Electronic structures of layered oxychalcogenides, LaCuOCh (Ch=S, Se, Te) and La2CdO2Se2, were studied using ab-initio band calculations in relation to their optical and electronic properties. It was found that the dispersions of the top valence bands are much smaller in Γ-Z direction than in Γ-X direction, indicating that the electronic structure is highly two-dimensional, and that holes are confined in the CuCh or CdSe layers. The two-dimensional electronic structure is supported experimentally by staircase-like structure observed in optical absorption spectra at 10 K associated with two excitonic absorption peaks split by spin-orbit interaction of Ch ions. La2CdO2Se2has the largest bandgap due to the two-dimensional network structure of CdSe tetrahedra.

A method has been developed for specifying the growth location of Cu2O nanodotson SrTiO3 (100) substrates. Growth location has been specified by using a focused ion beam (FIB) to modify microscopic and nanoscopic regions of the SrTiO3substrate prior to Cu2O deposition. Deposition onto the modified regions under carefully selected process conditions has generated nanodot growth at the edge of microscopic FIB-induced features and on top of nanoscopic FIB-induced features. For this work, an array of evenly spaced FIB implants was first patterned into several regions of each substrate. Within each sub-division of the array, the FIB implants were identical in Ga+ energy and dosage and implant diameter and spacing. After FIB surface modification and subsequent in-situ substrate cleaning, Cu2O nanodots were synthesized on the patterned SrTiO3 substrates using oxygen plasma assisted molecular beam epitaxy. The substrates and nanodots were characterized using atomic force microscopy at various stages of the process; in-situ X-ray photoelectron spectroscopy and Auger electron spectroscopy analysis demonstrated that the final stoichiometry of the nanodots was Cu2O. The photocatalytic decomposition of water on Cu2O under visible light irradiation has been reported. If the Cu2O can be located in the form ofislands on a carefully selected substrate, then it could be possible to greatly enhance the efficiency of the photochemical process.

Hafnium oxide (HfO2) and silicon containing hafnium oxide (HfSixOy) thin films were deposited by thermal and plasma enhanced chemical vapor deposition (PECVD) using Hf (IV) t-butoxide and either O2, N2O, H2O, O2 plasma or N2O plasma as an oxygen source. Silane, 2% in He, was added to the reactant gas mixture to incorporate Si. Deposition rate and composition dependence on substrate temperature was studied and the deposited films were annealed in air for 30 min at 1100°C to observe changes in crystallinity and composition. Silicon incorporation was higher for H2O deposited HfSixOy films (5 at.%) than O2 and N2O deposited films (2 at.%) and had a lower deposition rate. Arrhenius plots reveal a non-simplistic reaction scheme since higher temperatures result in lower deposition rates due to precursor desorption. XRD indicate that as-deposited films using H2O are amorphous while O2 and N2O deposited films are microcrystalline with a monoclinic phase.

In the path to the introduction of high-k dielectric into IC components, a large number of challenges have still to be solved. Some of the major issues concern the low mobility of carriers and the reliability of the devices. Trapped charges in the stack have been identified as being the cause of these issues. With this in mind, we used Conducting Atomic Force Microscopy, combined with physical analysis to understand the nature of these charges. In this contribution, we have studied the uniformity of thin HfO2 layers, with and without anneal. The Conducting Atomic Force microscopy measurements show spots of higher conductivity. Recording local IV's in those ‘weak’ spots suggests that they consist of positive charge. On the other hand, XPS and ToFSIMS analysis show a diffusion of the interfacial SiO2 upwards into the high-k layer. Finally, the comparison of samples with differing high-k material and crystallinity indicates a strong correlation between the weak spots and the presence of silicon in the film.

Defect energy levels of oxygen vacancies in various high K oxides HfO2, ZrO2, La2O3 and SrTiO3 have been calculated using methods which give the correct band gap, such as the screened exchange and weighted density approximation.

The interface layer between thin sputter-deposited tantalum oxide (TaOx) high-k film and silicon substrate was engineered with the Hf doping method and the insertion of a thin 5Å TaNx interface. The following results have been obtained: 1) the Hf dopant in the TaOx film was involved in the interface formation process, e.g., forming a new, thinner high-k HfSixOy interface layer rather than the SiOx layer, 2) when the TaNx interface was inserted, the interface layer composition was even more complicated, e.g., including TaOxNy and HfSixOy structures. No hafnium nitride or oxynitride was detected, 3) the interface layer structure was changed, e.g., from single-zone to multi-zone with different compositions, 4) when a low concentration of Hf existed in the TaOx film, the high-k dielectric properties, such as the k value, fixed charge density, dielectric strength, were improved, and 5) when the thin TaNx interface layer was inserted, the above electric properties were further improved. However, the fixed charge density and interface states were increased due to the insertion of the TaNx interface layer. These results were contributed by factors such as the charge-trapping characteristics in the interface layer and the some damage repairing mechanisms. In summary, this research proved that the high-k film's interface layer and bulk properties could be were improved with the doping process as well as the insertion of an ultra-thin TaNx interface film.

