Electroless‐Plated Gold Contacts for High‐Performance, Low Contact Resistance Organic Thin Film Transistors

Abstract

Deposition of metallic electrodes on a semiconductor medium is an indispensable factor in governing carrier injection, and a metal/semiconductor contact that can be formed via solution process is highly desired in printed electronics. However, fine-patterning the solution processes of metallic electrodes without damaging the excellent electronic properties of organic semiconductors (OSCs) is still a challenge. In this work, electroless plating, a metal coating technique that involves auto-catalytic reaction in an aqueous solution, is used to fabricate top-contact organic thin-film transistors (OTFTs). An electrolessplated gold pattern with a spatial resolution of 10 micrometers is transferred and laminated on a monolayer of OSCs to serve as a hole-injection electrode. The fabricated OTFTs exhibit reasonably high field-effect mobility of up to 13 cm 2 V −1 s −1 and decent contact resistance as low as 120 Ω • cm, which implies that an ideal metal/semiconductor contact can be realized. This electroless plating technique can provide possibilities for practical mass production of organic integrated circuits because it is in principle cost-effective, capable of covering large areas, high-vacuum free, and environmentally friendly.

The Origin of Low Contact Resistance in Monolayer Organic Field‐Effect Transistors with van der Waals Electrodes

“…Regarding the single crystal active layer, R SH is related to the intrinsic mobility and the gate‐channel capacitance per unit area ( C i ) via Equation ().Equation () is the main equation used for evaluation of contact resistance by TLM. [ 2,3,13,20–23,34 ]…”

“…Equation ( 4) is the main equation used for evaluation of contact resistance by TLM. [2,3,13,[20][21][22][23]34] By transferring Au electrodes onto the single crystalline C 10 -DNTT layer, five OFETs with the channel lengths of 11, 22, 30, 36, and 40 μm are constructed (inset in Figure 3a). The transfer curves of all these OFETs with different channels are measured at a small V DS ¼ À1 mV (Figure 3a), and the contact resistance is extracted from the intercept of R T W (L) plot (Figure 3b).…”

“…[22] In principle, reducing active layer thickness can significantly lower the access resistance. [13,23] Most commonly, the contact resistance is extracted by the so-called transmission line method (TLM), which yields a combined value, [2,3,13,[20][21][22][23] with the individual contributions of the interface resistance (R I ) and the access resistance (R A ) difficult to disentangle. However, knowing their contributions to R C is very valuable, especially in high-mobility and/or short-channel OFETs, where the channel resistance (R CH ) could be smaller than R C .…”

Nano‐Ground Glass as a Superhydrophilic Template for Printing High‐Performance Organic Single‐Crystal Thin Films

“…Herein, we selected N,N'-diphenethyl-3,4,9,10benzo[de]isoquinolino [1,8-gh]quinolinetetracarboxylic diimide (PhC 2 -BQQDI), which is a bench-marked n-type material recently developed by our group (Figure 3a). [10] PhC 2 -BQQDI exhibits high electron mobility of above 1 cm 2 V −1 s −1 , [10,26,29,30] and sufficient compatibility with solution processing and is sufficiently air-stable to withstand the water-based transfer process. But, relatively high substrate temperature (≈150 °C) is required to obtain high-quality single-crystal films.…”

“…In a recent study, we developed an ideal transfer method for large‐area OSC single‐crystal thin films, [ 24 ] as well as for patterned electrodes. [ 25,26 ] The developed method revolutionized the conventional bottom‐up approach for fabricating OTFT devices. Particularly, the reported transfer technique enables the application of the high‐performance, solution‐processed OSC thin films on various underlayers/substrate and overcomes the issues generally associated with solution processing.…”