Formation of Ge nanocrystals embedded in HfAlO high-k dielectric by co-sputtering of HfO2, Al2O3, and Ge, followed by rapid thermal annealing was demonstrated. Analysis by transmission electron microscopy and x-ray photoelectron spectroscopy confirmed the formation of nonoxidized Ge nanocrystals with a minimum size of about 5nm embedded in HfAlO dielectric. We also demonstrated the application of such nanocrystals in nonvolatile memory devices, achieving a 2.2V memory window as obtained from the C–V characterization of the memory device.
A self-assembly of high-density Al2O3 nanodots (NDs) on SiO2 has been demonstrated by employing a two-step controlled annealing method. Results show that the conglomeration of Al is impeded by oxygen and the size and density of Al2O3 NDs can be controlled by the initial Al film thickness and annealing temperature. Memory devices with Al2O3 NDs fabricated using this technique show improved retention properties compared to those with Al2O3 continuous films. A comparison of temperature dependency shows that the good retention property originates from the suppression of lateral migration of electrons via Frenkel–Poole tunneling.
In this paper, we studied the phase-separation phenomenon of Hf0.5Si0.5O2 film deposited on SiO2 or sandwiched by SiO2, by x-ray photoelectron spectroscopy and transmission electron microscopy. The Hf0.5Si0.5O2 film underwent phase separation to form a doublet-phase HfO2–HfxSi1−xO2 (x<0.5) film, and was used as a trapping layer in a metal-blocking oxide-silicon nitride-tunnel oxide-silicon-type memory structure, where the dual-phase HfO2–HfxSi1−xO2 (DPHSO) film replaces the conventional silicon nitride (Si3N4) trapping layer. The charge storage properties of the DPHSO film were investigated and compared with HfO2 and Si3N4. It was found that for a given electric field applied to the tunnel oxide, the programming speed of memory devices using a DPHSO or HfO2 film as a trapping layer is faster than that using Si3N4. This indicates the higher electron-capture efficiency of the DPHSO and HfO2 films. In addition, the double-phase microstructure of the DPHSO film also provided better retention property than pure HfO2.
In this paper, we investigate the chemical vapor deposition (CVD) of Ge nanocrystals (NCs) directly on hafnium oxide HfO2 dielectric for non-volatile memory applications. Germane GeH4 was used as a precursor. Atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize the Ge NCs. The dependence of the Ge NC size and density on the deposition temperature, deposition time, and flow rate was explored. A high Ge NC density of 1011 cm-2 was obtained at a deposition temperature of 600°C, with a mean diameter of about 16 nm. MOS capacitors with CVD Ge NCs embedded in the HfO2 gate dielectric were fabricated. Hysteresis of capacitance-voltage (C-V) characteristics of capacitors with Ge NCs was observed, demonstrating memory effect.
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