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Research / Completed Projects

Joao Gomes - Completed Project


Joao Gomes

I am a research student from Porto, Portugal. My PhD project is entitled “Fracture mechanisms of microelectromechanical systems (MEMS)”, which I am due to complete by October 2006.

Before starting my PhD I received a Degree in Physics (Licentiate Degree) at the University of Porto, Portugal. The title of my final year undergraduate thesis was “Transport and magnetotransport tunnel processes of nanogranular layers”

My Project

The objective of my project is to investigate the fracture mechanisms of polycrystalline silicon (polysilicon)-based MEMS, in particular fatigue failure modes of 2-µm thick polysilicon films. This research aims to provide a basis for characterizing the long term durability and stability of polysilicon films, a material widely used for the fabrication of micron-scale devices. Figures 1 and 2 show two types of MEMS structures designed for this investigation where 1 is an SEM micrograph and 2 is an optical microscope photograph of the structure during testing. Figures 3 and 4 show SEM micrograph of a polysilicon fractured surfaces obtained whilst testing the device shown in Figure 2.

A bit about MEMS

MEMS is a field that deals with the study of small electro-mechanical devices or systems at the micron-scale. These “specks of dust” sized devices typically range from tens of micrometers to thousands of micrometers, and combine electronics and mechanical components in the same substrate. They are mainly fabricated from silicon-based technologies (such as surface micromachining) and they can be as simple as a notch cantilever, or more complex, with lots of moving parts, such as a micro engine or a microrobot. In this field one is also interested to study all-kind of phenomena at the small scale. And, things behave differently at that scale! Indeed, due to the small scale the surface to volume ratio of a micro device is large and surface forces such as surface tension or electrostatics dominate volume forces such as inertia and weight. This opens a new range of possibilities in the engineering and science fields and new applications are emerging as the existing technology is applied to the miniaturization and integration of conventional devices. In this context, the understanding of the material properties of the materials relevant to the MEMS field, such as polysilicon films, when subjected to different loading and environmental conditions will strongly contribute to the maturity of the field.

The OU

MEMS technology is an exciting multidisciplinary field of research! Since October 2003, I was offered the opportunity to investigate this field of research at the Department of Materials Engineering of The Open University. The department has excellent research facilities such as laboratory equipments, numerical and computational software, and well equipped libraries. During my PhD work I have had the opportunity to work at the Oxford Research Unit, in Oxford (first year of the PhD work) and at the Milton Keynes campus of the OU where I am currently developing my experimental work. This work has been developed under the brilliant guidance from my supervisors and support from departmental colleagues that maintain an open and friendly environment.

Results

The results of my work (including undergraduate research work) can be seen below:

J. F. Polido Gomes, J. Kowal, L. Edwards, “An Electrostatic actuated micro-structure for high-cycle fatigue testing” to be published at the Proceedings of the Society of Experimental Mechanics conference 2005, Portland, Oregon.

Yu. G. Pogorelov, J. F. Polido, “Charge accumulation and relaxation in tunnel conductance through nanogranular layers”, at the ICCE/8 review, pg. 741-742, Oct 2001.

Yu. G. Pogorelov, J. F. Polido, “Transport processes in metal-insulator granular layers”, arXiv.org, cond-mat/0106034, Jun 2001.

Yu. G. Pogorelov, J. F. Polido, “Charge accumulation and relaxation in tunnel conductance through nanogranular layers”, presentation at conference ICCE/8, Canary Islands, Aug 2001 (Presentation).

My supervisors are : Jan Kowal and Prof Lyndon Edwards .

If you want to contact me, please do so at : j.f.gomes@open.ac.uk

Figure 1 - MEMS device designed for fracture testing investigations. The large frame at the centre is the loading frame of the device while the fracture specimen attached to the frame, is located at the far right of the picture.

Figure 2 - Optical photograph of a fatigue characterization device under testing.

Figure 3 - SEM micrograph of a polysilicon fractured surfaces obtained whilst testing the device shown in Figure 2

Figure 4 - also an SEM micrograph of a polysilicon fractured surfaces obtained whilst testing the device shown in Figure 2


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