Abstract
The refractory transition metal nitride (TMN) film Hafnium nitride (HfNx) was successfully prepared on silicon-based substrates as bottom electrodes for resistive random access memory (RRAM) cells in Pt (top)/metal oxide/ HfNx (bottom) sandwich structure. The reproducible resistive switching (RS) characteristics of the memory cells were studied systematically for RRAM applications. The advantages of adopting HfNx instead of Pt as bottom electrode material were demonstrated, including the improvement of the low resistive state value, the RS endurance and the uniformity of RS parameters. The composition and chemical bonding states of the prepared HfNx was analyzed by X-ray photoelectron spectroscopy (XPS) technique. The nitrogen content in the HfNx and the Gibbs free energy of the corresponding metal oxide formation has great influences on the RS properties. The oxygen reservoir ability and diffusion barrier effect of the HfNx play a key role in the RS performance improvement of the RRAM devices.
Highlights
INTRODUCTIONFrom the viewpoints of controlling or confining the moveable oxygen vacancies (ions) at a local place and improving the thermal stability of the resistive random access memory (RRAM) devices to effectively resolve above mentioned resistive switching (RS) problems, it may be a feasible way to introduce the complementary metal-oxide semiconductor (CMOS)-process-friendly conductive refractory transition metal nitrides (TMN) into RRAM device cells as electrode or buffer layer considering that the TMN, such as WNx,[15,16] HfNx,[17] MoN,[18] VNx,[19,20] ZrNx,[21] CrN22 are good diffusion barriers with high thermal stability
Among the newly emerged kinds of non-volatile memories (NVM) such as phase-change random access memory (PRAM), ferroelectric RAM (FERAM), magneto-resistive RAM (MRAM), and the resistive random access memory (RRAM), etc., the RRAM is doubtless proving to be the front line runner as an alternative choice to replace conventional NVM according to the criteria such as simple structure, compatibility with standard complementary metal-oxide semiconductor (CMOS) process, low power operation, high density integration, especially the excellent scalability and high-speed write and erase operations
The resistive switching (RS) behaviors may partially come from the electron induced effects such as the charge by trapping/detrapping effects in the films,[8] in this study, we mainly focus our attention on the ions induced RS behaviors because of its better device scalability and data retention ability than that of the electron induced, even we should mitigate the electron induced RS effect to as low level as possible from the viewpoints of power saving and device reliability in RRAM devices
Summary
From the viewpoints of controlling or confining the moveable oxygen vacancies (ions) at a local place and improving the thermal stability of the RRAM devices to effectively resolve above mentioned RS problems, it may be a feasible way to introduce the CMOS-process-friendly conductive refractory transition metal nitrides (TMN) into RRAM device cells as electrode or buffer layer considering that the TMN, such as WNx,[15,16] HfNx,[17] MoN,[18] VNx,[19,20] ZrNx,[21] CrN22 are good diffusion barriers with high thermal stability. The influence of the nitrogen content in the TMN films and the Gibbs free energies of formation of corresponding metal oxides on the RS properties were discussed
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