Fragile‐to‐Strong Crossover in Supercooled Liquid Ag‐In‐Sb‐Te Studied by Ultrafast Calorimetry

Abstract

Phase‐change random‐access memory relies on the reversible crystalline‐glassy phase change in chalcogenide thin films. In this application, the speed of crystallization is critical for device performance: there is a need to combine ultrafast crystallization for switching at high temperature with high resistance to crystallization for non‐volatile data retention near to room temperature. In phase‐change media such as nucleation‐dominated Ge2Sb2Te5, these conflicting requirements are met through the highly “fragile” nature of the temperature dependence of the viscosity of the supercooled liquid. The present study explores, using ultrafast‐heating calorimetry, the equivalent temperature dependence for the growth‐dominated medium Ag‐In‐Sb‐Te. The crystallization shows (unexpectedly) Arrhenius temperature dependence over a wide intermediate temperature range. Here it is shown that this is evidence for a fragile‐to‐strong crossover on cooling the liquid. Such a crossover has many consequences for the interpretation and control of phase‐change kinetics in chalcogenide media, helping to understand the distinction between nucleation‐ and growth‐dominated crystallization, and offering a route to designing improved device performance.

Amorphous to Crystal Phase Change Memory Effect with Two-Fold Bandgap Difference in Semiconducting K2Bi8Se13

“…Thus, the T g / T m ratio is a figure of merit that helps to define the amorphous-to-crystalline conversion rates. In this context, the T g / T m ratio for GST and AIST ranges from ∼0.42 to 0.56. , These ratios are in line with the fast crystallization rate in GST and AIST on the time scale of a few nanoseconds. − The glass transition feature is the result of a small enthalpy of relaxation of the amorphous material. For KBS, we were unable to determine this small relaxation event by DSC because of the small amount (∼1 mg) of the KBS film sample.…”

Amorphous to Crystal Phase Change Memory Effect with Two-Fold Bandgap Difference in Semiconducting K2Bi8Se13

“…Thus, the T g / T m ratio is a figure of merit that helps to define the amorphous-to-crystalline conversion rates. In this context, the T g / T m ratio for GST and AIST ranges from ∼0.42 to 0.56. , These ratios are in line with the fast crystallization rate in GST and AIST on the time scale of a few nanoseconds. − The glass transition feature is the result of a small enthalpy of relaxation of the amorphous material. For KBS, we were unable to determine this small relaxation event by DSC because of the small amount (∼1 mg) of the KBS film sample.…”

Experimental Nonevidence of Fragile-to-Strong Crossover

“… , Beyond metallic systems, FTS behavior has also been frequently reported for chalcogenide materials. Ultrafast scanning calorimetry revealed FTS crossover in chalcogenide phase-change materials (PCMs), , where it is regarded as a potentially critical property for their technological applicability. , A comprehensive review by Lucas further explores the FTS crossover.…”

“…Ultrafast scanning calorimetry revealed FTS crossover in chalcogenide phase-change materials (PCMs), , where it is regarded as a potentially critical property for their technological applicability. , A comprehensive review by Lucas further explores the FTS crossover. A significant part of Lucas’ work deals with the chalcogenide materials and the existence of the crossover in Ge 15 Te 85 and compositions from Ge–Se system.…”

Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials

“…The role of the glass transition in the FTS crossover is still a matter of debate and leads to the question whether the PCMs below the crossover are in a supercooled liquid or glassy state. Orava et al reported a strong liquid state of AIST based on Tg=378 K for a standard cooling rate of 20 K/min (20). The kinetic data underlying this scenario, however, agree with data reported by Salinga et al (9) for the glass (Fig.…”

“…The state for the kinetic data below the FTS crossover is still a matter of debate because of experimental difficulties in determining its kinetic properties. Orava et al reported a strong liquid state of AIST based on T g = 378 K for a standard cooling rate of 20 K/min (20). The kinetic data underlying this scenario, however, agree with data reported by Salinga et al (9) for glass (Fig.…”

Amorphous to Crystal Phase Change Memory Effect with Two-Fold Bandgap Difference in Semiconducting K2Bi8Se13

