**4.1.2 Diamond film patterning**

To make the pattern of diamond or diamond films is not easy task for fabrication of microstructure. The authors of this chapter are continuously trying to etch the DLN films for MEMS structure. But till now we are unable to get the success for patterning [48]. Hence, some of the diamond films (DLN) also applicable as coating materials in MEMS devices. But the other diamond films are able to pattern for MEMS device. Diamond films have very high chemical inertness. So wet chemical etching is almost impossible for diamond etching. The dry etching is possible for diamond films. The plasma based etching like Reactive Ion etching (RIE) is possible for diamond pattern. RIE has higher anisotropy, better uniformity and control, better selectivity compared to wet etching [49]. Generally RIE consists two electrode which creates the electric field to accelerate the ions towards the surface of the samples. Diamond pattern also possible by Inductive Couple Plasma (ICP). The plasma density of ICP is two times higher in order of magnitude compare to RIE plasma. In ICP, the RF power are capacitivly coupled and magnetic coil surrounded into the chamber for active species generation. The AC field is induced by RF coil which located in front of RF transducer helps to generate high density plasma due to confinement of electrons. In ICP process the plasma densities is very high around 1011 ion/cm2 [50]. By this ICP process the diamond patterning is extremely fast with good shape under low self-bias condition [51]. The oxygen based diamond etching as shown in Fig. 12, where diamond pattern with 1.7 μm thick films etch by ICP [52].

Fig. 12. Nano Crystalline Diamond (NCD) patterned by ICP etching using an Al hard mask. The etching time was 5 minutes, ([52], permission to reprint obtained from John Wiley & Sons, Ltd.).

Another diamond pattern technique is known as Focused Ion Beam (FIB). The FIB process commercially very expensive but we can etch the material very preciously even in nm level.

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

To make the pattern of diamond or diamond films is not easy task for fabrication of microstructure. The authors of this chapter are continuously trying to etch the DLN films for MEMS structure. But till now we are unable to get the success for patterning [48]. Hence, some of the diamond films (DLN) also applicable as coating materials in MEMS devices. But the other diamond films are able to pattern for MEMS device. Diamond films have very high chemical inertness. So wet chemical etching is almost impossible for diamond etching. The dry etching is possible for diamond films. The plasma based etching like Reactive Ion etching (RIE) is possible for diamond pattern. RIE has higher anisotropy, better uniformity and control, better selectivity compared to wet etching [49]. Generally RIE consists two electrode which creates the electric field to accelerate the ions towards the surface of the samples. Diamond pattern also possible by Inductive Couple Plasma (ICP). The plasma density of ICP is two times higher in order of magnitude compare to RIE plasma. In ICP, the RF power are capacitivly coupled and magnetic coil surrounded into the chamber for active species generation. The AC field is induced by RF coil which located in front of RF transducer helps to generate high density plasma due to confinement of electrons. In ICP process the plasma densities is very high around 1011 ion/cm2 [50]. By this ICP process the diamond patterning is extremely fast with good shape under low self-bias condition [51]. The oxygen based diamond etching as shown in Fig. 12, where diamond pattern with 1.7 μm thick films etch by ICP [52].

Fig. 12. Nano Crystalline Diamond (NCD) patterned by ICP etching using an Al hard mask.

Another diamond pattern technique is known as Focused Ion Beam (FIB). The FIB process commercially very expensive but we can etch the material very preciously even in nm level.

The etching time was 5 minutes, ([52], permission to reprint

obtained from John Wiley & Sons, Ltd.).

photoresist pattern (subtractive process)

**4.1.2 Diamond film patterning** 

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

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 the diamond substrate using FIB, ([52], permission to reprint obtained from John Wiley & Sons, Ltd.).

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

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 component laterally [55].

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

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,

Diamond, Diamond-Like Carbon (DLC)

and Diamond-Like Nanocomposite (DLN) Thin Films for MEMS Applications 473

 Fig. 15. Diamond material based acceleration sensors including a piezoresistive elements and seismic mask, ([52], permission to reprint obtained from John Wiley & Sons, Ltd.).

