K. S. Grabowski

In situ deposition of epitaxial PbZrxTi(1−x)O3 thin films by pulsed laser deposition

Epitaxial thin films of PbZrxTi(1−x)O3 (PZT) with 0≤x≤0.6 have been deposited in situ by pulsed laser deposition from stoichiometric targets onto 〈100〉 oriented single crystals of MgO and SrTiO3. Film composition was extremely sensitive to the substrate temperature and the oxygen deposition pressure. In a high (200–300 mTorr) oxygen ambient, phase‐pure 〈100〉 oriented PZT films (x=0.54) were formed at a substrate temperature of 550 °C on SrTiO3. On MgO, competition between formation of the ferroelectric phase and a nonferroelectric (pyrochlore) phase was observed for compositions near the morphotropic phase boundary (x∼0.54). Polycrystalline PZT films which were 70%–90% PZT were also deposited on Pt coated Si and GaAs under similar conditions.

The magnetic and structural properties of pulsed laser deposited epitaxial MnZn–ferrite films

The magnetic and structural properties of pulsed laser deposited MnZn–ferrite films have been examined. The results show that the uniaxial anisotropy, ferromagnetic resonance linewidth and coercive force are strongly influenced by the microstructure of the films, and the saturation magnetization and first‐order magnetocrystalline anisotropy constant depend on intrinsic properties such as composition and cation site occupation. A comparison of bulk and film magnetic properties shows that the magnetic properties of the films are comparable to the bulk, which makes pulsed laser deposition ferrite films a prime candidate for thin film high‐frequency microwave device applications.

Microwave measurement of the dielectric constant of Sr0.5Ba0.5TiO3 ferroelectric thin films

Measurement of the relative dielectric constant of a Sr0.5Ba0.5TiO3 (SBT) thin film is presented as a function of electric field strength and temperature over a broad frequency range using a microstrip transmission line. The transmission line was fabricated from a trilayer structure where the SBT film, grown by pulsed laser deposition, was bounded by silver and platinum metallization layers. Such structures involving ferroelectric films could be useful for microwave applications because of the substantially smaller bias voltages (≊1–10 V) compared to those required for bulk material. The SBT film was found to exhibit a dielectric constant of ≊120–250 and a large electric field modulation of ≊50% at 200 kV/cm. These properties of the material as well as the Curie temperature are compared to those of bulk SBT.

Pulsed laser deposition of oriented PbZr.54Ti.46O3

We report the growth of oriented PbZrxTi1-xO3 (PZT) films, formed in situ by pulsed laser deposition onto heated substrates. The films were deposited from a pressed pellet of PbO - ZrO2 - PbTiO3 of composition PbZr.54Ti.46O3 using a KrF excimer laser (248 nm, ∽2 J/cm2, 5 hz). Typically, 300 to 1500-nm-thick films were deposited onto a heated substrate of MgO or SrTiO3. The deposition temperature was varied from RT to 750°C in ambient oxygen pressures between 10-6 and 0.3 Torr. Films were analyzed form structure (XRD), composition and thickness (EBS), and surface morphology (SEM). For substrate temperatures up to at least 250°C, an amorphous film was deposited. Isochronal annealing of such a film produced crystallization only after heating for 1 h at 550°C. In contrast, crystalline films were deposited at temperatures as low as 350°C, although <100gt; oriented PZT required at least 550°C. Films deposited beyond 600°C, or in too low an oxygen pressure were Pb deficient.

SrxBa(1−x)TiO3 thin films for active microwave device applications

Abstract Thin (0.3–50 μm) films of SrxBa(1−x)TiO3 (SBT) with x=0.35 − 0.8 have been deposited by pulsed laser deposition onto single crystals of MgO, LaAlO3 and thin films of YBa2Cu3O7−δ. The SBT films were characterized morphologically, structurally and electrically at frequencies ≤ 13 GHz. On MgO, smooth, oriented single phase films were obtained at substrate temperatures ≥ 825°C. Films as thick as 10 μm were exclusively (100) oriented. At thicknesses approaching 50 μm SBT films were phase pure but polycrystalline. The dielectric constant of SBT films, as determined from patterned structures using microstrip geometries, was ∼20% of that observed in bulk SBT (emax(film)=1100 for x=0.5 at 200 K). The temperature dependence of the dielectric constant was broad in comparison to the sharply peaked behavior of the bulk material. The ferroelectric thin film properties described, while significantly different from bulk material, are very encouraging for use in active devices at microwave frequencies.

