Solid-State Electrochemical Micromachining Enables Direct Surface Patterning
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RESEARCH/RESEARCHERS
Solid-State Electrochemical Micromachining Enables Direct Surface Patterning Electrochemical micromachining (EM) has been used as a “shaving off” method to fabricate textured or patterned surfaces. It has become one of the most widely used methods because it requires simple equipment and enables more rapid etching than techniques such as ion-beam milling and laser abrasion. However, during the EM process, a liquid electrolyte, which can be difficult to handle, is required as a conducting medium between the two electrodes. Furthermore, high-resolution patterning processes require masking or the use of focused laser writing or focused ion-beam writing of patterns. Now, K. Kamada of Kyushu University, K. Izawa of Kumamoto University, and their colleagues have proposed an electrochemical micromachining procedure that eliminates the need for wet processing and allows fine patterns to be written. As reported in the April 19 issue of Chemistry of Materials (p. 1930; DOI: 10.1021/cm0502929), the researchers describe a route for solid-state micromachining using an anodic electrochemical reaction at the microcontact between an ion-conducting microelectrode and a metal substrate, which they call the solidstate electrochemical micromachining (SSEM) method (schematically shown in Figure 1). During the SSEM process, the metal substrate is locally incorporated into the ion-conducting microelectrode in the form of metal ions through the microcontact under a dc bias. Continuous application of an electric field produces micromachining of the substrate, thereby removing the need for wet processing. The microelectrode is formed from a pyramid-like (tetrahedral shape) piece of β’’-Al2O3 (typically, Na-β’’-Al2O3) with a contact radius of ~10 μm. It is very light-
Figure 1. Model for ion migration during solid-state electrochemical micromachining of a metal substrate; M is the target metal substrate. Reprinted in part with permission from Chem. Mater. 17 (April 19, 2005) p. 1931. ©2005 American Chemical Society.
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weight (~0.02 g), which reduces the mechanical stress at the microcontact to a minimum and keeps it constant. The solid-state electrochemical cell consists of a Ag plate (cathode)/pyramid-like Na-β’’Al2O3 microelectrode/ target metal substrate (thickness, 0.5 mm; M: Ag or Zn; anode) system. The researchers said that since the contact radius at the Na-β’’Al2O3/M interface is on the order of 10 μm, a position-selective dissolution occurs at the microcontact, which makes it an excellent tool to pattern the metal surface directly in either a dot or scan-line format. The researchers also said that further work is needed to solve some remaining problems with this technique, including a slow etching rate, low current efficiency, and roughness of the micromachined surface. FENGTING XU
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