Dielectric Constant Oxide Research Articles

Electrical analysis of three-stage passivated In0.53Ga0.47As capacitors with varying HfO2 thicknesses and incorporating an Al2O3 interface control layer

The atomic layer deposition of high dielectric constant oxides like HfO2 on III-V substrates such as In0.53Ga0.47As leads to a poor interface, with the growth of In0.53Ga0.47As native oxides regardless of the surface pretreatment and passivation method. The presence of the native oxides leads to poor gate leakage current characteristics due to the low band gap of the native oxides and the presence of potential wells at the interface. In addition, the poor quality of this interface leads to very large interface state defect densities, which are detrimental to metal-oxide-semiconductor-based device performance. A wide band gap interlayer replacing the native oxide layer would remove the potential wells and provide a larger barrier to conduction. It may also assist in the improvement of the interface quality, but the problem remains as to how this native oxide interlayer cannot only be removed but prevented from regrowing. In this regard, the authors present electrical results showing that the atomic layer deposition (ALD) growth of a thin (∼1 nm) Al2O3 layer before the ALD growth of HfO2 causes a removal/reduction of the native oxides on the surface by a self-cleaning process without subsequent regrowth of the native oxides. As a result, there are significant improvements in gate leakage current densities, and significant improvements in the frequency dispersion of capacitance versus gate voltage, even when a defective In0.53Ga0.47As epitaxial layer on an InP substrate is employed. Measurements at different temperatures confirm that the frequency dispersion is mainly due to interface state defect responses and another weakly temperature dependent mechanism such as border traps, after accounting for the effects of nonideal In0.53Ga0.47As epitaxial layer growth defects where applicable.

Thin film colossal dielectric constant oxide La2−xSrxNiO4: Synthesis, dielectric relaxation measurements, and electrode effects

We have successfully synthesized the colossal dielectric constant oxide La2−xSrxNiO4 in thin film form by reactive cosputtering from metallic targets and careful annealing protocols. Composition and phase purity was determined through energy dispersive spectra and x-ray diffraction, respectively. The dielectric constant exceeds values of over 20 000 up to 1 kHz and the activation energy for the frequency-independent conductivity plateau was extracted to be approximately 155 meV from 300 to 473 K, both in agreement with measurements conducted on bulk single crystals. However, unlike in single crystals, we observe early onset of relaxation in thin films indicating the crucial role of grain boundaries in influencing the dielectric response. ac conductivity at varying temperatures is analyzed within the framework of the universal dielectric law leading to an exponent of approximately 0.3, dependent on the electrode material. Impedance spectroscopy with electrodes of different work function (Pt, Pd, and Ag) was further carried out as a function of temperature and applied bias to provide mechanistic insights into the nature of the dielectric response.

Metallic Nanoshells with Semiconductor Cores: Optical Characteristics Modified by Core Medium Properties

It is well-known that the geometry of a nanoshell controls the resonance frequencies of its plasmon modes; however, the properties of the core material also strongly influence its optical properties. Here we report the synthesis of Au nanoshells with semiconductor cores of cuprous oxide and examine their optical characteristics. This material system allows us to systematically examine the role of core material on nanoshell optical properties, comparing Cu(2)O core nanoshells (ε(c) ∼ 7) to lower core dielectric constant SiO(2) core nanoshells (ε(c) = 2) and higher dielectric constant mixed valency iron oxide nanoshells (ε(c) = 12). Increasing the core dielectric constant increases nanoparticle absorption efficiency, reduces plasmon line width, and modifies plasmon energies. Modifying the core medium provides an additional means of tailoring both the near- and far-field optical properties in this unique nanoparticle system.

Bonding and gap states at GaAs-oxide interfaces

The nature of bonding and possible causes of Fermi level pinning at high mobility–high dielectric constant oxide GaAs:HfO 2 interfaces are discussed. It is argued that these are atoms with defective bonding, rather than states due to the bulk semiconductor of its interface. Electron-counting rules are used to define interfaces which are insulating, and which can be used in future as hosts for interfaces containing defects.