X‐ray characterization of extremely high quality (Sr,Ba)TiO3 films grown by pulsed laser deposition

Thin films of Sr0.5Ba0.5TiO3 have been grown on MgO (100), SrTiO3 (100), and LaAlO3 (012) substrates using pulsed laser deposition. These films were characterized by a variety of x‐ray diffraction techniques. Deposited films exhibited true single crystal morphology. X‐ray rocking curves for the (002) reflection as measured by double and triple crystal spectrometers showed unusually narrow full width at half‐maximum (FWHM) values of 72 arcsec for films grown on LaAlO3, and 140 arcsec for films deposited onto SrTiO3. The FWHM for films deposited on MgO were significantly broader (∼2500 arcsec). While the quality of the epitaxial films is related to the lattice mismatch between the film and the substrate, extremely well aligned films can be grown on substrates with a relatively large lattice mismatch.

Anion‐assisted pulsed laser deposition of lead zirconate titanate films

A modification of the conventional pulsed laser deposition technique is presented whereby a low energy (≤0.5 eV) electron emitting filament was placed over the substrate during deposition. Using this experimental arrangement, it was possible to deposit oriented films of the ferroelectric perovskite PbZr0.52Ti0.48O3 on 〈100〉 MgO substrates at 550 °C. When optimized in terms of emission current, the use of the filament caused a decrease by six orders of magnitude in the ratio of a nonferroelectric pyrochlore phase relative to the ferroelectric perovskite phase. The surface morphology concomitantly changed from porous to essentially smooth as the electron emission current was increased. The surface reaction of oxygen anions generated by electron attachment to oxygen molecules is believed to be responsible for these crystallographic and morphological changes.

The preparation of epitaxial platinum films by pulsed laser deposition

Abstract A systematic study of the effects of ambient deposition pressure Pd and substrate temperature Ts on the morphology and crystal structure of platinum films deposited onto 〈100〉 MgO by pulsed laser deposition (PLD) is presented. Depositions were performed over a Ts range of 20–650 °C and a Pd range of 10-5-1 Torr of O2. Different crystallographic orientations and a dramatic change in morphology were observed as a function of Pd and Ts. For depositions performed at room temperature and for pressures greater than 10-5 Torr, the films were comprised of mostly platinum oxide. At Ts of 350–500 °C and at all pressures studied, the platinum films were very smooth and oriented. At Ts>500 °C, deposited films were characterized by islands whose average diameter varied from several nanometers to over a micrometer depending on the average film thickness; islands were prevalent Pd⩾ 0.05 Torr. Over the broad range of conditions examined, the film crystal structure varied from (100) epitaxy with a rocking curve width of less than 0.2°, to films of mixed (100) and (111) preferred orientations. At a given Ts, the deposition rate per laser shot was found to depend on Pd. In general, the deposition rate was found to increase monotonically from about 0.1 A per shot at 10-5 Torr to a maximum of about 0.16 A per shot near 0.05 Torr, then decrease to a minimum of about 0.08 A per shot near 0.3 Torr and then increase again at pressures greater than 0.3 Torr. These effects can be explained in terms of a combination of gas dynamic processes and gas-surface interactions which occur between the platinum atoms and the oxygen molecules during deposition.

Pulsed laser deposition of electronic ceramics

Abstract Pulsed laser deposition (PLD) is a unique physical vapor deposition technique which has gained considerable attention recently in the deposition of high quality, high temperature superconductors. In this technique, a short pulsed laser ( 2 Cu 3 O 7-δ thin films deposited by PLD have excellent d.c. and high frequency transport properties. For YBa 2 Cu 3 O 7-δ epitaxial multilayer structures of superconductor/dielectric/superconductor are reported. Microwave devices fabricated from superconducting thin films and multilayer films have demonstrated significant performance improvements over devices fabricated from conventional materials. High quality ferroelectric thin films are also being deposited by PLD. The deposition and electrical characterization of oriented PbZr x Ti 1- x O 3 thin films are reported. PLD is shown as a versatile physical vapor deposition technique and will soon be an important industrial coating technique.

Magnetic and transport properties of radiation damaged La0.7Ca0.3MnO3.0 thin films

Magnetization and resistivity measurements are reported for a series of radiation damaged La0.7Ca0.3MnO3 pulsed laser deposited thin films. When plotted as a function of activation energy, trends in the electrical transport properties are similar to those exhibited in the magnetic properties. A sharp drop in both Tc and Tp in samples with activation energies greater than ∼110 meV suggests a “decoupling” of the magnetic and transport properties. The results suggest the magnetic order is no longer sufficient to delocalize the system of the extra disorder induced by the radiation damage.