Chuen-Horng Tsai

Structural transformation and field emission enhancement of carbon nanofibers by energetic argon plasma post-treatment

Vertically aligned carbon nanofibers (CNFs) grown by plasma enhanced chemical vapor deposition (PECVD) were transformed into cone-shaped nanostructures after treatment by argon (Ar) plasma. Significant enhancement of field emission characteristics of the post-treated CNFs has been achieved. Analysis by electron microscopy and energy dispersive spectroscopy (EDS) suggests that the structural transformation is a result of a cosputtering∕deposition process by energetic plasma ions. The enhancements can be attributed to the combining effects of an additional Si∕C layer coverage, catalytic nanoparticles removal and the sharpening of CNFs tips. The argon plasma post-treatment processes developed here can be easily extended to in situ PECVD processes for fabricating CNFs based emitters.

Effect of high-voltage sheath electric field and ion-enhanced etching on growth of carbon nanofibers in high-density plasma chemical-vapor deposition

The results of a parametric study on the growth of vertically aligned carbon nanofibers (CNFs) by high-density inductively coupled plasma (ICP) chemical-vapor deposition are reported. We investigated the mechanisms that cause the detachment of CNFs during the growth process by high-density plasma-enhanced chemical-vapor deposition with high substrate bias voltage and atomic hydrogen concentration. A simplified model, combining the Child law for sheath field, floating sphere model for field enhancement at the fiber tip and electric-field screening effect, was employed to estimate the detachment electrostatic force on individual CNFs induced by plasma sheath electric field. The force was found to increase with substrate bias voltage, bias current, and lengths of CNFs, consistent with the experimental observations that CNFs density decreases with ICP power, bias power, and growth time. However, the magnitude of the electrostatic force per se cannot explain the detachment phenomena. The other factor is believ...

Optical properties of Pb(Zr, Ti)O3 thin films on sapphire prepared by metalorganic decomposition process

Pb(Zr0.52Ti0.48)O3 (PZT) thin films were synthesized on a sapphire substrate for application as planar optical waveguide devices using a metalorganic decomposition (MOD) process. Pyrochlore phase, which always forms preferentially when the PZT thin films (∼200 nm) are deposited on a sapphire substrate directly, has been effectively suppressed by using a SrTiO3 (STO) film (∼190 nm) as a buffer layer. The PZT/sapphire thin films have a significantly larger refractive index than the STO/sapphire ones: nPZT=2.2012 and nSTO=2.0639 (at 632.8 nm) by prism coupling measurement and nPZT′=2.215 and nSTO′=2.084 (at 632.8 nm) by optical transmission spectroscopic measurement. The STO layer cannot only serve as buffer layer for enhancing the crystallization kinetics of the subsequently deposited PZT thin films, but can also serve as cladding layer in a ridge-type planar waveguide, which uses PZT thin film as core materials.

Optical properties of Pb(Zr1−xTix)O3 thin films by incorporation of nano-sized particles in metal organic decomposition process

Abstract The PZT films were synthesized on Pt/Ti/SiO2/Si and MgO (100) substrates by the conventional Metal Organic Decomposition (MOD) and nanopowdered MOD processes. Effects of incorporating nano-sized PZT powders into carboxylate solution on the characteristics of PZT films were examined. Addition of nano-sized PZT powders into the carboxylate enhanced the stability of the materials such that the films could be post-annealed at higher temperatures without deterioration. The ferroelectric and optical properties of PZT films were thus improved. The remnant polarization (Pr) increased to 18.05 μC/cm2, the corecive field (Ec) decreased to 45.90 kV/cm, the surface roughness (RMS) was in 4.2 nm level and the refractive index at 633 nm increased to 2.4.

On the growth of carbon nanofibers on glass with a Cr layer by inductively coupled plasma chemical vapor deposition : The effect of Ni film thickness

We have studied the effect of the thickness of catalytic Ni film for the growth of vertically aligned carbon nanofibers (VA-CNFs) on glass substrates coated with a conductive underlayer of Cr. Both the pretreatment process through which the catalytic Ni nanoparticles were formed and the growth of well-aligned CNFs were carried out in an inductively coupled plasma chemical vapor deposition (ICP-CVD) system. The VA-CNFs were characterized by scanning electron microscopy, Raman spectroscopy, as well as field emission measurements. The results of VA-CNF growth shows that as the Ni film thicknesses decrease, not only the length but also the density of the CNFs drop, although the density of catalytic Ni nanoparticles increases. The variation of CNF density with Ni film thicknesses is believed to be a result of the detachment of the CNFs from the substrate, caused by the electrostatic force produced by the plasma sheath electric field, as well as an ion-enhanced chemical etching effect due to atomic/ionic hydrog...

Effect of nitrogen content in HfxTayN metal gate on work function and thermal stability of advanced metal-oxide-semiconductor devices

The effects of nitrogen composition in HfxTayN metal-gate electrodes and postmetal annealing (PMA) treatment on the electrical properties of metal-oxide-semiconductor (MOS) devices were investigated in this work. The work function of HfxTayN gate electrodes can be adjusted by incorporating various nitrogen contents. It is found that the HfxTayN metal gate with higher nitrogen content can achieve better electrical characteristics in terms of leakage current and reliability while with only a slight increase in equivalent-oxide-thickness value. The face that only slight variation on electrical characteristics of MOS device with HfxTayN gate electrodes is observed after various PMA temperatures designates the excellent thermal stability of HfxTayN gate electrodes. The present study indicates that HfxTayN is a promising metal-gate-electrode material for advanced MOS devices.

