Yong-Hyun Ham

Design, fabrication, and experimental demonstration of a piezoelectric cantilever for a low resonant frequency microelectromechanical system vibration energy harvester

Abstract. We compare the performances of vibration-powered microelectromechanical system (MEMS) electrical generators using a Pb(Zr,Ti)O3 (PZT) material. With the aid of a finite element method simulation, we have designed a PZT cantilever-based energy-harvesting system that uses mechanical vibration. We fabricate cantilevers on the MEMS scale with an integrated variable Si proof mass to obtain a low resonant frequency and high current. Based on simulation results, we fabricate cantilever devices with integrated Si proof masses with volumes of about 0.32 and 0.53  mm3. These devices compare favorably to the data obtained through simulation. Further, by comparing variable mass volumes, we obtain a high current and low resonant frequency. Similar results are obtained by simulation and experiment. Therefore, we offer a new and predictable means of obtaining a low resonant frequency for application to a micropower source area. Furthermore, from the size effect of the proof mass volume, we obtain the current and resonant frequency of these energy harvester systems. The possibility of a MEMS-scale power source for energy conversion experiments is also tested.

Etching characteristics and mechanism of indium tin oxide films in an inductively coupled HBr∕Ar plasma

The investigations of etch characteristics and mechanisms for indium tin oxide (In2O3)0.9:(SnO2)0.1 (ITO) thin films using HBr∕Ar inductively coupled plasma were carried out. The ITO etch rate was measured in the range of 0%–100% Ar in the HBr∕Ar mixture at fixed gas pressure (6mTorr), input power (700W), and bias power (200W). Plasma parameters and composition were examined with a combination of plasma diagnostics by double Langmuir probe and global (zero-dimensional) plasma model. It was found that the ITO etch rate follows the behavior of Br atom flux but contradicts with that for H atoms and positive ions. This suggests that the ITO etch process is not limited by the ion-surface interaction kinetics and appears in the reaction-rate-limited etch regime with the Br atoms as the main chemically active species.

Study on surface modification of silicon using CHF3/O2 plasma for nano-imprint lithographya)

In this article, we report the surface modification of silicon by an inductively coupled CHF3/O2 plasma treatment for demolding process in nano-imprint lithography. The effects of O2 addition to the CHF3 plasma on the surface polymer were investigated. The Si surface energy remained nearly constant at O2 gas fraction from 0% to 50%, but it increased up to ∼60 mN/m at O2 gas fraction of 60%. In order to examine the relationship between the plasma and surface energy of Si, we attempted to conduct a model-based analysis of the CHF3/O2 plasma. Plasma diagnostics were performed by using a double Langmuir probe. At the same time, the surface analysis of Si was carried out by contact angle measurements and x-ray photoelectron spectroscopy.

Etching characteristics and mechanism of vanadium dioxide in inductively coupled Cl2∕Ar plasma

Abstract. An investigation of a VO 2 etch mechanism in Cl 2 /Ar induc-tively coupled plasma under the condition of low ion bombardment en-ergy is carried out. It is found that an increase in Ar mixing ratio results anonmonotonic VO 2 etch rate, which reaches a maximum of70 to 80 nm/min at 70 to 75% Ar. The model-based analysis of the etchmechanism shows that the VO 2 etch kinetics correspond to the ion-flux-limited etch regime. This is most likely due to the domination of lowvolatile VCl 3 and/or VCl 2 in the reaction products.

Etching Characteristics of VO2 Thin Films Using Inductively Coupled Cl2/Ar Plasma

A study on both etching characteristics and mechanism of VO2 thin films in the Cl2/Ar inductively coupled plasma was carried. The variable parameters were gas pressure (4–10 mTorr) and input power (400–700 W) at fixed bias power of 150 W and initial mixture composition of 25% Cl2 + 75% Ar. It was found that an increase in both gas pressure and input power results in increasing VO2 etch rate while the etch selectivity over photoresist keeps a near to constant values. Plasma diagnostics by Langmuir probes and zero-dimensional plasma model provided the data on plasma parameters, steady-state densities and fluxes of active species on the etched surface. The model-based analysis of the etch mechanism showed that, for the given ranges of operating conditions, the VO2 etch kinetics corresponds to the transitional regime of ion-assisted chemical reaction and is influenced by both neutral and ion fluxes with a higher sensitivity to the neutral flux.

Etching Characteristics and Mechanism of ZnO and Ga-Doped ZnO Thin Films in Inductively Coupled HBr/Ar/CHF3 Plasma

The etching characteristics and mechanisms of ZnO and Ga-doped ZnO (Ga-ZnO) thin films in a HBr/Ar/CHF3 inductively coupled plasma were investigated. The etching rate of ZnO was measured as a function of the CHF3 mixing ratio in the range of 0–15% in a HBr:Ar = 5:2 plasma at a fixed gas pressure (6 mTorr), input power (700 W), bias power (200 W), and total gas flow rate (50 sccm). The plasma chemistry was analyzed by a combination of the global (zero-dimensional) plasma model, Langmuir probe diagnostics (LP) and quadrupole mass spectrometer (QMS) analysis. It was found that the densities of both HBr and Br are significantly affected by the reactions with the CHF3 dissociation products, while both the ZnO and Ga-ZnO etching rates follow the behavior of the Br atom density and flux. This suggests that the ZnO and Ga-ZnO etching processes are not limited by the ion-surface interaction kinetics and appear in the reaction-rate-limited etching regime.