| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Wednesday Sessions |
| Session TF1+EM-WeA |
| Session: | Nonvolatile Memory |
| Presenter: | Calvin Pham, University of California Los Angeles |
| Authors: | C.D. Pham, University of California Los Angeles J.H. Choi, University of California Los Angeles J.P. Chang, University of California Los Angeles |
| Correspondent: | Click to Email |
Multiferroic materials exhibit two or more forms of ferroic order such as (anti)ferroelectricity, (anti)ferromagnetism, ferroelasticity, or ferrotoroidicity. Materials containing both ferroelectricity and ferromagnetism will exhibit some amount of magnetoelectric coupling which is a desirable aspect for the future of non-volatile memory, as these materials could potentially be used for devices that will be written magnetically and read electronically or vice versa, as well as the prospect of four-state memory devices. Materials which exhibit magnetoelectric coupling have been well studied, however, the synthesis methods may not easily translate into large scale integration.
One possible route for synthesis on a commercial scale, atomic layer deposition (ALD) is a thin-film processing technique which involves alternatively flowing non-self reacting precursor vapors or gases onto a substrate. As a result of the self limiting reaction, the precursors only form a single monolayer per cycle. The sequential and self-limiting nature of the deposition is used to deposit thin films with good compositional control, high conformity, high uniformity, and excellent thickness control.
To create multiferroic crystal structures, a 1:1 stoichiometric ratio between cations is desired with low contamination by organic ligands in order to form the crystal phases that permit multiferroicity. Therefore, in this work, multiferroic YMnO3 and BiFeO3 on various substrates are synthesized by radical enhanced atomic layer deposition (RE-ALD) using Y(tmhd)3 (tmhd = 2,2,6,6-tetramethylheptane-3,5 dione), Mn(tmhd)3, Fe(tmhd)3, and Bi(tmhd)3 as metal precursors and oxygen radicals as the oxidizer. By varying the cycle sequences, controlled composition is demonstrated and verified through XPS. Growth rates are shown on a thickness per cycle basis as a function of deposition temperature, precursor pulse times, and substrate. The crystal structure as well as atomic environment are examined by XRD and extended x-ray absorption fine structure spectroscopy (EXAFS) respectively and are accompanied by TEM micrographs. Finally, magnetic measurements made by a super conducting quantum interference device (SQUID) magnetometer, zero-field cooled and field cooled (ZFC-FC) M vs. T and M vs. H, are shown on 1:1 YMnO3 stoichiometric films showing a Néel temperature TN = ~45 K and a coercive magnetic field HC = 130 Oe for Si(111) and HC = 300 Oe for YSZ(111).