Polyimide Gate Insulator Research Articles

Synthesis and characterization of a perfluorocyclobutane-containing cross-linked polyimide gate insulator for thin film transistor

We have synthesized a thermally curable polymeric gate insulator (TFVOB-SPI) through the modification of soluble polyimide (SPI) using a 4-(1,2,2-trifluorovinyloxy)benzoyl (TFVOB) chloride. The thermal cross-linking of TFVOB-SPI was done and prepared the cross-linked TFVOB-SPI thin film having the perfluorocyclobutane (PFCB) structure. The PFCB structure was formed by the radical mediated thermal cycloaddition of trifluorovinyl ether of TFVOB. The cross-linked TFVOB-SPI showed excellent thermal stability up to 495 °C with only 5% weight loss and excellent chemical resistance to common organic solvents. The pentacene thin-film transistor (TFT) with the cross-linked TFVOB-SPI as a gate dielectric exhibited a field effect mobility of 0.28 cm2/Vs with almost no hysteresis during the TFT operation.

Photo-crosslinkable and low-temperature processable polyimide gate insulator for pentacene thin-film transistors

We have prepared a photo-crosslinkable, low-temperature processable, and soluble polyimide (SPI-Cinnamoyl: SPI-CM) gate insulator. Firstly, the soluble polyimide with hydroxyl group (SPI-Hydroxyl: SPI-OH) was synthesized through one-step condensation polymerization of monomers, 5-(2,5-dioxytetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA) and 3,3’-dihydroxy-4,4’-diaminobiphenyl (HAB). And, then SPI-OH was further reacted with cinnamoyl chloride to make a photo-crosslinkable polyimide (SPI-CM). The thin film of photo-crosslinked SPI-CM (C-SPI-CM) exhibited a dielectric constant as 3.7 at 10 kHz, and leakage current density of <9.7 × 10−11 A/cm2. In addition, SPI-CM could be easily patterned by selective UV-light exposure. A pentacene thin-film transistor (TFT) with the photo-crosslinked SPI-CM as a gate dielectric showed a field effect mobility of 0.16 cm2/Vs.

Metal-oxide assisted surface treatment of polyimide gate insulators for high-performance organic thin-film transistors.

We developed a facile method for treating polyimide-based organic gate insulator (OGI) surfaces with self-assembled monolayers (SAMs) by introducing metal-oxide interlayers, called the metal-oxide assisted SAM treatment (MAST). To create sites for surface modification with SAM materials on polyimide-based OGI (KPI) surfaces, the metal-oxide interlayer, here amorphous alumina (α-Al2O3), was deposited on the KPI gate insulator using spin-coating via a rapid sol-gel reaction, providing an excellent template for the formation of a high-quality SAM with phosphonic acid anchor groups. The SAM of octadecylphosphonic acid (ODPA) was successfully treated by spin-coating onto the α-Al2O3-deposited KPI film. After the surface treatment by ODPA/α-Al2O3, the surface energy of the KPI thin film was remarkably decreased and the molecular compatibility of the film with an organic semiconductor (OSC), 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10), was increased. Ph-BTBT-C10 molecules were uniformly deposited on the treated gate insulator surface and grown with high crystallinity, as confirmed by atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis. The mobility of Ph-BTBT-C10 thin-film transistors (TFTs) was approximately doubled, from 0.56 ± 0.05 cm2 V-1 s-1 to 1.26 ± 0.06 cm2 V-1 s-1, after the surface treatment. The surface treatment of α-Al2O3 and ODPA significantly decreased the threshold voltage from -21.2 V to -8.3 V by reducing the trap sites in the OGI and improving the interfacial properties with the OSC. We suggest that the MAST method for OGIs can be applied to various OGI materials lacking reactive sites using SAMs. It may provide a new platform for the surface treatment of OGIs, similar to that of conventional SiO2 gate insulators.

The effect of thermal annealing on the layered structure of smectic liquid crystalline organic semiconductor on polyimide gate insulator and its OFET performance

The electrical performance of organic field-effect transistors (OFETs) depends on the quality of thin-film organic semiconductors, which is significantly affected by solution-processing conditions and additional processes. We investigated the effects of post-thermal annealing on the thin-film morphologies of liquid crystalline organic semiconductors on polyimide gate insulator surface and the FET performances of the films. The active material selected for the OFETs was 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-C10), which shows a highly ordered smectic E (SmE) mesophase and polycrystalline thin films feature very high mobility. We aimed to produce well defined molecular orientation and crystal structure in thin-film Ph-BTBT-C10 on polyimide gate insulator not typical SiO2 gate insulator via thermal annealing process. Uniform bilayer- or monolayer-structured polycrystalline thin films were obtained on polymer gate insulator after thermal annealing at a SmE (over 148°C) and SmA (over 213°C) liquid crystalline phase temperature, respectively. The OFET using bilayer-structured thin film showed high performance with a mobility of 2.27cm2/Vs.

