Strain Tuning of Negative Capacitance in Ferroelectric KNbO₃ Thin Films

Abstract

Ferroelectrics with negative capacitance effects can amplify the gate voltage in field-effect transistors to achieve low power operation beyond the limits of 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 ferroelectrics. However, it is a great challenge to experimentally tune the negative capacitance effect. Here, the observation of the tunable negative capacitance effect in ferroelectric KNbO 3 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 effects can be controlled by imposing various epitaxial strains. The adjustment of the negative curvature region in the polarization-energy landscape under different strain states is responsible for the tunable negative capacitance. Our work paves the way for fabricating low-power devices and further reducing energy consumption in electronics.

Insights into Strain Engineering: From Ferroelectrics to Related Functional Materials and Beyond

“…These factors have already been adjusted through strain engineering, leading to the high sensitivity of the NC effect to lattice strains. Theoretical and experimental investigations have both demonstrated that the change in the transient NC can be tuned by epitaxial strains, ranging from the (Ba 0.8 Sr 0.2 )­TiO 3 /LaAlO 3 superlattice and Pb­(Zr,Ti)­O 3 and KNbO 3 films to Hf 0.2 Zr 0.75 O 2 layers in flash memory and HfAl x O 2 -based NC-FETs . In these examples, compressive strain strengthens dipole interactions and deepens potential wells, broadening the negative curvature region in the energy landscape (Figure c).…”