**4. Diamond, DLC, DLN for MEMS technology**

466 Microelectromechanical Systems and Devices

The average friction coefcient of DLN lms using conical diamond tip is estimated which is nearly 0.03–0.05. The tribological properties of DLN lms are most important for their use as protective coatings in MEMS/NEMS technology. Recently, the DLC lms have been used as rigid disk for microelectromechanical or nanoelectromechanical devices. These protective coatings must have excellent wear and tear resistance, high adhesiveness and very low friction coefcient. For DLC lms, the friction coefcient is around 1 but for DLN lms, friction coefcient is around 0.03–0.05 as stated above. Hence, for modern microsystems or nanosystems *i.e.* MEMS or NEMS, we can use the films as protective coatings compared to DLC lms. The surface morphologies of DLN lms are analyzed by using AFM. Fig. 8 shows the AFM image of DLN lms in two dimensional (2D) and three dimensional (3D)

Fig. 8. The Surface morphology of DLN lms deposited on silicon substrate:

From AFM analysis, we have estimated the mean surface roughness (Ra) and maximum peak-to-valley height (Rmax) of the DLN lms, which are 0.292–3.2 nm and 6.1–33 nm, respectively. From this analysis, it is also conrmed that all the DLN lms have no surface

2D view (top)…view (bottom).

views.

Recently, the microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) technology are fully dominated by Si based materials for their fabrication. These materials have good mechanical and electrical properties for fabrication of MEMS/NEMS based sensors and actuators. Also the silicon materials have large surface area to fabricate the device. However, these materials have some limitation like high temperature withstanding capability, aggressive media, high energy particle radiation etc. For these limitations, diamond films would be good choice for fabrication of MEMS/NEMS device. Some advantageous properties of different materials including diamond and silicon are given in Table 2.


Table 2. Different material properties compared with diamond.

Recently researchers are concentrating for ceramic based materials as well as diamond to fabricate the MEMS devices instead of silicon materials. As structural properties, diamond has much more sp3 phase content, which improves the very good mechanical properties. Also much more sp2 content DLC can improve the electronic properties of materials compared to silicon material. Finally, very high hardness, high modulus of elasticity, high tensile strength, low surface roughness, low coefficient of friction, good wear rate of diamond, DLC and DLN can act as promising materials for MEMS/NEMS devices.

#### **4.1 Microfabrication, pattern transfer and diamond film patterning 4.1.1 Microfabrication and pattern transfer**

The standard process for microfabrication is to deposit of thin films into whole over the wafer and then need to remove the unwanted part by etch or polishing of thin films from the wafer. The microfabrication process can come in two ways, one is the directional process and another is the diffusion process. Fig. 9 shows the directional and diffuse process. The directional process which include electron or ion , photons, beam of atom which impinges into the whole wafer (such as lithography, e-beam evaporation, ion implantation etc.). The diffuse process which include the immersion process where the whole wafer surrounded by vapor, liquid or gases (By CVD or oxidation). To deposit the specific region in both process, need to use the mask in which the unwanted portion will be cover by mask and the open portion of the mask will be deposited metal or ions. The masking of the substrate can prevent the ions or atoms to react with the substrate material.

The another process is called the localized process by where the beam energy can falls into specific region of the substrate. The localized process can be divided in to focused beam

Diamond, Diamond-Like Carbon (DLC)

and Diamond-Like Nanocomposite (DLN) Thin Films for MEMS Applications 469

can deposit on to the wafer and reaming metal will be remove from the wafer. The electroplating technique can provide high aspect ratio structure compared to lift off technique.

Fig. 11. Pattern transfer process, (a) lift-off technique, (b) electroplating , (c) etching of thin

In lift off technique the deposited metal film thickness should be one third of the photoresist thickness in order to make the discontinuity of the films . But electroplating technique can

film, (d) etching of substrate material

Fig. 9. (a) Directional process and (b) diffusion process

processing and microstructure assisted processing. By this process the reaction will occurred when beam of microstructure will provide energy. Fig. 10 shows the localized processing of focused beam supplies energy and microstructure provide energy.

Fig. 10. Localized processing (a) focused ion beam supplies energy and (b) microstructure provide anergy.

The photolithography process is important for film patterning. By this process in the beginning the surface preparation of the films is more important. This process start from cleaning of the wafer for remove the moisture, baked the wafer, increase the adhesion promotion of the wafer by apply hexamethyldisiloxane (HMDS), (CH3)3-Si-NH-Si-(CH3)3. The HMDS treatment can reduce the pressure to form the monolayer onto the surface of the wafer, causes the more hydrophobic of the wafer which prevents the moisture condensation. After that spin coating, soft bake, UV exposure with mask alignment, development and hard bake technique is required for whole process. After this lithographic process of the photoresist on to the wafer, the wet etching or dry etching techniques is important to pattern the any type of substrate materials. For this photolithographic pattern, the photoresist uses basically polymeric resist. This resist can dissolve or it can insoluble in the developer solution according to the positive or negative photoresist to react with UV light. The pattern is form by this polymeric resist only use of mask in front of UV light. To pattern the polymeric resist on to the substrate , different process can be applicable. This process can be divided into additive or subtractive process. By which we can add some material into the substrate or we can remove the material from the substrate by using the photoresist with mask pattern. Fig. 11 shows the different additive and subtractive process. Fig 11(a) shows the lift off process. By this process we pattern the photoresist to fall the UV light on to the mask. Then deposit the metal on the top of the wafer and finally we remove the photoresist from the wafer by development process. Fig. 11(b) is the electroplating process by which, we can deposit the metal on top of the pattern photoresist on to the wafer and finally remove the photoresist. So required metal

processing and microstructure assisted processing. By this process the reaction will occurred when beam of microstructure will provide energy. Fig. 10 shows the localized processing of

