FABRICATION AND CHARACTERIZATION OF ZNO NANOSTRUCTURED … · As the technology advanced, there has...

FABRICATION ANDCHARACTERIZATION OF ZNONANOSTRUCTURED THIN FILMPIEZOELECTRIC SENSOR FOR

ACCELEROMETER APPLICATION

Kiruthika.R1, Priyadharshini.E1,Kirubaveni.S1, Radha.S2,

1,2Department of Electronicsand Communication Engineering,

SSN College Of Engineering,Chennai-603110

[email protected],[email protected],

[email protected],[email protected].

May 28, 2018

Abstract

Accelerometers are used to measure acceleration, vibra-tion and mechanical shocks. From the available accelerom-eter, the need for efficient self-powered application at nanolevel with reduced powered consumption, biocompatibilityand eco-friendly characteristics has led to ZnO based piezo-electric based accelerometer from pre-existing commerciallyavailable capacitive and resistive accelerometer. Concen-trating on these issues, the fabrication of ZnO based nanos-tructured accelerometer is done on rigid FTO (Fluorine

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International Journal of Pure and Applied MathematicsVolume 118 No. 24 2018ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

doped Tin Oxide) glass substrate using low cost hydrother-mal growth technique. PEDOT: PSS is used as p-type layerto establish PN junction which is confirmed using I-V char-acteristic curve. Optical characterization for obtaining bandgap and Photoluminescence study for analyzing defects werealso analyzed.

Keywords:Piezoelectric, Hydrothermal, Zinc oxide, Bandgap, Photoluminescence.

1 INTRODUCTION

As the technology advanced, there has been more research on thefuture implications of nanotechnology. One such application wherenanostructures are used is accelerometer [1][2].An accelerometer isa measure of physical acceleration experienced by an object due toforces or mechanical excitation. Most accelerometers are Micro-Electro-Mechanical System (MEMS)[3].Improvement in terms ofefficiency and reduced size leads to NEMS accelerometers whichare suitable for NEMS based applications. For a better perfor-mance accelerometer, it is mandatory to use materials of goodpiezoelectric coefficient. Piezoelectric materials such as ZnO, PZT,AIN[4][5] have this property which decides its behaviour for var-ious NEMS based applications. Of all the mentioned piezoelec-tric materials, Zinc oxide (ZnO) in Wurtzite structure is stable [6]non-toxic, biocompatible, have high coupling coefficient, easily syn-thesizable [7][8].ZnO being a piezoelectric material can be used tosynthesize nanorods for sensing the vibration or movement of any-body[9].Different nanostructures of ZnO like nanorod, nanoflowers,nanosheets, nanoflakes, etc., can be synthesized [10]. The perfor-mance dependents on factors like ZnO nanostructures surface den-sity[11],synthesizing methods [12], seed and growth solution con-centration[13],type of dopants added , type of junction formed likeP-N junction, Schottky junction etc.. The proper optimization ofthe nanostructures and dependency factors is recommended to en-hance the output performances. ZnO material is used in multi-functional applications such as biosensors, nanogenerators [14] andresonators [15] that have already been reported. From the com-mercially available accelerometer, this reports main aim is to haveself-powered NEMS based piezoelectric accelerometer at reduced

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International Journal of Pure and Applied Mathematics Special Issue

cost and increased sensitivity.

2 MECHANISM OF PIEZOELECTRIC

ACCELEROMETER

When mechanical vibration is given on piezoelectric material, anAC is generated .In this type, when the body of the accelerometer issubjected to vibration, it compresses and stretches the piezoelectriccrystal. This force results in the generation of charge. Piezoelectricaccelerometer generates an electric charge signal proportional to thevibration acceleration. This principle requires no external energyand is self-generating [3].When compared with the available othertypes accelerometers, piezoelectric based accelerometer is highlyadvantageous as far as the power consumption and efficiencies aretaken into account. It is also less expensive and small in size andhence preferred comparatively.

3 EXPERIMENTAL DETAILS

The FTO glass substrates were pre-cleaned to achieve contami-nant free device for the fabrication process. General process flow isshown in Fig.1.Next is the deposition of seed layer which comprisesof Ethanol, Zinc Acetate and Potassium Hydroxide. The preparedZnO seed layer was deposited on the pre-cleaned FTO substrate us-ing spin coating technique at 3000 rpm for 30 seconds and annealedat 350 C for 1hour [16].The growth solution of ZnO nanostructurewas prepared using DI water, HMTA and Zinc Nitrate at equimolarratio. The prepared solution is stirred for 30 minutes continuouslyin the magnetic stirrer. After that, the solution prepared is pouredinside Teflon-lined autoclave with the substrate dipped inside it.Then the autoclave is kept inside the hot air oven. The oven tem-perature is set to 95degree Celsius for 4 hours and then cooled toroom temperature. After slow cooling, the substrate is taken outand cleaned using DI water and again annealed at 450 degree Cel-sius for 1 hour. Then, the PEDOT: PSS is spin coated on the grownZnO nanostructures. Finally, Silver paste is deposited to have elec-trical contact. The pictorial representation of the device is shown

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using Fig.2.

