ROCHESTER INSTITUTE OF TECHNOLOGY MICROELECTRONIC ENGINEERING Impact-Tek, LLC, Oil Sensors Phase 2, Design Review Dr. Lynn Fuller Ivan Puchades Webpage: http://people.rit.edu/lffeee 82 Lomb Memorial Drive Rochester, NY 14623-5604 Email: Lynn.Fuller@rit.edu Department webpage: http://www.microe.rit.edu This research was funded in part by CEIS, a NYSTAR-designated Center for Advanced Technology 9-30-2008 Oil_Sensors.ppt Page 1
OUTLINE Introduction Statement of Work 1 st Interdigitated Capacitive Sensor on Silicon 2 nd Sensor on Quartz Understanding Measured Results Theoretical Modeling Multisensor MEMS Chip Measured Results from Multisensor MEMS Chip Proposed Design of New MEMS Chip (Phase Two) Summary References Appendix: Fabrication Details Stepper Job Wafer Saw Recipes MEMS Fabrication Sequence Page 2
INTRODUCTION The objective of this project is to investigate the design and fabrication of Microelectromechanical systems (MEMS) based sensors for assessing the quality of oil. We will use RIT s interdigitated electrodes with Impact s patented broadband electrochemical impedance spectroscopy (EIS) interrogation of oil paired with direct temperature and relative humidity (RH) measurements. If the initial investigation shows that such a device can work we will design integrated sensors for EIS, temperature and RH in one MEMS device. Funding from Impact-Tek, LLC (Phase 1 and possibly Phase 2, each 3 months) and NYSTAR (1 to 2 matching money for up to 1 year) Page 3
DELIVERABLES Page 4
FLOWTONICS SENSOR Page 5
RIT CHEMICAL SENSOR LAYOUT 2005 (5120µm, 4610µm) 20 fingers 50µm width 50µm space 1000µm length (0,0) Page 6
1 ST TRY RIT s first oil sensor is gold/chrome interdigitated fingers on oxide/silicon wafer. Page 7
SENSOR CHIPS FROM QUARTZ WAFER RIT s 2nd oil sensor is Chrome interdigitated fingers on Quartz wafer. 20 fingers 50µm width 50µm space 1000µm length Page 8
VIRGIN PREMIUM BLUE RIT MEMS Sensor Coaxial interconnect wires Page 9
VIRGIN MIL RIT MEMS Sensor Coaxial interconnect wires Page 10
1% SOOT MIL RIT MEMS Sensor Coaxial interconnect wires Page 11
EXPORTED DATA IS USED TO GENERATE PLOT EIS MEASUREMENT 4.5E+09 4.0E+09 3.5E+09 3.0E+09 Im(Z) 2.5E+09 2.0E+09 1.5E+09 1.0E+09 5.0E+08 0.0E+00 0.0E+00 1.0E+09 2.0E+09 3.0E+09 4.0E+09 5.0E+09 6.0E+09 7.0E+09 8.0E+09 9.0E+09 1.0E+10 Re(Z) Virgin Mil 1% Soot Mil Page 12
UNDERSTANDING EXPERIMENTAL RESULTS Sensor on silicon substrate in Air Sensor on quartz substrate in Air Sensor on quartz substrate in oil Sensor on quartz in oil with 1% soot Page 13
MATERIAL PROPERTIES Name Symbol er Rho TCE Q ohm-cm ppm/ C w/cmk Silicon Si 11.7 0.0001-1E15 2.4 1.5 Poly Silicon Si 11.7 0.0001-1E15 2.4 1.5 Silicon Dioxide SiO2 3.9 ~1E15 0.3 0.014 Quartz SiO2 3.9 ~1E15 0.3 0.014 Chrome Cr - 13.5E-6 0.90 Gold Au - 2.25 3.19 Aluminum Al - 2.73 22 2.36 Polyimide Polyimide 2.8 Air Air 1 0.00026 Oil Oil 3 Water H2O 84 0.0061 Gasoline Gas? e = e o e r eo = 8.85E-12 F/m Page 14
MODELING OF INTERDIGITATED CAPACITOR N = number of fingers d 1 d1 and d2 (interrogation depth) e r1 d 2 e r2 e r = e r1 + e r2 Page 15
ELECTRIC FIELD SIMULATIONS USING COMSOL COMSOL is a software package for simulation of electric and magnetic fields, thermal and mechanical stress and strain, and more. We are still working on this but we think that thin lines with small w and s can be modeled by interrogation depths approximately equal to s. This implies that if we build interdigitated sensors on thin films of oxide on silicon the spacing should be chosen to be equal or smaller than the oxide thickness in order to eliminate the effect of the silicon substrate. For example: a three micrometer oxide and two micrometer space should work. We think that the oil sample that we are measuring is of similar dimensions. For this example we would measure a two micrometer depth of oil on the sensor. Page 16
