Yongsoo Oh

Bismuth-zinc-niobate embedded capacitors grown at room temperature for printed circuit board applications

We fabricated metal-insulator-metal (MIM) thin film capacitors with Bi1.5Zn1.0Nb1.5O7 (BZN) dielectric films. The BZN films were deposited at room temperatures by pulsed laser deposition and annealed below 200°C which is compatible with the used polymer-based substrates. The dielectric constant of BZN films increases from 2 to 70, when they are annealed at 150°C, but still in amorphous phase. We found that a considerable portion of Bi metallic phase still remains in the as-deposited film. They turn into oxides upon annealing at >120°C, causing the dramatic change of the dielectric properties. Amorphous BZN thin films exhibit superior dielectric characteristics, capacitance density of 150nF∕cm2, and leakage current less than 1μA∕cm2 at 5V. The MIM capacitors using amorphous BZN thin films will be a promising candidate for the PCB-embedded capacitors.

Realization of a high capacitance density in Bi2Mg2∕3Nb4∕3O7 pyrochlore thin films deposited directly on polymer substrates for embedded capacitor applications

Bi2Mg2∕3Nb4∕3O7 (BMN) thin films were deposited on copper clad laminate substrates at temperatures below 150°C for embedded capacitor applications by pulsed laser deposition. The BMN films deposited at temperatures below 150°C showed smooth surface morphologies having root mean square roughness of approximately 3.0nm. 130-nm-thick films deposited at 150°C exhibit a dielectric constant of 47, a capacitance density of approximately 302nF∕cm2, and breakdown strength of 0.7MV∕cm. The origin exhibiting high dielectric constant in BMN films deposited at low temperatures was attributed to the nanocrystallines having grain sizes of approximately 4.0nm in the films. The low temperature processed-BMN films are suitable candidate for capacitor applications embodied directly on printed circuit board substrates.

Fabrication of Poly(3-hexylthiophene) Thin Films by Vapor-Phase Polymerization for Optoelectronic Device Applications

The vapor-phase polymerization (VPP) of poly(3-hexylthiophene) (P3HT) was achieved successfully as an alternative method to conventional solution-based thin film fabrication. Using Fe(III)Cl(3).6H(2)O, a spontaneous reaction of 3-hexylthiophene monomers resulted in the rapid formation of conducting P3HT thin films directly on substrates, such as glass, indium-tin-oxide, and poly(ethylene terephthalate), at thicknesses ranging from 50 to 1000 nm. The VPP of P3HT was achieved using ferric chloride hexahydrate and a 1:1 ratio of a methanol/ethanol mixture as the solvent system. The developed VPP technique can provide good processing consistency with an electrical conductivity, a transmittance, and a surface roughness of approximately 10(-2) S/cm, >90%, and <10 nm, respectively.

Planar inductor with ferrite layers for DC-DC converter

The demand for miniaturized magnetic passive devices in power modules has been rapidly growing with mobile handset technology. Thus, we developed a minimum construction and sized planar inductor for micro DC-DC converters with a ferrite plating method and conventional flexible PCB processes. The ferrite plating process made it possible to deposit Ni-Zn spinel ferrite on a Cu electroplated planar coil without a non-magnetic insulation layer. These samples of a planar inductor with ferrite layers achieved a high quality factor of 17/spl sim/24 at 3/spl sim/5 MHz and inductance of 1.25/spl sim/1-30 /spl mu/H in 6.0/spl times/6.0/spl times/0.19/spl sim/0.20 mm/sup 3/, respectively. In addition, the estimated power loss of this developed inductor at 5 MHz in a switching buck DC-DC converter was about 15.7%. It showed excellent capability for portable power systems.

Thermal transformation of solvent-processable organosilicon compounds into inorganic silicone-based thin films

In this study, a solution-processable precursor, decaphenycyclopentasilane (DPCPS) was synthesized and successfully converted into an inorganic thin film through the heat treatment process. When the DPCPS coating was heat-treated at various temperatures up to 900 °C, the organic DPCPS was converted into an inorganic compound composed of Si, C and O atoms in the form of SiCxOy. The relative compositions of Si, C, and O changed with the heat-treatment temperatures changing the carbon content, for example, from 88.9% for the pristine DPCPS to 3.0% for the specimen heat-treated over 700 °C, consequently becoming SiC0.05O1.7. The dielectric constant of the heat-treated DPCPS could be tailored with the heat treatment temperatures from high- to low-dielectric materials, i.e., 10.8 at 300 °C and 2.3 at 900 °C, providing tunable dielectric properties for various optoelectronic applications. The resulting inorganic thin films had excellent coating characteristics with low RMS roughness (<1.0 nm).

