Ferroelectric Aluminum Scandium Nitride Thin Film Bulk Acoustic Resonators with Polarization‐Dependent Operating States

Abstract

Given the recent discovery of ferroelectricity in highly doped AlN films and their widespread use in bulk acoustic wave (BAW) filters, the ferroelectric and acoustic performance of AlScN‐based devices at two distinct polarization states, i.e., nitrogen (N)‐polar and metal‐polar states, is investigated. Unreleased metal−ferroelectric−metal (MFM) capacitors, as well as suspended MFM structures in the form of thin‐film bulk acoustic resonators (FBARs), are fabricated based on Mo/AlScN/Mo‐sputtered films with ≈30% Sc concentration. The hysteresis polarization−electric field (P−E) loops and internal resistance of the MFM capacitors are characterized. The FBAR devices are characterized at the two polarization states, where the polarization inversion is accompanied by the modulation of thin‐film stress and resistance. Furthermore, the as‐fabricated N‐polar FBAR shows a fundamental thickness‐mode resonance frequency of 3.17 GHz, with a quality factor (QBode) of 572 and a high effective electromechanical coupling coefficient (kt2) of 11.4%. The FBAR frequency response changes when the polarization is switched from N‐polar to metal‐polar. Herein, the first investigations of electric and acoustic properties of N‐polar and metal‐polar AlScN‐based devices are demonstrated, paving the way for the realization of high‐kt2‐reconfigurable acoustic filters for next‐generation communication systems operating at the super‐high‐frequency (SHF) range.

Ferroelectric Nitride Heterostructures on CMOS Compatible Molybdenum for Synaptic Memristors

“…Additionally, Mo has low acoustic attenuation due to the high acoustic velocity , and can also be easily wet-etched . As such, Mo has been commonly used as the bottom electrode for high frequency acoustic filters and resonators. , Therefore, epitaxially grown III-N heterostructures on Mo will provide a viable path to achieve not only CMOS compatible ferroelectric nitrides and fully nitride-based complementary circuits but also a new class of integrable, ultralow loss, and ultrahigh frequency acoustoelectronic devices. This strategy also offers a vital path for the tight integration of nonvolatile ferroelectric ScAlN memristors with processors, which is a building block for rapid data transmission and analysis in artificial neural networks. , …”

Compensation of the Stress Gradient in Physical Vapor Deposited Al1−xScxN Films for Microelectromechanical Systems with Low Out-of-Plane Bending

“…There are numerous collisions that impact the mean free path of atoms and which control coverage on all surfaces. These processes also introduce stresses within the resulting film [ 10 , 11 ]. Reush et al grew 001 polycrystalline AlN films using reactive RF magnetron sputtering directly on Silicon [ 7 ].…”

Dual-Mode Scandium-Aluminum Nitride Lamb-Wave Resonators Using Reconfigurable Periodic Poling

“…This facilitates the creation of radio-frequency (RF) filters with significantly lower loss and higher bandwidth compared to AlN counterparts [ 2 , 3 , 4 , 5 ]. Besides the enhancement, the recent discovery of ferroelectricity in Sc x Al 1−x N [ 6 ] has initiated extensive research efforts for the creation of configurable RF components, such as varactors, and tunable and switchable resonators and filters [ 7 , 8 , 9 , 10 , 11 , 12 ]. These components are of particular interest for emerging wireless communication systems that require multi-band adaptive operation over a wide frequency spectrum [ 13 , 14 ].…”