High‐Mobility Nonvolatile Memory Thin‐Film Transistors with a Ferroelectric Polymer Interfacing ZnO and Pentacene Channels

Abstract

Non-volatile memory (NVM) thin-film transistors (TFTs) with organic channels have been investigated with a ferroelectric gate material, poly(vinylidenefluoride-trifluoroethylene) [P(VDF-TrFE)] [1][2][3][4][5][6] under the basic principles from conventional Si-based ferroelectric field-effect transistors (FeFET), preparing the advent of transparent or flexible device technologies on glass and plastic substrates. Beta-phase crystalline P(VDF-TrFE) films generally have an induced remnant polarization of %10 mC cm À2 if polarized over their coercive electric field (E-field), formed through spin casting and subsequent optimum curing processes. [2,4,7] Researchers presented decent NVM properties of polymer channel NVM-TFT with P(VDF-TrFE) in their recent works: low leakage, relatively low switching voltage, [2] and a quite high switching speed. [1,2,6] They also reported the physical properties of the unit ferroelectric polymer layer. [8][9][10][11][12][13][14][15] Nonetheless, a challenging problem remains to be overcome prior to any practical application of this ferroelectric polymer towards NVM-TFT on flexible plastic or glass substrates: it is the inferior field mobility (less than %10 À2 cm 2 V À1 s À1) of present polymer-based NVM-TFTs, which is due to the intrinsic low channel mobility of polymer-based semiconductors and also due to the rough surface of spin-cast P(VDF-TrFE) layers. Moreover, obtaining low leakage current from spin-cast crystalline ferroelectric polymer films may require quite sensitive care [2] in the solvent selection and in the coating processes of purified polymers. Our previous report shows some high mobility (0.36 cm 2 V À1 s À1 ) ZnO-based NVM-TFTs with poly-4-vinylphenol (PVP)/P(VDF-TrFE) double layers, where the PVP overlayer suppressed current leakage of P(VDF-TrFE) but also caused poor retention, inducing depolarization electric field in the ferroelectric P(VDF-TrFE) layers.[16] Here, we adopt a single P(VDF-TrFE) layer of short-range-order crystalline phase as the nonvolatile memory component for a reproducible lowcurrent-leakage ferroelectric, to be applied onto high-mobility p-channel pentacene channels on flexible plastic substrates and also onto high-mobility n-channel ZnO channels on glass. Our limited-crystalline ferroelectric layer still showed good remnant polarization of maximum %7 mC cm À2, and the pentacene-and ZnO-based NVM-TFTs with such short-range-order crystalline P(VDF-TrFE) layer reproducibly demonstrated maximum field mobilities of 0.1 and 1 cm 2 V À1 s À1 , respectively, with low leakage current densities of a few nanoamperes (%1 Â 10 À6 A cm À2 ), low switching voltages of %20 V for write/erase (in 50 ms pulse), low operation (after switching) voltages of %5 V, and long retention of over 10000 s. In particular, our ZnO-based NVM-TFTs displayed a large memory window of 20 V, which is the maximum obtainable from 200 nm-thick P(VDF-TrFE).Device cross-sections in Figure 1a display our pentacene-and ZnO-based NVM TFTs with the short-range-order crystalline P(VDF-TrFE)...

Electrical memory devices based on inorganic/organic nanocomposites

“…The device area is defined by the overlap between the top and the bottom electrodes; therefore, a very high memory density can be easily achieved by using cross-bar arrays. [1][2][3][4][5] The organic material used can consist of small organic molecules or polymers. Small organic molecules have low molecular weight and can be deposited under high vacuum without decomposition by using thermal evaporation.…”

Review—Organic-Inorganic Hybrid Functional Materials: An Integrated Platform for Applied Technologies

“…The device area is defined by the overlap between the top and the bottom electrodes; therefore, a very high memory density can be easily achieved by using cross-bar arrays. [271][272][273][274][275] The organic material used can consist of small organic molecules or polymers. Small organic molecules have low molecular weight and can be deposited under high vacuum without decomposition by using thermal evaporation.…”

Organic nonvolatile memory transistors with self-doped polymer energy well structures

“…The functionality of the ferroelectric OFET memory devices arises from the ferroelectric gate insulating layers that are polarized under appropriate electric fields (gate voltages); therefore, the research objective is to maintain the polarized state under continuous (repetitive) reading operations. [11][12][13] In the case of charge-storage OFET memory devices, the gate insulating layers with polar groups have a charging role for controlling the gate voltage. [14][15][16][17] To improve the switching performance, further insulating layers have been inserted between the gate insulating layer and the channel layer (organic semiconductors).…”

“…[1][2][3][4] Among the various types of organic memory devices, a considerable number of studies have been devoted to nonvolatile memory systems that include organic-resistive-switching diode memory and organic fieldeffect transistor (OFET) memory. [5][6][7][8][9][10][11][12][13][14][15][16][17] The organic-resistive-switching diode memory devices consist of organic-resistive layers between two electrodes, which typically act as either electrically insulating components or electrically conducting components under appropriate voltage conditions. [5][6][7][8][9][10] However, the organic-resistiveswitching diode memory devices require transistors for addressing signals in two-dimensional memory arrays because they do not possess third electrodes for signal addressing.…”

“…In contrast, OFET memory devices can essentially perform the signal addressing function alone because there are three electrodes in the unit transistors. [11][12][13][14][15][16][17] The OFET memory devices can be classified into two types based on the memory effects. The first type is a ferroelectric OFET memory device and the second is a charge-storage OFET memory device.…”