Coating of Si Nanowire Array by Flexible Polymer

Hee- Jo An1∙, Seung-jin Lee2∙, Taek-soo Ji3*

1,2.3Department of Electronics and Computer Engineering, Chonnam National University, Korea *Corresponding author e-mail: 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: Silicon nanowire, PDMS, HMDS, Dissolved substances,

Chloroform

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

Advanced Science and Technology Letters Vol.139 (EEC 2016), pp.422-426

http://dx.doi.org/10.14257/astl.2016.139.84

ISSN: 2287-1233 ASTL Copyright © 2016 SERSC

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%), 𝐻2𝑂2(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).

Advanced Science and Technology Letters Vol.139 (EEC 2016)

Copyright © 2016 SERSC 423

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].

Advanced Science and Technology Letters Vol.139 (EEC 2016)

424 Copyright © 2016 SERSC

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.

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