Failure mechanisms in thermal inkjet printhead analyzed by experiments and numerical simulation

This paper presents a failure analysis result for enhancing the reliability of thermal inkjet printhead. A novel inkjet printhead is fabricated using MEMS process, and we analyze the failure mechanism of inkjet head based on detailed experimental observations and numerical simulations. The failures presented in this work showed three primary factors influencing the failure modes and lifetime of printhead; bubble cavitation damage, thermal fatigue, and electromigration of heater. The design modification of micro heater to avoid an early stage of failure by electromigration yields the reliability enhancement of thermal inkjet printhead.

Fabrication of a Touch Sensor for Flat Panel Displays Using Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) with Dimethylsulfoxide by Soft Lithography

In this study, a transparent conductive-polymer-based sensor array designed for use in a touch screen panel was fabricated using soft lithography. One of the most promising conductive polymers, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), was used as the conductive material, and the secondary dopant dimethyl sulfoxide (DMSO) was used to increase the conductivity. The experiments were conducted using various DMSO concentrations in PEDOT:PSS in order to identify the optimum conditions to achieve high conductivity and transmittance. The electrical properties of PEDOT:PSS thin films were investigated using a four-point probe, and their transmittance was determined using an UV–vis spectrometer. The surface morphology was observed by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). A stable conductivity in the range of 110–204 S/cm was obtained at 0–30% DMSO concentrations, and the transmittances were greater than 92% in the visible range.

CHARACTERISTICS OF BISMUTH-BASED THIN FILMS DEPOSITED DIRECTLY ON POLYMER SUBSTRATES FOR EMBEDDED CAPACITOR APPLICATION

ABSTRACT B2Mg2/3Nb4/3O7 (BMN) thin films were deposited at low temperature (< 200°C) on Copper Clad Laminates (CCL) with various Ar/O2 flow ratios and film thicknesses by sputtering system. 200 nm-thick BMN thin films were deposited at Ar/O2 = 10: 10 had rms roughness of 54.3 ÅA, capacitance density of 155 nF/cm2 at 100 kHz, dissipation factor of 0.017 and leakage current density of ∼10− 5 at 3 V. Surface roughness of the BMN thin films increased a little with increasing the film thickness. However leakage current density decreased and the dielectric constant of that was maintained at 40.

The Effects of Driving Waveform of Piezoelectric Industrial Inkjet Head for Fine Patterns

This paper presents the effect of driving waveform for piezoelectric bend mode inkjet printhead with optimized mechanical design. Experimental and theoretical studies on the applied driving waveform versus jetting characteristics were performed. The inkjet head has been designed to maximize the droplet velocity, minimize voltage response of the actuator and optimize the firing frequency to eject ink droplet. The head design was carried out by using mechanical simulation. The printhead has been fabricated with Si(100) and SOI wafers by MEMS process and silicon direct bonding method. To investigate how performance of the piezoelectric ceramic actuator influences on droplet diameter and droplet velocity, the method of stroboscopy was used. Also we observed the movement characteristics of PZT actuator with LDV(laser doppler vibrometer) system, oscilloscope and dynamic signal analyzer. Missing nozzles caused by bubbles in chamber were monitored by their resonance frequency. Using the water based ink of viscosity of 4.8 cps and surface tension of 0.025N/m, it is possible to eject stable droplets up to 20kHz, 4.4m/s and above 8pL at the different applied driving waveforms.

The Fabrication of Monolithic Micro Droplet Ejector using MEMS

This paper presents the fabrication of a micro droplet ejector for the application of digital printing system. The ejector makes the ink droplets of approximately 80 squaremum diameter on demand. The ejecting system is the type of face-shooter. The method of actuating membrane is bending mode using d31 of PZT. The size of ejector is 27.6 mm x 27.75 mm x 1.1 mm, and the pitch between nozzles is 2.54 mm, 10 npi. The nozzle and restrictor are very important part for the performance of the ejector such as droplet size and velocity. Therefore, the roundness and straightness of nozzle and depth profile of the restrictor have an influence on the characteristic of droplet. Those are made by deep silicon etching technique for the accuracy and uniformity. The ejector is successfully operated and the measured ejection speed, size of droplet and the ejection frequency are 1 m/s, 80 mum and 1 kHz, respectively.