Hsuan-Chun Chang

Polymeric charge storage electrets for non-volatile organic field effect transistor memory devices

In this review, we present the effects of the chemical structure and composition of polymer or composite electrets on tuning the memory characteristics of the non-volatile organic field effect transistor (OFET) memory devices, including surface polarity, π-conjugation length, architecture, donor–acceptor strength, and interface energy barrier. The recent progress in developing polymer-based charge storage electrets is highlighted in order to provide insights into understanding the operation mechanism and the molecular design–memory properties relationship, as well as improving the overall performance of OFET memory devices.

Single‐Crystal C60 Needle/CuPc Nanoparticle Double Floating‐Gate for Low‐Voltage Organic Transistors Based Non‐Volatile Memory Devices

Low-voltage organic field-effect transistor memory devices exhibiting a wide memory window, low power consumption, acceptable retention, endurance properties, and tunable memory performance are fabricated. The performance is achieved by employing single-crystal C60 needles and copper phthalocyanine nanoparticles to produce an ambipolar (hole/electron) trapping effect in a double floating-gate architecture.

High Performance Transparent Transistor Memory Devices Using Nano-Floating Gate of Polymer/ZnO Nanocomposites.

Nano-floating gate memory devices (NFGM) using metal nanoparticles (NPs) covered with an insulating polymer have been considered as a promising electronic device for the next-generation nonvolatile organic memory applications NPs. However, the transparency of the device with metal NPs is restricted to 60~70% due to the light absorption in the visible region caused by the surface plasmon resonance effects of metal NPs. To address this issue, we demonstrate a novel NFGM using the blends of hole-trapping poly (9-(4-vinylphenyl) carbazole) (PVPK) and electron-trapping ZnO NPs as the charge storage element. The memory devices exhibited a remarkably programmable memory window up to 60 V during the program/erase operations, which was attributed to the trapping/detrapping of charge carriers in ZnO NPs/PVPK composite. Furthermore, the devices showed the long-term retention time (>105 s) and WRER test (>200 cycles), indicating excellent electrical reliability and stability. Additionally, the fabricated transistor memory devices exhibited a relatively high transparency of 90% at the wavelength of 500 nm based on the spray-coated PEDOT:PSS as electrode, suggesting high potential for transparent organic electronic memory devices.

Improving the characteristics of an organic nano floating gate memory by a self-assembled monolayer.

We demonstrate a novel approach to improve the characteristics of the gold nanoparticle-based organic transistor memory devices by using self-assembled monolayers (SAM) with different functional groups as interfacial modifier. SAM-based interfacial engineering significantly improved the hysteresis, memory window, and on/off ratio of a nano floating gate memory (NFGM) at zero gate voltage. This NFGM showed a large memory window of up to 190 V and on/off current ratio of 10(5) during writing and erasing with an operation voltage of 100 V of gate bias in a short time, less than 1 s. Furthermore, the devices show excellent nonvolatile behavior for bistable switching. The ON and OFF state can be stably maintained for 10(3) s with an I(on)/I(off) current ratio of 10(6) for a pentafluorophenyl trimethoxysilane modified device. The results suggested the importance of SAM-modified interface for the memory performance of NFGMs.

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.

Nonvolatile organic thin film transistor memory devices based on hybrid nanocomposites of semiconducting polymers: gold nanoparticles.

We report the facile fabrication and characteristics of organic thin film transistor (OTFT)-based nonvolatile memory devices using the hybrid nanocomposites of semiconducting poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) and ligand-capped Au nanoparticles (NPs), thereby serving as a charge storage medium. Electrical bias sweep/excitation effectively modulates the current response of hybrid memory devices through the charge transfer between F8T2 channel and functionalized Au NPs trapping sites. The electrical performance of the hybrid memory devices can be effectively controlled though the loading concentrations (0-9 %) of Au NPs and organic thiolate ligands on Au NP surfaces with different carbon chain lengths (Au-L6, Au-L10, and Au-L18). The memory window induced by voltage sweep is considerably increased by the high content of Au NPs or short carbon chain on the ligand. The hybrid nanocomposite of F8T2:9% Au-L6 provides the OTFT memories with a memory window of ~41 V operated at ± 30 V and memory ratio of ~1 × 10(3) maintained for 1 × 10(4) s. The experimental results suggest that the hybrid materials of the functionalized Au NPs in F8T2 matrix have the potential applications for low voltage-driven high performance nonvolatile memory devices.

Ambipolar field-effect transistors using conjugated polymers with structures of bilayer, binary blends, and paralleled nanofibers

In this paper, we explore ambipolar organic field-effect transistor (FET) characteristics using bilayer, binary blends, and paralleled nanofibers of poly(3-hexylthiophene) (P3HT; p-type) and poly{[N,N′-bis(2-decyltetradecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl] -alt-(thiophene-2,5-diyl)} (P(NDI-T); n-type). Ambipolar transistors with paralleled single P3HT and P(NDI-T) electrospun nanofibers showed high and well-balanced mobilities of 8.25 × 10−2 cm2 V−1 s−1 for holes and 7.51 × 10−2 cm2 V−1 s−1 for electrons with Ion/Ioff ≈ 104. This ambipolar nanofiber FET was also applied to a complementary inverter with a gain of up to 20.5.

CHAPTER 10:Organic Floating Gate Transistor Memory Devices

Floating gate charge storage devices are one of the largest families of organic transistor-type memory electronics. The quantity of charge carriers stored in a specific trapping site can be precisely controlled in floating gate memory, breaking through the limitations of device size and meeting the requirement for high density data storage. In this chapter, we briefly introduce common charge storage materials, mostly metallic nanoparticles, used as charge storage elements. Then floating gate materials with various fabrication processes and chemical structures are discussed. In addition, the operating mechanism and future flexible digital memory electronic devices using floating gate charge storage layers are presented.

CHAPTER 11:Organic Ferroelectric Memory Devices

Ferroelectrics are polar substances of either solid (crystalline or polymeric) or liquid crystals, in which inverting the external electric field can reverse the spontaneously generated electric polarization. The bistable hysteresis of ferroelectric materials offers the possibility to develop electrically switchable data storage devices. Organic non-volatile memory devices based on ferroelectricity are a promising approach towards the development of low-cost memory technology. In addition, ferroelectric memory devices generally possess the advantages of long data or operating endurance, short switching time, and low-voltage operation. In this chapter, we discuss the latest developments of ferroelectric data storage memory devices based on three main device configurations, including capacitors, field-effect transistors, and diodes. Key materials and process issues for optimizing memory performance in each device architecture and thus realizing organic ferroelectric memory are discussed. The effects of the polymer orientation, interfacial engineering, device structure, and processing parameters on the memory switching characteristics are explored systematically.