Electrical Properties Of Thin Films Research Articles

Investigation of effects of ionizing radiation exposure on material properties of organic semiconducting oligomer – Pentacene

Organic semiconducting materials are known for their chemical affinity and sensitivity to environmental conditions. In this manuscript we investigate the changes in various material properties of a very well-known organic semiconducting oligomer – pentacene, upon exposure to ionizing radiation of γ-rays using Cobalt-60 radiation source. The changes in the optical properties were observed by studying UV–Visible Absorbance spectra of the pentacene thin-film. The effects on the valance electronic structure of the pentacene were studied by ultraviolet photoelectron spectroscopy of pristine pentacene, and after exposure of the same to different total-doses of ionizing radiation. Moreover, X-ray photoelectron spectra of the material were recorded to study the core-level changes in the pentacene when exposed to ionizing radiation. These photoelectron spectroscopy techniques suggested p-type doping into the material and presence of newly generated oxidized energy-states in the energy band gap of the material upon exposure to ionizing radiation. Electrostatic force microscopy imaging was done to observe the changes in the electrical properties of pentacene thin-film which suggested an increase in the conductivity upon exposure to ionizing radiation. Moreover, the effect of newly generated oxidized energy-states, in the band gap of the material, on the hopping transport in the pentacene thin-film was studied by measuring changes in the resistance as a function of temperature before and after different total-doses of ionizing radiation, and observing the changes in the slope. Thus, exposure to ionizing radiation is proposed here as a controlled method of doping the organic semiconducting materials and changing their conductivity. Moreover, the changes in the electrical properties of the thin-film upon exposure to ionizing radiation enable its use in sensors for determining ionizing radiation using organic electronic devices as sensors.

Structural, Optical and Electrical Characteristics of Polycrystalline ZnO Thin Film Prepared by Sol-Gel Spin-Coating Method

The effect of annealing temperatures on the Zinc Oxide (ZnO) thin films properties has been investigated. 1.0 M ZnO solution was prepared by sol-gel method as coating solution for ZnO thin films deposition process. The thin films deposition was conducted by spin-coating technique on the silicon and glass substrates. The scanning electron microscopy (SEM) images reveal the evolution of ZnO surface morphology with annealing temperatures. The crystallinity improvement occurred at higher annealing temperature as shown by x-ray diffraction (XRD) result. The optical properties found to be varied at different annealing temperatures. The current-voltage (I-V) measurement results suggested the improvement of ZnO thin film electrical properties with annealing temperatures.

Structure and improved electrical properties of Pr-doped PbZrO3 antiferroelectric thin films with (111) preferential orientation

Pr-doped PbZrO3 antiferroelectric thin films have been fabricated on Pt/Ti/SiO2/Si substrates by a chemical solution deposition method. All the thin films with different Pr doping contents crystallized in perovskite phase with strong (111)-preferred orientation. When Pr doping amount was 1 mol%, the thin film exhibited a large saturation polarization of 59.4 μC cm−2, a high energy storage density of 14.2 J cm−3 at about 600 kV cm−1, and a dielectric constant of about 354 at 1 kHz. The high (111) orientation and occupying site of Pr ions were suggested to be responsible for the improved electrical properties of the thin films.

