Andruszkiewicz, Leanne

Hesketh, Peter J.

English

Scholarly Materials And Research @ Georgia Tech

Project Report 	 February 26 th 2008 Fabrication of Corrosion Monitoring Cantilever Sensors By Leanne Andruszkiewicz and Peter J. Hesketh Woodruff School of Mechanical Engineering, Georgia Institute of Technology Submitted to William England, Purafill Inc., 2654 Weaver Way, Doraville, GA 30340 Cantilever Sensor Figure 1 shows a SEM micrograph of an array of cantilever sensors with piezoresistive strain gauges. These sensors are described fully in the papers published by our group [1], [2] and in the dissertation of Arnab Choudhury [3]. Several sensors have been coated with a thin layer of copper or silver to accommodate corrosion sensing principle. The thickness of the copper and silver is approximately <100nm. The sensor resistance values were measured prior to delivery to Purafill. They are listed in table 1. Some of the sensors on each die are not functional; the devices highlighted in yellow are working devices. An instrument box has been loaned to Purafill for measurement of the cantilever sensors. Figure 3 shows schematic diagram of the circuit building blocks. A constant current of approximately 200uA is supplied to each sensor. A buffer outputs a voltage in proportion to the resistance value of the sensor, as indicated in Figure 4. This calibration curve was measured with the instrument box supplied. Finally the temperature of the sensor (and its resistance) is a function of the flow rate, see Figure 5. However, by monitoring a coated sensor and uncoated sensor (silica surface) the difference in resistance for surface stress and temperature compared to just temperature changes can be distinguished. The coated sensor responds to surface stress and temperature, while the uncoated sensors just respond to just temperature. 1 Temperature-Resistance Calibration 8000 7500 7000 a) U 5s 6500 0; a) CC 6000     y = 8.219*x + 5363 5500   50000 	50 	100 	150 	200 	250 	300 Temperature ( °C) Figure 1: SEM picture of (A) sensor array and (B) individual cantilever sensor. Figure 2: Temperature calibration for a typical cantilever sensor. 2 Table 1: List of sensor resistance values. Device Number Cantiliever 1 2 1 	4 5 	61 	7 8 9 10 19 300 x 300 	300 x x Exp Reistance 300 300 300 300 300'300 1 300 x 	x 	x Actual Resistance x x x x 26 400 x 350 	300 550 	500 x 3.78 x 5.84 400 350 300 4.4 x 	3.3 good Exp Reistance 550 500 Actual Resistance x x 12 good Exp Reistance 300 3001 300 3001 	300 300 300 300 300 300 x Actual Resistance x 4.71 1x 4.8 	4.85 2.6 4.82 2.6 x 32 1  400 	400 400 4.3 	4.33 	4.3 400 4.25 400 400 400 4.3 x 	4.4 Exp Reistance 400 400400 2252 2190 Actual Resistance 2.17 28 400 	400 	400 4.36 	4.26 	4.23 400 	400 400 	400 4.2 	4.21 	4.2 	2.14 1.  400 400 1 410 4.2 x x good good _good Exp Reistance Actual Resistance 22 200 	200 	200 2.21 	2.23 	2.22 200 	200 200 	200 2.1 	2.14 	2.2 200 200 200 2.2 	2.3 Exp Reistance Actual Resistance 231 1 300 	300 300 	300 x x 3.1 	3.15 300 300 300 32 	3.4 	3.2 Exp Reistance 300 300 300 Actual Resistance x x 	x 113 375 	300 4.12 	3.6 260 	225 425 	375 2.9 	2.46 	4.6 	4.12 300 260 225 3.3 	2.9 	2.5 good Exp Reistance 425 x Actual Resistance 31 275 	250 	200 175 	150 275 	250 1.68 x 1.24 x 	x 3.1 	2.74 200 175 150 2.3 	1.9 	1.7 good good Exp Reistance Actual Resistance 33 1 300 x 300 	300 300' 	300 x x x 	,x ,x 300 300 300 x 	x Exp Reistance 300 x 300 x Actual Resistance 30 200 	200 	200 2.1 	1.34 	2.23 200 	200 200 	200 200 200 200 2.2 	2.2 	2.2 	2.2 x 	x 	,x Exp Reistance Actual Resistance 33 300 3001300  cracked 3001300 300 Exp Reistance Actual Resistance . 	300 300 300 300 3 Variation of Resistance is converted to Cor r esponding Voltage Measu red R Did One-chamiel of the fabricated chip WY MN woo awg vw, Figure 3: Block diagram of measurement interface for 10 sensors that converts the resistance to an output voltage. A constant DC current is supplied to each sensor of approx 200uA. Resistance Vs. Voltage y = -0.1609x + 3.6081 RT + 0 986 3.2 31 0 4. 2.9 2.8 2.7 2.6 25 	3 	3 5 	 4 	 4.5 	5 	5.5 	 6 Resistance (kohms) Figure 4: Calibration curve of instrumentation box. 4 120 0 2 100 0_) 80 E a) F- 60 No Flow-N 2 2 sccm-N 2  5 sccm-N 2 8 sccm-N 2 No Flow-He 2 sccm-He 5 sccm-He — 8 sccm-He  	i 	ei 4, 9/ 	 0.4 I 	 ri Of r,Alf 	* 2, r,r,  0 re' 10C 	41, Wer 200 6 	8 	10 	12 	14 	16 Input Voltage (V) Figure 5: Temperature of sensor (calculated from resistance calibration curve, figure 2 above) as a function of nitrogen and helium flow rate. References [1] A. Choudhury, P. J. Hesketh, Z. Hu, T. Thundat, "A piezoresistive microcantilevers array for surface stress measurement: Curvature model and fabrication," Journal of Micromechanics and Microengineering, vol. 17, pp. 2065-2076, 2007. [2] A. Choudhury, P. J. Hesketh, Z. Hu, T. Thundat, "Low noise chemical detection with a Piezoresistive Microcantilever," Transactions of the ECS, vol. 2, pp. 473-482, 2006. [3] A. Choudhury, P. J. Hesketh, "A Piezoresistive Microcantilever Array for Chemical Sensing Applications," in Mechanical Engineering. vol. Ph.D. Atlanta: Georgia Institute of Technology, 2007, p. 178. 5 160 140 40 /41 

Fabrication of corrosion monitoring cantilever sensors

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Fabrication of corrosion monitoring cantilever sensors

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