Characterization of direct patterned Ag circuits for RF application Jong-Woong Kim a , Young-Chul Lee a , Jong-Min Kim b , Wansoo Nah b , Hyo-Soo Lee c , Hyuk-Chon Kwon c , Seung-Boo Jung a, * a School of Advanced Materials Science and Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon 440-746, Republic of Korea b School of Electrical and Computer Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon 440-746, Republic of Korea c Advanced Material Development Center, Korea Institute of Industrial Technology, 7-47 Songdo-dong, Yeonsu-gu, Incheon 406-840, Republic of Korea article info Article history: Received 6 April 2009 Received in revised form 4 June 2009 Accepted 22 June 2009 Available online 26 June 2009 Keywords: Radio frequency Screen printing Conductive nano-paste Sintering temperature abstract We investigated the effects of sintering temperature on microstructural evolution and electrical charac- teristics of screen printed Ag patterns. A commercial conducting paste containing Ag nanoparticles was screen printed onto a Si substrate passivated with SiO 2 and sintered under a sintering temperature range from 150 °C to 300 °C. Four point probe method was used to measure the DC resistance, while a network analyzer and Cascade’s probe system in the frequency range from 10 MHz to 30 GHz were employed to measure the S-parameters of the sintered Ag conducting patterns. The resistivity under the application of a DC decreased from 398 lX cm to 9 lX cm with increasing sintering temperature from 150 °C to 300 °C. From the measured S-parameters, the electrical losses in high frequencies also decreased with increasing sintering temperature (about 1.2 dB at 30 GHz) due to the formation of an interparticle neck after heat treatment at high temperatures. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Direct printing technologies, e.g., ink-jet, gravure, and screen printing methods, have been indicated as alternative methods to conventional lithography technology for patterning conducting cir- cuits on account of their low-cost, large-area patternability and pattern flexibility. Among the methods, we have been trying to ex- plore the screen printing method for the circuit formation due to its high printing speed and high resolution. Screen printing is one of the oldest printing techniques, and the basic equipment for printing is inexpensive but has a high throughput. The tech- nique of the screen printing involves spreading a thixotropic fluid evenly over a mesh screen, which defines the shape and size of the desired electrode, using a squeegee. The thixotropic fluid or ink contains a variety of substances, typically graphite, solvents and a polymeric binder but its precise formulation is the proprietary information of the ink supplier [1]. Screen printing uses silk or other fabrics stretched tightly over a frame. The images are created by blocking parts of the screen with stencils created by hand- drawn or photographic techniques [2]. Despite the merits of the printing for the conductive circuits, their usage in microwave and millimeter-wave applications has been limited. Today one of the most prominent applications of the printed circuits is low-cost radio frequency identification (RFID) tag, which is utilizing signal frequency of only several tens or hundreds mega hertz. This is because there is not still sufficient information for the high frequency performance of the conductive circuits that is formed by the printing method at this time. In order to expand the application areas of the printing methods, we need to focus on the radio frequency (RF) and rather higher frequency signal transmission properties of the printed circuits. Recently, a variety of research has been conducted and reported on the electri- cal property of the conductive circuits fabricated by the printing techniques, however, most of them were focused on direct current (DC) resistance and resulting conductivity of the circuits. In order to achieve physical understanding of the electrical transmission properties, it is important to clarify and confirm the phenomeno- logical facts by RF signal transmission measurements on the basis of proper design techniques [3]. Only then we can enhance the applicable area of the printing technology into various RF devices utilizing higher frequencies, e.g., cellular phones, Bluetooth mod- ules, and various mobile internet devices, etc. In this study, the electrical characteristics of the screen printed Ag patterns with a varying sintering temperature were investigated. For the characterization of the circuits, a network analyzer was em- ployed to measure the scattering parameters (S-parameters). We tried to explain the electrical behaviors of the circuits by micro- structural evolution of the printed paste during sintering process. 2. Experimental An Ag nano-paste consisting of Ag nanoparticles of dispersed in a-Terpineol matrix (product name: silver nano-paste DGP, 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2009.06.012 * Corresponding author. Tel.: +82 31 290 7359; fax: +82 31 290 7371. E-mail address: sbjung@skku.ac.kr (S.-B. Jung). Microelectronic Engineering 87 (2010) 379–382 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee