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Recently, many efforts have been made to improve the device performance of nanocrystal memory by replacing the SiO2 with various high dielectric constant (high-k) materials, especially embedded with Ge nanocrystals. This paper demonstrates the floating gate memory effect by embedding nanometer-sized Ge nanocrystals in hafnium aluminate (HfAlO) high-k gate dielectric. A 5 nm-thick amorphous thin film of HfAlO was first deposited on (100) p-Si substrates as a tunneling gate oxide layer by laser molecular beam epitaxy deposition using a HfO2 and Al2O3 composite target. Well-defined (~10 nm in diameter) nanometer-sized Ge dots were subsequently deposited on this thin tunneling gate oxide followed by a 30 nm-thick top control gate oxide of HfAlO. Transmission electron microscopy has been carried out for a detailed study of structural properties of the Ge nanocrystals embedded in the HfAlO films, and their relationships to electrical properties. Electrical properties have been characterized by means of high-frequency capacitance-voltage (C-V) and current-voltage (I-V) measurements on the metal-oxide-semiconductor capacitors. A counter-clockwise hysteresis C-V loop has been obtained and a threshold voltage shift of 1.0 V has been achieved indicating stored electrons (up to a density of 2x1012 cm-2) in the Ge-nanodots floating gate and thus the memory effect. Time-dependent I-V measurement also showed low leakage current of floating gate system. These results suggest that the Ge nanocrystals embedded in HfAlO are promising for floating gate memory device application.
Pui Fai Lee,Wei Li Liu,Zhi Tang Song, andJi Yan Dai
"Ge nanocrystals embedded in Hf-aluminate high-k gate dielectric for floating gate memory application", Proc. SPIE 5650, Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems II, (23 February 2005); https://doi.org/10.1117/12.582062
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Pui Fai Lee, Wei Li Liu, Zhi Tang Song, Ji Yan Dai, "Ge nanocrystals embedded in Hf-aluminate high-k gate dielectric for floating gate memory application," Proc. SPIE 5650, Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems II, (23 February 2005); https://doi.org/10.1117/12.582062