High temperature processes give rise to the interdiffusion and interaction between SBT thin films and Pt electrods. Especially, bismuth included in SBT is expected to have an enormous effect on electrical properties of SBT this film capacitors. The annealing conditions such as temperature, time and atmosphere can change the distribution among metallic Bi, Bi-oxide, and Bi-Pt compounds and the interface properties. Therefore, it is useful to investigate the interface behavior during annealing in order to understand electrical properties of SBT this film capacitor well. In this study, we focus on the interface behavior with annealing conditions and the correlation between interface phases and leakage current characteristics.
SBT thin films were deposited on Pt(100nm)/Ti(50nm)/SiO2(100nm)/Si substrate by metal organic deposition (MOD) method. The as-deposited films were crystallized in oxygen ambient at 800℃ for 60 min. The thickness of SBT thin films was about 180nm. Top Pt electrodes (160μm diameter) were deposited by DC magnetron sputtering method, followed by the top electrode annealing. The top electrode annealing was carried out at various conditions in order to investigate the effects of annealing conditions on the leakage current characteristics.
Electrical properties of SBT this film capacitors with Pt electrodes werecharacterized immediately and 24hr after the top electrode annealing. The leakage current density was abruptly decreased 24hr after annealing, whereas it was very high over ＄10^｛-4｝＄A/㎠ at 3V immediately after annealing. The dielectric dispersion was observed immediately after annealing and was weaker with increasing the stabilization time (the sustaining time under air after annealing is finished). From the fitted results of dielectric properties-frequency plot, it can be concluded that the interface properties gain control of the time dependence of dielectric pro[erties. The decreasing interface resistance and increasing interface capacitance imply that the interface region is transformed from the semiconducting region to the dielectric region. We inferred that the time dependence of electrical properties might be due to the interaction of metallic Bi formed at the interface with oxygen atoms during top electrode annealing. It was also obseved that the imprint of SBT capacitors was strongly dependent upon the initial poled state. The imprint property was improved as the stabilization proceeded and it may be due to the relative reduction of electronic carriers participating in the trapping/detrapping.
The top electrode annealing was carried out in various conditions in order to inverstigate the correlation of leakage current characteristics in SBT thin films with Bi-Pt compounds at the interface region. The annealing time with the maximum leakage current density was observed after the top electrode annealing in oxygen ambient. On the other hand, the annealing time with the minimum leakage current density was observed after annealing in argon ambient. The annealing atmosphere effects may be related with the Bi-Pt compounds formed during annealing. From XRD results after annealing of Pt/Bi-oxide structure, it can be concluded that Bi-Pt oxides were formed at the interface region after annealing in oxygen ambient, whereas Bi-Pt alloys partially including oxygen atoms were formed after annealing in argon ambient. The Bi-Pt compounds at the interface region can control the interface conductivity affecting the leakage current density of SBT capacitors.
We also investigated thermal stability of SBT this films with Pt and Ir top eletrodes, sustaining at 120℃. Voltage shift of C-V plot was observed with increasing sustaining time and the direction of voltage shift was determined by the poling direction. This voltage shift can be explained to the asymmetric distribution of space charge near the interface region. Then, peak split of C-V plot was observed in the case of negative poling in SBT this films with Ir top electrodes annealed in oxygen ambient. This result may be attributed to the formation of inhomogeneous interface near top electrodes during the top electrode annealing.