Tzu-Feng Tseng

Improvement of (Pb1−xLax)(ZryTi1−y)1−x/4O3 ferroelectric thin films by use of SrRuO3/Ru/Pt/Ti bottom electrodes

This work deposits (Pb1−xLax)(ZryTi1−y)1−x/4O3 (PLZT) thin films, possessing good ferroelectric properties (Pr=14.4 μC/cm2), on Pt/Ti/SiO2/Si substrates, using SrRuO3 perovskite as bottom electrodes. Precoating a metallic Ru layer on Pt/Ti/SiO2/Si substrates prior to depositing SrRuO3 bottom electrode further improves the film electrical properties. The optimum ferroelectric properties achieved are Pr=25.6 μC/cm2, Ec=47.1 kV/cm, and er=1204. Analyzing the elemental depth profiles using secondary ions mass spectroscopy reveals that the presence of the metallic Ru layer effectively suppresses the outward diffusion of Ti and Si species. The interdiffusion between the SrRuO3 layer and the subsequently deposited PLZT is also substantially reduced, an effect that is presumed to be the primary factor in improving ferroelectric properties for PLZT thin films.

Effect of LaNiO3/Pt double layers on the characteristics of (PbxLa1 – x)(ZryTi1 – y)O3 thin films

Characteristics of LaNiO3 (LNO) thin films deposited by rf sputtering process were compared with that prepared by pulsed laser deposition (PLD) process. rf sputtered LNO films were [200] preferentially oriented with a low surface resistivity (ρs=0.55 mΩ cm) and the PLD deposited films were [110] predominated with a slightly larger surface resistivity (ρs=6.38 mΩ cm). Using Pt coating as underneath layer markedly reduced the surface resistivity (ρs=0.05 mΩ cm) without modifying the texture characteristics of the LNO layers. PLZT films subsequently deposited on LNO layers inherited the texture characteristics of the underlying LNO layers. Ferroelectric properties of PLZT films were optimized when using LNO–Pt double layers as bottom electrodes. The remanent polarization and coercive force obtained were Pr=14.9 μC/cm2 and Ec=3.5 kV/cm, respectively.

Ferroelectric properties of (Pb0.97La0.03)(Zr0.66Ti0.34)0.9875O3 films deposited on Si3N4-coated Si substrates by pulsed laser deposition process

(Pb0.97La0.03)(Zr0.66Ti0.34)0.9875O3, PLZT, thin films deposited on either LaNiO3 (LNO) or LNO/Pt coated Si3N4/Si substrates, possessing good ferroelectric properties, were successfully obtained by the pulsed laser deposition process. Using LNO/Pt as double layer electrodes not only resulted in PLZT films with superior electric properties, but also of better handling endurance. The former is attributed to the low surface resistivity of electrode materials (i.e., ρLNO/Pt=0.5 mΩ cm) due to the bypassing effect of the Pt layer, whereas the latter is ascribed to the induction of compressive stress on PLZT and LNO layers due to a relatively larger thermal expansion coefficient (CTE) of the Pt layer. The ferroelectric properties of (PLZT )LNO/pt films were Pr=16.5 μC/cm2 and Ec=63.5 kV/cm, while the dielectric constant and leakage current were K=1.028 and Je⩽8×10−6 A/cm2 (under 150 kV/cm), respectively. Their fatigue life was longer than 2×109cycles under action of 300 kV/cm pulse.

Crystallization Characteristics of LaNiO3 Layers and Their Effect on Pulsed Laser Deposited (Pb 1-xLax)(ZryTi 1-y)O 3 Thin Films

Crystallization characteristics of LaNiO3 (LNO) thin films prepared by either rf magnetron sputtering or pulsed laser deposition (PLD), and their effect on the ferroelectric properties of subsequently pulsed-laser-deposited (Pb1-x Lax )(Zry Ti1-y )O3 (PLZT) films were examined. Post-annealing of the amorphous LNO layers, which were prepared by room-temperature sputtering, revealed that the LNO crystallized at temperatures higher than 450° C, and the annealed LNO layers were randomly oriented. However, a substrate temperature of only 250° C was required to form crystalline LNO films in a high-temperature sputtering process and the resultant films were preferentially (100) oriented with low electrical resistivity (ρ S=0.55 m Ωcm). On the other hand, a substrate temperature of 400° C was required in situ to grow crystalline LNO phase by the PLD process and the obtained films were predominantly (110) oriented with a high resistivity (ρ S=6.38 m Ωcm). The Pt used as an underlay markedly reduced the resistivity (ρ S=0.05 m Ωcm) without changing the texture characteristics of LNO layers. It was also found that a reduction of gas pressure in the deposition chamber could enhance the (100)-oriented crystallization of LNO in both sputtering or PLD process. PLZT films subsequently deposited by PLD on the LNO layers required a substrate temperature ≥500° C to completely eliminate the pyrochlore phase. The structural characteristics of the PLZT films inherit that of the underlying LNO layer. Ferroelectric and dielectric properties of PLZT films were optimized when using the (100) LNO-Pt double-layers were used as bottom electrodes. The remanent polarization and coercive field obtained were P r=14.9 µ C/cm2 and E c=3.5 kV/cm, respectively, and the dielectric constant was 950 with a loss of tan δ<0.05 at 1 kHz.

