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IEEE journal of the Electron Devices Society 7, 997 - 1006 (2019). doi:10.1109/JEDS.2019.2940086, Published by IEEE, [New York, NY]

Micro- and nanowires with high aspect ratios, arranged as slim and tall standing metal pillars offer promising features for microsystems [1–7]. The goals are: - 1st fabrication of high aspect ratio out of plane metal wires next to low aspect ratio blocks, - 2nd multilayer material link of these metal structures (one wire + two metal blocks), - 3rd realization and characterization of an acceleration sensor applying these structures. The KNMF services refer to the fabrication of templates made by aligned X-ray lithography. The high aspect ratio templates provide vertical cylindrical holes with aspect ratios from 16 to 33 next to template openings with low aspect ratios (Fig. 1 d). The remaining process steps are to be processed at Technische Universität Darmstadt (TUD). Results from KNMF 2010-004-000365 proposal are shown in Tab. 1. Two main issues still remain before the MEMS can prove to work as an inertial sensor: a) The structures (columns) on the X-ray exposure mask are approximately 1 µm smaller than designed. Therefore, the vertical wire is less robust and buckles (Tab. 1 b, c). Hence, the mass load has to be reduced and the process steps in Fig. 1 g have to be designed for a better wire protection. The mass load reduction can be achieved by a reduced electroforming height in Fig. 1 f. The process steps can more efficiently protect the wire, if the seed layer is designed differently. The connection from the bottom circuit path to the top of the sacrificial SU-8 3005 layer currently runs at the outer edges of the mass block (Fig. 2 a). There, it has to be wet etched for an efficient removal of the sacrificial layer. This step can be omitted, if the connection from the circuit path to the seed layer runs at the inner edges of the mass block (Fig. 2 a). The inner connection offers enough flexibility for the movement of the metal blocks when measuring acceleration. b) The electrodeposition shows to be inhomogeneous due to the design of the circuit path layer. The circuit path layer shows substantial resistances and it delivers the electrodeposition current. A layer redesign including local thickening can solve this problem (Fig. 2 b). Both improvements shown in Fig. 2 have been successfully implemented in a similar UV lithography approach at TUD [2–4], [7] and are scheduled in the KNMF proposal 2012-008- 000970. Acknowledgements The aligned X-ray exposures in the KNMF proposal 2010-004-000365 done by F J Pantenburg and P Meyer are greatly acknowledged. References [1] P. F. Greiner, J. Eberhardt, and H. F. Schlaak, “Metallic Micro Nails MAde by direct LiG process - MiNiMAL,” in Proceedings of the 2nd KNMF User Meeting, Karlsruhe, 2010, p. 69. [2] P. F. Greiner and H. F. Schlaak, “High Aspect Ratio Metal Nano and Micro Pillars as Suspension Elements in MEMS,” in 9th International Workshop on High Aspect Ratio Micro Structure Technology, HsinChu, Taiwan, 2011, pp. 53–54. [3] F. Greiner, J. Eberhardt, and H. F. Schlaak, “Senkrechte metallische Nano- und Mikrodrähte mit hohem Aspektverhältnis als neuartige Federelemente in Mikrosystemen - Vertical High Aspect Ratio Nano and Micro Wires as Novel Suspension Elements in MEMS,” in Proceedings of the Mikrosystemtechnik Kongress 2011, Berlin, Offenbach, 2011, pp. 328–331. [4] F. Greiner and H. Schlaak, “High aspect ratio metal micro and nano pillars for minimal footprint MEMS suspension,” Microsystem Technologies, pp. 1–7, 2012. [5] J. J. Schneider, H. F. Schlaak, D. Pavlidis, F. Küppers, and W. Ensinger, “Elektromechanische Sensoren mit eindimensionalen Nanoobjekten - ELEMENT, FKZ 16SV5475,” Berlin, 18-Jun-2012. [6] F. Dassinger, M. Hottes, F. Greiner, H. F. Schlaak, and W. Ensinger, “Mikro-Nano-Integration für die Inertialsensorik,” Sensor Magazin, vol. 27, no. 3, p. 24, Sep-2012. [7] F. Greiner, S. Quednau, F. Dassinger, R. Sarwar, H. F. Schlaak, M. Guttmann, and P. Meyer, “Fabrication techniques of multiscale 3D-MEMS with vertical metal micro- and nanowire integration,” J. Micromech. Microeng., submitted, 2012.

