As the typical surface separations in Micro Electro-Mechanical Systems (MEMS) are reduced to below one micrometer, detailed knowledge of the interaction forces down to this scale is required. In this context, we have developed a dedicated experimental platform to directly investigate electrostatic and physical effects in a high-aspect-ratio electrostatic-capacitive MEMS device based on commercial technology. In the present work, we report on an extensive experimental characterization, focused on the influence of the surface separations, electric surface potentials, and pressure on the static and dynamical behaviour of the device under precisely controlled conditions. For the proper analysis of the bias position and small-displacement response of the device, we have developed a comprehensive electro-mechanical model capable of describing the aforementioned effects, and allowing to extract the mechanical and electrical device parameters from the experimental data. Based on the developed model, a strong experimental evidence is found for significant variations in device characteristics upon reduction of surface separation to below one micrometer. (C) 2017 Elsevier B.V. All rights reserved.
The ongoing trend for miniaturization below the microscale calls for the investigation of the relevant surface interactions acting at short distance range. In this work, we presented theoretical and experimental methods to perform such an analysis in a high‑aspect‑ratio electrostatic-capacitive MEMS device based on actual commercial technology. First, we developed a comprehensive one-dimensional lumped-element electro-mechanical model describing the static and dynamic behaviour of the MEMS for a wide range of operating parameters. The model can be calibrated via an electric DC response measurement, from which intrinsic device parameters were extracted by a nonlinear fitting procedure. Once calibrated, the model was validated by comparing analytic predictions to the results of an extensive experimental characterization, as well as to the results of a dedicated finite element analysis (FEA). Subsequently, a characterization of the pull-in behaviour of the MEMS was performed. The experimental results validate the theoretical model for surface separations down to 650 nm. Below this distance, multiple contacts of group of lamellae occur, probably caused by imperfect parallelism between lamellae. In a second step, we extended the analytic model for an analysis of small-signal dynamics around the bias position. The influence of the plate separation, electric surface potentials and hydrodynamic effects onto the mechanical static and dynamic response of the device has been investigated by considering the measured mechanical resonant frequency, damping factor and electrical parasitic components. A validation by comparison of analytic and numeric FEA results was performed. We observed a negative shift of the mechanical resonance frequency for reduced sensing plate separation caused by the electrostatic spring softening effect. At the nominal pressure of 0.7 mbar, comparable to the one used in commercial devices, no significant hydrodynamic spring stiffening could be detected down to a plate separation of 650 nm. The experimental and analytic methods presented here allow for an extensive and unambiguous characterization of electrostatic-capacitive MEMS. These methods could be immediately applied to study the influence of the Casimir force and hydrodynamic effects at effective surface separation below 500 nm − an important issue for future generations of Nano Electro‑Mechanical Systems (NEMS). F. Cerini was born in Brescia, Italy, in 1986. He received the MSc in Electronics Engineering and the PhD in Electronics Engineering, Sensors and Instrumentation at the University of Brescia, Brescia, in 2012 and 2016, respectively. His research interests include energy harvesting for autonomous sensors, MEMS and microsystems. He is currently a MEMS Design Engineer at STMicroelectronics, in Castelletto R&D site, Italy, where he works on design and modelling of acoustic MEMS. M. Ferrari was born in Brescia, Italy, in 1974. He received the Laurea degree in Electronics Engineering and the Research Doctorate degree in Electronic Instrumentation from the University of Brescia, Brescia, in 2002 and 2006, respectively. Since2007 he has been an Assistant Professor and since 2015 he has become an Associate Professor with the Department of Information Engineering of the University of Brescia. He is also an associate member of the Italian National Research Council and IEEE member. His research activity deals with the energy conversion via the piezoelectric and thermoelectric effect for powering autonomous microsystems, sensors for physical and chemical quantities, signal-conditioning electronics, oscillators and frequency-output interface circuits, resonant microsensors and MEMS. He has authored over 70 publications in international peer-reviewed journals and international conference proceedings. V. Ferrari received the Laurea degree cum laude in Physics in 1988 at the University of Milan, and the PhD degree in Electronic Instrumentation in 1993 at the University of Brescia, Italy, where since 2006 he has been a full professor of Electronics. He is also an associate member of the Italian National Research Council and IEEE senior member. He and his group are active in research projects, with both academic and industrial participation, on piezoelectric transducers and resonant microsensors, energy harvesting for autonomous sensors, MEMS and microsystems, sensors with contactless inter-rogation, electronic interfaces for sensor signals, sensing systems for fluidics, and wearable devices. He has authored and co-authored more than 200 publications in international peer-reviewed journals and conference proceedings, invited presentations, book chapters, and 6 patents. He serves in international panels, conference committees and boards in the field of sensors and electronic instrumentation. He was programme chair at Eurosensors Conference 2014. A. Russo was born in Biancavilla, Italy, in 1972. He received the Laurea degree in Physics in 1999. After a period spent as high school professor, since 1999 he worked at STMicroelectronics in R&D department of Catania site. He is currently new compound material device manager. His major research interests include SiC and GaN technology development and reliability of diode, power MOSFET, HEMT and UV sensors. Since 2009 he manages the MEMS no stiction project. M. Azpeitia Urquia received the M.S. Degree in Electronics Engineering from the Universität Stuttgart, Stuttgart, Germany, in 2004, and a postgraduate specialization in Materials for Nano and Microtechnology at the European School in Materials’ Science, Pavia, Italy, in 2005. He is currently a Senior Process Integration Engineer in MEMS at STMicroelectronics, Agrate Brianza, Italy. His major research interests include the field of technology development and reliability of microelectromechanical systems. R. Ardito is associate professor of Structural Mechanics at Politecnico di Milano. He graduated in 2000 (cum laude) and he received the Ph.D. degree (cum laude) in 2004. Since 2004–2006 he has been research fellow at the National Institute for Nuclear Physics, working on solid mechanics in cryogenic conditions. In 2007, he started working on Micro-Electro-Mechanical Systems (MEMS), at Politecnico di Milano. He spent, in 2008 and 2010, two periods of research at the Research Laboratory of Electronics, Massachusetts Institute of Technology, as visiting scientist. He is co-inventor of two patents and co-author of more than 80 publications on structural mechanics and numerical methods. His scientific interests are theoretical and computational aspects of multi-physics behavior of MEMS. B. De Masi received the master degree in solid-state physics from the University of Pisa (Italy) in 1998. After a period spent at the CNR Biophysical Institute and at the Physics Department working on scanning probe microscopy he moved at APE Research in Area Science Park (Trieste, Italy) where he worked on Scanning Near-Field Optical Microscopy (SNOM). From 2000–2005, he was a MEMS designer at STMicroelectronics (Milan, Italy) where he was responsible of the MACROS European Project (IST-2001-34 714) on characterization and reliability of microelectromechanical systems. He is currently working as external collaborator of the Department of Civil and Environmental Engineering of the Politecnico di Milano where his activities are focused on MEMS measurement techniques and the design of new MEMS devices. R. I.P. Sedmik has studied physics and information technology in Vienna, where he received his MSc in numerical plasma physics in 2005. After several years of experimental work for the Austrian Institute of Technology and Ruag Space he returned to the Technical University of Vienna to finish his PhD in theoretical physics in 2009. Since 2010 he is investigating surface interactions at sub-μm separations and dark energy at the VU University Amsterdam.
- Bias position
- Casimir
- Dynamical small-displacement characterization
- Electro-mechanical modelling
- Electrostatic-capacitive MEMS
- Interaction forces
- Parasitic electrostatics
- Pull-in
- Stiction
