Dipolar Polyimides With a Clever Balance in Dielectric Performance by Introducing a Twisted Fluorene Structure for the Development of Electronic Applications

Temperature resistant amorphous polyimides with high intrinsic permittivity for electronic applications

been realized using organic thin-fi lm transistors (OTFTs) as the essential element. In the majority of these applications OTFTs are integrated either in the form of arrays or as digital logic. The fundamental building block of digital logic is the inverter, a circuit that inverts an input signal. Much work has been devoted in the last fi ve years to design unipolar inverters using p-typeonly OTFTs. [ 18‐23 ] Unfortunately, unipolar logic based on single gate OTFTs always suffers from high power consumption and low noise margin coupled with high noise margin variability and therefore impedes the fabrication of complex circuits having hundreds or more logic gates. [ 19,22,23 ] In this context, it stands

Low-voltage operation is one of the prerequisites for the practical applications of the organic thin-film transistors (OTFTs). Up to date, the most reported low-voltage operatable OTFTs use a bottom-gate structure, and are fabricated by several different technologies in the whole process, in which the organic semiconductors and/or gate dielectrics are prepared in the expensive vacuum equipment. The simple fabricating technologies and fewer processes can better demonstrate the inherent advantages, and enhance the commercial competitiveness of OTFTs. Here, we propose a strategy to fabricate the binary polymers gate dielectric by one-step spin-coating in the top-gate structured flexible OTFTs, by which not only the device performances are prominently improved, but also the fabricating process of the OTFTs is minimized. As a result, the flexible OTFTs exhibit a high mobility over 0.5 cm2 Vs−1, low threshold voltage near to −0.5 V, and excellent mechanical bending durability with a very slightly performances degradation after the tensile and compressive bending at a small curvature radius of 3.0 mm over 1000 cycles.

ABSTRACTIn the past decades organic thin film transistors (OTFTs) have been notably studied due to their interesting properties. Not only they can be processed by simple methods such as inkjet printing but also open the doors to new applications for cheap plastic electronics including electronic tags, biosensors, flexible screens,… However, the measured field-effect mobility in OTFTs is relatively low compared to inorganic devices. Generally, such low field-effect mobility values result from extrinsic effects such as grain boundaries or imperfect interfaces with source and drain electrodes. It has been shown that reducing the number of grain boundaries between the source and drain electrodes improves the field effect mobility.1-3 Therefore, it is important to understand the transport mechanisms by studying the structure of organic thin films and local electrical properties within the channel and at the interfaces with source and drain electrodes in order to improve the field-effect mobility in OTFTs. Kelvin probe force microscopy (KPFM) is an ideal tool for that purpose since it allows to simultaneously investigation of the local structure and the electrical potential distribution in electronic devices. In this work, the structure and the electrical properties of OTFTs based on dioctylterthiophene (DOTT) were studied. The transistors were fabricated by spin-coating of DOTT on the transistor structures with treated (silanized) and untreated channel oxide. The potential profiles across the channel and at the metal-electrode interfaces were measured by KPFM. The effect of surface treatment on hysteresis effects was also studied. Smaller crystals and a lower threshold voltage were observed for the silanized devices. Hysteresis effects appeared to be less important in modified devices compared to the untreated ones.

We report here on the design, processing, and dielectric properties of low surface energy organic/inorganic hybrid dielectric films for low‐voltage operation of organic thin‐film transistors (OTFTs). The hydrophobic hybrid dielectric films are easily fabricated by one‐step spin coating of a zirconium chloride precursor in an octadecyltrimethoxysilane solution under ambient conditions, followed by thermal curing at low temperatures (approximately 150°C). These novel dielectrics exhibit excellent surface smoothness (root‐mean‐square roughness is <0.5 nm), great insulating property (leakage current densities <10−6 A/cm2), and high capacitance (365 nF/cm2). In addition, the surface nature of the hybrid dielectric is hydrophobic (water contact angle is 105°), without any further surface modifications, which is highly compatible with organic semiconductors. Consequently, the hybrid dielectrics integrated into the pentacene OTFTs function at relatively low voltages (< −2.5 V) with excellent TFT characteristics (mobility: 0.31 cm2/V·s, on/off current ratio: 105, low threshold voltage: down to −0.7 V).

Inkjet printed silver (IJP Ag) source/drain (S/D) and gate electrodes were incorporated into a bottom-gate bottom-contact organic thin film transistor (OTFT) architecture to develop all-solution-processed low voltage OTFTs. With well controlled ink wetting on a cross-linked polyvinyl-alcohol surface, IJP Ag S/D electrode pairs were fabricated with controllable short channels down to 20 μm using a Dimatix 2831 inkjet printer with a 10 pL cartridge, and formed good contacts with the organic semiconductor layer. IJP gate electrodes with a low flat surface profile were also achieved to obtain OTFTs of high quality gate dielectric layer for low leakage current. The fabricated low voltage all-solution-processed OTFTs present good device performance with a low operation voltage below 2 V, a mobility of 0.3 cm2 V−1 s−1, and an ON/OFF current ratio larger than 104.

