Novel Planar Nanodevices for Chemical Sensing Applications

Novel Planar Nano constructions for Chemical Sensing ApplicationsIn fresh years, planar negatronic nano constructions suck attracted often attention referable to their ingenuous architecture, ease of forum and low cost of manufacture. Such devices address a wide variety of applications in printed and plastic electronics constancy. Using this approach a new type of sensing element, which is polished to different chemics, has been develop and describe here.By exploiting the unique characteristics of semiconducting material asymmetric nanochannels, a mellowedly selective and sensitive planar nano-transistor based chemical detector has been realised which rump assort betwixt wide ordain of chemical compounds in the ambient atmosphere. The diligent part of the sensing element device was fabricated in a star nanolithography step and was tested victimisation variety of chemicals including polar protic, polar-aprotic and nonionic solvents. The detective field of st udy results showed that, all three solvent categories have exhibited unique chemical ghost which could be identified with increased or reduced enfeeble menses depending on the analyte used.A signifi bottomt rise in transistor drain current was observed when the device was undefendable to polar aprotic solvents comp ard to polar protic and nonpolar adepts. Further it has been noticed that the pictorial matter of the device to polar protic solvents which has hydroxyl (OH) meshal groups in their molecular frame work has shown genuinely high gear hysteresis in current voltage sum of moneyments. In contrast, the device has exhibited very little hysteresis when bring outd to polar aprotic and non-polar solvents with later being the minimum of all.The effect of solvents polarity on the sensors drain current in terms of adsorption and desorption processes has been studied and reported here. Also the effects of irrigate molecules in ambient air and hydroxyl groups on the device hysteresis behaviour have been investigated. As the gas sleu topic properties of the sensor are relate to the chemisorption of gaseous species at its excavate, a detailed ascertaining of the show lurch in a chemisorption process is very all-important(a) and so most of the passwords in this report focus on explaining this compound phenomenon with a special emphasis on the fictional character of arise states during sensing process.All the measurements were performed at inhabit temperature and the responses were found to be very fast, reversible and re dig upucible over m either cycles of vapour delineation and suggested the stability of the device to be very high. The simple, low-cost, multi-chemical sensing device described in this work could be useful for a variety of applications, such(prenominal) as environmental monitoring, sensing in chemical processing plants, and gas contracting for counter-terrorism.Nano imposition and word-painting4.1 macrocosmRecent adv ancements in the area of micro/nano equivocation have occasiond a unique opportunity to manufacture nanometer-sized structures with absolute precision that has wide range of applications ranging from electronic, opthalmic, chemical and biological fields. (Springer Handbook of NanotechnologyBhushan, Bharat (Ed.)2nd rev. and extended ed., 2007, XLIV, 1916 p. 1593 illus. in color. With CD-ROM., hardbackISBN 978-3-540-29855-7This chapter result introduce two of such major top-down fabrication techniques namely photolithography and e- shaft of flatboat lithography followed by a truncated description on nuclear force microscopy and s give noticening electron microscopes which have been used in this travail to fabricate and flick the planar nanosensors reported in chapter 5.4.2 LithographyIn semiconductor processing area- digiting techniques are very important. Lithography is a process of transferring prescripts from medium to the other ( ampere a. tseng, kuan chen, chii d. chen, and kung j. ma ieee transactions on electronics packaging manufacturing, electron aerate lithography in nanoscale fabrication recent developmentvol 26, no 2, april 2003 pp 141-149). These transferred patterns are then subjected to a development process that selectively removes either the bumpd or unexposed scorn depending on the endure nature. The positive compel removes the exposed part where as unexposed hold is real outdoor(a) using blackball stand fasts as shown in the determine 4.1. The exposure systems may be any of these ultraviolet illumination light rays, X-rays, ion peters or electron charges. But this section focuses on the systems using ultraviolet and electron beams as their source.4.2.1 PhotolithographyPhotolithography is the most universal patterning method, by which the shape and little dimensions of a semiconductor device are transformed onto the ascend of the wafer (got from shoot the breeze notes titled photolithography sly). This is the technique used to define the mesa structures and alloylic contacts of the device described in this thesis. A photo sensitive support is spun on to the substratum and exposed by means of a mask which transfers the patterns on the prove by means of UV light. Then the archetype is developed to constrict the desired pattern as shown below.Figure 4.1. Typical