  We report a proof-of-concept demonstration of negative capacitance effect in
a nanoscale ferroelectric-dielectric heterostructure. In a bilayer of
ferroelectric, Pb(Zr0.2Ti0.8)O3 and dielectric, SrTiO3, the composite
capacitance was observed to be larger than the constituent SrTiO3 capacitance,
indicating an effective negative capacitance of the constituent
Pb(Zr0.2Ti0.8)O3 layer. Temperature is shown to be an effective tuning
parameter for the ferroelectric negative capacitance and the degree of
capacitance enhancement in the heterostructure. Landau's mean field theory
based calculations show qualitative agreement with observed effects. This work
underpins the possibility that by replacing gate oxides by ferroelectrics in
MOSFETs, the sub threshold slope can be lowered below the classical limit (60
mV/decade).
