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Ferroelectric (FE) materials have garnered huge research interest in the last 50+ years as these materials possess a variety of interactions between electrical, mechanical, and thermal properties that can enable multiple functionalities. The reports of ferroelectric behavior in Aluminum Scandium Nitride (Al1-xScxN) with remnant polarization, 2PR > 100 μC/cm2 have widened the potential use of ferroelectric functionality in microelectronics beyond HfOx based ferroelectrics. Particularly, in the realm of FE non-volatile memory (NVM) applications, with devices such as the Ferroelectric Random-Access Memory (FE-RAM), Ferroelectric Tunnel Junction (FTJ) and Ferroelectric Field Effect Transistor (FeFET), these materials are at forefront of driving significant advancements and enabling next generation memory technologies. Hence, it becomes extremely important to investigate these III-V nitrides and explore the ferroelectric behavior.
This dissertation explores potential ferroelectric behavior in RF sputtered ferroelectric-AlN based thin films. Often considered piezoelectric, AlN thin films have been characterized by the lack of ferroelectric switching hindered by dielectric breakdown even before polarization reversal. While the main core of this work focusses on Sc-doped AlN, potential for ferroelectric behavior was also explored in undoped-AlN thin films. AlN thin films were deposited under multiple conditions for process parameter optimization. The electronic and microstructural properties of AlN have been investigated when grown with and without a metal bottom electrode (viz., directly on p-Si substrate).
Sc-doped AlN thin films are often characterized by large leakage current due to intrinsic material properties influenced strongly by growth related factors, most studies on the ferroelectric properties have been focused on thicker AlScN films (over 100nm), indicating that a more comprehensive understanding of ferroelectricity in sub-100nm AlScN thin films remains an active research area. Role of electrodes and interfacial layers when AlScN is integrated in FeFETs is also under scrutiny. The present work reports the role of bottom electrodes on the ferroelectric switching of sub -100nm Al1-xScxN (x<10%) films deposited via reactive co-sputtering. The influence of different metal bottom electrodes such as W, Ti/Ru and Sc has been studied in metal-insulator-metal configuration.
Finally, potential applications of these AlN-based thin films as a Back-end-of-line compatible Ferroelectric memory devices have been explored along with the observation of a conductive filament achieved through soft breakdown and interface engineering. This work is important for tailoring III-V nitrides and interfaces to achieve the desired device performance as well as multifunctionality in III-V Nitrides.