Room-Temperature Negative Capacitance in a Ferroelectric- Dielectric Superlattice Heterostructure

摘要

We demonstrate room-temperature negative capacitance in a ferroelectric-dielectric superlattice heterostructure. In epitaxially grown superlattice of ferroelectric BSTO (Ba_(0.8)Sr_(0.2)TiO_3) and dielectric LAO (LaAlO_3), capacitance was found to be larger compared to the constituent LAO (dielectric) capacitance. This enhancement of capacitance in a series combination of two capacitors indicates that the ferroelectric was stabilized in a state of negative capacitance. Negative capacitance was observed for superlattices grown on three different substrates (SrTiO_3 (001), DyScO_3 (110), and GdScO_3 (110)) covering a large range of substrate strain. This demonstrates the robustness of the effect as well as potential for controlling the negative capacitance effect using epitaxial strain. Room-temperature demonstration of negative capacitance is an important step toward lowering the subthreshold swing in a transistor below the intrinsic thermodynamic limit of 60 mV/decade and thereby improving energy efficiency.