Recent developments in phase‐change memory

Abstract

Phase-change memory (PCM) belongs to the nonvolatile solid-state memory techniques. Usually, a chalcogenide is sandwiched between two conductive electrodes and data are stored by setting each cell to a low-resistance (crystalline) or a high-resistance (amorphous) state. Switching between these states is relatively fast, which makes phase-change random access memories (PCRAMs) highly interesting for nonvolatile memories. Multilevel cells, which can store more than 1 bit per cell, and multilayer high-density memory arrays have also been reported as advantages of PCRAM. Writing currents and data retention, on the other hand, still show potential for optimization. This review gives an overview of the most recent developments in new material compositions and material-related optimization of PCM in comparison with already produced PCM.

Reduction of write current with improved thermal stability in GeSe2 doped Sb2Te3 films for phase change memory applications

“…Phase change materials composed of chalcogenide elements have been considered for their extraordinary properties which can be exploited for non-volatile memory devices i.e. Phase Change Random Access Memory (PCRAM) or optical devices (CDs, DVDs and Blu-Ray Discs) [1][2][3][4][5][6][7]. Advanced computing architecture, such as Neuromorphic based computing the existing memory or storage technologies (flash memory, DRAM, SRAM, HDD, and SSD) and finding an alternative technology [6].…”

“…The search for potential phase change material has been increasing ever since Ovshinsky gave the idea of reversible electrical switching between two structurally stable states in chalcogenide alloys in 1968 [13]. Multilevel data storage based on intermediate states between two fully amorphous and fully crystalline states increases the storage capacity by storing multiple bits in a single cell [7,14]. The phase transition is realized by applying either electrical or optical (laser) pulses.…”

Minority-carrier transport through an isotype amorphous-crystalline Ge2Sb2Te5 heterojunction under forward bias

“…Typically, a single bit of information is stored using the two distinct resistance levels of a PCM. However, in multilevel PCM devices, the size of the amorphous region within the active material can be varied to achieve a continuum of resistance levels so that multiple bits of information can be stored in a single PCM cell [2,3]; ergo greater storage densities can be achieved.…”

Evaluation of vibrational properties and local structure change during phase transition in Ge2Sb2Te5 and In3SbTe2 phase change materials

“…These two phases correspond to binary logic '0' and '1', the two memory states, respectively. Most commercial optical data storage media (DVD and Blu-ray) utilized Ge 2 Sb 2 Te 5 (GST), a conventional and prevailing phase change material [1,9]. GST is also widely used in the PCM due to its rapid phase transition feature [1].…”

“…Henceforth, the phase transition is governed by the chemical bonds in the chalcogenide material. The covalent bonds in the amorphous phase of GST material transform into the unique metavalent bonds in the crystalline phase [9,17]. Neighbouring atoms in a molecule share two electrons in a covalent bond, whereas the metavalent bond shares only one electron [16,17].…”