Efficiency of Ferroelectric Field-Effect Transistors: An Experimental Study

While the theoretical maximum of the memory window $Delta V_{t}$ in a ferroelectric field-effect transistor (FEFET) is $2E_Ct_F$ , $E_C$ and $t_F$ being coercive field and FE thickness, respectively, experimentally $Delta V_{t}$ is observed to be much less than that, even in the case of complete polarization switching in the ferroelectric layer. This occurs because trapped charges in the gate oxide stack partially or completely screen the ferroelectric polarization, only a fraction of which gets ``electrostatically'' reflected in the semiconductor channel. In this article, we provide a generalized experimental framework to quantify the efficiency of practical FEFETs in converting the switched ferroelectric polarization into the memory window. To that end, we propose three efficiency metrics: 1) switched ferroelectric polarization $Delta P_F$ to memory window conversion ratio, $eta_{MW}=Delta V_{t}/Delta P_F$ ; 2) switched ferroelectric polarization to the semiconductor charge ( $Delta Q_S$ ) conversion efficiency or the charge conversion efficiency $eta_{c}=Delta Q_s/Delta P_F$ ; and 3) the ratio of memory window to the width of polarization versus gate voltage hysteresis characteristics ( $Delta V_P$ ) or the voltage conversation efficiency $eta_V=Delta V_{t}/Delta V_P$ . We measure and compare these efficiency metrics in n-type and p-type FEFETs, fabricated in different facilities by different groups. In all the cases, we find that the maximum values of memory window efficiency $(eta_{MW})_{max}$ , charge conversion efficiency $(eta_{c}$ ) $_{max}$ , and voltage conversion efficiency ( $eta_{V}$ ) $_{max}$ are in the range: 2.5-5.5 Vm(2)/C, 4%-10%, and 5%-20%, respectively.