PLANAR INTERDIGITATED SENSOR 1 C = ( N 1) L ( e r 1 e r 2 ) e 0 K [( 1 2 K ( k ) k 2 ) 2 ] e r1 k = cos 2 ( s w w ) d 1 d 2 e r2 K ( k ) = 1 0 1 dt 2 2 2 1 t 1 k t e r = e r1 + e r2 Jo is zero order Bessel function V.F.Lvovich, C.C.Liu, M.F.Smiechowski Page 17
MODELING OF INTERDIGITATED CAPACITOR Capacitance for very Thin Interdigitated Fingers Capacitance, C = 8.57E-13 F Number of Fingers, N = 20 relative dielectric constant, er = 4.9 Length of finger overlap, L = 1000 µm er = er1 + er2 width of fingers, w = 50 µm space between fingers, s = 50 µm Capacitance Between Two Closely Spaced Wires Capacitance per unit length, C = 13.95 pf/m relative dielectric constant, er = 3 half center to center space, h = 100 mm conductor radius, r = 0.5 mm Capacitance of a Coaxial Cable Capacitance per unit length, C = 51.80 pf/m relative dielectric constant, er = 3 radius of outer conductor, b = 5 mm radius of inner conductor, a = 0.2 mm Page 18
FINGERS ON SILICON SUBSTRATE N=20 L=1mm S=50µm W=50µm Silicon Substrate C measured = 100 pf R measured = variable 3 to 9 Meg Ohm Gold Chrome SiO 2 Silicon Gold Chrome 1000Å 300Å 5000Å er=11.7 C calculated = C fingers + C to substrate + C of leads = 2.22 pf + 69 pf + 20 pf = ~91 pf R calculated = infinite (silver epoxy making contact to the silicon substrate which is semi-conductive) Page 19
FINGERS ON QUARTZ SUBSTRATE N=20 L=1mm S=50µm W=50µm Quartz Substrate C calculated = C fingers + C to substrate + C of leads = 0.8 pf + 0 pf + 0 pf = ~ 0.8 pf zero the meter C calculated of close 16 leads = 14.6pF, measured = 10.1 pf C calculated of spread 16 leads =??, measured = 0.9 pf C calculated of short spread leads =??, measured 0.2 pf R calculated = infinite C measured = 0.8 pf R measured = over range at DC Gold Chrome SiO 2 Quartz Gold Chrome 1000Å 300Å 5000Å er=3.9 Page 20
EIS MODELING BASICS Nyquist Plot Imag Z vs. Real Z -ImZ Increasing C R/2 Z Z = R R 1 j C 1 j C = Z = R j CR + 1 R Note: Rochester to Institute get of a Technology full curve, need data points for two decades above 1/RC and two decades below 1/RC Theta R/2 @ = zero, ReZ = R, ImZ=0 @ = 1/(RC), ReZ= R/2 = -ImZ @ = large, ReZ=0, ImZ=-1/ C R = 2 f ReZ Page 21
EIS MODELING BASICS (CONT.) Simulation Test Frequencies, = o/100, 2 o/100, 3 o/100.10 o/100, 20 o/100, 30 o/100. 100 o/100 o, 1.1 o, 1.2 o, 1.3 o 2 o, 3 o, 4 o 10 o.100 o, where o = 1/RC -ImZ = o Z C R R/2 R/2 Increasing ReZ R R large R medium R smaller R is the maximum value of ReZ at lowest C can be found by finding where ImZ is maximum, and set equal to 1/RC Page 22
MODELING VIRGIN PREMIUM BLUE Actual Test Frequencies f =1 1.2 1.6 1.8 2.1 2.5 2.9 3.4 4 4.6 5.4 6.3 7.4 8.6 10 12 14 16 18 21 25 29 34 40 46 54 63 74 86 100 140 160 210 250 290 340 400 460 540 630 f = 740 1..to 8600 1000 1200 1400 hz 1600 1800 2100 2500 2900 3400 4000 4600 5400 6300 7400 8600 Measured: R=4e9 ohm, C=1.6pF, fo = 25hz N=20 L=1mm S=50µm W=50µm Calculated: R = infinite C = 1.2pF (spread sheet) fo = 1/(2 RC) = 0 = 1/(2 4E9(1.2e-12)) = 33 hz Page 23
