CHARACTERIZATION OF SCANDIUM-DOPED ALUMINUM NITRIDE THIN FILMS FOR BULK ACOUSTIC WAVE RESONATORS

The current research focuses on examining the effect of Scandium (Sc) doping on Aluminum Nitride (AlN) thin films with respect to the performance of MEMS piezoelectric resonators. The primary objective of this work is to analyze the impact of Scandium doping on the structural, morphological, and piezoelectric characteristics of thin films. Additionally, the research project aims to assess the effectiveness of these films in applications involving BAW resonators. The present study is structured into three five chapters. The initial chapter serves as an introductory section for the thesis, providing an overview of the current advancements in the field of MEMS resonators. Additionally, it discusses into the fundamental principles of piezoelectricity and ferroelectricity, which are the primary technologies investigated in this research endeavor. The subsequent part of the study centers on the methodologies employed for producing Scandium Aluminum Nitride (ScAlN) thin films, wherein the Scandium doping concentrations are varied. The achievement of precision control over doping levels and film qualities is facilitated through the systematic manipulation of deposition parameters, including temperature, pressure, chuck height, gas flow, and dopant precursor concentrations. The third chapter of the dissertation elucidates the technique used proceed for characterizing the manufactured ScAlN thin films. The stress exerted following the deposition of ScAlN is measured using a laser scanning approach. The X-ray diffraction (XRD) approach is employed to ascertain the crystal structure and phase orientation, whereas scanning electron microscopy (SEM) and atomic force microscopy (AFM) are utilized to examine the topology, morphology, and surface roughness of the films. The succeeding section present the effects of varying doping levels of Sc on the surface topography, crystal structure, and applied stress of AlN thin films. In the final section, an evaluation on the piezoelectric response of the films is conducted by means of measuring the piezoelectric coefficient (d33) by using of the Double Beam Laser Interferometry (DBLI) technique. The initial section of the discourse focuses on the examination of the ferroelectric characteristic exhibited by ScAlN. This section provides a concise introduction to the aixACCT DBLI instrument, followed by a detailed explanation of the building procedure employed for the sample capacitors utilized in the extraction of the piezoelectric coefficient d33. Based on the observations detailed in this chapter, the incorporation of Scandium as a dopant has been found to exert a substantial influence on the characteristics of Aluminum Nitride (AlN) thin films in comparison to their undoped equivalent. The thin films of ScAlN demonstrate enhanced piezoelectric response, suggesting the possibility of enhanced performance in BAW resonators. The d33 value of 13.5 pm/V was obtained from measurements conducted on a sample of ScAlN thin films with a doping level of 30%. This study presents a comparative investigation of the piezoelectric effect shown by samples consisting of various Sc-doped AlN thin films. The present study has expanded the potential for further investigation in defining the ferroelectric behavior of 𝑆𝑐𝐴𝑙𝑁 and exploring the effects of doping 𝑆𝑐𝐴𝑙𝑁 with additional materials to enhance its performance.