistivity at intermediate fluorine content. Despite high fluorine content in the FZO films, the carrier concentration remained below 1.2?×?10²⁰ cm^?3, leading to very low doping efficiency level. Upon vacuum-annealing, the resistivity of FZO films decreased substantially due to increase in both the carrier concentration and the Hall mobility. From the structural analysis made by X-ray diffraction study, it was shown that addition of small amount of fluorine enhanced the crystallinity of FZO films with (002) preferred orientation, and that large amount of fluorine addition yielded disruption of preferred orientation. It was also shown that doping of fluorine rendered a beneficial effect in reducing the absorption loss of ZnO films in visible range, thereby substantially enhancing the figure of merit.     

Ferroelectric properties of plzt thin films prepared by mocvd

Abstract

Lanthanum-modified lead zirconate titanate (PLZT) thin films have been grown on Pt/SiO₂/Si substrate at 650[ddot]C by metalorganic chemical vapor deposition. The relative dielectric constant increased as the La content was increased up to about 5 atomic percent (at%). The remanent polarization and coercive field decreased from 30 to 20 μC/cm² and from 53 to 30 kV/cm, respectively, with increasing La content in the range of 0–13 at%. The leakage current of PLZT film was 3 × 10^?9 A/cm² at an applied voltage of 3 V. The degradation of switched charge density of PLZT film was not observed even at 2 × 10¹¹ cycles.     

Structural and electrical properties of low resistance Pt/Pd/Au contact on p-GaN

We have investigated electrical and structural properties of Pt/Pd/Au ohmic contact on p-type GaN:Mg (2.5 × 10¹⁷ cm⁻³) using Auger electron spectroscopy (AES) and glancing angle x-ray diffraction (GXRD) analysis. It was shown that the specific contact resistivity improved with increasing annealing temperature. The annealing of the contact at 600^∘C for 2 min in flowing N₂ atmosphere resulted in a specific contact resistivity of 3.1 × 10⁻⁵ Ω cm². Both GXRD and AES depth profile results show that Ga₃Pt₅, Ga₂Pd₅, and Au₇Ga₂ phases are formed at the interface region between metal and GaN when annealed at temperatures 600^∘C. Possible explanation is suggested to describe the annealing dependence of the specific contact resistivity of the Pt/Pd/Au contacts.     

Electrical properties of Pb(Zr0.53Ti0.47)O3 thin film capacitors with modified RuO2 bottom electrodes

Abstract

Growth of Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films on RuO₂ electrodes by the sol-gel process is usually accompanied by the formation of second phases. The resulting RuO₂/PZT/RuO₂ capacitors are fatigue-free up to nearly 10¹¹ switching cycles, but they have high leakage currents (J～10^?3 A/cm² at 1 volt) and large property variation. We have developed several modifications of the RuO₂ bottom electrode which enhance nucleation of the perovskite phase, eliminate or reduce the second phases, and control film orientation and properties. The PZT films deposited on the modified RuO₂ electrodes have leakage current densities which are two to four orders of magnitude lower than those of PZT films deposited on the unmodified RuO₂ electrodes. In most cases, the excellent resistance to polarization fatigue which is characteristic of the RuO₂/PZT/RuO₂ capacitors, is maintained.