An Organic Field‐Effect Transistor with Programmable Polarity

Abstract

Organic thin-film field-effect transistors (FETs) have been studied extensively over the last decade, and tremendous progress in device performance has been achieved.[1] OrganicFETs have worked mainly as unipolar p-type transistors, in which positive charges are accumulated in the channel by applying a negative gate voltage, V G . As a result, the state-ofthe-art integrated circuits based on organic FETs are based on unipolar p-type logic.[2] For memory applications, organic transistors with a ferroelectric gate dielectric have recently been investigated. [3][4][5] In this type of device the memory effect arises from the attenuation of the surface charge density in the semiconductor by the remanant polarization of the ferroelectric. The fingerprint of ferroelectric switching, a sharp change of the channel conduction at the coercive field of the ferroelectric, was clearly observed in solution-processed polymer ferroelectric FETs (FeFETs) with a p-type unipolar semiconductor layer. [3] It was shown that the induced surfacecharge density has a high value compared to what can be obtained with conventional Si ++ /SiO 2 transistors, and, as a result, high on/off ratios of 10 4 were achieved.From a performance point of view, however, complementary metal oxide semiconductor (CMOS) logic is crucial. The advantages compared with unipolar logic are low power dissipation, higher operating frequencies, a good noise margin, and robust operation. Therefore, the transport of electrons and holes, the so-called ambipolar charge transport, in FETs is a highly desirable property. Although the first single-channel inorganic ambipolar FETs have been demonstrated more than two decades ago, [6] their organic counterparts have only become a reality in recent years. [7][8][9][10][11][12][13] For organic FETs employing only a single active film, ambipolar charge transport was reported for heterogeneous blends consisting of polymerbased interpenetrating networks as well as narrow bandgap organic semiconductors. [12] We present a new type of organic FET consisting of an ambipolar semiconductor with a fer- COMMUNICATIONS 2692

Stability of polarization in organic ferroelectric metal-insulator-semiconductor structures

“…4.12(b) clearly indicates a ferroelectric switching, although not as clear as for depletion voltages, since its superimposed with an increased DC current component. 78,79 Thus, it can be concluded that, the output characteristic starts to accumulate at voltages below V c , before the ferroelectric polarisation was reversed. The fact that I D (V DS ) does not reflect the ferroelectric switching may serve as a further confirmation for the existence of negative charges, which compensate the ferroelectric polarisation charge of the insulator.…”

Nonvolatile memory devices based on organic field-effect transistors

“…Most of the organic memory transistors reported to date exploit the electric field induced remnant polarization in ferroelectric polymer films [32][33][34][35][36][37][38][39][40][41][42][43][44][45]. Inorganic ferroelectric FET memories have been studied for decades; a memory performance of practical value has been achieved in recent years [46,47].…”

“…200 at a gate bias of 2.5 V, one of 30 at zero gate bias and a retention time of three hours [33]. In 2005, Naber et al fabricated ferroelectric OFET memory devices containing the ferroelectric copolymer poly(vinylidene fluoride/ trifluoro-ethylene) (P(VDF/TrFE)) as a gate insulator and poly[2-methoxy, 5-(2′-ethyl-hexyloxy)-p-phenylene-vinylene] as a semiconductor [34,35]. The devices had an on/off ratio of 10 4 , with a programming time of 0.3 ms and a memory stability of more than 1 week.…”

Adsorbate/absorbate interactions with organic ferroelectric polymers

“…Organic heterojunction diodes [28,29,70,[79][80][81] and transistors [82][83][84][85][86][87][88][89][90][91][92][93][94] have been fabricated with the crystalline ferroelectric P(VDF-TrFE). As the copolymer poly(vinylidene fluoride with trifluoroethylene) is ferroelectric, transistors, both fully organic heterojunctions [82][83][84][85][86][87][88][89][90][91][92][93][94] and hybrid heterojunctions with an inorganic semiconductor [95][96][97][98][99], exhibit gate voltage dependent hysteresis, indicating the potential of P(VDF-TrFE) copolymers for nonvolatile random access memory devices.…”

“…As the copolymer poly(vinylidene fluoride with trifluoroethylene) is ferroelectric, transistors, both fully organic heterojunctions [82][83][84][85][86][87][88][89][90][91][92][93][94] and hybrid heterojunctions with an inorganic semiconductor [95][96][97][98][99], exhibit gate voltage dependent hysteresis, indicating the potential of P(VDF-TrFE) copolymers for nonvolatile random access memory devices. An example of this type of gate voltage dependent hysteresis for an organic heterojunction transistor fabricated with polyaniline as a p-layer [69,70] on top of P(VDF-TrFE 70:30) where the latter is the gate dielectric layer is illustrated in Figure 15.…”