**3. Advance manufacturing methods for chemical, gas and bio sensor applications**

Prototyping and manufacturing sensor devices (Gas, Chemical or Bio sensor) required that the sensors materials be deposited or coated on an electrode for easy contact and connection to the device electronic circuitry or source measuring unit of the gas sensing and test station. Interdigitated electrode (IDE) type have been widely used for sensors laboratory research, prototyping and manufacturing of sensors and related products. This is a cost-effective method which often made from an

*Nanofibers - Synthesis, Properties and Applications*

is not new per se, it is a name that was given to a number of fields of research that share common principles, and hence it is referred to as an interdisciplinary science. Nanotechnology integrates a wide range of sciences which includes; Physics,

device atom-by-atom using the principles of mechanosynthesis [7].

**technologies**

scopic, microscopy and spectroscopy ones.

**2. Significance of micro and nano fabrication in novel devices and** 

devices and technologies. Many sciences, technology and engineering oriented products are developed using the concept of micro and nano fabrication. From radio transistors, integrated circuits, personal computers, to micromechanical systems (MEMS), transducers, sensors, batteries and super capacitors, solar cells, water treatment membranes and filters and other novel devices, micro and nano techniques have played significant and important role in realizing reliable technology. However, huge credit relating to the success of these technologies must be ascribed to the materials development and analyses techniques such as the analytical, macro-

Micro and nano fabrication is an essential process in the manufacturing of novel

For instance, before one can realize product of gas sensor, chemical sensor and biosensor device, especially in the case of metal oxide semiconductors, carbon materials and polymers, critical studies and analyses of the materials properties is required to qualify the performance of the sensing element. The first set of investigation which must be performed on the materials intended to build these devices are crystal structure and microstructures, morphological and surface roughness studies, defects studies, thermal stability and adsorption property [8–10]. Hence, the material must be thoroughly characterized with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HR-TEM) methods to study its crystal structure. X-ray diffraction spectroscopy which is commonly used technique for characterization of crystalline materials provides information about elemental analyses such as structures, phases and preferred crystal orientations. Physical measurements like average particle size of material, homogeneous and inhomogeneous strain and crystal defect could also be estimated from the data collected using XRD technique [8–11]. The HRTEM approach has been severally employed in sensors material research to unveil material's crystallographic structures at an atomic scale [8–9]. The scanning electron microscope (SEM), scanning tunneling microscope (STM) and atomic force microscope (AFM) are important for all surface structure studies such as morphology, particles distribution, nanoscale topography and

Chemistry, Biology, Microbiology, Engineering, Surface Science, and Biotechnology, and apply them to practical devices [5]. There are two major approaches normally employ in fabrication techniques namely; **top-down approach** (Larger to smaller: a materials perspective) and **bottom-up approach** (Simple to complex: a molecular perspective). Top-down approach involves creating Nano-scale materials by physically or chemically breaking down larger materials. These include statistical mechanical effects, as well as quantum mechanical effects. Solid-state techniques can also be used to create devices known as nanoelectromechanical systems or NEMS, which are related to micromechanical systems or MEMS [6] while bottom-up approach simply involves simple to complex: i.e. a molecular perspective technique. These techniques are used today to manufacture a wide variety of useful chemicals such as pharmaceuticals or commercial polymers. Molecular nanotechnology, sometimes called molecular manufacturing, describes engineered nanosystems (nanoscale machines) operating on the molecular scale. Molecular nanotechnology is especially associated with the molecular assembler, a machine that can produce a desired structure or

**164**

aluminum oxide (Al2O3) substrate whose front-side surface is coated with platinum (Pt) metal in comb-like structures for sensors electrical signal measurement and the rear-side coated with nickel (Ni) metal as Microheater [9, 24]. **Figure 1** showed a schematic layout of KSGA565 KENOSTATIC gas detection station where μ-nano IDE was used as the sensor's electrode. The layout consists of an enclosed chamber called sensing chamber containing IDE with deposited sensor material. The front-side of the IDE is connected to the Keithley pico-meter source meter and the rear-side to the power supply.

During fabrication, sensor materials are usually deposited onto the IDE using micro-nano deposition technologies such as chemical vapor deposition (CVD), pulse laser deposition (PLD), physical vapor deposition (PVD) and magnetron sputtering technique [25–27]. These technologies are physical methods which have been reported to offer thin and homogenous film surface with excellent gas, chemical and bio molecule sensing properties. These technologies have also been used severally to deposit non-IDE pattern like glass, silicon wafer etc. for sensors and related device fabrication [28].

The printed patterned substrate and Lab-on-a-chips are another micro-nano contacting and printing technology commonly used when manufacturing Gas, Chemical or Bio sensor devices. These techniques are expensive and regarded as state of the art method which required specialized equipment like photolithography (PL), plasma enhanced chemical vapor deposition (PECVD) and electron beam lithography (EBL). The methods offer patterned deposition of nanostructures such as nanowires, nano-rods, nano-tubes etc., high precision contacting, highly aligned printing and deposition onto flexible substrates as advantages over others [25–30].

