Showing papers by "Qi Liu published in 2007"

Fabrication and charging characteristics of MOS capacitor structure with metal nanocrystals embedded in gate oxide

Abstract: Metal–oxide–semiconductor capacitor structure with metal nanocrystals embedded in the gate oxide for the application of nonvolatile memory (NVM) is fabricated. Optimal process parameters are investigated and Au nanocrystals are adopted in this paper. High-frequency capacitance versus voltage (C–V) and conductance versus voltage (G–V) measurements demonstrate the memory effect of the structure which is shown to originate from the confined states of metal nanocrystals. Capacitance versus time (C–t) measurement under a constant gate bias is executed to evaluate the retention performance and an exponential decaying trend is observed and discussed. It is found that with respect to semiconductor counterparts, Au nanocrystals can provide enhanced retention performance, which confirms the high capacity of Au nanocrystals for NVM applications.

Modeling of retention characteristics for metal and semiconductor nanocrystal memories

Abstract: The charge retention characteristics of metal nanocrystal (MNC) and semiconductor nanocrystal (SNC) memory devices are comparatively studied in this paper. A charge retention model is proposed, taking into account the quantum confinement effect, to account for the better retention characteristics of metal nanocrystal memory observed in the experiment. Simulation results are in good agreement with experimental data, which confirms the validity of this model. The impact of the nanocrystal size, tunneling dielectric materials (especially high-κ dielectrics), and tunneling dielectric thickness on the retention characteristics are all investigated for both the metal nanocrystals and the semiconductor nanocrystals.

Seed rain and soil seed bank of Picea asperata Mast. in subalpine coniferous forest of western Sichuan, China

Abstract: Dragon spruce (Picea asperata Mast.) is widely planted on clear-cuts from natural subalpine coniferous forests in western Sichuan. To assess the natural regeneration potential of this species in spruce plantations of different ages, field studies on the seed rain, seed bank, and seedling recruitment were conducted in 20-year, 30-year, and 60-year plantations, and in a retained natural forest ca. 150 years old for comparison. Moreover, a series of temperature and light regimes were also designed in March 2003 to test germination/dormancy responses of the P. asperata seeds to different conditions. In the plantations considered, both the densities of seed rain and soil seed bank increased with increasing stand age, whereas they were both low beneath the natural forest partially due to low adult density of P. asperata adult trees. P. asperata has a transient seed bank, and ca. 60% of seeds were found in the litter layer. Seed decay and seed predation were the two most important factors affecting soil...

Analysis of Charge Retention Characteristics for Metal and Semiconductor Nanocrystal Non-volatile Memories

Abstract: A charge retention model for nanocrystal MOSFET memory structure is proposed, taken into account the quantum confinement effect, to account for the better retention characteristics of metal nanocrystal memories over their semiconductor counterparts observed in the experiment. Simulation results are in consistent with experimental data, which confirms the validity of this model. The impact of nanocrystal size, tunneling dielectric material (especially high-k dielectrics) and thickness on the retention characteristics are investigated for both of the metal nanocrystal and semiconductor nanocrystal memories.

A hybrid method for fabrication of Au nanocrystals nonvolatile memory

Abstract: This paper demonstrates the integration of Au nanocrystals (NCs) into nonvolatile metal-oxide-semiconductor (MOS) with a hybrid method operated at room temperature. The comparison of structural and electrical characteristics between the hybrid Au NCs fabricated by chemical syntheses and film deposition Au NCs fabricated by rapid thermal annealing (RTA) was carried out. The size of the Au NCs formed by chemical method has been investigated more unique and small than the ones by the film deposition and RTA process. The electrical characteristics of MOS structure with two kinds of Au NCs has shown the larger memory window, lower P/E voltage and good retention time for the hybrid NCs due to its small diameter and low temperature process.