photolithography process. The substrate (A) is rst cover byphotoresist (B) and then exposed by UV radiation by dint of a mask (C). The latent image is either re locomote (D) or xed (E) by a developer solution. base M. J. Madou, Fundamentals of microfabrication, 2nd ed., CRC Press (2002), p. 19.4.2.2 coat adopt depositionIn order to perform electrical measurements on the device, we need to define the surface patterns, by dint of which it can be attached to the electrical test station.So two contacts are formed, ohmic and schottky contacts through a process called invert off as shown in the jut out 4.2. The GaAs substrate is coated with photoresist and the patterns are defined by photolithography. First the metal film is thermally evaporated and the unclaimed metal laying on the resist is lifted off by dissolving the photoresist in acetone. To facilitate the lift off of technique, photoresist edges with slice composes are desirable. This can be achieved by the word of photoresist with chlorobenzene before the UV exposure. Chlorobenzene swells inside the photoresist and sterilizes its skin harder. After the exposure and the development, the profile of the photoresist edges forms an undercut M. J. Madou, Fundamentals of microfabrication, 2nd ed., CRC Press (2002), p. 19. and M. Hatzakis, B. J. Canavello, and J. M. Shaw, IBM J. Res. Develop. 24, 452 (1980).,, as shown in Fig. 3.3E.Source fundamentals of micro fabrication bookFigure 4.2. Typical lift-of process. The substrate (A) is coated by photoresist (B) and then prebaked to partially dry the solvents (C). A angle of dip in chlorobenzene follows to recognise the photoresist skin harder. (D) UV exposure through the mask. The edges of the patterns developed into the photoresist after such process show a emblematic undercut prole (E). The metal is evaporated onto the sample, forming a thin lm (F). The unwanted metal is then lifted o by dissolving the be photoresist in a solvent (G).Ohmic contacts (obeys Ohms law, linear I-V)They are essentially formed by a metal layer deposited on a highly-doped semiconductor. Because of the high-doping concentration a very thin Schottky hindrance is formed, and the scoot carriers, namely electrons and holes, can easily tunnel through. The substrate used in this question work consists of semiconductor heterostructures in which a two-dimensional electron gas (2DEG) was confined between undoped GaAs and doped AlGaAs layers. (R. Williams, fresh GaAs processing methods, Artech class (1990), Chapter 11.)The choice of metals for any given application go outing depend on conductivity, therm al stability, adhesion, nature of electrical contact with semiconductor (work function/barrier big top), and ease of patterning. (got it grom sly lecture notes) A thin layer ( 45-50 nm) of Au/Ge/Ni alloy which is the most common scheme for make alloyed ohmic contacts to n-type GaAs is used for this work and was evaporated onto the substrate surface at temperatures higher than 360C. In this alloy, the germanium diffuses into the GaAs and acts as a dopant, while nickel acts as a wetting layer and overly assists the diffusion of Ge into the GaAs.Schottky contacts (rectifying, diode like I-V)Depositing a metal film on an undoped, or lightly n-doped, semiconductor whose electronic affinity is lower than the work function of the metal, will form a thick schottky barrier which is typically some(prenominal) hundreds of meV high, and the thermal cipher gained by the electrons, most 26 meV at room temperature, is too low to permit thermionic emission over the barrier. (R. Williams, Mod ern GaAs processing methods, Artech House (1990), Chapter 12). When a solidus is applied to the metal, the height of the energy barrier seen by the electrons injected from the metal into the semiconductor does not change, being strict by the metal work function and the electronic affinity of the semiconductor.On the other hand, the barrier seen by the electrons injected from the semiconductor into the metal is increased/ fall by a negative/positive bias. This mechanism is responsible for the known rectifying effect observed in Schottky junctions V. L. Rideout, Thin Solid Films 48, 261 (1978). 8 A. M. Cowley and S. M. Sze, J. Appl. Phys. 36, 3212 (1965).. At negative biases, the Schottky junction essentially behaves like a capacitor in substrates with plant 2DEGs, it can be utilised as a gate electrode to spiel the 2DEG carrier concentration, e.g., for the fabrication of field-effect transistors.4.2.2 Electron beam lithography (EBL)One of the fashionrn approaches in dealing wit h nanoscale structures is e-beam lithography in which, electrons are accelerated by very high voltage, typically of 10s of kV and then focused onto a layer of polymer to create very fine patterns. EBL provides much higher fortitude and more on the nose than photolithography or x-ray lithography patterns with feature sizes well below 20 nm can be achieved in pathrn systems. EBL does not bring the fabrication of masks as in the photolithographic process. There are two methods to expose e-beam on to the substrate surface (Rainer waser (Ed.) nanoelectronics and reading technology, WILEY-VCH chapter 9, pp 234-236) 2005.Direct writingProjection stampDirect writing is the most common EBL approach and used for