Influence of Deposition Parameters and Substrate on the Quality of Pulsed-Laser-Deposited Pb 1-x Ca x TiO 3 Ferroelectric Films Marı ´a Jose´ Martı ´n, Jesu´s Mendiola, and Carlos Zaldo ² Instituto de Ciencia de Materiales de Madrid. Consejo Superior de Investigaciones Cientı ´ficas, Cantoblanco, 28049 Madrid, Spain Pb 1-x Ca x TiO 3 (PCaT) thin films have been prepared by pulsed laser deposition (PLD) on Pt/TiO 2 /SiO 2 /(100)Si, (100)MgO, and Pt/(100)MgO substrates. A Pb deficiency with regard to the target composition occurs in films pre- pared on heated substrates, while the Ca concentration in the film remains congruent with the target composition. The onset temperature for the Pb loss changes from 250°C using nonsintered targets to 450°C if sintered targets are used; moreover, the sintered targets also produce a low particle density on the film surface (0.4 μm -2 ). Increasing the laser fluence to about 10 J/cm 2 improves the crystalline quality of the films. PCaT (x = 0.24) films obtained by PLD on Si-based substrates have a lattice tetragonality c/a = 1.014, lower than the value obtained in films prepared by other methods. The film tetragonality can be slightly in- creased to c/a = 1.022 by using MgO substrates and much more efficiently by reducing the Ca concentration, up to reach c/a = 1.048 in Ca free films. The increase of the film tetragonality induces an enhancement of the film orienta- tion with the [001] axis perpendicular to the substrate sur- face; moreover, the typical values of the spontaneous and remanent polarizations increase up to P r ≈ 34 μC?cm -2 . I. Introduction F ERROELECTRIC thin films are of great interest because of their applications as ferroelectric nonvolatile memories and in other integrated technologies. 1 A large amount of the work related to ferroelectric thin films is based on modified lead titanate because of the possibility to taylor the material perfor- mance for specific applications. Lead titanate (PbTiO 3 ) is a perovskite-type ferroelectric with a Curie temperature T c 4 490°C. Above this temperature the material is in the cubic phase (Pm3m space group), but at T c it undergoes a structural phase transition to the tetragonal phase (P4mm space group). The distortion of the latter phase is char- acterized by the ratio between the lattice parameters (c/a, here- after called tetragonality). For bulk PbTiO 3 ceramics at room temperature, c/a . 1.06. The stress induced by cooling through the phase transition produces cracking in bulk ceramics. To overcome this problem, the lattice tetragonality of bulk ceram- ics is reduced by the partial substitution of Pb and Ti for dif- ferent cations. 2 Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) films have attracted particular at- tention as ferroelectric random access memories 3 because of the increase obtained in the spontaneous and remanent polar- izations with regard to PbTiO 3 4 and due to its mechanical stability. The substitution of Ca for Pb in bulk ceramics reduces T c , 5 which implies that the room-temperature coercive field, E c , decreases, but simultaneously the remanent polarization, P r , decreases. If the Ca concentration is above 30%, the remanent polarization reaches a steady-state value lower than 50% of its value at low Ca concentrations; therefore, the ferroelectric properties are partially inhibited. In addition, the Ca substitu- tion also modifies other physical properties. For example, Ca modification reduces the lattice tetragonality having a benefi- cial influence on cracking, and it increases the room- temperature dielectric constant, but decreases the piezoelectric coefficients. It is generally considered that 24 mol% concen- tration of Ca (x 4 0.24) allows cracking to be avoided while still having optimized ferroelectric properties. 5 The composi- tion Pb 0.76 Ca 0.24 TiO 3 has attracted particular attention for op- timized pyroelectric applications. 6 Pb 1-x Ca x TiO 3 thin films (PCaT) have been previously pre- pared by RF sputtering 7 and sol–gel. 8 The pulsed laser depo- sition (PLD) technique has been recently used to prepare mul- ticomponent oxides due to the congruence between the film and target compositions. In particular, it has been successfully applied to prepare ferroelectric thin film oxides including PZT films. 9 PLD has the potential of providing highly oriented and pyrochlore-free PbTiO 3 perovskite phase. In this paper we have studied in detail the influence of the deposition parameters and substrate on the composition and crystalline properties of PCaT; moreover, the films have been electrically characterized. Brief reports of this work have been given elsewhere. 10,11 II. Experimental Techniques A pulsed KrF excimer laser was focused on rotatable targets in a vacuum chamber. The laser output light intensity was calibrated with a Molectron pyroelectric joulemeter. The laser fluence (J ) was changed in the range J 4 3–16 J/cm 2 by focusing the laser beam and by changing the laser intensity. The determination of the laser beam size on the target produced a large uncertainty, estimated to be about 50% for the largest fluences used in this work. Film deposition was performed in a dynamic 10 -1 mbar pressure of oxygen. The substrate was heated at the desired temperature in the 25–650°C range. To obtain a uniform thickness, the film was held between 4 and 6 cm from the target. More details on the experimental setup have been given elsewhere. 10,12 Ceramic targets were prepared using two different proce- dures: (a) Nonsintered targets were produced by mixing and pressing PbO, TiO 2 , and CaCO 3 powders. Starting powders were dried at 120°C, later mixed, and further heated to 600°C to eliminate carbon. This mixture was uniaxially pressed at 300 kg/cm 2 and isostatically pressed at 2000 kg/cm 2 , and finally the resulting pellet was heated to 600°C for 6 h. (b) Sintered targets were produced by solid-state reaction at 1050°C following a method previously described. 13 With regard to the theoretical PCaT (x 4 0.24) density, 7.2 g?cm -3 , the density of the targets obtained by both methods was in the range 80–85% for non- sintered targets and 95–98% for sintered ones. To compensate for the expected Pb loss, 14,15 10 wt% excess PbO was added to the Ca-modified PbTiO 3 ceramics prepared by using the two methods. In most experiments the nominal B. A. Tuttle—contributing editor Manuscript No. 191341. Received December 10, 1996; approved April 6, 1997. ² Author to whom correspondence should be addressed. J. Am. Ceram. Soc., 81 [10] 2542–48 (1998) J ournal 2542