Characteristics of OUM Phase Change Materials and Devices for High Density Nonvolatile Commodity and Embedded Memory Applications

Abstract

Phase change memory devices were originally reported by S. R.Ovshinsky [1] in 1968. A 256-bit phase-change memory array based on chalcogenide materials was reported in 1970 [2] Recent advances in phase change materials, memory device designs, and process technology have resulted in significant advances in phase change device performance, and a new memory device, called Ovonic Unified Memory (OUM), has been developed. This paper will discuss various device and materials characteristics of OUM phase change memory materials of interest in applications for nonvolatile high-density memories. These materials are generally Te chalcogenide based, exploiting the congruent crystallization of the FCC phase and the associated reduction in resistivity that results from crystallization from the quenched amorphous state. Data storage is a thermally initiated, rapid, reversible structural phase change in the film. While rewriteable DVD disks employ laser heat to induce the phase change and modulate reflectivity, OUM technology uses a short electrical current pulse to modulate resistivity. The device geometry and thermal environment dictate the power and energy required for memory state programming.

Finite Element Analysis of Dependence of Programming Characteristics of Phase-Change Memory on Material Properties of Chalcogenides

“…16) As previously reported by our group and other research groups, the fcc crystalline phase has a resistivity of approximately 10 mÁcm. 8,15) Furthermore, as shown in Fig. 1, our experimental results indicate that the resistivity of crystalline GST (c-GST) increases by up to two or three orders of magnitude with the nitrogen concentration in the GST, which can be easily controlled by adjusting the flow ratio of N 2 gas to Ar gas during sputtering.…”

“…Figures 3(a), 3(c), and 3(e) show the thermal and heat flux distributions just after the application of a programmable current pulse of 1.2 mA and 30 ns in the three cases of the c-GST resistivities of 2, 10, and 100 mÁcm, respectively. The c-GST resistivities are about one order of magnitude lower, close to and about one order of magnitude higher than that of the resistive heater (12 mÁcm 15) ), respectively. Figures 3(b), 3(d), and 3(f) show the temperature profiles in the on-current period along the y-axis in the above three cases, respectively.…”

Innovation Providing New Multiple Functions in Phase-Change Materials To Achieve Cognitive Computing

“…Ge, Sb and Te have been the archetypical elements for the Ovonic memory material from its beginnings [8,[12][13][14][15] to which other elements can be added. Ovonyx has several licensees, including STMicroelectronics, and the work is progressing very well [17]. Our Ovonic electrical phase-change memories are the basis of our joint venture Ovonyx with Tyler Lowrey, Intel and others [16].…”

Why are chalcogenide glasses the materials of choice for Ovonic switching devices?

“…His discovery led to the commercialization of digital optical random access memory discs [2] and the development of a new non-volatile electrical memory technology [3][4][5]. The physics of the electronic switching effect was discussed in the late 1970s [6] and early 1980s [7].…”