Develop compact dual‐band bandpass filters on the aluminum oxide

AbstractFor the purpose of minimizing the dual‐band bandpass filters (2.4 and 5.7 GHz), two stepped impedance resonator structures are modified and involved in a pair of distorted coupled lines to form a compact structure.And because the designed filter is printed on the high quality factor and dielectric constant aluminum oxide ceramic substrate by the screen‐printing technique, the characteristics of the filters could be improved and the size of the filters could be minimized to only 22.2 × 12 mm2. Furthermore, the modified SIR structure can be used to tune the second resonant frequency (harmonic) for the applications of dual bands, and the modified coupled line structures can be used to excite additional transmission zeros and adjust its locations, which can improve the characteristics of the filters effectively. In this article, the optimum measured insertion loss and bandwidth for 2.4 GHz are −0.98 dB and 11.1%, respectively, and for 5.7 GHz are −1.05 dB and 10.1%, respectively. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1091–1094, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25126

Band alignment at metal–semiconductor and metal–oxide interfaces

AbstractThe mechanisms of Schottky barrier formation are reviewed from the metal‐induced gap state model to the universal defect model, and the chemical reaction model. The recent progress in understanding barrier heights and band offsets in Si – high dielectric constant oxide and metal high dielectric constant oxide systems is then discussed, and interesting they contain components of each model. The greater emphasis on understanding defect reactions has allowed us to separate the effects of intrinsic mechanisms, metal induced gap states (MIGS) and extrinsic mechanisms (defects).

Dielectric and impedance performances of giant dielectric constant oxide CaCu3Ti4O12

Pure colossal dielectric constant oxide CaCu 3 Ti 4 O 12 (CCTO) compound was prepared by traditional ceramic processing. Dielectric dispersion and complex impedances spectra were investigated using a impedance analyzer within a temperature range of 10—420 K. The data were simulated by “ZVIEW” software. The result indicates that there are two obvious relaxations in the dielectric dispersion spectra when the temperature is higher than room temperature and the dielectric constant increases remarkably with increasing temperatures at a low frequency, which indicates a thermal ionic polarization. However, the frequency spectra becomes similar to Debye-type relaxation when the temperature is lower than room temperature and the low-and high-frequency relaxation step almost keeps unchanged with temperature, which reveals a feature of interface polarization and considerable temperature stability for CCTO. The relaxation revealed in the frequency spectra corresponds to the three different semicircles revealed by the impedance spectra, which indicated there are three inhomogeneous regions or polarization processes in CCTO ceramics and the colossal dielectric constant mainly comes from the extrinsic polarization of these inhomogenities. The activation energies are found to be respectively 0.05 eV, 0.58 eV and 0.49eV for the three different polarization processes by simulating the impedance semicircles using an equivalent circuit.

Electrical and Reliability Characteristics of Barrierless Cu-Based Contact for High Dielectric Constant Oxide Thin-Film Device Integration

We report a stable Cu-based contact stack to overcome Cu diffusion and oxidation problems encountered during the high dielectric constant oxide thin-film device integration. Our contact stack is also beneficial from the barrierless scheme for improving the thin-film device performance. Interfacial investigation reveals no extensive interaction between and barrierless Cu contact stack after annealing up to . on the low resistivity Cu-based contact stack behaves fairly similar to that on the Pt counterpart as the symmetry of the leakage current is obtained using different work function contacts (Cu and Pt). As Cu is compatible with integrated circuit processing, our barrierless contact stack is readily applicable for integration with Si-based devices.

Modeling of Alternative High-k Dielectrics for Memory Based Applications

Significant research efforts are devoted to the development of alternative high dielectric constant oxides (high-k) to sustain the requirements of the next generations of DRAM and FLASH memories. For the metal-insulator-metal applications, the identification of an oxide with a dielectric constant higher than 50 and a crystallization temperature lower than 650 C is a corner stone in the selection of the materials; while for non volatile memory (NVM) applications, an oxide with a dielectric constant ranging between 9 and 30, a large band gap (> 6 eV) are targeted. While significant efforts have been dedicated to the integration of possible material candidates, little is known on their intrinsic properties. Through this paper, we provide an overview of the parameters that determine the electronic and the polarizability response of tantalates, niobiates and rare-earth based scandates oxides eligible for the development of the next generation of memory based applications.

Properties of Sr7Nb13O36/Nb2O5/Sr7Nb13O36 Laminated Films for Gigabit Memory Capacitors

Properties of Sr7Nb13O36/Nb2O5/Sr7Nb13O36 laminated films for gigabit memory capacitors were investigated. The equivalent oxide thicknesses (EOT), dielectric constant, band gap and leakage current for a single layer Sr7Nb13O36 having 10 nm film thickness were 1.12 nm, 34.8, 4.45 eV and 3×10-9 A/cm2 at 1 V, respectively. Those properties for a single layer Nb2O5 having 20 nm thickness were 0.72 nm, 108, 4.25 eV, and 2×10-8 A/cm2, respectively. The Sr7Nb13O36/Nb2O5/Sr7Nb13O36 laminated films satisfied the EOT of 0.77 nm, effective dielectric constant of 51, effective band gap of 4.35 eV and leakage current density of 6.4×10-9 A/cm2 at 1 V. The fraction of applied voltage across the Sr7Nb13O36 film was dominant so that the voltage across the high dielectric constant Nb2O5 film could be reduced. The Sr7Nb13O36/Nb2O5/Sr7Nb13O36 laminated film is a solution for gigabit memory capacitors.

