A Printed and Flexible Field‐Effect Transistor Device with Nanoscale Zinc Oxide as Active Semiconductor Material

Abstract

Since the development of the electronic transistor 60 years ago its technical utilization has revolutionized modern society. Consequent miniaturization was the key to this development. The challenge to develop flat printable electronics based on inorganic materials could give this area further input. It could be the basis for flexible displays or electronic paper when the active material is processable from solution, shows very good adherence to flexible substrates and excellent physical performance.[1] To meet these challenges any material considered requires a tuned set of functional properties. In general inorganic semiconductors are in advantage over organic materials as far as their physical performance is concerned. However, often processing and adherence to substrates is a problem with inorganic semiconductors. ZnO is available in various morphologies as transparent oxide, is non toxic, inexpensive and has shown promising physical semiconductor properties. [2][3][4] For solution processedZnO field-effect transistor (FET) devices, the highest electron mobility values are currently 1.65 cm 2 V À1 s À1 , however obtainable only after calcinations at temperatures >300 8C.[5] So far, despite promising physical performance parameters, neither synthesis conditions, nor processing techniques are yet compatible with existing printing technologies envisioned for flexible printing of ZnO semiconductors on polymer substrate basis. Currently the utmost challenge in the field is to gain a most complete understanding of the interplay between the parameters synthesis, processing and semiconductor performance for future development of printable electronic devices based on inorganic semiconductors such as ZnO. Despite a couple of recent reports on the deposition of zinc oxide thin layers in FET devices, processing from solution and conversion into the active FET channel electrode under fairly mild conditions is a great challenge. Chemical bath deposition techniques [6,7] and sol-gel processes were mainly investigated in this regard. [5,[8][9][10] However, both techniques typically require either high processing temperatures (above 300 8C) or long reaction times and are thus inappropriate for printing applications on flexible polymer based substrates under state of the art printing conditions. Processing temperatures well below 200 8C are the goal for the formation of semiconducting inorganic thin films onto such substrates. The application of soft processes like spin or dip coating or any kind of printing or stamping rely on the formation and adherence of such thin films on flexible substrates. Herein we report our investigations on the formation, characterization, low temperature processing and printing behavior of a molecular precursor and its conversion to unifom ZnO thin films and promising electronic performance of such films in an FET device.Our process starts from a modified synthesis of the ZnO single source precursor bis [2-(methoxyimino)propanoato]zinc 1 [11,12] (Scheme 1) which we developed for depositing thin tr...

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