Showing papers by "Roozbeh Tabrizian published in 2017"

Power-insensitive silicon crystal-cut for amplitude-stable frequency synthesis

Abstract: This paper reports on the theoretical prediction and experimental verification of the existence of a power-insensitive crystal cut in doped single crystal silicon (SCS). The existence of such a cut enables fully harmonic excitation of extensional elastic waves with negligible dispersion. Aligning bulk acoustic resonators to this power-insensitive cut along with suppression of boundary-induced nonlinearities enable realization of vibration-amplitude insensitive frequency references. An analytical formulation is presented to characterize the anisotropic anharmonic behavior of SCS elasticity, predicting the existence of the power-insensitive cut at ∼30° offset from axis. This prediction is experimentally verified through implementation and characterization of an array of waveguide-based resonators aligned to different crystallographic directions. The resonators are optimized for substantial suppression of boundary induced nonlinearities through dispersive energy trapping technique. Among these, the waveguide-based resonator aligned to 22.5° cut shows a 1-dB compression point at 29dBm, which is 50× higher power-handling compared to / counterparts. Dispersive energy trapping used for elimination of geometrical nonlinearities simultaneously realizes a high Q of ∼7,000 at 80MHz, which is independent of the crystallographic orientation.

High-Q silicon fin bulk acoustic resonators for signal processing beyond the UHF

Abstract: This paper reports, for the first time, on the silicon Fin Bulk Acoustic Resonator (FinBAR) technology that enables extreme scaling of integrated signal processing beyond the ultra-high-frequency (UHF) regime High-aspect-ratio fins are etched in silicon substrate and covered by aluminum nitride films to enable efficient electromechanical transduction of bulk acoustic resonance modes with large coupling coefficient (k t 2) The low phononic dissipation of single crystal silicon, along with suppression of piezoelectric charge redistribution loss in the sidewall transduction result in unprecedentedly high quality-factors (Q) in ultra-and super-high-frequency (SHF) regimes A prototype FinBAR is presented operating in 3rd and 9th width-extensional modes at 2 GHz and 6 GHz, with Q of 4,800 and 2,300, and k2 of %12 and %05, respectively The resulting record f×Q of 14×1013, the large kt2×Q of 58, and lithographical frequency scalability demonstrate the potential of FinBARs to realize SHF acoustic processors for emerging 5G multi-frequency systems

d 15 -Enhanced shear-extensional aluminum nitride resonators with k 2 t > 4.4% for wide-band filters

Abstract: This paper presents a novel aluminum nitride (AlN) resonator technology that fuses transverse (d 31 ) and shear (d 15 ) piezoelectric constants to realize a large electromechanical coupling factor (k2 t ), while having a frequency defined by the lateral dimensions. An antisymmetric Lamb wave with co-existing in-plane extensional and thickness-shear elastic energy distribution is used to simultaneously exploit transverse and shear electromechanical coupling of AlN film. Specifically, the shear transduction (k2 t,15 ) benefits from the large d 15 constant (due to the columnar single crystallinity of the film) as well as low in-plane (e 11 ) relative permittivity (due to the in-plane poly crystallinity) of the AlN film, and hence significantly improves the overall k2 t . A proof of concept device at 733MHz is demonstrated based on this technology, showing a Q of ∼1,400 with a k2 t of ∼4.4%. A ladder filter is also demonstrated, through electrical coupling of the d 15 -enhanced resonators, with a −3dB-bandwidth of 18MHz, at 745MHz.

The effect of elastic anharmonicity on the nonlinear behavior of waveguide-based AlN resonator

Abstract: This paper presents the effect of elastic anharmonicity in AlN film on the nonlinear performance of extensional AlN resonators. Elastic energy distribution is tailored through dispersion engineering of the waveguide to avoid boundary-induced nonlinearities and enable the study of the elastic anharmonicity contribution on the amplitude-frequency (A-f) characteristic. A 97MHz resonator with a Q of ∼2,250 is demonstrated with a linear A-f coefficient of −3.47 ppm/μm2 and a yield power of 5dBm. Excitation of the device beyond this yield power derives the AlN film into plastic regime and induces a hysteresis in resonator frequency response. A consistent Q over the elastoplastic cycling of the device suggests the dominant contribution of non-structural energy dissipation mechanisms.

Fabrication Process Flows for Implementation of Piezoelectric MEMS Resonators

Abstract: Since the first demonstration of thin-film piezoelectric resonators [1], high performance MEMS devices including low insertion-loss resonators and filters [2, 3], small form factor energy harvesters [4], large-force actuators [5], and highly sensitive resonant sensors [6–8] have been successfully demonstrated using piezoelectric materials such as AlN, ZnO, and PZT. Thin film AlN has been of great interest mainly due to the high quality of its film growth and CMOS compatibility, as well as well-developed process recipes. The processing advantages in addition to the superior piezoelectric and acoustic properties of AlN, including large wave propagation velocity [9] and low thermoacoustic dissipation [10], have made it a popular choice for piezoelectric transduction of MEMS resonant devices.

Phononic detection of morphological phase transition in atomic-layered Hafnium-Zirconium-Oxide

Abstract: This paper presents a novel technique for high-resolution spectroscopy of the morphology and dynamic phase transitions in atomically synthesized polymorph films with sub-10nm thickness. A multi-mode nano-resonant test-vehicle is developed to excite and trap acoustic phonons in the ultra-thin polymorph film. The dispersion signature of the phonons is interrogated, using digital holographic microscopy, to extract the morphological content of the film and its dynamics under device-level thermal treatments. As a proof of concept, the notion of the phononic spectroscopy is demonstrated for the in-situ detection of crystal phase transitions in a ∼10nm thick Hafnium-Zirconium-Oxide film. The phononic constituents of multiple resonance modes of the test-vehicle are extracted to construct the dispersion signature of the film, before and after crystal phase transition stimulation through in-situ rapid thermal annealing. The experimentally extracted phononic dispersion diagram is compared with the numerically extracted counterpart to confirm the fractional transition between tetragonal and orthorhombic phases in the film.