Plasma-based processes are key applications in microsystems technology and are mainly used for the deposition and modification of thin films. A strong dependence on used equipment and materials can easily affect plasma processes and results in many differences of process characteristics like energy flow and deposition rates. For a deeper understanding of inclined magnetron-deposited thin films, a passive thermal probe was used to investigate the correlation between the film growth of two commonly used metallic target materials (Cu and Ni 46.8/Ti 53.2) and the energy flow from the plasma to the substrate. The special design of the sputtering system with a fixed angle of 45° between targets and substrate allows homogeneous coating of 200mm wafers with 100mm targets. The passive thermal probe measurements were performed radially across the substrate area for two different magnetron positions. Complementary surface and cross-sectional analysis of the deposited layers by atomic force microscopy, focused ion beam technique, and fracture edge analysis by scanning electron microscopy were performed on thin film samples on silicon substrate to investigate the growth rate and structure of the films. The films deposited in these experiments exhibit randomly oriented crystalline grains and heavily position-dependent change in surface topography and morphology from compact films to columnar growth, for Cu and NiTi respectively.

Superconducting thin films of NbN on SiO2 are prepared at ambient temperature by direct current magnetron sputtering with varying external deposition parameters, i.e. pressure, target-substrate distance, and power. Internal deposition parameters such as the plasma properties are determined with both a Langmuir probe and a calorimetric probe providing insight regarding the energy flux, the electron temperature, the plasma potential, and the ion current density of the plasma. Grazing incident x-ray diffraction and atomic force microcopy measurements reveal that the thin films have cubic polycrystalline structures with grain sizes of up to 51 angstrom, which define the superconducting behavior. Structural and electrical properties are related to the plasma parameters, showing a high correlation between the ion current density and the superconducting properties of the films. The results attest to the potential of plasma characterization as a powerful tool to optimize the deposition of thin NbN films and to predict their film properties.

Memristive devices have been the object of intensive studies for non-volatile memories, neuromorphic engineering and image processing algorithms. The intrinsic properties of these devices are determined by its I-V characteristics influenced by different process parameters. The double-barrier memristive devices investigated in this work are based on the motion of charged species, i.e. oxygen vacancies or ions, within a NbO x layer. Since the layers are deposited by magnetron sputtering, it is important to understand the physics of the discharge and its effect on the film properties. For plasma diagnostics we used a calorimetric probe, which can be operated simultaneously as a passive thermal probe for energy flux measurement and as a planar Langmuir probe for measuring the ion current, the floating and plasma potentials and the electron temperature. In particular, we investigated the reactive sputter deposition of the NbO x layer by a floating and a biased probe. The parameters were determined in dependence on the radial position of the probe across the substrate region. The results allowed us to find correlations between the plasma parameters and the electrical properties of the memristive devices produced on one 100-mm wafer. Furthermore, we could point out the dominating factors affecting strongly the properties of these thin films.

Sputter deposition is one of the most important techniques for the fabrication of memristive devices. It allows us to adjust the concentration of defects within the fabricated metal-oxide thin film layers. The defect concentration is important for those memristive devices whose resistance changes during device operation due to the drift of ions within the active layer while an electric field is applied. Reversible change of the resistance is an important property for devices used in neuromorphic circuits to emulate synaptic behavior. These novel bioinspired hardware architectures are ascertained in terms of advantageous features such as lower power dissipation and improved cognitive capabilities compared to state-of-the-art digital electronics. Thus, memristive devices are intensively studied with regard to neuromorphic analog systems. Double-barrier memristive devices with the layer sequence Nb/Al/Al2O3/NbOx/Au are promising candidates to emulate analog synaptic behavior in hardware. Here, the niobium oxide acts as the active layer, in which charged defects can drift due to an applied electric field causing analog resistive switching. In this publication, crucial parameters of the process plasma for thin film deposition, such as floating potential, electron temperature, and the energy flux to the substrate, are correlated with the I-V characteristics of the individual memristive devices. The results from plasma diagnostics are combined with microscopic and simulation methods. Strong differences in the oxidation state of the niobium oxide layers were found by transmission electron microscopy. Furthermore, kinetic Monte Carlo simulations indicate the impact of the defect concentration within the NbOx layer on the I-V hysteresis. The findings may enable a new pathway for the development of plasma-engineered memristive devices tailored for specific application.

Observation and study of the impressive polar lights marks the beginning of the gas discharge physics. Even though a remarkable progress was reached by the improvement of gas discharge tubes. The first constructed tube goes back to the Englishman Hauksbee. After that the German glassblower Heinrich Geissler developed more innovative discharge tubes by reducing the gas pressure and by using electrodes of aluminium. The Geissler tubes enabled a lot of scientists such as Plucker, Hittorf and Tesla to study the properties of glow discharges in more detail. At the same time Sir William Crookes developed similar tubes, which found a use in the laboratories of English physicists. Ultimately there were more seminal insights which led to the development of plasma physics as a seperate field and as foundation for many industrial applications.

Observation and study of the impressive polar lights marks the beginning of the gas discharge physics. Even though a remarkable progress was reached by the improvement of gas discharge tubes. The first constructed tube goes back to the Englishman Hauksbee. After that the German glassblower Heinrich Geissler developed more innovative discharge tubes by reducing the gas pressure and by using electrodes of aluminium. The Geissler tubes enabled a lot of scientists such as Plucker, Hittorf and Tesla to study the properties of glow discharges in more detail. At the same time Sir William Crookes developed similar tubes, which found a use in the laboratories of English physicists. Ultimately there were more seminal insights which led to the development of plasma physics as a seperate field and as foundation for many industrial applications.

SummaryThe History of Gas Discharge PhysicsObservation and study of the impressive polar lights marks the beginning of the gas discharge physics. Even though a remarkable progress was reached by the improvement of gas discharge tubes. The first constructed tube goes back to the Englishman Hauksbee. After that the German glassblower Heinrich Geißler developed more innovative discharge tubes by reducing the gas pressure and by using electrodes of aluminium. The Geißler tubes enabled a lot of scientists such as Plücker, Hittorf and Tesla to study the properties of glow discharges in more detail. At the same time Sir William Crookes developed similar tubes, which found a use in the laboratories of English physicists. Ultimately there were more seminal insights which led to the development of plasma physics as a seperate field and as foundation for many industrial applications.