• MEM resonators and resonant-gate transistors

This lecture will present a detailed overview of the Micro-Electro-Mechanical (MEM) resonators: technology, design and communication circuit applications exploiting the size and power consumption reduction offered by these devices. The figures of merit of flexural and bulk mode silicon and silicon-on-insulator MEMS resonators in single device and in array configuration are detailed from MHz to GHz. MEMS resonator scalability (size and frequency), thermal drift challenges, non-linear phenomena and packaging are discussed as limiting factors for RF applications. A part of the presentation is concerned with NEM resonators based on emerging materials such as Carbon Nanotubes and the promises and challenges related to them. In the second part of the lecture, the principle, theory and design of MEM resonators with intrinsic detection based on MOS transistor (called Resonant-Gate MOSFET) are detailed. These hybrid MEM-MOS devices open new in-CMOS fabrication opportunities and offer some particular figures-of-merit with specific oscillator design. It is also shown that RSG MOSFET can also serve as very abrupt current switch and 1T MEM memory.

• Resonant Piezoelectric RF MEMS

This Lecture will cover the basics of RF MEMS resonator and filter design with special emphasis on the new class of piezoelectric contour-more resonators.  Fundamentals of microfabrication techniques will be reviewed and simple analytical and FEM based resonator and filter design procedures will be presented. Lastly, performance comparison of several state-of-the-art resonant MEMS devices will be offered and new RF front-end architectures that will be enabled by these MEMS technologies will be introduced.
Recent advancements in the field of wireless communications have dictated the need for new micromechanical RF components capable of multi-frequency low-loss filtering and frequency synthesis on the same silicon chip.  The growing demand for newer functionalities and applications has crowded the frequency spectrum to the point that several RF bands are now closely spaced within a few MHz.  These needs translate in performance requirements in terms of insertion losses, rejection, integration and quality factor that state-of-the-art resonator technologies such as SAW and FBAR can hardly meet altogether.  A new class of vibrating RF MEMS resonators has emerged as a potential solution for next generation wireless communications.  These devices, either electrostatically or piezoelectrically transduced, are bulk acoustic wave resonators that have their fundamental frequency set by their in-plane dimensions and therefore dubbed contour-mode resonators.  They have already demonstrated high quality factors, small size, good linearity, and especially the ability to span frequencies from few MHz up to GHz on the same silicon chip.

• How to Build a Reliable RF Microswitch?

This lecture will cover the fundamentals of Ohmic and capacitive microswitch design, with an emphasis on device reliability.

For Ohmic-contact microswitches, performance and reliability are affected by the coupled influences of actuator properties, contact materials and processes, packaging, and device thermal properties.  A common failure mechanism is the increase of resistance due to surface contamination.  In many cases, the magnitude of the resistance increase, together with elementary contact mechanics demonstrates that this increase is not because of increased hardness of the contact, or decreases in the conductivity of the contact material due to microstructural changes, but must be due to contamination of the surface with a low-conductivity material.  Surface films, such as oxide films on Ru and Rh, that decrease adhesion and passivate the surface, may inhibit this mechanism.  Different contact materials show large differences in immunity to contamination.  The second major failure mode is adhesion, which prevents contact separation.  In addition, over a large number of cycles, the structure and surface properties of the contact may slowly evolve, with contact materials transferring between surfaces, leading to changes in resistance and adhesion.

For capacitive microswitches, the dominant failure mechanism is failure of the switch to separate, either because of adhesion at contact points, or because the dielectric separating the two conductors in the closed state becomes charged and holds the capacitor in the closed position with no voltage applied to the actuator.  Again materials selection coupled with actuator design and packaging are critical to reliable device operation.

• Piezoelectric Thin Films Integration for MEMS

Piezoelectricity is a very attractive transducer property for Microsystems. Indeed, it can induce a linear strain when an electric field is applied (actuator) or an electric charge proportional to an applied stress (sensor). Moreover, the yield of this phenomenon can be high so that the consumption of piezoelectric devices can be made very low. However, the use of piezoelectricity in MEMS means introduction of new materials in microelectronic fabrication lines. Then, besides the actual piezoelectric performances of these new materials, the main issue is the integration of this technology in standard processes.
In this tutorial, we will discuss some aspects of piezoelectric thin film integration for MEMS. As an introduction, the different actuation principles so far developed for MEMS will be benchmarked according to the required energy. Then, the various piezoelectric materials showing integration capabilities will be detailed. This discussion will concern pure piezoelectric materials but also ferroelectric and electrostrictive materials as well. Then, the main technology issues for integration will be discussed. In this part, we will detail deposition and annealing, electrodes, etching, process compatibility and contamination issues. Finally, a state of the art of piezoMEMS will be presented with a special focus on three examples: acoustic filters using Bulk Acoustic Waves (BAW) resonators, resonant micro-mirrors and RF micro-switches

Pr. Adrian M. Ionescu is an Associate Professor at the Swiss Federal Institute of Technology, Lausanne, Switzerland. He received the B.S./M.S. and Ph.D. degrees from the Polytechnic Institute of Bucharest, Romania and the National Polytechnic Institute of Grenoble, France, in 1989 and 1997, respectively. He has held staff and/or visiting positions at LETI-CEA, Grenoble, France, LPCS-ENSERG, Grenoble, France and Stanford University, USA, in 1998 and 1999.
His research interests focus on micro- and nano-electronic devices aimed at Integrated Circuit design - especially process development, modeling and electrical characterization. His research group is working on subjects in the field of silicon micro/nano-electronics with special emphasis on low- and high-voltage CMOS microelectronic devices, nanoscale solid-state devices, SOI devices and their applications and RF MEMS/NEMS for in- and above-IC integration. Dr. Ionescu has published more than 100 articles in international journals and conferences. He served in the ISQED and IEDM conference technical committees in 2003 and 2004 and as Technical Program Committee Chair of ESSDERC in 2006. He is director of the Laboratory of Micro/Nanoelectronic Devices (LEG-2) and also served as Director of the Institute of Microelectronics and Microsystems of EPFL from 2002 to 2006. He is appointed as national representative of Switzerland for the European Nanoelectronics Initiative Advisory Council (ENIAC).