N-type Organic Thin-film Transistors Research Articles

Perylene diimides functionalized with N-thiadiazole substituents: Synthesis and electronic properties in OFET devices

Two new perylene diimide derivatives N,N′-bis(5-tridecyl-1,3,4-thiadiazol-2-yl)perylene-3,4,9,10-tetracarboxylic 3,4:9,10-diimide (PDI-T1) and N,N′-bis[5-(1-hexyl)nonyl-1,3,4-thiadiazol-2-yl]perylene-3,4,9,10-tetracarboxylic 3,4:9,10-diimide (PDI-T2), achieved by functionalizing the basic perylene molecular core at imide nitrogen with 1,3,4-thiadiazole rings, have been synthesized. Both these compounds make possible the fabrication of n-type organic thin-film transistors able to work in air, even when bare SiO2 surfaces are utilized as gate dielectric. As active channels of transistors in the bottom-contact bottom-gate configuration, PDI-T1 evaporated films exhibited a maximum mobility of 0.016cm2/Vs in vacuum. For evaporated PDI-T2 films, instead, mobility values were found to be more than one order of magnitude lower, because of their reduced degree of crystalline order. However, PDI-T2 films can be also deposited by solution techniques and field-effect transistors were fabricated by spin-coating, displaying mobility values ranging between 10−6 and 10−5cm2/Vs. Similar to what previously found for other perylene diimide derivatives, our experimental work also demonstrates that the electrical response of both PDI-T1 and PDI-T2 transistors under ambient conditions can be improved by increasing the level of hydrophobicity of the dielectric surface.

8.2: Flexible N‐type Organic Thin Film Transistors

AbstractN‐type organic thin film transistors have been successfully fabricated on G1 production line. Simple solution‐spin‐coating method followed by conventional photolithography process is used for all organic thin film deposition and patterning in the devices The devices can be used for electrophoretic display (EPD).

Improved Performance of Fluorinated Copper Phthalocyanine Thin Film Transistors Using Para-hexaphenyl as the Inducing Layer

We demonstrate n-type organic thin film transistors (OTFTs) employing copper hexadecafluorophthalocyanine (CuPcF16) as the active layer and para-hexaphenyl (p-6p) as the inducing layer. Compared with the CuPcF16-based OTFTs without the p-6p inducing layer, the performance of the CuPcF16/p-6p OTFTs is greatly improved. The charge carrier field-effect mobility μ, on-off current ratio Ion/Ioff and threshold voltage VT of the CuPcF16/p-6p OTFTs are 0.07 cm2/V·s, 1.61 × 105 and 6.28 V, respectively, approaching the level of a single crystal device. The improved performance is attributed to the introduction of p-6p to form a highly oriented and continuous film of CuPcF16 with the molecular π-π stack direction parallel to the substrate.

Simulation of organic inverter

Pentacene and N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13H27) have been used as organic semiconductors for the fabrication of p-type and n-type organic thin-film transistors (OTFTs). Both types of semiconductors are well-established and demonstrate good performance in single devices, but few competitive results have been reported in complementary circuits. In this manuscript, we show the fabrication, electrical characterization and simulation of an organic complementary inverter using pentacene and PTCDI-C13 as active semiconductors. Simulation was done using a model with physical aspects. We report good fitting of p-type and n-type parameters for the OTFT model and good results for DC transfer characteristics of the organic complementary inverter. The fitting of the parameters of the OTFT model is performed using an optimized parameter extraction technique which is using fuzzy logic to adjust the parameters to its optimal value.

