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Dive into the research topics where Steffen Leopold is active.

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Featured researches published by Steffen Leopold.


Journal of Vacuum Science & Technology. B. Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena | 2011

Formation of silicon grass: Nanomasking by carbon clusters in cyclic deep reactive ion etching

Steffen Leopold; Christoph Kremin; Angela Ulbrich; S. Krischok; Martin Hoffmann

Initial cluster formation on silicon surfaces in cyclic deep reactive ion etching (c-DRIE) using c-C4F8/SF6 plasma is investigated. These clusters act as a nanomask for the fabrication of nanostructured surfaces such as silicon grass. Different wafer preconditioning regimes and subsequent x-ray photoelectron spectroscopy show that no wafer or process contaminations are the reason for nanomasking in c-DRIE. Furthermore, no Si-containing compounds, such as SiFxOy, SiOx, or SiC, are detected. The clusters consist of residues of the fluorinated carbon layer deposited in c-DRIE. Experimental process analysis using design of experiments shows the dependence of nanomask morphology on passivation time and power. The results indicate that the properties of the nanomask, in particular, density, are determined during passivation.


Journal of Micromechanics and Microengineering | 2013

Variation of the intrinsic stress gradient in thin aluminum nitride films

Hannes Mehner; Steffen Leopold; Martin Hoffmann

The intrinsic stress gradient variation of thin aluminum nitride (AlN) films is the central objective in this paper. For the first time, significant influence parameters on the stress gradient are identified and varied during the deposition process. The process power induced in the plasma and the gas flow ratio of the sputter gases argon and nitrogen are the two major parameters for controlling the stress gradient of deposited AlN films. The controlled avoidance as well as the controlled generation of positive and negative gradients is shown. The stress gradient was investigated by analysis of released one-side clamped cantilever test structures.


Proceedings of SPIE | 2010

Tunable compound eye cameras

Daniel Pätz; Steffen Leopold; Fabian Knöbber; Stefan Sinzinger; Martin Hoffmann; O. Ambacher

We present design and realization concepts for thin compound eye cameras with enhanced optical functionality. The systems are based on facets with individually tunable focus lengths and viewing angles for scanning of the object space. The active lens elements are made of aluminum nitride (AlN)/nanocrystalline diamond (NCD) membranes. This material system allows slow thermally actuated elements with a large deformation range as well as fast piezoelectric elements with a smaller deformation range. Due to the extreme mechanical stability of these materials, we are able to realize microoptical components with optimum surface qualities as well as an excellent long-term stability. We use facets of microlenses with 1 mm in diameter and a tunable focusing power to compensate for the focus shift for different viewing angles during the scanning procedure. The beam deflection for scanning is realized either by laterally shifting spherical elements or by a tunable microprism with reduced aberrations. For both actuators we present a design, fabrication concept and first experimental results.


Journal of Micro-nanolithography Mems and Moems | 2013

MOEMS tunable microlens made of aluminum nitride membranes

Steffen Leopold; Tobias Polster; D. Paetz; Fabian Knoebber; O. Ambacher; Stefan Sinzinger; Martin Hoffmann

Abstract. We present tunable lenses based on aluminum nitride membranes. The achievable tuning range in the refractive power is 0 to 25 dpt with an external pressure load of ≤20  kPa. The lenses are manufactured using MOEMS technology. For 500-nm-thick membranes with a diameter of 3 mm, a spherical deflection profile is found. The system provides good long-term stability showing no creep or hysteresis. A model for the refractive power versus applied pressure is derived and validated experimentally. Based on this model, design guidelines are discussed. One essential parameter is the residual stress of the aluminum nitride layer that can be controlled during deposition.


MOEMS and Miniaturized Systems XII | 2013

Tunable cylindrical microlenses based on aluminum nitride membranes

Steffen Leopold; D. Paetz; Fabian Knoebber; O. Ambacher; Stefan Sinzinger; Martin Hoffmann

We introduce sputtered aluminum nitride thin films for tunable micro-optics. During lens fabrication, AlN is deposited on a silicon substrate. Silicon is structured by using DRIE, which allows fabrication of circular, rectangular and irregular membrane shapes. In this contribution, we present the design, fabrication and characterization of AlN membranes for tunable cylindrical lenses. An optimized “dogbone” membrane is presented, which deflects cylindrically and has a small footprint. Compared to conventional rectangular membranes the optically useful area is doubled. The load deflection characteristic is investigated and basic relations between the refractive power and applied pressure are found. The relation can be used for tailoring the membrane properties, i.e. their residual stress, for a specific application. According to this calculation, a refractive power of 25 dpt with a lens aperture of 3x3 mm2 is achieved for 12 kPa of applied pressure. The cylindrical deflection of the “dogbone” membrane is measured. The maximum shape difference in measured to be 270 nm.


