×10 Fast write, 80% energy saving temperature controlling set method for multi-level cell phase change memories to solve the scaling blockade

Abstract

This paper presents a new set method with temperature control to reduce both energy dissipation and write time of multi-level cell (MLC) phase change memories (PCMs). Since the set energy of PCM is quite larger than reset due to long set time, reducing the set energy is a critical issue to realize MLC PCM. Moreover, this paper shows the set time and energy become longer and lager as the diameter of a tungsten heater is scaled down due to thermal dissipation. To solve these problems, this paper proposes a unique set pulse which combines two pulses: the 1st pulse is high voltage and short width and the 2nd pulse is low voltage and long width. The 1st pulse contributes to faster set time and the 2nd pulse controls the crystallization of GST film. As a result, ∼80% of energy saving and ∼10-times fast write speed are achieved for a 90nm MLC PCM. The proposed set method overcomes the scaling blockade due to thermal dissipation and is essential for a nano-scale MLC PCM.