Switching Studies on Ge15In5Te56Ag24 Thin Films
Germanium Telluride based quaternary thin film switching devices with composition Ge15In5Te56Ag24, have been deposited in sandwich geometry on glass substrate with aluminum as top and bottom electrodes. The bulk glassy form of the said composition is prepared by melt quenching technique. In this technique, appropriate quantity of elements with high purity are taken in a quartz ampoule and sealed under a vacuum of 10-5 mbar. Then, it is allowed to rotate in a horizontal rotary furnace for 36 hours to ensure homogeneity of the melt. After that, the ampoule is quenched into a mixture of ice - water and NaOH to get the bulk ingot of the sample. The sample is then coated on a glass substrate using flash evaporation technique at a vacuum level of 10-6 mbar. The XRD report reveals the amorphous nature of the thin film sample and Energy - Dispersive X-ray Analysis (EDAX) confirms that the film retains the same chemical composition as that of the base sample. Electrical switching behavior of the device is studied with the help of Keithley (2410c) source-measure unit interfaced with Lab VIEW 7 (National Instruments). Switching studies, mainly SET (changing the state of the material from amorphous to crystalline) operation is conducted on the thin film form of the sample. This device is found to manifest memory switching as the device remains 'ON' even after the removal of the electric field. Also it is found that amorphous Ge15In5Te56Ag24 thin film unveils clean memory type of electrical switching behavior which can be justified by the absence of fluctuation in the I-V characteristics. The I-V characteristic also reveals that the switching is faster in this sample as no data points could be seen in the negative resistance region during the transition to on state and this leads to the conclusion of fast phase change during SET process. Scanning Electron Microscopy (SEM) studies are performed on the chosen sample to study the structural changes at the time of switching. SEM studies on the switched Ge15In5Te56Ag24 sample has shown some morphological changes at the place of switching wherein it can be explained that a conducting crystalline channel is formed in the device when the device switches from high resistance to low resistance state. From these studies it can be concluded that the material may find its application in fast switching Non-Volatile Phase Change Memory (PCM) Devices.
Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1124405Procedia APA BibTeX Chicago EndNote Harvard JSON MLA RIS XML ISO 690 PDF Downloads 1071
 M. Wuttig, “Phase-change materials: Towards a universal memory,” Nat. Mater., vol 4, pp. 265-266, April 2005.
 R. Bez and A. Pirovano, “Non-volatile memory technologies: emerging concepts and new materials,” Mater. Sci. Semicond. Process, vol 7, Issue 4-6, pp. 349-355, Jan 2004.
 H.A. Abd El Ghani, M.M. Abd El Raham, M.M. Wakkad, A. Abosehli, N. Assraan, “Crystallization kinetics and thermal stability of some compositions of Ge-In-Se chalcogenide system,” Physica B, vol 381, Issue 1-2, pp. 156-163, May 2006.
 J. Fusong and M. Okuda, “The effect of doping on the erasure speed and stability of reversible phase change optical recording films,” Jpn. J. Appl. Phys., vol 30, pp. 97, Jan 1991.
 P. Sharma, M. Vashistha, I.P. Jain, “Theoretical investigation of the optical properties of Ge20Se80-xBix thin films,” Chalc.Lett., vol 2, Number 11, pp. 113, Nov 2005.
 M. A. Majeed khan, M. Zulfequar, S. Kumar, M. Hussain, “Optical band gap and optical constants in a-Se100-xSbx thin films,” J. Mod. Opt, vol 50, Issue 2, pp. 251-263, Jan 2003.
 S. R. Ovshinsky, “Reversible Electrical Switching Phenomena in Disordered Structures,” Phys. Rev. Lett., vol 21, Issue 20, pp. 1450, Nov 1968.
 J. Bicerano and Stanford R. Ovshinsky, “Chemical bond approach to the structures of chalcogenide glasses with reversible switching properties,” J. Non-cryst. Solids, vol 74, Issue 1, pp. 75-84, Sept 1985
 S. Murugavel and S. Asokan, “Composition tunable memory and threshold switching in Al20AsxTe80-x semi conducting glasses,” J. Mater. Res., vol 13, pp. 2982, 1998.
 R. A. Narayanan, S. Asokan, and A. Kumar, “Influence of chemical disorder on electrical switching in chalcogenide glasses,” Phys. Rev. B, vol 63, Issue 9, pp. 092203, Feb 2001.
 S. R. Ovshinsky and H. Fritzche, “Amorphous semiconductors for switching, memory and imaging applications,” IEEE. Trans. Electron Devices, vol 20, Issue 2, pp. 91-105, Feb 1973.
 H. Fritzche, “Amorphous and Liquid Semiconductors,” Pletinum Press, London, 1974, pp. 221-312.
 N. F. Mott and E.A. Davis, Electronic processes in Non-Crystalline Materials, Clarendon Press, London, 1979.
 E. Bebenskas, S. Balyavichyus, A. Deksins, A. Poshkus, N. Shiktorov, “Past switching in sandwich structures on the basis of GexTe1-x alloys,” J.Non. Cryst. Solids, vol 90, Issue 1-3, pp. 601-604, Feb 1987.
 D. P Gosain, M. Nakamura, T. Shimizu, M. Suzuki, S. Okano, “Nonvolatile memory based reversible phase transition phenomena in telluride glasses,” Jap.J.Appl. Phys., vol 28, Part 1, Number 6, pp. 1013, June 1989.
 S. S. K. Titus, R. Chatterjee, S. Asokan, A. Kumar, “Electrical switching and short-range order in As-Te glasses,” Phys. Rev. B, vol 48, pp.1460, Nov 1993.
 K. Ramesh, S. Asokan, K.S. Sangunni, E.S.R. Gopal, “Electrical switching in germanium telluride glasses doped with Cu and Ag,” Appl. Phys. A., vol 69, pp. 421, 1999
 S. Prakash, S. Asokan, D.B. Ghare, “Easily reversible memory switching in Ge As Te glasses,” J. Phys. D. Appl. Phys, vol 29, pp.1, 1996.
 G. Sreevidya Varma, D.V.S. Muthu, A.K. Sood, S. Asokan, “Electrical switching, SET-RESET, and Raman scattering studies on Ge15Te80-xIn5Agx glasses,” J. Appl. Phys., vol 115, pp. 164505, 2014.
 M. Frumar and T. Wagner, “Ag doped chalcogenide glasses and their applications,” Curr. Opin. Solid State Mater. Sci, vol 7, Issue 2, pp. 117-126, April 2003.
 S. Murugavel and S. Asokan, “Local Structure and electrical switching in chalcogenide glasses,” Phys. Rev. B, vol 58, pp. 3022, 1998.
 N. Manikandan and S. Asokan, “Effect of indium doping on the electrical switching behavior of Ge-Te glasses,” Philos. Mag., vol 87, pp. 5109, 2007.
 C. N. Murthy, V. Ganeshan, and S. Asokan, “Electrical Switching and Topological Thresholds in Ge-Te and Si-Te Glasses,” Appl. Phys. A., vol 81, pp. 939, 2005.
 Z. U. Borisova, “Glassy Semiconductors,” Plenum Press, New York, 1985.
 J. Z. Liu and P.C. Taylor, “The formal valence shell model for structure of amorphous semiconductors,” J. Non-Cryst. Solids, vol 114, pp. 25-30, Dec 1989.