Polyimide/polyvinyl alcohol bilayer gate insulator for low-voltage organic thin-film transistors

In this paper, we report the fabrication of a polyimide/polyvinyl alcohol (PVA) bilayer gate insulator for low-voltage organic thin-film transistors (TFTs). The introduction of a PVA layer to form a bilayer structure improves the dielectric and insulating properties of the gate insulator. Organic TFTs with 150nm-thick polyimide and PVA gate insulators were inactive at low operation voltages below 5V. Conversely, organic TFTs with 150nm-thick polyimide/PVA bilayer gate insulators exhibited excellent device performances. Our results suggest that the introduction of a PVA layer with a high dielectric constant could be a simple and efficient way to improve the device performance of low-voltage organic TFTs.

Low-temperature-annealed alumina/polyimide gate insulators for solution-processed ZnO thin-film transistors

Abstract We report here a low-temperature-annealed alumina/polyimide gate insulator with excellent electrical insulating properties for solution-processed ZnO TFTs. In this study, 150 nm-thick polyimide and 20 nm-thick alumina thin films were deposited by a simple spin-coating followed by a 200 °C-annealing process. With the deposition of the alumina interlayer, the surface of the polyimide film was successfully modified. We prepared ZnO TFTs annealed at 230 °C to investigate the potential of the prepared gate insulator. The field-effect mobility and the on/off current ratio of solution-processed ZnO TFTs with an alumina/polyimide gate insulator were 0.11 cm 2 /V s and 1.8 × 10 5 , respectively, whereas a ZnO TFT with a polyimide gate insulator was inactive. The alumina interlayer introduced here might provide a compatible interface for the ZnO semiconductor.

A high-temperature resistant polyimide gate insulator surface-modified with a YOx interlayer for high-performance, solution-processed Li-doped ZnO thin-film transistors

We report here a fully aromatic polyimide film with excellent electrical insulating properties and thermal stability. To use the polyimide as a gate insulator for high-performance solution-processed metal oxide thin-film transistors, the surface of a 350 nm thick polyimide film was modified with a 25 nm thick yttrium oxide interlayer. The YOx/polyimide gate insulator showed excellent gate insulating properties with a dielectric constant of 3.2 at 10 kHz and a leakage current density of 3.3 × 10−10 A cm−2 at 2 MV cm−1 after the 300 °C annealing process. We prepared solution-processed Li-doped ZnO thin-film transistors with the prepared gate insulators. After the surface modification with the interlayer, the field-effect mobility of the 300 °C annealed Li-doped ZnO thin-film transistor increased from 0.1 cm2 V−1 s−1 to 4.9 cm2 V−1 s−1.

Enhanced Performance of Solution-Processed Organic Thin-Film Transistors with a Low-Temperature-Annealed Alumina Interlayer between the Polyimide Gate Insulator and the Semiconductor

We studied a low-temperature-annealed sol-gel-derived alumina interlayer between the organic semiconductor and the organic gate insulator for high-performance organic thin-film transistors. The alumina interlayer was deposited on the polyimide gate insulator by a simple spin-coating and 200 °C-annealing process. The leakage current density decreased by the interlayer deposition: at 1 MV/cm, the leakage current densities of the polyimide and the alumina/polyimide gate insulators were 7.64 × 10(-7) and 3.01 × 10(-9) A/cm(2), respectively. For the first time, enhancement of the organic thin-film transistor performance by introduction of an inorganic interlayer between the organic semiconductor and the organic gate insulator was demonstrated: by introducing the interlayer, the field-effect mobility of the solution-processed organic thin-film transistor increased from 0.35 ± 0.15 to 1.35 ± 0.28 cm(2)/V·s. Our results suggest that inorganic interlayer deposition could be a simple and efficient surface treatment of organic gate insulators for enhancing the performance of solution-processed organic thin-film transistors.

Surface Modification of a Polyimide Gate Insulator with an Yttrium Oxide Interlayer for Aqueous-Solution-Processed ZnO Thin-Film Transistors

We report a simple approach to modify the surface of a polyimide gate insulator with an yttrium oxide interlayer for aqueous-solution-processed ZnO thin-film transistors. It is expected that the yttrium oxide interlayer will provide a surface that is more chemically compatible with the ZnO semiconductor than is bare polyimde. The field-effect mobility and the on/off current ratio of the ZnO TFT with the YOx/polyimide gate insulator were 0.456 cm(2)/V·s and 2.12 × 10(6), respectively, whereas the ZnO TFT with the polyimide gate insulator was inactive.

Surface energy control of soluble polyimide gate insulators by copolymerization method for high performance pentacene thin-film transistors

We have synthesized a series of surface energy controlled soluble polyimide (PI) gate insulators (KSPI-C1, KSPI-C3, and KSPI-C5) by one-step copolymerization method of the monomers 5-(2,5-dioxytetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride, 4,4-diaminodiphenylmethane, and 1-(3,5-diaminophenyl)-3-octadecylpyrrolidine-2,5-dione (DA-18-IM). The long alkyl chain containing DA-18-IM monomer was used to control the surface energy of PI polymers. Fully imidized PI polymers were found to be completely soluble in organic solvents such as N-methyl-2-pyrrolidone, dimethylacetamide, etc. Thermal gravimetric analysis exhibited that all polymers are stable up to more than 432°C with only 5wt.% weight loss. The glass transition temperatures of polymers are found to be between 208°C and 242°C by differential scanning calorimetry measurement. Thin films of all polymers could be fabricated at only 150°C and a pentacene thin-film transistor (TFT) with KSPI-C3 as a gate dielectric was found to exhibit the highest field effect mobility of 0.53cm2/Vs. Surface energy controlled PI polymers are promising candidates for gate dielectrics for organic TFTs.

Photo-patternable polyimide gate insulator with fluorine groups for improving performance of 2,7-didecyl[1]benzothieno[3,2-b][1]benzothiopene (C10-BTBT) thin-film transistors

Surface properties of gate insulators strongly affect the device performance of organic thin-film transistors (OTFTs). To improve the performance of OTFTs, we have developed photo-sensitive polyimide gate insulator with fluorine groups. The polyimide gate insulator film could be easily patterned by selective UV exposure without any photoinitiator. The polyimide gate insulator film, fabricated at 130°C, has a dielectric constant of 2.8 at 10kHz, and leakage current density of <1.6×10−10A/cm2 while biased from 0 to 90V. To investigate the potential of the polyimide with fluorine groups as a gate insulator, we fabricated C10-BTBT TFTs. The field-effect mobility and the on/off current ratio of the TFTs were measured to be 0.76±0.09cm2/Vs and >106, respectively.

Surface modification of polyimide gate insulators for solution-processed 2,7-didecyl[1]benzothieno[3,2-b][1]benzothiophene (C10-BTBT) thin-film transistors

The surface property of a polyimide gate insulator was successfully modified with an n-octadecyl side-chain. Alkyl chain-grafted poly(amic acid), the polyimide precursor, was synthesized using the diamine comonomer with an alkyl side-chain. By adding a base catalyst to the poly(amic acid) coating solution, the imidization temperature of the spin-coated film could be reduced to 200 °C. The 350 nm-thick polyimide film had a dielectric constant of 3.3 at 10 kHz and a leakage current density of less than 8.7 × 10(-10) A cm(-2), while biased from 0 to 100 V. To investigate the potential of the alkyl chain-grafted polyimide film as a gate insulator for solution-processed organic thin-film transistors (TFTs), we fabricated C(10)-BTBT TFTs. C(10)-BTBT was deposited on the alkyl chain-grafted polyimide gate insulator by spin-coating, forming a well-ordered crystal structure. The field-effect mobility and the on/off current ratio of the TFT device were measured to be 0.20-0.56 cm(2) V(-1) s(-1) and >10(5), respectively.

Probing a two-step channel formation process in injection-type pentacene field-effect transistors by time-resolved electric-field-induced optical second-harmonic generation measurement

By using time-resolved electric-field-induced optical second-harmonic generation measurement, we studied carrier motion in pentacene field-effect transistors (FETs) with poly-4-vinylphenol (PVP) and with polyimide (PI) gate-insulator whose active layers were depleted by pre-biasing. Upon removal of the pre-biasing, channel formation proceeded as a two-step process in FETs with PVP gate-insulator and a conduction channel was formed eventually. On the other hand, no conduction channel was formed in FETs with PI gate-insulator but two-step carrier propagation was observed in a similar way. Results showed that a local electric field induced on the gate-insulator surface gives a significant effect on the carrier injection and the following carrier transport.

Direct photo-patternable, low-temperature processable polyimide gate insulator for pentacene thin-film transistors

We have developed photo-sensitive, low-temperature processable, soluble polyimide (PSPI) gate insulator with excellent resistance to the photo-patterning process. The PSPI was synthesized through one-step condensation polymerization of monomers 5-(2,5-dioxytetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic anhydride (DOCDA) and 3,5-diaminobenzyl cinnamate (DABC). PSPI thin film, fabricated at 160°C, has a dielectric constant of 3.3 at 10kHz, and leakage current density of <1.7×10−10A/cm2, while biased from 0 to 100V. PSPI could be easily patterned by selective UV-light exposure and dipping into γ-butyrolactone. To investigate the potential of the polyimide as the photo-patternable gate insulator, we fabricated pentacene OTFTs and confirmed the PSPI’s resistance to the photo-patterning process. The photo-patternable polyimide shows promise as gate dielectrics for OTFTs.

Gamma-ray Irradiated Organic Thin Film Transistors Based on Perfluoropentacene with Polyimide Gate Insulator

Gamma-ray Irradiated Organic Thin Film Transistors Based on Perfluoropentacene with Polyimide Gate Insulator

Flexible Transistors with Low Temperature Curable Polyimide Gate Insulator

Flexible Transistors with Low Temperature Curable Polyimide Gate Insulator

&lt;sup&gt;60&lt;/sup&gt;Co Gamma–Ray Irradiation Effects on Pentacene-Based Organic Thin-Film Transistors

Electrical characterization of 60Co γ-ray radiation effects on pentacene-based organic thin-film-transistors having two kinds of gate insulator have been carried out. For transistors with SiO2 gate insulator, the threshold voltage shifts are consistent with positive charge trapping in the oxide and a “rebound” effect is observed. This “rebound” effect is attributed to the negatively charged interface traps generated during irradiation. For polyimide gate insulator, the threshold voltage continually decreases with an increasing total-dose. At total-dose of 1200 Gy (Si), for the SiO2 gate insulator, the field-effect mobility decreased by almost 80%, and for polyimide gate insulator, it decreased by 40%.

Environmentally Stable Transparent Organic/Oxide Hybrid Transistor Based on an Oxide Semiconductor and a Polyimide Gate Insulator

We fabricated environmentally stable and transparent organic/oxide hybrid transistor on a glass substrate using the conventional photolithography. The obtained device, which was composed of an In-Ga-Zn-O active layer/soluble polyimide (KSPI) organic insulator, showed a mobility of 6.65 cm2/Vs, a subthreshold swing slope of 350 mV/decade, a threshold voltage (VT) of 3.10 V, and an on-off ratio of 3.9 × 109. The transistor also showed good uniformity characteristics and was found to be environmentally stable for 90 days under ambient conditions.

Photocurable Polyimide Gate Insulator for Pentacene Thin-Film Transistor With Excellent Chemical Resistance by Low Temperature Processing

We introduce a photo-curable polyimide-based gate insulator for organic thin-film transistors (OTFTs) that allows low-temperature and solution-based processing and provide low leakage current density and high field-effect mobility in devices. Organic gate insulator (PI-TTE) was prepared from a blend of 75.2 wt% hydroxyl group containing polyimide (PI) and 23.8 wt% trimethylolpropane triglycidyl ether as the crosslinker, 0.5 wt% benzoyl peroxide, and 0.5 wt% triphenylsulfonium triflate as the photoacid generator (PAG). PI-TTE showed extremely low leakage current density as 2.33 × 10−10 A/cm2 at 3.3 MV/cm and exhibited a very stable capacitance (96.74 pF/mm2) and it is unchangeable up to 600 hrs. Pentacene TFT using PI-TTE as a gate dielectric showed a field effect mobility as 0.203 cm2/Vs and an on/off ratio of 1.55 × 105 with almost no hysteresis.

Comparative Study on Gate Insulators of Polymers and SiO2 in Transport Properties of p- and n-Type Organic Field-Effect Transistors

Field-effect mobilities and threshold voltages in organic field-effect transistors (OFETs) were studied to elucidate the difference of the OFETs performance between Si/SiO2 and flexible polymer substrates. The polymer OFETs were built on poly(ethylene naphthalate) (PEN) film as the substrate with polyimide (PI) as the gate-insulators. Pentacene and N,N'-ditridecylperylene-3,4,9,10-tetracarboxylicdiimide (PTCDI-C13) were employed as p- and n-type semiconductors. The n-type OFET on polymer substrates exhibited higher electron mobility and smaller threshold voltages compared with those on Si/SiO2. On the contrary, the p-type OFET on the Si/SiO2 substrate showed better transport performance than that on the polymer substrate. The results are discussed taking the difference of surface potential between SiO2 and PI gate-insulator, which possibly modifies OFET characteristics.