Fig. 16. Diamond based microgears (top fig.) and accelerometer (bottom fig.),

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

the gauge factor must be need as small as possible to achieve the reasonable activation and for low sheet resistance. The gauge factors of the diamond films has been found in the range of 70- 4000 and even its remain unchanged in high temperatures [58-59]. As a sensor of diamond material, the aim to measurement of mechanical effect like acceleration, pressure from piezoelectric diamond or piezoresistive diamond transducers elements. These diamond materials have been utilize for different type of sensors like pressure or UV [60-61], temperature sensors [62-63] up to 700 0C. The pressure sensors of diamond materials are based on hermitically sealed membrane structure, that can detect the bowing pressure difference. The diamond pressure sensors can be made by doped diamond as a piezoresistor or undoped diamond as a flexible diaphragm. Fig. 14, shows the boron doped piezoresistive diamond pressure sensors [64]. The undoped and boron doped diamond deposited on silicon substrate by CVD process. To improve the sensitivity of this pressure sensors, the diaphragm thickness and boron doped was varied from 62 to 5 µm and 2 to 0.5 µm respectively. This sensors evaluated from room temperature to 250 0C and pressure between 0-0.07 MPa.

Fig. 14. Boron doped polycrystalline diamond based pressure sensors. (a) Chip layout (left fig.) (b) Pressure sensors (right fig), ([64], permission to reprint obtained from Elsevier).

Diamond films can act as a high acceleration sensors also. Diamond films have high fracture strength and high stiffness. So these films can withstand in high acceleration and shock also. Fig. 15, shows the diamond based acceleration sensors. In this figure the piezoresistive transducers elements located on the four suspended bridge which looks like whetstone bridge [65]. The sensors structure realized based on the movement of center seismic mask which suspended by four arms.

The diamond material can be act as a actuators. The microthermal actuators based on bilayer structure which delivers an out of plane motion [66] and the shape bimorph structure made by single material [67]. The bilayer which consists two layer of materials with different thermal expansion of coefficient. The deflection of bilayer actuators depends upon coefficient of thermal expansion of the materials. The diamond, DLC, and DLN have have very low coefficient of thermal expansions around 10-6 K-1. Hence, diamond and DLC materials can be used as bi-layer thermal actuators. The high tensile strength and very high elastic modulus of diamond, DLC, and DLN materials is the potential candidate to fabricate the contact mode micro-actuators. Also these materials used to fabricate the micro-engine, gears, rotors etc. Fig. 16, shows the diamond based micro-gears and accelerometers [68].

the gauge factor must be need as small as possible to achieve the reasonable activation and for low sheet resistance. The gauge factors of the diamond films has been found in the range of 70- 4000 and even its remain unchanged in high temperatures [58-59]. As a sensor of diamond material, the aim to measurement of mechanical effect like acceleration, pressure from piezoelectric diamond or piezoresistive diamond transducers elements. These diamond materials have been utilize for different type of sensors like pressure or UV [60-61], temperature sensors [62-63] up to 700 0C. The pressure sensors of diamond materials are based on hermitically sealed membrane structure, that can detect the bowing pressure difference. The diamond pressure sensors can be made by doped diamond as a piezoresistor or undoped diamond as a flexible diaphragm. Fig. 14, shows the boron doped piezoresistive diamond pressure sensors [64]. The undoped and boron doped diamond deposited on silicon substrate by CVD process. To improve the sensitivity of this pressure sensors, the diaphragm thickness and boron doped was varied from 62 to 5 µm and 2 to 0.5 µm respectively. This sensors

evaluated from room temperature to 250 0C and pressure between 0-0.07 MPa.

Fig. 14. Boron doped polycrystalline diamond based pressure sensors. (a) Chip layout (left fig.) (b) Pressure sensors (right fig), ([64], permission to reprint obtained from Elsevier). Diamond films can act as a high acceleration sensors also. Diamond films have high fracture strength and high stiffness. So these films can withstand in high acceleration and shock also. Fig. 15, shows the diamond based acceleration sensors. In this figure the piezoresistive transducers elements located on the four suspended bridge which looks like whetstone bridge [65]. The sensors structure realized based on the movement of center seismic mask

The diamond material can be act as a actuators. The microthermal actuators based on bilayer structure which delivers an out of plane motion [66] and the shape bimorph structure made by single material [67]. The bilayer which consists two layer of materials with different thermal expansion of coefficient. The deflection of bilayer actuators depends upon coefficient of thermal expansion of the materials. The diamond, DLC, and DLN have have very low coefficient of thermal expansions around 10-6 K-1. Hence, diamond and DLC materials can be used as bi-layer thermal actuators. The high tensile strength and very high elastic modulus of diamond, DLC, and DLN materials is the potential candidate to fabricate the contact mode micro-actuators. Also these materials used to fabricate the micro-engine, gears, rotors etc. Fig. 16, shows the diamond based micro-gears and accelerometers [68].

which suspended by four arms.

