Impact of crystallization process in multilevel optical switching in Ge₂Sb₂Te₅ and Ag₅In₅Sb₆₀Te₃₀ phase-change materials

Abstract

Phase change materials including GeSbTe and AgInSbTe have successfully demonstrated multilevel switching capabilities, yet achieving precise controllability and reproducibility are crucial towards technological applications. In this study, we demonstrate nine distinct optical levels in Ge2Sb2Te5 (GST225) and Ag5In5Sb60Te30 (AIST) phase-change materials using pump-probe experiments under identical device conditions and the role of the crystallization mechanism is examined for realization of reliable multi-level programming. Nucleation-dominated GST225 material corroborates improved performance characteristics of low threshold fluence (6 mJ cm−2), least optical variation (±0.25%), and high reflectivity contrast (∼2.5%) between any two consecutive levels as compared to growth-dominated AIST material. Furthermore, the opto-thermal simulations depict a gradual change in the crystalline fraction in GST225 and an abrupt change in AIST, which further confirms the improved controllability in nucleation-dominated crystallization. Hence, these identical measurements along with the opto-thermal simulations elucidate that the role and nature of crystallization play a critical role in precise control of variation of reflectivity in multi-level states of GST225 and AIST, respectively. These findings will be useful towards the development of reliable multi-bit phase-change photonic memory devices.

Realization of 4-Bit Multilevel Optical Switching in Ge2Sb2Te5 and Ag5In5Sb60Te30 Phase-Change Materials Enabled in the Visible Region

“…Thus, the standard deviation in error for 4-bit multilevel states performed has been calculated to be 0.25% and plotted in Figure b. This result is found to be consistent with the previously reported value in GST225 …”

“…On the other hand, AIST exhibits lower optical variations of 0.22% (Figure b), which shows comparatively an improved signal-to-noise ratio than the previously reported value in AIST (0.35%) . Furthermore, the reversible cycles shown in Figure a demonstrate stable optical levels with minimum variations.…”

Multilevel Switching in Phase‐Change Photonic Memory Devices

“…To overcome this problem, single‐shot laser pulses of variable fluence have been introduced to produce multilevel states with higher optical contrast. [ 53,61–63 ] There is a linear rise in the optical contrast between the SET and RESET process with an increase in the laser fluence (performed in free‐space optics), as shown in Figure . [ 64 ] By carefully tuning the laser fluence, the optical contrast can be increased significantly, which enables precise tunability of amorphous/crystalline volumetric fraction.…”

Fiber-Integrated All-Optical Signal Processing Device for Storage and Computing

“…To overcome these fundamental limitations, researchers have begun to pay attention to nonvolatile phase change materials (PCMs) for all-optical signal processing − devices due to several unique properties: high scalability and simple fabrication, state retention for years in no need of extra power–nonvolatile, phase transition between amorphous and crystalline states with considerable modulation in optical constants, and high endurance up to 10 15 switching cycles . Particularly, Ge 2 Sb 2 Te 5 (GST) is a kind of typical PCMs, which performs well in terms of speed and stability, , and is a very promising candidate material for all-optical signal processing.…”