Sevison, G., Farzinazar, S., Burrow, J., Perez, C., Kwon, Heungdong, Lee, J., Asheghi, M., Goodson, K.E., Hendrickson, J., Afha, I., 2020, “Phase Change Dynamics and 2-Dimensional 4Bit Memory in Ge2Sb2Te5 Via Telecom-Band Encoding,” ACS Photonics, Vol. 7, pp. 480-487.

Abstract

PDFAs modern computing gets continuously pushed up against the von Neumann Bottleneck-limiting the ultimate speeds for data transfer and computation- new computing methods are needed in order to bypass this issue and keep our computer’s evolution moving forward, such as hybrid computing with an optical co-processor, all-optical computing, or photonic neuromorphic computing. In any of these protocols, we require an optical memory: either a multilevel/ accumulator memory, or a computational memory. Here, We propose and demonstrate a 2-dimensional 4-bit fully optical non-volatile memory using Ge2Sb2Te5 (GST) phase change materials, with encoding via a 1550 nm laser. Using the telecom-band laser, we are able to reach deeper into the material due to the low-loss nature of GST at this wavelength range, hence increasing the number of optical write/read levels compared to previous demonstrations, while simultaneously staying within acceptable read/write energies (maximum 60 nJ/bit for write, depending on the number of pulses). For our experimental results 50 ns long pulses with a 25 ns fall time, a peak power of 200 mW, and a 125 kHz repetition rate were used. We verify our design and experimental results via rigorous numerical simulations based on finite element and nucleation theory, and we successfully write and read a string of characters using direct hexadecimal encoding.