Low Power Phase Change Memory via Block Copolymer Self-assembly Technology
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Low Power Phase Change Memory via Block Copolymer Self-assembly Technology Beom Ho Mun1, Woon Ik Park1, You Yin2, Byoung Kuk You1, Jae Jin Yun1, Kung Ho Kim1, Yeon Sik Jung1*, and Keon Jae Lee1* 1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea 2 Graduate School of Engineering, Gunma University, 1-5-1 Tenjin, Kiryu, Gunma 376-8515, Japan
ABSTRACT We report the demonstration of low power phase change memory (PCM) by forming thin self-assembled SiOx nanostructures between Ge2Sb2Te5 (GST) and a TiN heater layer utilizing a block copolymer (BCP) self-assembly technology. The reset current was decreased about threefold as fill factor, which is the occupying area fraction of self-assembled SiOx nanostructures on a TiN heater layer, increased to 75.3%. The electro-thermal simulation shows the better heat efficiency due to the nano-patterned insulating oxide. INTRODUCTION The self-assembly of diblock copolymers has been considered as an alternative method for photolithography generating sub-10 nm patterns because it has the scalability and costeffectiveness [1]. Despite many advantages of BCP lithography, there have been few demonstrations for its practical application to electronic device [2-5]. Recently, we the first have demonstrated the low power PCM device using the thin nanostructured SiOx layer formed by a BCP self-assembly process, in which switching power of memory devices is significantly reduced up to 20 times [6]. Although our previous study demonstrate BCP self-assembled nanostructures improve the PCM device with 2 um diameter hole, The possibility of practical applications in current industry have to be proven through tests on submicron PCM structures. In this study, we formed self-assembled SiOx nanostructures at the interface between a GST thin film and a TiN resistive heater within the 500nm circular hole of a PCM cell by microphaseseparation of two mutually incompatible blocks. This approach has notable advantages: (1) Substantial reduction of reset current; By patterning dielectric SiOx nanostructures on TiN heater layer, the contact area between TiN and GST decreased significantly, resulting in the reset current down from 26 mA to 7.5 mA in our research (Figure 3a). (2) Cost-effectiveness; block copolymer self-assembly is a simple, cost-effective, and scalable maskless nanofabrication technique. (3) Excellent scalability; we previously reported that well-ordered patterns were obtained in 77-nm-wide circular holes [7]. BCP self-assembly can create ordered arrays of sub20 nm features [8], (4) Tunability; PS-b-PDMS BCP can be self-assembled into insulating SiOx nanostructures by adjusting the molecular weight and solvent-vapor treatment [9].
EXPERIMENTAL
Figure 1. (a) A device architecture of the PCM device. (b - f) Schematic fabrication procedures of the PCM device. To know changes of properties depending on the fill factors, we controlled the geometries of SiOx nanostructures on 50
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