High Performance Organic Thin Film Transistors with Solution Processed TTF-TCNQ Charge Transfer Salt as Electrodes

Fabrication of high-performance organic thin film transistors (OTFTs) with solution processed organic charge transfer complex (TTF-TCNQ) film as bottom contact source-drain electrodes is reported. A novel capillary based method was used to deposit the source-drain electrodes from solution and to create the channel between the electrodes. Both p- and n-type OTFTs have been fabricated with solution deposited organic charge transfer film as contact electrodes. Comparison of the device performances between OTFTs with TTF-TCNQ as source-drain electrodes and those with Au electrodes (both top and bottom contact) indicate that better results have been obtained in organic complex film contacted OTFT. The high mobility, low threshold voltage, and efficient carrier injection in both types of OTFTs implies the potential use of the TTF-TCNQ based complex material as low-cost contact electrodes. The lower work function of the TTF-TCNQ electrode and better contact of the complex film with the organic thin film owing to the organic-organic interface results in efficient charge transfer into the semiconductor yielding high device performance. The present method having organic metal as contact materials promises great potential for the fabrication of all-organics and plastic electronics devices with high throughput and low-cost processing.

Ultra-low voltage air-stable polyelectrolyte gated n-type organic thin film transistors

Complementary circuits, processing digital signals, are a cornerstone of modern electronics. Such circuits require both p- and n-type transistors. Polyelectrolytes are used as gate insulators in organic thin film transistors (OTFTs) to establish an electric double layer capacitor upon gate bias that allows low operational voltages (<1 V). However, stable and low-voltage operating n-channel organic transistors have proven difficult to construct. Here, we report ultra-low voltage n-channel organic polymer-based transistors that are stable in ambient atmosphere. Our n-type OTFTs exhibit on/off ratios around 103 for an applied drain potential as low as 0.1 V. Since small ions are known to promote electrochemical reactions within the semiconductor’s channel bulk and typically slow down the transistor, we use a solid polycationic gate insulator that suppresses penetration of anions into the n-channel semiconductor. As a result, our n-channel OTFTs switch on in under 5 ms and off in less than 1 ms.

Inkjet printing of transparent, flexible, organic transistors

Two different types of all-organic, transparent transistors, namely Organic Thin Film Transistors (OTFTs) and Organic Electrochemical Transistors (OECTs), were fabricated on transparent, flexible plastic substrates by means of inkjet printing. In OTFTs the source, drain and gate electrodes were inkjet printed using a poly(3,4ethylenedioxythiophene)/polystyrene sulfonate (PEDOT:PSS ) solution, while a thermally sublimated layer of Parylene C acted as gate dielectric. Two kinds of organic semiconductors were used as active layers: 6,13-bis(triisopropylsilylethynyl) pentacene for p-type and N1400 for n-type OTFTs. For OECTs, all electrodes were also realized by inkjet printing deposition of a PEDOT:PSS solution. Electrical output characteristics of both kinds of devices are reported, demonstrating that the performances of our devices may be compared to those of transistors fabricated employing different realization techniques.

Making Contacts to n-Type Organic Transistors Using Carbon Nanotube Arrays

We investigated the performance of carbon nanotube (CNT) array electrodes applied to n-type and ambipolar phenyl-C61-butyric acid methyl ester (PCBM) thin film transistors on a SiO(2) dielectric substrate. Compared to conventional Au electrodes, CNT arrays provide better injection efficiency, improved switching behavior, higher electron mobility, and lower contact resistance. Experiments on ambipolar PCBM transistors indicate that the injection performance is enhanced by the electrostatics of the CNT contacts, which promotes electron and hole tunneling across Schottky barriers at the PCBM/nanotube interface. The use of CNT arrays is a valid replacement to low workfunction metals, which are often reactive in air and difficult to process. Our work paves the way for a widespread use of carbon nanotube array electrodes in high-performance n-type and p-type organic thin film transistors.

Air-stable n-type organic thin-film transistor array and high gain complementary inverter on flexible substrate

Air-stable n-type organic thin-film transistor (TFT) arrays and a complementary inverter circuit were fabricated on a flexible substrate. A benzobis(thiadiazole) (BBT) derivative-based TFT showed excellent air- stability and performances such as an electron mobility of over 0.1 cm2/V s, a large ON/OFF ratio over 108 when combined with a cross-linkable olefin-type polymer gate dielectric. In addition, an organic complementary inverter that combined the BBT derivative and a pentacene TFT demonstrated a sharp switching behavior and a high gain of over 150. We attribute these excellent characteristics to a combination of the low-lying lowest unoccupied molecular orbital level of n-type semiconductor material and the low interface trap of the gate dielectric.

Fabrication of n‐ and p‐Type Organic Thin Film Transistors with Minimized Gate Overlaps by Self‐Aligned Nanoimprinting

A nanoimprinting process that enables fabrication of self-aligned p- and n-type organic thin film transistors with small channel lengths is presented. Nanoimprint lithography with back-side exposure permit precise definition of the channel length down to the submicrometer regime and a diminutive gate to source/drain overlap. The self-aligned manufacturing process enables transistor setups with minimized electrode overlaps resulting in distinct decrease of parasitic capacitances and considerable increase in transition frequency. Fully functional small channel OTFTs with p- and n-type semiconductors are fabricated on glass as well as on flexible substrates with transition frequencies up to 400 kHz.

Analyses of Electrical Properties and Stability of Organic Complementary Transistors

Organic complementary inverters were fabricated by integrating organic - and -channel thin film transistors. Bottom-gate and top-contact organic thin film transistors (OTFTs) with polyimide (PI)-modified silicon oxide dielectrics and silver electrodes exhibit similar carrier mobilities, threshold voltages, drain currents, and hysteresis. A gate-bias stress test was performed on both p- and n-type OTFTs. The threshold voltages and hysteresis decreased according to the space charge separation in the PI layer which could be explained by a space charge model. The complementary inverters based on these organic transistors exhibit high noise margins (NMs), a transfer voltage located at , and a gain of 40 with supply voltage of . The electrical stability of the inverters measured during gate-bias stress reveals that the variations in the NMs and transition voltage remained below 5%.

Properties of C60 thin film transistor based on polystyrene

This paper reports that the n-type organic thin-film transistors have been fabricated by using C60 as the active layer and polystyrene as the dielectric. The properties of insulator and the growth characteristic of C60 film were carefully investigated. By choosing different source/drain electrodes, a device with good performance can be obtained. The highest electron field effect mobility about 1.15 cm2/(V · s) could reach when Barium was introduced as electrodes. Moreover, the C60 transistor shows a negligible ‘hysteresis effect’ contributed to the hydroxyl-free of insulator. The result suggests that polymer dielectrics are promising in applications among n-type organic transistors.

Improved Injection in n-Type Organic Transistors with Conjugated Polyelectrolytes

To improve injection in n-type organic thin film transistors (OTFTs), a thin conjugated polyelectrolyte (CPE) layer was interposed between electrodes and the semiconductor layer. OTFTs were fabricated with [6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) and Au source and drain contacts. We demonstrate that the insertion of CPEs beneath top-contact Au source/drain electrodes can be a very effective strategy for improving the carrier injection and reducing turn-on threshold voltages of n-channel OTFTs. Ultraviolet photoemission spectroscopy (UPS) indicates that the decrease of the electron injection barrier is consistent with organized dipoles at the metal/organic interface.

Low-Voltage and Hysteresis-Free N-Type Organic Thin Film Transistor and Complementary Inverter with Bilayer Gate Insulator

In this paper, we report on a low-voltage-operation n-type organic thin film transistor (OTFT) and a complementary inverter circuit using a thiazolothiazole derivative as an organic semiconductor (OSC). To achieve the low voltage and stable operation of the n-type OTFT, a bilayer structure consisting of a thin low-k polymer layer and a high-k Ta2O5 layer was used and investigated as the gate insulator. Atomic force microscopy images of the OSC film on the hydrophobic polymer showed densely distributed small grains, and the corresponding OTFT exhibited hysteresis-free and excellent n-type performance, for example, an electron mobility of 0.23–0.35 cm2 V-1 s-1. In addition, the n-type OTFT with a thinner polymer layer exhibited a low operating voltage of less than 10 V while maintaining excellent characteristics. A complementary inverter based on the thiazolothiazole derivative and pentacene was also fabricated using the bilayer gate insulator. The switching operation of the inverter was achieved at a low voltage of 5–10 V.

