Abstract
Filament-type HfO2-based RRAM has been considered as one of the most promising candidates for future non-volatile memories. Further improvement of the stability, particularly at the “OFF” state, of such devices is mainly hindered by resistance variation induced by the uncontrolled oxygen vacancies distribution and filament growth in HfO2 films. We report highly stable endurance of TiN/Ti/HfO2/Si-tip RRAM devices using a CMOS compatible nanotip method. Simulations indicate that the nanotip bottom electrode provides a local confinement for the electrical field and ionic current density; thus a nano-confinement for the oxygen vacancy distribution and nano-filament location is created by this approach. Conductive atomic force microscopy measurements confirm that the filaments form only on the nanotip region. Resistance switching by using pulses shows highly stable endurance for both ON and OFF modes, thanks to the geometric confinement of the conductive path and filament only above the nanotip. This nano-engineering approach opens a new pathway to realize forming-free RRAM devices with improved stability and reliability.
Highlights
Insulating states and filament growth[15]
We present an effective geometric approach by nanotip electrodes processed by complementary metal–oxide–semiconductor (CMOS) compatible technology to confine the filament location by localized electrical field enhancement effects so that we are able to report highly stable endurance and retention of HfO2 resistance switching random access memory (RRAM) devices
Structural and chemical analyses were performed by employing transmission electron microscopy (TEM) and energy-dispersive x-ray spectroscopy (EDX)
Summary
We study a TiN/Ti/HfO2/CoSi2/Si-tip device, where the CoSi2 bottom electrode is locally deposited at the top of the Si nanotip. It should be firstly noted here that the additional forming process done by the first set process, which is normally required in RRAM devices with planar electrodes, is not needed for our nanotip devices This behaviour is certainly related to the good control of the VO generation and distribution and the electrical field enhancement on the tip edges (almost double) by using our method. The nanotip based devices show good RS properties including the forming-free feature, the stable endurance and retention etc These behaviours are all thanks to the confinement of the VO distribution and the filament location by the localized electrical field distribution and ionic current density. Future works will focus on two topics: 1) to image the space charge distribution in ON- and OFF-states in nanotip devices for a detailed insight into the VO distribution by using TEM electron holography and 2) to setup an array of individually addressable Si nanotip electrodes to integrate this concept into a viable test module for the technological testing
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