Phase Change Dynamics and Two-Dimensional 4-Bit Memory in Ge<sub>2</sub>Sb<sub>2</sub>Te<sub>5</sub> via Telecom-Band Encoding
Gary A. Sevison, Shiva Farzinazar, Joshua A. Burrow, Christopher Perez, Heungdong Kwon, Jaeho Lee, Mehdi Asheghi, Kenneth E. Goodson, Andrew Sarangan, Joshua R. Hendrickson, Imad Agha
Abstract
We propose and demonstrate a two-dimensional 4-bit fully optical nonvolatile 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.