Siegfried Menzel

Magnetic force microscopy sensors using iron-filled carbon nanotubes

Probes for magnetic force microscopy (MFM) were prepared by pinning iron-filled multiwall carbon nanotubes to conventional scanning force microscopy probes. These nanotube MFM probes reveal a great potential for high spatial resolution of both topography and magnetic stray field. The ends of the high aspect ratio iron nanowires within the nanotubes can be considered as stationary effective magnetic monopole moments which opens the possibility of quantitative stray field measurements in a straightforward manner. The carbon shells around the iron nanowires provide wear resistance and oxidation protection.

Iron-filled carbon nanotubes as probes for magnetic force microscopy

Iron-filled carbon nanotubes (Fe-CNTs) were used to prepare probes for magnetic force microscopy (MFM) by attaching them to the tips of conventional atomic force microscopy cantilevers. An optimized chemical vapor deposition process, employing a two stage furnace and ferrocene as a precursor, supplied the homogeneously filled Fe-CNTs required for the MFM probes. These can be regarded as cylindrically shaped single-domain nanomagnets that are protected from oxidation by a carbon shell. Carbon nanotubes are known to possess both great mechanical stability and elasticity, which lead to a much longer lifetime of these probes compared to conventional magnetically coated probes. It is shown that the prepared probes are suitable for magnetic imaging and so far show no sign of deterioration. Even very long nanotubes can be used as probes, which implies that they are extraordinarily stiff. It is also shown that attached Fe-CNTs can subsequently be tailored by electron-beam induced oxidation (e.g., to remove distur...

Investigation of high power effects on Ti/Al and Ta-Si-N/Cu/Ta-Si-N electrodes for SAW devices

Damage behavior of two different metallization systems (Ti/Al bilayer and Ta-Si-N/Cu/Ta-Si-N multilayer) as finger electrodes in surface acoustic waves (SAW) devices was investigated. A special test structure was developed for this reason. The samples were loaded with traveling SAWs varying input power and loading time. Simultaneously during these experiments, the electric behavior of the SAW structure was measured and damage development by voids and hillock formation was observed using optical microscopy, too. The damaged structures were investigated by means of different microscopy techniques. Results show that the Cu-based metallization system has a significantly higher acoustomigration resistance and power durability in comparison with the Al thin film system.

Microstructural investigation of electrodeposited CuAg-thin films

In this article we present microstructural investigations of electrodeposited CuAg-alloy metallization thin films. The deposition was carried out on Si(100)/SiO2Ta/TaN/Cu-seed substrates at room temperature without any additives. It was found that the mean grain size decreases with increasing dc current density whereas a dependence on the Ag content was not observed. Additionally the crystalline structure and, particularly, the formation of CuAg-solid solutions and grain boundary segregation is discussed on the basis of XRD measurements. The Ag content within a supersaturated copper matrix increases with increasing dc current density.

Damascene technique applied to surface acoustic wave devicesa)

A new process technology for the wafer-level fabrication of surface acoustic wave (SAW) structures in piezoelectric LiNbO3 is reported. The complete Cu-based metallization system is embedded in the surface by applying the damascene technology. This technique includes ion based dry etching procedures, metallization by sputter deposition (physical vapor deposition) and electrochemical deposition, and finally planarization by chemical-mechanical polishing. The process steps were monitored by means of different evaluation techniques. SAW wave field measurements provided evidence for a good surface quality after planarization.

Damaging of metallization layers by high power surface acoustic wave fields

Similar to interconnection lines in integrated circuits patterned metallization structures are used as electrodes and reflecting elements in surface acoustic wave (SAW) devices. As electromigration is known to be a damaging mechanism in interconnects also the metallization of SAW devices tends to be degraded under high power conditions. Corresponding to the source of degradation, namely the elastic waves, the latter is called acoustomigration. Aim of this work is an approach to understand damage mechanisms by corresponding loading conditions and failure occurrences in the metallization. Our work is focused on in situ experiments with standing SAWs combining electrical measurements and different microscopic investigations (OM, SEM, FIB), detailed consideration of SAW stress field structure in connection with model experiments, and making use of the route of Cu technology. First results of a comparative study of fully metallized Al and Cu areas supporting high amplitude travelling SAWs are presented showing...

