Nonvolatile Organic Field-effect Transistor Research Articles

Nonvolatile organic field effect transistor memory devices using one-dimensional aligned electrospun nanofiber channels of semiconducting polymers

We report the nonvolatile memory characteristics of organic field effect transistors (OFETs) using one-dimensional aligned electrospun (ES) nanofibers of semiconducting poly(9,9-dioctyl-fluorene-co-bithiophene) (F8T2). The effects of the nanofiber diameter associated with the polymer chain orientation on the charge transport and storage ability were explored. The OFET devices using the F8T2 ES nanofibers exhibited a large average memory window of ∼30 V, an on–off ratio of 102–103 and a hole mobility of 10−4 to 10−2 cm2 V−1 s−1. The write, erase and read processes of the memory device were performed by voltages across the nanofiber channels for at least 100 cycles and could be stabilized for at least 1000 s. The reversible hysteresis characteristics were attributed to the shallow trapping in the ordered/disordered domains of the F8T2 nanofibers from the in situ grazing incidence wide angle X-ray scattering (GIWAXS) analysis. Our results suggest that the semiconducting ES nanofibers could have potential applications for high performance OFET-based nonvolatile organic memory devices.

Kelvin probe microscopic visualization of charge storage at polystyrene interfaces with pentacene and gold

Charge carriers trapped in polystyrene (PS) were investigated with Kelvin probe microscopy (KPM) and thermally stimulated discharge current (TSDC). Lateral heterojunctions of pentacene/PS were scanned using KPM, effectively observing polarization along a side view of a lateral nonvolatile organic field-effect transistor dielectric interface. TSDC was used to observe charge migration out of PS films and to estimate the trap energy level inside the PS, using the initial rise method.

Non-volatile organic field-effect transistor memory comprising sequestered metal nanoparticles in a diblock copolymer film

In this study, we fabricated p-channel-type non-volatile organic field-effect transistor (OFET) memory devices featuring an asymmetric PS-b-P4VP diblock copolymer layer incorporating high- and low-work-function metal nanoparticles (NPs) in the hydrophilic and hydrophobic blocks, respectively. We chose the highly asymmetric diblock copolymer PS56k-b-P4VP8k as the polymer electret to create the memory windows, and used the different work functions of the ex situ-synthesized metal NPs to tune the memory window for either p- or n-channel applications. The transfer curves of non-volatile OFET memory devices incorporating an asymmetric PS56k-b-P4VP8k layer embedded with high-work-function Pt NPs (5.65 eV) in the P4VP block exhibited a positive threshold voltage shift and a large memory window (ca. 27 V). In contrast, the transfer curves of the corresponding non-volatile OFET memory devices featuring embedded low-work-function (4.26 eV) Ag NPs exhibited a negative threshold voltage shift and a smaller memory window (ca. 19 V). This approach provides a versatile way to fabricate p- or possibly n-channel-type non-volatile organic field-effect transistor (OFET) memory devices with the same processing procedure.

Nonvolatile memory organic field effect transistor induced by the steric hindrance effects of organic molecules

We report a nonvolatile memory organic field effect transistor (OFET) using ambipolar organic molecules as nano-interfaced semiconductor materials. Newly synthesized push-pull organic molecules (PPOMs) containing triarylamine as an electron donating group, thiophene as a spacer, and malononitrile as an electron withdrawing group are proposed. The tilted PPOMs with side chains could control the charge trapping of the conducting channel formed between pentacene and PPOMs. Quantum chemical calculations were carried out to estimate the dihedral angle at the neutral and electron charged anion molecules and to explain the charging effects for the memory OFET performance (write-read-erase-read cycles). The charge mobilities of OFETs comprising the nano-interfaced PPOMs were affected by the dihedral angles derived from the steric hindrance of the bulky side chain of the spacer. The memory OTFT with higher dihedral angle material exhibited a wider memory window as well as reduced current flow. The memory OFET devices showed a memory window of −40 to +40 V, a memory ratio of 100 for “ON” to “OFF” currents, and long retention time for the nonvolatile memory.

Charge transfer and trapping properties in polymer gate dielectrics for non-volatile organic field-effect transistor memory applications

We investigate here charge transfer and trapping characteristics of various chargeable polymer dielectric layers, polystyrene (PS), poly(4-vinyl naphthalene) (PVN), and amorphous fluoropolymer (Teflon ® AF) in non-volatile pentacene field-effect transistor (FET) memory devices. Non-volatile memory properties, i.e., the degree of threshold voltage ( V Th) shifts (memory window), the programming and erasing bias, and the retention time, strongly depended on the selection of a charge storage layer, due to its electronic and dielectric properties. The pentacene FETs with PVN or PS showed reversible positive and negative V Th shifts by an application of external gate bias. In Teflon ® AF device, most significant positive V Th shift was obtained indicating a efficient electron injection whereas showed inefficient erasing characteristics via hole injection and storing due to a high electronegative properties of fluorine units in the dielectric. This result indicates importance of a selection of the chargeable polymer dielectric to obtain efficient organic non-volatile memory with a long retention time.

Programmable memory in organic field-effect transistor based on lead phthalocyanine

A nonvolatile organic field-effect transistor (OFET) with a polymeric electret as gate insulator and spun cast film of lead phthalocyanine (PbPc) as semiconductor channel is reported. Hysteresis induced by gate–bias stress was exploited to study nonvolatile memory effects. The observation of the hysteresis and memory window is proposed to originate from charge storage in the polymeric electret. The on state retention time for the OFET memory device is more than 5 h and the device can reproduce continuous write–read–erase–read switching cycles.

Nonvolatile organic field-effect transistor memory element with a polymeric gate electret

Organic field-effect transistors with a polymeric electret as gate insulator and fullerenes as a molecular semiconductor were fabricated. We observed an amplification of the drain–source current Ids on the order of 104 upon applying a gate voltage Vg. Reversing the gate voltage Vg features large metastable hysteresis in the transfer characteristics Ids(Vg) with a long retention time. The observation of a switchable channel current Ids is proposed to originate from charge storage in the organic electret. As such, this device is a demonstration of an organic nonvolatile memory element switchable with the gate voltage.