Fig. 2. Polarization measurements on H-NNO films.

a The schematic of the H-NNO device and the electric-field distribution simulated with COMSOL. The arrow size denotes the norm of the electric field and the color denotes the potential. b, c The electric displacement vs. applied electric field measured at 2 kHz for pristine NNO and H-NNO films. d The PUND measurement for the H-NNO film. The period of the half wave ${\tau }_{\mathrm{half}}$ is 0.1 ms. Inset is the extracted PUND loop as a function of the electric field from the measurement. e PUND loops with different maximum electric fields and the same period of half wave of 0.1 ms. f Remanent polarizaton vs. electric field. P_r in blue dots is obtained from PUND loops and P_r in red dots is from modeling as described in Supplementary Note 1. Inset is an enlarged plot of P_r vs the electrield field ranging from 0 to 350 kV/cm. g Remanent polarization as a function of period of half wave ${\tau }_{\mathrm{half}}$ with the same maximum electric field of 200 kV/cm. h $△P$ as a function of t_relax. $△P$ is the difference of the polarization by the pulses P and U. t_relax is the time interval between two pulses as shown in the inset. i P_r measured by PUND loops versus the number of switching cycles.