Jung Yup Yang

Enhanced electrical characteristics of Au nanoparticles embedded in high-k HfO2 matrix

We present experimental results for laser-induced Au nanoparticle (NP) embedded in a HfO2 high-k dielectric matrix. Cross-sectional transmission electron microscopy images showed that the Au NPs of 8nm in diameter were clearly embedded in HfO2 matrix. Capacitance-voltage measurements of Pt∕HfO2∕AuNPs∕HfO2 on p-type Si substrate reliably exhibited metal-oxide-semiconductor behavior with a large flatband shift of 4.7V. In addition, the charge retention time at room temperature was found to exceed 105h. This longer time was attributed to the higher electron barrier height via high work function of the Au NP.

Room temperature operation of magnetic tunnel transistors with half-metallic Fe3O4 emitter source

Magnetic tunnel transistors (MTTs) based on a half-metallic Fe3O4 emitter source were investigated to obtain a high efficiency of spin-dependent hot electron transport. The MTTs include magnetic tunnel junctions with an AlOx insulating barrier. The insulating barrier formed by a remote rf plasma oxidation method was used to enhance electrical and structural properties of MTTs. The highest magnetocurrent ratio of the MTTs was experimentally observed to be about 51% at room temperature. Especially, the transfer ratio of about 10−2 was obtained by systematically varying the heights of emitter and collector barrier.Magnetic tunnel transistors (MTTs) based on a half-metallic Fe3O4 emitter source were investigated to obtain a high efficiency of spin-dependent hot electron transport. The MTTs include magnetic tunnel junctions with an AlOx insulating barrier. The insulating barrier formed by a remote rf plasma oxidation method was used to enhance electrical and structural properties of MTTs. The highest magnetocurrent ratio of the MTTs was experimentally observed to be about 51% at room temperature. Especially, the transfer ratio of about 10−2 was obtained by systematically varying the heights of emitter and collector barrier.

Postannealing effect on pseudobilayer HfO2∕HfSixOy∕Si gate oxides formed by an inductively coupled sputtering process

Pseudobilayer HfO2∕HfSixOy gate dielectrics in metal-oxide-semiconductor devices were prepared using an inductively coupled rf plasma sputtering technique. This sputtering method was designed to improve the uniformity and efficiency of formation of high-quality gate dielectrics at room temperature. Crystallization of the gate dielectrics was easily controlled from amorphous to monoclinic by varying the external power from 0to60W at RT. The chemical bond states of the interfacial layers in the as-deposited and postannealed samples were analyzed with an x-ray photoelectron spectroscopy (XPS) system. The XPS results revealed that the interfacial layers of the as-deposited and annealed samples were hafnium silicide and hafnium silicate, respectively. Compared with the as-deposited sample, the pseudobilayer HfO2∕HfSixOy gate dielectric annealed at 750°C yielded excellent electrical characteristics due to the hafnium silicate interfacial layer. The dielectric constant and leakage current of the postannealed sam...

Efficient fabrication and characterization of cobalt nanoparticles embedded in metal∕oxide∕semiconductor structures for the application of nonvolatile memory

Metal-oxide-semiconductor (MOS) capacitors with Co nanoparticles (Co NPs) were successfully fabricated by utilizing an external laser irradiation method for the application of nonvolatile memory. Experimental images of cross-sectional transmission electron microscopy showed that the Co NPs of 5nm in diameter were clearly embedded in SiO2 layer. Capacitance-voltage measurements of Pt∕SiO2∕Co NPs∕SiO2 on p-type Si (100) substrate certainly exhibited typical MOS behavior with a flatband voltage shift of 1.1V. In addition, the charge retention characteristics of MOS capacitors with the Co NP were investigated using capacitance-time measurements. The present results indicate that their unique laser process gives rise to a possible promise for the efficient formation or insertion of metal NPs inside the MOS structures.

Surface plasmon resonance analysis of insulating AlO/sub x/ thin film for magnetic tunnel junctions prepared by natural oxidation method

The AlO/sub x/ insulating barrier in MTJ was fabricated and analyzed by utilizing a natural oxidation and surface plasmon resonance spectroscope (SPRS) technique. The basic structure of MTJ was Ta/CoFe/AlO/sub x/:natural oxidation/NiFe/Ta. SPRS was used to investigate optimum thickness and dielectric properties of the AlO/sub x/ layers. The SPRS results exhibited changes in the oxidation state of the barrier, depending on the oxidation time. Natural oxidation depth and speed were calculated by comparing SPRS simulation results with experimental ones. It was also found that 8 /spl Aring/ of Al layer is the optimum thickness when MTJ was formed using natural oxidation method.

Enhanced thermal stability of magnetic tunnel junctions formed by in situ radiation annealing process on AlOx insulating barriers

An in situ direct radiation annealing (IDRA) technique on the AlOx insulating barrier was performed to enhance the thermal stability of magnetic tunneling junctions (MTJs). Our method was found to improve the dielectric and structural properties of AlOx insulating barrier in MTJs. After the proper IDRA process, the conventional ex situ annealing process exhibited an additional enhancement of thermal stability by significantly reducing the interdiffusion process between Co80Fe20 electrode and AlOx insulating barriers. Experimentally observed tunneling magnetoresistance of MTJs after the IDRA process showed about 55% up to 350°C. Finally, a surface-plamon resonance spectroscope measurement observed that the dielectric constant of insulating barriers was increased from 2.7 to 3.2 after the IDRA process.

Magnetic properties of laser-induced ferromagnetic cobalt quantum dots passivated by ultrathin Ta film

The ferromagnetic quantum dots (FMQDs) are fabricated by exposing a pulsed Nd:YAG laser (wavelength=355 nm) on ultrathin cobalt (Co) films under an external magnetic field of 1000 Oe. Various dot diameters and densities of more than 3.5×1010/cm2 are ultimately realized by changing laser power, scan condition and initial film thickness. In addition, both AlN and Ta thin films as capping layers are used to protect the FMQDs from natural oxidation effect. The observed coercivity values of uncapped and capped FMQDs are changed from 600 up to 200 Oe with the initial Co thickness of 2 nm, respectively. The observation of magnetic force microscopy and hysteresis loops clearly confirms in-plane single domain state for the Ta-capped FMQDs.