A comparison of Ti/Pt and TiN/Pt electrodes used with ferroelectric SrBi2Ta2O9 films

The effects of Ti and TiN adhesion layers, used below the Pt bottom electrode, on the purity, phase distribution and electrical properties of ferroelectric SrBi2Ta2O9 (SBT) thin films have been examined and compared. Changes in electrode morphology were observed as a function of temperature, using atomic force microscopy (AFM) and scanning electron microscopy (SEM). A distinct improvement was seen when TiN is used; there are fewer shorting capacitors and the remnant polarisation of the ferroelectric increases markedly. However, the adhesion is not as good. Secondary ion mass spectrometry (SIMS) shows that when Ti/Pt bottom electrodes are used, Ti diffuses through the Pt film causing spurious phases to crystallise in the SBT film. These depth profiles also show evidence of Bi diffusion to the surface of the oxide film and through the Pt towards Ti rich regions.