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.

Organic thin-film transistor (OTFT)-driven 5×5 polymer-dispersed liquid crystal (PDLC) display cells on a flexible plastic substrate have been developed. It is necessary to increase the maximum usable gate voltage of OTFT to obtain a high contrast ratio. We propose a stacked gate insulator that consists of polyvinylphenol and anodized Ta2O5 for decreasing the gate leakage current and increase the maximum voltage. The OTFT with the insulator showed a field-effect mobility of 0.4 cm2/(V s), a current on/off ratio of 105, a low threshold voltage of 1.1 V, and a subthreshold slope of 0.2 V/decade. Leakage current was successively decreased up to a gate voltage of 15 V, maintaining a low-voltage operation of OTFT. Double passivation layers using polyvinylalcohol and photosensitive acrylic material are also proposed to prevent the degradation of OTFT by liquid crystal. The bending characteristics of OTFT on plastic substrates were also measured for various radiuses of curvature. The OTFT can operate at a radius of curvature exceeding 20 mm. On the fabricated display cells, we confirmed a good display operation with a contrast ratio of 10:1 with a low driving voltage of 12–13 V.

Pentacene organic thin-film transistors (OTFTs) using LaxNb(1−x)Oy as gate dielectric with different La contents (x = 0.347, 0.648) have been fabricated and compared with those using Nb oxide or La oxide. The OTFT with La0.648Nb0.352Oy as gate dielectric can achieve a high carrier mobility of 1.14 cm2V−1s−1 (about 1000 times and 2 times those of the devices using Nb oxide and La oxide, respectively), and has negligible hysteresis of −0.130 V, small sub-threshold swing of 0.280 V/dec, and low threshold voltage of −1.35 V. AFM and XPS reveal that La can suppress the formation of oxygen vacancies in Nb oxide while Nb can alleviate the hygroscopicity of La oxide, which results in a more passivated and smoother dielectric surface, leading to larger pentacene grains grown and thus higher carrier mobility. The OTFT with Nb oxide has an anticlockwise hysteresis but the device with La oxide shows an opposite direction. This can be explained in terms of donor-like traps due to oxygen vacancies and acceptor-like traps originated from hydroxyl ions formed after La2O3 absorbing water moisture.

ABSTRACT: Thin-Film Transistors (TFTs) are a substantial technological advancement in recent decades for various applications. The source/drain electrode layer and organic active layer thicknesses of Organic Thin-Film Transistors (OTFTs) should be optimized for better device performance. Organic electronics have been used for a wide range of applications, including flexible screens, smart digital devices, and photovoltaic cells, because of their flexibility and environmental sensitivity. The OTFT has the capability to match the efficiency of thin-film amorphous Silicon transistors, while also being companionable with low-temperature solution/printing-processed fabrication on flexible coupling substrates. The OTFTs are a valuable tool for determining unipolar carrier transport parameters in various situations.In this present research work, authors have utilized the concept of OTFTs in the assessment of bipolar transport properties in active layer blends. It offers a strategy to improve the precision of the assessment. Thereafter, in this this research work, impacts of active layer thickness on physical parameters of OTFT device performance have been realized. The 2D numerical device simulators have been used to examine the proposed OTFT structures. The discussion focuses on the various characteristics and parameters of OTFTs. The OTFTs are transistors that manage electric current flow using organic semiconductors as an active layer. The output and transfer characteristics of various OTFT structures have been used to calculate the performance characteristics of OTFTs. Optimizing the OTFT's organic active layer thickness is critical for high device performance. Both photo-current and photo-responsivity exhibit the same variation trend with increasing organic active layer thicknesses, increasing rapidly for a while and then tending to saturate at high values. The research findings demonstrate the impact of these parameters on device performance and temperature and the need to optimize these variables in the device. The carrier mobility of the high-performance P3HT: PCBM-based OTFT structure was approximately 10 cm2/Vs, and an ON/OFF current ratio of ~103. These results are compatible with those OTFTs fabricated previously. Research Methodology, Results, and Discussions A schematic structure is shown in Figure 1(a) proposed structure top view, and 1(b) a side view of the proposed structure used for simulation. Top-gate OTFT and bottom-gate OTFT geometrical structures have been used in this OTFT. The device's contact resistance, field mobility, and threshold voltage degrade subjected to bias stress. Since top-gate OTFT has a higher device degradation, the authors used bottom-gate OTFT. Due to the distinct properties here in this work the authors utilized conventional materials such as a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as the active layer. A P3HT: PCBM mix is simulated with an electronic device simulator and analyses the variation in active layer thickness that affects the device's performance and the factors that influence the performance of the device in this research work. The output and transfer characteristics of OTFTs have been realized using proper boundary conditions and OTFT physics. The proposed OTFT structures' output and transfer characteristics have been evaluated, and the simulated results show that the optimized structure's drain current (Id, max) is ~2.85 μA. The obtained results show that the device has good transfer and output characteristics at lower gate voltages. With increasing organic active layer thicknesses, both photo-current and photo-responsivity exhibit the same variation trend of increasing sharply at first and then tending to saturate at high values. Conclusion The simulation results examined the performance of devices built with bottom-gate OTFTs. A detailed analysis of the influence of active layer thickness on the OTFT configuration was realized. The device has the advantage of operating at a lower gate voltage, transforming it into a gate efficient control device. The operation at a lower voltage improves electrical stability. The electric field of the OTFT is 1.4x106 V/cm is obtained. The ON/OFF current ratio is higher. The outcomes of this analysis have been optimized and extracted after being tested in various contexts. The findings demonstrated that the suggested concept might be used to make rollable active-matrix displays, nonvolatile memory, sensors, and printed electronic devices. This work also reduces the SCEs and shows more efficient performance than traditional MOSFETs. Together with all application areas, the most important research area has been argued to be the simple manufacturing technique of OTFT with low production cost and non-breakable impacts that can be bent and folded. This device will be optimized with fabrication using these materials in the future, and thereafter, its characteristic will be verified with the simulated results. Figure 1

