Changes in Resistance and Bandgap of V 2 O 5 and Ge 2 Sb 2 Te 5 during Phase Transition
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https://doi.org/10.1007/s11664-020-08599-5 2020 The Minerals, Metals & Materials Society
ORIGINAL RESEARCH ARTICLE
Changes in Resistance and Bandgap of V2O5 and Ge2Sb2Te5 during Phase Transition YONGKANG XU,1 YIFENG HU
,1,3,4 SONG SUN,1 and TIANSHU LAI2,5
1.—School of Mathematics and Physics, Jiangsu University of Technology, Changzhou 213000, China. 2.—State Key Laboratory of Optoelectronic Materials and Technology, School of Physics, Sun Yat-Sen University, Guangzhou 510275, China. 3.—National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China. 4.—e-mail: [email protected]. 5.—e-mail: [email protected]
V2O5 and Ge2Sb2Te5 (GST) films have been prepared by magnetron sputtering, and their transformation from amorphous to crystalline state studied by in situ resistance temperature measurements. During the heating process, a two-step transition was observed for both films, revealing three resistances corresponding to amorphous, intermediate, and crystalline states. The two phase-transition temperatures were 371.1C and 394.0C for V2O5, much higher than the values of 172.4C and 240.4C for GST. Compared with GST, the resistance of V2O5 was two orders of magnitude higher. The changes in the resistance and bandgap of V2O5 and GST during phase transition were investigated in detail. A phase-change memory device based on V2O5 was fabricated. Compared with GST, V2O5 exhibited a lower operating power and shorter phase-transition time. The application potential of V2O5 and GST for multilevel storage was compared. Key words: V2O5, bandgap, resistance, phase-change memory, phase-transition time
INTRODUCTION Phase-change memory (PCM) is considered to represent a new generation of nonvolatile memory. The size of PCM devices can be reduced to 5 nm and the storage speed to less than 1 9 109 s, resulting in higher storage density and lower power consumption.1 Chalcogenides are commonly used as phase-change materials in PCM. Among them, GST exhibits a successive phase transition under the action of current pulses from an amorphous (highresistivity) to intermediate (intermediate resistivity) phase and crystalline (low resistivity) phase, accompanied by obvious electrical performance changes and reversible structural transformations.2,3 In the SET process, a low, wide voltage pulse can cause the temperature of the amorphous region to exceed its crystallization temperature.3 In
(Received August 24, 2020; accepted October 30, 2020)
contrast, during the RESET process, rapid cooling (> 109 K/s) is used to change the molten region into an amorphous phase.3,4 In PCM, high amorphous resistance and low programming power are required.5 Moreover, the crystal structure of the PCM should be stable and the segregation of components during the phasechange process should be reduced.5,6 As a traditional phase-change material, GST shows various weaknesses, such as low crystalline resistivity, narrow bandgap, poor amorphous thermal stability, etc., resulting in an urgent need to explore new PCMs with
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