Application of GeTe phase-change films in the directly heated two-port switch design

Abstract

Phase-change (PC) materials offer the property of thermally induced reversible change and exhibit different resistance values due to the structure changes between crystalline and amorphous phases. In this work, GeTe films with a thickness of 100 nm were deposited on the glass substrates by radio-frequency magnetron sputtering and annealed at different temperatures. The XRD analysis showed diffraction peaks corresponding to the rhombohedral structure of c-GeTe (021), (200), (202), and (220), respectively. Upon annealing at 300 and 340°C, the rhombohedral structure would transform into a rock salt structure. The Raman analysis revealed that a-Ge-Te covalent bond is the mixed structure of tetrahedron and defective octahedron changing into tetrahedral cells. The resistivity declined sharply from 0.72 to 3.8× 10−6 Ω-m, whereas the Hall mobility of holes sharply rose to 300 m2/Vs. Based on the above films, a two-port directly heated switch device was designed and fabricated in sandwich structure to verify its phase-change characteristics. Low-resistance state was converted from crystallization with a 20ns 9V voltage pulse, while high-resistance state was by passing a 2 μs 2V voltage pulse. The on/off resistance ratio of switch could reach five orders of magnitude, while the switch state remained stable after the process termination. The results obtained strongly suggest that GeTe is a promising material for RF switches.