Dipolar Alignment in a Ferroelectric Dielectric Layer of FeFETs to Boost Charge Mobility and Nonvolatile Memory

Abstract

Influence of dipolar alignments of a ferroelectric poly-vinylidine fluoride trifluroethylene [P(VDF-TrFE)] thin film on the charge mobility and nonvolatile property of ferroelectric field-effect transistors (FeFETs) has been explored. The electrical properties of the ferroelectric microstructures can be tuned by adopting different cooling procedures after annealing the spin-coated ferroelectric polymer P(VDF-TrFE) substrates. For example, a higher degree of alignment of the C–F dipoles in the polymeric chains is observed along the substrate surface for the samples with fast quenching. The dielectric constant of the fast-quenched sample is found to be ∼10 at 1 kHz, while the same is found to be ∼8.5 when the rate of cooling is relatively slower. Furthermore, the fabrication of a metal–insulator–metal capacitor using the fast-quenched substrate leads to a high remnant polarization of Pr ∼ 5.5 ± 0.2 μC/cm2, as compared to that of the normally cooled sample to ∼2.7 ± 0.2 μC/cm2, at an applied field intensity of 200 MV/m. Emergence of such characteristics encouraged the use of P(VDF-TrFE) as a gate dielectric layer, which leads to improved nonvolatile characteristics of the device. The measured charge carrier mobility of FeFETs embedded with a fast-quenched ferroelectric polymer as a gate dielectric is found to be ∼3.4 × 10–2 cm2 V–1 s–1, which is ∼35% higher than the normally cooled samples. The strongly correlated C–F dipoles in the fast-quenched ferroelectric layers lead to the reduction in width of the trap density of states near the semiconductor–dielectric interface. The XPS and UPS characterizations show the formation of a superior transport channel in the semiconductor near its dielectric interface when the fast-quenched polymer is used as the gate dielectric in the FeFETs.

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