Nanoscale Metal-insulator Transition for Sub-10 nm Memory Devices

I-Wei Chen
University of Pennsylvania / USA

Nanometallic RRAM is a new non-volatile memory concept that is completely CMOS-compatible in composition and in fabrication. Internally, the device contains (a) dopant levels that allow extrinsic electrons to gain access to conducting states, and (b) bi-stable charge trapping sites/states that regulate electron flow. With the attachment of two electrodes of different work functions, these built-in channels (a) and gates (b) in random materials can be operated in a two-terminal, bipolar-mode manner. Nanometallic RRAM has been demonstrated to function in 2.5 nm devices, to turn on in 10-13 s, to have excellent retention (years) and uniformity (the highest Weibull modulus in the literature), and to write/erase at the same switching voltage (≈1 V) regardless of the write-time. The short switching time and the constant switching voltage also portend extremely energy-lean (10-16 J) devices. Recent experiments have shed light onto their switching and transport mechanisms: electron-phonon interactions and correlated electron effects are definitely operational, and such understanding will guide future device development (e.g., Si-RRAM) and modeling (e.g., size effect and noise). Last but not least, the built-in channels and gates suggest the possibility to realize logic operations in these devices, although this is a challenging project because of the decidedly nanoscale length-requirement for nanometallicity.

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