• Journal of the Microelectronics and Packaging Society
• /
• v.17 no.3
• /
• pp.43-49
• /
• 2010

Direct printing technology is an attractive metallization method, which has become immerging as "Green technology" to the conventional photolithography, on account of low cost, simple process and environment-friendliness. In order to commercialize the printed electronics in industry, it is essential to evaluate the electrical properties of conductive circuits using direct printing technology. In this contribution, we focused on the electrical characteristics of inkjet-printed circuits. A Cu nanoink was inkjet-printed onto a Bisaleimide triazine(BT) substrate with parallel transmission line(PTL) and coplanar waveguide(CPW) type, then was sintered at $250^{\circ}C$ for 30 min. We calculated the resistivity of printed circuits through direct current resistance by the measurement of I-V curve: the resistivity was approximately 0.558 ${\mu}{\Omega}{\cdot}cm$ which is about 3.3 times that of bulk Cu. Cascade's probe system in the frequency range from 0 to 30 GHz were employed to measure the Scattering parameter(S-parameter) with or without a gap between the substrate and the probe station chuck. The result of measured S-parameter showed that all printed circuits had over 5 dB of return loss in the entire frequency range. In the curve of insertion loss, $S_{21}$, showed that the PTL type circuits had better transmission of radio frequency (RF) than CPW type.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.344-344
• /
• 2014

Transparent amorphous oxide semiconductors such as a In-Ga-Zn-O (a-IGZO) have advantages for large area electronic devices; e.g., uniform deposition at a large area, optical transparency, a smooth surface, and large electron mobility >10 cm2/Vs, which is more than an order of magnitude larger than that of hydrogen amorphous silicon (a-Si;H).1) Thin film transistors (TFTs) that employ amorphous oxide semiconductors such as ZnO, In-Ga-Zn-O, or Hf-In-Zn-O (HIZO) are currently subject of intensive study owing to their high potential for application in flat panel displays. The device fabrication process involves a series of thin film deposition and photolithographic patterning steps. In order to minimize contamination, the substrates usually undergo a cleaning procedure using deionized water, before and after the growth of thin films by sputtering methods. The devices structure were fabricated top-contact gate TFTs using the a-IGZO films on the plastic substrates. The channel width and length were 80 and 20 um, respectively. The source and drain electrode regions were defined by photolithography and wet etching process. The electrodes consisting of Ti(15 nm)/Al(120 nm)/Ti(15nm) trilayers were deposited by direct current sputtering. The 30 nm thickness active IGZO layer deposited by rf magnetron sputtering at room temperature. The deposition condition is as follows: a rf power 200 W, a pressure of 5 mtorr, 10% of oxygen [O2/(O2+Ar)=0.1], and room temperature. A 9-nm-thick Al2O3 layer was formed as a first, third gate insulator by ALD deposition. A 290-nm-thick SS6908 organic dielectrics formed as second gate insulator by spin-coating. The schematic structure of the IGZO TFT is top gate contact geometry device structure for typical TFTs fabricated in this study. Drain current (IDS) versus drain-source voltage (VDS) output characteristics curve of a IGZO TFTs fabricated using the 3-layer gate insulator on a plastic substrate and log(IDS)-gate voltage (VG) characteristics for typical IGZO TFTs. The TFTs device has a channel width (W) of $80{\mu}m$ and a channel length (L) of $20{\mu}m$. The IDS-VDS curves showed well-defined transistor characteristics with saturation effects at VG>-10 V and VDS>-20 V for the inkjet printing IGZO device. The carrier charge mobility was determined to be 15.18 cm^2 V-1s-1 with FET threshold voltage of -3 V and on/off current ratio 10^9.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.454-454
• /
• 2014