Fig. 10. Localized processing (a) focused ion beam supplies energy and (b) microstructure

The photolithography process is important for film patterning. By this process in the beginning the surface preparation of the films is more important. This process start from cleaning of the wafer for remove the moisture, baked the wafer, increase the adhesion promotion of the wafer by apply hexamethyldisiloxane (HMDS), (CH3)3-Si-NH-Si-(CH3)3. The HMDS treatment can reduce the pressure to form the monolayer onto the surface of the wafer, causes the more hydrophobic of the wafer which prevents the moisture condensation. After that spin coating, soft bake, UV exposure with mask alignment, development and hard bake technique is required for whole process. After this lithographic process of the photoresist on to the wafer, the wet etching or dry etching techniques is important to pattern the any type of substrate materials. For this photolithographic pattern, the photoresist uses basically polymeric resist. This resist can dissolve or it can insoluble in the developer solution according to the positive or negative photoresist to react with UV light. The pattern is form by this polymeric resist only use of mask in front of UV light. To pattern the polymeric resist on to the substrate , different process can be applicable. This process can be divided into additive or subtractive process. By which we can add some material into the substrate or we can remove the material from the substrate by using the photoresist with mask pattern. Fig. 11 shows the different additive and subtractive process. Fig 11(a) shows the lift off process. By this process we pattern the photoresist to fall the UV light on to the mask. Then deposit the metal on the top of the wafer and finally we remove the photoresist from the wafer by development process. Fig. 11(b) is the electroplating process by which, we can deposit the metal on top of the pattern photoresist on to the wafer and finally remove the photoresist. So required metal

Fig. 9. (a) Directional process and (b) diffusion process

provide anergy.

focused beam supplies energy and microstructure provide energy.

can deposit on to the wafer and reaming metal will be remove from the wafer. The electroplating technique can provide high aspect ratio structure compared to lift off technique.

Fig. 11. Pattern transfer process, (a) lift-off technique, (b) electroplating , (c) etching of thin film, (d) etching of substrate material

In lift off technique the deposited metal film thickness should be one third of the photoresist thickness in order to make the discontinuity of the films . But electroplating technique can

Diamond, Diamond-Like Carbon (DLC)

from John Wiley & Sons, Ltd.).

component laterally [55].

and Diamond-Like Nanocomposite (DLN) Thin Films for MEMS Applications 471

By this process focused beam of ions concentrate on a surface in order to create very small structures. This technique are widely used in microelectronics industry also. This Ion beam technique can cut the materials in very precise way. By this process, the materials can be milling to accelerate the concentrated gallium ions source on a specific site. The gallium ion source react with the surface and metallic precursor gases to produce the precise cut of conductive lines. In the FIB systems, where liquid metal ion sources are capable to form very small probes with high

Fig. 13. Micrometer-scale bridge structure machined in single-crystal diamond released by chemical etching of graphitic layer. The graphitic layer produced by ion implantation into

Diamond, DLC and DLN films have high hardness, high modulus of elasticity, low thermal expansion coefficient, low surface roughness and low coefficient of friction and good wear properties. This all properties are very important to apply this materials as a anti-stiction coating or tribological coating on MEMS/NEMS devices. The moving parts of any microactuators, like microgears, microengine or bearing have surface contact of their won functions during operations. Due to very low coefficient of friction and surface roughness of DLC and DLN films, the films can be act as a excellent solid lubricants of microgears or microengine based MEMS devices. Very small surface roughness can reduce the friction and wear rate in microstructure component during operations [54-56]. DLC coating which can improve the lifetime of linear motor actuated by electrostatic force which drive by sliding

Diamond, Diamond-like carbon(DLC) and Diamond-like Nanocomposite(DLN) have wide band gap, good thermal conductivity and very good piezoelectric properties, high chemical stability, high fracture strength and very high stiffness. These key properties of diamond are potentially applicable for sensing and actuating application in harsh environments [57]. For piezoresistive diamond materials mainly the nanocryastalline diamond materials are used for minimize the grain boundary influence. The piezoresistive boron doped diamond materials,

current densities [53]. Fig. 13 shows the FIB based diamond film pattern.

the diamond substrate using FIB, ([52], permission to reprint obtained

**4.3 Diamond, DLC, DLN films for sensors and actuators applications** 

**4.2 Diamond, DLC, DLN films as coating material for MEMS** 

deposited the large thickness of metal with photoresist pattern compare to lift-off technique. The lift-off technique and electroplating technique is the additive process. Where as in Fig.11 (c) demonstrate the thin film etching technique by photoresist pattern, which indicate the subtractive process. Fig. 11(d) demonstrate the etching technique of substrate material by photoresist pattern (subtractive process)
