The Effects of Process Variation on the Parametric Model of the Static Impedance Behavior of Programmable Metallization
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The Effects of Process Variation on the Parametric Model of the Static Impedance Behavior of Programmable Metallization Cell (PMC) Mehdi Saremi1, Saba Rajabi1, Hugh J. Barnaby1, Michael N. Kozicki1 1
Arizona State University, 650 E. Tyler Mall, Tempe, AZ, 85287-8406, U.S.A.
ABSTRACT Among the new non-volatile memories gaining attention as a potential replacement for flash technology is the programmable metallization cell (PMC) that works by creating and dissolving a conductive bridge across a solid electrolyte film. This enables switching between a high resistance state (HRS) and a low resistance state (LRS). The dominant mechanism for resistance switching is field dependent ion transport in the film. In this work, we examine, through numerical simulation, the effects of process variation on the impedance characteristics of the PMC in both HRS and LRS, by changing key parameters of the device. These parameters include the material bandgap, affinity and permittivity of each device layer. Finally, we show which parameters have the greatest effects on the impedance behavior. INTRODUCTION For next generation of low power and high density non-volatile memory [1-7], Boolean and non-Boolean computation [8-10], resistive switching random access memory (ReRAM) is a strong candidate. In this paper, we focus on one type of ReRAM devices, the programmable metallization cell (PMC), also known as conductive bridge random access memory (CBRAM) [11-12]. The PMC is highly scalable and compatible with standard CMOS, readily integrated into the back-end-of-line (BEOL) process. PMCs operate through the electrochemical control of nano-scale quantities of metal in thin films of chalcogenide glass (ChG) solid electrolyte [1-2]. The cells switch between a low resistance state (LRS) and a high resistance state (HRS) through the formation and dissolution of conductive filaments within the thin ChG film (~ 60 nm). The difference between the HRS and LRS resistance can be up to several orders of magnitude [5, 13]. Metallic ions (typically Ag or Cu), accelerated by an applied electric field, create conductive filaments, which can be formed or dissolved by electrochemical reduction-oxidation (redox) reactions at the device electrodes [1-7, 12-16]. It is worthwhile to mention that even with metal concentrations as high as tens of atomic percent in the LRS, the resistivity of PMCs is still several orders of magnitude higher than that of pure Ag or Cu metal. Because PMC and CBRAM devices are targeted for use in highly scaled ultra-deep submicron technologies, which are often characterized by tight manufacturing tolerances, it is important to quantify the effects of process variation. In this paper, we model variation in the fabrication process by varying the material bandgap, affinity and permittivity of each layer in the material stack. These parameters are known to be impacted by processing steps, particularly those that control film composition and stoichiometry. Simulations performed on models representative of PMCs, in both the HRS and LRS, ar
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