We have demonstrated a uniform, robust interface for high-k deposition with significant improvements in device electrical performance compared to conventional surface preparation techniques. The interface was a thin thermal oxide that was grown and then etched back in a controlled manner to the desired thickness. Utilizing this approach, an equivalent oxide thickness (EOT) as low as 0.87 nm has been demonstrated on high-k gate stacks having improved electrical characteristics as compared to more conventionally prepared starting surfaces.

We have investigated electrical and optical properties of the lead strontium titanate {(PbxSr1-x)TiO3 or PST} ceramic and dielectric properties of the thin films of PST at low and high frequencies. (PbxSr1-x)TiO3 compositions with × ≤ 0.4 are paraelectric at room temperature and exhibit ferroelectric phase transition below room temperature. Only one phase transition in the PST system (compared to three in BaxSr1-xTiO3) was recorded. The studies indicated that PST has potential for tunable microwave devices in the paraelectric phase. In the present studies, Pb0.3Sr0.7TiO3 (PST30) ceramic was prepared by the conventional solid-state reaction method and thin films of PST were prepared by sol-gel technique. Structural, microstructural, dielectric, and Raman measurements were performed on these samples. Sharp phase transition was observed in case of the ceramic by dielectric and Raman measurements at 283 K. Raman measurements revealed well-pronounced soft-mode behavior below the Curie temperature in PST ceramic. The thin film of PST deposited on lanthanum aluminate substrate was highly (100) oriented and showed dielectric maxima at ∼280 K, which was close to that in case of the bulk. Eight element coupled micro-strip phase shifters (CMPS) was fabricated on the PST film and tested in the frequency range of 15-17 GHz. The average figure of merit of 49 °/dB for PST30 film in the Ku band at 533 kV/cm suggests the potentiality of these films for high frequency tunable dielectric devices.

In the present work we use a scanning tunneling microscope to modify the surface structure of epitaxial SrRuO3 thin films. Point and line etching experiments were carried out in ultra-highvacuum, using tungsten tips. The point etchings showed that pulses fired at small (< 4.5V) bias voltages did not bring about any physical modifications of the film surface, while voltages in excess of4.5 V led to etched holes accompanied by mounds. Moreover, well-defined line etching was achieved with atypical depth of approximately two unit cells and linewidths as small as 5 nm. The experiments demonstrate that a scanning tunneling microscope can be used for nanometer-scale patterning of SrRuO3 thin film surfaces.

The electrical properties of epitaxial La0.8Sr0.2MnO3 films on a SrTiO3(STO) substrate prepared by changing the laser fluence, the irradiation time and the film thickness using excimer laser metal organic deposition(ELMOD) at 500/cm2, the film showed a 3.9 % maximum temperature coefficient of resistance (TCR: defined as 1/R•dR/dT) which was obtained by the ArF laser irradiation at 80mJ/cm2 for 10min. At a constant fluence of 80mJ/cm2, the Tm (temperature of the maximum TCR) of the La0.8Sr0.2MnO3 films increased from 225K to near 250K with an increase in the irradiation time to 90min at which the TCR was almost 3.9%. The La0.8Sr0.2MnO3 film that showed the maximum TCR of 4.0% at 275K was obtained by the ELMOD process at 500°C using the optimum conditions (Flence:80mJ/cm2, Irradiation time: 90min, Film thickness: 80nm).

We proposed the magnetoelectric (ME) effect as a new function of oxides electronic devices. The ME effect is characterized by the appearance of an induced magnetization with electric field applied and also is true in the opposite way. As one of the oxides devices we proposed a new type of Josephson field effect transistor (JFET) as adopting the ME materials to a gate insulator. In such the device, considering the Fraunhofer pattern, large IC modulation was expected by the induced magnetic field. Representative ME material, Cr2O3 films were deposited on Josephson junctions which were formed bygrain boundaries in YBa2Cu3OX (YBCO) films grown on MgO substrates. The multilayered films, Cr2O3 /YBCO and Cr2O3 / Y2O3 / YBCO were studied as the model of JFET.