Silicon microwire array is one of the promising platforms as a means for developing highly efficient solar cells thanks to the enhanced light trapping efficiency. Among the various fabrication methods of microstructures, deep reactive ion etching (DRIE) process has been extensively used in fabrication of high aspect ratio microwire arrays. In this presentation, we show precisely controlled Si microwire arrays by tuning the DRIE process conditions. A periodic microdisk arrays were patterned on 4-inch Si wafer (p-type, $1{\sim}10{\Omega}cm$) using photolithography. After developing the pattern, 150-nm-thick Al was deposited and lifted-off to leave Al microdisk arrays on the starting Si wafer. Periodic Al microdisk arrays (diameter of $2{\mu}m$ and periodic distance of $2{\mu}m$) were used as an etch mask. A DRIE process (Tegal 200) is used for anisotropic deep silicon etching at room temperature. During the process, $SF_6$ and $C_4F_8$ gases were used for the etching and surface passivation, respectively. The length and shape of microwire arrays were controlled by etching time and $SF_6/C_4F_8$ ratio. By adjusting $SF_6/C_4F_8$ gas ratio, the shape of Si microwire can be controlled, resulting in the formation of tapered or vertical microwires. After DRIE process, the residual polymer and etching damage on the surface of the microwires were removed using piranha solution ($H_2SO_4:H_2O_2=4:1$) followed by thermal oxidation ($900^{\circ}C$, 40 min). The oxide layer formed through the thermal oxidation was etched by diluted hydrofluoric acid (1 wt% HF). The surface morphology of a Si microwire arrays was characterized by field-emission scanning electron microscopy (FE-SEM, Hitachi S-4800). Optical reflection measurements were performed over 300~1100 nm wavelengths using a UV-Vis/NIR spectrophotometer (Cary 5000, Agilent) in which a 60 mm integrating sphere (Labsphere) is equipped to account for total light (diffuse and specular) reflected from the samples. The total reflection by the microwire arrays sample was reduced from 20 % to 10 % of the incident light over the visible region when the length of the microwire was increased from $10{\mu}m$ to $30{\mu}m$.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.40 no.7
• /
• pp.673-677
• /
• 2016

Recently, engineering applications have started to adopt solutions inspired by nature. The peculiar adhesive properties of gecko skin are an example, as they allow the animal to move freely on vertical walls and even on ceilings. The high adhesive forces between gecko feet and walls are due to the hierarchical microscopical structure of the skin. In this study, the effect of metal coatings on the adhesive strength of synthetic, hierarchically structured, dry adhesives was investigated. Synthetic dry adhesives were fabricated using PDMS micro-molds prepared by photolithography. Metal coatings on synthetic dry adhesives were formed by plasma sputtering. Adhesive strength was measured by pure shear tests. The highest adhesion strengths were found with coatings composed of 4 nm thick layers of Indium, 8 nm thick layers of Zinc and 6 nm thick layers of Gold, respectively.

• Journal of Sensor Science and Technology
• /
• v.9 no.1
• /
• pp.22-27
• /
• 2000

Amorphous FeCoSiB films with high saturation magnetostriction and excellent soft magnetic properties have been studied to evaluate their strain sensitivity. Films were subjected to a strain by bending of their substrates, which caused a change in the magnetic anisotropy of films via magnetoelastic coupling. Films were exhibited a figure of merit $F=({\Delta}{\mu}/{\mu})/{\varepsilon}$ (change in film permeability $\mu$ per unit strain $\varepsilon$) of $1.2{\times}10^5$, which is comparable with that of amorphous ribbons. To make a study of application of magnetostrictive films as strain sensor elements, we have prepared a micro-patterned film by means of the photolithography and ion milling processes. Impedance change in the patterned films, when strain was applied, was measured over the frequency range from 1 MHz to 1 GHz. Reflecting a large value of figure of merit F, a variation of 46% impedance of films was shown at 100 MHz frequency when a strain of $300{\times}10^{-6}$ was applied.

