Photoemission Study of Energy Band Alignment of Ge 2 Sb 2 Te 5 and Common CMOS Materials
- PDF / 847,042 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 89 Downloads / 193 Views
1072-G02-08
Photoemission Study of Energy Band Alignment of Ge2Sb2Te5 and Common CMOS Materials Lina Wei-Wei Fang1, Ji-Sheng Pan2, Andy Eu-Jin Lim1, Rinus Tek-Po Lee1, Minghua Li3, Rong Zhao3, Luping Shi3, Tow-Chong Chong3, and Yee-Chia Yeo1 1 Department of Electrical and Computer Engineering, National University of Singapore, Blk E4A #02-04, Engineering Drive 3, Singapore, 117576, Singapore 2 Institute of Materials Research and Engineering, A*STAR, 3 Research Link, Singapore, 117602, Singapore 3 Data Storage Institute, A*STAR, DSI Building, 5 Engineering Drive 1, Singapore, 117608, Singapore ABSTRACT We report the energy band alignment of Ge2Sb2Te5 and a variety of common complementary-metal-oxide-semiconductor (CMOS) compatible materials. These materials include silicon, silicon oxide, hafnium oxide, silicon nitride as well as nickel silicide. Highresolution X-ray photoelectron spectroscopy was employed as the main tool to obtain the corelevel spectra, the valence band spectra, and the energy loss spectra. A precise determination of the valence band offsets of Ge2Sb2Te5 and the various materials were obtained. The conduction band offsets were then determined. The energy band line-ups of Ge2Sb2Te5 and these CMOS compatible materials were established. INTRODUCTION Aggressive scaling of the floating gate technology is approaching imminent physical limitations. Alternative memory architecture such as magnetic random access memory (MRAM), ferroelectric random access memory (FeRAM), and resistive random access memory (RRAM), polymer memory, have been proposed to overcome the scaling challenges faced by flash technology. Phase change random access memory (PCRAM) is a promising candidate due to its fast access time, high overwrite cycle capability and low cost [1]. Data storage is achieved by exploiting the reversible electrical switching between the crystalline and amorphous phases induced by Joule heating [2]. The crystalline state is a low resistance state attained by applying a current pulse with a small magnitude and long pulse duration, while the amorphous state is a high resistance state, achieved by applying a current pulse with a greater magnitude and shorter pulse width. The GeSbTe alloy is a common phase change recording media used in PCRAM applications due to its wide composition tolerance for high-speed crystallization. The most prevalent ternary compound employed is the Ge2Sb2Te5 (GST) alloy. Most PCRAM devices employ a vertical structure comprising the GST sandwiched between a resistive bottom metal electrode and a top metal electrode [1,3-6]. Depending on the current applied, the resistive bottom electrode heats up the GST in contact with it to either the crystalline or amorphous phase, storing the ‘1’ or ‘0’ bit. The interface between the bottom electrode and the phase change material is crucial in order to manipulate device characteristics, as it affects the IRESET of the memory device. Although the fundamental electronic properties such as band alignment of GST with common microelectronic materials emp
Data Loading...
