Heinz D. Wanzenboeck

Synthesis of individually tuned nanomagnets for Nanomagnet Logic by direct write focused electron beam induced deposition.

Nanomagnet Logic (NML) is a promising new technology for future logic which exploits interactions among magnetic nanoelements in order to encode and compute binary information. This approach overcomes the well-known limits of CMOS-based microelectronics by drastically reducing the power consumption of computational systems and by offering nonvolatility. An actual key challenge is the nanofabrication of such systems that, up to date, are prepared by complex multistep processes in planar technology. Here, we report the single-step synthesis of NML key elements by focused electron beam induced deposition (FEBID) using iron pentacarbonyl as a gas precursor. The resulting nanomagnets feature an inner iron part and a 3 nm iron oxide cover (core-shell structure). Full functionality of conventional NML gates from FEBID-nanowires was achieved. An advanced structure maintaining the gate functionality based on bended nanowires was realized. The unique design obtained by direct-writing reduces the error probability and may merge several NWs in future NML elements.

Focused ion beam induced surface amorphization and sputter processes

Focused ion beam techniques are among the most important tools for the nanostructuring of surfaces. As the physical phenomena during milling are not fully understood yet, we have applied the phase imaging capabilities of tapping mode atomic force microscopy to the investigation of surface amorphization, sputtering, and redeposition caused by focused ion beam irradiation. We have performed single spot as well as large area (20×20 μm2) irradiation of silicon (100) wafers. We describe the localized formation of amorphous and electrostatically charged domains, which do not correlate to topographic features.

Compositional and electrical properties of zirconium dioxide thin films chemically deposited on silicon

High-k ZrO2 thin films are grown on p-type silicon by metal–organic chemical vapor deposition based on zirconiumtetrakistrifluoroacetylacetonate as single-source precursor system. Annealing of the as-grown films is performed to investigate the impact of oxidative and reductive atmospheres on thin film properties. The composition of the ultrathin films is examined by Auger spectroscopy, whereas metal–oxide–semiconductor (MOS) structures are employed to extract electrical characteristics. Equivalent oxide thicknesses down to 2 nm and interface trap densities of 5×1011 cm−2 eV−1 at midgap are obtained. MOS capacitors show extremely low leakage currents, promising to reduce gate leakage by more than a factor of 103 compared to SiO2. The correlation between compositional and electrical properties is discussed on the basis of postdeposition annealing procedures resulting in a consistent explanation of the observed effects.

Direct-Write Deposition and Focused-Electron-Beam-Induced Purification of Gold Nanostructures

Three-dimensional gold (Au) nanostructures offer promise in nanoplasmonics, biomedical applications, electrochemical sensing and as contacts for carbon-based electronics. Direct-write techniques such as focused-electron-beam-induced deposition (FEBID) can provide such precisely patterned nanostructures. Unfortunately, FEBID Au traditionally suffers from a high nonmetallic content and cannot meet the purity requirements for these applications. Here we report exceptionally pure pristine FEBID Au nanostructures comprising submicrometer-large monocrystalline Au sections. On the basis of high-resolution transmission electron microscopy results and Monte Carlo simulations of electron trajectories in the deposited nanostructures, we propose a curing mechanism that elucidates the observed phenomena. The in situ focused-electron-beam-induced curing mechanism was supported by postdeposition ex situ curing and, in combination with oxygen plasma cleaning, is utilized as a straightforward purification method for planar FEBID structures. This work paves the way for the application of FEBID Au nanostructures in a new generation of biosensors and plasmonic nanodevices.

Free-Standing Magnetic Nanopillars for 3D Nanomagnet Logic

Nanomagnet logic (NML) is a relatively new computation technology that uses arrays of shape-controlled nanomagnets to enable digital processing. Currently, conventional resist-based lithographic processes limit the design of NML circuitry to planar nanostructures with homogeneous thicknesses. Here, we demonstrate the focused electron beam induced deposition of Fe-based nanomaterial for magnetic in-plane nanowires and out-of-plane nanopillars. Three-dimensional (3D) NML was achieved based on the magnetic coupling between nanowires and nanopillars in a 3D array. Additionally, the same Fe-based nanomaterial was used to produce tilt-corrected high-aspect-ratio probes for the accurate magnetic force microscopy (MFM) analysis of the fabricated 3D NML gate arrays. The interpretation of the MFM measurements was supported by magnetic simulations using the Object Oriented MicroMagnetic Framework. Introducing vertical out-of-plane nanopillars not only increases the packing density of 3D NML but also introduces an extra magnetic degree of freedom, offering a new approach to input/output and processing functionalities in nanomagnetic computing.