High K Dielectrics for Future CMOS Devices

The properties and materials selection of high dielectric constant oxides and metals for advanced CMOS FETs are reviewed. The basic problems of high K oxides and metal gate stacks have been implemented in practical devices by a number of industrial groups. The control of the FET gate threshold voltage and its effective work function has been difficult to achieve. Atomistic models of factors affecting the effective work function are described.

Electrical Properties of Al/HfO2/n-GaN Prepared by Reactive Sputtering Method

In this study, the effects of the doping concentration of n-type GaN on Al/HfO2/GaN metal–oxide–semiconductor capacitors that incorporated sputtered HfO2 gate dielectric were determined. Electron mobility decreased and conductivity increased as doping concentration increased. The FWHM of the X-ray rocking curves of GaN(0002) also increased with doping concentration. A positively shifted and stretched capacitor–voltage (C–V) curve relative to the ideal one was obtained. Accumulation capacitance increased slightly as doping concentration increased, increasing the dielectric constant and effective oxide thickness. A moderately doped sample (ND∼2 ×1018) with the lowest flat-band voltage shift (∼1.6 V) showed the least stretched C–V curve, and the lowest effective oxide charge (3.2 ×1012 cm-3) and interface density (1.2 ×1012 cm-2) among the studied samples. Results of this study significantly contribute to the development of GaN-based metal–oxide–semiconductor field-effect transistors (MOSFETs) or metal–oxide–semiconductor heterojunction field-effect transistors (MOSHFETs).

Band offsets and work function control in field effect transistors

The article summarizes the development of metal gate materials and the control of the effective work function on high dielectric constant (high K) oxides for use in advanced Si field effect transistors. The Schottky barrier heights of metals on HfO2 are calculated accurately for ideal interfaces of various stoichiometries and for interfaces with defects.

Photoresist Removal Using Alternative Chemistries and Pressures

Approximately 20% of the processing steps in integrated circuit (IC) fabrication involve surface cleaning and removal of photoresist and plasma etch residues. Continuous device minimization requires the use of thin films (<20 nm), closely spaced features, and ultra shallow junctions (<50nm); as a result, the challenges associated with effective surface cleaning are intensified. In addition, to insure high device performance, incorporation of alternate materials such as copper, ruthenium, and molybdenum, porous low dielectric constant SiO2-based insulators, and hafnium or zirconium oxides or silicates into device structures is taking place. Integration of these materials into working devices requires precise control of surface properties. In order to eliminate damage to films or substrates, avoid modification of surfaces, promote contaminant removal rates and enhance process control, approaches such as use of downstream plasmas, liquid cleaning with low concentrations of reactive chemicals, mechanical agitation, and liquid or particle jets have been implemented [1].

Electrical, structural, and chemical properties of HfO2 films formed by electron beam evaporation

High dielectric constant hafnium oxide films were formed by electron beam (e-beam) evaporation on HF last terminated silicon (100) wafers. We report on the influence of low energy argon plasma (∼70 eV) and oxygen flow rate on the electrical, chemical, and structural properties of metal-insulator-silicon structures incorporating these e-beam deposited HfO2 films. The use of the film-densifying low energy argon plasma during the deposition results in an increase in the equivalent oxide thickness (EOT) values. We employ high resolution transmission electron microscopy (HRTEM), x-ray photoelectron spectroscopy (XPS), and medium energy ion scattering experiments to investigate and understand the mechanisms leading to the EOT increase. We demonstrate very good agreement between the interfacial silicon oxide thicknesses derived independently from XPS and HRTEM measurements. We find that the e-beam evaporation technique enabled us to control the SiOx interfacial layer thickness down to ∼6 Å. Very low leakage current density (<10−4 A/cm2) is measured at flatband voltage +1 V into accumulation for an estimated EOT of 10.9±0.1 Å. Based on a combined HRTEM and capacitance-voltage (CV) analysis, employing a quantum-mechanical CV fitting procedure, we determine the dielectric constant (k) of HfO2 films, and associated interfacial SiOx layers, formed under various processing conditions. The k values are found to be 21.2 for HfO2 and 6.3 for the thinnest (∼6 Å) SiOx interfacial layer. The cross-wafer variations in the physical and electrical properties of the HfO2 films are presented.