• Applied Chemistry for Engineering
• /
• v.24 no.6
• /
• pp.593-598
• /
• 2013

In this study, we have evaluated the water absorption phenomenon of photoresist dry film, which is commonly used to build circuits on PCB (Printed Circuit Board) by photolithography, by using ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared). We have firstly observed significant change in fracture mode of dry film with respect to temperature and humidity, which we assumed the material transition from ductile to brittle. Secondly, we have established the process of absorption test for determining the diffusion coefficients of water into the dry film both with gravimeter and ATR-FTIR. We have successfully calculated the diffusion coefficients for each environmental conditions from the results which we achieved by gravimeter and ATR-FTIR. Compared to the gravimeter which is a conventional method for absorption test, the ATR-FTIR method in this study has been found to be very easy to use and have the same accuracy as gravimeter. Moreover, we are expecting to use the ATR-FTIR as an appropriate method to study the absorption phenomena related to any kinds of solvent and polymer system.

• Journal of the Korean Magnetics Society
• /
• v.25 no.4
• /
• pp.117-122
• /
• 2015

The holes with a diameter of $35{\mu}m$ inside the GMR-SV (giant magnetoresistance-spin valve) film were patterned by using the photolithography process and ECR (electron cyclotron resonance) Ar-ion milling. From the magnetoresistance curves of the GMR-SV film with holes measuring by 4-electrode method, the MR (magnetoresistance ratio) and MS (magnetic sensitivity) are almost same as the values of initial states. On other side hand, the $H_{ex}$ (exchange bias coupling field) and $H_c$ (coercivity) dominantly increased from 120 Oe and 10 Oe to 190 Oe and 41 Oe as increment of the number of holes inside GMR-SV film respectively. These results were shown to be attributed to major effect of EMD (easy magnetic domian) having a region positioned between two holes perpendicular to the sensing current. On the basis of this study, the fabrication of GMR-SV applying to the hole formation improved the magnetoresistance properties having the thermal stability and durability of bio-device.

• Proceedings of the Optical Society of Korea Conference
• /
• 2005.07a
• /
• pp.28-29
• /
• 2005

본 논문에서는 MEH-PPV와 DFPP의 폴리머 물질을 이용하여 photovoltaic device가 제작되었고, 그림 1에 두 물질의 분자 구조가 보여진다. Photovoltaic cell의 전기-광학적 특성은 활성층의 폴리머 물질에 의해 결정된다. 이러한 특성을 알아보기 위해서 홉수 스펙트럼이 측정되었다. DFPP는 chloroform, chlorobenzen, THF, acetone에 잘 녹았으며, 본 논문에서는 chloroform이 용매로 사용되었다. 제작 공정은 다음과 같다. 인듐 주석 산화물 (ITO)이 증착된 유리기판은 photolithography 공정을 거친 후, 왕수(HNO$_{3}$ + HCL)로 식각됨으로서 전극의 패턴이 제작되었다. 그리고 ITO 전극 패턴 된 유리기판 위에 PEDOT (CH8000, Baytron)이 코팅된 후 Ar이 주입되는 Convection Oven을 이용하여 120$^{\circ}$C에서 2시간 동안 열처리되어 수분이 제거되었다. 활성층에는 MEH-PPV와 DFPP가 9:1과 2.33:1로 혼합된 폴리머가 사용되었고, 이것은 0.3 %w.t.가 되도록 chloroform에 넣어 5시간 동안 스핀바를 돌려서 용해되었다. 이 용액은 ITO 전극 패턴이 형성된 글라스 위에 3000 rpm으로 45 초간 스핀코팅 되었다. 이 때 얻어진 유기물 박막층은 80$^{\circ}$C의 Ar이 주입되는 convection oven에서 3시간 동안 경화되었다. 경화된 단층 유기물 박막층 위에 Li-Al이 1000 ${\AA}$의 두께로 증착되어 전극이 형성되었고, 이후 질소가 채워진 globe box에서 소자는 encapsulation되어 산소와 수분에 대한 영향으로부터 차단되었다. 상기의 공정으로 제작된 소자의 박막구조는 그림 2에서 보여진다. 그림 3은 MEH-PPV와 DFPP를 혼합했을 때의 흡수 스펙트럼이다. 최대 흡수 파장은 511 nm였다. 그리고 photovoltaic cell의 V-I 특성 결과가 그림 4와 같이 측정되었다. 측정에서는 300${\sim}$700 nm의 파장대를 갖는 태양광 모사계가 사용되었고, 셀의 면적은 10 mm$^{2}$였다. 그림 5의 I-V 특성으로부터 MEH-PPV와 DFPP가 9:1 로 혼합했을 때보다 2.33:1 로 혼합했을 때, photovoltaic device의 효율이 향상됨을 확인할 수 있다. 빛이 75 mW/cm$^{2}$ 의 세기로 조사될 때 9:1과 2.33:1로 혼합된 소자의 open circuit voltage (V$_{oc}$)는 비슷하지만, short circuit current Density (J$_{sc}$)는 각각 -1.39 ${\mu}$A/cm$^{2}$ 와 -3.72${\mu}$A/cm$^{2}$ 로 약 2.7배 정도 증가되었음을 볼 수 있다. 이러한 결과를 통해 electron acceptor인 DFPP의 비율이 높아질수록 photovoltaic cell의 conversion efficiency가 더 크게 됨을 확인할 수 있다. 그러므로 효율이 최대가 되는 두 폴리머의 혼합 비율이 최적화되는 조건을 찾는 것은 매우 중요한 연구가 될 것이다.

