Indium selenide (In₂Se₃) thin film for phase-change memory

A cross-point type phase-change random access memory (PRAM) device without an access transistor is successfully fabricated with the In₂Se ₃-phase-change resistor, which has much higher electrical resistivity than Ge₂Sb₂Te₅ and of which electric resistivity can be varied by the factor of 10⁵ times, related with the degree of crystallization. Due to its higher electrical resistivity, the switching power can be delivered more effectively. Since In₂Se ₃ is single-phase binary compound, the device failure related to phase decomposition can be avoided. Since the volume of phase change is very limited, and the heating duration is only for few tens of nanoseconds to 10 μs, the transition of In₂Se₃-phase-change material is done under very far from its thermodynamic equilibrium condition, and thus, formation of the secondary phases or different crystalline phases was not observed. The static mode switching (dc test) is tested for the 5 μm-sized In₂Se₃ PRAM device. In the first sweep, the as-grown amorphous In₂Se₃ resistor showed the high resistance state at low voltage region. However, when it reached the threshold voltage, the electrical resistance of the device was drastically reduced through the formation of an electrically conducting path. The pulsed mode switching of the 5 μm-sized In₂Se₃ PRAM device shows that the reset (crystalline → amorphous) of the device was done with a 70 ns-3.1 V pulse and the set (amorphous → crystalline) of the device was done with a 10 μs-1.2 V pulse. As high as 100 of switching dynamic range (ratio of R _high to R_low) was observed.