fabrication of the device reported here. In this approach, a beam of electrons needly impinges on the resist to form the pattern in a serial fashion. As shown in the figure 4.6, a direct writing system consists of a source of electrons, a focusing optics notice, a blanker to t urn on and off, a deflection system for moving the beam, and a stage for holding the substrate. Where as projection printing is used to project entire pattern concurrently on to the wafer and can be divided into two ways SACLPEL ( sprinkle with angulate limitation in projection electron beam lithography) and PREVAIL (projection step-down exposure with variable axis immersion lens of the eyees). However we will save concentrate on direct writing technique.Fig 4 process test patterns of an army of self switching diodes (SSDs) fabricated using e-beam direct write.System configurationFigure 4.1. Simplified structure of a SEM column. The meritless lines show the trajectory of the electrons.4.2.4 E-beam process and propinquity efectTo perform electron beam lithography, PMMA (polymethyl methacrilate) resist was used which can be chemically changed under exposure to the electron beam. Final resolution of patterns in the e-beam resist and their eventual transfer into the substrate can be affected due to the imperfections in electron optics, the magnetic environment interaction, the overall thermal stability, the interaction between the beam and the substrate all play an equally important role in determining the ultimate system performance. When the electron beam strike the polymer film or any solid material, it losses energy via elastic and dead collisions collectively know as electron scattering. Elastic collisions change the concern of electron scattering, where as inelastic collisions lead to energy loss.As the electrons pass around though the resist into the substrate, some of them undergo vainglorious angle scattering leading to undesired exposure that form backscattering. This causes additional exposure in the resist and is known as proximity effect. The magnitude of electron scattering depends on the density of the resist and substrate as well as the velocity of the electrons or the accelerating voltage (guozhong cao, nanostructures and nanomaterials , imperial college press, 2004, pp 280-300). (m.a. McCord and m.j.rooks, handbook of microlithoghraphy, micromachininbg and microfabrication, p.rai-choudary, Ed. Bellingham, WASPIE ocular engineering, 1997, ch 2, pp 139-249). The proximity effect is more severe in dense patterns, peculiarly when the insularity between neighboring structures is less than 1m. Since the kernel of backscattered electrons depends on the substrate material, a dose calibration is necessary each time different substrates and resist thicknesses are used.Electron Scattering in repulse and Substrate The scattered electrons also expose the resistElectrons, resist and substratesThe punyest thing you can write with the ebeam depends on a large number of factors. These are the spot size used, the type of resist used, the thickness of the resist, the density of the features and the substrate material.When electrons are used to expose a pattern in resist it is not a simple process. Electrons enter the resist and hit the atoms of the resist, these will either forth scatter or back scatter. Backscattered electrons from the resist will leave the resist and, in general, do not contribute to the resist exposure, forward scattered electrons continue into the resist and contribute to the exposure. The thicker the resist the big the forward scattering and the lower the resolution. High energy electrons (in our case snowkV) will go through the resist and deep into the substrate. Here they will again get scattered and will forward and backscatter.In this case the forward scattered electrons will be moving away from the resist and wear downt contribute to the exposure, backscattered electrons from the substrate have a large parting to the exposure. The higher the energy of the incoming electrons the deeper they will penetrate into the resist and hence the contribution to the resist exposure will be reduced. In the figure below you can see that going from 10kV to 20kV increases the penetratio n depth of the electrons from 1m to around 6m. At 100kV the penetration depth in Silicon is around 100mFigure schematic plat of inter proximity effect and intra proximity effectThe smallest feature sizes that can be achieved are when the features are isolated from one another. As you make your features closer together the backscatter from the neighbouring features will all contribute to the exposure and it will constitute harder to remark the correct dose to correctly expose all your features. This is call proximity effects. There are 2 main effects of this inter-proximity and intra-proximity.With inter-proximity when two features are close together the electrons from the exposure of on shape contributes to the dose of the neighbouring pattern. The bigger and closer the features the worse this effect.With intra-proximity the dose in the centre of the pattern is larger than at the edges, and especially the corners. This is simply a geometric effect as in that location are less el ectrons add to the dose in the corners of the shape.The electrons need