Letter Fast, simple ZnO/organic CMOS integrated circuits Devin A. Mourey a,b, * , Sung Kyu Park d , Dalong A. Zhao a,c , Jie Sun a,c , Yuanyuan V. Li a,c , Sankar Subramanian e , Shelby F. Nelson d , David H. Levy d , John E. Anthony e , Thomas N. Jackson a,c a Center for Thin Film Devices and Materials Research Institute, Penn State University, University Park, PA 16802, USA b Department of Material Science Engineering, Penn State University, University Park, PA 16802, USA c Department of Electrical Engineering, Penn State University, University Park, PA 16802, USA d Eastman Kodak Company, Rochester, NY 14650, USA e Department of Chemistry, University of Kentucky, Lexington, KY 40506, USA article info Article history: Received 10 April 2009 Received in revised form 4 August 2009 Accepted 27 August 2009 Available online 1 September 2009 PACS: 85.30.Tv 73.61.Ga 73.40.Qv 73.61.Le Keywords: Inorganic-organic hybrid Organic circuits Organic thin film transistors CMOS abstract Hybrid organic–inorganic CMOS thin-film circuits are a simple, potentially low-cost, approach for large-area, low-power microelectronic applications. We have used atmo- spheric pressure processes to deposit inorganic ZnO and organic diF TES-ADT semiconduc- tor layers and an Al 2 O 3 gate dielectric. The organic semiconductor uses a contact- treatment-related microstructure that allows circuits to operate without directly pattern- ing the organic layer. Using a simple 4-mask process with bifunctional Ti/Au contacts for both ZnO and organic transistors, 7-stage ring oscillators were fabricated and operated at >500 kHz corresponding to a propagation delay of <150 ns/stage at a supply bias of 35 V. These are the fastest organic–inorganic CMOS circuits reported to date. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The demand for low-cost, high-mobility, thin-film tran- sistor (TFTs) technologies has generated particular interest in low-temperature-process organic and metal oxide semi- conductors. CMOS circuits are likely to be important for low-power and especially battery-powered applications and also because CMOS allows simplified and more robust circuit design. In particular, low-cost, low-temperature de- vice fabrication processes often result in devices with a distribution of characteristics. For unipolar circuits this typically results in digital circuits with varying response to input signals and varying output voltages. While this can be accommodated to some extent by appropriate cir- cuit design, the result is often slower, less reliable, and lower yield circuits. Because CMOS digital circuits use complementary switches, they typically provide output logic levels at or close to the power supply rails. This al- lows many CMOS digital circuits to tolerate large devia- tions from ideal device behavior and substantial variation in device-to-device characteristics. ZnO is currently one of the most promising n-type semiconductors for thin-film applications because it allows high-quality thin films and high-mobility TFTs (>10 cm 2 / V s) using low-temperature deposition processes. How- 1566-1199/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2009.08.021 * Corresponding author. Address: Center for Thin Film Devices and Materials Research Institute, Penn State University, University Park, PA 16802, USA. Tel.: +1 814 867 0023. E-mail address: dxm381@psu.edu (D.A. Mourey). Organic Electronics 10 (2009) 1632–1635 Contents lists available at ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel