Low-thickness high-quality aluminum nitride films for super high frequency solidly mounted resonators

Abstract

We investigate the sputter growth of very thin aluminum nitride (AIN) films on iridium electrodes for electroacoustic devices operating in the super high frequency range. Superior crystal quality and low stress films with thicknesses as low as 160 nm are achieved after a radio frequency plasma treatment of the iridium electrode followed by a two-step alternating current reactive magnetron sputtering of an aluminum target, which promotes better conditions for the nucleation of well textured AIN films in the very first stages of growth. Solidly mounted resonators tuned around 8 GHz with effective electromechanical coupling factors of 5.8% and quality factors Q up to 900 are achieved.

Surface Morphology and Microstructure of Pulsed DC Magnetron Sputtered Piezoelectric AlN and AlScN Thin Films

“…In order to examine the microstructure of the Al 1−x Sc x N, SEM was used for planar and cross‐sectional imaging of the samples. Typically, the well c ‐axis oriented Al 1−x Sc x N shows pebble‐like surface morphology . Figure (a) and (b) show the films grown with N 2 /(Ar + N 2 ) = 50% concentration.…”

“…Previous studies already discussed a lot about the characterization of high quality AlN and AlScN: typically, such films would have pebble-like surface morphology [1,14,15,25,26] and homogeneous columnar structure [19,30] can be observed in cross-section. Additionally, 000l (l ¼ 2, 4, 6) reflections in XRD 2θ/θ scan [4] and low rocking curve FWHM values indicate high degree of c-axis orientation.…”

“…Typically, the well c-axis oriented Al 1Àx Sc x N shows pebble-like surface morphology. [1,14,15,25,26] Figure 3(a) and (b) show the films grown with N 2 /(Ar þ N 2 ) ¼ 50% concentration. Based on the planar SEM (Figure 3(a)), large triangular shape grains are randomly distributed on the surface and based on cross-sectional analysis (Figure 3(b)) they start forming in the early stages of the growth.…”

Piezoelectric aluminum nitride thin films for microelectromechanical systems

“…High resolution TEM analyses have shown that these ultrathin fi lms have a fi ne columnar texture and a continuous lattice microstructure within a single grain from the interface with the Mo layer through to the AlN surface, thus confi rming the presence of a strong orientation even in the 25-nm-thick fi lm. 65 Preliminary characterizations of these ultrathin AlN fi lms performed in collaboration with Polytechnic University of Madrid (solidly mounted BAW resonators), 62 University of California-Berkeley (Lamb wave resonators), 68 and University of Pennsylvania piezoelectric nanoelectromechanical actuators) 10 , 69 validate the study's potential as a technological base by which to further increase operation frequency and overall performance of different types of electroacoustic devices.…”

Growth of AlN/Pt heterostructures on amorphous substrates at low temperatures via atomic layer epitaxy

“…Although sputtering has the advantage of growing AlN at a lower temperature than other AlN growth techniques, such as molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD), it is not a conformal growth process and compromises the material quality. The rocking curve FWHM of sputtered AlN is more than 1°, compared to MOCVD or MBE AlN of a few hundred (100-1000) arcsec, and is not designed to control thickness at the atomic scale [4,[6][7][8][9]. Thus, the current challenge is to grow a good-quality, uniform, conformal and thin AlN layers on metals or patterned devices at relatively low temperatures.…”