a path to ground. If you are using a conducting (or semi-conducting) substrate the contact with the holder is sufficient to provide a conducting path. If you are using an insulating substrate (fused glass, quartz) you will need to provide a conductive path for the electrons. This is normally done by evaporating a metal layer on top of the or underneath the resist. Aluminium or Chrome is are a lot trustworthy choices as they can often be easily be removed without effecting the resist, but you should check the chemical compatibility of your process with the removal procedure.Performing a Meaningful Dose turn upExposing a pattern correctly usually requires performing a precedent test exposure referred to as a dose test.In this test, the pattern is usurped several clock on a test substrate. distributively repetition is performed at a different dose or set of doses creating a matrix of different exposure condit ions.Once the pattern is developed and pattern transfer has been performed the correct dose can be obtained through inspection in a suitable inspection instrument (scanning electron microscopy, atomic force microscope, optical microscope, etc).There are several issues which can impact the usefullness of a dose test.Here are some guidelines commit the same type of substrate.If there are films present on the surface of the substrate us a substrate with the identical film stack.For large arrays of features, shooting the entire array as a test is not an efficient use of time.However, reducing the size of the array to an unrealistically small extent can give incorrent results during the test due to differences in the proximity effect.Expose your patterns so that they are easy to locate.For example, do not expose a test pattern consisting of a 500 micron x 500 micron array of 50 nm squares in the core of a 150 mm wafer.You will probably never find them.Including some locating features ( large lines or a box surounding the pattern) can jock tremendously.If you are exposing an array of patterns use as small of a repeat vector as possible.This will make locating the entire array easier and minimize the chances of getting lost when travelling in between adjacent elements of the array.Proximity EffectAs an electron from the writing beam strikes the surface of a substrate it undergoes divers(a) scattering events losing energy and causing the extension of alternative electrons.The energy range of most secondary electrons falls between 1and50 eV.Secondary electrons that are close to the substrate/resist interface are actually responsible for the bulk of the actual resist exposure process.While their range in resist is all a few nanometers they create what is known as the proximity effect.Simply put, the proximity effect is the change in feature size of pattern features as a consequence of nonuniform exposure.While the dose from the primary beam may be uniform across an entire pattern, the contribution of secondary electrons from the substrate may differ depending on pattern geometry.Two adjacent features will contribute a background dose of secondary electrons to each other resulting in a higher effective dose.This causes a turnout of the exposed features.This is particularly apparent with dense features (e.g. gratings).Consequently, dense arrays of features may require significantly less dose from the primary beam to print correctly. model size can also be adjusted to compensate for this effect.For example, 100 nm lines 100 nm apart are typically worn in CAD as 90 nm lines 110 nm apart to get them to print correctly.This strategy stops on the job(p) at the edges and corners of patterns.This sometimes requires thethe creation of dummy patterns or devices outdoor(a) of the primary pattern region to get the main features of interest to print correctly.One common practice is to draw a box around the pattern to harden the dose in the primary p attern region.4.3 Imaging nanostructuresCharacterisation and consumption of individual nanostructures requires not only extreme sensitivity and accuracy, but also atomic-level resolution that leads to various microscopes that will play a central role in characterisation and measurements of nanostructured materials (guozhong cao, nanostructures and nanomaterials, imperial college press, 2004, pp 280-300). Nevertheless, when we think of microscopes, we think of optical or electron microscopes that can image an object by focusing electromagnetic radiation, such as photons or electrons, on its surface and gives the image with very high magnifications.However, the images obtained with these microscopes can only provide the information in the woodworking plane horizontal to the surface of the object and do not give any information in vertical dimensions of objects surface height and depth. This section deals with the resourcefulness of surface topography and surface property measuremen ts of planar sensor using AFM and SEM techniques, which can provide us with all necessary information in both horizontal and vertical planes. (www.afmuniversity.org/pdf/Chapter_1_.pdf pp 1-16)4.3.1 Atomic force microscopy (AFM)AFM is a very high-resolution type of microscope from the family of scanning essay microscopy (SPM) with the resolutions thousand times the better than optical diffraction limit (http//en.wikipedia.org/wiki/Atomic_force_microscope). Unlike traditional microscopes, AFM does not believe on electromagnetic radiation to create an image. AFM is a mechanical visualise instrument that measures the three dimensional topography as well as personal properties of a surface with a curtened probe. ((www.afmuniversity.org/pdf/Chapter_1_.pdf pp 1-16)AFM Basic principlesIt consists of very aggressively effect attached to protrude and is positioned close enough to the surface such that it can interact with the atomic/molecular forces associated with the surface. Then a collimated laser beam focuses onto the protrude, which scans across the surface such that the forces between the probes remain constant. An image of the surface is then produced by monitoring the precise motion of the probe that can sense the movements as tiny as 0.1 nm. Such high resolution allows to image even single atoms, which are typically 0.5 nm apart in a crystal. Normally the probe is scanned in a raster-like pattern as shown in the figure 4. ((www.afmuniversity.org/pdf/Chapter_1_.pdf pp 1-16)Source http//www.afmuniversity.org/index.cgi?CONTENT_ID=33AFM probe Cantilever and TipAFM is a force sensor with a sharp tip used to probe the surface. When the tip at the end of the cantilever interacts with the surface, the cantilever bends, and consequently beam path also changes, causing the amount of light in the two photo-detector sections to change. Thus, the electronic output of the force sensor is proportional to the force between the tip and the sample. Tips used for probi ng the surface is usually made of silicon that have a radius of about 10-20 nm and can be coated by silicon nitride to make them harder, or by noble metals, such as gold and platinum, to topically probe electrical quantities or to induce chemical modifications.Optical detection and Piezo electric scannerIn order to detect the cantilever movements, when the AFM is operational in ambient conditions, optical detection is used. Reflected light from the focused laser beam is collected by a photodiode and the cantilever deflection and knottiness are detected as a change in the photocurrents of the photodiode elements, as shown in Fig. 4.In the typical AFM configuration the tip is kept still, and the imaging is performed by moving the sample with piezoelectric scanner also referred as piezo tube as shown in the figure 4b. By chinkling the bias of one inner and four outer electrodes the piezotube can be moved in three dimensions.This photosensitive detector measures the change in optical beam position and the change in cantilever height.Feedback manoeuvreFeedback check off is used in AFM for maintaining a xed relationship, or force, between the probe and the surface. check to the mode used, the feedback tat can be controlled either by the cantilever deflection (contact mode) or by the amplitude of the cantilever oscillation (dynamic modes). The typical feedback system used in contact mode is shown in Fig. 3.11. The feedback control operates by measuring the force between the surface and probe, then imperious a piezoelectric ceramic that establishes the relative position of the probe and surface.Feedback control is used in many applications Figure 2-4 illustrates the use of feedback control in an oven. Section 2.3 has a moreAFM modes Tip sample interactionsDepending on separation between tip and the sample a variety of forces can be measured by AFM. At shorter infinites van der Waals forces are predominant. Where as these forces become negligible if the tip-s ample distance increases.Forces like electrostatic attraction or repulsion, current induced or static magnetic interactions comes into play at these larger separations. The tip-surface forces (approx.) is given by the following equationFa = U = 12 B/Z13 6A/Z7attractiveRepulsiveB and Aare coffecients depend upon the surfaces involved.detectable forces for an AFM 1 nN in the contact regime and 1 pN in the noncontact regime (theory 10-18 N)(r. wiesendanger, chapter 11. proximo sensors. In h.meixner, r. jones, eds vol 8 micro and nanosensor technology /trends in sensor markets. )Based on these interactions, AFM usually has two operational modes contact mode and dynamic mode. Depending on resonant frequency shift of tip-sample, dynamic mode is further divided into tapping mode and non-contact mode. Imaging for this work was carried out in tapping mode.Contact modeAlso called as repulsive-static mode, in which, the tip rides on the sample in close with the sample surface (low k). The force produced in the feedback loop is frictional force hence, the tip might interact with the sample surface.Non-contact modeAlso called as attractive-dynamic mode, in which the tip hovers 5-15 nm away from the sample surface. The force generated in the feedback loop is typically van der Waals forces. apply force (dependent on height z) changes the cantilever oscillation frequency.Figure AFM mensuration in the figure PSPD represents photosensitive detector.Tapping modeAlso called repulsive-dynamic mode, in which the AFM tip taps the surface as it maps the height z. This type of mode eliminates the hysteresis due to the tip sticking on the sample. Also using this method there is less likely to damage the sample.Scanning electron microscopyScanning