A film-texture driven piezoelectricity of AlN thin films grown at low temperatures by plasma-enhanced atomic layer deposition

Abstract

Simultaneously inducing preferred crystalline orientation with a strong piezoelectric response in polycrystalline aluminum nitride (AlN) thin films by atomic layer deposition is a technical challenge due to the upscaling of the integration of piezoelectric functionalities, such as sensing and actuation, in micro-devices without any poling process. Utilizing low-temperature plasma-enhanced atomic layer deposition (PE-ALD), highly c-axis-oriented AlN films have been prepared with precise control over the relative composition, purity levels, and chemical states of constituent elements. Tailoring thermodynamic parameters, such as the growth temperature and purging time after the trimethylaluminum precursor pulsing before the N2:H2:Ar plasma reaction, provide the possibility of modulating the texture coefficient and the relative piezoelectric response. The effective transverse piezoelectric e31,f coefficient of 0.37 C/m2 was achieved on the AlN film grown at 250 °C and 30 s with the highest texture coefficient TC(002) of 2.75 along the c-axis orientation. The process proposed, at a low temperature with the highly conformal growth of aluminum nitride thin films by PE-ALD, opens up pathways to design novel piezoelectric functional materials for micro-electro-mechanic system devices with complementary metal oxide semiconductor process temperature compatibility.

Low-Temperature Growth of AlN Films on Magnetostrictive Foils for High-Magnetoelectric-Response Thin-Film Composites

“…Significant amounts of O, Al, and N in the transition layer are observed, implying that the transition layer is amorphous with Al x O y oxides and a potential oxynitride forms AlO x N y . It is worth noting that a remarkable amount of oxygen is also observed in the AlN film that is coincident with our previous report, showing that about 6 atom % of O was presented in the AlN film. No formation of Ni x O y has been detected.…”

“…Akiyama et al revealed a significant increase of the full width half maximum of the (002) diffraction peak and a remarkable decrease of the piezoelectric response as the oxygen concentration increased. That could explain why a low piezoelectric coefficient e 31,f of 0.37 C·m –2 was obtained in our films . However, those impurity levels are comparable to those found in the literature. , Minimization of those impurities is really challenging in chemical vapor deposition due to the presence of residual moisture in the reactor chamber and the carrier gases.…”

“…The film grown on a Co foil contains the highest C contamination, whereas the film grown on a Ni foil contains the highest O contamination. In addition, the previous study reported that the atomic percentages of C and O in the bulk were about 2 and 7.5 atom %.…”

“…The AlN films presented in this study were grown by 5000 cycles to obtain a 550 nm thick film. Details in the optimization of AlN film growth can refer to our previous work . The films were grown at a temperature of 250 °C on three different substrates: (1) 2 × 2 cm 2 Ni (NI000270), Fe (FE000160), and Co (CO000170) foils (Goodfellow GmbH, Germany), (2) 150 nm thick nickel-coated silicon substrates by sputtering (Baltec Med-020 high vacuum coating system, Ni target purity level of 99.999%, reference NI000565, Goodfellow GmbH, Germany), and (3) pristine (100) silicon substrates (1 × 1 cm 2 pieces of a single-crystal Si(100) wafer, grade Monitor, Siegert GmbH, Germany).…”

Metalorganic chemical vapor deposition of aluminum nitride on vertical surfaces

“…Recently, the crystal quality of ALD AlN has been significantly improved using in situ atomic layer annealing (ALA) [30]. Plasma-enhanced (PE)ALD (without ALA) has also produced AlN films with measurable piezoelectric coefficients e 31, f of up to 0.4 C/m 2 [31].…”