Won-Ju Cho

NBTI and hot carrier effect of SOI p-MOSFETs fabricated in strained Si SOI wafer.

Comparative study on NBTI and hot carrier effects of p-channel MOSFETs fabricated by using strained SOI wafer and unstrained SOI wafer has been performed, respectively. It is observed that NBTI and hot carrier degradation are more significant in strained SOI devices compared with unstrained SOI devices. Since the devices fabricated in strained SOI wafer are SiGe free strained devices, the more generation of interface states during gate oxidation is the main cause for enhanced NBTI and hot carrier degradation in strained SOI devices.

Dependence of temperature and self-heating on electron mobility in ultrathin body silicon-on-insulator n-metal-oxide-semiconductor field-effect transistors

We investigated the dependence of temperature and self-heating on electron mobility in ultrathin body fully depleted silicon-on-insulator n-metal-oxide-semiconductor field-effect transistors as a function of silicon thickness by analyzing their electron states and electrical characteristics. We found that as the temperature increases, electron mobility decreases regardless of the silicon thickness. We also found that there is a less decrease when the silicon thickness is less than 3 nm than when it is greater than 3 nm. This is because there is a greater electron occupancy in a twofold valley. We demonstrated that the quantum size-effect, i.e., the higher electron mobility in silicon with a thickness less than 3 nm caused by the size-effect, can be eliminated by self-heating.

Formation of a self-aligned hard mask using hydrogen silsesquioxane

A process to form a self-aligned hard mask using hydrogen silsesquioxane (HSQ) was investigated. Application of the flowing property of HSQ to form a hard mask is the main concept underlying the proposed process. When HSQ is coated on a wafer, most of it remains beside the pattern. Using the thick remaining HSQ beside the pattern as a hard mask, we could reduce the height of the pattern exclusively without etching beside the pattern region by the dry etching process. The proposed mask process was successfully applied to fabricate a poly-Si elevated source drain ultrathin body silicon on insulator metal-oxide-semiconductor field effect transistor.

Recessed source-drain (S/D) SOI MOSFETs with low S/D extension (SDE) external resistance

We introduce a novel ultra-thin body (UTB) SOI MOSFET with a recessed source-drain (S/D) structure to solve the high source-drain extension (SDE) external resistance problem. Fabricated devices with 30 nm gate length and 5 nm channel are characterized. By the device simulation, we have shown that devices with a recessed S/D structure have a better electrical properties than those with a elevated S/D structure.

Effects of vacuum rapid thermal annealing on the electrical characteristics of amorphous indium gallium zinc oxide thin films

We investigated the effects of vacuum rapid thermal annealing (RTA) on the electrical characteristics of amorphous indium gallium zinc oxide (a-IGZO) thin films. The a-IGZO films deposited by radiofrequency sputtering were subjected to vacuum annealing under various temperature and pressure conditions with the RTA system. The carrier concentration was evaluated by Hall measurement; the electron concentration of the a-IGZO film increased and the resistivity decreased as the RTA temperature increased under vacuum conditions. In a-IGZO thin-film transistors (TFTs) with a bottom-gate top-contact structure, the threshold voltage decreased and the leakage current increased as the vacuum RTA temperature increased. As the annealing pressure decreased, the threshold voltage decreased, and the leakage current increased. X-ray photoelectron spectroscopy indicated changes in the lattice oxygen and oxygen vacancies of the a-IGZO films after vacuum RTA. At higher annealing temperatures, the lattice oxygen decreased and...

Effect of microwave annealing on SOI MOSFETs: Post-metal annealing with low thermal budget

Abstract We investigate the effect of microwave irradiation (MWI) on silicon-on-insulator (SOI) based MOSFETs. The MWI technique is used for post-metal annealing (PMA) in air ambient, and compared with conventional thermal annealing in a forming gas ambient. This type of annealing not only constitutes a low cost, short time, low temperature, vacuum-free alternative to conventional post-metal annealing methods, but it also allows much lower thermal budgets, which, in turn, minimizes dopant motion, redistribution, and diffusion. The MWI treated MOSFETs showed superior electrical characteristics in terms of field effect mobility, on-off ratio, subthreshold swing, interface trap density, stability, and hot carrier effect immunity. Therefore, MWI technology is expected to become a promising annealing method for silicon-based processes, with low cost and low thermal budget.

AlGaN/GaN high-electron-mobility transistor pH sensor with extended gate platform

In this paper, we fabricated an AlGaN/GaN high electron mobility transistor (HEMT) pH sensor with an extended-gate (EG). As the carrier mobility of the transducer that is used as the biosensor is increased, the electrical signal conversion efficiency of the biomaterials is improved. Therefore, the HEMT is a more suitable transducer platform than the conventional silicon-based transistor. The fabricated AlGaN/GaN device showed an electron density of 9.0 × 1012 cm-2, and an electron mobility of 1,990 cm2/V-s. In order to reduce the gate leakage current, which is a drawback of conventional HEMT devices, we deposited a 3-nm thick Al2O3 layer as a top-gate oxide by the atomic layer deposition (ALD) method; the fabricated HEMT has a metal–insulator semiconductor (MIS) structure. In addition, we used the EG to implement the disposable biosensor. Although the EG (a sensing membrane) is contaminated and destroyed, the HEMT (a transducer) can be reused. We evaluated the pH sensing characteristics using a pH sensor, which was implemented by connecting the HEMT and EG. The EG HEMT pH sensor showed a sensitivity of 57.6 mV/pH, which is close to the Nernst limit (approximately 59 mV/pH), and a linearity of 98.93%. To verify the stability and reliability of the implemented EG HEMT pH sensor, we measured the real-time response. The EG HEMT pH sensor has an error of only 2.39% of the signal. Therefore, we expect that the EG-based AlGaN/GaN HEMT pH sensor will be a suitable next-generation biosensor platform for a high electrical signal change efficiency of biomaterials, disposable, and point-of-care systems.In this paper, we fabricated an AlGaN/GaN high electron mobility transistor (HEMT) pH sensor with an extended-gate (EG). As the carrier mobility of the transducer that is used as the biosensor is increased, the electrical signal conversion efficiency of the biomaterials is improved. Therefore, the HEMT is a more suitable transducer platform than the conventional silicon-based transistor. The fabricated AlGaN/GaN device showed an electron density of 9.0 × 1012 cm-2, and an electron mobility of 1,990 cm2/V-s. In order to reduce the gate leakage current, which is a drawback of conventional HEMT devices, we deposited a 3-nm thick Al2O3 layer as a top-gate oxide by the atomic layer deposition (ALD) method; the fabricated HEMT has a metal–insulator semiconductor (MIS) structure. In addition, we used the EG to implement the disposable biosensor. Although the EG (a sensing membrane) is contaminated and destroyed, the HEMT (a transducer) can be reused. We evaluated the pH sensing characteristics using a pH sensor,...

Post-RTA Effect on Electrical Characteristics of Nano-scale Strained Si Grown on SiGe-on-Insulator n-MOSFET

The effect of rapid thermal annealing (RTA) and post-RTA annealing (PRA) on the electrical characteristics of both strained Si and conventional SOI n-MOSFETs was investigated. The authors demonstrated that post-RTA heat treatment rather than typical RTA is inevitable to obtain enhanced DC characteristics in strained Si n-MOSFET. This is attributed to the suppression of channel surface roughness owing to post-RTA