Electron beam induced deposition of iron nanostructures

Electron beam induced deposition is among the most prospective methods for size- and position-controllable nanofabrication of three-dimensional structures. Direct-write maskless nanostructure fabrication was performed with a scanning electron microscope. Three-dimensional iron structures were obtained by locally confined electron induced dissociation of an iron carbonyl (Fe(CO)5) precursor. Vertical nanopillars consisting of Fe with O and C contaminations were deposited. Two different growth regimes—electron induced growth and autonomous growth—were observed. The precursor pressure was shown to have a significant influence on the growth mode.

Slow trap response of zirconium dioxide thin films on silicon

In this work, we explore the electrical properties of a metal–oxide–semiconductor system that incorporates a high-k zirconia dielectric with an equivalent oxide thickness of 3 nm deposited by metalorganic chemical vapor deposition. In general, the thin films examined exhibit excellent electrical properties. However, dynamic I–V measurements unveil the presence of trapping sites with response times up to 3 s. By applying a recently proposed model, this slow trap response can be consistently explained by traps located at the inner interface of a two-layer dielectric consisting of the high-k material itself and a transition layer in contact with the semiconductor. Trap energies are found to be distributed around two distinct levels.

Metal-organic chemical vapor deposition and nanoscale characterization of zirconium oxide thin films

Abstract We report on the growth of ZrO2 thin films on silicon wafers by metal-organic chemical vapor deposition from zirconiumtrifluoroacetylacetonate at deposition temperatures between 350 and 550 °C. The evolution of surface roughness of the deposited films is thoroughly investigated. Relative roughness is found to be minimum at a deposition temperature of 450 °C and also essentially independent of film thickness. The attained values of relative roughness are shown to be competitive to advanced deposition methods such as atomic layer deposition. Chemical composition of the films is examined in dependence of deposition temperature and post-deposition annealing procedures. Experimental results indicate that optimum properties in regard to chemical composition are obtained after thermal treatment at 650 °C. The film composition is not significantly altered by annealing at higher temperatures. Also the ambient atmosphere during the annealing process is shown to be of minor influence.

Focused-ion-beam-inflicted surface amorphization and gallium implantation—new insights and removal by focused-electron-beam-induced etching

Recently focused-electron-beam-induced etching of silicon using molecular chlorine (Cl(2)-FEBIE) has been developed as a reliable and reproducible process capable of damage-free, maskless and resistless removal of silicon. As any electron-beam-induced processing is considered non-destructive and implantation-free due to the absence of ion bombardment this approach is also a potential method for removing focused-ion-beam (FIB)-inflicted crystal damage and ion implantation. We show that Cl(2)-FEBIE is capable of removing FIB-induced amorphization and gallium ion implantation after processing of surfaces with a focused ion beam. TEM analysis proves that the method Cl(2)-FEBIE is non-destructive and therefore retains crystallinity. It is shown that Cl(2)-FEBIE of amorphous silicon when compared to crystalline silicon can be up to 25 times faster, depending on the degree of amorphization. Also, using this method it has become possible for the first time to directly investigate damage caused by FIB exposure in a top-down view utilizing a localized chemical reaction, i.e. without the need for TEM sample preparation. We show that gallium fluences above 4 × 10(15) cm(-2) result in altered material resulting from FIB-induced processes down to a depth of ∼ 250 nm. With increasing gallium fluences, due to a significant gallium concentration close beneath the surface, removal of the topmost layer by Cl(2)-FEBIE becomes difficult, indicating that gallium serves as an etch stop for Cl(2)-FEBIE.

Highly conductive and pure gold nanostructures grown by electron beam induced deposition

This work introduces an additive direct-write nanofabrication technique for producing extremely conductive gold nanostructures from a commercial metalorganic precursor. Gold content of 91 atomic % (at. %) was achieved by using water as an oxidative enhancer during direct-write deposition. A model was developed based on the deposition rate and the chemical composition, and it explains the surface processes that lead to the increases in gold purity and deposition yield. Co-injection of an oxidative enhancer enabled Focused Electron Beam Induced Deposition (FEBID)—a maskless, resistless deposition method for three dimensional (3D) nanostructures—to directly yield pure gold in a single process step, without post-deposition purification. Gold nanowires displayed resistivity down to 8.8 μΩ cm. This is the highest conductivity achieved so far from FEBID and it opens the possibility of applications in nanoelectronics, such as direct-write contacts to nanomaterials. The increased gold deposition yield and the ultralow carbon level will facilitate future applications such as the fabrication of 3D nanostructures in nanoplasmonics and biomolecule immobilization.