Nonvolatile memories using deep traps formed in HfO₂ by Nb ion implantation




Choul Kim, Min
Oh Kim, Chang
Taek Oh, Houng
Choi, Suk-Ho
Belay, K.
Elliman, R. G.
Russo, S. P.

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American Institute of Physics (AIP)


We report nonvolatile memories (NVMs) based on deep-energy trap levels formed in HfO₂ by metal ion implantation. A comparison of Nb- and Ta-implanted samples shows that suitable charge-trapping centers are formed in Nb-implanted samples, but not in Ta-implanted samples. This is consistent with density-functional theory calculations which predict that only Nb will form deep-energy levels in the bandgap of HfO₂. Photocurrent spectroscopy exhibits characteristics consistent with one of the trap levels predicted in these calculations. Nb-implanted samples showing memory windows in capacitance–voltage (V) curves always exhibit current (I) peaks in I–V curves, indicating that NVM effects result from deep traps in HfO₂. In contrast, Ta-implanted samples show dielectric breakdowns during the I–V sweeps between 5 and 11 V, consistent with the fact that no trap levels are present. For a sample implanted with a fluence of 10¹³Nb cm⁻², the charge losses after 10⁴ s are ∼9.8 and ∼25.5% at room temperature (RT) and 85°C, respectively, and the expected charge loss after 10 years is ∼34% at RT, very promising for commercial NVMs.



Keywords: Band gaps; Capacitance voltage; Charge loss; Deep traps; Density-functional theory calculations; Dielectric breakdowns; Energy level; Energy trap; Fluences; I - V curve; Implanted samples; Memory window; Nonvolatile memories; Photocurrent spectroscopy; Ro



Journal of Applied Physics


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