Crystalline and optical properties of PLZT films prepared by pulsed laser deposition

Abstract The PLZT (3/66/34), PLZT (3/46/54), PLZT (9/65/35) and PLZT (28/0/100) thin films were deposited on MgO (100), Sapphire (0001) and fused silica substrates by using pulsed KrF excimer laser deposition technique. The conventional in-situ and 2-step heating processes were utilized to facilitate the synthesis of a large area of uniform PLZT thin film. Pure perovskite phase can be obtained only under very narrow process conditions, the highly textured PLZT films can be easily obtained by in-situ heating process. For PLZT (28/0/100) material, epitaxial films were successfully coated on MgO (100) substrates by 600°C in-situ and RTA 650°C 2-step heating processes. The latter was found to possess higher refractive index and lower extinction coefficient.

National project on 45 to 32 nm metal oxide semiconductor field effect transistors for next century IC fabrications

It is well known that the Taiwan Semiconductor industries play the very key roles for the worldwide IC foundry, and the advanced research of nanoelectronics is the lifeline for its long term developments. Professor Huey-liang Hwang effectively integrated the most outstanding research team and resource in Taiwan on the National Project on Nanometer CMOS Transistors for the 21 century, which is sponsored by the Ministry of Economic Affairs of ROC. A dozen of Professors from NTHU( National Tsing Hua University) with expertise at the novel materials and analysis and NCTU( National Chiao Tung University) with expertise at devices and reliability are devoted to the studies and are in collaboration with the world-wide-known company such as TSMC, and breakthrough of the key technologies of 45-32 nm technologies are achieved. The objective of this project is focused on the development of advanced metal gate/high-k MOSFET for 45 nm node generation and beyond, the efforts include the world first successful suppression the oxide/Si interfacial layer formation by using a bi-layer composite of HfO2 3.2 nm (ALD)/HfO2 1.5 nm (MBE), the results show a dielectric constant of 16 and an EOT of 1.15 nm, a Dit was estimated to be 4.6times1011 cm-2eV-1 with the leakage at Vfb-1V being 8.5times10-6 A/cm2. Also, the thermal stability of HfO2, HfAlOx alloy and Al2O3/HfO2 stack, prepared by ALD were compared, the incorporation of Al in alloy form gave superior characteristics by retaining an amorphous structure up to 1000 C, which suppress the leakage current and retards growth of the interfacial layer giving the least increment of EOT and interface traps. Besides, by incorporating Al into TiO2 gave an EOT value of the Al2O3/TiAlOx/Al2O3 film down to 0.8 nm. Furthermore, high selectivity was obtained via etching the HfAlO and silicon wafer with pattern using the ICP Plasma. In this project, YbSi metal gate for n-MOSFET and IrSi metal gate p-MOSFET were successfully fabricated for the HfAlON MESFET. The results showed the good effective workfunction of 4.15 and 4.9 eV and no degradation of gate dielectric current and mobility in the YbxSi/ HfAlON and IrxSi/ HfAlON FUSI-gates by reducing the metal diffusion at lower temperatures.

Numerical and experimental investigation of 2/spl times/2 optical switch in silica-on-silicon

In this paper, we designed a 2/spl times/2 Mach-Zehnder (MZI) thermooptic switch based on multimode interference (MMI) couplers in silica-on-silicon. Issues concerning the influence of a number of design parameters for a 2/spl times/2 multimode interference couplers are discussed. The beam-propagation method (BPM) was used to demonstrate the feasibility of the proposed design of compact MMI coupler. Instead of standard fabrication process, we utilized a different lithography metrics to define the desired waveguide patterns. P-doped silica films were deposited on Si substrates using a plasma-enhanced chemical vapor deposition system. Optical properties of the films including refractive index, thickness and uniformity were examined by a prism coupler of optical interference method. We successfully used reactive ion etching (RIE) to fabricate a low loss straight waveguide with smooth sidewall. For silica waveguides, the thermo-optic effect is used to tune the local refractive index of the guiding layer. A resistive material such as aluminum was used as heating element. The silica-on-silicon technology with surface micromachining revealed an optimal design of a low power compact thermooptic switch. This paper would summarize the development of this novel process for the realizing of the designed optical switch and its applicability in fabricating planar waveguide circuit.

Etching Characteristics of Silica-Based Optical Waveguide for Planar Lightwave Circuit

We have successfully synthesized high quality silica by using plasma enhanced chemical vapor deposition (PECVD) of tetraethyl orthosilicate (TEOS) precursors. Optical transmission spectroscopy and Fourier transform infrared (FTIR) spectroscopy indicated that, the TEOS/O 2 ratio had pronounced influence on the deposition rate and optical properties for SiO 2 films. Modification on refractive index (n) for the synthesis of single mode optical waveguide can be easily achieved in PECVD process, by addition of TMP in the precursors. Based on this, a Si/SiO 2 /P-SiO 2 /SiO 2 ridge-type waveguide structure could be derived following a photolithography, lift-off and reactive ion etching (RIE) process sequence. In this study, silica etch characteristics of different etching parameters were investigated using CHF 3 /O 2 as the etch gases. Metal mask could offer higher selectivity and yielded smaller deposition of polymer, so that an optical quality ridge structure with high vertical sidewall angle and dimension controllability, and smooth sidewall surface became possible. The results came out that the etching parameters such as RF power and CHF 3 /O 2 ratio had significant influence on the etch rates, etch selectivities and etch profiles. Under optimal etching conditions and post-treatment, a single mode waveguide with vertical etch profile and smooth sidewall could be fabricated successfully.