First-principles simulation of negative capacitance in a polydomain ferroelectric-paraelectric bilayer capacitor under bias

The use of negative capacitance materials is gaining attention in recent years as a path to achieving further scaling of nanoelectronic devices [1]. For example, it has been reported that the ferroelectric thin film in a ferroelectric (FE)-paraelectric (PE) bilayer capacitor exhibits negative capacitance, i.e., the bilayer capacitor has a higher capacitance than the capacitor with a single PE layer [2]. However, the mechanism for this effect, especially with regard to the dynamics of polarization domains under bias voltage, is poorly understood. To tackle this issue, we performed first-principles simulation of a metal/FE/PE/metal capacitor with 180$^\circ$ stripe domains under bias using our recently developed orbital-separation approach [3]. We find an antiferroelectric-like behavior with a polydomain-monodomain transition under 0.3 V. Capacitance boost (i.e., negative capacitance) is observed within the monodomain regime, and the transition itself is also found to be a source of capacitance enhancement. [1] G. Catalan et al., Nature Mater. 14, 137 (2015). [2] D. Appleby et al., Nano Lett. 14, 3864, (2014); A. I. Khan et al., Appl. Phys. Lett. 99, 113501 (2011). [3] S. Kasamatsu et al., Phys. Rev. B 84, 085120 (2011); Phys. Rev. B 92, 115124 (2015).