Electrical Switching Characteristics of Ge1Se1Te2Chalcogenide Thin Film for Phase Change Memory

Abstract

The changes of the electrical conductivity in chalcogenide amorphous semiconductors, <TEX>$Ge_{1}Se_{1}Te_{2}$</TEX>, have been studied. A phase change random access memory (PRAM) device without an access transistor is successfully fabricated with the <TEX>$Ge_{1}Se_{1}Te_{2}$</TEX>-phase-change resistor, which has much higher electrical resistivity than <TEX>$Ge_{2}Sb_{2}Te_{5}$</TEX> and its electric resistivity can be varied by the factor of <TEX>$10^5$</TEX> times, relating with the degree of crystallization. 100 nm thick <TEX>$Ge_{1}Se_{1}Te_{2}$</TEX> thin film was formed by vacuum deposition at <TEX>$1.5{\times}10^{-5}$</TEX> Torr. The static mode switching (DC test) is tested for the <TEX>$100\;{\mu}m-sized$</TEX> <TEX>$Ge_{1}Se_{1}Te_{2}$</TEX> PRAM device. In the first sweep, the amorphous <TEX>$Ge_{1}Se_{1}Te_{2}$</TEX> thin film showed a high resistance state at low voltage region. However, when it reached to the threshold voltage, <TEX>$V_{th}$</TEX>, the electrical resistance of device was drastically reduced through the formation of an electrically conducting path. The pulsed mode switching of the <TEX>$20{\mu}m-sized$</TEX> <TEX>$Ge_{1}Se_{1}Te_{2}$</TEX> PRAM device showed that the reset of device was done with a 80 ns-8.6 V pulse and the set of device was done with a 200 ns-4.3 V pulse.