Fig. 15. Diamond material based acceleration sensors including a piezoresistive elements and seismic mask, ([52], permission to reprint obtained from John Wiley & Sons, Ltd.).

Fig. 16. Diamond based microgears (top fig.) and accelerometer (bottom fig.), ([68], permission to reprint obtained from Elsevier).

Diamond, Diamond-Like Carbon (DLC)

and Diamond-Like Nanocomposite (DLN) Thin Films for MEMS Applications 475

reaction of materials in biological environment [77]. The biomaterial, to apply our human body, should be chemically and biologically inert to the surrounding cells and our body fluids. In these diamond structure, they have two phase. One is sp2 hybridized carbon atoms in hexagonal ring formed by graphite structure. It is the disorder of bond angle, resulting due to disappearance of the long range translation symmetry of polycrystalline graphite and amorphous carbon lms. On the other hand, the C-C stretching vibration of sp3 hybridized carbon atoms in both the rings and chains. Which indicate the disorder diamond phase. In the films if percentage of sp3 carbon is much more, then films should be good mechanical properties. The diamond and DLC films have good orthopedic applications. In our human body, the hip and knee joint are subjected the friction and wear, as a result which forms the polyethylene debris at a rate of 1010 particulates per year [78]. These phagocytosed particulates forms osteolysis, granulomatosis lesions and bone resorptions which causes the aseptic loosening of the prosthesis and pain. In last couple of years researchers are trying to apply this diamond, DLC, and DLN films coating for knee and hip replacement to decrease the wear rate. The DLC with Co-Cr alloy can reduce the significant wear rates of both sliding surfaces [79]. The amorphous diamond coatings which can improve the wear and

corrosion resistance by a factor of millions compare to conventional materials [80].

indicates that the cell have greater chance to adhere onto the substrate.

formation as like closed packed islands formation.

surface is much more compered to other surfaces [81].

biodiamond stent [83].

The biocompatibility of DLC and DLN films have determined by the interaction of cells with DLC and DLN surface. The biocompatibility of the films can be performed by characterization of cytotsicity, protein adsorption or microphase adhesion property of the films. In the study of cell adhesion on different substrates, the increase of number of cell adhesion onto the substrate

Fig. 18 shows fluoresce microscopic image of the different cells growth on different surface and Fig. 19 shows the corresponding scanning electron microscope (SEM) image of cell growth on different surface. From both of these figures, the PC 12 cells growing characteristic in neuronal process. This process interact with platinum and ultrananocrystalline diamond (UNCD) diamond surface. In silicon surface the cells

The PC 12 cells growth on the platinum and UNCD surface exhibiting distinctive outgrowth of axons and dendrites on the surface. The growth of the PC 12 cells on the surfaces are quite less compare to HeLa cells. The figure shows that, PC 12 cells growth on UNCD surface most suitably compared to other surfaces. The area cover by PC 12 cells is almost highest in UNCD surface compared to another material surface. Which indicates that the UNCD surface have much more biocompatibility compared to other surfaces. Finally the maximum cells attachment, cell spreading and nuclear area coverage of the cell in UNCD

In medical application DLC can coat over the stent. Where a stent is a metal tube that inserted permanently into an artery. Stent helps to open an artery for blood circulation through it. Recently, the use of cardiovascular implantation of stent increasing in the world. The side effect of the artery stent lies in its release of metal ions and thrombogenecity. So it is desirable in such a material that can prevent the release of metal ions and that materials also will be hemocompatible, very high corrosion resistance and long lasting in human blood environment [82]. DLC coat stent are suitable for this pour pose. Some of the companies are made the DLC coted stent for medical purpose use. Fig. 20 shows the multilayer nanocomposite coated with DLC as an intermediate layer under the name
