Resistive switching effect for ZnO hybrid memory with metal-oxide nanocrystals Dong Uk Lee a , Eun Kyu Kim a, ⁎, Won-Ju Cho b , Young-Ho Kim c , Hyunsik Im d a Quantum-Function Research Laboratory and Department of Physics, Hanyang University, Seoul 133-791, Republic of Korea b Department of Electronic Materials Engineering, Kwangwoon University, 447-1 Wolgye-dong, Nowon-gu, Seoul 139-701, Republic of Korea c Division of Materials Science and Engineering, Hanyang University, Seoul 133-791, Republic of Korea d Department of Semiconductor Science, Dongguk University, Seoul 100-715, Republic of Korea abstract article info Available online 15 February 2012 Keywords: Nano-crystals Hybrid SnO 2 Nonvolatile memory Resistance random access memory Polyimide ZnO memory device with SnO 2 nanocrystals embedded in a biphenyl-tertracarboxylic dianhydride–phenylen diamine polyimide layer was fabricated, and its electrical properties were evaluated. The complementary re- sistive switching effects with a current bistability appeared during voltage sweeping in the range of ± 4 V and ± 5 V, respectively. This switching effect of current–voltage may be originated from a resistance fluctuation due to the charge trapping into SnO 2 nanocrystals. In the bipolar resistance switching behavior, the ratio of high-resistance state (HRS) and low-resistance state (LRS) currents was about 4.4 × 10 4 at 1 V. The data re- tention of LRS/HRS currents was maintained about 2.2 × 10 3 after 10 3 s. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Nanocrystal memories with various kinds of materials, such as Si, metals, metal-oxides, and metal-silicides, have been studied to super- sede a floating-gate non-volatile memory. Using metal-oxide nano- crystals embedded in a polyimide layer, some emerging nonvolatile memory devices have been reported. Especially, the metal nano- particles make the deep quantum wells between control oxide and tunnel oxide due to the difference of work functions [1–3]. Recently, the fabrication of In 2 O 3 Cu 2 O, and ZnO nano-particles embedded in polyimide layer, and the nano-floating gate memory devices with these metal oxide nano-particles were reported [4,5]. Then, the poly- imide layer has good thermal stability and chemical endurance, and it can be employed as a matrix of nano-particles. Additionally, the metal-oxide nano-particles embedded in polyimide layer have attrac- tive characteristics of high density, good uniformity, single layer con- trollability and feasibility for memory applications [6,7]. Also, the resistance random access memory has been investigated to use the resistive switching effect in various kinds of oxide thin films such as a binary oxides, perovskite oxides, and chalcogenide materials. And then the device structures of the oxide thin films and organic devices on glass such as thin-film transistor, light-emitting di- odes, photo sensor, and organic/inorganic hybrid electrical device have been studied. The hybrid nanocrystal nano-floating gate memo- ry device and the transparent hybrid memory device with the metal- oxide nanocrystals have proposed to improve the retention property and applicative the next generation memory devices [8–13]. In this study, we demonstrated and proposed the ZnO hybrid mem- ory device with SnO 2 nanocrystals in the polyimide for application of the transparent flexible nonvolatile memory device. The device struc- tures of Al/biphenyl-tertracarboxylic dianhydride–phenylen diamine (BPDA–PDA)/SnO 2 nanocrystals/ZnO/ITO/glass substrate were con- firmed by cross-sectional high resolution field-emission transmission electron microscopy (FE-TEM) measurements. Their electrical proper- ties were evaluated by using semiconductor parameter analyzer. 2. Experiments The SnO 2 nanocrystal memory devices embedded in polyimide layers were fabricated on glass substrates. The indium–tin–oxide (ITO) layer with 190-nm thickness was grown by a radio-frequency (RF) magnetron sputter. And then, a ZnO layer with a thickness of 160 nm was deposited on the ITO layer by an ultra-high vacuum RF magnetron sputtering system which base pressure is 6.6 × 10 -8 Pa. These two sputtering processes were carried out under the same con- ditions: 50 W of working power and 3 × 10 -1 Pa of working pressure at room temperature. The Sn with thickness of 5 nm was deposited onto ZnO/ITO/glass sapphire substrate using a thermal evaporator. Then 50-nm-thick polyamic acid (PAA) was spin coated onto the de- posited indium films. Here, a commercial BPDA–PDA type PAA (PI- 2610D) was used. In this study, the PAA solution was composed of BPDA–PDA in N-methyl-2-pyrrolidone (3 wt.%). Then the samples were cured at 400 °C for 1 h after soft baking at 135 °C for 30 min in a rapid thermal annealing system in a N 2 atmosphere. Finally the Al gates with a diameter of 200 μm were deposited by using a thermal evaporator. The fabricated device and cross-sectional schematic dia- gram are shown in Fig. 1. Especially, the photography of the ZnO hybrid memory device with SnO 2 nanocrystal showed high transparent Thin Solid Films 521 (2012) 98–101 ⁎ Corresponding author. Tel.: + 82 2 2220 0914; fax: + 82 2 2295 6868. E-mail address: ek-kim@hanyang.ac.kr (E.K. Kim). 0040-6090/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2012.02.044 Contents lists available at SciVerse ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf