Ion Beam Assisted E-beam Evaporation Research Articles

Titanium Nitride Microelectrodes Deposited by Ion Beam Assisted E-beam Evaporation

Titanium Nitride Microelectrodes Deposited by Ion Beam Assisted E-beam Evaporation

Characterization of Mo/Si soft X-ray multilayer mirrors by grazing-incidence small-angle X-ray scattering

The morphology of buried interfaces plays a key role in high performing Mo/Si soft X-ray mirrors. We show that grazing-incidence small-angle X-ray scattering is a highly effective and non-destructive diagnostic technique for analysis of buried interfaces. The parameters of average interface autocorrelation function can be determined unambiguously. Additionally period thickness, roughness of interfaces and an effective number of vertically correlated periods can be extracted. The multilayer mirrors were prepared by e-beam evaporation on heated and unheated substrates, ion beam assisted e-beam evaporation, ion beam sputtering and RF magnetron sputtering. The latter three techniques produce multilayer mirrors with comparable interface roughness. The differences in lateral correlation length and Hurst parameter are found.

Indium oxides by reactive ion beam assisted evaporation: From material study to device application

Indium oxides were deposited by reactive ion beam assisted e-beam evaporation at room temperature. A material study was conducted through a variety of material characterization including crystal structure, electrical properties, optical properties, and chemical composition, along with an investigation of material properties as a function of primary deposition parameters such as ion flux and deposition rate. Implementing the developed semiconducting indium oxide as a channel material, the authors further demonstrated high-performance indium oxide thin-film transistors (TFTs) with conventional silicon dioxide gate dielectric derived by plasma-enhanced chemical vapor deposition (PECVD). The n-channel TFT has a threshold voltage of ∼2.0 V, a field-effect mobility of 33 cm2/V s at a gate bias of 20 V, an ON/OFF current ratio of 108, and a subthreshold slope of 2.0 V/decade. The stability study displays a small threshold voltage shift of ∼0.6 V under a 60 h constant current stress condition. The TFT reported here has one of the best performance characteristics in terms of field-effect mobility, ON/OFF current ratio, OFF current and device stability, using conventional and large-area foundry-compatible PECVD gate dielectrics. The device performance coupled with PECVD dielectrics makes ion beam assisted e-beam evaporation derived indium oxide TFT a promising candidate for active matrix flat-panel displays.

Indium oxide thin‐film transistor by reactive ion beam assisted deposition

AbstractThis work reports on the fabrication and characterization of indium oxide semiconducting films and their application in thin‐film transistors (TFTs). The films have been deposited at room temperature by oxygen ion beam assisted e‐beam evaporation. The influence of deposition conditions on film properties including the crystal structure, conductivity, and intrinsic stress is analyzed. It is found that the electrical properties of indium oxide films can be engineered from metallic to insulating and the film structure can be varied from amorphous to microcrystalline by adjusting deposition rate, oxygen ion energy, and ion beam flux. Furthermore, the highly‐resistive films with considerable microstructural crystallinity exhibit n‐type field‐effect behaviour. A field‐effect mobility of 1.4 cm2/V s, and ON/OFF current ratio of ∼106 are observed for transistors with a silicon dioxide gate dielectric. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication and characterization of NiO/ZnO/ITO p–i–n heterostructure

Transparent oxide semiconductors (TOSs) are promising materials for a variety of optoelectronic applications such as UV detectors. While several TOS-based p–n and p–i–n diodes have been recently reported, the high reverse dark current still poses a major issue. In this work, we report on a NiO/ZnO/ITO p–i–n heterostructure with reduced dark current level suitable for practical applications. Ion beam-assisted e-beam evaporation was used to deposit both p-type NiO and intrinsic ZnO layers, while a conventional sputtering system was used to prepare the ITO layer. Samples with sputtered ZnO layer were also fabricated for comparison. The diodes demonstrated clear rectifying I–V characteristics with a current rectification ratio up to 104 at bias voltages of ±1 V. The lowest level of reverse dark current (∼10 nA/cm2 at −5 V) is observed in samples with ZnO deposited by ion beam-assisted e-beam evaporation. In comparison, diodes with sputtered ZnO layer show two orders of magnitude higher dark current. Analysis of the quasi-static J–V characteristics, including time dependence behavior, shows that the dark current can be attributed to thermal generation of charge carriers via deep defects states in the ZnO layer and charge injection from the contacts. Electrical and optical properties of the TOS films are presented and discussed along with deposition conditions and device performance.

Optically transparent ZnO-based n–i–p ultraviolet photodetectors

An optically transparent tin-doped indium oxide/ZnO/NiO n–i–p heterostructure photodiode was fabricated by ion beam assisted e-beam evaporation. The diode clearly demonstrates rectifying current–voltage (J–V) characteristics with a current rectification ratio up to 10 4 at bias ± 2 V and a low reverse current of ∼ 100 nA/cm 2 at − 5 V. Analysis of J–V characteristics including time dependence of the dark current shows that the leakage current at low biases is attributed to thermal generation via defect states, and at high biases, field-enhanced carrier generation from the ZnO layer dominates. Spectral response and linearity measurements indicate that such a diode is particularly suitable for low level of ultraviolet detection.

