THIN FILMS MEASURED BY USING FOUR- POINT PROBE METHOD

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Average Electrical conductivity(mho/m)Average electrical resistivity(m)KATHMANDU UNIVERSITY JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGYVOL. 8, No. II, DECEMBER, 2012, pp 31-36RESULTS AND DISCUSSIONSThe variation of electrical resistivity with films thickness is shown in Figure- 3. It shows thatwith increase of thickness of Al thin films, the resistivity decreases. Fig. 4 shows the plot ofconductivity as a function of film thickness. Similarly, sheet resistance decreases when filmsthickness increases as shown in Fig. 5. These values obtained for the thin films differ fromthe bulk values. Thus, the electrical resistivity, conductivity and sheet resistance of aluminumthin films were measured and compared with bulk value. Table 1 shows the results of averageelectrical resistivity, average electrical conductivity and average sheet resistance which weredetermined for aluminum thin films of different thicknesses.9.0x10 -78.0x10 -7ExperimentalFitted7.0x10 -76.0x10 -75.0x10 -74.0x10 -73.0x10 -70.14 0.16 0.18 0.20 0.22 0.24Thickness of Al Thin Film(m)Fig 3. Variation of average electrical resistivity (ρ) with thickness of Al thin films3.5x10 63.0x10 6ExperimentalFitted2.5x10 62.0x10 61.5x10 61.0x10 60.14 0.16 0.18 0.20 0.22 0.24Thickness of Al Thin Films(m)Fig 4: Variation of average electrical conductivity (σ) with thickness of Al thin films34

KATHMANDU UNIVERSITY JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGYVOL. 8, No. II, DECEMBER, 2012, pp 31-366Average Sheet resistance()5432ExperimentalFitted10.14 0.16 0.18 0.20 0.22 0.24Thickness of Al Thin Films(m)Fig 5: Variation of average sheet resistance (R s ) with thickness of Al thin filmsTable 1. Average electrical resistivity, average electrical conductivity, sheet resistance andthickness of Al thin filmsS.N.Al thinFilmssamplesThicknessof Al Thinfilms d(µm)Average ElectricalResistivity ρ(Ωm)Average ElectricalConductivityσ(mho/m)AverageSheetResistanceR s (Ω)1 S 1 0.225 31.28×10 -8 ±4.0×10 -8 3.20×10 6 ±0.82×10 6 1.39±0.172 S 2 0.1775 68.64×10 -8 ±7.35×10 -8 1.46×10 6 ±1.46×10 6 3.88±0.423 S 3 0.1822 61.07×10 -8 ±13.80×10 -8 1.64×10 6 ±0.21×10 6 3.35±0.754 S 4 0.1483 83.42×10 -8 ±11×10 -8 1.20×10 6 ±0.14×10 6 5.62±0.745 S 5 0.1900 62.39×10 -8 ±7.02×10 -8 1.60×10 6 ±0.16×10 6 3.08±0.376 S 6 0.2150 51.82×10 -8 ±11.56×10 -8 1.93×10 6 ±0.24×10 6 2.41±0.547 S 7 0.1650 67.63×10 -8 ±7.66×10 -8 1.48×10 6 ±0.10×10 6 4.10±0.46Unlike the properties of bulk materials, the resistivity, conductivity and sheet resistance in thethin film depends on several factors such as rate of deposition, thickness, temperature andgrain boundaries between others[8]. As the thickness of the film decreases, the electroncollisions with surfaces become important . Such confinement effect due to film thickness isclearly observed on Al thin films whose electrical resistivity values are higher than bulk.Aluminum usually presents a native oxide film (Al 2 O 3 ) when exposed to atmosphericpressure, which changes substantially its surface properties[8]. As can be seen in Table1, the35

KATHMANDU UNIVERSITY JOURNAL OF SCIENCE, ENGINEERING AND TECHNOLOGYVOL. 8, No. II, DECEMBER, 2012, pp 31-36measured ρ, σ and R s values show variation with thickness. The analysis and behavior of theoxide layer in aluminum films require a more detailed study and will be the subject of anotherwork.CONCLUSIONWe have studied the resistive properties of Al thin films with thickness between 0.1483 µmto 0.225 µm deposited on glass substrates. A methodology to characterize metallic thin filmsand to measure electrical properties as a function of thickness is discussed. The electricalresistivity measured on Al thin films is larger than those measured in bulk. The present studywill be extended in future to investigate the optical and mechanical properties.REFERENCES[1] Chopra K L, Thin Film Phenomena MC Graw Hill Co., New York, USA, (1969).[2] Maissel L I & Glang R, (eds) Hand book of Thin Film technology, MC Graw HillCo., New York, USA, (1970).[3] Ohring M, Engineering Material Science, Academic Press, Salt Lake City, USA,(1995).[4] Eckertov’a L, Physics of Thin Films ,Plenum Press, New York, USA, (1986)[5] Ohring M, Materials Science of Thin Films , Academic Press , Salt Lake City,USA, (2002).[6] Pulker H K, Coatings on Glass, Elsevier, Ave New York ,USA,(1999).[7] Oliva A I ,Quintana P Ceh O, Corona J E & Aguilar M ,Thin Solid Film, Elsevier, 353(1999)1.[8] Oliva A I, Aviles F& Ceh O, Physical properties of AU and AL thin films measuredby resistive heating, Surface Review and Letters, Vol.12, No.1(2005),101- 106,WorldScientific Publishing Company.36