Investigations of High Endurance Asymmetric Phase Change Random Access Memory
- PDF / 187,741 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 213 Views
1072-G03-19
Investigations of High Endurance Asymmetric Phase Change Random Access Memory Hock Koon Lee1, Luping Shi1, Rong Zhao1, Hongxin Yang1,2, Kian Guan Lim1, Jianming LI1, and Tow Chong Chong1,2 1 Optical Materials & Systems Division, Data Storage Institute, A*STAR (Agency for Science, Technology and Research), DSI Building, 5 Engineering Drive 1 (Off Kent Ridge Cresent, NUS), Singapore, 117608, Singapore 2 Electrical & Computing Engineering Department, National University of Singapore, Singapore, Singapore ABSTRACT Asymmetric PCRAM cells were investigated and when the upper contact opening just offset from the bottom contact opening, the reset current was reduced tremendously compared to that of a conventional symmetrical structure due to the improved heat confinement. When the phase change material, Ge2Sb2Te5 was sputtered with a N2/Ar gas flow ratio of 0.2, the asymmetric PCRAM cells lasted 2.4 X 1010 cycles and it lasted 10 times longer than N-doped symmetrical PCRAM cells. INTRODUCTION The world’s demand for non-volatile memory (NVM) is rising due to its increasing usage in devices such as mobile phones, digital cameras, digital camcorders, etc. At present Flash dominates due to its existing infrastructure, established position and low cost. However, among the emerging NVM technologies, PCRAM has the most potential to replace FLASH due to its many ideal memory properties such as fast accessing time, low power consumption, high endurance, good data retention, high scalability [1]. PCRAM are based on chalcogenide material which switches between crystalline and amorphous states on the application of electrical pulses. To set the memory, a long but low amplitude electrical pulse is applied during which the material is heated to above its crystallization temperature and is changed from amorphous, high resistance state to crystalline, low resistance state. To reset the memory, a short but high amplitude electrical pulse is applied so that the material is heated above the melting point and rapidly quenched into amorphous state. Simulation results showed that asymmetric PCRAM cells have much better heat confinement as compared to that of a conventional symmetrical structure and in this paper, further investigations including nitrogen doping of Ge2Sb2Te5 [2] were carried out experimentally to study the cell endurance which is also one of the important memory properties. EXPERIMENT Structure Designs In this work, the PCRAM cell consists of a 100 nm thick of Ge2Sb2Te5 as the phase change layer (PCL) which is capped with 10 nm TiW protective layer to prevent oxidation, 200 nm bottom TiW electrode, 100 nm ZnS-SiO2 dielectric layers and 190 nm top TiW
electrode. For a standard symmetrical PCRAM cell structure shown in Fig 1a, the top and bottom openings for the electrodes in contact the PCL are along the same vertical axis. For the asymmetric structure shown in Fig. 1b, both the top and bottom electrode contact are 1 um and they are at an offset from each other.
Figure 1a: Schematic of a conventional symmetrical PC
Data Loading...
