Lattice Distortion in In3SbTe2 Phase Change Material with Substitutional Bi.

Phase change random access memory (PRAM) is the best one of candidates for next-generation universal memory. Phase change material, known as chalcogenide, is a core material to divide resistances according to phase change by electrical pulse converted into joule heating. Phase change alloys have been intensively investigated for PRAM applications because of their reversible switching between the amorphous and crystalline states, resulting in variable resistance levels1,2,3,4,5. This universal storage could replace existing data storage (non-volatile memory, CD&DVD disk, and hard disk), further, develop new fields (storage class memory and neuromorphic system). However, a number of switching operation, repeated by electric pulses, would induce decoding error with gradual change of resistance. The resistance drift within the narrow resistance difference leads to random fluctuations in the programmed levels6,7,8. Among several phase change alloys, In-Sb-Te alloys have been suggested as promising candidates for multi-level PRAM because IST alloys demonstrate a stable multi-phase change mechanism from amorphous to NaCl-type cubic, leading to multiple resistance levels9,10,11. However, the thermal stability of IST may not correspond with the higher switching speed because of the energy required. The role of vacancies for GST alloys has been investigated, verifying that switching occurs between the metastable NaCl state and the amorphous state, and those phase transitions can be formed with low activation energies12,13,14,15 at the short timescales due to the vacancies16. The structural features of GST alloys allow local lattice distortions and reduce the activation energy. Similarly, if a certain impurity atom is added into IST, the relationship between the switching speed and lattice distortion can be confirmed. In this work, Bi atoms are selected as the impurity because Bi and Sb are part of the same group in the periodic table. The GST, IST, and IST with incorporated Bi atoms (Bi-IST) are investigated to identify the relationships between the atomic lattice structure, energy stability, activation energy, and switching speed.