A novel accelerated life cycle methodology for actuating MEMS membranes via mechanical contact : innovation report

In the emerging technology of Micro Electronic Mechanical Systems (MEMS) there are challenges such as adoption, economies of scale, packaging and reliability incurred by many nascent technologies. The advantages of MEMS devices such as small micron scale, low power consumption and lab on a chip style data processing clearly outline the practical potential for the technology. Packaging and reliability driven by cost, however; are the factors that hinder progress of the technology and further entry into market. In the case of MEMS however, existing methods must be reassessed as fundamentally the concepts and scales have changed. MEMS is a market that despite challenges of the economy is still committed to heavy global investment from figures of $7bn in 2009 with 13% growth in 2010 with a projected growth rate of 14-15% over the years 2011 – 2015. (Dempsey, 2010) Reliability in essence holds the key to driving down the unit cost of production and technology adoption; if units are more reliable there is a potential for increased sales, further refinement and development as the case with mobile phones and the automotive industry. Thus the aim of this project is to create and apply a methodology of assessing the reliability of MEMS components. This research project focused on using a scientific based research methodology, conventional metrology and engineering techniques to produce a method of predicting lifetime information for a particular device component. A broad selection of experimental techniques were assessed and deemed unsuitable, primarily due to inflicting unnecessary damage of the fragile structures, range restrictions on forces that could be loaded and availability of equipment. Following laboratory work and iterative refinement, a successful methodology was created and refined; allowing to mechanically actuate a MEMS membrane to high cycle fatigue failure without damage due to contact force. This used with the bulge test can provide information on new MEMS composites and how they behave as realistically as possible in their future application space. Working closely with QinetiQ and an international collaboration funded by the European Defence Agency (EDA), on a broader MEMS reliability project called POLYNOE; it is now possible to achieve lifetime information for MEMS membranes and use the created experimental technique to cater for any micron sized membrane for any duration at a cycle rate not known or explored in this domain before. Characterisation data, of the membrane and thin film with substrate structure was obtained and using traditional Finite Element Analysis (FEA) and Accelerated Life Cycle Prediction techniques the stresses incurred and Mean Times to Failures (MTTF) for the membranes was calculated as 32million cycles at a comparative operating force of 0.14mN. Suggestions have been made at the possibilities of implementing the methodology and techniques at QinetiQ; to complement their traditional low cycle method of stressing the membranes and therefore iterate the useful information back into the development cycle to refine designs increase reliability and therefore reduce unit cost