Matthias Staab

Applications of Novel High-Aspect-Ratio Ultrathick UV Photoresist for Microelectroplating

The new acrylic photoresist named AZ 125 nXT is a serious option for low-cost high-aspect-ratio UV LIGA applications. It offers advantages compared to SU-8 like good adhesion to Si substrates, rapid processing, and easy removal after electroplating. Film thicknesses of 400, 800, and 1400 μm with an aspect ratio of 20 : 1 have been shown by the authors. The photoresists excellent electroforming behavior has been proved in an extremely acid copper electrolyte at room temperature as well as in an almost neutral nickel electrolyte at 50°C. The easy removal (wet: dimethyl sulfoxide or acetone, dry: plasma with reactive radicals) releases freestanding metal structures with aspect ratios of 13 : 1 and 16 : 1.

Novel electrothermally actuated magnetostatic bistable microrelay for telecommunication applications

A new energy efficient latching micro relay is presented. Its design and production process allows a subsequent industrial realization. Concerning its large contact travel (100 µm) and large contact force (12.4 mN) corresponding to a low contact resistance (33.8 mOhm for gold/gold contacts), the micro relay is well suited for matrices in telecommunication applications. The MEMS relay (3.6 × 5.8 × 0.25 mm3) is produced using a surface micromachining process with AZ 9260, AZ nXT 125 and SU-8 2025 UV lithography and micro electroplating of copper and nickel. The integration of the electrical path and the magnetostatic bistable mechanism enables fast switching (< 8 ms), although the actuation is performed by electrothermal actuators.

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.