Fig. 4: Nanostructure and device performance of (Ge4Sb6Te7) GST467.
From: On-the-fly closed-loop materials discovery via Bayesian active learning
Newly identified phase-change memory material GST467 shows large optical contrast ideal for photonic-switching device applications such as neuromorphic computing. a High resolution transmission electron microscopy image reveals formation of coherent nanocomposite of GST structure matrix and SbTe. The dotted lines denote the atomically sharp interface. The FFT (inset) of this region indicates structural similarity of the adjacent phases; b endurance of the GST467: it is stable over 30,000 cycles indicating the robustness of the nanocomposite structure defined by local composition variation. The dotted lines indicate the range of each state in relative optical transmission ΔT/To at 1500 nm. Laser pulses were 50 ns with 183 pJ for quenching and 500 ns with 3.3 nJ for crystallization. The fluctuations in ΔT/To are due to the thermal fluctuation of the device measurement set-up; c comparison of the optical contrast here indicated by difference in the extinction coefficient k between crystalline and amorphous phases (kc − ka) for the wavelength range of 1000–1500 nm for various compositions within Ge–Sb–Te system. GST225 and GST467 data are from this work. The GeTe data are from ref. 55. GST467 shows higher extinction difference over other known compositions; one-to-one comparison of d GST225 (left) and e GST467 (right) for multi-level switching in optical transmission at 1500 nm (ΔT/To) using 500 ns, 6 pJ pulses: GST467 having larger optical contrast results in substantially more states than GST225. Device fabrication and characterization details are in Methods.
