Study of memory effect in amorphous chalcogenide semiconductor GST225 thin films

We explored phase change memory phenomena in thin film of chalcogenide-glass semiconductors GST225 by passing through the film a sequence of triangular current impulses with increasing amplitude. Initially the film was in amorphous state. We took simultaneous oscilloscope pictures of the voltage across the thin-film “sandwich” type sample and the current passing through the above unit as a function of time. Then we got the current-voltage characteristics of the unit done. Distinctive features observed on some of the oscilloscope pictures and current-voltage characteristics are places with rapid decrease in voltage and negative differential resistance. After passing current impulse with the biggest amplitude the current-voltage characteristic of the unit is becoming almost ohmic. Analysis of all the current-voltage characteristics obtained allows us to suggest that the memory state formation apparently occurs in stages with gradual crystallization of amorphous substance of the film on thickness depending on amplitude of the triangular current impulses passing through the unit. This possible scenario is discussed here only from qualitative point of view. The rapid decreases in voltage apparently can under certain conditions be explained by peculiarities of crystallization process (“explosive” crystallization) while crystallization itself is initiated by electrical field. Taking also into account that under injection of current, when the film is in poorly conducting state, a space charge appears to form and as consequence a nonuniform distribution of field on thickness of the film can arise we can assume that crystallization starts at one of electrodes where the field is the biggest. “Explosive” crystallization of amorphous substance dies down when the field near the front of crystallization turns out to be not enough for holding it. After a part of the film is crystallized such a way and conditions for “explosive” crystallization are not more fulfilled the further crystallization can run by heating. As to a part of current-voltage characteristic with negative differential resistance they apparently are connected with switching phenomena that is characteristic of amorphous chalcogenide semiconductors.

1. Bogoslovskij N.A., Tsendin K.D. Electronic–thermal switching and memory in chalcogenide glassy semiconductors. Journal of Non-Crystalline Solids, 2011, vol. 357, pp. 992–995.

2. Bogoslovskiy N.A., Tsendin K.D. Multiphonon tunnel ionization of negative-U centers – the origin of switching and memory effects in chalcogenide glasses. Journal of optoelectronics and advanced materials, 2011, vol. 13, no. 11–12, pp. 1423–1428.

3. Bogoslovskiy N.A., Tsendin K.D. Fizika effekta pereklucheniya i pamyati v khalkogenidnykh stekloobraznykh poluprovodnikakh. Fizika I tekhnika poluprovodnikov, 2012, vol. 46, no. 5, pp. 577–608. (In Russ.)

4. Fefelov S.A., Kazakova L.P., Kozyukhin S.A., Tsendin K.D., Arsova D., Pamukchieva V. Osobennosti volt-ampernykh kharakteristik v tonkikh plenkakh sostava Ge2Sb2Te5 pri ispolzovanii izmeritelnoi tsepi s istochnikom toka. Zhurnal tekhnicheskoi fiziki. 2014, vol. 84, no. 4, pp. 80 – 84. (In Russ.)

5. Fefelov S.A., Kazakova L.P., Arsova D., Kozyukhin S.A., Tsendin K.D., Prikhodko O.Yu. Ostsillyatsii napryazheniya pri effekte pereklyuchenia v rezhime tokovoi mody v tonkikh sloyakh khalkogenidov sistemy Ge-Sb-Te. Fizika i tekhnika poluprovodnikov, 2016, vol. 50, no. 7, pp. 958–962. (In Russ.)

6. Glukhenkaya V.B., Romashkin A.V., Yakubov A.O., Lazarenko P.I., Sherchenkov A.A., Kozyukhin S.A. Lokalnye strukturnye perestroeniya v tonkikh plenkakh Ge2Sb2Te5 v protsesse termicheskoi kristallizatsii. Amorfnye i mikrokristallicheskie poluprovodniki / Proceedings of the International conference. Saint-Petersburg (Russia), July, 05–07, 2021. St. Petersburg (Russia):[Politech-Press], 2021, pp. 73–74. (In Russ.)

7. Kolomiets B.T., Lebedev E.A. Voltampernaya kharakteristika tochechnogo kontakta so stekloobraznymi poluprovodnikami. Radiotekhnika i elektronika, 1963, vol. 8, pp. 2097–2098. (In Russ.)

8. Lampert M.A., Mark P. Current injection in Solids. New York: Academic Press, 1970.

9. Nardone M., Simon M., Karpov I. V., Karpov V. G. Electrical conduction in chalcogenide glasses of phase change memory. J. Appl. Phys., 2012, no. 112, 071101

10. Ovshinsky R.S. Reversible electrical switching phenomena in disordered structures. Phys. Rev. Lett., 1968, vol. 21, pp. 1450–1453.

11. Raoux S., Welnic W., Ielmini D. Phase change materials and their application to nonvolatile memories. Chem. Rev., 2009, vol. 110, no. 1, pp. 240–267.

12. Sherchenkov A.A., Kozyukhin S. A., Borgardt N.I., Lazarenko P.I., Babich A.V., Yakubov A.O., Trekhov D.Yu., Zybina Yu.S. Vliyanie metoda osazhdeniya na svoistva tonkikh plenok materialov fazovoi pamyati. Amorfnye i mikrokristallicheskie poluprovodniki / Proceedings of the International conference. Saint-Petersburg (Russia), November, 19–21, 2018. St. Petersburg (Russia):[Politech-Press], 2018, pp. 83–84. (In Russ.)

13. Sherchenkov A.A., Kozyukhin S. A., Lazarenko P.I., Babich A.V., Bogoslowsky N.A., Sagunova I. V., Redichev E.N. Elektrofizicheskie svoistva i mekhanizmy perenosa v tonkikh plenkakh materialov fazovoi pamyati na osnove khalkogenidnykh poluprovodnikov kvazibinarnogo razreza GeTe-Sb2Te3. Fizika I tekhnika poluprovodnikov, 2017, vol. 51, no. 2, pp. 154–160. (In Russ.)

14. Shklovskii V.A., Kuzmenko V.M. Vzryvnaya krisstalizatsiya amorfnykh vetshestv. Uspekhi fizicheskikh nauk, 1989,vol. 157, no. 2, pp. 311–338. (In Russ.)

15. Volkov A.F., Kogan S.M. Fizicheskie yavleniya v poluprovodnikakh s otritsatelnoi differentsialnoi provodimostyu. Uspekhi fizicheskikh nauk, 1968, vol. 96, no. 4, pp. 633–672. (In Russ.)

16. Yakubov A.O., Sherchenkov A.A., Babich A.V., Lazarenko P.I., Trekhov D.Yu. Izuchenie osobennostei kinetiki kristallizatsii tonkikh plenok materialov fazovoi pamyati po resultatam izmerenii temperaturnykh zavisimostei udelnykh soprotivlenii. Amorfnye i mikrokristallicheskie poluprovodniki / Proceedings of the International conference. Saint-Petersburg (Russia), November, 19 – 21, 2018. St. Petersburg (Russia):[Politech-Press], 2018, pp. 96–97. (In Russ.)

17. Yamada N., Ohno E., Nishiuchi K., Akahira N., Takao M. Rapid-phase transitions of GeTe-Sb2Te3 pseudobinary amorphous thin films for an optical disk memory. J.Appl.Phys, 1991, vol. 69, no. 5, pp. 2849–2856.