Micro Electro Mechanical Systems (MEMS)

Research focus

The Peer review has evaluated this group as Excellent

This reseach topic, started in 2002, is concerned with the study, design, experimentation and numerical modelling of Micro Electro Mechanical Systems (MEMS). MEMS are sophisticated devices in which electronics is coupled with mechanical part for the purpose of creating micro and nano sensors and/or micro and nano actuators. MEMS are nowadays largely used in the automotive, aerospace and consumer markets. Other fields of application open up in the future; among them Structural Engineering, where MEMS could be used for monitoring and self-actuation. MEMSoriented research implies an high multi-disciplinary approach and deep knowledge of fundamentals of physics, mechanics, electronics and sophisticated approaches for numerical modelling and simulations. The research activity on MEMS sprang from a cooperation with ST-Microelectronics (STM), a leading company in the ICT world (ranked fifth in the world semiconductor market in 2005). The first problem solved was the mechanical characterisation of polysilicon at the scale of MEMS through the use of newly designed devices which allow for a so-called on-chip characterisation, in which MEMS are used which contain an actuator, a specimen to be tested and a sensor for displacement measurement. The research activity in this field continuously increased in the period 2003-2006 as witnessed by the funds obtained: two different PRIN projects co-financed by the Italian Ministry for University and Research (MIUR) (2004 and 2005), the second one coordinated at the national level by the group leader Alberto Corigliano; a Cariplo foundation project proposed in cooperation with the Department of Mathematics of Politecnico and an European NoE named Patent- DfMM (www.Patent-DfMM.org), in the period 2004-2007. Moreover, the MEMS group acted as a promoter at the level of the Politecnico and is now collaborating with various researchers in the Departments of Electronics and Mathematics. Finally, the group coordinator initiated a collaboration with Prof. Espinosa at the Department of Mechanical Engineering, Northwestern University, IL on the study of micro-systems for nano scale testing. Among the various research activities on MEMS carried out at Politecnico-DIS, the following topics are briefly described. (A) Mechanical characterisation of polysilicon at the micro scale Various problems have been tackled in order to be able to characterize the mechanical behaviour of polysilicon. Of these, the most relevant, is the way in which mechanical tests might be performed on micro devices. The so-called on-chip approach has been pursued and ad hoc devices have been designed, modelled and experimentally used in order to obtain elastic parameters and rupture strength of polysilicon produced by STM. This activity continues with the goals of capturing fracture mechanics parameters such as toughness and performing mechanical tests on increasingly small devices. (B) Modelling and simulation of rupture phenomena in MEMS Topic (A) has been constantly complemented by the development of numerical tools able to describe rupture phenomena in polycrystals. To this purpose a 2D code has been developed for the simulation of rupture initiation and propagation in polysilicon devices. The polycrystal is first created by making use of Voronoi tessellation and subsequently simulated as an aggregate of anisotropic grains in which fracture can start and propagate, governed by a cohesive zone approach. Intergranular and transgranular fracture can be simulated and complicated rupture processes in MEMS reproduced. The code is now being transformed into a 3D simulation tool. (C) Simulation of damping phenomena in MEMS In many inertial MEMS it is very important to correctly reproduce the dynamic response; in particular the energy dissipated must be computed and damping coefficients to be inserted in reduced 43 models precisely quantified. The MEMS group of Polimi DIS has developed an original approach for the simulation of damping due to the resistance opposed by the fluid to the movement of solid parts. A multi-pole boundary element procedure has been developed and implemented in a in-house code for the simulation of Stokes fluid with special boundary conditions. For extremely low values of fluid pressure, the gas surrounding the movable part must be treated with rarefied gas theory, based on Boltzmann equation; this has been done in cooperation with a group of the Mathematics Department which has expertise in rarefied gas dynamics. (D) Nano scale testing by means of electro-thermo-mechanical actuators This activity began in 2004 with a collaboration with Northwestern University (IL, USA). A new device for nano scale testing was studied on the basis of analytical and numerical multi-physics modelling. The device is based on a electro-thermo-mechanical actuator and allow for Carbon Nano Tube mechanical testing. New thermo devices have been designed and are now being tested.

Dipartimento di afferenza

Dipartimento di Ingegneria Strutturale (DIS)

Docenti afferenti

Full Professors
Alberto Corigliano
Claudia Comi
Associate Professors
Attilio Frangi
Assistant Professors
Stefano Mariani