2016, Yeh, Chia-Pin, Lisker, Marco, Kalkofen, Bodo, Burte, Edmund P.

Ferroelectric capacitors made by lead zirconate titanate (PZT) thin films and iridium electrodes are fabricated on three-dimensional structures and their properties are investigated. The iridium films are grown by Plasma Enhanced MOCVD at 300°C, while the PZT films are deposited by thermal MOCVD at different process temperatures between 450°C and 550°C. The step coverage and composition uniformity of the PZT films on trench holes and lines are investigated. Phase separation of PZT films has been observed on both 3D and planar structures. No clear dependences of the crystallization and composition of PZT on 3D structure topography have been found. STEM EDX line scans show a uniform Zr/(Zr+Ti) concentration ratio along the 3D profile but the variation of the Pb/(Zr+Ti) concentration ratio is large because of the phase separation. 3D ferroelectric capacitors show good ferroelectric properties but have much higher leakage currents than 2D ferroelectric capacitors. Nevertheless, during cycling tests the degradation of the remnant polarization between 2D and 3D capacitors is similar after 109 switching cycles. In addition, the sidewalls and bottoms of the 3D structures seem to have comparable remnant polarizations with the horizontal top surfaces.

2016, Yeh, Chia-Pin, Lisker, Marco, Kalkofen, Bodo, Burte, Edmund P.

Reactive ion etching (RIE) technology for iridium with CF4/O2/Ar gas mixtures and aluminum mask at high temperatures up to 350 °C was developed. The influence of various process parameters such as gas mixing ratio and substrate temperature on the etch rate was studied in order to find optimal process conditions. The surface of the samples after etching was found to be clean under SEM inspection. It was also shown that the etch rate of iridium could be enhanced at higher process temperature and, at the same time, very high etching selectivity between aluminum etching mask and iridium could be achieved.

2014, Guo, E.J., Das, S., Herklotz, A.

The effect of a magnetic field on the ferroelectric switching kinetics of BiFeO3 (BFO) capacitors with La0.8Ca0.2MnO3 (LCMO) bottom electrode and Pt top contact has been investigated. We find a strong dependence of the remnant polarization and coercive field on the magnetic field. The switching time can be systematically tuned by magnetic field and reaches a tenfold reduction around the Curie temperature of LCMO at 4 T. We attribute this behavior to the splitting of the voltage drops across the BFO film and the LCMO bottom electrode, which can be strongly influenced by an external magnetic field due to the magnetoresistance. Further experiments on the BFO capacitors with SrRuO3 bottom electrodes show little magnetic field dependence of ferroelectric switching confirming our interpretation. Our results provide an efficient route to control the ferroelectric switching speed through the magnetic field, implying potential application in multifunctional devices.