Comparative Study on Temperature Coefficient of Resistance (TCR) of the E-beam and Sputter Deposited Nichrome Thin Film for Precise Temperature Control of Microheater for MEMS Gas Sensor
Nichrome (Ni–Cr 80/20 wt %), alloy of Ni and Cr is used as a microheater element of the MEMS microhotplate embedded in the metal oxide based gas sensor. Nichrome is used as a heater element for its unique properties like high resistivity, low cost, low Temperature Coefficient of Resistance (TCR), anti oxidant, anti corrosive nature, no need for extra adhesive layer as required for Pt or Au and also compatibility with standard silicon fabrication technology. Microheater with low TCR is the very important property to avoid localized hotspot and precisely controlling the active area temperature of the microhotplate for sensing the gases at different temperature. In this paper, Temperature Coefficient of Resistance (TCR) of the thin film of nichrome was studied by depositing two popular physical vapor deposition (PVD) methods one is Electron Beam Evaporation and other is DC Sputtering. The TCR parameter was extracted by placing the resistor in wafer level on the thermal chuck and measurement was done by varying the temperature of the thermal chuck using ATT System from room temperature up to 200 °C and measuring the resistance of the microheater using Agilent 4284A LCR meter. The structural characterization was carried out for finding the grain size and elemental composition of Ni/Cr of the as-deposited thin film using FESEM and EDX respectively. The effect of annealing at 300 °C temperature in N2 ambient of the e-beam deposited nichrome thin film on the TCR was also analyzed.
KeywordsNichrome Microhotplate TCR PVD
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Director, CSIR-CEERI, Pilani Dr. Chandra Shekhar is thanked for his constant encouragement and support. FESEM images were taken at JMI New Delhi for analyzing the grain size of Nichrome thin film. This work is related to 12th five year (2012-2017) plan project on MEMS gas sensors platform-II (WP-5) at CSIR-CEERI.
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