**3. Properties of diamond films**

#### **3.1 Structural properties**

In this section we analyze the details about High Resolution Transmission Electron Microcopy (HRTEM), Fourier Transform Infrared (FTIR) spectroscopy and Raman spectroscopy of DLN films. These DLN films are prepared by using liquid gas precursor as hexamethyldisilane (HMDS), hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDSN) with argon and nitrogen as a source gas by Plasma Enahanced Chemical Vapor Deposition (PECVD). The HRTEM image in Fig. 3 of DLN films for HMDSN precursor on silicon substrate confirm the nucleation and growth of Si3N4 nanoparticles in the amorphous matrix of sizes 6–30 nm. On the other hand, SiC and SiOx nanoparticles having same sizes were found in the DLN films using HMDS and HMDSO precursors, respectively.

The FTIR analysis of DLN films shows that the films predominantly consist of C-C, C-H, Si-C and Si-H bonding. FTIR and Raman spectroscopic results conform to a large extent with structural model [35-36]. DLN films are consisting of mostly two interpenetrating networks of a-Si:O and a-C:H. FTIR spectroscopy is a well known method for investigating the bonding structure of atoms by using the IR absorption spectrum which is related to vibration of atoms [37]. DLN films are deposited in same bias voltages. FTIR spectra of DLN

three electrons are used in σ-bonds and the forth electron forms a π-bond, which lies normal to the σ -bonding plane. In sp2 -site, only the π-bond is weakly bonded, and hence, it usually lies closest to the Fermi level and controls the electronic properties of the lms. On the other hand, in sp3 -site, the σ-bond controls the mechanical properties of the lms [34]. These electrical and mechanical properties are very important parameters for every

Fig. 2. SEM micrographs of diamond film surfaces deposited at different CH4/H2 ratios. (a) 1% (b) 2%, (c) 5% and (d) 8%. ( ▬ Scale bar 20 µm for all figures), ([28], permission to reprint

In this section we analyze the details about High Resolution Transmission Electron Microcopy (HRTEM), Fourier Transform Infrared (FTIR) spectroscopy and Raman spectroscopy of DLN films. These DLN films are prepared by using liquid gas precursor as hexamethyldisilane (HMDS), hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDSN) with argon and nitrogen as a source gas by Plasma Enahanced Chemical Vapor Deposition (PECVD). The HRTEM image in Fig. 3 of DLN films for HMDSN precursor on silicon substrate confirm the nucleation and growth of Si3N4 nanoparticles in the amorphous matrix of sizes 6–30 nm. On the other hand, SiC and SiOx nanoparticles having same sizes

The FTIR analysis of DLN films shows that the films predominantly consist of C-C, C-H, Si-C and Si-H bonding. FTIR and Raman spectroscopic results conform to a large extent with structural model [35-36]. DLN films are consisting of mostly two interpenetrating networks of a-Si:O and a-C:H. FTIR spectroscopy is a well known method for investigating the bonding structure of atoms by using the IR absorption spectrum which is related to vibration of atoms [37]. DLN films are deposited in same bias voltages. FTIR spectra of DLN

were found in the DLN films using HMDS and HMDSO precursors, respectively.

DLC and DLN based materials.

obtained from Elsevier).

**3.1 Structural properties** 

**3. Properties of diamond films** 

films are given in Fig. 4 The main absorption band is the Si-C stretching in 750-800 cm-1 due to Si-(CH3)3 vibration. Strong Si-O (Si-O-H) stretching in the range of 850-1000 cm-1 is due to Si-(CH3)2 vibration. A very weak C=C stretching peak appears in the range of 1560 cm-1, which indicates non graphite bonding of carbon [38]. The Si-H absorbance band appears in the range 2200 cm-1 region. C-H stretching band appears in 2850 cm-1 -3100 cm-1 region. This type of stretching is very important for DLN films. In DLN films CO2 vibration appears due to atmospheric carbon present during experiment, and N-H vibration in 3450 cm-1 region is due to presence of nitrogen in the precursors. Here C-H stretching and Si-O stretching mainly comprise of the a-C:H and a-Si:O networks.

Fig. 3. HRTEM image of DLN films on silicon substrate (a) HMDSO precursor (Left fig.) (b) HMDSN precursor (right fig.), ([6], permission to reprint obtained from American Institute of Physics (AIP)).

Fig. 4. FTIR spectra of DLN films.

Diamond, Diamond-Like Carbon (DLC)

([6], permission to reprint obtained from Elsevier).

**0.0 0.5 1.0 1.5 2.0 2.5 3.0**

**Stroke Length (mm)**

**Normal Load**

Tractional Force

**3.3 Tribological properties** 

DLN lms are shown in Fig. 7.

normal load (right fig.).

**Normal Load &** 

**Tractional Force (N)**

**Load on Sample (mN)**

and Diamond-Like Nanocomposite (DLN) Thin Films for MEMS Applications 465

unloading forces versus displacement into the lms, at maximum load up to 20 mN are shown in Fig. 6. This gure shows a good reproducibility of the nanoindentation test [47]. The average hardness of the DLN lms is measured using three indents with 20 mN load which is around 9-17 GPa. The average reduced elastic modulus of the DLN lms is measured under

**50 100 150 200 250 300 350**

**-0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35**

**Coefficient of friction**

Fig. 7. Scratch Behavior for DLN coating sample (a) Variation of normal load and tractional force with stroke length (left fig), (b) Corresponding coefficient of friction variation with

**0 2 4 6 8 10 12 14 16 18**

**Normal Load (N)**

**Displacement into Surface (nm)** Fig. 6. Loading unloading curve of DLN sample film by Nanoindentation test for DLN films,

To measure the friction coefcient of the DLN lms by scratch test method, the loading rate was 16 N for both normal force and tractional force and the scratch length was about 3 mm. The friction coefcient of the DLN films is estimated by taking the ratio of normal force to the lateral force. The variation in normal load and tractional force with respect to stroke length, and the corresponding variation in coefcient of friction against normal load, for

the 20 mN loading force with 300 nm displacement which is around 90-160 GPa.

The first order Raman spectra of DLN films as shown in Fig. 5, which is excited by visible light, is usually decomposed into two bands, the D and G bands. Broad asymmetric diamond-like peaks in the region 1000-1800 cm-1 are typical characteristics of amorphous carbon films. Raman spectra were deconvoluted into Gaussians D and G peaks by curve fitting. DLN films are example of amorphous carbon phase, much like DLC films and probably dominated by sp3 bonding [39].

The shape of the spectra varies with substrate material composition. The position of D and G peak widths can be correlated to the film properties such as hardness, wear and electrical characteristics for conventional diamond like carbon films [40]. The position of D and G peak can be shifted due to film structure, light source of Raman spectroscopy, Gaussian fitting method and so on. Rosenblatt and Vairs have suggested the existence of new structural type of diamond-like form of carbon in which phonon frequency is around (1540±20) cm-1 depending on the distortion from the graphite structure. The D band (which is around 1330 cm-1) corresponds to breathing mode of sp2 atoms in hexagonal ring formed by graphite structure, which means disorder of bond angle resulting due to disappearance of the long range translation symmetry of polycrystalline graphite and amorphous carbon films, while G peak (located around 1535 cm-1 ) is related to C-C bond stretching vibration of all pair of sp2 atoms in both ring and chains of graphite layer for single crystalline graphite structure [41-44]. Here D means disorder G means graphite.

Fig. 5. Raman spectra of DLN films.

#### **3.2 Mechanical properties**

The method of measuring hardness and elastic modulus of thin lms by nanoindentation test is explained by Oliver and Pharr [45-46]. This method is widely adopted to characterize the mechanical behavior of low dimensional materials, while the numerous renements have been made to further improvement of its accuracy. The curve for DLN samples of loading and unloading forces versus displacement into the lms, at maximum load up to 20 mN are shown in Fig. 6. This gure shows a good reproducibility of the nanoindentation test [47]. The average hardness of the DLN lms is measured using three indents with 20 mN load which is around 9-17 GPa. The average reduced elastic modulus of the DLN lms is measured under the 20 mN loading force with 300 nm displacement which is around 90-160 GPa.

Fig. 6. Loading unloading curve of DLN sample film by Nanoindentation test for DLN films, ([6], permission to reprint obtained from Elsevier).