• Journal of the Korean Magnetics Society
• /
• v.16 no.3
• /
• pp.157-162
• /
• 2006

In this study, a high sensitive giant magnetoresistance-spin valve (GMR-SV) bio-sensing device with high linearity and very low hysteresis was fabricated by photolithography and ion beam deposition sputtering system. Detection of the Fe-hemoglobin inside in a red blood and magnetic nanoparticles using the GMR-SV bio-sensing device was investigated. Here a human's red blood includes hemoglobin, and the nanoparticles are the Co-ferrite magnetic particles coated with a shell of amorphous silica which the average size of the water-soluble bare cobalt nanoparticles was about 9 nm with total size of about 50 nm. When 1 mA sensing current was applied to the current electrode in the patterned active GMR-SV devices with areas of $5x10{\mu}m^2 $ and $2x6{\mu}m^2 $, the output signals of the GMRSV sensor were about 100 mV and 14 mV, respectively. In addition, the maximum sensitivity of the fabricated GMR-SV sensor was about $0.1{\sim}0.8%/Oe$. The magnitude of output voltage signals was obtained from four-probe magnetoresistive measured system, and the picture of real-time motion images was monitored by an optical microscope. Even one drop of human blood and nanopartices in distilled water were found to be enough for detecting and analyzing their signals clearly.

• Journal of the Microelectronics and Packaging Society
• /
• v.12 no.2 s.35
• /
• pp.111-119
• /
• 2005

Stack specimen with three dimensional interconnection structure through Cu via of $75{\mu}m$ diameter, $90{\mu}m$ height and $150{\mu}m$ pitch was successfully fabricated using subsequent processes of via hole formation with Deep RIE (reactive ion etching), Cu via filling with pulse-reverse electroplating, Si thinning with CMP, photolithography, metal film sputtering, Cu/Sn bump formation, and flip chip bonding. Contact resistance of Cu/Sn bump and Cu via resistance could be determined ken the slope of the daisy chain resistance vs the number of bump joints of the flip chip specimen containing Cu via. When flip- chip bonded at $270^{\circ}C$ for 2 minutes, the contact resistance of the Cu/Sn bump joints of $100{\times}100{\mu}m$ size was 6.7m$\Omega$ and the Cu via resistance of $75{\mu}m$ diameter, $90{\mu}m$ height was 2.3m$\Omega$.