The Effects of Fatigue of The Ferroelectric Thin Film on The Device Characteristics of Metal-Ferroelectric-Semiconductor FET

초록

Changes of device characteristics of the metal-ferroelecric-semiconductor FET (MFSFET) with the progress of fatigue of the ferroelectric thin film are simulated in this study. The field-dependent polarization model and the square-law FET model are employed in our simulation. Our simulation model takes into account the fatigue of the ferroelectric thin film through the accumulation of oxygen vacancies near interface between the ferroelectric thin film and the metal electrode. In the simulation of switching, the relative switched charge before fatigue is assumed as 0.74 nC, which reduces to 0.15 nC when the thickness of the oxygen layer becomes 50 Å after progress of fatigue. This result indicates that the generation of oxygen vacancies strongly suppress polarization reversals. C-VG curves generated from our MFSFET simulation exhibit the accumulation, the depletion and the inversion regions clearly. They also exhibit the memory window of 2 V. VG-ID curves show the smooth ones composed of increasing and saturated-flat region before fatigue, but show only distorted increasing ones without saturated-flat region up to 8 V of VG after fatigue. ID-VD curves are composed of the increasing and the saturated flat region. The difference of saturation drain currents of the MFSFET device at the dual threshold voltages in ID-VD curve is 6 mA/cm2, which decreases as much as 50 % after fatigue. Rapid decrease of the difference of saturation drain currents by fatigue implies that the accumulation of oxygen vacancies with the progress of fatigue should be avoided in the MFSFET applications. Our simulation model is expected to be very useful in the estimation of the behaviour of MFSFET devices with the progress of fatigue of various combinations of ferroelectric thin films and electrodes.