Memory Functions of Nanocrystalline Indium Tin Oxide Embedded Zirconium-Doped Hafnium Oxide MOS Capacitors

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 O 2 ) 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 O 2 allows for the enhanced hole retention while eliminating the possibility of electron retention.