Recent Developments in Functional Thin Films

Thin film technology is a significant focus of academic, governmental, and industrial research efforts. The economic impact of thin film use is significant and is growing at an impressive rate. BCC Research assigned the thin film global market a value of $9.3 billion in 2011; it is anticipated to reach a value of $14.9 billion by 2016. 1 Drivers of thin film research at this time include lowering the processing cost and environmental burden associated with thin film processing. 2 In addition, efforts are underway to develop thin films on flexible substrates for use in medical prostheses and in energy harvesting devices. Functional thin films have other potential biomedical applications, including use in drug delivery. 3 A search using Thomson Reuters’s Web of Knowledge indicates that the number of published items involving functional thin films has steadily increased each year since 1994; more than 1150 papers were published on this topic and nearly 30,000 citations involved this topic in 2012. 4 In this issue of JOM, the development of thin films for biomedical, corrosion resistance, electronic, optical, radiation detection, thermal barrier, and tribological applications is described. In ‘‘Improved Mobility and Transmittance of Room-Temperature Deposited a-IGZO Films with Low-Temperature Post-Fabrication Anneals,’’ T.L. Alford et al. demonstrate radio frequency (RF) sputtering of amorphous indium gallium zinc oxide onto flexible poly ethylene naphthalate substrates. Annealing the film at low temperatures in an oxygen atmosphere and in vacuum is shown to modify the optical and electrical properties of the thin films. In ‘‘Inkjet Printing of Amphotericin B onto Biodegradable Microneedles using Piezoelectric Inkjet Printing,’’ R.D. Boehm et al. demonstrate modification of the surfaces of Gantrez (ISP Investments, Inc., Wilmington, DE) 169 BF microneedles with amphotericin B using piezoelectric inkjet printing. A radial diffusion assay is used to demonstrate the activity of these drug-loaded microneedles against the yeast Candida parapsilosis. In ‘‘Effect of LowTemperature Microwave Processing and Copper Content on the Properties of Ag-Cu Thin Film Alloys,’’ S. Das and T.L. Alford examine the use of microwave annealing for enhancing the structural and electrical properties of silver-copper thin films. Their work indicates that copper oxide encapsulation layers are formed by microwave annealing. In ‘‘Reflectance Spectroscopy of Functional Ag-Cu Thin Films: Correlation of Reflectivity with Cu Content,’’ S. Das and T.L. Alford evaluate the use of magnetron sputtering to co-sputter pure silver and copper targets. The electrical mobility and optical reflectivity properties of silver-copper thin films on silicon substrates are evaluated. In ‘‘Thermo-mechanical

Preparation and Electrical Properties of BiFeO3 Thin Films Doped with Nd and Co

BiFeO3 (BFO), BiFe0.95Co0.05O3 (BFCO), Bi0.9Nd0.1FeO3 (BNFO) and Bi0.9Nd0.1 Fe0.925Co0.075O3 (BNFCO) thin films were prepared on Pt/Ti/SiO2/Si(111) substrates by chemical solution deposition (CSD) method. The structural and electrical properties of the thin films were studied. X-ray diffraction analysis showed that the films were single perovskite structure and a phase transition appeared in BNFO and BNFCO thin films. Electrical measurements indicated that the ferroelectric properties of BFO thin films were significantly improved by Nd and Co codoping. Well saturated hysteresis characteristic with large remanent polarization were observed in BNFCO thin film. The conduction mechanisms were investigated to understand the different conduction behavior in these thin films.

Optical and Electrical Properties of Thin Films of CuS Nanodisks Ensembles Annealed in a Vacuum and Their Photocatalytic Activity

Effects on the optical, electrical, and photocatalytic properties of undoped CuS thin films nanodisks vacuum annealed at different temperatures were investigated. The chemical bath prepared CuS thin films were obtained at 40°C on glass substrates. The grain size of13.5±3.5 nm was computed directly from high-resolution transmission electron microscopy (HRTEM) images. The electrical properties were measured by means of both Hall effect at room temperature and dark resistivity as a function of the absolute temperature 100–330 K. The activation energy values were calculated as 0.007, 0.013, and 0.013 eV for 100, 150, and 200°C, respectively. The energy band gap of the films varied in the range of 1.98 up to 2.34 eV. The photocatalytic activity of the CuS thin film was evaluated by employing the degradation of aqueous methylene blue solution in the presence of hydrogen peroxide. The CuS sample thin film annealed in vacuum at 150°C exhibited the highest photocatalytic activity in presence of hydrogen peroxide.

