Sebastian Uhlig

A contribution to the expansion of the applicability of electrostatic forces in micro transducers

Electrostatic actuation is highly efficient at micro and nanoscale. However, large deflection in common electrostatically driven MEMS requires large electrode separation and thus high driving voltages. To offer a solution to this problem we developed a novel electrostatic actuator class, which is based on a force-to-stress transformation in the periodically patterned upper layer of a silicon cantilever beam. We report on advances in the development of such electrostatic bending actuators. Several variants of a CMOS compatible and RoHS-directive compliant fabrication processes to fabricate vertical deflecting beams with a thickness of 30 μm are presented. A concept to extend the actuation space towards lateral deflecting elements is introduced. The fabricated and characterized vertical deflecting cantilever beam variants make use of a 0.2 μm electrode gap and achieve deflections of up to multiples of this value. Simulation results based on an FE-model applied to calculate the voltage dependent curvature for various actuator cell designs are presented. The calculated values show very good agreement with the experimentally determined voltage controlled actuation curvatures. Particular attention was paid to parasitic effects induced by small, sub micrometer, electrode gaps. This includes parasitic currents between the two electrode layers. No experimental hint was found that such effects significantly influence the curvature for a control voltage up to 45 V. The paper provides an outlook for the applicability of the technology based on specifically designed and fabricated actuators which allow for a large variety of motion patterns including out-of-plane and in-plane motion as well as membrane deformation and linear motion.

A novel electrostatic micro-actuator class and its application potential for Optical MEMS

Electrostatic actuation is highly efficient at micro and nanoscale. However, due to pull-in instability large deflection requires large electrode separation and thus large driving voltages. We report on a novel electrostatic actuator class, which allows deflections in the μm-range based on electrode separations of a few 100 nm, only. Specifically designed and fabricated actuators allow for a large variety of motion patterns including out-of-plane and in-plane motion as well as membrane deformation. A CMOS compatible and RoHs compliant fabrication process enable straight-forward integration. The potential for actuator based Optical MEMS devices is discussed.

Electrostatically Driven In-Plane Silicon Micropump for Modular Configuration

In this paper, an in-plane reciprocating displacement micropump for liquids and gases which is actuated by a new class of electrostatic bending actuators is reported. The so-called “Nano Electrostatic Drive” is capable of deflecting beyond the electrode gap distance, enabling large generated forces and deflections. Depending on the requirements of the targeted system, the micropump can be modularly designed to meet the specified differential pressures and flow rates by a serial and parallel arrangement of equally working pumping base units. Two selected, medium specific micropump test structure devices for pumping air and isopropanol were designed and investigated. An analytical approach of the driving unit is presented and two-way Fluid-Structure Interaction (FSI) simulations of the micropump were carried out to determine the dynamic behavior. The simulation showed that the test structure device designed for air expected to overcome a total differential pressure of 130 kPa and deliver a flow rate of 0.11 sccm at a 265 Hz driving frequency. The isopropanol design is expected to generate 210 kPa and pump 0.01 sccm at 21 Hz. The device is monolithically fabricated by CMOS-compatible bulk micromachining processes under the use of standard materials only, such as crystalline silicon, silicon dioxide and alumina.

Instrumentation and Experimental Setup

The setup for the experimental investigations is based on a commercial ”solid state” femtosecond laser system from Spectra Physics, USA. The system provides femtosecond laser pulses from a mode-locked Titan:sapphire (laser medium a sapphire crystal doped with Titan ions Ti3+:Al2O3) oscillator (Spectra Physics Tsunami, Model 3960) with a central wavelength of λlaser=800nm and a spectral width at the full width half maximum (FWHM) of Δλ=15nm.

Generation of White Light Supercontinuum

Supercontinuum generation (SCG) is a process, where laser pulses with narrow spectral bandwidth (quasi-monochromatic) are converted to pulses with very broad spectral bandwidth.

Characterization of White Light Supercontinuum

In this chapter, the measurements of the white-light continuum characteristics in the spectral, spatial and temporal domain are presented and discussed. Of major scientific interest, is for once, the behavior of the white-light continuum to the applied input power of the pump-laser beam. The goal is to later obtain an efficient and possibly flat spectrum (here, moderate slope in narrow spectral intervals), with a large spectral broadening and sufficient white-light fluence F WL , for the formation of LIPSS on the samples. The investigation also includes the determination of the output power of the filtered spectra after the three short pass filters.

Introduction to Laser-Ablation &-Surface Structuring

Femtosecond (fs) laser ablation is the rapid removal of material from the surface region of a target, induced by laser pulses with duration in the order of tens to hundreds of femtoseconds (10−15s). Thereby the duration of the laser pulse is so short that it addresses only the target electrons. Every other process and response of the material takes place after the pulse.

Self-Organized Pattern Formation with Ultrafast White-Light

A broad-band white-light (WL) spectrum (filtered, roughly ranging from ≈ 400nm≤ λ\(\approx 400\text{nm}\le {{\lambda }_{wl}}\le 800\text{nm}\) ≤ 800nm), with significantly reduced spatial coherence, can only be obtained at the highest available input pump energy. For this reason, it was chosen to irradiate the samples, in the corresponding set of experiments, with a constant WL pulse energy and vary the irradiation dose (I D = f(N · F)), through the number of applied pulses N.