Negative Capacitance from the Inhomogenous Stray Field in a Ferroelectric–Dielectric Structure

Abstract

The phenomenological Landau–Ginzburg–Devonshire model provides a fundamental background for an understanding of the peculiar charge–voltage behavior of ferroelectric (FE) materials. However, the model cannot explain the polarization behavior of multidomain FE materials. The experimentally observed negative capacitance (NC) effect, which is interpreted as an emergence of the Landau barrier effect, involves particular conceptual difficulty. This work provides a new conceptual framework to explain the quasi‐static NC effect based on the energy formula for a stacked dielectric/ferroelectric (DE/FE) layer structure with the multidomain configuration with arbitrary shape. The presence of such domain configuration causes the energy–displacement curve of the inhomogenous Helmholtz energy term to have negative curvature. This is caused by the stray field between the neighboring domains. The model can be further extended to the DE/FE system with polycrystalline FE grains using the advanced phase‐field analysis. It is determined that the NC effect from the stray field is a universal phenomenon. These models provide quantitative explanations for the previously reported short‐pulse measurement results for various DE/FE material systems, which have lacked accurate interpretations.

Direct Measurement of Negative Capacitance in Ferroelectric/Semiconductor Heterostructures

“…Compared with the NC phenomenon in the FE/DE series structure, which is often manifested as charge boost, , what we observed here for the FE/S structure is more intuitive. Moreover, by investigating the variation of capacitance with DC bias and measuring frequency, we can further explore the role of different kinds of movable charges, which is valuable for the research and application of NC in heterostructures.…”

“…In the following years, NC in ferroelectric-based structures has been extensively studied, ,− which can be divided into two categories: steady NC and transient NC. Steady NC originates from the inherent characters of ferroelectric materials. ,, The NC state can be thermodynamically stable in a ferroelectric/dielectric (FE/DE) series structure, showing an increased total capacitance compared with that of the dielectric layer, and often referred to as the charge-boost effect. , Transient NC appears during the short process of the polarization switching in the ferroelectric/resistor (FE/ R s ) series structures. Because of the mismatch between the switching rates of free charges in the circuit and the bound charges in the FE layer, the divided voltage of the ferroelectric layer has a decreasing stage, while the polarization (bound) charges keep increasing .…”

Emerging Fluorite-Structured Antiferroelectrics and Their Semiconductor Applications

“…However, in principle the NC in AFE is theoretically similar to that in FE films. Therefore, the major technical challenges would be the suppression of hysteresis originating from the formation of multidomain states, the lack of understanding of the stray-field effect, 96 and insufficient information on the gradient coefficients observed in energy−polarization curves. 97 The nonvolatility induced in fluorite-structured AFEs by built-in field engineering is another important method for developing storage memory and artificial synapse devices.…”

“…However, the NC region corresponding to the negative curvature region in the energy–polarization curve is thermodynamically unstable, and the oppositely polarized domains are formed before reaching the NC region in the homogeneous polarization state. Thus, the NC mechanism remains a hot research topic to date and includes several categories such as the intrinsic negative capacitance originating from the negative Landau coefficient of FEs and extrinsic negative capacitance caused by the inhomogeneous stray field, gradient energy coefficient effect, and transient uncompensated polarization . The fundamental theory of NC is very broad and has not been the focus of researchers despite its recent review .…”

“…However, the transient NC phenomenon has severe drawbacks, including a hysteresis of the I DS – V GS curve and low switching speed at gigahertz frequencies . Therefore, stacked FE/dielectric capacitor designs were considered to enable hysteresis-free operation and stabilize NC regions. ,− Although the origin of the NC phenomenon remains debatable, the superior performance of NCFETs containing fluorite-structured ultrathin films (<3 nm) has been reported recently. , …”