INVESTIGATION OF ZrxLa1-xOy NANOCRYSTALLITES IN METAL–HIGH-k OXIDE–SILICON-TYPE NONVOLATILE MEMORY DEVICES

To investigate characterization of Zr x La 1-x O y nanocrystallites as a buffer oxide in forming the metal-oxide-semiconductor field effect transistors (MOSFETs) structure, we synthesized Zr x La 1-x O y nanocrystallites by sol–gel method. Moreover, from the solution prepared, thin films on silicon wafer substrates have been realized by "dip-coating" with a pulling out speed of 5 cm min -1. The structure, morphology, electrical properties of thin film was examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques. Electrical property characterization was performed with metal-oxide-semiconductor (MOS) structures through capacitance–voltage (C–V) and current density–voltage (J–V) measurements. The leakage current density was below 1.0 ×10-6 A/cm 2 at 1 MV/cm.

ALD Growth Behavior of High-K Nanolayers on Various Substrates Characterized by X-Ray Spectrometry in Gracing Incidence Geometry

Thin films of high-k material are becoming more and more used for semiconductor devices. A further shrinking of the devices requires also a further reduction of the high-k film thickness. With this reduction of the high-k thickness down to just a few nanometers two technical challenges have to be addressed. The first one is the ALD process for the deposition of the high-k material. Usually the ALD process can be well controlled by tuning the number of process cycles. But it is theoretically predicted [1] that the growth-per-cycle of the first cycles can be different than the steady growth-per-cycle which is obtained for high cycle numbers. This effect is caused by a not fully covered initial surface during the first cycles. Only when the deposited material forms a closed surface and the surface probabilities are the same for each following cycle the deposition rate will be constant. The second challenge is that the electrical properties of thin films with a thickness of a few nanometers are significantly determined by the quality of the interface between the film and the substrate.

Determining the planar Nernst effect from magnetic-field-dependent thermopower and resistance in nickel and permalloy thin films

We present magnetic-field-dependent measurements of thermopower, $\ensuremath{\alpha}$(H), and resistance, $R(H)$, for ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}$ and Ni thin films. We conducted these experiments in fields oriented parallel and perpendicular to the applied thermal gradient, $\stackrel{P\vec}{\ensuremath{\nabla}}T$, for $\ensuremath{\alpha}$(H) and applied current for $R(H)$. We deposited the 20-nm-thick films on 500-nm-thick suspended Si-N thermal isolation platforms that enable in-plane measurements of thermal and electrical properties of thin films. Both $\ensuremath{\alpha}(H)$ and $R(H)$ in Ni-Fe and Ni films exhibit evidence of spin-dependent scattering through an even field dependence and a linear proportionality between $\ensuremath{\alpha}(H)$ and $1/R(H)$. Finally, we use $\ensuremath{\alpha}({\mathrm{H}}_{\ensuremath{\parallel}})$ and $\ensuremath{\alpha}({\mathrm{H}}_{\ensuremath{\perp}})$ to determine the planar Nernst coefficient in Ni-Fe and Ni thin films and use this coefficient to predict the size of the planar Nernst effect (PNE) in the micromachined platform. The measured field dependence of the PNE is well matched by the prediction obtained from our $\ensuremath{\alpha}$(H) results.

Optical and Electrical Properties of Thin Films of Polyaniline and Polypyrrole

Optical and Electrical Properties of Thin Films of Polyaniline and Polypyrrole

Observation and study of the negative magnetoresistance in porous silicon

We investigate the effect of a static magnetic field on the electrical properties of thin films of porous silicon. We observe a relative variation of the resistance with respect to intensity of the applied magnetic field. This effect called magnetoresistance (MR) has been found to be negative at room temperature in the entire range of the applied magnetic field (under 8000G). The negative MR effect depends strongly of the applied voltage and reaches up to 5% at the value of magnetic field of 8000G. The analysis has been based on the 1D weak localization theory (WL) in diffusive semiconductors, from which a consistent picture emerges, considering the PS film as networks of quasi-one-dimensional wires. We give an explicit expression for the WL correction depending only of the phase coherence length Lφ. A good agreement is observed between experimental data and theory.

