R&D: Multi-Level Optical Storage Scheme via Two-Step Picosecond Laser Irradiations: Time/Space Modulations of Microstructure and its Optical Property

Semiconductor Science and Technology has published an article written by Yongzhi Zhang, Institute of Laser Engineering, Beijing University of Technology, Beijing, China, Furong Liu, Zhao Han, Beijing University of Technology Institute of Laser Engineering, Beijing, China, Wenqiang Li, Beijing University of Technology, Beijing, China, Yin Huang, Institute of Laser Engineering, Beijing University of Technology, Beijing, China, and Nian Sun, Electrical and Computer Engineering Department , Northeastern University, 360 Huntington Avenue, 409 Dana Boston,, MA 02115, USA, Boston, USA.

Abstract: “Nowadays, achievement of multi-level properties of chalcogenide phase change materials is urgently requested for the high-density data storage, photonic switches and neuromorphic computing etc. In this paper, we reported a multi-level implement scheme via a two-step picosecond laser irradiation strategy on the basis of time/space modulations of microstructure and property of Ge2Sb2Te5 (GST) phase change thin films. Different from the common grey-scale method by multiple laser irradiations at a fixed position, multi-levels of optical properties were obtained by two-step overlapping laser irradiations together with such varied parameters as the overlapping ratio, input energy and two-pulse duration. Variations of the microstructure and optical property were characterized by transmission electron microscope (TEM) and microarea reflectance testing. It showed that the overlapping ratio was an important factor to adjust microstructure patterns and optical properties. With the increase of the overlapping ratio, the optical reflectivity presented a trend of increasing first and then decreasing, mainly because of the effects of the size and distribution of grains from the second laser irradiations. Based on the scheme proposed, a 10-level optical reflectivity could be obtained. The fundamental research performed in the present study is of importance to give guideline for the high-density storage or big-data processing with phase change materials in the future.“