The Fabrication And Optical Property Research Of The Microstructures Based On Phase Change Material GeSbTe

In recent years,tunable and reconfigurable metamaterials and metasurfaces have been the research hotspots,and phase change material GeSbTe(GST)alloy’s reversible phase transition process provides a realization scheme for the tunability or reconfigurability of microstructures.GST has been widely applied in rewritable optical discs as the recording medium,because of its reversible phase transition and low energy requirement.Reversible phase transition between crystalline and amorphous phases of GST can be achieved under different nanosecond laser pulses,and both crystalline and amorphous phases can exist stably for decades at room temperature.The optical discs use the reflectance difference between crystalline and amorphous of GST to store binary digital information.In this paper,the crystallization of amorphous GST thin film in small area to form microstructures is realized with laser direct writing method.GST thin films are prepared on glass substrate by radio frequency magnetron sputtering with a film thickness of about 100 nm,which are in their amorphous state as deposited.After that,some of the amorphous thin films are crystallized using a heating table.Both amorphous and crystalline films have metallic luster and high reflectivity.Then the as-prepared amorphous and crystalline GST films are optically characterized: their optical constants and transmission spectra are measured.In visible to infrared region,amorphous and crystalline GST thin films have large extinction coefficients and low transmittance.And the transmittance of crystalline thin film is always smaller than that of amorphous film.The transmission matrix calculation results show that the reflectivity of the crystalline film is always higher than that of the amorphous state.A laser beam with a wavelength of 442 nm is guided into the microscope and focused on the amorphous thin film to crystallize the thin film.According to the line with higher reflectance after the laser moved,it can be judged that crystallization is achieved in this area.Then the laser heating process is simulated with COMSOL multiphysics commercial software and the temperature distribution inside the thin film and its evolution with time are given,which reflects the crystallization process.Then with Lab VIEW’s automatic control of the motor-driven micropositioning stage and the mechanical shutter,a millimeter-scale grating structure and zone plate structure composed of micrometer-scale crystalline lines are prepared on the amorphous GST thin film.The results of the AFM analysis of the grating surfaces indicate that the surface damage of thin film due to laser heating is negligible.Finally,the gratings and zone plates’ optical characteristics are studied in experiment,and their corresponding functions are achieved,which indicates that the fabrication of microstructures by laser direct writing method has certain feasibility.