The thesis describes the achievements to create miniaturized, proportional control valves for minute gas flows. Four valve designs were presented, based on silicon-on-insulator (SOI) technology and surface channel technology (SCT). ‘We focused on MEMS-based fabrication processes,’ says Maarten Groen. ‘Manufacturability was an important guideline in this project. The work resulted in four main publications and also two patents were acquired. Though promising for many years already, microfluidic systems only entered market applications in limited numbers thus far. I hope to contribute to shorten the distance between lab research and market introduction.’
When analyzing successful product introductions stemming from academic research, Maarten Groen distinguishes between two main stages: fundamental research in an academic setting and product development in an industrial setting. ‘The intermediate step is often neglected,’ he says. ‘I feel at ease in this particular phase of research, in which creative unrest, freedom of research and focus on future applications are at stake all at once.’
Bronkhorst High-Tech (Ruurlo), Demcon (Enschede) and Finapres (Amsterdam) were intimately involved in this thesis research. Especially in the beginning of the PhD period, and towards the final stages, Maarten consulted the partners regularly. Also strategic meetings were organized. Maarten: ‘At the start various ideas were proposed. The partners were of great help in converging these into feasible concepts.’
Contradictory design requirements
Valve functionality, flow sensing and integrated electronics were all to be met in these chip designs. Maarten points out some serious challenges, resulting from contradictory design requirements, are present especially for miniaturized devices.
‘Actuation, for example, is imposing a set of technical challenges,’ he says. ‘The actuator has to withstand quite some gas pressure conditions while at the same time the switching process should be performed lightly and swiftly. Therefore, choosing the best piezo-electrical solution was always compromising.’
Maarten happily shares his results by describing one of his prototypes, based on SOI wafers. Using only three masked etching steps and one sacrificial layer etch in a single wafer, he succeeded in producing a proportional control valve.
Maarten: ‘Fabrication yields increase significantly when only few mask steps and no wafer bonding steps are required. So this is a good result. During my PhD I was present in the cleanroom for quite some time, working on several MEMS fabrication techniques. Integration of functionalities was done by hands-on assemblage, after which the prototypes were characterized. Also simulations were used, for example for dimensioning the actuator on the valve device. Gluing/bonding demands high precision geometry here, as the actuator should be firm and flexible, in order to perform its tasks properly.’
In the future Maarten favors working on projects bringing new ideas closer to the market, in an industrial setting using micro fabrication technologies. During his PhD project he learnt to appreciate performing research even more, finding his way with more confidence now.
‘My view on research has widened, and my approach is much more well-balanced now,’ he says. ‘Working independently on complex projects using a purposeful creative attitude would be a great challenge in my future job.’