MESA+ University of Twente
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Johan Engelen (promotion date: 14 January 2011)

Optimization of comb-drive actuators : nanopositioners for probe-based data storage and musical MEMS

Promotion date: 14. January 2011

Promotor: Prof. dr. Miko Elwenspoek

Assistant promotor: Dr. ir. Leon Abelmann

One promising technology is parallel probe-based data storage, using a nanometre-scale probe to write data on a moving platform. Several nano-positioner designs for probe data storage are found in the literature. It is not clear which actuator type (electromagnetic, electrostatic, or piezoelectric) is most suited for probe data storage.

Electrodynamic actuators were replaced by electrostatic comb-drives in the scanner prototype by IBM, to enable a direct comparison. A comb-drive’s areal efficiency is low, due to a relatively low electrostatic force. Therefore, we optimized comb-drive finger profiles for probe data storage, for an increased shock resistance.

Three scanner designs using electrodynamic, electromagnetic and electrostatic comb-drive actuators are described. Their performance is approximately equal, however electrostatic comb-drive actuation requires an order of magnitude less energy.

Was your research application oriented?

Using comb drives in the scan table of IBM was aimed towards future applications. The project was part of research sponsored by STW, and was a cooperation with another PhD student in the Computer Science department.

A probe data storage system has several important requirements. The displacements have to be precise, the whole apparatus must be shock-proof, and by refining the comb-structure – exploiting the way they are pressed together – we could obtain enough force. The energy consumption is an important issue too. For mobile storage, for example a flash-card in a photo-camera, the total power budget is around 300 mW. Reading a line with the electrodynamic IBM scanner equals already 20 mW for just the scan table.

In fact, I kind of missed the scientific challenge a little bit in my research. After successfully fabricating a scanner with comb drives, I was busy optimizing several new ideas. The devices performed well, most of the time. No really strange things popped up, desperately in need of scientific explanation. So to say. In my new job, I hope to find that aspect of the work a little more. I like the mix of theoretical work with experimental skills needed in the lab.

Where is your new workplace located?

I am working at IBM in Zürich, since two months now. It involves large-scale data-storage on tape media, still actual for big companies, like banks, being able to have long-term access to these data. The positioning of the read/write-head has to be more accurate and quicker in future. Reaching this goal is far from easy, and we stumble on several features which we don’t fully understand yet. This research-job at IBM is a great combination of dealing with academic-like issues in a company environment. As such, it is a real challenge to me.

Was a lot of publicity involved in your thesis project?

I had some nice publications, for example in the Journal of Micromechanics & Micro-engineering. Also, I was present at some conferences with oral and poster presentations.

Most of all, however, I enjoyed creating our microinstrument ‘the micronium', making use of MEMS structures. Besides teaching students about MEMS technology in a fun way, the micronium succeeded in presenting MEMS technology to a broad audience. MEMS are part of every mobile phone, but people cannot know what they are if they never come into contact with them. We succeeded in that, in an creative way.

What, in your opinion, is important for Mesa+ to stay successful in the future?

Let me assure you, Mesa+ is well-known all over the world, in academics as it is with renowned companies like IBM. If Mesa+ can keep up that standard, it will be fine.