An optical programming/electrical erasing memory device: Organic thin film transistors incorporating core/shell CdSe@ZnSe quantum dots and poly(3-hexylthiophene) Mao-Yuan Chiu a , Chen-Chia Chen a , Jeng-Tzong Sheu b , Kung-Hwa Wei a, * a Department of Materials Science and Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 30050, Taiwan, ROC b Institute of Nanotechnology, National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu 30050, Taiwan, ROC article info Article history: Received 27 February 2009 Received in revised form 26 March 2009 Accepted 26 March 2009 Available online 2 April 2009 PACS: 85.60.Dw 85.30.Tv 82.35.Np Keywords: Organic thin film transistor Memory Conjugated polymers Quantum dot Core/shell abstract An optical programming/electrical erasing memory device was fabricated by adopting organic thin film transistors incorporating core/shell CdSe@ZnSe quantum dots (QDs) and poly(3-hexylthiophene) (P3HT) as active layers. After illumination, the presence of quantum well-structured core/shell CdSe@ZnSe QDs within the P3HT film enhanced the maximum ON/OFF ratio substantially to 2700; this value was maintained for 8000 s with- out noticeable decay. The ON state current could be erased effectively when using a single pulse of the gate voltage (10 V). This fabrication approach opens up the possibility of improving the memory performance of polymeric materials prepared at low cost using simple processes. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The development of conjugated polymers for use in or- ganic optoelectronic devices is an area of intense investiga- tion. Several research groups have recently reported the photoresponse and memory functions of organic thin film transistors (OTFTs) [1–9]. One such early device took advantage of the illumination of poly(3-hexylthiophene) (P3HT) with light at a wavelength of 632.8 nm to create electric charges that were later trapped at the polymer– dielectric interface [1]; this system featured an ON/OFF ra- tio of ca. 30 for the memory window at a gate voltage (V GS ) of 60 V under a light intensity of 70 mW/cm 2 . This device exhibited a loss of 70% in its drain current and a short retention time after turning the light off. An alternative ap- proach involves the use of conjugated polymers or quan- tum dots (QDs) as photosensitive materials along with carbon nanotube (CNT)-based field effect transistors for the fabrication of optoelectronic memory devices that function through optical programming and electrical eras- ing. One such memory device featuring a CNT transistor coated with poly(3-octylthiophene) (P3OT) exhibited an ON/OFF ratio of ca. 10 3 after lasing at a wavelength of 457 nm at a value of V GS of 4 V under a laser power of ca. 190 mW/cm 2 . For this system, a several percentage loss of the ON state current occurred 40 s after the laser light was turn off [2]. The same research group reported that for a similar device structure that exposed to a much higher laser power [3], it showed an absence of current de- cay after light turn-off or there exist two regimes: one decaying and one non-volatile [4]. Another optoelectronic 1566-1199/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.orgel.2009.03.011 * Corresponding author. Tel.: +886 35 731871; fax: +886 35 724727. E-mail address: khwei@mail.nctu.edu.tw (K.-H. Wei). Organic Electronics 10 (2009) 769–774 Contents lists available at ScienceDirect Organic Electronics journal homepage: www.elsevier.com/locate/orgel