Thermal stability of electrical and structural properties of GaAs-based metal-oxide-semiconductor capacitors with an amorphous LaAlO3 gate oxide

We report on thermal stability of the electrical and structural properties of metal-oxide-semiconductor capacitors with amorphous LaAlO3 high dielectric constant (high k) oxide on GaAs epitaxial layers with and without an interface amorphous silicon (a-Si) passivation layer to prevent Fermi level pinning at the III-V/high-k interface. The electrical properties of a-Si passivated GaAs improved with annealing temperature, demonstrating reduced equivalent oxide thickness, small (∼50mV) hysteresis of capacitance-voltage characteristics, and low interface state density (⩽2×1011eV−1cm−2). Transmission electron microscopy with x-ray microanalysis revealed densification of the amorphous LaAlO3 and its reaction with an oxidized a-Si layer.

Metal-oxide-junction, triple point cathodes in a relativistic magnetron

Triple point, defined as the junction of metal, dielectric, and vacuum, is the location where electron emission is favored in the presence of a sufficiently strong electric field. To exploit triple point emission, metal-oxide-junction (MOJ) cathodes consisting of dielectric "islands" over stainless steel substrates have been fabricated. The two dielectrics used are hafnium oxide (HfO(x)) for its high dielectric constant and magnesium oxide (MgO) for its high secondary electron emission coefficient. The coatings are deposited by ablation-plasma-ion lithography using a KrF laser (0-600 mJ at 248 nm) and fluence ranging from 3 to 40 J/cm(2). Composition and morphology of deposited films are analyzed by scanning electron microscopy coupled with x-ray energy dispersive spectroscopy, as well as x-ray diffraction. Cathodes are tested on the Michigan Electron Long-Beam Accelerator with a relativistic magnetron, at parameters V=-300 kV, I=1-15 kA, and pulse lengths of 0.3-0.5 micros. Six variations of the MOJ cathode are tested, and are compared against five baseline cases. It is found that particulate formed during the ablation process improves the electron emission properties of the cathodes by forming additional triple points. Due to extensive electron back bombardment during magnetron operation, secondary electron emission also may play a significant role. Cathodes exhibit increases in current densities of up to 80 A/cm(2), and up to 15% improvement in current start up time, as compared to polished stainless steel cathodes.

High performance n-channel thin-film transistors with an amorphous phase C60 film on plastic substrate

We fabricated high mobility, low voltage n-channel transistors on plastic substrates by combining an amorphous phase C60 film and a high dielectric constant gate insulator titanium silicon oxide (TiSiO2). The transistors exhibited high performance with a threshold voltage of 1.13V, an inverse subthreshold swing of 252mV/decade, and a field-effect mobility up to 1cm2∕Vs at an operating voltage as low as 5V. The amorphous phase C60 films can be formed at room temperature, implying that this transistor is suitable for corresponding n-channel transistors in flexible organic logic devices.

Characteristics of Nanocomposite ZrO2/Al2O3 Films Deposited by Plasma-Enhanced Atomic Layer Deposition

Nanocomposite ZrO2/Al2O3 (ZAO) films were deposited on Si by plasma-enhanced atomic layer deposition and the film characteristics including interfacial oxide formation, dielectric constant (k), and electrical breakdown strength were investigated without post-annealing process. In both the mixed and nano-laminated ZAO films, the thickness of the interfacial oxide layer (T(IL)) was considerably reduced compared to ZrO2 and Al2O3 films. The T(IL) was 0.8 nm in nano-composite films prepared at a mixing ratio (ZrO2:Al2O3) of 1:1. The breakdown strength and the leakage current level were greatly improved by adding Al2O3 as little as 7.9% compared to that of ZrO2 and were enhanced more with increasing content of Al2O3. The k of ZrO2 and mixed ZAO (Al2O3 7.9%) films were 20.0 and 16.5, respectively. These results indicate that the addition of Al2O3 to ZrO2 greatly improves the electrical properties with less cost of k compared to the addition of SiO2.

Electronic structure characterization of ultra low-k carbon doped oxide using soft X-ray emission spectroscopy

In this study we report the electronic structure of ultra low-k dielectric constant carbon doped oxide (CDO) films, which have a k value of 2.4, using synchrotron radiation-excited resonant soft X-ray emission (SXE) spectroscopy. Conventional X-ray photoemission spectroscopy was used to determine that the chemical composition of the material was Si-31%, C-15% and O-54%. The C and O partial density of states for the valence bands has been measured by SXE. Radiation induced changes in the chemical bonding in the material have been identified and these can be minimised by continuously translating the sample during measurement. The spectral changes induced by the radiation damage are consistent with the breaking of Si–CH 3 bonds in the material and the formation of graphitic C = C double bonds. Investigation of the origin of a low energy subband in the C Kα spectrum reveal that it can be attributed to O Kα emission excited by second order rather than the hybridization of C 2p states in the CDO layer.