A WORM-Type Memory Device with Rectifying Effect Based on a Conjugated Copolymer of PF6Eu on Si Substrate
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A WORM-Type Memory Device with Rectifying Effect Based on a Conjugated Copolymer of PF6Eu on Si Substrate Y.P Tan1, Q.D Ling2, Y.H Teo Eric1, Y. Song1, S.L Lim2, G.Q Lo Patrick3, E.T Kang2, Chunxiang Zhu1, and D.S.H Chan1 1 Silicon Nano Device Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore, 119260, Singapore 2 Department of Chemical and Biomolecular Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore, 119260, Singapore 3 Institute of Microelectronics, 11 Science Park Road, Singapore Science Park II, Singapore, 117685, Singapore
ABSTRACT We report a non-volatile, write-once-read-many times (WORM) memory device based on a simple organic-inorganic heterojunction. The organic-based hybrid used is 9, 9-dihexylfluorene and Eu-complexed benzoate (PF6Eu (DBM)), which contains both electron-donor (9, 9dihexylfluorene) and electron-acceptor (europium complex) groups. The inorganic n-type silicon substrate is used as the bottom electrode, while the Al is used as the top electrode. Under currentvoltage testing, the device is able to switch from one initial non-conducting state (OFF) to a conducting state (ON) once a threshold voltage is reached under the first positive sweep. The “OFF” state is not recoverable with subsequent negative sweep after the device is turned “ON”. The ON/OFF current ratio is around 4x104. Diode rectifying characteristics is also observed for the turned-on device with a current ratio of 7x104, which is essential to address one memory cell in large passive matrix circuits. Reliability test is carried out and the device is able to sustain its “ON” state for at least 12 hours without any external bias. INTRODUCTION Over the past two decades, a lot of effort has been made to fabricate different functions of electronic devices using small molecular and polymer materials. Organic light emitting diodes [1], organic thin-film transistors [2], organic photovoltaic cells [3] and organic switches [4] are some of the examples. Very recently, non-volatile memory devices based on organic materials have been reported [5, 6], including rewritable type and write-once-read-many-time (WORM) type memory devices. The WORM type memory seems to exhibit a long retention time, which is of importance to non-volatile memory devices. A polymer/semiconductor WORM memory device has been reported by using PEDOT [7]. The as-fabricated device shows a high conductivity property and can be programmed to low conductivity state after applying a bias. Furthermore, a WORM memory device with rectifying characteristic has been demonstrated by depositing PEDOT on Si substrate [8]. The rectifying property of memory devices is of great importance to address one memory cell in a two dimension memory array. We reported a WORM type memory by using a conjugated copolymer containing fluorene and chelated europium complex [9], with a high ON/OFF current ratio of 106, and a transition voltage of 3V. The as-fabricated device show
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