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Multiferroic BiFeO3 Thin Films Deposited by MOCVD Method

Manish Singh, Dept of Chemical Engineering, University of Illinois at Chicago, 810 S Clinton St, Chicago, IL 60607, Yi Yang, Chemical Engineering, University of Illinois at Chicago, 810 S Clinton St, Chicago, IL 60607, and Christos G. Takoudis, Chemical Engineering and BioEngineering, University of Illinois at Chicago, 810 S Clinton St, Chicago, IL 60644.

BiFeO3 (BFO) is a novel multiferroic material which can couple both ferroelectric and antiferromagnetic effects in the same phase. This coupling provides an extra degree of freedom in design of devices and novel applications never thought to be possible before. Potential device applications include high speed low power electrically controlled magnetic memory elements, electrically tunable microwave devices and highly sensitive magneto sensors.

Most of the known single phase bulk magnetoelectric materials do not exhibit strong magnetoelectric coupling, have Néel or Curie temperatures far below room temperature, and are often difficult to grow in thin film form. Among the several known single-phase magnetoelectrics, BiFeO3 is known to be the only material that exhibits ferroelectromagnetism at room temperature. Recently, large magnetoelectric effects were reported in thin epitaxy-strained BiFeO3 films. This strong and robust ferroelectric and magnetic ordering in BiFeO3 provides an excellent opportunity for design of multifunctional oxides using it as a host.

Obtaining pure BiFeO3 with desirable properties is a challenge and several deposition approaches including pulsed laser deposition, molecular beam epitaxy, sputtering and solution based techniques have been used. Metalorganic chemical vapor deposition (MOCVD) can deposit conformal thin films over large areas with the right stoichiometry, high yield and high throughput at low cost making it ideal for fabrication of thin film-based devices. Strangely, compared to other deposition techniques, there have been extremely few reports on the use of MOCVD for multiferroic films. The choice of precursors is critical and herein we report MOCVD of crystalline BiFeO3 films on platinized silicon substrates using n-butylferrocene, triphenylbismuth and oxygen. Thermogravimetric analysis shows the suitability of these two precursors for depositing BiFeO3. Surface morphology was studied using scanning electron microscope. Composition analysis using x-ray photoelectron spectroscopy revealed that the films were stoichiometric BiFeO3 and did not have any carbon or organic impurities. X-ray diffraction studies indicated that BiFeO3 films were phase pure. Electrostatic force microscopy indicated that the film had polarizable domains that showed no deterioration in polarization over time long after electric poling.