Chih-Hung Li

Negative bias temperature instability of Rf-sputtered Mg0.05Zn0.95O thin film transistors with MgO gate dielectrics

This study investigated the negative bias temperature instability of rf-sputtered bottom-gate Mg0.05Zn0.95O active layer thin-film transistors (TFTs) annealed at 200 °C for 5 h and 350 °C for 30 min. The TFT devices initially exhibited similar electrical characteristics. When TFTs were stressed at room temperature, the TFTs (in both annealing conditions) showed typical negative shift of threshold voltage (ΔVth). When TFTs were stressed at 80 °C, a turnaround of ΔVth appeared for the 200 °C-annealed TFTs; the Vth shifted toward a negative direction initially and consequently turned positive. The turnaround phenomenon should result from the competing charge trapping and defect creation. On the other hand, the 350 °C-annealed TFTs still showed typical negative shift of threshold voltage when stressed at 80 °C.

Volume Shrinkage Induced by Interfacial Reaction in Micro-Ni/Sn/Ni Joints

Experiments are carried out to measure the volume shrinkage during solid-state reaction in micro-joints for three-dimensional integrated circuit applications. Surface profilometer is employed to measure the volume shrinkage for the reaction between Ni and Sn. The shrinkage is correlated with the microstructural evolution during the reaction. It is found that the volume shrinkage is released through both joint height reduction and void formation. The resulting internal stress and the void formation might post potential reliability issues.

Dynamically programmable surface micro-wrinkles on PDMS-SMA composite

We report on the development of a PDMS-SMA composite whose surface micro wrinkles can be dynamically programmed by an electrical current supplied to the SMA wire. It is advantageous over other techniques for surface topographical modulation, including portability, real-time programmability, no requirement for specific surface chemistry, operability under ambient conditions, and relative ease of control. A simplified mechanical model is also developed to describe the force-deflection balance of the PDMS-SMA composite. The wavelengths and amplitudes of the wrinkles when different currents applied to the SMA are characterized, and the experimental results agree with the theoretical model. The developed composite device can be applied to programmable modulations of surface adhesion, friction, wettability, etc.

Development of interconnection materials for Bi 2 Te 3 and PbTe thermoelectric module by using SLID technique

In this study, low-temperature Bi2Te3 and mid-temperature PbTe thermoelectric modules are assembled by the technique of Solid Liquid Interdiffusion (SLID). Scanning electron microscope is carried out for issues relating to factors limiting the reliability, growth of intermetallic compounds, and thermal stability. For low-temperature thermoelectric module, N-type Bi2Te3 is bonded to alumina substrates by using a Ni/Sn/Ag system. During bonding and subsequent aging reaction at 200 °C, Sn reacts with Ag to form Ag3Sn, and Ni reacts with Sn to form Ni3Sn4. This reaction process takes less than 72 h to exhaust the entire Sn layer to produce a bonding that can withstand temperature as high as 480 °C. The interfacial reaction, Ni penetration depth, and IMC kinetics between Ni and Bi2Te3 at 200, 250, and 300 °C are also investigated in detail. For mid-temperature thermoelectric module, N-type PbTe is bonded to alumina substrates by using a Ag/In/Ag system. During assembly at 190 °C, all Ag/In/Ag joint are transformed into Ag2In, which has the melting temperature above 670 °C, in less than 2 minutes. Furthermore, this Ag-In joint has passed high temperature storage test at 400 °C for 1000 h. The success of solid liquid interdiffusion technique and related contact materials provide a cost effective way to assemble thermoelectric modules for power generating or cooling applications which require long term operations at high temperatures.

Soldering reactions under space confinement for 3D IC applications

The microstructure features and the IMC kinetics of Cu-Sn and Ni-Sn soldering reaction under space confinement are studied in the present study. Experimentally, Cu/Sn(10 μm)/Cu and Ni/Sn(10 μm)/Ni sandwich structures were prepared through a hot-press bonding. Sn with a thickness of 10 μm was chosen to simulate the joints in 3D IC packages employing a severe space confinement. Microstructure characterisations showed that space confinement does not change the reaction products which are Cu6Sn5 and Cu3Sn for Cu-Sn reactions and Ni3Sn4 for Ni-Sn reactions. However, it was found that the interfacial morphology is very different to that of the conventional joints. IMCs in the space confined reactions occupy a very large or even entirety volume in the joint. In addition, voiding occurs in both Cu/Sn/Cu and Ni/Sn/Ni reactions, which having great impacts on the joint strength. According to the kinetics analysis, the IMCs growth rates measured in the present work are in the range of literature results, suggesting that the space confinement behaviour has very little effects on the IMC growth kinetics.

Microstructural, electrical, and optical properties of sol–gel derived HfMgZnO thin films

This paper reports the characterization of sol–gel derived HfxMg0.05Zn0.95−xO (x = 0, 0.025, 0.05, 0.1) thin films. The films show high transparency (~90%) in the visible light wavelength region. The incorporation of Hf in the thin films increases the bandgap and decreases the crystallinity in the as-deposited films. This may be due to the high bandgap of HfO2 and the crystal frustrating effect caused by mixing atoms of different sizes. As the annealing temperature increases, the bandgap changes because of the alteration of the stress status, grain growth, and atomic rearrangement. The resistivity also decreases slightly with an increase in the annealing temperature.