Aluminum nitride two-dimensional-resonant-rods

Abstract

In the last decades, Bulk-Acoustic-Wave (BAW) filters have been essential components of 1G-to-4G radios. These devices rely on the high electromechanical coupling coefficient (kt 2~7 %), attained by Aluminum Nitride (AlN) Film-Bulk-Acoustic-Resonators (FBARs), to achieve a wideband and low-loss frequency response. As the resonance frequency of FBARs is set by their thickness, the integration of multiple FBARs, to form filters, can only be attained through the adoption of frequency tuning fabrication steps, such as mass loading or trimming. However, as the ability to reliably control these steps significantly decays for thinner FBARs, manufacturing FBARs-based filters, addressing the needs of emerging IoT and 5G high-frequency applications, is becoming more and more challenging.Consequently, there is a quest for new acoustic resonant components, simultaneously exhibiting highkt 2 and a lithographic frequency tunability. In this work, a novel class of AlN resonators is presented.These radio-frequency devices, labelled as Two-Dimensional-Resonant-Rods (2DRRs), exploit, for the first time, the unconventional acoustic behavior exhibited by a forest of locally resonant rods, built in the body of a profiled AlN layer that is sandwiched between a bottom un-patterned metal plate and a top metallic grating. 2DRRs exhibit unexplored modal features that make them able to achieve highkt 2 , a significant lithographic frequency tunability and a relaxed lithographic resolution, while relying on an optimal AlN crystalline orientation. The operation of 2DRRs is discussed, in this work, by means of analytical and finite-element (FE) investigations. The measured performance of the first fabricated 2DRR, showing a kt 2 in excess of 7.4%, are also reported.In the last decades, acoustic resonators 1-4 and filters have represented key components for several radio-frequency (RF) applications and systems. For instance, their superior performance, when compared to conventional electromagnetic counterparts, have made them essential to form frequency selective passive components in miniaturized RF platforms. Aluminum Nitride (AlN) Film-Bulk-Acoustic-Resonators (FBARs) 2,5,6 have been extensively used to form filters in commercial RF frontends. In fact, thanks to their ability to attain large electromechanical coupling coefficient (kt 2~7 %), while being manufacturable through conventional semiconductor fabrication processes, FBARs have enabled commercial ultra-and super-high-frequency (U/SHF) acoustic filters, exhibiting fractional bandwidths and performance exceeding those required by 4G communication systems. However, despite their high-kt 2 , the resonance frequency (fres) of FBARs is set by the thickness of the different forming layers 7,8 . This feature renders the manufacture of FBARs, having different fres-values, only attainable through post-processing steps, like trimming and mass loading, thus leading to a much higher fabrication complexity. Such complexity becomes even more significant when FBAR-based filters,

Frequency Domain Acoustic-Based Subharmonic Tags for Far-Field Identification

“…It is worth emphasizing that achieving a 250 kHz lithographic frequency resolution can be challenging when relying on UHF SAW resonators, like the ∼ 420 MHz ones we used in this work. Nevertheless, as experimentally demonstrated in [41], such a strict resolution can be achieved by relying on bulk acoustic wave (BAW) resonators exploiting quasi thickness-extensional (TE) modes of vibration [42], like the Two-Dimensional-Mode-Resonators (2DMRs [41], [43], [44] ) or the Two-Dimensional-Resonant-Rods (2DRRs [45]) demonstrated by our group. In fact, even though these devices are not usable to build delay elements for TDR-based PTs due to their modal characteristics inhibiting the lateral propagation (8) f8 f16 fa (16) f24 f25 fa (24) C2 L2…”

Phononic Graded Meta-MEMS for Elastic Wave Amplification and Filtering

“…Their properties ultimately depend on the ability to achieve a high quality (Q) factor combined with a high electromechanical coupling κ 2 t [2]. While previous technologies were mainly restricted by material limits, recent metamaterial solutions enable unprecedented high Q factor and wide tuning range [3], [4]. Elastic and acoustic metamaterials have triggered intense research activity for their potential in wave control and manipulation [5], [6], bringing new benefits to the world of MEMS and Radio Frequency (RF) signal control.…”

Effective electromechanical coupling coefficient ( keff2 ) enhancement of a Lamb wave resonator with trapezoid grooves configuration

“…23) Cristian et al presented twodimensional-resonant-rods by vertically etching AlN between the IDTs, achieving a k eff 2 of 7.4%. 24) In addition, our group has investigated the relationship between the k , eff 2 spurious modes and the shape of the grooves by finite element method (FEM) simulations. 25) It has been estimated that the grooves can improve the k eff 2 in the S 0 mode LWR.…”