STUDY OF OPTICAL RECORDING CHARACTERISTICS OF SbSnIn, GeSbTe AND AgInSbTe BASED PHASE CHANGE MATERIALS AND DEVICE DESIGN GIRIRAJ NYATI

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1 STUDY OF OPTICAL RECORDING CHARACTERISTICS OF SbSnIn, GeSbTe AND AgInSbTe BASED PHASE CHANGE MATERIALS AND DEVICE DESIGN GIRIRAJ NYATI DEPARTMENT OF PHYSICS INDIAN INSTITUTE OF TECHNOLOGY, DELHI HAUZ KHAS, NEW DELHI , INDIA DECEMBER 2009

2 CERTIFICATE I am satisfied that the thesis entitled "Study of Optical Recording Characteristics of SbSnln, GeSbTe and AgInSbTe based Phase Change materials and Device Design" submitted by Giriraj Nyati is worthy of consideration for the award of the degree of Doctor of Philosophy and is a record of the original and bonafide research work carried out by him under our guidance and supervision and that the results contained in it have not been submitted in part or full to any other university or institute for award of any degree/diploma. Date: Prof. Vasant D. Vankar Professor of Physics, Department of Physics, Indian Institute of Technology Delhi Hauz Khas, New Delhi INDIA 1

3 Acknowledgements I take this opportunity to express my heartfelt thanks & gratitude to Prof. V. D. Vankar for his guidance all through my work. It indeed was a great pleasure for me to have a person of his repute as the main source of my inspiration. I am also thankful to Dr. S.K.Mishra, Director (Research & Development), at Sharda Group of Institutions, Greater Noida for his involvement & direction. I would like to thank the heads of the departments (during the years of my PhD work) Prof. D. K. Pandya and Prof. B. P. Pal & distinguished faculty members Prof. S. Chandra, Prof. K. Thyagarajan, Dr. (Mrs) Ratanmala Chatterjee and Dr. S. Choudhary for providing me the necessary help to complete my research work. I am thankful to the faculty members of Nanostech laboratory Dr. Pankaj Srivastava & research scholar Mr. Rajbeer Sharma who helped me in several ways in carrying out the experimental work and the fruitful discussions on the experimental data. I would like to thank Mr. Deepak Puri, CMD & Mr. Ratul Puri, Executive Director, Moser Baer India ltd for giving me the opportunity to carry out my research in IIT Delhi & Moser Baer's Greater Noida plant. It is an absolute pleasure for me to have association with such high visionary entrepreneurs. The faith they had in me and the freedom they have given me to carry out the research was tremendous.i am very much grateful to them for their care, constant encouragement and valuable guidance during the entire research period. I am thankful to my colleagues Dr. A. Majamdar, Dr. R. Jindal, Mr. Palanisamy. Mr. Khemchandani & Mr. Mohit Alagh for their valuable inputs & suggestions. I am also grateful to Moser Baer & Department of Science & Technology (DST), Government of India for funding the project. I would like to acknowledge the help from Solar Applied Materials Technology Corp., Taiwan on SEM, TEM & GAXRD studies. I am also thankful to Mr. Mathews for all the help in drafting this thesis. ii

4 This work would not have been possible without the constant support & unconditional love from my wife Mrs Hansa who allowed me to spend considerable time on my research after office hours that logically belonged to her. I am indebted to my parents & in-laws for their blessings & continuous inspiration. I express my gratitude to my sons Mr. Raghav & Parth for letting me off during study times they needed me the most. (Giriraj Nyati) iii

5 Study of Optical Recording Characteristics of SbSnln, GeSbTe and AgInSbTe based Phase Change materials and Device Design Abstract In this thesis an attempt is made to address some of the remaining technical challenges of the phase change optical recording such as higher data storage capacity at lower $/Mb, higher speed data transfer and prolonged thermal & chemical stability of written marks over long usages. As the first part of our study, we developed optimized material composition (Sbloo -XySn,Iny)p(ZnS-SiO2)Q that can be used as the parent recording material to develop Blu-ray Recordable (BDR) L2H discs. The L2H refers to transition of reflectivity from low to high upon formation of the recording marks. Using this material as the phase change layer, we subsequently worked on the device design in order to develop a new BDR L2H format that meets the current book specifications. Blu-ray Rewritable (BDRE) format is standardized as 1X-2X (1X BD corresponds to a data transfer rate of 36 Mbits/s at a linear recording velocity of 5 m/s). Eutectic composition Sb69Te31 is studied extensively world over as the possible Growth Dominant Materials (GDM) for high-speed data recording applications. In the second part of our study, we worked on addition of suitable elements for improving the crystallization speed of Sb69Te31 composition to develop a BDRE disc that can be recorded at higher speed than the current specification of 2X. First we studied (SbXTei-X)y Gel-y composition. Subsequently, We developed as new composition with the u'1

