JOURNAL OF MATERIALS SCIENCE: MATERIALS IN ELECTRONICS 9 (1998) 199 — 205 Thin film ferroelectrics for capacitor applications D. O’NEILL, G. CATALAN, F. PORRAS, R. M. BOWMAN, J. M. GREGG Condensed Matter Physics & Materials Science Research Division, School of Mathematics & Physics The Queen’s University of Belfast, Belfast BT7 1NN, UK E-mail: r.m.bowman@qub.ac.uk Pulsed laser deposition (PLD) has been used to fabricate simple thin film capacitor structures with a variety of ferroelectric materials. Thin film capacitors using the conventional ferroelectric material Ba x Sr 1—x TiO 3 (BSTO) have been made across the entire compositional series. Electrical characterization shows that in thin film form these ferroelectrics display Curie point behaviour which is largely independent of composition. This contrasts sharply with bulk behaviour. The thin film fabrication and characterization of relaxor ferroelectric ceramics, such as Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) and Pb(Zn 1/3 Nb 2/3 )O 3 -BaTiO 3 (PZN-BT), is also reported.  1998 Chapman & Hall 1. Introduction The continual trend towards miniaturization of elec- tronic components has forced the capacitor industry to look seriously at investment in thin film technology. While thin film deposition of simple metallic systems is well established, there are a great number of unknowns associated with the use of the complex ferroelectric oxides needed at the high end of capacitor performance. As a consequence there has been a concerted effort by the academic and industrial research community to fabricate thin film ferroelectrics and investigate their properties. Ferroelectric systems examined include the conventional ferroelectric perovskites such as (Ba, Sr)TiO  [1 — 4] and the relaxor ferroelectric sys- tems such as Pb(Zr, Ti)O  [5 — 7], and (Pb, La) (Zr, Ti)O  [8, 9]. Complex oxide films are difficult to grow by con- ventional industrial deposition techniques such as sputtering or chemical vapour deposition (CVD) and so for research purposes the technique of pulsed laser deposition (PLD) is often used. PLD is particularly valuable as it allows extremely good stoichiometric transfer of the cation species from the target material onto the deposition substrate [10]. The authors have used PLD to make a series of thin film capacitors with a variety of ferroelectric materials. This paper describes the fabrication of the capacitors and the results of chemical, crystallographic and elec- trical characterization. 2. Experimental 2.1. Preparation of targets for pulsed laser deposition In order to allow flexibility in the composition and types of ferroelectrics that were grown, target material was prepared and sintered in-house. For the (Ba, Sr)TiO  capacitors BaTiO  and SrTiO  powders were mixed in the desired stoichiometric ratios and ground in a pestle and mortar with methanol. The powder mixture was then fired at 1250 °C for 24 h before regrinding, cold pressing into discs &25 mm diameter and &6 mm thick, and sintering at 1425 °C for 30 min. For the lead based relaxor capacitors, fabrication of target material was more complicated. Lead-based relaxors can be difficult to stabilize in the perovskite crystal form, and will instead tend to exist in various pyrochlore phase states [11, 12]. Pyrochlores show extremely poor dielectric properties and should be avoided in capacitor applications [11]. In order to maximize the likely success of growing perovskite thin films, effort was made to prepare targets with high fractions of the perovskite as opposed to the pyro- chlore ceramic phase. To accomplish this two standard preparation routes were followed, known as the Columbite [12] and the Wolframite [13] methods. Both involve two stage reactions. Briefly, for making Pb(Mg  Nb  )O  —PMN— the Columbite reaction procedure involved mixing stoichiometric amounts of MgO and Nb  O  powders and firing at 800 °C for 2 h. The post fired powder was then reground and fired at 900 °C for 1 h, then re- ground and refired at 1000 °C for 2 h. This rather tortuous sequence of firing was found to produce almost 100% MgNb  O  (Columbite analogue) pow- der. The stoichiometric amount of PbO was added to this powder along with a small amount of excess MgO ( &5 — 10% above stoichiometry [12, 14]) and the mix- ture was again fired at 800 °C for 2 h in a lidded crucible. X-ray analysis showed that this processing route produced about 99% perovskite PMN. The powder was cold pressed as with the (Sr, Ba)TiO  targets and sintered at 1000 °C for 1 h. Sintering caused a slight rise in the pyrochlore content, how- ever, the target remained at over 90% perovskite. 0957—4522  1998 Chapman & Hall 199