Faculty Publications
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Item Pulsed DC magnetron sputtered titanium nitride thin films for localized heating applications in MEMS devices(Elsevier B.V., 2018) M.a, M.A.; Lakshmi Ganapathi, L.G.; G N V R, V.; Udayashankar, N.K.; Mohan, S.Titanium nitride (TiN) thin films are deposited on Si/SiO2 substratesby using Pulsed DC magnetron sputtering and are characterized for their structural, mechanical and electrical properties for their application as localized heating elements in microsystem devices. The influence of substrate temperature on the properties of TiN films has been investigated. The correlation between the structural orientation with mechanical and electrical properties has been established. The films deposited at a substrate temperature of 300 °C have shown better structural, mechanical and electrical properties. This film has been chosen for the fabrication of microheater and its characterization. A maximum temperature of 250 °C is achieved by applying a power of 2.8 W to the microheater. © 2018 Elsevier B.V.Item RF Sputtered CeO2 Thin Films-Based Oxygen Sensors(Institute of Electrical and Electronics Engineers Inc., 2019) Ramshanker, N.; Lakshmi Ganapathi, K.L.; Bhat, M.S.; Mohan, S.In this paper, we report the scalable, high sensitivity, fast response, and low operating temperature Cerium oxide (CeO2) thin film-based oxygen sensors by optimizing CeO2 film thickness. CeO2 thin films of thickness ranging from 90 to 340 nm have been deposited at 400°C using radio frequency (RF) magnetron sputtering on Al2O3 substrates. Ellipsometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) have been used to characterize the CeO2 films for their thickness, structural, compositional/chemical, and surface morphology properties. Gas sensors have been fabricated using CeO2 film as a sensing material and tested in an oxygen gas environment. CeO2 film with an optimum thickness of 260 nm has shown high sensitivity (12.6) and fast response time (?10 s) along with fast recovery time (15 s) at a low operating temperature of 400°C. To the best of our knowledge, these are the best values reported till date for undoped CeO2 thin film-based oxygen sensors. Furthermore, from the sensor's response, it was observed that there was no drifting from the baseline. This superior performance of CeO2 thin film-based oxygen sensor may be attributed to the combination of three factors, i.e., 1) high surface energy and reactivity due to the presence of (200) oriented CeO2 plane; 2) low resistance due to better crystallinity; and 3) perfect stoichiometry with required roughness. © 2001-2012 IEEE.Item Development of titanium nitride thin film microheaters using laser micromachining(Elsevier Ltd, 2022) M.a, M.A.; Lakshmi Ganapathi, K.L.; Ambresh, M.; Nukala, P.; Udayashankar, N.K.; Mohan, S.In this paper, we report the fabrication and characterization of titanium nitride (TiN) thin-film-based microheaters. TiN thin films have been optimized on Si and SiO2 substrates for their optimum electrical resistivities by controlling the process parameters, including argon:nitrogen (Ar:N2) ratio in reactive pulsed DC magnetron sputter (PDCMS) deposition technique. An optical emission spectroscope (OES) was used for monitoring the plasma characteristics at various nitrogen flow rates. The microstructural and surface properties of the TiN films have been investigated and correlated with the electrical properties. It has been observed that the amount of nitrogen flux in the TiN plasma plays an essential role in the microstructural, surface, and electrical properties of the TiN thin films. Micro-heaters have been fabricated with TiN thin films with low electrical resistivity using laser engraving techniques instead of conventional lithographic and micromachining techniques. The TiN microheater has shown excellent performance. A temperature of 406 °C has been achieved by applying an input power of 8 W. This work paves the path for developing scalable and economic TiN microheaters using laser micromachining techniques. © 2021