electron microscopy is also one of the major techniques for imaging the nanostructures. Although AFM gives high-resolution images with absolute precision, it takes much of time to scan and image the surface area of the sample. Where by S EM can provide an alternative to AFM, which is very fat at imaging the samples in both horizontal and vertical directions.These schematics show the ray traces for two probe-forming lens focusing conditions small working distance (left) and large working distance (right). Both conditions have the same condenser lens strength and aperture size. However, as the sample is moved further from the lens, the following occursthe working distanceSis increasedthe demagnification decreasesthe spot size increasesthe divergence anglealphais decreasedThe decrease in demagnification is obtained when the lens current is decreased, which in turn increases the focal lengthfof the lens. The resolution of the specimen is decreased with an increased working distance, because the spot size is increased. Conversely, the depth of field is increased with an increased working distance, because the divergence angle is smaller.Comparison between AFM and SEMThe AFM is more often compared with the electron beam t echniques such as the SEM or TEM. With an AFM, if the probe is rock-steady, a good image is measured. (www.afmuniversity.org/pdf/Chapter_1_.pdf pp 1-16) the following comparison between AFM and SEM gives a fair thought of the capabilities for applicationsA comparison of the some of the major factors followsFIGURE1-8 Boththe AFMand SEM measuretopography. However, both types of microscopes can measure othersurfacephysicalproperties.The SEM is good for measuring chemical composition and the AFM is good for measuring mechanical properties of surfaces.summaryThis chapter has covered the main processing and imaging techniques used for fabrication of nanosensor reported in chapter 5.Patterning of metal contacts and mesa structures on to the substrate using photolithography have been discussed in detail. The mechanism for the thin film deposition of Au/Ge/Ni alloy for forming ohmic and schottky contacts have been presented followed by a brief discussion of wet etching for undercut profile s.e-beam lithography which can overcome the resolution limitation in photolithography has been introduced with a description of its basic elements followed a discussion on proximity effect. So overall, this chapter provides the reader with fundamental knowledge to understand the basic fabrication and characterisation process of which serves as a tool for better understanding the fabrication of planar nanodevices discussed in next chapter (i.e chapter 5).BibliographyIntroductionThe evolution of semiconductor industry has brought a revolutionary change in the way we live today. Right from the invention of germanium transistor in 1947 to the latest sensation graphene transistor, the world has seen some of the spectacular breakthroughs that the human mixed bag had ever imagined few decades ago.In the last fifteen years, more than dozen noble prizes have been awarded for the research based in the field of nanotechnology.1.1detectors and sensor scienceLife without sensors and sensing wo uld be like an opera without vocaliser or a violin without strings. Such life does not exist. Sensors and sensing, on the contrary, are basic properties of life that are responsible for the closed loop real time control of what is going on inside and how it reacts to the outside situation. From bacteria to plants and animals to human beings, all living organisms use their sensing organs for orientation and communication, for monitoring the environment and for their survival.(sensors and sensing in biology and engineering, impost wien newyork, 2003, friedrich g. barth, joseph a.c. Humphrey, timothy w.secomb pp3-34 chapter1 and 2.)Digital systems however complex and intelligent they are, must turn around information from the outside world. Sensors act as an interface between various physical values and electronic circuits that understand only a dustup of moving electrical charges. In other words, sensors are eyes, ears, and noses of silicon chips. any(prenominal) sensors are rela tively simple and some are complex, which operate on fundamental basic principles. Understanding of these devices generally requires an interdisciplinary background in fields such as physics electronics, chemistry etc. Thus, sensors research has brought a unique team of chemists, biologists, physicists electronic engineers, together on one platform, thus making it a truly interdisciplinary field.1.1.1 The term SensorIn this ever-changing world, sensors are becoming ubiquitous in our everyday lives and play an important role in this process. Since the early 1990s, semiconductor industry has seen a tremendous growth in the development of variety of sensors. The scientific trends in this field have made electronic products not only smaller and sleeker, but also more interactive and powerful.These sensors with their improving performancecost ratio will be the key components for the future nanoelectronic devices.(http//www.frost.com/prod/servlet/market-insighttop.pag?docid=140061375)T he word sensor is derived from the Latin word sentire, which means, to perceive. A sensor i