Electrical properties of thin films deposited with MnO- and MnO2-modified BiFeO3 oxide targets

Mn-modified Bi1.05FeO3 thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by using a pulsed laser deposition method with BFO oxide targets modified with MnO or MnO2, and the effects of the Mn were investigated. The 3% MnO-modified BFO thin film capacitor exhibited a large remnant polarization (2P r = 179 µC/cm2) and low leakage currents over a wide electric-field range. However, different leakage current behaviors were observed in the 10% MnO-modified and 10% MnO2-modified BFO thin films. The leakage current mechanism of the 10% MnO-modified BFO thin film was Ohmic conduction while that of the 10% MnO2-modified BFO thin film was related to the oxygen vacancy-associated electrical conductivity.

Graphene and boron nitride lateral heterostructures for atomically thin circuitry

Precise spatial control over the electrical properties of thin films is the key capability enabling the production of modern integrated circuitry. Although recent advances in chemical vapour deposition methods have enabled the large-scale production of both intrinsic and doped graphene, as well as hexagonal boron nitride (h-BN), controlled fabrication of lateral heterostructures in these truly atomically thin systems has not been achieved. Graphene/h-BN interfaces are of particular interest, because it is known that areas of different atomic compositions may coexist within continuous atomically thin films and that, with proper control, the bandgap and magnetic properties can be precisely engineered. However, previously reported approaches for controlling these interfaces have fundamental limitations and cannot be easily integrated with conventional lithography. Here we report a versatile and scalable process, which we call 'patterned regrowth', that allows for the spatially controlled synthesis of lateral junctions between electrically conductive graphene and insulating h-BN, as well as between intrinsic and substitutionally doped graphene. We demonstrate that the resulting films form mechanically continuous sheets across these heterojunctions. Conductance measurements confirm laterally insulating behaviour for h-BN regions, while the electrical behaviour of both doped and undoped graphene sheets maintain excellent properties, with low sheet resistances and high carrier mobilities. Our results represent an important step towards developing atomically thin integrated circuitry and enable the fabrication of electrically isolated active and passive elements embedded in continuous, one-atom-thick sheets, which could be manipulated and stacked to form complex devices at the ultimate thickness limit.

Atomic layer deposition of rare-earth-based binary and ternary oxides for microelectronic applications

Atomic layer deposition (ALD) has been established as a powerful method for the growth of very thin and conformal films to be used in ultra-scaled conventional and novel microelectronic devices. We report the most recent advancements in the field of ALD of rare-earth-based oxides to be implemented as active dielectrics. The review is balanced between the development of new ALD processes and the assessment and the discussion of fundamental scientific issues related to the structural, chemical and electrical properties of thin films of rare-earth-based oxides. The deposition process of binary lanthanide oxides is critically reviewed focusing on the first (La) and last (Lu) element of the series. Concomitantly, the integration of rare earth elements as dopant atoms in HfO2 and ZrO2 is also systematically reported. A final overview is dedicated to the results obtained by ALD of more innovative lanthanum-based ternary oxides.

Concept of a thin film memory transistor based on ZnO nanoparticles insulated by a ligand shell

In this work, we report on the synthesis and the electrical properties of ZnO nanoparticles, which differ in their organic shell. The introduction of a 2-ethylhexanoate shell instead of a common acetate shell has an impact on the accessible size of the ZnO nanoparticles and changes the electrical properties of thin films in transistors. While acetate covered ZnO particles behave as a semiconductor with an electron mobility of 0.38 cm(2) V(-1) s(-1), the 2-ethylhexanoate ligand shell inhibits a charge transport resulting in insulating films (with an average ε(r) = 9.4). These films can be reconverted to semiconductive layers by removing the ligand shell with oxygen plasma treatment or they can be used as a solution processed dielectric layer in organic transistors. Its use as dielectric allows low voltage device operation and shows potential application as a charge storage layer as needed in non-volatile memory transistors.

Effect of deposition temperature on orientation and electrical properties of (K0.5Na0.5)NbO3 thin films by pulsed laser deposition

Lead-free ferroelectric K0.5Na0.5NbO3 (KNN) thin films have been prepared on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition process. The structures, crystal orientations and electrical properties of thin films have been investigated as a function of deposition temperature from 680°C to 760°C. It is found that the deposition temperature plays an important role in the structures, crystal orientations and electrical properties of thin films. The crystallization of thin films improves with increasing deposition temperature. The thin film deposited at 760°C exhibits strong (001) preferential orientation, large dielectric constant of 930 and the remnant polarization of 8.54μC/cm2.

