Solution-Processable, Thin, and High-κ Dielectric Polyurea Gate Insulator with Strong Hydrogen Bonding for Low-Voltage Organic Thin-Film Transistors

Abstract

We developed a solution-processable, thin, and high-dielectric polyurea-based organic gate insulator for low-voltage operation and high performance of organic thin-film transistors (OTFTs). A 60 nm-thick polyurea thin film exhibited a high dielectric constant of 5.82 and excellent electrical insulating properties owing to strong hydrogen bonding. The hydrogen bonding of the synthesized polyurea was confirmed using infrared spectroscopy and was quantitatively evaluated by measuring the interactive force using atomic force microscopy. Moreover, the effect of hydrogen bonding of polyurea on the insulating properties was systematically investigated through the combination of various monomers and control of the thickness of the polyurea film. The dinaphtho[2,3- b:2',3'- f]thieno[3,2- b]thiophene-based OTFTs with the polyurea gate insulator showed excellent thin-film transistor (TFT) performance with a field-effect mobility of 1.390 cm/V·s and an on/off ratio of ∼10 at a low operation voltage below 2 V. In addition, it is possible to fabricate flexible polymer organic semiconductor (OSC)-based TFT devices using a solution process, owing to excellent solvent stability in various organic solvents. We believe that the solution-processable polyurea gate insulator with a high dielectric constant and good insulation properties is a promising candidate for low-voltage-operated OTFTs using various OSCs.

Newly Synthesized Nonvacuum Processed High‐k Polymeric Dielectrics with Carboxyl Functionality for Highly Stable Operating Printed Transistor Applications

“…[ 5 ] Therefore, in order to overcome this issue, it is essential to increase the dielectric constant (k) or reduce the thickness of dielectric layers of the OFETs while maintaining their strong insulation characteristics, low leakage current, and high breakdown voltage, which yields a high capacitance per unit area value ( C i ), thereby allowing a maximized drain current to flow at low operating voltage conditions. [ 4,6 ]…”

“…In this regard, polymeric materials have many advantages over oxide‐based dielectric materials as gate dielectrics: 1)They have a natural compatibility with OFETs constructed with OSCs and plastic substrates, which reduces trapsites between the dielectrics and OSCs and improves the morphology of the OSC by endowing it with hydrophobic surface properties; [ 10 ] 2)Their structures can be easily tailored through molecular design strategies and chemical synthesis, which enables the functionalization of the dielectric layer for various purposes; [ 4b ] 3)They possess suitable characteristics for next‐generation devices, such as their intrinsic flexibility and capability to undergo solution‐processing at low temperatures. [ 4a,6 ] …”

“…value (C i ), thereby allowing a maximized drain current to flow at low operating voltage conditions. [4,6] To date, thin films of SiO 2 and other oxide-based dielectric materials have been generally utilized as gate insulating layers for low-voltage driving due to their small leakage current and relatively high-k values. [4a,7] However, conventional oxide-based materials generally contain intrinsic polar moieties such as hydroxyl groups which can act as charge generation and trapsites during the operation of OFETs, resulting in double-slope nonideality characteristics as well as a threshold voltage shift (ΔV th ) and concomitant reduction in current when the device is continuously biased.…”

When Flexible Organic Field‐Effect Transistors Meet Biomimetics: A Prospective View of the Internet of Things

“…Jang and co-workers developed a high-k polyurea-based dielectric by adopting the strong hydrogen bonding technique. [41] The as-fabricated 60 nm thick dielectric could obtain a high dielectric constant of 5.82 nF cm −2 . They fabricated an OFET employing this dielectric on poly(ethylene terephthalate) (PET) substrate.…”

“…Hydrogen bonding benefits to flexibility. Jang and co‐workers developed a high‐ k polyurea‐based dielectric by adopting the strong hydrogen bonding technique . The as‐fabricated 60 nm thick dielectric could obtain a high dielectric constant of 5.82 nF cm −2 .…”