The effect of anthanum substitution (0-20%) on phase formation, structural evolution and electrical properties of SrBi2Ta2O9 (SBT) ceramics were investigated. X-ray diffraction studies revealed that phase pure SBT bulk samples can be synthesized with lanthanum doping without any phase segregation. Raman spectroscopy was used to understand the lattice vibrational characteristics of La substituted SBT compound. The ferroelectric soft mode at 27 cm−1 was shifted towards the lower frequencies at room temperature with increase in La concentrations. The octahedral stretching mode (O-Ta-O) did not influenced by La substitution in SBT. The x-ray photoemission spectroscopy measurements showed the decrease of binding energy of Bi 4f core levels (5/2 and 7/2) upon La substitution in SBT. The dielectric constant was increased from 120 to 190 up to 10% La doping and decreased with further increase in La concentration.

We have established in-line characterization techniques for analyzing the bulk and interface-charge properties of dielectric films, for process optimization. Surface charge analysis (SCA) is used to determine the densities of interface states, fixed charge, and near-interface traps in ultra-thin dielectrics, and is useful for tracking the influence of post-deposition processing on interface-charge properties. Spectroscopic ellipsometry (SE) is used to obtain the absorption spectra in the conduction band-tail region. The intensity of an extra absorption peak inside the bandgap of HfO2 is clearly correlated with leakage current density and near-interface trap density. Based on the observed process dependencies, defects within the HfO2 films are likely to be oxygen vacancies. The relative scalability of HfO2 and Hf-silicate films of various compositions is examined using a figure of merit based on the direct-tunneling leakage current model. Pure HfO2 is expected to be more scalable than Hf-silicates. However, it is typically accompanied by an interfacial layer which significantly increases the equivalent oxide thickness (EOT). A 20% Hf silicate with relative permittivity of 11 or higher can be more scalable than HfO2 with an interfacial layer. Alternatively, an ultra-thin interfacial Si3N4 diffusion barrier can be used with HfO2, to allow for more aggressive EOT scaling. The dependencies of interface-charge properties and surface roughness on the nitride barrier formation process are presented.

New ALD processes for hafnium silicate films have been developed at Aviza Technology by co-injection of tetrakis(ethylmethylamino)hafnium and tetrakis(ethylmethylamino)silicon precursors. Alternating pulses of the Hf/Si precursor vapor mixture and ozone allow process temperatures below 400°C to grow HfxSi1-xO2 films. Film characterization, including film density, crystallinity, and thermal anneal effect, was performed on five 20 nm thick HfxSi1-xO2 films where x = 0.2, 0.4, 0.6, 0.8, 1.0. X-ray measurements revealed the film densities and thicknesses for the as-deposited and 1000°C annealed samples. The densification with anneals seen in the optical measurements were confirmed. The as-deposited amorphous HfO2 and Hf0.8Si0.2O2 were crystallized after a 600°C anneal. The HfO2 formed the well known monoclinic phase while the silicate formed a face-centered-cubic (fcc) structure. This fcc phase has only recently been mentioned in the literature [1].

In order to combine the merits of both HfO2 and Al2O3 as high-κ gate dielectrics for CMOS technology, high-κ nanolaminate structures in the form of either Al2O3/HfO2/Al2O3 or Al2O3/HfAlOx/Al2O3 were implemented in pMOSFETs and electrically and microstructurally charachterized. ALD TiN film was used as the metal gate electrodes for the pMOSFETs. After full transistor-processing including a rapid thermal processing step at 930 °C, the HfO2 film in the former nanolaminate was found to be crystallized. In contrast, the HfAlOx layer in the latter nanolaminate remained in the amorphous state. Both types of pMOSFETs exhibited a hysteresis as small as ∼20 mV in C-V characteristics in the bias range of +/− 2 V. They also showed a reduced gate leakage current. The pMOSFET with the Al2O3/HfAlOx/Al2O3 nanolaminate was characterized with a subthreshold slope of 77 mV/decade and a channel hole mobility close to the universal hole mobility curve. The pMOSFET with the Al2O3/HfO2/Al2O3, however, exhibited a subthreshold slope of 100 mV/decade and a ∼30% lower hole mobility than the universal curve.

To develop higher density FRAM requires reducing cell size. Therefore, the size effects resulting from device processing and the material's physical properties must be measured. Therefore, analyzing the electric characteristics of a single bit cell capacitor has become important. Two known characteristics of ferroelectric material are that the Vc increases at low temperatures, and the Pr falls at high temperatures. To further evaluate the impact of temperature on ferroelectrics, we constructed a new evaluation system based on a scanning probe microscope, that can measure the electric characteristics of a single bit cell capacitor. This system can be used in the temperature range from −120 degrees to 300 degrees C. We accomplished this by circulating liquid nitrogen around a SPM stage and by using an electrical heater. We measured the electrical properties of ferroelectric microcapacitors by using a sample with IrOx/PZT/Pt structure. Our measurements revealed that 2Pr really increases at low temperatures, and Pr decreases at high temperatures. That is, we have shown that Vc increases 30% at low temperatures and Pr decreases 10% also in an actual FRAM single bit cell capacitor.