The influence of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) agglomerated nanostructure on device performance of pentacene-based organic thin-film transistors (OTFTs) were reported. The presence of PCBM layers on a SiO2 gate dielectric resulted in a good electrical characteristics of pentacene-based OTFTs, including a relatively high mobility (μ = 0.95-2.2 cm2 V-1 s-1), low threshold voltages (Vth = -1.1 - -5.4 V), a high on/off current ratio (Ion/Ioff = 104), and a high value of subthreshold slope (SS = 6.5 V/decade). The surface topography studies reveal that the PCBM nanostructure could favor the reduction of grain boundaries, which resulted in a better transistor performance of pentacene-based OTFTs. The influence of PCBM on the molecular microstructure of pentacene thin films elucidates a reasonable explanation for higher performance on OTFTs.

Mono-chrome phosphorescence Organic light emitting diodes (OLEDs) operated by organic thin-film transistors (OTFTs) with a 32×32 array are fabricated with a novel method, and the results reveal a fabulous demonstration. The later isolation, which segregated source/drain electrodes and an OLED cathode, was designed in our OTFT-OLED pixel. In the OTFT-OLED process; we used the polymer isolating layer which was deposited by spin coating and patterned by traditional photo-lithography before the organic semiconductor and OLED deposition. However, the residue polymer affect of OTFT electric properties which have poor mobility (5×10-4 cm2/V-s), a lower on/off ratio (~103), and a positive threshold voltage (4.5 V), and devices, have poor uniformity. Using UV-Ozone treatment could enhance OTFT mobility (2×10-2 cm2/V-s) and permit higher devices uniformity, but the threshold voltage would still have a positive 5.1 V. This threshold voltage was not a good operation mode for display application because this operation voltage was not fit for our driving systems. In order to overcome this problem, a new structure of OTFT-OLED pixel was designed and combined with a new-material isolating layer process. This new process could fabricate an OTFT-OLED array successfully and have a nice uniformity. After the isolating layer process, OTFT devices have a higher mobility (0.1×10-2 cm2/V-s), a higher on-off ratio (~107) a lower threshold voltage (-9.7 V), and a higher devices uniformity.

Flexible inkjet-printed dual-gate organic thin film transistors and PMOS inverters: Noise margin control by top gate

(K0.5Na0.5)NbO3–Bi(Zn0.5Zr0.5)O3 perovskite ceramics: High relative permittivity, low dielectric loss and good thermal stability

The authors report on the solution-processed planar bottom-contact (pBC) organic thin-film transistors and contact effect on gate threshold voltage incorporating regioregular poly(3-hexylthiophene) active layer. By employing pBC configuration, the transistors on SiO2∕Si without surface modification show much higher mobility, lower threshold voltage, and narrower dispersion of threshold voltage when compared to the conventional bottom-contact counterparts. The high mobility and lower threshold voltage are attributed to an improved contact at the interface between the source/drain electrodes and the poly(3-hexylthiophene) active layer.