Reducing contact resistance in bottom contact organic field effect transistors for integrated electronics

Abstract

Organic field effect transistors (OFETs) are a promising technology for developing truly flexible, stretchable and bio-compatible integrated electronics. Understanding the contact resistance mechanisms and introducing strategies to minimize the contact resistance is vital for the continuous performance improvement of OFETs. This paper firstly discusses the suitability of various device structures for short channel OFETs and fine resolution integration. After describing the formation of the contact resistance composed of the injection and access parts, this paper comprehensively reviews approaches for reducing contact resistance with bottom contact structure OFETs, including by interface engineering and doping the organic semiconductor layer. The pros and cons of each approach are discussed in detail. It is concluded that a combination of various techniques is required to minimize the contact resistance for fine resolution integration.

Blurred Electrode for Low Contact Resistance in Coplanar Organic Transistors

“…The total on-state device resistance ( R on ) equals the sum of channel resistance ( R ch ) and contact resistance ( R c ) . The R c consists of two contributions: injection resistance ( R inj ) and access resistance ( R acc ). , Figure a 1 and b 1 show the equivalent circuit schematic of contact resistance distribution for BC and TC OTFTs, respectively. R inj is related to the properties of electrode/semiconductor interface, such as the mismatch of energy levels of electrode and semiconductor, , the presence of interfacial dipoles, and the charge injection area at metal contacts. ,, R acc reflects the transport properties of the injected charges traveling through the semiconductor layer between the electrode/semiconductor interface and the accumulation layer.…”

“…Similar to staggered OTFTs, the R c of coplanar OTFTs is also composed of two parts: the injection resistance ( R inj ) and the access resistance ( R acc ). , R inj stems from the carrier injection at the electrode/organic semiconductor interface, which is significantly affected by the injection barrier arising from mismatching between the Fermi level of the electrode and the transport energy level of the OSC, , and the small injection area results in a tiny fraction of the gate-field-induced carrier injection, while R acc originates from the resistance of transporting carriers to the channel after the carriers are injected into the OSC, which is primarily impacted by molecular packing and conductivity of the OSC near the electrode edge . Currently, various attempts have been implemented to improve the R c , such as functionalizing electrodes with self-assembled monolayers (SAMs), , inserting an injection layer between the OSC and metal electrode, , adopting carbon-based conductors as electrodes, , and doping semiconductors. , These approaches mainly focused on reducing the R inj through tuning the energy level alignment or improving molecular packing of the OSC on the electrode. , …”

Low-Temperature Solution-Processed All Organic Integration for Large-Area and Flexible High-Resolution Imaging

“…With the bottom-contact structure, the source/drain electrodes were deposited before the OSC layer, so that the mature metallization techniques with sputtering and photolithography were conveniently used for micrometerresolution electrode patterns. Compared to the bottom-gate bottom-contact structure, the TGBC one owns larger carrier injection area for smaller contact resistance [42][43][44]. When being used in photo imagers, the top gate metal can also shield the light from the top.…”

Review of porphyrin-based photodynamic therapy materials

“…Lang and co-workers reported an initial study of porphyrinic COFs bearing a 3D diamond-like structure via Schiffbase reaction for the photodynamic antibacterial effect. [168] The 3D porphyrinic COFs possessed not only high local loading concentration of porphyrin, but also the high singlet oxygen yield similar with the TPP molecules in good solvents. More recently, several efforts have been made to synthesis and use the porphyrin-based COFs in antitumor applications.…”