We have extended our invented high k dielectrics Ga2−xGdxO3 oxide to compound semiconductors of AlGaAs, InGaAs, and InP, and demonstrated the formation of low leakage, insulating barrier on the (100) surface. Fundamental studies of the MOS diodes consisting of Au/GGG mostly on InGaAs are reported, including the crystal-chemical and electrical properties to address the oxide reliability issue. An atomically abrupt interface between the oxide/GaAs interface was achieved by the MBE growth. Systematic post annealing studies of varying temperature and gas species were carried out to improve the dielectric performance such as the reduction of frequency dispersion, voltage hysteresis, and interfacial state density Dit. We show that our results are essential to device processing based on the oxide, and to establish a viable GaAs MOSFET technology.

As traditional poly-silicon gated MOSFET devices scale, the additional series capacitance due to poly-silicon depletion becomes an increasingly large fraction of the total gate capacitance, excessive boron penetration causes threshold voltage shifts, and the gate resistance is elevated. To solve these problems and continue aggressive device scaling we are studying metal electrodes with suitable work-functions and sufficient physical and electrical stability. Our studies of metal gates on HfO2 indicate that excessive inter-diffusion, inadequate phase stability, and interfacial reactions are mechanisms of failure at source drain activation temperatures that must be considered during the electrode selection process. Understanding the physical properties of the metal gate – HfO2 interface is critical to understanding the electrical behavior of MOS devices. Of particular interest is Fermi level pinning, a phenomenon that occurs at metal – dielectric interfaces which causes undesirable shifts in the effective metal work function. The magnitude of Fermi level pinning on HfO2 electrodes is studied with Pt and LaB6 electrodes. In addition, the intrinsic and extrinsic contributions to Fermi level pinning of platinum electrodes on HfO2 gate dielectrics are investigated by examining the impact of oxygen and forming gas anneals on the work function of platinum-HfO2-silicon capacitors. The presence of interfacial oxygen vacancies or Pt-Hf bonds is believed to be responsible for a degree of pinning that is stronger than predicted from the MIGS model alone. Interface chemistry and defects influence the effective metal work function.

In order to understand how N2 plasma conditions impact on the incorporation of nitrogen species into a thin SiO2 (1.4 nm), tuning of some pulsed RF (pRF) Decoupled Plasma Nitridation (DPN) process parameters was performed: duty cycle (DC) or on-time per period, frequency (f), process time (t) and some cross-combinations (DC*f, DC*t, DC*f*t). The N2 plasma and the SiOx Ny film were characterized using Langmuir probe analysis (LP) and Delay to Reoxidation (D2R) techniques, respectively. Correlations are established between ion density and electron temperature and the resultant nitrogen concentration and parasitic physical thickness increase. The LP results indicate that while DC impacts the ion density and energy, the frequency has no impact to first order. This is consistent with the physical characteristics of the film. From the combination of DC*f*t, the importance of the off-time portion of the pulse was revealed. With the help of a modified pulsed RF DPN generator, allowing a decrease of the frequency down to 2 kHz, a 5% improvement of the drive current for pMOS transistors was obtained.

Praseodymium oxide Pr2O3 (and Pr6O11) layers were deposited by innovative pulsed injection MOCVD technique on Si(100) in the temperature range 400-750°C. Praseodymium 2,2,6,6-tetramethyl-3,5-heptanedionate dissolved in monoglyme (1,2-dimethoxyethane) or toluene was used as precursor material. The influence of deposition conditions on film composition, growth rate, crystallization and surface roughness has been investigated. The main parameters influencing film composition and properties were substrate temperature and partial oxygen pressure during deposition. The presence of molecular oxygen in the reactor leads to the growth of Pr6O11 as the most stable phase or its mixture with PrO2, while deposition in inert atmosphere (Ar, 2 torr) allows to obtain Pr2O3 films which were amorphous or crystalline depending on the deposition temperature. Crystallized (polycrystalline) Pr2O3 films can be obtained at the growth temperatures 650°C and higher, while crystalline Pr6O11 films grow starting 400°C. Ex-situ annealing (750°C, vacuum, 2 hours) of the amorphous Pr2O3 films leads to film crystallization. Step coverage study has been performed for amorphous and crystallized Pr2O3 films. Electrical properties of thin (∼10 nm) Pr2O3 films were investigated and encouraging EOT (equivalent oxide thickness), leakage current data have been obtained.