Memory functions of nanocrystalline indium tin oxide embedded zirconium-doped hafnium oxide MOS capacitors
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abstract
A floating gate metal-oxide-semiconductor capacitor memory device utilizing nanocrystalline indium tin oxide (ITO) layer embedded in a zirconium-doped hafnium oxide (Zr-doped Hf O2) high- k gate dielectric has been fabricated and studied. The embedded ITO layer has crystalline structure with a grain size of about 5.4 nm. Capacitance-voltage and current-voltage measurements show positive charge trapping under the negative gate bias operation condition. Comparison to a control sample shows a fourfold increase (5.3 10-12 cm-2 to 1.4 10-12 cm-2) in oxide trapped charge density and opposite trapped charge polarity, indicating that the observed effects are due to the inclusion of the ITO floating gate layer. The device maintains a large postwrite window (>100 mV) over a ten-year period. Furthermore, the prominent charge transfer mechanism is direct tunneling. The negative differential resistance in the current-voltage curve shows the existence of the coulomb blockade effect that may limit negative charge storing and retention. The asymmetrical barrier of the Zr-doped Hf O2 allows for the enhanced hole retention while eliminating the possibility of electron retention. 2007 The Electrochemical Society.
