Room-temperature negative capacitance in a ferroelectric-dielectric superlattice heterostructure

We demonstrate room-temperature negative capacitance in a ferroelectric-dielectric superlattice heterostructure. In epitaxially grown superlattice of ferroelectric BSTO (Ba_0.8Sr_0.2TiO₃) and dielectric LAO (LaAlO₃), 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 (SrTiO₃ (001), DyScO₃ (110), and GdScO₃ (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.