“…Thus, the T g / T m ratio is a figure of merit that helps to define the amorphous-to-crystalline conversion rates. In this context, the T g / T m ratio for GST and AIST ranges from ∼0.42 to 0.56. , These ratios are in line with the fast crystallization rate in GST and AIST on the time scale of a few nanoseconds. − The glass transition feature is the result of a small enthalpy of relaxation of the amorphous material. For KBS, we were unable to determine this small relaxation event by DSC because of the small amount (∼1 mg) of the KBS film sample.…”

Experimental Nonevidence of Fragile-to-Strong Crossover

“… , Beyond metallic systems, FTS behavior has also been frequently reported for chalcogenide materials. Ultrafast scanning calorimetry revealed FTS crossover in chalcogenide phase-change materials (PCMs), , where it is regarded as a potentially critical property for their technological applicability. , A comprehensive review by Lucas further explores the FTS crossover.…”

“…Ultrafast scanning calorimetry revealed FTS crossover in chalcogenide phase-change materials (PCMs), , where it is regarded as a potentially critical property for their technological applicability. , A comprehensive review by Lucas further explores the FTS crossover. A significant part of Lucas’ work deals with the chalcogenide materials and the existence of the crossover in Ge 15 Te 85 and compositions from Ge–Se system.…”

Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials

“…The role of the glass transition in the FTS crossover is still a matter of debate and leads to the question whether the PCMs below the crossover are in a supercooled liquid or glassy state. Orava et al reported a strong liquid state of AIST based on Tg=378 K for a standard cooling rate of 20 K/min (20). The kinetic data underlying this scenario, however, agree with data reported by Salinga et al (9) for the glass (Fig.…”

“…The state for the kinetic data below the FTS crossover is still a matter of debate because of experimental difficulties in determining its kinetic properties. Orava et al reported a strong liquid state of AIST based on T g = 378 K for a standard cooling rate of 20 K/min (20). The kinetic data underlying this scenario, however, agree with data reported by Salinga et al (9) for glass (Fig.…”

Amorphous to Crystal Phase Change Memory Effect with Two-Fold Bandgap Difference in Semiconducting K2Bi8Se13

“…Thus, the T g / T m ratio is a figure of merit that helps to define the amorphous-to-crystalline conversion rates. In this context, the T g / T m ratio for GST and AIST ranges from ∼0.42 to 0.56. , These ratios are in line with the fast crystallization rate in GST and AIST on the time scale of a few nanoseconds. − The glass transition feature is the result of a small enthalpy of relaxation of the amorphous material. For KBS, we were unable to determine this small relaxation event by DSC because of the small amount (∼1 mg) of the KBS film sample.…”

Experimental Nonevidence of Fragile-to-Strong Crossover

“… , Beyond metallic systems, FTS behavior has also been frequently reported for chalcogenide materials. Ultrafast scanning calorimetry revealed FTS crossover in chalcogenide phase-change materials (PCMs), , where it is regarded as a potentially critical property for their technological applicability. , A comprehensive review by Lucas further explores the FTS crossover.…”

“…Ultrafast scanning calorimetry revealed FTS crossover in chalcogenide phase-change materials (PCMs), , where it is regarded as a potentially critical property for their technological applicability. , A comprehensive review by Lucas further explores the FTS crossover. A significant part of Lucas’ work deals with the chalcogenide materials and the existence of the crossover in Ge 15 Te 85 and compositions from Ge–Se system.…”

Femtosecond x-ray diffraction reveals a liquid–liquid phase transition in phase-change materials

“…The role of the glass transition in the FTS crossover is still a matter of debate and leads to the question whether the PCMs below the crossover are in a supercooled liquid or glassy state. Orava et al reported a strong liquid state of AIST based on Tg=378 K for a standard cooling rate of 20 K/min (20). The kinetic data underlying this scenario, however, agree with data reported by Salinga et al (9) for the glass (Fig.…”

“…The state for the kinetic data below the FTS crossover is still a matter of debate because of experimental difficulties in determining its kinetic properties. Orava et al reported a strong liquid state of AIST based on T g = 378 K for a standard cooling rate of 20 K/min (20). The kinetic data underlying this scenario, however, agree with data reported by Salinga et al (9) for glass (Fig.…”