Coating of Si Nanowire Array by Flexible Polymer

Transcription

1 , pp Coating of Si Nanowire Array by Flexible Polymer Hee- Jo An 1, Seung-jin Lee 2, Taek-soo Ji 3* 1,2.3 Department of Electronics and Computer Engineering, Chonnam National University, Korea * Corresponding author Prof. Taeksoo Ji, tji@chonnam.ac.kr Abstract. Using a suitable material chloroform solubility of PDMS (polydimethylsiloxane) and PDMS,, by adjusting the concentration of the PDMS, the development process of the two kinds of fused by applying a PDMS between a wire between the Nanowire in micros previously. Hybrid biomimetic tactile sensors based on silicon and poly rounded up all of the lead-based benefits. In addition, there is a derived problem easily applied using HMDS. Keywords: Chloroform Silicon nanowire, PDMS, HMDS, Dissolved substances, 1 Introduction This paper describes coating of Si nanowire array by Flexible Polymer: this coating is important considering the potential of Silicon Nanowire in numerous applications semiconductor nanowires gain much important as Sensitive tactile sensor in the future. silicon nanowire is sensitive to the external influence(like gas, chemicals, optical sensing, pressure) because of the large of surface area. When pressure/force is applied to semiconductor material, its electrical resistance changes, this phenomenon is called piezoresistance (PS) effect. Silicon nanowires are physically fragile So when excessive force applied, it made break. To overcome to problem, flexible polymer such as PDMS is used to provide additional support. PDMS coating transfer pressure and prevents crumbling of silicon nanowire under excessive pressure. However, the material properties of the silicon nanowires and PDMS are different. Figure 1(a) shows Silicon is hydrophilic and PDMS is hydrophobic. It is difficult for PDMS layer to infiltrate in to the spaces between nanowires. In this report we propose new method to overcome this problem. 2 Experimental Silicon nanowire array growth: P-type (111)-oriented Silicon wafers with a resistivity of 1~10Ω were used in experiment. The wafer was cleaned with acetone, isopropyl alcohol and Deionized water using ultrasonication. Then dipping the wafer for 4min in to buffered HF solution (1:10 v/v). to remove surface oxides. In nanosphere lithography process, Polystyrene nanospheres of diameter 600nm were used for circle pattering. PS nanospheres monolayer aligned on water surface ISSN: ASTL Copyright 2016 SERSC

2 and then scooped up using sample wafer. 30nm Au layer was deposited using RF sputtering. Au metal is higher in cost than Ag but it is more stable in Mac etching. Patterned wafer was immersed in carious ratio HF(49%), H 2 O 2 (30%) and Deionized water(25ml) mixed solution for 3min at room temperature. Polymer application and film removal: The PDMS base and curing agent were mixed in a 10:1 w/w ratio and stirred (Sylgard 184, Dowcorning) and the uncured polymer was diluted(2:1 w/w) with solution of chloroform(alfa Aesar, 99.8%) and spin-coat on the wire arrays at 1500rpm for 10min. 3 Result Herein, we report an effective method to coat SiNW array with PDMS by using HMDS (hexamethyldisilazane), Universally, HMDS is used to change the wafer or glass surface and make it more hydrophobic.(figure 1.b) Fig.1. SEM images show the results of Before and after using the HDMS in Silicon nano wire. (a) Before using the HDMS; (b) after using the HDMS The above figure 1b. PDMS was seeping between the wire. From the experimental observations, we conclude that there is a need to adjust the PDMS concentration. The viscosity of PDMS is lowered without affecting other parameters. Refering to Solvent Compatibility of Poly (dimethylsiloxane) -Based Microfluidic Devices, chloroform was selected [2]. Following results were observed by changing the ratio of chloroform and PDMS (Figure 2). Copyright 2016 SERSC 423

3 Fig. 2. SEM images show the results of diffent ratio of choroform and PDMS (a) 5 :1, V/V, chloroform/pdms (b) 3 : 1,V/V,chloroform/PDMS (b) 2 : 1, V/V, chloroform/pdms A certain volume of chloroform was used to dilute PDMS liquid. The resulting solution was used to spin-coat SiNW array. The samples were heated on a hot plate at 120 to accelerate the solidification of PDMS. Then the PDMS-embedded SiNW array can be readily peeled off with a high integrity and transferred to arbitrary substrates. And after cooling, the PDMS overlayer and wires were mechanically removed by scraping the substrate with a razor blade [3]. 424 Copyright 2016 SERSC

4 Fig.3. SEM images show PDMS-embedded SiNW arrays peeled off with to substrate Figure 3 shows the PDMS between the silicon nanowires array side by side. PDMS reinforces the nanowire, allowing the use of nanowires with high sensitivity per unit area as flexible and sensitive touch sensors. References 1. Wu, L.; Li, S. X.; He, W. W.; Teng, D. Y.; Wang, K.; Ye, C. H. Automatic release of silicon nanowire arrays with a high integrity for flexible electronic devices. Sci. Rep. 2014, 4, Lee, J. N., Park, C. & Whitesides, G. M. Solvent compatibility of poly(dimethylsiloxane)- based microfluidic devices. Anal. Chem. 75, (2003) 3. Plass, K. E. et al. Flexible polymer-embedded Si wire arrays. Adv. Mater. 21, (2009). 4. Tsakalakos L., Balch J., Fronheiser J. et al., Silicon nanowire solar cells, Appl Phys Lett, 91(23), (2007). 5. Chua J. H., Chee R.-E., Agarwal A. et al., Label-Free Electrical Detection of Cardiac Biomarker with Complementary Metal-Oxide Semiconductor-Compatible Silicon Nanowire Sensor Arrays, Analytical chemistry, 81(15), (2009). 6. Patolsky F., Zheng G., and Lieber C. M., Fabrication of silicon nanowire devices for ultrasensitive, label-free, real-time detection of biological and chemical species, Nature protocols, 1(4), (2006). 7. Chartier C., Bastide S., and Lévy-Clément C., Metal-assisted chemical etching of silicon in HF H2O2, Electrochimica Acta, 53(17), (2008). 8. Alexei Svizhenko, Leu P. W., and Cho K., Effect of growth orientation and surface roughness on electron transport in silicon nanowires, Physical Review B, 75(12), (2007). 9. Ma D. D. D., Lee C. S., Au F. C. K. et al., Small-Diameter Silicon Nanowire Surfaces, Science, 299(5614), (2003). 10. Jeonga G. H., Parka J. K., Leea K. K. et al., Fabrication of low-cost mold and nanoimprint lithography using polystyrene nanosphere, Microelectronic Engineering, Copyright 2016 SERSC 425

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