Facile Photo-cross-linking System for Polymeric Gate Dielectric Materials toward Solution-Processed Organic Field-Effect Transistors: Role of a Cross-linker in Various Polymer Types

Abstract

Energy-efficient solution-processed organic field-effect transistors (OFETs) are highly sought after in the low-cost printing industry as well as for the manufacture of flexible and other next-generation devices. The fabrication of such electronic devices requires high-functioning insulating materials that are chemically and mechanically robust to avoid lowering insulating properties during the device fabrication process or utilization of devices. In this study, we report a facile, fluorinated, UV-assisted cross-linker series using a fluorophenyl azide (FPA), which reacts with the C–H groups of a conventional polymer. This demonstrates the application of the cross-linked films in OFET gate dielectrics. The effects of the cross-linkable chemical structure of the FPA series on the cross-linking chemistry, photopatternability, and dielectric properties of the resulting films are investigated for low/high-k or amorphous/crystalline polymeric gate dielectric materials. The characteristics of insulating layers and behavior of OFETs containing these cross-linked gate dielectrics (for example, leakage current density (J), hysteresis, and charge trap density) depend on the polymer type. Furthermore, an organic-based complementary inverter and various printable OFETs with excellent electrical characteristics are successfully fabricated. Thus, these reported cross-linkers that enable the solution process and patterning of well-developed conventional polymer dielectric materials are promising for the realization of a more sustainable next-generation industrial technology for flexible and printable devices.

Mass-Synthesized Solution-Processable Polyimide Gate Dielectrics for Electrically Stable Operating OFETs and Integrated Circuits

“…As shown in Figure 3b, the pattern image represents the mixed molecular orientation of C 10 -DNTT with peaks related to face-on orientation (white asterisks) and edge-on orientation (white dotted line with 00l, 11l, 02l, and 12l peaks) [27], which is consistent with the AFM results. It was confirmed that this type of C 10 -DNTT morphology showed suitable charge transfer for OFETs, as in previous studies [20]; therefore, it was found that our PI dielectric thin film also gave rise to an organic semiconducting shape suitable for manufacturing OFETs and integrated circuits. The fabrication of bottom-gate top-contact OFETs was conducted according to the method described in the Materials and Methods section (Figure 4a).…”

“…Figure 2c shows the leakage current density (I leak ) of the PI films. I leak was 1.98 × 10 −9 A cm −2 at 2 MV cm −1 which is comparable or superior to that of other polymeric insulating materials [2,20]. Therefore, our synthesized PI layers have good insulating properties and suitable characteristics for gate dielectrics of OFETs or integrated circuits.…”

“…As illustrated in Figure 2b, the dielectric constant (k) values of the PI were yielded at the level of 2.6, the value of which was roughly similar over a wide range of operating frequencies, from 2.62 at 70 Hz to 2.57 at 1 MHz. This phenomenon of showing constant k values according to the frequency means that there is no irregular arrangement of dipoles in the dielectric layers, which suggests the possibility of implementing a device without hysteresis by dielectrics when applied to a logic device including a transistor [20,21]. Figure 2c shows the leakage current density (I leak ) of the PI films.…”

“…Figure 2a shows AFM images of the prepared PI layers. The AFM image exhibited a smooth amorphous surface with a root-mean-square (RMS) roughness value of 0.212 nm, and this low RMS roughness value of less than 0.5 nm can provide a favorable environment for the growth of organic semiconducting crystals [5,19,20]. Furthermore, in order to identify the possibility of using this PI thin film as a dielectric layer for OFETs, the electrical characteristics were evaluated by fabricating a metal-insulator-metal (MIM)-structured capacitor with Al and thermally prepared PI layers (thickness: 150 nm) on Si/SiO 2 wafers.…”

“…ing constant k values according to the frequency means that there is no irregular arrangement of dipoles in the dielectric layers, which suggests the possibility of implementing a device without hysteresis by dielectrics when applied to a logic device including a transistor [20,21]. Figure 2c shows the leakage current density (Ileak) of the PI films.…”