Available online at www.sciencedirect.com ScienceDirect Procedia CIRP 42 ( 2016 ) 733 – 736 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM XVIII) Fabrication of micro/nanoelectrode using focused-ion-beam chemical vapor deposition, and its application to micro-ECDM a a, a a b a Dengji Guo , Xiaoyu Wu * , Jianguo Lei , Bin Xu , Reo Kometani and Feng Luo aShenzhen Key Laboratory of Advanced Manufacturing Technology for Mould & Die, Shenzhen University, Shenzhen 518060, Guangdong, PR China bGraduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan * Corresponding author. Tel.: +86-755-2653-1066; fax: +86-755-2655-7471. E-mail address: [email protected] Abstract Micro electro-chemical discharge machining (micro-ECDM) is a key technology in the precision manufacturing. The electrode, which is the key element for achieving a high-precision ECDM, attracts the interests of many researchers. However, regarding the fabrication techniques of the electrode, the achievable precisions are still resting on micrometer scale, the processes are not simple, or electrodes with high complex three-dimensional (3D) shapes are difficult to be obtained. Basing on such a background, in this work, focused-ion-beam chemical vapor deposition (FIB-CVD) which is an effective tool in fabricating 3D micro/nanostructure for achieving various micro/nanoelectromechanical devices (MEMS/NEMS), was first time introduced to fabricate micro/nanoelectrode and furthermore ECDM processes using FIB-CVD- fabricated electrodes could be attempted. Differing to the conventional metallic electrodes, micro/nanoelectrodes in the material of amorphous platinum (Pt) were obtained. Three electrodes with the same diameter 10 Pm and height 28 Pm were fabricated on the polished tip surfaces of stainless needles, and consequently applied to micro-ECDM with varied low open voltages 10, 12.5 and 15 V. Microholes were fabricated on the 304 austenitic stainless steel. The hole diameter and the unilateral discharge gap were found to be almost linearly increasing with the increase of open voltage. In case of using the open voltage 10 V, the unilateral discharge gap was found to be 6.6 Pm. Moreover, fabrications of pillar, horn, corner, array types of 3D nanoelectrodes were demonstrated. These results indicate the potentialities of 3D micro-ECDM using complex 3D micro/nanoelectrode, and a deeper study into the science of ECDM/EDM phenomenon at submicron scale. © 20162016 The Authors. Published byby Elsevier Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license (Peerhttp://creativecommons.org/licenses/by-nc-nd/4.0/-review under responsibility of the organizing committee). of 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM PeerXVIII).-review under responsibility of the organizing committee of 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM XVIII) Keywords: Micro electro-chemical discharge machining; Micro/nanoelectrode; Micro-hole; Focused-ion-beam chemical vapor deposition; Three-dimensional; 1. Introduction used for scanning probe microscopes (SPM) as electrode for micro-EDM [5]. Li and Zhao et al proposed bunched- Micro electro-chemical discharge machining (micro- electrode EDM using powerful multi-hole inner flushing, ECDM) plays an important role in the precision aiming at improving the efficiency of material removal [6]. manufacturing. The electrode, which is the necessary tool for Zeng et al combined micro-EDM and micro-ECM to mill 3D performing micro-ECDM, attracts the interests of many metallic micro-structures [7]. Xu and Wu et al proposed researchers. Masuzawa et al proposed the method of wire micro-double-staged laminated object manufacturing (micro- electro-discharge grinding (WEDG) for EDM, in which the DLOM) to fabricate 3D micro-mould, in which steel foils tool electrode is a travelling wire so that the effect of electrode were firstly cut by femtosecond laser to obtain single-layer wear can be avoided [1]. Takahata et al utilized LIGA process graphics and then welded using the method of micro-electric to fabricate high aspect ratio electrode arrays, hence batch resistance slip welding [8-10]. However, most of these mode micro-EDM could be achieved [2, 3]. Shibayama and techniques have difficulty in fabricating a micro/submicron Kunieda developed tool electrode with microholes designed electrode with high complex 3D shape in a simple process. for the flow of dielectric liquid, and applied it to sinking EDM [4]. Egashira et al used silicon probes which are originally 2212-8271 © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of 18th CIRP Conference on Electro Physical and Chemical Machining (ISEM XVIII) doi: 10.1016/j.procir.2016.02.310 734 Dengji Guo et al. / Procedia CIRP 42 ( 2016 ) 733 – 736 On the other hand, in the field of micro/nanofabrication, focused-ion-beam chemical vapor deposition (FIB-CVD) was (a) proposed [11] and demonstrated to be an effective tool in fabricating various 3D nanostructures for micro/nanoelectromechanical devices (MEMS/NEMS) [12]. 