Organic field effect transistor based nonvolatile memory devices

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Organic field effect transistor based nonvolatile memory devices

 

Author: Ren, Xiaochen
Title: Organic field effect transistor based nonvolatile memory devices
Degree: M.Sc.
Year: 2011
Subject: Organic field-effect transistors.
Semiconductor storage devices.
Computer storage devices.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Mechanical Engineering
Pages: xii, 110 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2462940
URI: http://theses.lib.polyu.edu.hk/handle/200/6345
Abstract: Organic electronics have distinct advantages compared to the inorganic silicon based devices including simple fabrication process, capability of fabricated on flexible transparent substrates and for large area applications. As one of organic electronic devices, organic nonvolatile memory cells have drawn great attention since the last decade due to their potential application for large area sensor and next generation data storage system. In order to achieve high performance organic nonvolatile memory device, we demonstrate that with a thin layer of silver nanoparticles inserted into the organic field effect transistors, a large memory window of 90V is obtained. By varying the position and thickness of inserted silver nanoparticles, the memory transistor appears good nonvolatile memory property at the same time maintain high mobility. Hole trap is found as predominately trapped charges and it is verified by time domain method. The thickness dependent on/off ratio as well as trap state density is also compared. Our finding provides a direct approach for device performance optimization. As the temperature issue become important for large area applications, in order to study the temperature effect of device performance and reliability. We investigate the annealing and thermal effects of organic non-volatile memory with floating silver nanoparticles by real-time transfer curves measurements. During annealing, the memory window shows shrinkage of 23% due to structural variation of the nanoparticles. However, by increasing the device operating temperature from 20℃ to 90℃ after annealing, the memory window demonstrates an enlargement up to 100%. The significant differences in the thermal responses are explained and confirmed by co-existing of electron traps and hole traps. Our finding provides better understanding of organic memory performances under various operating temperatures and demonstrates their applications for temperature sensing or thermal memories. To further improve the mobility and charge retention property of memory transistors, we inserted a layer of LiF before the deposition of silver nanoparticles. By inserting a 3 nm LiF layer between the pentacene and Ag NPs, the on/off current ratio increases from 5 to 50 at a measurement time of 15 hours. This enhancement of charge retention behavior (~10 times improvement) is ascribed to the blocking effect from the wide bandgap LiF layer when the trapped charges are releasing from the trap centers. The saturation mobility is also increase for ten times. The results of the current work suggested the memory effect and retention property of the devices can be modulated by using various charge blocking layer to fulfill different application purposes.

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