Dielectric properties in thin film SrTiO3 capacitor

The dielectric behavior of Pt/SrTiO3/Pt thin films is reported in this paper. STO thin films (20 nm and 50 nm) were deposited by ion-beam-sputtering (IBS). This study was carried out in the temperature ranging from 25 degrees C to 150 degrees C and for frequencies in the range 0.01 Hz - 1 MHz. Results showed that the permittivity depends strongly on frequency, temperature and sample thickness. For this latter, the dielectric constant decreases as the film thickness is decreased. This can be explained by an interfacial "dead layer effect" that reduces the effective dielectric constant. Using approximative calculations based on the thickness dependence of the dielectric constant, we have estimated the thickness and the dielectric constant of this 'dead layer'. For a given STO thickness, when the frequency is decreased, we observe an increase in the permittivity. This behavior is more pronounced as temperature increases and for the STO with a thickness of 50 nm. A relaxation peak in the loss tangent in the same frequency range confirms a relaxation process. We suggest interfacial relaxations at the grains boundaries to explain this relaxation. This relaxation differs as a function of the thickness : at a given temperature, the relaxation peak is located at higher frequency and is less important for the thinner STO film. This relaxation explains the important increase in tan delta for the 50 nm STO film. An ionic space charge movement with blocking and accumulation of ions at the electrodes could explain the dielectric responses (permittivity and losses) in the lowest frequencies. To conclude, low frequency dielectric spectroscopy appears as essential tool to understand and optimize high permittivity integrated MIM capacitances.