AES depth profiling multilayers of 3d transition metals

Abstract Multilayer structures composed of 3d transition metals were investigated by AES in combination with sputter depth profiling. The samples were trilayers Permalloy/Cu/Permalloy, Co/Cu multilayers and a spin-valve structure. Overlapping Auger peaks were separated by a fit-to-spectra of bulk standards. Sample rotation during sputtering improves the depth resolution and made detection of unintentionally deposited Cu possible. For very thin films the depth profiles are influenced by measuring effects. The effects of atomic mixing, surface roughness and information depth onto the depth profiles in the spin-valve structure were simulated using the MRI model.

Tungsten as a Chemically-Stable Electrode Material on Ga-Containing Piezoelectric Substrates Langasite and Catangasite for High-Temperature SAW Devices

Thin films of tungsten on piezoelectric substrates La3Ga5SiO14 (LGS) and Ca3TaGa3Si2O14 (CTGS) have been investigated as a potential new electrode material for interdigital transducers for surface acoustic wave-based sensor devices operating at high temperatures up to 800 °C under vacuum conditions. Although LGS is considered to be suitable for high-temperature applications, it undergoes chemical and structural transformation upon vacuum annealing due to diffusion of gallium and oxygen. This can alter the device properties depending on the electrode nature, the annealing temperature, and the duration of the application. Our studies present evidence for the chemical stability of W on these substrates against the diffusion of Ga/O from the substrate into the film, even upon annealing up to 800 °C under vacuum conditions using Auger electron spectroscopy and energy-dispersive X-ray spectroscopy, along with local studies using transmission electron microscopy. Additionally, the use of CTGS as a more stable substrate for such applications is indicated.

Mechanical Properties of ZTO, ITO, and a-Si:H Multilayer Films for Flexible Thin Film Solar Cells

The behavior of bi- and trilayer coating systems for flexible a-Si:H based solar cells consisting of a barrier, an electrode, and an absorption layer is studied under mechanical load. First, the film morphology, stress, Young’s modulus, and crack onset strain (COS) were analyzed for single film coatings of various thickness on polyethylene terephthalate (PET) substrates. In order to demonstrate the role of the microstructure of a single film on the mechanical behavior of the whole multilayer coating, two sets of InSnOx (indium tin oxide, ITO) conductive coatings were prepared. Whereas a characteristic grain–subgrain structure was observed in ITO-1 films, grain growth was suppressed in ITO-2 films. ITO-1 bilayer coatings showed two-step failure under tensile load with cracks propagating along the ITO-1/a-Si:H-interface, whereas channeling cracks in comparable bi- and trilayers based on amorphous ITO-2 run through all constituent layers. A two-step failure is preferable from an application point of view, as it may lead to only a degradation of the performance instead of the ultimate failure of the device. Hence, the results demonstrate the importance of a fine-tuning of film microstructure not only for excellent electrical properties, but also for a high mechanical performance of flexible devices (e.g., a-Si:H based solar cells) during fabrication in a roll-to-roll process or under service.

The Influence of the Composition of Ru100−xAlx (x = 50, 55, 60, 67) Thin Films on Their Thermal Stability

RuAl thin films possess a high potential as a high temperature stable metallization for surface acoustic wave devices. During the annealing process of the Ru-Al films, Al2O3 is formed at the surface of the films even under high vacuum conditions, so that the composition of a deposited Ru50Al50 film is shifted to a Ru-rich alloy. To compensate for this effect, the Al content is systematically increased during the deposition of the Ru-Al films. Three Al-rich alloys—Ru45Al55, Ru40Al60 and Ru33Al67—were analyzed concerning their behavior after high temperature treatment under high vacuum and air conditions in comparison to the initial Ru50Al50 sample. Although the films’ cross sections show a more homogeneous structure in the case of the Al-rich films, the RuAl phase formation is reduced with increasing Al content.