The growing need of miniaturized and fully integrated microwave circuits is pushing designers to consider the use of microelectromechanical (MEMS) devices, such as resonators and filters, instead of Quartz and Surface Acoustic Wave (SAW) off-chip components.
Aluminum Nitride piezoelectric MEMS acoustic devices are particularly appealing as they can be fabricated through CMOS compatible fabrication processes, hence enabling the integration, on the same chip, of both electrical components and frequency selective elements. This feature renders their role crucial for the development of next-generation integrated wireless platforms. In this talk, the operation and performance of previously demonstrated Aluminum Nitride (AlN) film-bulk-acoustic resonators (FBARs) and contour-mode resonators (CMRs) are discussed. In addition, the operation of two new-classes of AlN piezoelectric resonators, labeled as “Cross-Sectional Lame’ Mode resonators (CLMRs)” and “Two-Dimensional Mode resonators (2DMRs)”, is described. Both technologies rely on the combined use of multiple piezoelectric coefficients of AlN to enable the excitation of two-dimensional modes of vibration in AlN plates. The adoption of CLMRs has allowed to achieve record-high kt2 (6.2%) and a Figure of Merit (FoM=Q∙k_t^2) in excess of 108 in AlN resonators operating around 920 MHz. Also, as the resonance frequency of CLMRs can be defined lithographically, the first two contiguous wideband ladder-filters, exclusively based on lithographically defined CLMRs, were demonstrated.
Such devices show a fractional bandwidth in excess of 3.3% and an insertion-loss (I.L.) lower than 0.4 dB, hence experimentally demonstrating the exciting capability of CLMRs to achieve similar performance of commercial FBAR-based filters, but through significantly reduced fabrication complexity and costs. Moreover, two novel RF systems based on the use of MEM devices and exploiting unique functionalities are showcased. One consists in the first fully-passive MEM-based sensor for near-zero power detection in radios. Such sensor behaves as a trigger capable of activating the CMOS-circuitry through extremely low-power (< -60 dBm) wake-up signatures. The achievement of such a low-power RF-sensor is a key advance towards the commercialization of energy-efficient wireless platforms, with supreme battery-time, to be used for the internet of things (IoT). The other system that will be discussed consists in the first MEM-based RF circulator for multiband SPAR platforms, thus relying on the same carrier frequency for both transmitter and receiver modules. Such system relies on the recently developed angular momentum biasing technique to achieve magneto-free non-reciprocity. The system can tolerate high power levels in excess of 35 dBm through the adoption of body-anchored AlN-CLMRs (i.e. a variant of AlN CLMRs using engineered supports to enable mitigation of thermal nonlinearities). The simulated performance of MIRC show fractional bandwidths in excess of 5%, low insertion-loss and high skirt-steepness through a CMOS-compatible fabrication process.

Cristian Cassella is currently an Associate Research Scientist in the Electrical and Computer Engineering department at Northeastern University, Boston. He received his B.S.E in 2006 at University of Rome – Tor Vergata. In 2009 he received his M.Sc at University of Rome – Tor Vergata.
In 2011, after two years spent in the aerospace industry, he was a visiting scholar at University of Pennsylvania, Philadelphia, USA. 
In 2012 he entered in a Ph.D program at Carnegie Mellon University which he completed in 2015. In 2015 he was a postdoctoral research associate at Northeastern University, Boston.
In 2016 he became Associate Research Scientist at Northeastern University. His research focuses on piezoelectric micro and nano electromechanical systems (M/NEMS) for RF wireless communication platforms.
His areas of interests include characterization and design of MEMS resonators and design of linear and nonlinear RF circuits. He is author of more than 30 publications in peer-reviewed journals and conference proceedings and holds one patent and 4 patent applications in the area of MEMS resonators and systems. One of his conference papers on phase-noise reduction was selected as Best Paper Award at the 2013 IEEE International Frequency Control Symposium (Prague).
One of his journal papers was identified as a paper of excellent quality, hence being highlighted as a JMEMS RightNow-Paper to a large community of readers and being released as open access for a limited time. He is a technical reviewer for several journals, such as Applied Physics Letter, IEEE Journal of MicroElectroMechanical devices and Electron Device Letter.