*3.2.1. Focused ion beam 3-D fabrication technique*

Miniaturization is the central theme in modern fabrication technology. Many of the compo‐ nents used in modern products are becoming smaller and smaller. Here, the focused ion beam (FIB) direct milling technique will be discussed with the focus on fabricating devices at the micrometer to nano-scale level. Because of the very short wavelength and very large energy density, the FIB has the ability for direct fabrication of structures that have feature sizes at or below 1 *μ*m. As a result, the FIB has recently become a popular candidate in making highquality microdevices or high-precision microstructures (Kim, 2008).

The FIB has been a powerful tool in the semiconductor industry mainly for mask repair‐ ing, device modification, failure analysis and integrated circuit debugging. Two basic working modes, ion beam direct write and ion beam projection, have been developed for these applications. The ion beam direct write process, also known as FIB milling (FIBM), is the process of transferring patterns by direct impingement of the ion beam on the substrate. It is a large collection of microfabrication techniques that removes materials from a substrate and has been successfully used for fabricating various three-dimensional (3D) micro structures and devices from a wide range of materials. For the ion beam projection process, a collimated beam of ions passes through a stencil mask and the reduced image of the mask is projected onto the substrate underneath. The ion beam projection process is also known as focused ion beam lithography (FIBL) and can serve as an alternative to conventional optical lithography (Kim, 1999).

For example, to develop the graphite stacked-junctions, planar-type nanostructures, a highresolution FIB instrument (SII SMI-2050) can be used. The photo-image of FIB unit and the schematic of FIB functions are presented in Figure. 5.

The 3-D etching technique can be followed by tilting the substrate stage up to 90° automatically for etching thin graphite flake. It has freedom to tilt the substrate stage up to 60° and rotate up to 360°. The steps of the fabrication process using a FIB etching are shown in Figure. 6 (a–d). The clear axes of the FIB process configurations with in-plane (x– y) and vertical axes (as z direction) are indicated in an axis diagram in Figure. 6(b). The in-plane area was defined by tilting the sample stage by 30° anticlockwise with respect to the ion beam and milling along the *ab*-plane. The in-plane etching process is shown in Figure. 6(a)-(c). The out of plane or the *c*-axis plane was fabricated by rotating the sample stage by an angle of 180°, then tilting by 60° anticlockwise with respect to the ion beam, and milling along the *c*-axis direction (Saini, 2010). The schematic diagram of the fabrica‐ tion process for the side-plane is shown in Figure. 6(d).

**Figure 5.** The photograph image of FIB unit and schematic of FIB machine

**3.2. Ion beam lithography**

devices (Seliger, 1979).

*3.2.1. Focused ion beam 3-D fabrication technique*

194 Advances in Micro/Nano Electromechanical Systems and Fabrication Technologies

conventional optical lithography (Kim, 1999).

schematic of FIB functions are presented in Figure. 5.

tion process for the side-plane is shown in Figure. 6(d).

quality microdevices or high-precision microstructures (Kim, 2008).

In this section, ion beam based patterning technique is discussed. For example Focused Ion Beam (FIB) based three dimensional etching method is followed for patterning micro/nano

Miniaturization is the central theme in modern fabrication technology. Many of the compo‐ nents used in modern products are becoming smaller and smaller. Here, the focused ion beam (FIB) direct milling technique will be discussed with the focus on fabricating devices at the micrometer to nano-scale level. Because of the very short wavelength and very large energy density, the FIB has the ability for direct fabrication of structures that have feature sizes at or below 1 *μ*m. As a result, the FIB has recently become a popular candidate in making high-

The FIB has been a powerful tool in the semiconductor industry mainly for mask repair‐ ing, device modification, failure analysis and integrated circuit debugging. Two basic working modes, ion beam direct write and ion beam projection, have been developed for these applications. The ion beam direct write process, also known as FIB milling (FIBM), is the process of transferring patterns by direct impingement of the ion beam on the substrate. It is a large collection of microfabrication techniques that removes materials from a substrate and has been successfully used for fabricating various three-dimensional (3D) micro structures and devices from a wide range of materials. For the ion beam projection process, a collimated beam of ions passes through a stencil mask and the reduced image of the mask is projected onto the substrate underneath. The ion beam projection process is also known as focused ion beam lithography (FIBL) and can serve as an alternative to

For example, to develop the graphite stacked-junctions, planar-type nanostructures, a highresolution FIB instrument (SII SMI-2050) can be used. The photo-image of FIB unit and the

The 3-D etching technique can be followed by tilting the substrate stage up to 90° automatically for etching thin graphite flake. It has freedom to tilt the substrate stage up to 60° and rotate up to 360°. The steps of the fabrication process using a FIB etching are shown in Figure. 6 (a–d). The clear axes of the FIB process configurations with in-plane (x– y) and vertical axes (as z direction) are indicated in an axis diagram in Figure. 6(b). The in-plane area was defined by tilting the sample stage by 30° anticlockwise with respect to the ion beam and milling along the *ab*-plane. The in-plane etching process is shown in Figure. 6(a)-(c). The out of plane or the *c*-axis plane was fabricated by rotating the sample stage by an angle of 180°, then tilting by 60° anticlockwise with respect to the ion beam, and milling along the *c*-axis direction (Saini, 2010). The schematic diagram of the fabrica‐

**Figure 6.** Nanoscale stack fabrication process using focused ion beam 3D etching method. (a) Scheme of the inclined plane has an angle of 60° with ion beam (where we mount sample). (b) The initial orientation of sample and sample stage. (c) Sample stage titled by 30° anticlockwise with respect to ion beam and milling along *ab*-plane. (d) The sam‐ ple stage rotated by an angle of 180° and also tilted by 60° anticlockwise with respect to ion beam and milled along the c-axis. (Venugopal, 2011d)

By varying the stack height length and in-plane area, the various sizes of stacked-junctions can be fabricated on the graphite layer. The number of elementary junctions in the stack will vary depends on the height of the junction. If junction height is more, the more number of elemen‐ tary junctions exists which provide larger more resistance in c-axis characteristics.
