Oxide Electronics

Models and materials for generalized Kitaev magnetism Stephen M Winter, Alexander A Tsirlin, Maria Daghofer et al.-Microstructure, critical current density and trapped field experiments in IG-processed Y-123 M Muralidhar, N Ide, M R Koblischka et al.-Recent citations Passive radiofrequency x-ray dosimeter tag based on flexible radiation-sensitive oxide field-effect transistor Tobias Cramer et al-Charge Transport in Low-Temperature Processed Thin-Film Transistors Based on Indium Oxide/Zinc Oxide Heterostructures Jan Krausmann et al-Surface Electronic States Induced High Terahertz Conductivity of Co3O4 Microhollow Structure Rupali Rakshit et al

Dr. Herbots, Belgian-born, Ph.D. graduate in applied physics of Catholic University of Louvain and a microelectronics specialist, made progress in the course of three years as an Oak Ridge Re- search Associate and four years as an MIT professor (1987-1991). At MIT she developed new methods for synthesizing thin film layers on chips at low temperatures, and for creating films that can’t be grown using thermal processes.

She joined Arizona State University in 1991,  to further develop a novel invention she had made at MIT. Called Combined Ion and Molecular Beam Deposition or CIMD, it is a  tech- nique for depositing materials on semiconductors that combines a so- phisticated evaporation system (molecular beam deposition) with an easily controlled ion beam.
But a life-threatening accident curtailed her research
After building a CIMD clean room at Arizona State University and getting research off to a good start, Nicole Herbot’s work, almost her life, came to an abrupt end in May 1994.  This is where the history of her research in ordered nanophases of SiO2 on Si(100) began. She had to rebuild her scientific understanding of matter,  interfaces, phase structures and nanophases after losing her short memory and developing "petit mal" (a milder form of epilepsy characterized by short or longer "absences" where the patient loses awareness of surroundings without loss of consciousness). The episodes increase with fatigue, mild illnesses and colds, to several a day.  They result in post-"absences" exhaustion, typical of epilepsy, where the patient needs to sleep for a period of time concomittant with the duration of the absences to recover.  The condition precludes driving.
The long hours spent on bed rest recovering from the petit mal absences gave her the time to reflect on the continuing mystery of SiO2/Si(100) extraordinary properties in microelectronics.  This is how her "Tsunami" model of structural collapse as Si(100) crystals oxidizes into an amorphous film came to be, and a new concept to prevent structure loss and thus grow heteroepitaxial SiO2 on Si(100) was conceived, and led to several patents (2003, 2010), PhD theses and papers.

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO 3 /SrTiO 3 , has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO 3 and (110)-oriented SrTiO 3 , which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO 3 / SrTiO 3 interface prepared on (110)-oriented SrTiO 3 , with a LaAlO 3 -layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO 2 /LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

""Three different HF:alcohol solutions are investigated to etch native Si0 2 and passivate Si(100) surfaces with H which can the be desorbed at low temperature (T < 600'C). The resulting passivated Si(100) surfaces are compared using as a reference Si(100) passivated by a standard aqueous HF: solution (1:98 parts of HF: H2 0). After a modified RCA cleaning, Si(100) etched by HF:Methanol, HF:IPA, or HF:Ethanol, is characterized by Ion Beam Analysis (IBA), Tapping Mode Atomic Force Microscope (TMAFM), and Fourier Transform Infrared Spectroscopy (FTIR). The absolute coverage of 0 and C is measured by nuclear reaction analysis (NRA) combined with ion channeling at 3.05 MeV for 0 and 4.265 MeV for C. Hydrogen is measured via the elastic recoil detection (ERD) of 4He2+at 2.8 MeV.
Compared to aqueous HF, HF:alcohol passivates Si(100) leaving a lower 0 residue by an average factor of 0.62 and a similar C residue. H coverage is higher by an average factor of 1.43. Surface coverages are found to be reproducible in average by 1.4 x 1014 atoms/cm2 for C, and by 1.25 x 1014 atoms/cm2 for 0 when measured by IBA on samples identically processed. H coverage is reproducible within 5.5% when measured by ERD.
Selective area analysis by TMAFM shows that an increasing number of particulates is responsible for the apparent increase in root-mean -square (nns) surface roughness when the rms is measured over a whole image. Taking this effect into account, all passivated surfaces exhibit similar roughness when compared to the original Si(100) surface with little difference between
alcohols and with the reference aqueous HF solution. FTIR in the attenuation total reflection (ATR) mode detected SiHx species mostly as a
dihydride. Both IBA and FTIR detected significant levels of oxygen on surfaces passivated HF in alcohol and aqueous HF. This indicates that while Si(100) exhibits more H when passivated with HF in alcohol and can be desorbed at lower temperature than when treated with aqueous HF, H is
not bonded to Si only but likely bonds into a more complex surface termination, such as SiOH.""

