Effect of dielectric layer on switching characteristics in ferroelectric Zr-doped HfO2 films

Abstract

There have been extensive studies on HfO2 as a ferroelectric material. HfO2 thin film, also used as high-k gate oxide in high-k metal gate structure, has gained great attention because it gives the probabilities to overcome the preexisting limits of ferroelectric-based memory devices. For dielectric/ferroelectric bilayer on the other hand, there has not yet been sufficient analyses so far. The insertion of the dielectric layer in ferroelectric thin film can be utilized in many ways, therefore it is worth to investigate the various properties in dielectric/ferroelectric bilayer structure. In this thesis, ferroelectric switching properties of TiN/Al2O3/Hf0.5Zr0.5O2/TiN stacks under high/low field cycling were examined. From polarization and current loops, the suppression of ferroelectric properties as the result of the intervened dielectric layer was observed in the pristine state. Wake-up effect induced by high field cycling was obtained in all samples. The split-up of switching current peak was resulted by the low field cycling. Using first-order reversal curve measurement, the microscopic switching density distribution was represented by a contour plot. Also, two-step waveform method and capacitance measurement revealed that the split-up of the switching current peak was not attributed to the domain wall pinning effect.