Impact of microstructure on the electrical stress induced effects of pulsed laser ablated (Ba,Sr)TiO₃ thin films

Abstract

Electrical stress induced degradation effects in thin films of (Ba,Sr)TiO₃ were studied. A comparison of the processing conditions of the films was made to examine its subsequent impact on the electrical stress induced degradation in this regard. Films from two different processing approaches were taken up for this study, which had different microstructures and grain sizes originating from their difference in annealing/thermal conditions. A continuous electron injection under low field conditions was found to cause a change in the capacitance and the leakage current characteristics of the thin films. It is generally observed that the process of electron injection causes an accumulation of charge at the trap sites, thereby changing the local field near the vicinity of the trapped charge. This leads to the change in the electrical properties, such as the capacitance of metal-insulator-metal capacitors as observed. Capacitance-voltage (C-V) measurements were performed to estimate the electronic capture cross section and the neutral trap density from the voltage shifts induced in the C-V curves. The trapping efficiency, capture cross section, and trap densities were obtained as functions of the injected charge fluence. The obtained values showed that in situ crystallized films exhibited better electrical response under continuous electrical stress than those which were ex situ crystallized. However, time-dependent dielectric breakdown studies (long-term response) on the two types of films indicated that ex situ crystallized films are more resistant toward breakdown than their in situ crystallized counterparts. The observations showed that the microstructure played an important role in the degradation properties. The electrical breakdown in both cases is believed to originate from different parts of the film. In the case of the ex situ crystallized films the breakdown takes place at the grain boundaries, while in the in situ case it appears to originate at the electrode/film interfaces.