Figure 1: Process FlowFigure 2: Pictorial Representa-tion

4 CHARACTERIZATIONS

The I-V characterization of ZnO nanostructured thin film sensor foraccelerometer application is performed using Keithley 6487 sourcemeter. The absorption spectrum investigation was done using UVvis-ible optical spectroscopy. The Photo luminance characteristic wasobtained using Spectroflurometer (RF- 5301, Shimadzu).

5 RESULTS AND DISCUSSIONS

5.1 Optical Characterization

The ZnO thin film samples absorption spectrum in the wavelengthrange of 300 to 600 nm at room temperature was analyzed usingUV-visible optical spectroscopy. The absorption spectrum of ZnOthin film device is shown in Fig.3. The relation between the ab-sorption coefficient and band gap is shown using (1). The opticalband gap Eg was calculated from the Tauc plot [17].

αhv = B(hv − Eg)1/2 (1)

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where, α is the absorption coefficient, B is a constant and h isthe photon energy. The optical band gap calculated and inferredfrom Fig.4 was 3.18eV which shows reduction in band gap of ZnOnanostructure from 3.37 eV. This shows the increased conductivityof the fabricated device.

Figure 3: Absorption spectra Figure 4: Tauc plot

5.2 Photoluminescence Study

The Photoluminescence study shows the PL spectra obtained usingxenon lamp at 325 nm excitation wavelength. The sample showstwo dominant peaks which are Ultra violet emission and blue-greenband emission. The green emission peak is at 468 nm and UVemission peak is at 376 nm .When compared to green emissionpeak, the intensity of UV peak is much higher in the range as in-ferred from Fig.5.The ratio between ultraviolet emission and visibleemission(Iuv/Ivis) shows the defects presenting the fabricated ZnOnanostructured device [17].

To understand P-N junction formation,I-V (Current density-voltage) characterization is very important. I-V curve shown inFig.5. Turn-on voltage and the reverse leakage current density cal-culated are0.6 V and 0.0003mA cm−2. Current rectification ratiocalculated using the ratio between the forward current and reversecurrent [16] is 1.4 V. The shunt and series resistance calculated are206 Ω and 984 Ω.

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Figure 5: PL intensity Figure 6: I-V characteristics

5.3 Accelerometer Testing

The vibration setup is shown below in Fig.7. It consists of microshaker, power amplifier and function generator[18] .The fabricateddevice is tested under different frequencies for which the output inthe form of voltage was observed. A sample of the observed outputvoltage is shown in Fig.8. The experiment demonstrated the prooffor conversion of mechanical vibration in to electrical voltage.

Figure 7: Device on ShakerFigure 8: Output Voltage Ob-served

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6 CONCLUSION

The ZnO nanostructures were grown on FTO substrate using hy-drothermal technique. The UV, PL and I-V characteristics were in-vestigated for the fabricated ZnO nanostructured thin film sensor.The optical band gap calculated from the Tauc plot showed decreasein band gap from the normal ZnO material. This shows increasein conductivity of the fabricated sensor. Electrical characteristicsfrom I-V characterization were calculated. These inferences fromthe calculations revealed the better performance of device takingconductivity in to account. Finally, the fabricated accelerometerwhen subjected to mechanical vibrations produced output voltagewhich proofs the use of the fabricated device in accelerometer ap-plication. Thus the fabricated device can be made to work as aself-powered piezoelectric accelerometer in future for NEMS basedapplications.

References

[1] C. Saayujya , J.S.Q. Tan, Y. Yuan, Y.R. Wong, and H.Du,“Design, fabrication and characterization of a zinc ox-ide thin-film piezoelectric accelerometer”, Intelligent Sensors,Sensor Networks and Information Processing (ISSNIP), IEEENinth International Conference, pp. 1-6, April 2014.

[2] A. Koka and H.A.Sodano, “High-sensitivity accelerometercomposed of ultra-long vertically aligned barium titanatenanowire arrays”, Nature communications,pp. 2682, Novem-ber 2013.

[3] S. Naduvinamani and N.C.Iyer,“Design and simulation of PZTbased MEMS piezoelectric accelerometer”, In Electrical, Elec-tronics, and Optimization Techniques (ICEEOT), Interna-tional Conference, pp. 3715-3721, March 2016.