This poster aims to show the possibilities of a small scale research lab that focusses on surface micromachining processes without CMOS compatibility. Its size of 100 m^2 cleanroom keeps the flexibility to easily introduce exceptional materials but nevertheless offers a set of standard procedures for UV lithography and UV depth lithography, wet etching, electroplating, PVD, dry etching, packaging and characterization, respectively. The installations are optimized for 100 mm wafers and low temperature (< 150°C) surface micromachining, see figure. The technology foci are Direct LIGA and long term stable ultra thick (200 µm .. 1.2 mm) functional materials based on epoxy resins. The combination of UV Direct LIGA (lithography, subsequent automatically driven electroplating and final release of metal structures from polymer molds) and nanotechnology offer potential for new MEMS and NEMS. The nanotechnology aspect is introduced by the wafer level integration of ion track etched polymer membranes, e.g. made by GSI material research. The membranes act as molds for electroplating while UV lithography shapes the outer dimensions of the nanowire arrays. Substrate materials currently comprise Silicon, glasses, ceramics and printed circuit board glass fibre reinforced plastic (FR4). Structures are made of Ni, Cu, Au, Cr, Al, epoxy resins like different SU-8 formulations, polycarbonate and combinations of those. Figure: Part of the cleanroom laboratory installations, for details see http://www.emk.tu-darmstadt.de/en/institute/equipment/

This talk aims to show the possibilities to build up micro electromechanical systems (MEMS) in a small scale research lab. Its size of 100 m^2 cleanroom keeps the flexibility to easily introduce new materials but nevertheless offers a set of standard procedures for UV lithography and UV depth lithography, wet etching, electroplating, PVD, dry etching, packaging and characterization, respectively. The installations are optimized for 100 mm wafers and low temperature (< 150°C) surface micromachining, for details see http://www.emk.tu-darmstadt.de/en/institute/equipment/. For instance, the apparatus enable the batch fabrication of 197 active MEMS chips with 5 mm x 5 mm outlines including large scale electrical connections for robust packaging, see SEM figure. The technology foci are Direct LIGA and long term stable ultra-thick (200 µm .. 1.2 mm) functional materials based on epoxy resins. The combination of UV Direct LIGA (lithography, subsequent electroplating and final release of metal structures) and nanotechnology offer potential for new MEMS and NEMS. Substrate materials currently comprise Silicon, glasses, ceramics and printed circuit board glass fiber reinforced plastic (FR4). Structures are made of Ni, Cu, Au, Cr, Al, epoxy resins like different SU-8 formulations, olycarbonate and combinations of those. The MEMS made in this small scale research lab can be distinguished by structure geometries with out of plane metal wires. These posts show diameters of 100 nm .. 50 µm, lengths of 10 µm .. 400 µm keeping aspect ratios from 10:1 to 500:1. Furthermore, nano- and microwires can easily be combined with millimeter structures and all of them can be freely clamped. The MEMS made in the small scale research lab offer the functionalities of inertial sensing (capacitively), gas flow sensing (thermally), out of plane actuation (electrostatically driven) and in plane actuation (electrothermomechanically with cN forces).

Nanodrähte sind durch ihr großes Oberflächen/Volumen-Verhältnis von hier etwa 1,6·10^7 m²/m³ ein interessantes Untersuchungsobjekt zur Minimierung der Ansprechzeit von Mikrogasflusssensoren. Diese Arbeit beschreibt die Modellierung von Nanodrahtarrays in Gasflüssen. Sie geht auf Temperatursprünge von 1 K bei Gasflüssen < 1 m/s ein. Die Simulationsergebnisse legen nahe, dass bei Nanodrahtarrays Zeitkonstanten von < 10^-3 s und bei einzelnen Nanodrähten um mehr als drei Größenordnungen kleinere Zeitkonstanten möglich sind. Weiterhin beschreibt diese Arbeit einen Prozessablauf zur Integration von Nanodrahtarrays in ein Mikrosystem zur Gasflussanalyse. Die Bündelung von drei Nanodrahtarrays ist experimentell realisiert und vereinfacht die Handhabung bei der Montage. Sie ermöglicht eine beidseitige Kontaktierung der Nanodrahtarrays mit einer planaren Mikrostruktur.