6 addition of indium into (SbTei_X)y Gel_y matrix to successfully discover a new 1X-2.5X BDRE format. As the third part of our study, we attempted to improve the archival life of Compact Disc Rewritable (CDRW) media format. We introduced N2 as a dopant during the course of sputtering in phase change layer and established that an optimum concentration of this gas significantly improved the archival life in comparison to the available commercial products of this category because the resultant nitrides of the constituent atoms of the phase change layer significantly suppressed the micro material flow. Giriraj Nyati (2005PHZ8062) IYA

7 Table of Contents Certificate Acknowledgements Abstract Table of Contents List of Figures List of Tables i ii iv vi ix xiii CHAPTER 1 Introduction Introduction Current storage technologies Magnetic Storage Main Memories Flash Memories Optical Storage Phase change technology Challenges of phase change technology High storage capacity High data transfer rate Over-write cyclability & archival life Objectives of the thesis Higher storage capacity through the development of low-to-high Blu-ray disc format Development of new high Speed (1X-2.5X) BDRE format Study of Impact of N2 doping on overwrite cyclability & archival life of 21 AgInSbTe based phase change media 1.6. Thesis plan 22 CHAPTER 2 Experimental procedures Introduction Development of samples Sputtering Technology Fundamental technology Magnetron sputtering DC Magnetron sputtering RF Magnetron sputtering 28 vi

8 2.2.2 Experimental setup for development of phase change materials Stand-alone multi chamber co-sputtering machine Selection & preparation of samples Experimental setup for development of sample media & devices Deposition of thin layers Deposition conditions Deposition of dielectric layers (ZnS-5i02) Deposition of phase change material for BDR/BDRE Deposition of phase change material for CDRW (AgInSbTe) Deposition of reflective layer for CDRW (A1Ti) Deposition of reflective layer for BDR/BDRE (Ag) Preparation of media samples Characterizations of the samples Glancing Angle X-Ray Diffraction UV/VIS/NIR Spectrophotometer Transmission Electron Microscopy Scanning Electron Microscopy Optical reflectance/transmittance measurement (ETA-RI') Optical Disc Unit for BDR/RE (BDT ODU 1000) Electrical resistivity measurements Atomic Force Microscopy 55 CHAPTER 3 Development of Phase Change Material for Write Once Blu-ray Disc Introduction Experimental Details Results and Discussion Conclusions 70 CHAPTER 4 Development of Low to High Blu-ray Recordable (BDR) Disc Introduction Experiment Result & Discussions Optimization of the groove geometry Optimization of the layer stack design Development and fine tuning of writing strategy Development of new phase change target material with reduced grain sizes of the 84 ceramics in order to improve upon the 2X jitter. 4.4 Conclusion 87 vii

9 CHAPTER 5 Development of new high speed (1X-2.5X) BDRE media Introduction Experiment Results and Discussion Crystallization speed (SbxTe100 _x)y Geloo ~, phase change material ((Sb.Teloo_.)y Geloo_y )~ Inl phase change material New BDRE media Conclusions 102 CHAPTER 6 Effect of N2 on the archival life of AgInSbTe based phase change media Introduction Experimental Procedure Development of media samples Accelerated Life expectancy test Results and Discussions Structural characterization of Ag5.5In6.5Sb59Te29 films Electrical characterization Kinetics of the structural transformation Optical characterization Micro structural analysis Surface morphological study Archival life Conclusion 128 CHAPTER 7 Conclusions & scope for further work Conclusions Scope for further work 131 REFERENCES 133 APPENDIX APPENDIX RESEARCH PUBLICATIIONS AND NATIONAL/INTERNATIONAL CONFERENCES 152 BRIEF BIO-DATA 154 viii