High-performance n-type organic field-effect transistors fabricated by ink-jet printing using a C 60 derivative

We report on the performance of ink-jet-printed n-type organic thin-film transistors (OTFTs) based on a C 60 derivative, namely, C 60-fused N-methyl-2-(3-hexylthiophen-2-yl)pyrrolidine (C 60TH-Hx). The new devices exhibit excellent n-channel performance, with a highest mobility of 2.8 × 10 −2 cm 2 V −1 s −1, an I On/I Off ratio of about 1 × 10 6, and a threshold voltage of 7 V. The C 60TH-Hx films show large crystalline domains that result from the influence of an evaporation-induced flow, thus leading to high electron mobility in the ink-jet-printed devices.

Perylrene-based n-type field-effect transistors prepared by the neutral cluster beam deposition method

We present the first application of the neutral cluster beam deposition (NCBD) method to prepare n-type organic thin-film transistors with a top-contact structure based on N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13). Systematic analysis was carried out to examine the effects of surface passivation and thermal post-treatment on the morphology and crystallinity of P13 active layers and device performance, together with operational stability as a function of time. The high room-temperature field-effect mobility of 0.58 cm 2/Vs for the thermally post-treated devices was obtained under ambient conditions. The comparative study of the transport mechanisms responsible for conduction of the electron carriers over a temperature range of 10–300 K indicated that surface modification and thermal post-treatment decrease total trap density and activation energy for carrier transport by reducing structural disorder.

N-type PTCDI–C 13H 27 thin-film transistors deposited at different substrate temperature

N-type organic thin-film transistors based on N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide have been fabricated by thermal evaporation at different substrate temperatures. The best device was obtained at 120 °C with a field-effect mobility of 0.12 cm 2/V·s and threshold voltage around 46 V. In this work, the microstructure of the films is correlated with the device performance. In particular, the dependence of the activation energy for the channel conductance on gate voltages has been related to the properties of the layers.

Anthraquinone derivatives affording n-type organic thin film transistors

New anthraquinone derivatives were prepared and used as active layers of organic field-effect transistors (OFETs); these devices showed good n-type characteristics and the quinones were found to be useful for organic semiconductors in OFETs.

High Performance N-type Organic Thin-Film Transistors with Inert Contact Metals

AbstractThin film growth by high vacuum evaporation of the n-type organic semiconductor 5, 5″′-diperfluorohexylcarbonyl-2,2′:5′,2″:5″,2″′-quaterthiophene (DFHCO-4T) on poly-(α-methylstyrene)-coated n++-Si/SiO2 substrates is investigated at various deposition fluxes and substrate temperatures. Film characterization by atomic force microscopy reveals typical Stransky-Krastanov growth. Transistors with Au source-drain top contacts and optimized DFHCO-4T deposition conditions attain an apparent saturation mobility of 4.6 cm2/Vs, whereas this parameter is 100× lower for similar transistors with LiF/Al top contacts. We explain this lower performance by the formation of a thin interfacial layer with poor injection properties resulting from a redox reaction between Al and DFHCO-4T.

Influence of the contact metal on the performance of n-type carbonyl-functionalized quaterthiophene organic thin-film transistors

Organic thin-film transistors using 5, 5‴-diperfluorohexylcarbonyl-2,2′:5′,2″:5″,2‴-quaterthiophene (DFHCO-4T) as the electron conducting organic semiconductor are fabricated and the performance of these transistors with different top-contact metals is investigated. Transistors with Au source-drain top contacts attain an apparent saturation mobility of 4.6 cm2/V s, whereas this parameter is 100 times lower for similar transistors with Al/LiF top contacts. We explain this lower performance by the formation of a thin interfacial layer with poor charge injection properties resulting from a redox reaction between Al and DFHCO-4T.