Effects of ambient gas pressure on (1−x) SrTiO3‐xBaTiO3 films prepared by pulsed laser deposition

Ambient gas pressure in pulsed laser deposition process has been observed to significantly modify the lattice parameters of (Sr1−xBax)TiO3 thin films. The lattice parameters a0 of the films deposited under low ambient pressure regime (P≤0.01 mbar) were larger than those found on the films grown under high ambient pressure regime (P≥0.1 mbar), regardless of the thin film composition (i.e., x value), substrate materials (Pt/Si or Si), or ambient gas species (O2 or N2). It is proposed from these observations that the large lattice parameters a0 of the films grown under low‐pressure environment result from higher concentration of vacancies, which, in turn, are induced by the bombardment of energetic species ejected by laser beams.

Influence of the characteristics of a SrTiO3 buffer layer on the superconductivity of laser-ablated YBa2Cu3O7−ϖ films

Abstract The superconductivity of YBa 2 Cu 3 O 7−∂ (YBCO) films grown on MgO substrate materials has been modified significantly using SrTiO 3 (STO) films as buffer layers. The role of the STO layer has been examined by conventional wide-angle X-ray diffraction (XRD), by atomic force microscopy (AFM) and by grazing-incident X-ray diffraction (GIXD) techniques and it has been found (i) to suppress the interaction between the films and the substrate materials and (ii) to enhance the nucleation and growth of (001)-oriented YBCO grains. The (001) epitaxial STO films are found to be of decisive importance to optimization of the superconductivity of the subsequently deposited YBCO films. Both the substrate temperature (720°C) and oxygen pressure (0.02 mbar) have to be stringently controlled for this purpose. The YBCO/STO/MgO films thus obtained possess excellent superconducting properties with T c =90 K and transition width δT =2 K.

Interdiffusion in (Pb1-xLax)(ZryTi1-y)1-x/4O3/SrRuO3 Multilayer Thin Films Examined by Secondary Ions Mass Spectroscopy

The interdiffusion between layers in multilayer thin films, including (Pb0.97La0.03)(Zr0.66Ti0.34)0.9875O3 (PLZT), SrRuO3, Ru, Pt and Si, was examined using secondary ions mass spectroscopy (SIMS). The PLZT thin films deposited on Pt-coated Si-substrate using SrRuO3 as buffer layer possessed ferroelectric properties substantially superior to those grown on Si (or Si3N4) surface. Procoating Ru-layer prior to the deposition of SrRuO3 layer further improved the electrical response of PLZT thin films, that was ascribed to the efficient suppression of Sr- and Ru-outward diffusion into PLZT materials. The optimum properties attained are remanent polarization Pr=25.6 µC/cm2, coercive force Ec=47.1 kV/cm, relative dielectric constant K=1,200 and leakage current <10-5 A/cm2 (under 50 kV/cm).

Influence of SrTiO/sub 3/ or Pt buffer layer on the formation of perovskite phase Pb/sub 1-x/La/sub x/(Zr/sub y/Ti/sub 1-y/)/sub 1-x/4/O/sub 3/ films prepared by pulsed laser deposition

Interdiffusion between layers in Pb/sub 1/-xLa/sub x/(Zr/sub 1/-yTi/sub y/)O/sub 3/(PLZT)/SrTiO/sub 3//Si thin films were studied. The structural profiles examined by grazing incident X-ray diffraction (GIXD) and the elemental profiles examined by secondary ions mass spectroscopy (SIMS) revealed that the SrTiO/sub 3/ buffer layer can effectively block the interdiffusion between PLZT and Si only when this layer has fully covered the Si substrates. The SrTiO/sub 3/ layer were proposed to grow islandwisely and did not form a continuous films when deposited for short interval, leaving behind a large proportion of uncoated Si surface. Serious interaction between Si and the subsequently deposited PLZT films was thus induced. However, pronounced film-to-substrate interaction did not lead to more marked Pb-loss at films surface. By contrast, slower crystallization kinetics of the deposited species was proposed to be the factor that caused Pb re-vaporization.

Growth behavior of LaNiO/sub 3/ and their effect on the pulsed laser deposited PLZT films

(Pb/sub 0.97/La/sub 0.03/)(Zr/sub 0.66/Ti/sub 0.34/)/sub 0.9875/O/sub 3/, PLZT, thin films were successfully deposited on either LaNiO/sub 3/ (LNO) or LNO/Pt coated Si/sub 3/N/sub 4//Si substrates by pulsed laser deposition process. Using LNO/Pt as double layer electrodes resulted in PLZT films with superior electric properties, that is attributed to the low surface resistivity of electrode materials (i.e., /sub /spl rho/LNO/Pt/=0 5 m/spl Omega//spl middot/cm). The ferroelectric properties of P/sub r/=21.6 /spl mu/C/cm/sup 2/, E/sub c/=89 kV/cm and the dielectric constant of K=1,028 were obtained for (PLZT)/sub LNO/Pt/ thin films.