20 Pm The basic principle of FIB-CVD is, under the irradiation of energetic FIB, CVD process of source gas that surrounds the substrate occurs and the deposited structure keeps grow if the irradiation of FIB lasts. By controlling the scanning of FIB via a computer pattern generator (CPG), complex 3D structure with desired shape and sizes can be achieved [13, 14]. The smallest characteristic dimension of structure created by FIB- CVD can be smaller than 100 nm. Amorphous structures in various materials such as platinum (Pt), tungsten (W) and carbon (C), can be obtained by choosing a corresponding source gas with the desired structure [15]. Aiming at establishing a novel effective fabrication technique of micro/nanoelectrode for micro-ECDM/EDM, investigating its fabrication characteristics, and supplying the possibility of the research on the ECDM phenomenon at (b) (c) submicron scale, in this paper, the micro/nanoelectrode was first time fabricated by means of FIB-CVD and micro-ECDM process using this kind of electrode was attempted. 10 Pm 2. Fabrication of microelectrode using FIB-CVD 5 Pm Fabrication of microelectrode using FIB-CVD was performed in a commercially available FIB system (FEI Corp.; 200), in which a Ga+ ion beam with an acceleration voltage of Fig. 1. Microelectrode fabricated on the polished tip surface 30 kV is equipped. A broad range of beam current from of a needle, (a) 3D, (b) side and (c) top view. picoampere (pA) to nanoampere (nA) order can be chosen. The achievable highest resolution of FIB is 5 nm. 3. ECDM process using the FIB-CVD-fabricated Microelectrode in the material of amorphous Pt was deposited microelectrodes using FIB-CVD. Normally FIB-CVD is carried out to deposit Concerning the small electrode size and the high-rate wear micro/nanostructures onto a silicon substrate, due to its vast of the electrode in EDM process, in this work, the applications related to semiconductor industry. However in microelectrode fabricated by FIB-CVD was applied to ECDM. this work, the microelectrode should be deposited onto a The ECDM was carried out on a specially-made metallic substrate, such as copper or stainless steel. Moreover, electrochemical micromachining system, as shown in Fig. 2. the electrode on the substrate is so tiny that, parallelism The system mainly consists of, between the top surface of the electrode and the workpiece surface should be strictly controlled. In order to decrease the x A three-axis motion platform with a stepper resolution of possibility of the direct contact between the substrate surface 0.2 Pm (PI, Germany; M511.DD). Unique program was and the workpiece surface, an ordinarily available needle in created using Visual C++ language on the computer to the material of stainless steel was cut and used as substrate. automatically control the motion. The tip of the needle was polished to form a horizontal neat x A pulsed power supply. High-frequency impulsing power surface, which is approximately in a shape of a disc with a source basing on FPGA was developed, with an adjustable diameter of around 70 Pm. pulse duration range and period range of 0-102 Ps and 0- Figure 1 shows the scanning electron microscope (SEM) 255 Ps, respectively. image of a cylinder-shaped microelectrode with a diameter of 10 Pm and a height of 28 Pm was fabricated on the tip surface In order to investigate the fabrication characteristic of of needle. The beam current and the fabrication time were ECDM using a microelectrode fabricated by FIB-CVD, three 3977 pA and 40 minutes 44 seconds, respectively. microelectrodes were fabricated using the same parameters that were introduced in Section 2. And they were applied to ECDM using the low open voltage 10 V, 12.5 V and 15 V, respectively. Table 1 shows the parameters of ECDM. Dengji Guo et al. / Procedia CIRP 42 ( 2016 ) 733 – 736 735 50 Pm Fig. 3. Micro-hole fabricated on the polished surface of 304 austenitic stainless steel using the open voltage of 15 V. 60 60 Hole diameter gap ( discharge Unilateral 50 Unilateral discharge gap 50 m) P 40 40 30 30 Fig. 2. Experimental setup of ECDM using microelectrode fabricated by FIB-CVD. 20 20 Hole diameter ( P Table 1. Parameters of ECDM 10 10 m) Fabrication parameters Value 0 0 Microelectrode diameter 10 Pm 10.0 12.5 15.0 Microelectrode height 28 Pm Open voltages (V) Working fluid Deionized Water Fig. 4. Open voltage dependencies of hole diameter and unilateral discharge gap. Workpiece Polished 304 austenite stainless steel 4. Fabrications of 3D nanoelectrodes using FIB-CVD Open voltage 10, 12.5, 15 V Pulse duration 800 ns By introducing FIB-CVD to the fabrication of Pulse separation 4200 ns micro/nanoelectrode for ECDM/EDM, Working depth 20 Pm Working step 0.5 Pm x Electrodes at micrometer scale or submicron scale can be easily fabricated due to the high resolution of FIB-CVD, therefore ECDM/EDM with a scale smaller than present By using different open voltages in ECDM for the may can possibly be achieved.