#### **3.3 Tribological properties**

464 Microelectromechanical Systems and Devices

The first order Raman spectra of DLN films as shown in Fig. 5, which is excited by visible light, is usually decomposed into two bands, the D and G bands. Broad asymmetric diamond-like peaks in the region 1000-1800 cm-1 are typical characteristics of amorphous carbon films. Raman spectra were deconvoluted into Gaussians D and G peaks by curve fitting. DLN films are example of amorphous carbon phase, much like DLC films and

The shape of the spectra varies with substrate material composition. The position of D and G peak widths can be correlated to the film properties such as hardness, wear and electrical characteristics for conventional diamond like carbon films [40]. The position of D and G peak can be shifted due to film structure, light source of Raman spectroscopy, Gaussian fitting method and so on. Rosenblatt and Vairs have suggested the existence of new structural type of diamond-like form of carbon in which phonon frequency is around (1540±20) cm-1 depending on the distortion from the graphite structure. The D band (which is around 1330 cm-1) corresponds to breathing mode of sp2 atoms in hexagonal ring formed by graphite structure, which means disorder of bond angle resulting due to disappearance of the long range translation symmetry of polycrystalline graphite and amorphous carbon films, while G peak (located around 1535 cm-1 ) is related to C-C bond stretching vibration of all pair of sp2 atoms in both ring and chains of graphite layer for single crystalline graphite

**400 600 800 1000 1200 1400 1600 1800 2000**

The method of measuring hardness and elastic modulus of thin lms by nanoindentation test is explained by Oliver and Pharr [45-46]. This method is widely adopted to characterize the mechanical behavior of low dimensional materials, while the numerous renements have been made to further improvement of its accuracy. The curve for DLN samples of loading and

**Raman Shift (cm-1)**

**Fitted Curve**

**D peak G peak**

**HMDSO**

probably dominated by sp3 bonding [39].

**0**

Fig. 5. Raman spectra of DLN films.

**3.2 Mechanical properties** 

**200**

**400**

**Intensity (a.u.)**

**600**

**800**

**1000**

structure [41-44]. Here D means disorder G means graphite.

**Experimental Curve**

To measure the friction coefcient of the DLN lms by scratch test method, the loading rate was 16 N for both normal force and tractional force and the scratch length was about 3 mm. The friction coefcient of the DLN films is estimated by taking the ratio of normal force to the lateral force. The variation in normal load and tractional force with respect to stroke length, and the corresponding variation in coefcient of friction against normal load, for DLN lms are shown in Fig. 7.

Fig. 7. Scratch Behavior for DLN coating sample (a) Variation of normal load and tractional force with stroke length (left fig), (b) Corresponding coefficient of friction variation with normal load (right fig.).

Diamond, Diamond-Like Carbon (DLC)

**Coefficient of thermal** 

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

devices.

and Diamond-Like Nanocomposite (DLN) Thin Films for MEMS Applications 467

defects such as macroparticles and pinholes. Again, very less surface roughness inuences the mechanical and tribological performances of the lms for microscale and nanoscale devices. Hence, DLN films could provide the better performance for the applications in microelectromechanical systems (MEMS) or nanoelectromechanical systems (NEMS)

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

**Diamond Silicon 3C-SiC AlN Ni** 

properties of different materials including diamond and silicon are given in Table 2.

Table 2. Different material properties compared with diamond.

**Young Modulus (GPa)** 1050 165 307 331 210

**expansion at RT (ppm/0C)** 1 4.2 3.8 4.6 13.4 **Density (g/cm3)** 3.52 2.33 3.21 3.26 8.91

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

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

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, DLC and DLN can act as promising materials for MEMS/NEMS devices.

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

prevent the ions or atoms to react with the substrate material.

**4.1.1 Microfabrication and pattern transfer** 

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) views.

Fig. 8. The Surface morphology of DLN lms deposited on silicon substrate: 2D view (top)…view (bottom).

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 defects such as macroparticles and pinholes. Again, very less surface roughness inuences the mechanical and tribological performances of the lms for microscale and nanoscale devices. Hence, DLN films could provide the better performance for the applications in microelectromechanical systems (MEMS) or nanoelectromechanical systems (NEMS) devices.
