An alternative explanation of negative capacitance

Steep-slope transistors are promising devices for low-power electronics. One variety, known as negative capacitance field effect transistors, are unique because they offer sub-60-millivolt-per-decade subthreshold swing through the negative capacitance of a ferroelectric network, which yields a higher ON/OFF current ratio.

Electrical capacitance is normally a positive value, but using a ferroelectric material in a transistor gate results in negative capacitance, which allows a transistor to consume less power.

In the Journal of Applied Physics, researchers provide an alternative explanation of the negative capacitance effect in resistor-ferroelectric (R-FE) and ferroelectric-dielectric (FE-DE) networks. For the first time, they describe this effect as an outcome of ferroelectric polarization lag and large change in capacitance near the coercive voltage — the voltage necessary to demagnetize the material completely.

Previous explanations of negative capacitance are based on the Landau-Khalatnikov equation, where the steady-state relation between polarization (P) and voltage (V) has a negative derivative (dP/dV) region. Co-author Atanu Saha said that the researchers’ new explanation implies that previously demonstrated enhanced capacitance effects in R-FE and FE-DE networks could be attributed to reasons beyond the existence of an S-shaped relation between polarization and voltage.

The authors came to their alternative explanation through mathematical and simulation-based analysis. They also plan to investigate negative capacitance further through experimentation, as this will ultimately help advance ferroelectric-based devices.

Source: ““Negative capacitance” in resistor-ferroelectric and ferroelectric-dielectric networks: Apparent or intrinsic?,” by Atanu K. Saha, Suman Datta, and Sumeet K. Gupta, Journal of Applied Physics (2018). The article can be accessed at https://doi.org/10.1063/1.5016152 .