Highly efficient transparent organic light-emitting diodes by ion beam assisted deposition-prepared indium tin oxide cathode

The authors have investigated the effects of indium tin oxide (ITO) deposited by ion beam assisted e-beam evaporation on the performance of polymer light-emitting diodes. ITO was evaporated as a cathode onto a thin Mg:Ag layer by an e-beam process, and its performance as a transparent cathode was subsequently compared to that of Mg:Ag and sputtering-prepared ITO. Polymer devices’ luminance and efficiency were improved by more than ten times by ion beam assisted deposition (IBAD)-prepared ITO deposition, with little observable damage to the organic layer. Implementation of the IBAD process resulted in the reduction of the interfacial energy barrier which induced band bending. Furthermore, outcoupling with ITO resulted in enhanced luminance.

Room Temperature Growth of Indium Oxide Films by Reactive Ion Beam Assisted Deposition

AbstractConducting and semiconducting indium oxide thin films have been grown at room temperature by oxygen ion beam assisted e-beam evaporation. We studied an influence of the deposition conditions on thin film properties including the crystal structure, resistivity, optical transmittance, stoichiometry, morphology, and intrinsic stress. X-ray diffraction analysis shows that the crystal structure of indium oxide films changes from amorphous to polycrystalline with preferred (222) orientation when the discharge current increases from 0.5 A to 2.0 A. Film resistivity is tailored in a wide range from 3E-4 ohm-cm to 2E9 ohm-cm by modifying both the evaporation rate of indium and the discharge current of the oxygen ion source. X-ray photoelectron spectroscopy data reveal that the highly-resistive films are more oxygen-enriched than the highly-conductive samples due to electrical activity of the oxygen vacancies. Morphological properties are evaluated using an optical profiler and a measured root-mean-square (RMS) roughness is ~1 nm for produced indium oxide films. All films being studied in this work have compressive stress ranging from 0.4 Gpa to 1.8 Gpa. They are highly transparent with a transmittance up to 90%.Thus, high-performance indium oxide films can be engineered by the reactive ion beam assisted deposition to meet the requirements of different applications such as solar cells, photodetectors, OLEDs, transparent TFTs, and optical coatings.

Low leakage p-NiO∕i-ZnO∕n-ITO heterostructure ultraviolet sensor

This letter reports a low leakage p-NiO∕i-ZnO∕n-ITO ultraviolet photodiode fabricated at room temperature by ion beam assisted e-beam evaporation. Analysis of its J-V characteristics, and time-dependent behavior, reveals that the dominant source of leakage current stems from deep defect states in the ZnO i layer, with its dynamic response at low signal levels limited by charge trapping in the absorption layer. Under a 5V reverse bias, the dark current density is 10nA∕cm2 and quantum efficiency is 18% at a wavelength of 380nm, with a photoresponse behavior that is linear over 5decades.

Ion beam assisted deposition of textured magnesium oxide templates on un-buffered glass and silicon substrates

Biaxially textured magnesium oxide (MgO) templates of 10-nm thickness were successfully fabricated on glass and silicon substrates without any buffer layers using Ar+ ion beam assisted e-beam evaporation. With an additional layer of 100 nm homoepi MgO on top, the in-plane misorientation of ∼6.5° and out-of-plane misorientation of ∼2.0° have been obtained. Prior to growth, the substrates were bombarded with the same Ar+ ion beam for a certain period ranging from 5 to 35 min to provide initial substrate conditions for textured MgO formation. The ion beam induced modification of the substrate surface morphology was characterized using atomic force microscopy. Reduced surface roughness Ra from 2 to 3 nm on the original glass substrates to below 1.0 nm after 5 min ion beam bombardment was found to be an important condition for the textured MgO formation. The nearly unchanged Ra ≤ 1 nm of the silicon substrate after the ion beam bombardment, however, suggests that additional surface modification is required for the textured MgO to form.

Reactive Deposition of Dielectrics by Ion Beam Assisted E-beam Evaporation

AbstractFabrication of high index contrast waveguide stacks for biosensing and other applications require nanometer scale thickness control. Nanoscale dielectric films from electron-beam evaporation can be difficult to obtain due to the resulting porosity and poor stoichiometry of the films. An alternative approach is the reactive deposition of the film from a metal source in the presence of oxygen ions. Using spectroscopic ellipsometry, we have shown that greater control over thickness and index of refraction of silicon dioxide depositions can be obtained through reactive depositions as compared to depositions from SiO2 dielectric source material itself. Through Fourier Transform Infrared Spectroscopy (FT-IR), the Si-O in-phase stretching peak at 1078 cm-1 can be traced, allowing us to determine the stoichiometry of the film.The effects of performing depositions of aluminum oxide dielectric source material in the presence of oxygen ions has also been investigated. Through the use of the oxygen ion source, greater control over index of refraction and optical losses has been observed. By controlling ion source parameters, the aluminum oxide films’ index of refraction can be engineered within a range of 1.58 to 1.64, and waveguide losses can be reduced to as low as 2.0 dB/cm.

