2018

Integrated throughflow mechanical microfluidic sensors

In this thesis are described: novel designs, fabrication methods and experiments of microfluidic sensors that use a mechanical transduction principle. ‘They can be integrated, throughflow, with other sensors on a single chip,’ says Dennis Alveringh. 

By measuring flow, pressure and fluid properties, such as density and viscosity, the composition of mixtures can be measured, provided that the ingredients are known. ‘Miniaturization of these sensors, using microtechnology, offers advantages in terms of: resolution, mass production, channel wall material and internal volumes,’ Dennis explains.

In this PhD project, microfabricated Coriolis mass flow sensors were central. These sensors, consisting of suspended silicon nitride channels of 10 – 100 µm, are fabricated using surface channel technology. With laser Doppler vibrometry, it is found that the resolution can be improved by at least a factor of 10. ‘In my PhD theoretical and experimental/characterization work alternated in a multidisciplinary way,’ Dennis says. ‘That feature of academic research, I appreciate and enjoy.’

Also, a universal and modular electronic platform was developed for characterization of these compound microfabricated sensors. ‘Characterization of these sensors is complicated, because we need to apply fluids and simultaneously apply and sense small electric signals,’ Dennis says.

A two-step approach suffices. With the new platform, the sensor only needs to be glued on a printed circuit board and wire-bonded. The printed circuit board can then be clamped into the main setup, which leads directly to 8 fluid connections and 72 electrical connections. Electronic modules can be connected to the main setup for actuation and sensing.

Surface channel technology is also suitable for the fabrication of throughflow pressure sensors. ‘In the thesis I present two designs,’ Dennis says. ‘I especially enjoyed presenting my first pressure sensor, at the international Transducers Conference in Alaska. The number of abstracts that are accepted at this Conference is quite low. It was a great feeling to find my work getting recognition from colleagues in the field. Knowing to have a worthy knowledge position in the world, boosted my self-confidence.’

Enabling technology

According to Dennis, Coriolis mass flow sensors serve as an enabling technology, with various promising application areas.

‘For several reasons the material used, silicon nitride, is very promising,’ he says. ‘In micro and nano devices, the freedom of design is great, as is the integrability with chip design. In food safety applications, silicon nitride is applicable as well. Perhaps one day, drug delivery for newborn babies may benefit from microfabricated Coriolis mass flow sensors. Continuity of dosage, during the whole cycle of drug delivery, must be very precise then.’

Clinical and industrial experts

Dennis was happy to cooperate with experts from two different hospitals: UMC Utrecht and Medisch Spectrum Twente.

‘Multiple clinical experts participated, as did people from Saxion Hogeschool and engineering company Bronkhorst High-Tech BV in Ruurlo, not far from here,’ Dennis says. ‘They were all willing to share their expertise, and we contacted regularly. It is essential to observe the project from different perspectives, especially since this technology is still in its first stage of research.’

Future job

After his PhD Defense Dennis plans to go and work at Salland Engineering in Zwolle, an international leading test technology and engineering company, specialized in solutions and services that enable semiconductor manufacturers to improve their products and testing quality.

‘Especially my analytical and experimental skills will be of added value, I expect,’ Dennis says. ‘Working on tomorrow’s products is fascinating. One cannot be sure at the present time which components will be decisive in tomorrow’s market. Perhaps right now I am working on chips that will be produced by the millions one day! Who knows that also goes for the Coriolis mass flow sensors.’

NanoLab

Dennis appreciated being part of the Integrated Devices and Systems Group (IDS) and working at the MESA+ Nanolab.

‘Apart from the advanced equipment and well organized labs at IDS and MESA+, I enjoyed working with the technicians,’ he says. ‘They think along with you, and they are the ones making the big difference. Also they pass on the expertise associated with the equipment. While I leave, they are staying, to help next generations of PhD researchers.'