  Ferroelectricity is characterized by the presence of spontaneous and
switchable macroscopic polarization. Scaling limits of ferroelectricity have
been of both fundamental and technological importance, but the probes of
ferroelectricity have often been indirect due to confounding factors such as
leakage in the direct electrical measurements. Recent interest in low-voltage
switching electronic devices squarely puts the focus on ultrathin limits of
ferroelectricity in an electronic device form, specifically on the robustness
of ferroelectric characteristics such as retention and endurance for practical
applications. Here, we illustrate how manipulating the kinetic energy of the
plasma plume during pulsed laser deposition can yield ultrathin ferroelectric
capacitor heterostructures with high bulk and interface quality, significantly
low leakage currents and a broad "growth window". These heterostructures
venture into previously unexplored aspects of ferroelectric properties,
showcasing ultralow switching voltages ($<$0.3 V), long retention times
($>$10$^{4}$s), and high endurance ($>$10$^{11}$cycles) in 20 nm films of the
prototypical perovskite ferroelectric, BaTiO$_{3}$. Our work demonstrates that
materials engineering can push the envelope of performance for ferroelectric
materials and devices at the ultrathin limit and opens a direct, reliable and
scalable pathway to practical applications of ferroelectrics in ultralow
voltage switches for logic and memory technologies.
