Thermodynamic equilibrium theory revealing increased hysteresis in ferroelectric field-effect transistors with free charge accumulation

Abstract

At the core of the theoretical framework of the ferroelectric field-effect transistor (FeFET) is the thermodynamic principle that one can determine the equilibrium behavior of ferroelectric (FERRO) systems using the appropriate thermodynamic potential. In literature, it is often implicitly assumed, without formal justification, that the Gibbs free energy is the appropriate potential and that the impact of free charge accumulation can be neglected. In this Article, we first formally demonstrate that the Grand Potential is the appropriate thermodynamic potential to analyze the equilibrium behavior of perfectly coherent and uniform FERRO-systems. We demonstrate that the Grand Potential only reduces to the Gibbs free energy for perfectly non-conductive FERRO-systems. Consequently, the Grand Potential is always required for free charge-conducting FERRO-systems. We demonstrate that free charge accumulation at the FERRO interface increases the hysteretic device characteristics. Lastly, a theoretical best-case upper limit for the interface defect density DFI is identified.

Ferroelectric based FETs and synaptic devices for highly energy efficient computational technologies

“…In devices where the ferroelectric is adjacent to dielectrics or semiconductors, the electrostatic energy due to the depolarization field must be included in the thermodynamic potential [24], [28]- [30]. The thermodynamic potential in the presence of conduction of free charges in the ferroelectric has been recently revisited in [25].…”

Polarization switching and AC small-signal capacitance in Ferroelectric Tunnel Junctions

“…The multi-domain Landau, Ginzburg, Devonshire (LGD) theory is well credited for the ferroelectric dynamics, and it has been used for negative capacitance effects [5]- [9], as well as for the operation of FTJs [10] and of FeFETs [11]. The most appropriate thermodynamic potential in the presence of free charges in the dielectric stack has been recently revisited in [12]. This paper presents an investigation of the AC small-signal C-V curves (SSCV) in metal-ferroelectricdielectric-metal (MFDM) FTJs (Fig.…”