Strain tuning of negative capacitance in ferroelectric KNbO3 thin films

Abstract Ferroelectrics with negative capacitance effect can amplify the gate voltage in field-effect transistors to achieve low power operation beyond the limits of the Boltzmann's Tyranny. The reduction of power consumption depends on the capacitance matching between the ferroelectric layer and gate dielectrics, which can be well controlled by adjusting the negative capacitance effect in the ferroelectrics. However, it is a great challenge to experimentally tune the negative capacitance effect. Here, the observation of tunable negative capacitance effect in ferroelectric KNbO3 through strain engineering is demonstrated. The magnitude of the voltage reduction and negative slope in polarization-electric field (P-E) curves as the symbol of negative capacitance effect can be controlled by imposing various epitaxial compressive strain. The expansion of negative curvature region in polarization-energy landscape under compressive strain is responsible for the tunable negative capacitance. Our work paves the way for fabricating low power devices and further reducing energy consumption in electronics.