#### **Figure 1.**

*Schematic diagram of KSGA565 KENOSISTEC gas sensing station illustrating how the μ-nano IDE sensor can be tested. The electronic circuit displays of the gas sensor's element showed RL, which is the load resistor connected in series with the sensor's element (RL = (V-VS)/I). V, is the voltage on the RL, VS = VC – IRL, represent the sensor's signal voltage. VC is a constant voltage applied on the RL and sensor's element and finally, RS is the sensor's resistance (RS = VS/I). Adapted from Ref. [24].*

**167**

**Figure 2.**

*the entire device. Adapted from Ref. [30].*

*Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification…*

A typical process involving the fabrication of TiO2 nanowires-based gas sensor is shown in **Figure 2**. The materials used for the fabrication are; p-type silicon wafer (**Figure 2(a)** and interdigitated Cr/Au electrodes which was initially fabricated using PL process on an oxidized Si substrate (**Figure 2(b)** [30]. The Cr and Au thin films were also blank deposited on the rear-side of the silicon wafer in an interdigitated fashion to make heating element (Microheater) (**Figure 2(c)**). Thereafter, EBL approach was used to pattern the chip surface and to produce photoresist on the film before depositing the p-type TiO2 on the top of the chip with aid of sputter machine. The photoresist was later lift-off to form the TiO2 nanowire array as shown in **Figure 2(d)**. **Figure 2(e)** showed the dimensions of each section of the

*Fabrication process of electron beam patterned TiO2 based gas sensor; (a) oxidation process of Si wafer, (b) Cr/Au contact fabrication, (c) microheater fabrication, (d) photoresist deposition, lift-off and TiO2 nanowire arry deposition, (e) showed the dimensions of each section of the device and (f) the optical image of* 

**4. Advance manufacturing methods for water purification, lithium ion** 

Electrospinning is one of the techniques suitable for the fabrication of materials through innovative technology. Membrane-based technologies through electrospinning have been employing for the fabrication of both nano- and micro-based materials which finds useful applications in various fields such as in the water

device and **Figure 2(f )** the optical image of the entire device.

purification, lithium ion batteries, medical applications etc.

**batteries and medical applications**

*DOI: http://dx.doi.org/10.5772/intechopen.94962*

*Micro Nano Manufacturing Methods for Chemical, Gas and Bio Sensors, Water Purification… DOI: http://dx.doi.org/10.5772/intechopen.94962*

**Figure 2.**

*Nanofibers - Synthesis, Properties and Applications*

power supply.

others [25–30].

related device fabrication [28].

aluminum oxide (Al2O3) substrate whose front-side surface is coated with platinum (Pt) metal in comb-like structures for sensors electrical signal measurement and the rear-side coated with nickel (Ni) metal as Microheater [9, 24]. **Figure 1** showed a schematic layout of KSGA565 KENOSTATIC gas detection station where μ-nano IDE was used as the sensor's electrode. The layout consists of an enclosed chamber called sensing chamber containing IDE with deposited sensor material. The front-side of the IDE is connected to the Keithley pico-meter source meter and the rear-side to the

During fabrication, sensor materials are usually deposited onto the IDE using micro-nano deposition technologies such as chemical vapor deposition (CVD), pulse laser deposition (PLD), physical vapor deposition (PVD) and magnetron sputtering technique [25–27]. These technologies are physical methods which have been reported to offer thin and homogenous film surface with excellent gas, chemical and bio molecule sensing properties. These technologies have also been used severally to deposit non-IDE pattern like glass, silicon wafer etc. for sensors and

The printed patterned substrate and Lab-on-a-chips are another micro-nano contacting and printing technology commonly used when manufacturing Gas, Chemical or Bio sensor devices. These techniques are expensive and regarded as state of the art method which required specialized equipment like photolithography (PL), plasma enhanced chemical vapor deposition (PECVD) and electron beam lithography (EBL). The methods offer patterned deposition of nanostructures such as nanowires, nano-rods, nano-tubes etc., high precision contacting, highly aligned printing and deposition onto flexible substrates as advantages over

*Schematic diagram of KSGA565 KENOSISTEC gas sensing station illustrating how the μ-nano IDE sensor can be tested. The electronic circuit displays of the gas sensor's element showed RL, which is the load resistor connected in series with the sensor's element (RL = (V-VS)/I). V, is the voltage on the RL, VS = VC – IRL, represent the sensor's signal voltage. VC is a constant voltage applied on the RL and sensor's element and finally,* 

*RS is the sensor's resistance (RS = VS/I). Adapted from Ref. [24].*

**166**

**Figure 1.**

*Fabrication process of electron beam patterned TiO2 based gas sensor; (a) oxidation process of Si wafer, (b) Cr/Au contact fabrication, (c) microheater fabrication, (d) photoresist deposition, lift-off and TiO2 nanowire arry deposition, (e) showed the dimensions of each section of the device and (f) the optical image of the entire device. Adapted from Ref. [30].*

A typical process involving the fabrication of TiO2 nanowires-based gas sensor is shown in **Figure 2**. The materials used for the fabrication are; p-type silicon wafer (**Figure 2(a)** and interdigitated Cr/Au electrodes which was initially fabricated using PL process on an oxidized Si substrate (**Figure 2(b)** [30]. The Cr and Au thin films were also blank deposited on the rear-side of the silicon wafer in an interdigitated fashion to make heating element (Microheater) (**Figure 2(c)**). Thereafter, EBL approach was used to pattern the chip surface and to produce photoresist on the film before depositing the p-type TiO2 on the top of the chip with aid of sputter machine. The photoresist was later lift-off to form the TiO2 nanowire array as shown in **Figure 2(d)**. **Figure 2(e)** showed the dimensions of each section of the device and **Figure 2(f )** the optical image of the entire device.
