Double Alkyl Side Chains Functionalized Polyimide as Gate Dielectrics for Application in Organic Transistors

Abstract

Compared with inorganic dielectrics, polymer-based gate dielectrics have received growing attention due to their flexibility, structural adjustability, and low cost in organic thin-film transistors (OTFTs) devices. Aromatic polyimides (APIs) stand out because of their outstanding thermal stability, structural diversity, mechanical flexibility, and large-area processability. In this work, we designed and prepared three API gate dielectrics by the low-temperature chemical imidization method. These API materials with double alkyl side chains can be easily processed into smooth, nonpinhole films with low surface energy. Simultaneously, these materials showed low leakage current densities (<10–9 A/cm2 at 2 MV/m), small dielectric loss (<0.02 at 102∼106 Hz), and good thermal stability. To inspect the potential of our modified APIs as gate dielectrics, para-sexiphenyl/vanadyl-phthalocyanine TFT devices were fabricated. As the length of alkyl side chains in the API structure increases, the field-effect mobility first rises and then drops, in line with the evolution trend of semiconductor film topography. Further, the threshold voltage shifted in a positive direction (from −3.00 to −0.01 V, which is one of the lowest values reported to date). Our results provide a strategy for the design of modified API materials as gate dielectrics to pursue high mobility and low threshold voltage OTFTs.

Methyl functionalization on polyimide side chains as gate dielectrics for organic transistors

“…Organic thin-film transistors (OTFTs) are one of the most promising devices in organic electronics due to their flexibility, solution processability, lightweight, and low fabrication cost, which makes them have wide application potential in wearable and stretchable devices, radio frequency identification, nonvolatile memory, various sensors, etc. 1–5 Organic semiconductors 6,7 and polymer gate dielectrics, 8,9 as core components of the OTFT, have become the key to optimizing device performance in the last two decades. In particular, for regular bottom-gate top-contact OTFT devices, it is of great importance to develop gate dielectric materials that are compatible with organic semiconductors, as carrier transport occurs at the dielectric layer and semiconductor interface, which are directly related to the mobility and operation voltage of OTFTs.…”

“…Besides the introduction of fluorine-containing structures into the PI chains, the addition of bulky side units to the polymer skeleton is also an important approach to effectively improve the performance of OTFTs. Zou and co-workers 4,24 synthesized a series of modified aromatic diamine monomers containing single or double different lengths of alkyl side chains and the corresponding functionalized PI-derived dielectric materials. They found that the appropriate length of the alkyl side chain helped to improve the compatibility between the PI and the organic semiconductor, leading to better interfacial properties and overall device performance.…”