[4] Ramadan, S. Khaled, D. Sameoto, and S. Evoy,“A review ofpiezoelectric polymers as functional materials for electrome-chanical transducers”, Smart Materials and Structures, vol.23,no. 3, pp. 033001, January 2014.

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[5] H. Bardaweel , O. Al Hattamleh, R. Richards, D. Bahr, and C.Richards, “A comparison of piezoelectric materials for MEMSpower generation”, In The sixth International Workshop onMicro and Nanotechnology for power generation and energyconversion applications, pp. 207-210, 2006.

[6] L. Guo, Y.L. Ji, H. Xu, , P. Simon, and Z. Wu , “Regularlyshaped, single-crystalline ZnO nanorods with Wurtzitestruc-ture”, Journal of the American Chemical Society, vol. 124, no.50, pp.14864-14865, December 2002.

[7] S.C. Lyu, Y. Zhang, C.J. Lee, H. Ruh, and H.J. Lee, “Low-temperature growth of ZnO nanowire array by a simple physi-cal vapor-deposition method”, Chemistry of materials, vol.15,no. 17 ,pp. 3294-3299, August 2003.

[8] R.B.M. Cross, M.M. De Souza, and E.S. Narayanan,“A lowtemperature combination method for the production of ZnOnanowires”, Nanotechnology, vol.16, no. 10 ,pp. 2188, August2005.

[9] S.M. Hatch, A. Sapelkin , G. Cibin, R. Taylor, A.Dent, J.Briscoe, and S. Dunn, “Investigating the source of deep-levelphotoluminescence in ZnO nanorods using optically detectedx-ray absorption spectroscopy”, Journal of Applied Physics,vol.114, no. 15 ,pp.153517, October 2013.

[10] N. Bao, L. Shen , G. Srinivasan, K. Yanagisawa, and A.Gupta, “Shape-controlled monocrystalline ferroelectric bariumtitanate nanostructures: from nanotubes and nanowires toordered nanostructures”, The Journal of Physical ChemistryC,vol.112, no. 23 ,pp.8634-8642, May 2008.

[11] X. Xue, Y. Nie,B. He, L. Xing, Y. Zhang, and Z.L. Wang,“Surface free-carrier screening effect on the output of a ZnOnanowire nanogenerator and its potential as a self-powered ac-tive gas sensor”, Nanotechnology, vol. 24, no. 22, pp.225501,April 2013.

[12] E.Galoppini, J. Rochford, H. Chen, G. Saraf, Y. Lu, A.Hagfeldt, and G. Boschloo, “Fast electron transport in metal

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organic vapor deposition grown dye-sensitized ZnO nanorodsolar cells”, The Journal of Physical Chemistry B, vol.110, no.33 , pp.16159-16161, August 2006.

[13] Y. Ling-min, F. Xin-hui, S. Jing-yi, and Y. Wen,“Shape-controlled cluster growth of ZnO nanoflowers using solgelmethod”, Micro & Nano Letters, vol.7, no. 10, pp.1046-1048,October 2012.

[14] Z.L. Wang, and J. Song,“Piezoelectric nanogenerators basedon zinc oxide nanowire arrays”, Science ,vol.312, no. 5771,pp.242-246, April 2006

[15] X.D. Bai, P.X. Gao, Z.L. Wang, and E.G. Wang, “Dual-modemechanical resonance of individual ZnO nanobelts”, AppliedPhysics Letters vol.82, no. 26, pp. 4806-4808, June 2003.

[16] K. Savarimuthu, G. Rajamanickam, R. Shankararajan, R. Pe-rumal, and A. Rayarfrancis, “Experimental Study on FlexibleZnO Based Nanogenerator Using Schottky Contact for EnergyHarvesting Applications”, IEEE Transactions on Nanotechnol-ogy,vol. 16, no. 3 ,pp. 469-476, May 2017.

[17] S. Murugesan, R. Shankararajan, K .Savarimuthu, K .Ramany,G. Rajamanickam, S. Narendhiran, and R. Perumalsamy, “Ef-fect of Precursor Concentration on Structural, Morphological,and Optical Properties of ZnO Thin-Filmed Sensor for EthanolDetection”, IEEE Transactions on Nanotechnology, vol.17, no.1, pp. 169-176, January 2018.

[18] B. Yaghootkar, S. Azimi, and B. Bahreyni, “A High-Performance Piezoelectric Vibration Sensor”, IEEE SensorsJournal ,vol.17, no. 13 ,pp. 4005-4012, July 2017.

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