Structural, Optical and Electrical Properties of Thin Films of Lanthanum Aluminum Oxide Synthesized by Spray Pyrolysis

The structural, optical and electrical properties of spray pyrolysis deposited lanthanum aluminum oxide are reported. The films were deposited from a spraying solutions of lanthanum nitrate and aluminum acetylacetonate in N, N- dimethylformamide using an ultrasonic generator on (100) Si substrates. The substrate temperature was in the 550-650°C range. The thickness was in below 300 Aå. The optical band gap was 5.3 eV, and the refractive index at 630 nm was up to 1.62 depending of the relation lanthanum-aluminum. The electrical characteristics of the films were determined from the capacitance and current versus voltage measurements of metal-oxide-semiconductor (MOS) structures incorporating them. A dielectric constant in the 6-12 range, interface states density of the order of 1012 X 1/eV cm2 as well as breakdown fields higher than 3 MV/cm were determine in this way.

Structural and Electrical Properties of Solution-Processed Gallium-Doped Indium Oxide Thin-Film Transistors

We fabricated solution-processed gallium-doped indium oxide (GIO) thin-film transistors (TFTs). The electrical property, crystallinity, and transmittance were investigated as a function of gallium content. Varying the gallium/indium ratio is found to have a significant effect on structural and electrical properties of thin films. The shrinkage of the lattice of a GIO film originates from substitution of Ga on In sites in the In2O3 lattice, which was verified by X-ray diffraction (XRD) analysis. By increasing the gallium ratio of the channel material, the GIO film shows an amorphous phase. The optimized GIO film (Ga/In= 0.35) has an electron mobility of 3.59 cm2 V-1 s-1, a threshold voltage of 0.1 V, an on/off current ratio of 8.2×107, and a subthreshold slope of 0.9 V/decade, and is highly transparent (∼92%) in the visible region.

Structural and Electrical Properties of Solution-Processed Gallium-Doped Indium Oxide Thin-Film Transistors

We fabricated solution-processed gallium-doped indium oxide (GIO) thin-film transistors (TFTs). The electrical property, crystallinity, and transmittance were investigated as a function of gallium content. Varying the gallium/indium ratio is found to have a significant effect on structural and electrical properties of thin films. The shrinkage of the lattice of a GIO film originates from substitution of Ga on In sites in the In2O3 lattice, which was verified by X-ray diffraction (XRD) analysis. By increasing the gallium ratio of the channel material, the GIO film shows an amorphous phase. The optimized GIO film (Ga/In= 0.35) has an electron mobility of 3.59 cm2 V-1 s-1, a threshold voltage of 0.1 V, an on/off current ratio of 8.2×107, and a subthreshold slope of 0.9 V/decade, and is highly transparent (∼92%) in the visible region.

Impedance spectroscopic investigation of the effect of thin azo-calix[4]arene film type on the cation sensitivity of the gold electrodes

In this work, we report the impedance spectroscopic investigation of the effect of the thin film type on the selectivity of gold/azo-calix[4]arene electrodes. For this purpose, two C1 and C3 azo-calix[4]arene derivative molecules, used as thin films, are deposited by spin-coating process on the gold surface. These thin films were first studied using contact angle measurements. This revealed a less hydrophobic character for C3 thin film, which has been attributed to the presence of hydroxyl groups at the lower rim. The sensitivity study, by Electrochemical Impedance Spectroscopy (EIS), towards Cu 2+ and Eu 3+ cations, has showed that the C3 thin film is more sensitive and selective towards Eu 3+ than C1. This best performance is due to the presence of two ester groups acting as clips and leading to more complexation stability. The EIS results were modeled by an appropriate equivalent circuit for the aim of elucidating electrical properties of thin films. This modeling has exposed that C3 thin film presents lower ionic conductivity and limited diffusion phenomenon at the interface.