Journal of Micromechanics and Microengineering | 2013

Online monitoring of the passivation breakthrough during deep reactive ion etching of silicon using optical plasma emission spectroscopy

Steffen Leopold; L Mueller; Christoph Kremin; Martin Hoffmann

We present optical emission spectroscopy (OES) as a technique for process optimization of the etch step during deep reactive ion etching of silicon. For specific process steps, the spectrum of optical plasma emission is investigated. Two specific wavelengths are identified (fluorine at 703.8 nm and CS compounds at 257.6 nm), which significantly change intensity during the etch step. Their intensity drop is used for the recognition of the passivation layer breakthrough. Thus, the net silicon etch time can be measured. This time can be used for process optimization. A structural analysis of the passivation layer shows its fragmentation during its breakthrough. The plasma–surface interaction and their correlation with the plasma emission are described. Within an application example, the passivation breakthrough is investigated in detail. For different process regimes, the residues of the fragmented passivation layer are analyzed by scanning electron microscopy. Residue densities of 14–38 µm−2 are fabricated. For silicon grass generation, the OES technique offers a versatile tool for the process optimization of the mask generating process within the first cycles.


MEMS Adaptive Optics V | 2011

Tunable refractive beam steering using aluminum nitride thermal actuators

Steffen Leopold; D. Paetz; Fabian Knoebber; Tobias Polster; O. Ambacher; Stefan Sinzinger; Martin Hoffmann

Step-structured thermo-mechanical actuators based on aluminum nitride (AlN) thin films and their application in refractive beam steering are investigated. The actuators will tilt a suspended plate and deform a liquid surface to realize a micro-prism. Arrays of tunable micro-prisms will increase the resolution of compound eye systems. A numerical actuator description is presented and the beam geometry is investigated, considering achievable tilt angles and actuator linearity. For an accurate design, the coefficient of thermal expansion (CTE) of AlN is determined, while measuring the bow of a coated silicon substrate at different temperatures. For a temperature difference of 300 K, the results show a maximum tilt angle of 7.1 °, which is independent of actuator length. Furthermore, the fabrication process is introduced and the nano-crystalline structure of AlN at facets, which are caused by pre-structured substrates, is investigated.


international conference on solid state sensors actuators and microsystems | 2017

Silicon grass based nano functional electrodes for MEMS supercapacitors of improved energy density

Pai Lu; Kang Du; Per Ohlckers; Einar Halvorsen; Lutz Muller; Steffen Leopold; Martin Hoffmann; Kestutis Grigoras; J. Ahopelto; Mika Prunnila; Xuyuan Chen

Nano-structure functional electrodes for high energy density MEMS supercapacitors have been fabricated by combining atomic layer deposition (ALD) and cyclic deep reactive ion etch (C-DRIE) in MEMS technology. The electrodes were structured with C-DRIE organized silicon grass (Si-g) as the scaffold for conformal coating with ALD nano-layer TiN as the current collector, and electrochemical loading pseudo-capacitive active material. As obtained Si-g/TiN/MnOx on-chip electrode results in 1) large surface gain scaffold with one dimensional ionic diffusion, 2) high conductivity and electrochemical stability current collector, 3) high effective number of redox centers per volume, which enable largely improved energy density.


international conference on optical mems and nanophotonics | 2014

Tunable anamorphotic imaging system based on fluidic cylindrical lenses

Daniel Pätz; Steffen Leopold; Martin Hoffmann; Stefan Sinzinger

We present an anamorphotic imaging system with a separately tunable magnification in horizontal and vertical direction in order to change the aspect ratio of the image. The design is based on cylindrical membrane lenses made of aluminum nitride with tunable focal power to realize a vario system without moving elements. We demonstrate the design concept of cylindrical lenses with a very compact geometry, the optical system as well as experimental results.


Additional Conferences (Device Packaging, HiTEC, HiTEN, & CICMT) | 2013

Multifunctional LTCC Substrates for Thermal Actuation of Tunable Micro-Lenses Made of Aluminum Nitride Membranes

Steffen Leopold; Thomas Geiling; C. Fliegner; Daniel Pätz; Stefan Sinzinger; Jens Müller; Martin Hoffmann

Thin membranes are widely used for tunable micro-lenses, where the membrane, usually made from polymers, defines the surface of a subjacent liquid. If the liquid is pressurized, the membrane deflects and forms a lens. In many cases, a macroscopic pump is used to generate the pressure. Here, we use a multifunctional LTCC substrate, which consists of two cavities. A micro-fluidic network allows their independent filling. For the actuation, the actuating cavity is filled with air and the optical cavity is filled with immersion oil. If the actuating cavity is heated by screen-printed resistors, the fluid expands and a pressure is transmitted to the optical cavity via a micro-fluidic channel. The optical cavity is covered with a glass chip and a membrane chip, respectively. We use 500 nm thick membranes of aluminum nitride (AlN), which have a 3 mm diameter and are fabricated using technologies of silicon based micro-electro-mechanical systems. With 6 W electrical heating power a temperature increase of 100 K w...

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Martin Hoffmann

Technische Universität Ilmenau

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Daniel Pätz

Technische Universität Ilmenau

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Stefan Sinzinger

Technische Universität Ilmenau

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Tobias Polster

Technische Universität Ilmenau

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D. Paetz

Technische Universität Ilmenau

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Pai Lu

University College of Southeast Norway

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Per Ohlckers

University College of Southeast Norway

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Xuyuan Chen

University College of Southeast Norway

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Christoph Kremin

Technische Universität Ilmenau

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J. Ahopelto

VTT Technical Research Centre of Finland

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