Pt/PbZr x Ti 1−x O 3 interfacial reaction and Schottky barrier formation studied by x-ray photoelectron spectroscopy: Effect of H2 and O2 annealing

Abstract

The Pt/PbZrxTi1−xO3 (PZT) interfacial reaction caused by low-temperature (320 °C) annealing and resulting change in the surface Fermi level position (Schottky barrier height) has been studied by using in vacuo x-ray photoelectron spectroscopy (XPS). A thin (2 nm) Pt layer was deposited on a polycrystalline PZT film and annealed in 0.5-Torr H2 and O2 in a chamber connected to the XPS chamber. For the PZT samples annealed prior to Pt deposition, a small amount of metallic Pb was produced after the Pt deposition. The annealing also moved the surface Fermi level (EF) at the Schottky interface toward the conduction band minimum (EC) of PZT by 0.4 eV, as evidenced by the band-bending shift of the PZT core levels. Excess metallic states appeared in the valence-band spectra of an annealed bare PZT surface. There was no appreciable annealing-atmosphere dependence in the amount of metallic Pb produced and surface EF position at the PT/PZT interface. However, a clear annealing-atmosphere dependence was observed for the samples annealed after the Pt deposition. The H2 annealing enhanced the production of metallic Pb, whereas the O2 annealing suppressed the metallic Pb formation. The H2 annealing moved the surface EF toward EC by 1.0 eV, whereas the O2 annealing caused no measurable change in the surface EF position. The catalytic effect of Pt during the annealing was postulated to explain the observed annealing-atmosphere dependence.

Reduction-induced Fermi level pinning at the interfaces between Pb(Zr,Ti)O3 and Pt, Cu and Ag metal electrodes

“…It has particularly been observed that the changes may already occur at room temperature. The strong dependence of the barrier height on the chemical state of the interface has also been reported by other groups [22,23]. The effect is not restricted to PZT/Pt but also observed at other oxide/metal interfaces [24,25].…”

“…While Pb can dissolve in Pt and therefore remain close to the interface, it is not dissolved in Cu and Ag and hence segregates to the surfaces of these films. The variation of barrier height observed with Pt contacts is accompanied by an increase/decrease of the metallic Pb species [16,22,23]. This suggests that the insensitivity of the barrier height on the metal work function is related [14], respectively, into account, the dipole potential δ can be derived form the discontinuity of the vacuum level E VAC at the interfaces.…”

“…The Schottky barrier heights may be modified by post-deposition treatments, as previously demonstrated for the PZT/Pt interface [16,22,23]. It is currently not clear if such modification is also possible for Cu and Ag contact materials, as these exhibit a different chemical structure of the interface.…”

Thickness profiles through fatigued bulk ceramic lead zirconate titanate

“…16 Often both effects arise simultaneously to different extent. Potential mechanisms that have been considered during the last two decades are microcracking, 2,22 oxygen vacancy clustering at electrodes, 23 defect cluster growth, 24 suppression of domain nucleation at the electrode interface, 25 charge carrier drift, [26][27][28] breakdown, 28 charge carrier injection, 17,29 depletion regions in the electrodes, 30 injection of protons during processing, 31 ionization of foreign dopants, 32 or ionization even of the host ions. 14 The role of grain boundaries is yet unclear.…”

Hydrogen-Sensitive Amorphous Ferroelectric Thin Film Capacitive Devices

“…In their studies, a prototype Pd/BST/Pt capacitive device was fabricated, and the voltage shift due to the presence of hydrogen at 1000 ppm as high as 4.5 V was measured, which is about 7 times larger than the best value reported in the literature [9][10][11][12][13][14][15][16][17][18][19]. Such voltage shift is believed to originate from the high dielectric constant of amorphous BST thin films, HYDROGEN-SENSITIVE FERROELECTRIC THIN FILM DEVICES 27 which would enhance the dipolar polarization potential at the Pd/BST interface in presence of hydrogen ions. Similarly, a hydrogen-sensitive conduction behavior was also reported in a Pd/amorphous PZT film/Pt capacitive device by Deng et al [22].…”