Photo-Patternable ZnO Thin Films Based on Cross-Linked Zinc Acrylate for Organic/Inorganic Hybrid Complementary Inverters

Abstract

Complementary inverters consisting of p-type organic and n-type metal oxide semiconductors have received considerable attention as key elements for realizing low-cost and large-area future electronics. Solution-processed ZnO thin-film transistors (TFTs) have great potential for use in hybrid complementary inverters as n-type load transistors because of the low cost of their fabrication process and natural abundance of active materials. The integration of a single ZnO TFT into an inverter requires the development of a simple patterning method as an alternative to conventional time-consuming and complicated photolithography techniques. In this study, we used a photocurable polymer precursor, zinc acrylate (or zinc diacrylate, ZDA), to conveniently fabricate photopatternable ZnO thin films for use as the active layers of n-type ZnO TFTs. UV-irradiated ZDA thin films became insoluble in developing solvent as the acrylate moiety photo-cross-linked; therefore, we were able to successfully photopattern solution-processed ZDA thin films using UV light. We studied the effects of addition of a tiny amount of indium dopant on the transistor characteristics of the photopatterned ZnO thin films and demonstrated low-voltage operation of the ZnO TFTs within ±3 V by utilizing Al2O3/TiO2 laminate thin films or ion-gels as gate dielectrics. By combining the ZnO TFTs with p-type pentacene TFTs, we successfully fabricated organic/inorganic hybrid complementary inverters using solution-processed and photopatterned ZnO TFTs.

Photo-patternable high-k ZrOx dielectrics prepared using zirconium acrylate for low-voltage-operating organic complementary inverters

“…As some acrylic monomers containing zinc atoms have been utilized as photo-patternable ZnO precursors, we used zirconium acrylate (ZrA) as ZrO x precursors [27,28]. ZrA enabled the preparation of a micro-patterned precursor film through photo-induced crosslinking under 254 nm UV exposure and developing in a solvent.…”

Recent Progress in Photonic Processing of Metal‐Oxide Transistors

“… On the other hand, the output optical power density can be significantly affected by the geometry of the setup and particularly by the distance between the UV source and the sample . Similarly, the duration of the illumination process is also critical and is often found to vary between a few minutes up to 12 h, although times between 15–30 min are the most frequently used . Finally, the oxygen content and relative humidity (RH) in ambient air are also critical parameters when photonic processing is performed in air.…”

“…Overall, for the fabrication of metal‐oxide electronic devices such as thin‐film transistors, there is a wide range of precursors to choose from. The most common choices include metal compounds based on nitrates, acetylacetonates, alkoxides, or acetates and to a lesser extent chlorides, acrylates, and hydroxides . The kinds of materials that were successfully processed with the help of DUV irradiation include all those that are required to form metal‐oxide TFTs, i.e., semiconductors, dielectrics, and conductors.…”

“…The kinds of materials that were successfully processed with the help of DUV irradiation include all those that are required to form metal‐oxide TFTs, i.e., semiconductors, dielectrics, and conductors. Among them, the most commonly employed n‐type semiconductors are IGZO, IZO, zinc tin oxide (ZTO), as well as the binary compounds ZnO, In 2 O 3 , and GaO x . For p‐type oxides, there are far fewer studies available, with Cu 2 O being one of the exceptions …”

“…To date, two different approaches that rely on the use of DUV to pattern solution‐processed metal‐oxide films have been reported (Figure 4): i)Direct light patterning through solubility contra‐st: Here, exposure of the precursor layer to DUV irradiation is altering the solubility of the film in the exposed areas due to partial photoconversion of the precursor to an MOM network. Following a few minutes of exposure through a shadow mask, the unexposed areas of the precursor film remain soluble and can be dissolved/etched using common solvents or dilute etchant solutions. ii)Patterning through surface wetting contrast: Substrate exposure to DUV increases the surface energy as compared to nonexposed areas.…”