K. Seemann

Preparation and applications of magnetostrictive thin films

Amorphous magnetostrictive films of the binary compound SmxFe1−x as well as of the ternary compound (TbyDy1−y)xFe1−x were prepared by rf or dc magnetron sputtering using either a multitarget arrangement with pure element targets or cast composite‐type targets. The magnetostrictive properties of (Tb0.3Dy0.7)0.4Fe0.6 and Sm0.4Fe0.6 films were investigated in relation to their preparation conditions. Depending upon these conditions (especially upon the deposition rate, the bias voltage, and the Ar sputtering pressure) amorphous films with a giant magnetostriction of about 250 ppm (−220 ppm) at 0.1 T and 400 ppm (−300 ppm) at 0.5 T for the TbDyFe (SmFe) and an in‐plane magnetic easy axis could be prepared. In view of applications in microsystem technologies (e.g., pumps, valves, positioning elements) these films have been tested in a simple cantilever arrangement and the predicted deflection of a magnetostrictive actuated membrane has been calculated.

Fabrication and simulation of magnetostrictive thin-film actuators

Abstract Sputter-deposited magnetostrictive films present an interesting opportunity to realize actuators in microsystems, as they offer features like contactless high-frequency operation, simple actuator designs and a cost-effective manufacturing technique. Amorphous magnetostrictive films of the binary compound SmFe as well as of the ternary compound TbDyFe have been prepared by d.c. magnetron sputtering using either a multitarget arrangement with pure element targets or cast composite-type targets. Depending upon the composition and the sputtering conditions, particularly upon the bias voltage, amorphous films with a giant magnetostriction of about 250 ppm (−220 ppm) at 0.1 T and 440 ppm (−300 ppm) at 0.5 T for TbDyFe (SmFe) and an adjustable magnetic easy axis can be prepared. In view of their applications in microsystem technologies (e.g., pumps, valves, positioning elements), these films have been tested in cantilever arrangements. The design of the actuators, such as the lateral patterning of the magnetostrictive films, has been modulated by means of finite-element calculations. For double-clamped beams or clamped membranes, these calculations reveal that lateral patterning of the magnetostrictive films is essential in order to obtain large deflections.

Development of high power density cathode materials for Li-ion batteries

Abstract Cathode material for Li-ion batteries can be synthesised by r.f. magnetron sputtering of LiCoO2 targets in a pure Ar plasma. This technique is suitable for large-scale implementation in foil coating set-ups. By choosing the process parameters and by employing post heat treatment nanocrystalline, stoichiometrical LiCoO2 films can be fabricated which exhibit the desired high temperature phase. The determination of the elementary composition is possible by optical emission spectroscopy including plasma stimulation and carrier gas temperature extraction. The proof of crystal structure is carried out by X-ray diffraction and Raman spectroscopy. Heat treatment can be conventionally realised in a furnace or by laser impact. With regard to increasing the power density, the surface of the cathode material can be enhanced six-fold by laser-assisted surface patterning.

Epitaxially stabilized TiN/(Ti,Fe,Co)N multilayer thin films in (pseudo-)fcc crystal structure by sequential magnetron sputter deposition

Multilayer thin films were grown by non-reactive sequential magnetron sputter deposition from ceramic TiN and metallic FeCo targets addressing a combination of wear resistance and sensoric functionality. Coatings with bilayer period values ranging from 449 nm down to 2.6 nm were grown with the total amount of either material maintained constant. The multilayer thin films were post-annealed ex situ at 600 °C for 60 min in vacuum.X-ray diffraction results imply the multilayer thin films undergo significant changes in their crystalline structure when the bilayer period is decreased. Using high-resolution transmission electron microscopy as well as selected-area electron diffraction it is shown that in the case of multilayer thin films with bilayer periods of several tens of nanometres and higher, FeCo layers and TiN layers in their respective common CsCl- and NaCl-type crystal structures alternate. In contrast, in the multilayer thin films with bilayer periods of only a few nanometres, grain growth across the interfaces between the individual layers takes place and a strongly textured microstructure is formed which features columns in (pseudo-)fcc crystal structure grown in heteroepitaxial growth mode.It is suggested that the experimental findings imply the latter multilayer thin films to be alternately composed of TiN layers and (Ti,Fe,Co)N solid solution layers which have been formed by a solid-state reaction during the deposition process. As a consequence, heteroepitaxially stabilized columnar grains in strongly textured (pseudo-)fcc crystal structure are formed. This crystal structure is preserved after the annealing procedure which qualifies these coatings for use in applications where temperatures of up to 600 °C are reached.

Thermal Stability of the Ferromagnetic In-Plane Uniaxial Anisotropy of Fe-Co-Hf-N/Ti-N Multilayer Films for High-Frequency Sensor Applications

In this study, the thermal stability of the in-plane uniaxial anisotropy field of Fe₃₂Co₄₄Hf₁₂N₁₂/Ti₅₀N₅₀ multilayer films was investigated from room temperature up to 500 °C with regard to contactless high-frequency sensor applications. The uniaxial anisotropy field of about μ_oH_u ≈ 5 mT was thermally induced by annealing the films in a static magnetic field of 50 mT in vacuum for one hour either at an annealing temperature of T_α = 400 °C or T_α = 600 °C. The films which were annealed at T_α = 600 °C show a clear distinction between the easy and hard axis of polarization up to temperatures of 500 °C. Hence, the uniaxial anisotropy, thermally induced at T_α = 600 °C, is stable at working temperatures up to 500 °C. In contrast, films with a uniaxial anisotropy induced at T_α = 400 °C show a different behavior. Here, hysteresis loop measurements indicate that above a working temperature of 200 °C the uniaxial anisotropy field turns away from its direction at room temperature. In conclusion, only the Fe₃₂Co₄₄Hf₁₂N₁₂/Ti₅₀N₅₀ multilayer films with a uniaxial anisotropy field induced at T_α = 600 °C promise a great potential for contactless high-frequency sensor applications up to 500 °C.

Towards In Situ-Process Control in Tribological or Tool Applications: A Material Concept for the Design of Smart Thin Film Wear Sensors

The optimization of processes for tribological or machining applications requires the development of (i) high performance substrate materials, especially ultra fine grain cemented carbides for cutting tools, (ii) complex tool geometries and (iii) innovative, nano-scaled hard and tough multi-functional protective coatings. Very important is also the in-situ process control which can be realized with (i) sensors which are embedded in the protective coating using microsystem technology or (ii) if possible, by using tailored coating designs which show itself both protective and sensor functionality.