Charge Retention Loss in a HfO2 Dot Flash Memory via Thermally Assisted Tunneling

The charge loss mechanism in a hafnium oxide (HfO₂ ) dielectric dot flash memory is investigated. We measure the temperature and time dependence of a charge loss induced gate leakage current in a large area cell directly. We find that (1) the charge loss is through a top oxide in the cell and (2) the stored charge emission process exhibits an Arrhenius relationship with temperature, as opposed to linear temperature dependence in a semiconductor-oxide-nitride-oxide-semiconductor flash memory. A thermally activated tunneling front model is proposed to account for the charge loss behavior in a HfO₂ dot flash memory.