Chemical vapor deposition of high-quality epitaxial bismuth ferrite films*

High-quality thin films of room-temperature multiferroic BiFeO3 (BFO) have thus far been deposited primarily by pulsed laser deposition (PLD), a technique that cannot be scaled up readily. For device applications, it is essential to develop large-area thin film growth techniques such as chemical vapor deposition (CVD). We have used a direct liquid injection chemical vapor deposition (DLI-CVD) process to reproducibly grow high-quality epitaxial BFO films ranging in thickness from 20-200 nm, on SrTiO3 and DyScO3 substrates, using triphenyl bismuth(III) and Fe(III) acetylacetonate as metal-organic precursors. Smooth films having a root mean square (RMS) roughness ≤ 1nm are obtained that exhibit saturated ferroelectric hysteresis loops at room temperature for 200 nm thick films. BFO films that are slightly (2-4%) Bi-rich are found to have improved ferroelectric properties as compared to Fe-rich or stoichiometric films. The dependence of the morphological quality and ferroelectric properties on the stoichiometry and deposition parameters has been explored.  Ferroelectric phase switching of thinner films (20-80 nm) has been studied using piezo-response force microscopy (PFM) technique and the Kay-Dunn scaling law of switching field with film thickness is validated.