Characterization of Ge-Sb-Te based film by MOCVD for phase change memory application

Abstract

In the early 1960s, new reversible phase change materials and electrically and optically programmable devices were reported, and these devices were proposed for use in digital computers as non-volatile memory. 650 MByte PD and CD-RW disks and 5.2 GByte DVD-RAM optical memory disks using a laser-induced structural phase change in a chalcogenide alloy are now in production. Recently, strong interest has focused on the Ge-Sb-Te alloy materials, especially $Ge_2Sb_2Te_5$ for phase change random access memory (PRAM), because PRAM is most appropriate to the requirements such as nonvolatile, fast speed, high endurance among the next generation memories. PRAM technologies using GST thin films are based upon the reversible switching between the amorphous and the crystalline phase. According to the phase change from amorphous to crystalline phase, GST thin films have very different optical and electrical properties. In the last years, extensive experimental studies have been conducted to understand the crystallization phenomena. The important issues in PRAM are low writing current, endurance and so on. The writing current flows from TEC through GST to BEC and the phase transition occurs at around the BEC-GST interface. The writing current is mainly determined by contact size between phase change material and BEC. Reduced contact size increases the local current density and joule heating in GST material. The induced heat is directly dependent on current density. So, the contact size of the BEC to GST is very decisive factors. To fabricate the small contact size of the BEC to GST, we need the C thin films by sputtering, thermal evaporation, and pulsed laser deposition was already demonstrated. Generally, chemical vapor deposition (CVD) is a process whereby a solid material is deposited from a vapor by a chemical reaction occurring on or in the vicinity of a normally heated substrate surface. CVD is employed in many thin film applications. Among various deposition te...