The Influence of Substrate Bias and Sputtering Pressure on The Deposited Aluminum Nitride for Magnetoelectric Sensors
Hafid Suharyadi
Mechanical Engineering Department, Polytechnic of Energy and Mineral (PEM) Akamigas Jalan Gajah Mada No. 38 Cepu, Blora, Jawa Tengah 58315, Indonesia
Abstract
A residual stress of Aluminum nitride (AlN) thin films has been a problem in the magnetoelectric (ME) composites that are used in the AC magnetic field sensors. The present work aims to optimize the deposition process of AlN in order to fabricate a nearly-zero stress of AlN thin films as well as ME composites without losing the microstructural and piezoelectric properties. The influences of RF bias power and sputtering pressure on the residual stress, microstructure, and piezoelectric response have been investigated, which are measured by the stylus profilometer, X-ray diffractometry, and 4-point bending method, respectively. Two different stacks are deposited on Si/SiO$_2$ substrates: Ta/Pt/AlN and Ta/FeCoSiB/Ta/Pt/AlN. Pulsed DC reactive sputter depositions have been performed to deposit AlN films. With increasing the substrate bias, stress of the AlN films and the stacks with the magnetostrictive layer are augmented. This might be attributed to the void formation and and ion entrapment under the applied bias. A variation of the sputtering pressure is a promising way to fabricate nearly zero stress of the AlN films and the stacks without the magnetostrictive layer. Here, a higher energetic incident atoms and an enhanced surface diffusion are the dominating factors. A transition from tensile to compressive stress has been observed at the low sputtering pressure. Sputtering pressure also affects the stress of AlN films and the stacks with the magnetostrictive layer. Though, tensile stress is preserved within the sputtering pressure range. FWHM of AlN (0002) peaks are nearly constant within the ranges of the substrate bias. By reducing the sputtering pressure, FWHM is broadened due to lower ionization degree associated with AlN formation and greater number of micro-arcs. However, the magnitude of $e_{31,f}$ is increased due to a lower residual stress at the low sputtering pressure.
Keywords: Aluminum nitride; Substrate bias power; Sputtering pressure; Residual stress; Microstructure; Effective piezoelectric transverse coefficient
Topic: Mechanical Engineering