Low-voltage operation of metal-ferroelectric-insulator-semiconductor diodes incorporating a ferroelectric polyvinylidene fluoride copolymer Langmuir-Blodgett film

Abstract

Kohlstedt, Hermann; Fitsilis, M.; Waser, R.; Reese, T.J.; Ducharme, Stephen; and Rije, E., "Low-voltage operation of metalferroelectric-insulator-semiconductor diodes incorporating a ferroelectric polyvinylidene fluoride copolymer Langmuir-Blodgett film" (2006 We report the electrical characteristics of metal-ferroelectric-insulator-semiconductor structures, where the ferroelectric layer is a Langmuir-Blodgett film of a copolymer of 70% vinylidene fluoride and 30% trifluoroethylene. The 36-nm thick copolymer films were deposited on thermally oxidized ͑10 nm SiO 2 ͒ p-type silicon and covered with a gold gate electrode. Polarization-field hysteresis loops indicate polarization switching in the polymer film. The device capacitance shows hysteresis when cycling the applied voltage between ±3 V, exhibiting a zero-bias on/off capacitance ratio of over 3:1 and a symmetric memory window 1 V wide, with little evidence of bias that can arise from traps in the oxide. Model calculations are in good agreement with the data and show that film polarization was not saturated. The capacitance hysteresis vanishes above the ferroelectric-paraelectric transition temperature, showing that it is due to polarization hysteresis. The retention time of both the on and off states was approximately 15 min at room temperature, possibly limited by leakage or by polarization instability in the unsaturated film. These devices provide a basis for nonvolatile data storage devices with fast nondestructive readout.

Origin of the drain current bistability in polymer ferroelectric field-effect transistors

“…2,17 The contrasting results can be explained by the present use of an organic semiconductor instead of silicon. The latter forms a native oxide layer at the gateinsulator interface which can suppress ferroelectric switching.…”

Ferroelectric field effect transistors using very thin ferroelectric polyvinylidene fluoride copolymer films as gate dielectrics

“…The width of the hysteresis loop is called the memory window and is one of the most important characteristics of an FeFET memory element. The memory window is also evident in measurements of device capacitance C versus gate voltage V g as in an MFIS, 24 as shown in Fig. 3.…”

“…Once the ferroelectric polarization in the off state falls so that this condition is no longer met, the on and off states of the FeFET are indistinguishable even if the on state is completely stable. Therefore, the capacitance state retention study that was previously reported 24 is better suited for a discussion of the dominant mechanisms for state relaxation. Since the capacitance hysteresis ͑Fig.…”

“…3͒ is highly symmetric we can conclude that charge trapping is not significant and that state retention is primarily limited by polarization stability. 24,30 ͑Charge injection is a much bigger problem with oxide ferroelectrics, which are in effect semiconductors. 31 ͒ Nevertheless, this hypothesis needs further study to clarify the mechanisms for retention in FeFETs, and properly prescribe a remedy.…”

“…With coercive fields of 50 MV/m and higher, 21 films must be quite thin, less than 100 nm, to allow for operation voltages below 5 V. The early devices, 9 for example, required up to 200 V to operate, while the more recent examples still require 30 V or more. [11][12][13][14][16][17][18]22 A proven means of making ultrathin films of P͑VDF-TrFE͒ is Langmuir-Blodgett ͑LB͒ deposition on silicon wafers, which has produced ferroelectric films as thin as one nanometer 23 and nonvolatile memory devices operating at less than 10 V. 18,[24][25][26] This report describes the successful low-voltage operation of a silicon-based FeFET nonvolatile memory device with a gate insulator consisting of a 35 nm thick P͑VDF-TrFE͒ LB film and a 10 nm thick SiO 2 layer, operating in the low-voltage range between Ϯ5 V.…”