Oxide electronic materials provide a plethora of possible applications and offer ample opportunity for scientists to probe into some of the exciting and intriguing phenomena exhibited by oxide systems and oxide interfaces. In addition to the already diverse spectrum of properties, the nanoscale form of oxides provides a new dimension of hitherto unknown phenomena due to the increased surface-to-volume ratio. Oxide electronic materials are becoming increasingly important in a wide range of applications including transparent electronics, optoelectronics, magnetoelectronics, photonics, spintronics, thermoelectrics, piezoelectrics, power harvesting, hydrogen storage and environmental waste management. Synthesis and fabrication of these materials, as well as processing into particular device structures to suit a specific application is still a challenge. Further, characterization of these materials to understand the tunability of their properties and the novel properties that evolve due ...

The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO 3 /SrTiO 3 , has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO 3 and (110)-oriented SrTiO 3 , which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO 3 / SrTiO 3 interface prepared on (110)-oriented SrTiO 3 , with a LaAlO 3-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO 2 /LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.

New dielectric materials based on SiGe have been formed at room temperature by direct ion beam oxidation and nitridation. Si0.8Ge0.2 layers were deposited by molecular beam epitaxy on Si(100) and then exposed to a low-energy ion beam of O-18-2+ to form oxides and N-14-2+ to form nitrides. The ion energies investigated ranged from 100 eV to 1 keV. Thin films of SiGe oxide and SiGe nitride were formed at all energies used as evidenced by in situ x-ray photoelectron spectroscopy analysis. They were found to be insulating by ex situ scanning electron microscopy observations. During the ion beam processing, the Ge content of the alloy layer decreases, due to preferential sputtering of Ge and the Ge compounds. However, as the ion energy is decreased, the concentration of Ge in the alloy remains closer to the original content. The thermal stability of these new SiGe dielectrics was also assessed up to 500-degrees-C.

High-k dielectric oxides are supposedly ideal gate-materials for ultra-high doping in graphene and other 2D-crystals. Here, we report a temperature-dependent electronic transport study on chemical vapor deposited-graphene gated with SrTiO3 (STO) thin film substrate. At carrier densities away from charge neutrality point the temperature-dependent resistivity of our graphene samples on both STO and SiO2/Si substrates show metallic behavior with contributions from Coulomb scattering and flexural phonons attributable to the presence of characteristic quasi-periodic nano-ripple arrays. Significantly, for graphene samples on STO substrates we observe an anomalous ‘slope-break’ in the temperature-dependent resistivity for T = 50 to 100 K accompanied by a decrease in mobility above 30 K. Furthermore, we observe an unusual decrease in the gate-induced doping-rate at low temperatures, despite an increase in dielectric constant of the substrate. We believe that a complex mechanism is at play as a consequence of the structural phase transition of the underlying substrate showing an anomalous transport behavior in graphene on STO. The anomalies are discussed in the context of Coulomb as well as phonon scattering.

Epitaxial growth requires an initial surface that is ordered and as free as possible of contaminants such as C, 0, or
metallic impurities. Wet chemical etching of Si( 111) wafers by a solution of HF in alcohol after a modified RCA clean, has
been shown to produce (1 X 1) H-terminated hydrophobic Si surfaces that are ordered at room temperature and can be
desorbed at 200°C in UHV. Less is known about a similar treatment on Si(lO0) wafers, more commonly used in
semiconductor technology. However, high temperature (T> 800°C) thermal desorption of the native oxide on Si(lO0) is
known to induce detrimental effects such as surface roughness, precipitation and dopant segregation. Therefore, this study is
motivated by the development of a low-temperature (T < 600°C) surface cleaning method for Sit 100). RBS combined with
ion channeling and nuclear reaction analysis is conducted to measure the coverage of C, 0, and H as well as the residual
disorder at the surface at different steps of wet chemical cleaning prior to low temperature desorption. Hydrogen is detected
by the forward elastic recoil of H by 4He2+ at 2.8 MeV. 0 and C are detected by nuclear reaction analysis (NRA) at 3.05
and 4.265 MeV, respectively, in combination with ion channeling along the Si( 111) direction to increase the detection
sensitivity for C and 0 as well as to measure the Si surface peak to correlate it to surface disorder. Atomic force microscopy
of these surfaces has shown different degrees of roughness in addition to defect formation and is correlated to the ion beam
analysis results. Our results indicate a strong dependence of final H-passivation on the pretreatment of the Si surfaces before
the final dip in the HE/alcohol solution.