Enhancing the Performance of Phase Change Memory for Embedded Applications

Abstract

Focusing on meeting the requirements for embedded applications of faster switching and sensing, lower-power consumption, higher reliability, longer cycling endurance, and higher temperature retention, a lot of progress in the phase change memory (PCM) field has been made, including materials improvement, process optimization, new circuits design, and better operation algorithms. Finally, a 128 MB embedded PCM chip has been demonstrated in 40 nm node. Using carbon-doped Ge 2 Sb 2 Te 5 phase change material and 3 nm thick heating bottom electrode contact (BEC) with nitride coating, a resistance ratio of more than two orders of magnitude has been achieved in Reset and Set states. Combined with the parasitic matched sensing circuit, optimized ramp-down SET pulses, adaptive pre-read and write-verify methods, and automatic configure and test procedures, the chip exhibits excellent data retention and endurance characteristics with minimum program time of 200 ns, and the Reset/Set resistance ratio becomes even larger after 260 C soldering test. The estimated data retention time is 10 years at 128 C, and in a 128 MB full integrated chip the endurance over 10 9 cycles is achieved. It is confirmed that this PCM technology is suitable for embedded applications, especially for those with crucial requirements of high access speed, high thermal stability, and cycling endurance.

Phase change thin films for non-volatile memory applications

“…25 In order to enhance the crystallisation speed, several strategies have been developed, including doping of the material or using GST based heterostructures. 14,106,[147][148][149] Recently, a promising approach to study the crystallization capabilities of GST225 has been presented based on interfaceassisted epitaxial recrystallization of GST225 phase I (c-GST225) in epitaxially grown GST225 thin lms. 83 In detail, single ns-laser pulse irradiation of an epitaxial trigonal GST225 (t-GST225) thin lm caused partial melting of the lm followed by ultrafast recrystallization during the cool down process.…”

Ab initio molecular dynamics and materials design for embedded phase-change memory

“…Storage-oriented applications, such as embedded memories, require PCMs with higher amorphous-phase stability at (very) high temperature. This is important, for instance, in the automotive industry, where the ability of the material to endure high operating temperatures outweighs an associated reduction in switching speed 23,24 . Resistance drift is also not an issue for binary storage based embedded memories, as the resistance window widens with time (making the contrast larger and the distinction between 'ones' and 'zeroes' clearer).…”

High Contact Resistivity Enabling Low‐Energy Operation in Cr2Ge2Te6‐Based Phase‐Change Random Access Memory

“…[ 1–3 ] Recently, PCM‐based storage‐class memory, which can mitigate the speed and capacity gaps between dynamic random access memory and flash memory, has become commercially available. [ 4,5 ]…”