Christian Nakic

SU-8 Electrothermal Actuators: Optimization of Fabrication and Excitation for Long-Term Use

In this paper we examine the suitability of SU-8 2000 as a construction material for electrothermal actuators and the actuator stability for long-term operation. The fabrication of SU-8 was optimized for mechanical and thermal stability. Samples with different softbake duration, exposure dose and postbake temperature were evaluated using Fourier-Transform IR-spectroscopy and dynamic-mechanical analysis. The exposure dose and postbake temperature proved to have a strong influence on the cross-linking and the glass transition temperature. A final hardbake levels the effects of the process history. A high degree of crosslinking, a low drop of the dynamic modulus over temperature (30%) up to the glass transition temperature 100–140 °C were achieved for SU-8 with an exposure dose of 1500 mJ/cm², a postbake temperature of 95 °C and hardbake of 240 °C. Electrothermal actuators proved to be stable until the end of the experiment after 2400 duty cycles. Actuator deflections up to 55 μm were measured (actuator length: 4 mm) for input powers up to 160 mW and a maximum operating temperature of 120 °C. Higher temperatures led to permanent deformations and failure. An offset drift of up to 20% occurs during actuation, but converges after a burn-in phase of about two hours.

Electrothermal out-of-plane-drive with novel bistable mechanism for portable Braille displays

A novel polymer-based bistable out-of-plane (OoP)-drive with electrothermal actuation for portable Braille area displays is presented. The drive consists of an OoP-actuator which moves a tactile Braille-pin out of the display surface and an in-plane (IP)-actuator which locks the pin position. The system is fabricated using UV-lithography of the epoxy based dry film photo resist SUEX. It has a small footprint of 10.7 × 2.5 mm2 and is suited for a 2.5 mm Braille grid. A high OoP-deflection up to 580 μm at 125 mW power consumption is achieved.

Development of an electrothermal micro positioning platform for laser targets with two degrees of freedom

This work presents the development of an electrothermal actuated micro positioning platform with two degrees of freedom for use in pump-probe-experiments. The platform consists of a monolithic kinematic system, actuated by local thermal expansion due to defined Joule heating. Samples are manufactured with UV-Lithography of SUEX™ dry films for the polymer body and metallic thin films for the heating elements. Characterization of the samples shows deflections up to 177 μm × 119 μm. Controlling the actuators driving power allows a positioning accuracy of less than 5 μm.