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Tungsten micro-heater resistance (Ω)200198500 o C196194192190400 o C1880 20 40 60 80 100Time (hour)Fig. 9. Tungsten micro-heater resistance change with time.0.524-26 September 2008, Rome, Italyinto account, it was found that the drift in the thermodiodeforward voltage was only 1-2mV (~1°C) (shown in Fig. 10).The relative change comparison between ΔR/R (for tungstenmicro-heater) and ΔV/V (for thermodiode) is shown in Fig. 11(a) and (b). It confirms that the performance of thethermodiode temperature sensor is more reliable than tungstenRTDs, which might suffer from electro-migration andpiezoresistive effect (as the stress increases with temperature).ΔR/R, ΔV/V (%)43210-1Change in resistance of tungsten micro-heaterChange in voltage of the thermodiode400 o CForward voltage drop (V)0.40.30.20.1500 o CMeasured forward voltage dropCorrected forward voltage drop400 o C-22015100 20 40 60 80 100Time (hour)(a)Change in resistance of tungsten micro-heaterChange in voltage of the thermodiode0.00 20 40 60 80 100Time (hour)Fig. 10. Long term continuous operation of thermodiode at 400 and 500°C for100 hours. The first curve (black) is the measured forward voltage drop acrossthe thermodiode. The second curve (red) has been corrected by taking intoaccount the temperature change (due to the change in micro-heater resistance)to more accurately represent the thermodiode characteristic.thermodiode. However, for this study, we did not take intoaccount the indirect effect of stress caused by the thermalcycling during operation on both the membrane itself and thedie attach to the package. We have also ignored any effect ofmoisture at these high temperatures. The maximum deviationsin the thermodiode forward voltage over the 100 hour timeperiod were 10mV (~7°C) and 48mV (~40°C) for 400 and500°C respectively. A more detailed investigation showed thatthis change was not due to a change in the thermodiodeparameters, but due to an increase in the resistance of thetungsten micro-heater (shown in Fig. 9) which caused acorresponding increase in the actual temperature. Taking thisΔR/R and ΔV/V (%)5500 o C0-5-10-15-200 20 40 60 80 100Time (hour)(b)Fig. 11. Relative change in tungsten micro-heater resistance andthermodiode voltage with time at (a) 400°C and (b) 500°C.V. CONCLUSIONIn this paper the performance and long term stability of a SOI©EDA Publishing/THERMINIC 2008 198ISBN: 978-2-35500-008-9