Film thickness-dependent ferroelectric polarization switching dynamics of undoped HfO2 thin films prepared by atomic layer deposition

摘要

Metal-ferroelectric-metal capacitors were fabricated to evaluate the ferroelectricity and switching dynamics of the undoped-HfO2 thin films prepared by atomic layer deposition. The film thickness was controlled to be 9 to 16 nm as an important control parameter. The value of remnant polarization (P-r) decreased with increasing the film thickness owing to the modulations in amounts of ferroelectric orthorhombic phase. The 11-nm-thick HfO(2 )thin film, which was strategically suggested as a critical film thickness, showed the P-r value of 8.47 mu C/cm(2). Based on the accurately calculated P-r by double-pulse switching measurement and Kolmogorov-Avrami-Ishibashi (KAI) model, the ferroelectric polarization switching time (t(s)) and the activation electric field (BO for polarization reversal were estimated with the variations in film thickness of the HfO2 thin films. The t(s) and E-a showed decreasing and increasing trends with increasing the film thickness, respectively. The values of P-r for the MFN capacitor were also found to be gradually modulated by controlling the ferroelectric partial polarization with pulse-width and pulse-number modulations, which corresponded to the emulations of assigning the synaptic weights for the synapse device applications.