Low-voltage driven method of ferroelectric memory device using optical polarization property

We propose low-voltage driven method of ferroelectric memory device by using optical polarization measurement for detecting slightly difference of the polarized state as the difference in fast axis of birefringence. Non-volatile ferroelectric memory has a necessity to apply a voltage higher than coercive electric field for inverting spontaneous polarizations. Furthermore, repeated operation of these memory devices causes fatigue of ferroelectric ceramics due to the strain of a crystal structure which arise from the changing an electric polarization. For confirming the amount of memory effect as a function of the applied electric field, the hysteresis curve in the optical polarization property of PLZT (Lead Lanthanum Zirconate Titanate) has been measured. The coercive electric field Ec and Emax which is an electric field to align directions of all electric polarizations of a sample PLZT-8.9/65/35 are 14 and 3 kV/cm, respectively. Azimuth angle exhibited the amount of memory effect of 5.4° at the maximum electric field 4.5 kV/cm. In addition, in the range from 0 kV/cm to 3.0 kV/cm, the amount of memory effect becomes small values less than 1°. These results mean to allow us to use the memory effect in a driving electric field less than Emax by using the optical polarization property.