“A Review Pertinent to Next Generation RRAM (Resistive Random Access Memory) Reliability” by Professor Chao Sung LAI, Dean of Institute of Engineering, Chang Gung University, Taiwan. IEEE Distinguished Lecturer.

June 26, 2015 (Friday)
10:30 am – 1:30 pm
Dewan Kuliah A, Engineering Campus, University Science Malaysia, 14300 Nibong Tebal, Penang, Malaysia

Admission is free.

Abstract

Resistive random access memory (RRAM) has been proposed as the most promising candidate to replace the conventional floating gate flash memory because of the scaling issues of low program/erase speeds and poor data retention. The advantages of simple structure, easy fabrication, fast operation speed, excellent scalability, multilevel potential, and compatible with CMOS process make RRAMs become more attractive. To recyclingly change the conductivity of the resistive switching (RS) layer of RRAMs between the high resistance state (HRS) and low resistance state (LRS), the sweep or pulse voltage operation are performed. The bistable resistive switching behavior can be realized by applying a simple metal insulator metal (MIM) structure with a transition metal oxide such as SiO2, NiO, TiO2, HfO2, GdxOy, etc., which have been used as the dielectric layer of MOSFET. For the resistive switching mechanism of RRAM devices, the change of Schottky barrier height of the interface between metal electrode and RS layer has been proposed to be the interfacetype resistive switching. Further, the control of conductive filaments within the RS layer to modulate the space charge limited conduction (SCLC) can be referred to the bulktype resistive switching. The amount and distribution of oxygen vacancies within the transition metal oxide are responsible for the resistive switching of both of these two mechanisms. Performance dependence of top electrode (TE) alloy, fluorine, nitrogen, and hydrogen contained plasma treatment, and post metallization annealing (PMA) process on gadolinium oxide (GdxOy) resistance random access memory (RRAM) has been investigated. The resistive switching (RS) characteristics of GdxOy RRAMs such as operation voltages and retention behavior can be significantly improved by using the CF4 and NH3 plasma treatment on GdxOy RS layer and Pt–Al alloy TE with a 10 v/v% Al incorporation because of the defects passivation and the suppression of Pt crystallization with the AlxOy layer formation at Pt/GdxOy interface respectively.

On the other hand, the nitrogen and hydrogen plasma immersion ion implantation (PIII) changes the RS mechanism from Schottky emission to space charge limited conduction (SCLC) due to the elimination of oxygen vacancies at the surface of GdxOy film. Further, even after a 3 month waiting time, the GdxOy RRAMs with PMA at 400 oC in O2 gas ambient can sustain a sample yield of more than 60%. The comprehensive study of GdxOy RRAMs with material and process techniques provides an opportunity of RRAM application in nextgeneration nonvolatile memory.