MORE ADVANCED MODEL FOR SENSOR Measured: R=4e9 ohm, C=2.1pF, fo = 25hz Z Cb Rb Ci Ri Cb = Bulk Capacitance, 1.2 pf (spread sheet) Rb = Bulk Resistance, 3000M (fit to make ImZ match) Ci = Interface Capacitance, very thin 35nm, 50 pf (spread sheet) Ri = Interface Resistance,1000M (fit to make Rdc match) Page 24
WHAT WE LEARNED Parasitic capacitance needs to be kept small Insulator under the sensor, thickness > S Leads need to be kept small, separated, shielded We can extract R from DC resistance (low freq. ReZ) We can extract C from frequency at ImZ equal maximum Oxide under fingers should be thicker than spacing Finger width should be small to reduce Ci (interface) Finger length should be long (or many fingers) Page 25
MULTI-SENSOR MEMS MICROCHIP Photo Diode Diffused Heater Actuator Pressure Sensor Humidity Sensor Chem. Capacitor Diode Temperature Sensor Page 26
PHOTO OF SINGLE CHIP Page 27
RIT MEMS SENSOR CALCULATIONS N = 20 L = 2.76 mm S = 20 µm W = 20 µm er = 3.9 +1 C = 2.36 pf in air Page 28
PCB FOR MMC TO BE USED IN GEN-4 PACKAGE PCB Layout Packaged Humidity Sensor Packaged Oil Sensor Page 29
OIL SENSING TEST RESULTS Page 30
HUMIDITY SENSOR TEST RESULTS In Bottle In Air In Bottle In Bottle We put a small quantity of water in a 1000ml bottle. The sensor was put into the bottle and the capacitance increased, when removed from the bottle the capacitance decreased. In Bottle Page 31
HUMIDITY SENSOR TEST RESULTS (more) 500 ppm water in oil, we saw very small change in capacitance ~1pF Page 32
SUMMARY We did a literature search,.pdf versions of documents (on CD) Evaluation of Interdigitated Capacitive Sensors (ICS) Theoretical Modeling ICS Theoretical Modeling of EIS Design of a Multisensor MEMS Chip (MMC) Fabrication of First MMC Testing of First MMC Started Proposed Next MMC Design Proposed a Plan of Work for Phase Two Page 33
REFERENCES 1. J. S. Kim and D. G. Lee, "Analysis of dielectric sensors for the cure monitoring of resin matrix composite materials," Sensors and Actuators B, 30, 159-164, 1996. 2. Timmer, Sparreboom, Olthuis, Bergveld and van de Berg, Optimization of an electrolyte conductivity detector for measuring low ion concentrations, Lab Chip, 121-124, 2002. 3. V. F. Lvovich, C. C. Liu and M. F. Smiechowski, Optimization and fabrication of planar interdigitated impedance sensors for highly resistive non-aqueous industrial fluids, Elsevier B. B., Jan. 2006. 4. C. Byington, R. Brewer, V. Nair, A. Mott, Experiences and testing of an autonomous on-line oil quality monitor for diesel engines, Impact Technologies, LLC, 2007. 5. Dr. Fuller s Web Page, http://people.rit.edu/lffeee 6. P. M. Harrey, B. J. Ramsey, P. S. A. Evans and D. J. Harrison, Capacitive-type humidity sensors fabricated using the offset lithographic printing process, Department of Design, Brunel University, Runnymede Campus, Egham, Surrey, UK, Available online 12 Sept. 2002. Page 34
REFERENCES (cnt d) 7. D. Sparks, D. Goetzinger, D. Riley and N. Najafi, A by-pass sensor package design enabling the use of microfluidics in high flow rate applications, ASME International Mechanical Engineering Congress and Exposition, November 2006, Chicago, IL, 1-5, 2006. 8. S. Jagannathan and G.V.S. Raju, Remaining Useful Life Prediction of Automotive Engine Oils Using MEMS Technologies, American Control Conference, Chicago, IL, 3511-3512, 2000. 9. D. Sparks, R. Schneider, R. Smith, A. Chimbayo, M. Straayer, J. Cripe and N. Najafi, In-line chemical concentration sensor, Sensor Exposition and Conference Spring 2003, Chicago, IL, 2003. Page 35