Effects of sputtering atmosphere on the properties of c-plane ScAlN thin films prepared on sapphire substrate

Abstract

In this work, scandium aluminum nitride alloy (ScAlN) thin films were prepared on c-sapphire substrates by DC reactive magnetron sputtering with a scandium aluminum alloy (Sc 0.06 Al 0.94 ) target. The crystal orientation and surface morphology were detected by XRD and AFM, respectively. The electrical properties were analyzed by a standard ferroelectric test system and piezoelectric response force microscopy. The results show that the sputtering atmosphere, including N 2 /Ar flow ratio and sputtering pressure, appears to be important to influence the crystal quality and electrical properties of ScAlN films. With the N 2 /Ar flow ratio increasing from 3.1:7 to 3.6:7, the crystal orientation and surface morphology of ScAlN films firstly improves and then gets worse. Meanwhile, the electrical qualities of the films performs a similar variation. When the sputtering pressure increases from 0.3 to 0.7 Pa, the properties of the films change obviously too, and the best sputtering pressure is determined as 0.5 Pa. Finally, highly c-axis ScAlN films can be obtained with a N 2 /Ar flow ratio of 3.4:7 and a sputtering pressure of 0.5 Pa, and the FWHM value of the rocking curve, the RMS roughness, the resistivity, the dielectric constant e r and piezoelectric constant d 33 are 2.6°, 2.650 nm, 2.9 9 10 12 X/cm, 12.2 and 8.1 pC/N, respectively.

Implications of heterostructural alloying for enhanced piezoelectric performance of (Al,Sc)N

“…Subsequent studies took one of two directions: epitaxial stabilization of the rocksalt structure for x > 0.5 with interest in the electronic structure [4] or effects of alloying on piezoelectric properties of the wurtzite phase for x < 0.5 [5]. After increases in the longitudinal piezoelectric strain coefficient (d 33 ) were reported by Akiyama et al, the majority of the reported efforts focused on the effect of deposition parameters on crystal quality [6][7][8][9][10], residual stress [11,12], dielectric properties [6,7,13], and overall electromechanical response [11,14,15]. Motivated by industrial interest in the improved performance in AlN-based piezoelectric microelectromechanical systems (piezoMEMS) devices, the breadth of this work was focused on compositions with 0 < x < 0.4, where single-phase textured wurtzite materials could be synthesized.…”

Tuning the piezoelectric and mechanical properties of the AlN system via alloying with YN and BN

“…With the discovery of the anomalously large increase in the piezoelectric moduli of wurtzite AlN when alloyed with ScN 11 or YN, 9,12 AlN-based alloys have received a lot of attention as materials for improved telecommunications, sensors, and surface acoustic wave devices. 13,14 The origin of the enhanced piezoelectricity was revealed to be an intrinsic effect of alloying, as opposed to textural or microstructural effects, 6 with the obvious implication that controlling the piezoelectric enhancement can be done mainly by increasing composition of YN or ScN. However, such alloying softens the material significantly, 6 which actually makes the material less attractive for resonant applications for which k 2 Q is a common figure of merit 15 wherein k is an electromechanical coupling coefficient and Q is a quality factor that is inversely proportional to mechanical dissipation.…”

Epitaxial Growth of Sc0.09Al0.91N and Sc0.18Al0.82N Thin Films on Sapphire Substrates by Magnetron Sputtering for Surface Acoustic Waves Applications

“…This work has been started by many research groups, studying the influence of sputtering process parameters on the crystalline quality of the films. Parameters such as substrate temperature [25], gas pressure, discharge power [26] and gas ratio [27] have been investigated. The synthesis of Sc x Al 1−x N films by other techniques, such as molecular beam epitaxy (MBE) [28] and metal organic chemical vapor deposition (MOCVD) [29], has also been studied.…”