Organic Complementary Integrated Circuits Fabricated with Reverse Offset Printed Electrodes
Authors: Takeda Yasunori , Hayasaka Kazuma , Shiwaku Rei , Morita Susumu , Sekine Tomohito , Okamoto Tomoko , Tanaka Yasuhiro , Matsui Hiroyuki , Kumaki Daisuke , Tanabe Kousuke , Tokito Shizuo 
Published: February 2020

<Introduction>
The resolution, thickness and printing speed range of the printed electrode are determined by the printing method. Printing method having a film thickness (50-200 nm) that can be used for organic thin film transistors (OTFTs) include ink-jet printing, flexographic printing, mCP, etc. In general, the reproducible line spacing (channel length) that can be realized by 10 pL ink-jet printing is about 10 micrometer, and special patterning assistance is necessary for further higher resolution. The reverse offset printing method is known as a printing method with resolution approaching that of photolithography, and it is possible to realize line spacing below 1 micrometer[1]. In previous study, we have fabricated OTFTs with short channel length by using reverse offset printing method. In this study, we fabricated complementary inverter circuit[2], ring oscillator, operational amplifier by integrating printed p-type and n-type OTFT. Those integrated circuits including ring oscillators showed good results with short channel and small overlap electrodes.
<Experiments>
The p-type and n-type OTFT have a bottom-gate, bottom-contact structure and a top-gate, bottom-contact structure, respectively[2]. Crosslinked poly(4-vinylphenol) was used as a base layer for controlling the surface wettability of the glass substrat. The silver nanoparticle inks were prnited by using an offset printer for all electrodes. The silver nanoparticle ink was patterned onto the base layer to form source / drain (S/D) electrodes for the n-type OTFTs. Next, an amorphous fluoropolymer solution was printed using a dispenser system to create hydrophobic bank layer. Before depositing the n-type semiconductor, the substrate was treated with 4-methylbenzenethiol (4-MBT). A n-type semiconductor (TU-3, FIC) ink was printed using dispenser system in the bank region. A parylene (diX-SR) layer was deposited to form a gate dielectric layer of the n-type OTFT. The silver nanoparticle ink was printed under the same conditions as the S/D electrodes to form gate electrodes. After forming the gate electrodes, the parylene was deposited under the same conditions as those for the n-type OTFT dielectric layer to form the gate dielectric layer for the p-type OTFT. Next, the silver nanoparticle ink was printed under the same condition as the S/D electrodes of n-type OTFT for S/D electrodes of the p-type OTFT. The hydrophobic bank layers were printed using the dispenser system to define the channel width (W) of the p-type OTFT under the same conditions as for the n-type semiconductor bank layer. Prior to printing the p-type semiconductor layer, the S/D electrode surfaces were treated with PFBT. Finally, a mesitylene-based solution containing the p-type semiconductor (diF-TES-ADT/PS blend) was printed in the areas defined by bank layer using the inkjet printer.
<Results and Discussion>
Transfer characteristics of the fabricated OTFT were measured by semiconductor parameter analyzer (4200A-scs, Keithley). Each of the OTFT devices with diF-TES-ADT/PS as the p-type and TU-3 as the n-type exhibited negligible hysteresis with excellent carrier mobilities of 0.05 and 0.03 cm2/Vs, respectively. The fabricated ring oscillator started oscillating at an operating voltage of 1.25 V. The propagation delay time was 51.7 microsecond at 12.5 V, which is high speed operation in the printed type organic circuit. The operational amplifier also operated well, succeeded in amplifying a weak signal (50 mV) by 20 times (1.0 V).[3]

<Acknowledgments>
This work was partially supported by the Japan Science and Technology Agency (JST, the center of Innovation Program).
<References>

K. Fukuda et al., Advanced Electronic Materials, 1, 1500145 (2015).

Y. Takeda et al., Advanced Electronic Materials, 4, 1700313 (2018).

Y. Takeda et al. JSPS Spring meeting 2018, 18p-D102-6.