Materials Science and Engineering B 159–160 (2009) 14–17 Contents lists available at ScienceDirect Materials Science and Engineering B journal homepage: www.elsevier.com/locate/mseb Memory effects in MIS structures based on silicon and polymethylmethacrylate with nanoparticle charge-storage elements M.F. Mabrook a,∗ , A.S. Jombert a,b , S.E. Machin a , C. Pearson a , D. Kolb a , K.S. Coleman b , D.A. Zeze a , M.C. Petty a a School of Engineering and Centre for Molecular and Nanoscale Electronics, Durham University, South Road, Durham DH1 3LE, UK b Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK article info Article history: Received 2 May 2008 Accepted 1 September 2008 Keywords: Gold nanoparticles C60 Carbon nanotubes PMMA Memory devices abstract We report on the electrical behaviour of metal–insulator–semiconductor (MIS) structures fabricated on p-type silicon substrates and using polymethylmethacrylate (PMMA) as the dielectric. Gold nanoparticles, single-wall carbon nanotubes and C 60 , deposited at room temperature, were used as charge-storage ele- ments. In all cases, the MIS devices containing the nanoparticles exhibited hysteresis in their capacitance versus voltage characteristics, with a memory window depending on the range of the voltage sweep. This hysteresis was attributed to the charging and discharging of the nanoparticles from the gate electrode. A relatively large memory window of about 2.2V was achieved by scanning the applied voltage of an Al/PMMA/C 60 /SiO 2 /Si structure between 4 and -4 V. Gold nanoparticle-based memory devices produced the best charge retention behaviour compared to the other MIS structures investigated. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Memories fabricated from metal–insulator–semiconductor (MIS) structures incorporating nanoparticulate materials as the charge-storage elements are receiving considerable attention in the literature. Devices based on organic materials have the potential to overcome many of the fabrication problems associated with silicon structures. For example, organic materials can be deposited at room temperature on almost all surfaces, including flexible substrates, by low-cost methods. Various storage media have been reported, including: aluminium nanocrystals [1], germanium nanocrystals [2], gold nanocrystals [3] and Au nanoparticles [4,5]. Charging of the nanomaterials occurs on the application of a voltage to the gate electrode by electron transport, either through a thin tun- nelling oxide [3] or via the top insulator [6]. Some recent research has explored the use of high-k dielectrics for the formation of the tunnelling oxide [7]. Carbon nanotubes are attractive materials for nanotechnol- ogy applications because of their exceptional electronic properties and mechanical strength [8]. A typical single-wall carbon nan- otube (SWCNT) has dimensions of about 1.2nm in diameter and 1–20 m in length. As such, SWCNTs offer an attractive proposition as conductive wires in micro- or nano-scale elec- ∗ Corresponding author. Tel.: +44 1913342435; fax: +44 1913342407. E-mail address: m.f.mabrook@durham.ac.uk (M.F. Mabrook). tronic devices. Many applications have now been suggested for nanotubes, including field-effect transistors, advanced composite materials and chemical sensors [9,10]. There are a few reports of SWCNT-based MIS memory structures and the combination of the fullerene C 60 with poly(4-vinylphenol) (PVP) has been shown to produce a large hysteresis in the current–voltage characteristics of metal–insulator–metal structures [11,12]. In our previous work [6,13,14], we have reported on MIS devices and transistor structures in which a monolayer of gold nanoparti- cles was incorporated into Langmuir–Blodgett (LB) insulating films. Here, we extend our studies to other storage charge elements, in particular single-wall carbon nanotubes and C 60 and compare the devices to those based on gold nanoparticles. In this investiga- tion, we used a thin film of polymethylmethacrylate (PMMA) as the insulating layer. 2. Experimental details The preparation of the gold nanoparticle solution involved adding 1 ml of 1% aqueous HAuCl 4 ·3H 2 O (99.9%) to 100 ml of deionised water under vigorous stirring. After 1 min, 1 ml of 1% aqueous sodium citrate was added, followed by 1ml of 0.075% NaBH 4 (99.99%) in 1% sodium citrate 1min later. The solution was stirred for a further 5 min and then stored in the refrigerator at about 4 ◦ C. The resulting gold nanoparticles were approximately 5nm in diameter, including the thickness of the organic capping layer. 0921-5107/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mseb.2008.09.003