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Geert Altena (promotion date: June 2006)

Evanescent field sensing in hybrid MOEMS devices

Promotion Date: June 2006

Geert Altena

MOEMS devices are devices combining MEMS (Micro Electrical Mechanical Systems, small mechanical chips) and optics. The optics are mounted on the chip to measure the mechanical movement on the chip. An evanescent field could be simply described as a bit of light escaping the structure in which it is trapped. The mechanical movement on the chip influences the intensity of the light and that is what we measure.

What was your thesis about?

MOEMS devices are devices combining MEMS (Micro Electrical Mechanical Systems, small mechanical chips) and optics. The optics are mounted on the chip to measure the mechanical movement on the chip. An evanescent field could be simply described as a bit of light escaping the structure in which it is trapped. The mechanical movement on the chip influences the intensity of the light and that is what we measure.

Why use such a complicated measuring method?

There are manufacturers of MEMS aiming at certain applications for their chip, but want to know during the production process whether their chip meets the required specifications.

Optical methods can help out here.

Are MEMS important?

They are of increasing importance. They are applied for movement sensors (in airbags of cars for instance), and other applications are pressure measuring devices.

Is that optical method for measuring mechanical movement a new principle?

The principle itself is not new, within our group it is applied in the chemical optical area because also different chemical substances change the intensity of the light, but there is hardly any literature on measuring mechanical properties using optics.

You were part of the European project of OCMMM (Optical characterization methods for MEMS manufacturing). Did that involve a lot of international collaboration?

We worked together with a number of universities, institutes and industries. We proved our principle in a number of demonstrators. In one demonstrator the mechanical moving part was a rotating micro mirror, we worked on that with the University of Chemnitz in Germany.

In another demonstrator there was a moving membrane; we worked on that one with Thales in France, and there was another one with a gyroscope application. We also did that with Thales.

Did you enjoy participating in such a big international project?

Not everything went smoothly. Our colleagues in Germany on whom we depended for the mechanical side of the rotating mirror produced without fail, but we had problems with the demonstrators from France, mainly delays. But there were also technical problems with their chips, they were not compatible with our systems here. So we more or less copied in a strongly simplified form one of the chips we had to receive from France in order to make our demonstrator work. And that led to quite a few rewarding results.

On the other hand I did enjoy the international collaboration, you work together with different nationalities, you go places… every half year there was a project meeting, so I have been to the south of France, Poland, Germany.

What did you like best about your research?

The finished product. After all, what we have made is pretty unique.

The first part of my research involved a lot of designing and to see your design actually work is exhilarating. I worked with a technician, Meindert Dijkstra, who did all the cleanroom work and it was perfect.

What didn’t you like?

The slow communication with the partners involved and the delays were somewhat frustrating at times.

What are you going to do next?

I’m going to work at the R&D institute Holst Centre/IMEC in Eindhoven. They are working in the field of autonomous wireless transducer solutions and systems-in-foil. It is a fairly new institute so I am very exited about it.