Hyoung Gin Nam

Microfabrication and characteristics of low-power high-performance magnetic thin-film transformers

We investigated low-power (1.5-W), solenoid-type magnetic thin-film transformers with a Ni/sub 81/Fe/sub 19/ core for a 5-MHz drive dc-dc converter application. We used 2-/spl mu/m-thick Ni/sub 81/Fe/sub 19/ films covered by 20-/spl mu/m-thick copper coils as the core materials. The transformers fabricated in this study range in size from 3.08 mm /spl times/ 25.5 mm to 6.15 mm /spl times/ 12.75 mm. The design of the transformers was optimized by utilizing the conventional equations, a Maxwell three-dimensional field simulator, and parameters obtained from the magnetic properties of NiFe magnetic core materials. The 6.15 mm /spl times/ 12.75 mm transformers exhibit inductance (L) of 0.83 /spl mu/H, dc resistance of 2.3 /spl Omega/, coupling factor of 0.91, and gain of -1 dB at 5 MHz. These results are comparable to those reported in recent literature for various types of transformers sandwiched by more complex magnetic core materials. The calculated data obtained by using the well-known equation of L and the equivalent circuit agreed well with the high-frequency data for L and gain of the transformers.

Characterization of Al-As codoped p-type ZnO films by magnetron cosputtering deposition

We report the preparation of Al–As codoped p-type ZnO films by rf magnetron cosputtering deposition. The p-type conductivity of the films was revealed by Hall measurements, x-ray photoelectron spectroscopy (XPS), and photoluminescence measurements after being annealed in O2. It was observed by XPS that Al content increased with increasing AlAs target power from 80 to 160 W and reached a maximum value at an AlAs target power of 160 W. Hole concentration decreased with increasing Al content. With increasing AlAs target power greater than 160 W, the samples exhibit increases in As and O contents and decreases in Al and Zn contents, which contribute to the increase in hole concentration. A high hole concentration of 2.354×1020 cm−3, a low resistivity of 2.122×10−2 Ω cm, and a Hall mobility of 0.13 cm2/V s for the films with high As content of 16.59% were obtained. XPS has also been used to address the unresolved issues related to the p-type formation mechanism of As-doped ZnO, supporting that the acceptor is ...

Reliability of Silicon Nitride Gate Dielectric in Vertical Thin-Film Transistors

This paper presents results of a systematic investigation of the impact of film thickness on leakage current and electrical breakdown of plasma enhanced chemical vapor deposited (PECVD) silicon nitride (SiNx). We consider SiNx films of various thicknesses, in the range 50 to 300 nm, deposited on both planar and vertical sidewalls in resemblance to the structural topology of the vertical thin film transistor (VTFT). The electrical breakdown strength for 150-300 nm thick films was approximately 7 MV/cm, while the value dropped to ~3 MV/cm for 50 nm thick films deposited under the same process conditions. In all cases, failure is inevitably accompanied by an increase in pinhole density. The results show that the reliability and leakage current of the gate dielectric in vertical thin film transistors depends on the step coverage of the SiNx on the vertical sidewall.

Low temperature process for nano-structure formation with Si films

Abstract Effects of sample preparation conditions on the formation of Si nano-structures were investigated. The samples were formed by various deposition methods with various deposition conditions, and subsequent oxidation and/or annealing was carried out. It was found that the film structure as well as the morphology of the thermally treated samples is greatly affected by not only the substrate temperature and the deposition rate but the presence of O2 during deposition. In particular, O2 flow during deposition was observed to apparently enhance formation as well as growth of Si grains. It was stated that the enhancement of crystallization is a consequence of formation and subsequent evaporation of SiO. These results were accounted for by formation kinetics of Si nano-structures. Furthermore, it was suggested that an optimized process for Si nano-structure may be obtained through modifications of the kinetics involved by systematic variations of the deposition conditions. In addition, I–V characteristics observed from the multiple junctions showed tunneling behavior implying the feasibility of fabricating novel devices such as single electron transistors.

Growth of very low temperature polysilicon film by remote plasma-enhanced chemical-vapor deposition

Silicon thin films have been prepared on SiO2 substrates by remote plasma-enhanced chemical-vapor deposition using H2/SiH4/Ar gases. The film properties were found to critically depend on the variations of deposition parameters, which include the SiH4 flow rate with a fixed H2 flow rate, Ar flow rate, and radio frequency (rf) power. The substrate temperature was fixed at 280±5 °C. The best quality polysilicon film was obtained when the rfpower/Ar ratio was set near 0.5±0.05. In addition, the electrical mobility was observed to increase with the increasing SiH4 flow rate. The effects of the deposition parameters variation were discussed to properly account for the observed properties of the thin films studied.

Feasibility of Microelectronic Quartz Temperature and Pressure Sensors

Under the non-isotropic boundary conditions, piezoelectric quartz crystal discovers electrical response on scalar actions, the same as pyroelectric crystal. Thus, uniform change of temperature causes a secondary-type artificial pyroelectricity, while hydrodynamic change of pressure gives rise to a volumetric piezoelectric effect. Quartz voltage responsivity and figure of merit are of the same values of magnitude as in conventional pyroelectrics. Quartz type piezoelectric crystals, with their excellent mechanical, chemical, thermal and electrical properties, extend the number of pyroelectric materials and possibilities of their application.

Formation of Nanostructures by Oxidation of Si at Low Temperature

Formation processes of Si nanostructures were investigated. The samples were formed by remote plasma enhanced chemical vapor deposition of Si and subsequent annealing in an oxidizing ambient at 560°C. It was found that the film structure of the annealed samples critically depends on the crystallinity of the as-deposited samples. Amorphous films resulted in dot formation when annealed, whereas grain agglomeration was observed in the case of crystalline films. In addition, the dots were embedded within SiO 2, whereas the agglomerated grains were isolated with no insulating material between them. These results were accounted for by taking into consideration the difference in kinetics involved during annealing.

Estimation of Minimum Liquidus Free Energy Concentration for Silicide and Germanide Systems

Thermodynamic functions of Co-Si and Au-Si systems were studied. The validity of these functions were confirmed by successfully calculating phase diagrams. It was revealed that the composition of the first nucleated compound is close to the concentration of the minimum free energy of the liquid alloy with respect to the two solid components (ΔG) of the binary systems. In addition, the minimum ΔG concentration was found to be located by interpolating the portion of the liquidus, where the liquid alloy is in equilibrium with the two solid constituents, into the central region of the diagram where compounds exist. The minimum ΔG concentration of other silicide and germanide systems were estimated by the suggested interpolation method. A new model for predicting the first nucleated compound in silicide as well as germanide systems was proposed based on the findings.

Microscopic Mechanism of Electrical Noise in Co/Si Thin Film Structures

A microscopic mechanism of the production of electrical fluctuations in noncrystalline structures has been studied by measuring 1/f noise parameters and analyzing microstructure of Co/Si interfaces along the silicide nucleation reaction path. The measured noise power spectral density presents the largest fluctuations near the structural (noncrystalline-to-crystalline) transition and the electronic (semiconducting-to-metallic) transition region. The amplitude of the noise spectral density at the frequency of 1 Hz drops more than 3 orders after the nucleation of the first cobalt silicide phase. The variation of the noise parameter is assumed to be an indication of the phase transformation along the nucleation reaction path in a Co/Si thin film system. Structural studies suggest that the observed electrical noise might originate from cobalt atom movements in reversible processes between different chemical structures.