(A) study on the micro-structural properties of N-incorporated ZnO thin films for FBAR devices

Abstract

Zinc Oxide (ZnO) is the II-VI group compound semiconductor composed of abundant elements, and has many interesting properties, thereby leading to various and large-scale applications of ZnO in the aspects of the mechanical, electrical, optical devices and so on. Especially, the FBAR (Film Bulk Acoustic Resonator) devices based on the piezoelectric characteristics of the ZnO have attracted a great attention as a promising novel filter technology mainly because it may be fully integrated with the conventional complementary metal oxide semiconductor/radio frequency integrated circuit (CMOS/RFIC) fabrication technologies, eventually allowing for the realization of a single-chip radio or a transceiver in the future. In order to achieve a good FBAR performance by reducing the insertion loss of the devices, it is essential to make the high quality piezoelectric film which has perfect c-axis texture, extremely smooth surface, sharp interface, and high electrical resistivity. On the other hand, intrinsic ZnO has been observed to be natively n-type with the compensated electron concentrations reduced to less than $10^{14} cm^{-3}$ on bulk samples grown hydrothermally. Thus, the compensatory doping of the ZnO films is required to obtain the high resistivity piezoelectric thin films, hence leading to the performance improvement of FBAR devices. In this research, the compensatory nitrogen [N] doping into the ZnO films by an RF magnetron sputtering system using $N_2O$ gas as a doping source was attempted in an effort to achieve a good return loss ($S_{11}$) characteristics of the FBAR device. Interestingly, it was observed that the nitrogen doping could cause the micro-structural change of the ZnO films. From this standpoint, a micro-structural analysis was done for more precise control of the N-incorporated ZnO films, thereby contributing to the improvement of devices. In this thesis, the micro-structural effects of the N-incorporation into the ZnO films were inspected ...