R&D: Thermoelectric Effects on Amorphization Process of Blade-Type Phase Change RAM

IEEE Transactions on Electron Devices has published an article written by Xiaojuan Lian, College of Electrical and Optical Engineering, the College of Microelectronics, and the National and Local Joint Engineering Laboratory of RF Integration and Micro-Assembly Technology, Nanjing University of Posts and Telecommunications, Nanjing, China, Jinke Fu, Zhixuan Gao, College of Electrical and Optical Engineering, and the College of Microelectronics, Nanjing University of Posts and Telecommunications, Nanjing, China, and Lei Wang, College of Electrical and Optical Engineering, the College of Microelectronics, and the National and Local Joint Engineering Laboratory of RF Integration and Micro-Assembly Technology, Nanjing University of Posts and Telecommunications, Nanjing, China.

Abstract: “Commercial prospect of phase-change random access memory (PCRAM), considered as an encouraging option for future “universal” memory, is however challenged by its large programming current that severely impairs device scalability. The recent advent of the blade-type PCRAM configuration can effectively address this issue by shrinking the heated region. However, the thermoelectric (TE) effects that play a key role in write performances of conventional Lance-type PCRAM have not been systematically studied for this blade-type case to date. The influence of TE effects on the amorphization process of the blade-type PCRAM cell is therefore investigated here through the establishment of a comprehensive 3-D electrothermal and phase-transformation model. Two main typical TE effects, i.e., Thomson heat inside the Ge ₂ Sb ₂ Te ₅ (GST) bulk region and Peltier heat at the GST-TiN heater interface, have been mimicked and discussed in detail. Simulation results show that both TE effects depend on the polarities of the programming currents, and the calculated Thomson heat is more than 20 times as much as Peltier heat. Accordingly, a novel skutterudite-based heater that exhibits more pronounced TE effects than TiN heater has been proposed. The practicality of reducing programming current by 13.8% and peak power by 17.9% is demonstrated using the improved version of the PCRAM cell.“