Influence of the Ion-to-Atom Ratio on the Structure of CeO2 Buffer Layer by Ion Beam Assisted E-Beam Evaporation

Using ion-beam assisted e-beam evaporation with the ion beam directed at 55° to the normal of the film plane, (200) oriented CeO2 films with biaxial texture were deposited on Hastelloy C276 substrates at room temperature. The crystalline quality and in-plane orientation of films was investigated by X-ray diffraction 2θ-scan and Φ-scan, atomic force microscopy (AFM). It was shown that the in-plane and out-of-plane textures of the CeO2 films were controlled by the deposition parameters. The orientation of the films was studied as a function of ion-to-atom ratio and film thickness. The ion-to-atom ratio was varied by independently adjusting the deposition rate and the ion current density. Under optimum condition, (200) textured CeO2 films have been successfully grown on Hastelloy C276.

PROPERTIES OF MULTILAYER CERAMIC CAPACITOR WITH BaTiO3 THIN LAYERS DEPOSITED BY E-BEAM EVAPORATION

ABSTRACT For the purpose of enhancing the capacitance of MLCCs, thin BaTiO3 dielectric layers and inner electrodes were prepared by ion beam assisted e-beam evaporation method. BaTiO3 films deposited at 300°C showed an amorphous structure and the films annealed above 550°C showed polycrystalline structure. XPS analysis showed the complete oxidation from Ti metal source to TiO or BaTiO3 phase. The dielectric constant of 130∼150 and dissipation factor of 2∼ 4% were obtained from BaTiO3 of single layer. The capacitance decreased with increasing the temperature and satisfied the specification of ± 15% limit at 125°C. There was only small capacitance change with DC bias voltage and after annealing of films, leakage current was 10− 8∼10− 9 A at 10 V. The overall results showed that BaTiO3 thin films by e-beam evaporation were suitable candidates for MLCC application.

Spectroscopic ellipsometry study on e-beam deposited titanium dioxide films

Spectroscopic ellipsometry (SE) was applied to study the optical inhomogeneity of TiO 2 films deposited by the technique of ion-beam assisted e-beam evaporation. A three-sub-layer model of ellipsometry analysis can successfully simulate the structure variation of TiO 2 films, which consists of a dense amorphous layer near the substrate, a crystal columnar layer, and a very thin roughness layer on top. Such a theoretical model is further confirmed by microscopic observations with SEM, TEM, and AFM. The structure variation of TiO 2 films is related to the increase of chamber temperature during the e-beam evaporation process. Annealing evolution of as-deposited TiO 2 films in atmospheric environment at elevated temperatures of 150 and 250 °C was also investigated. The ellipsometry analysis shows that the total film thickness of TiO 2 film increases with the annealing time at both temperatures. A more detailed analysis further reveals that thickness of the top sub-layer increased; whereas the region of the bottom amorphous sub-layer shrunk when the film was annealed at 250 °C.

Indium-tin-oxide thin film deposited by a dual ion beam assisted e-beam evaporation system

Indium-tin-oxide (ITO) thin films were deposited on polycarbonate (PC) substrates at low temperatures (<90°C) by a dual ion beam assisted e-beam evaporation system, where one gun (gun 1) is facing ITO flux and the other gun (gun 2) is facing the substrate. In this experiment, effects of rf power and oxygen flow rate of ion gun 2 on the electrical and optical properties of depositing ITO thin films were investigated. At optimal deposition conditions, ITO thin films deposited on the PC substrates larger than 20 cm×20 cm showed the sheet resistance of less than 40 Ω/sq., the optical transmittance of above 90%, and the uniformity of about 5%.

Observation of a negative electron affinity for boron nitride

This study reports UV-photoemission (UPS) measurements made on boron nitride crystals and thin films. The materials examined are commercial grade c-BN powder and thin films of BN deposited with ion beam assisted e-beam evaporation and laser ablation. The thin film samples examined exhibited varying amounts of sp3 (cubic) and sp2 (hexagonal, amorphous) bonding as determined by FTIR measurements. The UPS measurements displayed the spectral distribution of the low energy photoemitted electrons and the total energy width of the spectra. These characteristics can be related to the electron affinity. The measurements on several of the BN powder and thin film samples revealed features in the emission spectra which are indicative of a negative electron affinity (NEA) surface.