Young-Hwan Son

Characterization of oxide traps leading to RTN in high-k and metal gate MOSFETs

We proposed a new method for characterization of oxide traps leading to Random Telegraph Noise (RTN) in high-k and metal gate MOSFETs considering their energy band structure. Through this method and drain and gate current RTN measurement, we extracted positions, energy levels and activation energies of oxide traps in high-k dielectric as well as in interfacial layer.

Characterization of an Oxide Trap Leading to Random Telegraph Noise in Gate-Induced Drain Leakage Current of DRAM Cell Transistors

An accurate method for extracting the depth and the energy level of an oxide trap from random telegraph noise (RTN) in the gate-induced drain leakage (GIDL) current of a metal-oxide-semiconductor field-effect transistor (MOSFET) is developed, which correctly accounts for variation in surface potential and Coulomb energy. The technique employs trap capture and emission times defined from the characteristics of GIDL. Ignoring this variation in surface potential leads to an error of up to 116% in trap depth for 80-nm technology generation MOSFETs. RTN amplitude as a function of MOSFET drain-gate voltage is also investigated.

Investigation of Gate Etch Damage at Metal/High-

Plasma damage on a high-k/SiO2 dielectric at a gate edge during a dry etch process is investigated. The damage was observed to generate slow oxide traps, causing a random telegraph noise (RTN) in a gate edge direct tunneling current. Through the analysis of the RTN, the distribution of the oxide traps in the high-k/SiO2 dielectric was obtained, and the plasma-damage-induced oxide traps were found to be distributed over a wide area of the high-k/SiO2 sidewall at the gate edge region.

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To study the relationship between the original leakage current fluctuation and the detected variable retention time (VRT) from the retention test of dynamic random access memory (DRAM), we simulated the real procedure of the VRT measurement of DRAM. By investigating the results of the simulation, we proposed a new effective VRT measurement method based on the comparison between measurement and simulation. In addition, we investigated the characteristics of the VRT phenomenon in DRAM using the VRT characterization method developed in this study.

Gate Dielectric Stack Through Random Telegraph Noise in Gate Edge Direct Tunneling Current

To study trap models related to the variable retention time (VRT) phenomenon in dynamic random access memory (DRAM), we derived equations to calculate the data retention time tret of DRAM and the activation energy for two trap models, i.e., the metastable and oxide trap models. Measuring the tret of VRT cells for various bias and temperature conditions, the dependence of activation energy differences in tret on bias at high and low retention states was extracted. Furthermore, the dependence of the electric field on bias at high and low retention states was also extracted. Using those parameters, we successfully distinguished the two types of trap models.

Characterization of the Variable Retention Time in Dynamic Random Access Memory

The multifrequency charge pumping (MFCP) experiments have been investigated by many research groups for the characterization of oxide traps in high-permittivity (high-κ ) dielectric metal-oxide-semiconductor field-effect transistor samples. In these previous studies, the duty cycle was changed for control of charging and discharging depths. In this paper, the spatial and energy distributions of border traps in the metal gate/high-κ dielectric/silicon dioxide (SiO2) interfacial layer stack structure were characterized as a three-dimensional (3-D) mesh profile by using the MFCP technique. The presented MFCP technique was based on the frequency of the gate pulse in conjunction with the tunneling model of trapped charges and was not the duty cycle. The methodological basis and the accurate model were introduced for the analysis of the measured MFCP data in dual-layer gate oxide. The low-frequency noise measurement and the MFCP technique were used for the analysis of the constant gate bias stress induced trap generation, and the 3-D mesh profile of generating trap density was presented. Moreover, the energy distribution of stress-induced traps was investigated within high-κ, SiO2, and high-κ/SiO2 interface.

Study of Trap Models Related to the Variable Retention Time Phenomenon in DRAM

Thermostability of the lipase (EC 3.1.1.3) was found to be increased by the enzyme-entrapment in 50 mM AOT/isooctane reverse micelles. The half-life (15.75 h) of Pseudomonas fluorescens lipase entrapped in reverse micelles at 70 °C was 9.72- and 11.41-fold longer than those solubilized in a glycerol pool or in 10 mM phosphate buffer (pH 8.0), respectively. The enzyme deactivation model considering a two-step series-type was employed, and deactivation constants for the second step (k₂) at all temperatures were drastically decreased after the lipase was entrapped in reverse micelles. In particular, k₂ (0.0354 h⁻¹) at 70 °C in reverse micelles was 12.33- and 13.14-fold lower than in a glycerol pool or in the phosphate buffer, respectively. The deactivation energies (from k₁, k₂) for the lipase entrapped in the reverse micelles, solubilized in a glycerol pool, or in the aqueous buffer were 7.51, 26.35 kcal/mol, 5.93, 21.08 kcal/mol, and 5.53, 17.57 kcal/mol, respectively.

Characterization of Border Trap Density With the Multifrequency Charge Pumping Technique in Dual-Layer Gate Oxide

Bottom Ash is industrial by-product from a thermoelectric power plant. An immense quantities of bottom ash have increased each year, but most of them is reclaimed in ash landfill. In this study, in order to raise recycling rate of Bottom Ash, it is suggested to cure Bottom Ash (BA) mixtures mixed with cement, lime, Fly Ash (FA), and oyster shell (OS). Mixtures of 5~20 % mixing ratio had been cured for 1, 3, 7, 14, and 28 days using sealed curing and air-dry curing method. Unconfined compressive strength test was conducted to determine strength and deformation modulus () change for mixtures as mixing ratio and curing day, water contents of mixtures were measured after test. As a result, strength and were increased as mixing ratio and curing days, but values and tendencies of them appeared in different as kind of mixture, mixing ratio, curing method, and curing days. The results showed the addition of cement, lime, Fly Ash, and oyster soil in Bottom Ash could improved strength and and enlarge its field of being used.

Thermal deactivation kinetics of Pseudomonas fluorescens lipase entrapped in AOT/isooctane reverse micelles.

The random telegraph noise in a gate leakage current in an accumulation mode has been studied to characterize slow oxide traps at nMOSFET devices having a TiN/HfO2/SiO2 gate stack. New equations for the traps vertical location and energy level were derived by means of the relation between the traps energy and Fermi levels in the accumulation mode. Through our analysis in both the accumulation and inversion modes, we found that the measurement in the accumulation mode is complementary to that in the inversion mode in order to assess the traps within a wide range of energy levels.

Analysis of Strength Characteristic for Bottom Ash Mixtures as Mixing Ratio and Curing Methods

According to the different environmental systems for lipase reactions, changes in thermal stability were investigated by employing the Chromobacterium viscosum lipase and a two-step series-type deactivation model. The half-life (6.81 h) of the lipase entrapped in reverse micelles at 70 °C was 9.87- and 14.80-fold longer than that in glycerol pool or in aqueous buffer. The deactivation constants for the first and second step (k1 and k2) at all temperatures drastically decreased when the lipase was entrapped in reverse micelles. In particular, k1 (3.84 h(-1)) at 70 °C in reverse micelles was 1.57-fold lower than that in aqueous buffer (6.03 h(-1)). Based on the fluorescence spectrometry, the amount of excited forms of tryptophan and tyrosine increased markedly during the thermal-treatment in aqueous buffer, whereas no significant fluctuation was noted in the reversed micellar system. These results indicated that the encapsulation in reverse micelles could be favorable for preventing the enzyme from heat-induced denaturation.