MEMS and Nanotechnology Research at TST

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1 MEMS and Nanotechnology Research at TST Remco Wiegerink Theo Lammerink Marcel Dijkstra Jeroen Haneveld MESA+ Institute for Nanotechnology University of Twente P.O. Box 217, 7500 AE Enschede The Netherlands GERG Academic Network Event

2 Outline Introduction to MEMS MEMS flow sensors Thermal flow sensors Coriolis flow sensors Gravity sensors/acceleration sensors Conclusion GERG Academic Network Event

3 Micromechanics Anisotropic Wet Chemical Etching Isotropic Wet Chemical Etching KOH-Etching Reactive Ion Etching Hillocks DEEMO PowderBlasting PZT Chemical-Mechanical Polishing Surface Micromachining May 27, 2009 Waferbonding 3

4 Introduction to MEMS GERG Academic Network Event

5 Micromachining example SiO 2 deposition (sacrificial layer) SiO 2 structuring p-silicon deposition p-silicon structuring Selective SiO 2 etching and release A B C D E GERG Academic Network Event

6 Why silicon? Strong material Ideal spring no creep no hysteresis Batch fabrication Strain (%) 4 2 Steel 2 4 Silicon 6 Stress (Gpa) Integration with electronics? Brittle material? Silicon load cell 1000 kg at 1 cm 2 GERG Academic Network Event

7 Thermal flow sensors GERG Academic Network Event

8 Thermal flow sensors Examples outlet inlet bensor beam GERG Academic Network Event

9 Surface micromachined channels Easy integration of sensor elements on top of the channels Sensor elements isolated from fluid Removing the bulk silicon results in free-hanging channels Limited channel height results in high pressure drop GERG Academic Network Event

10 Surface channel technology M. Dijkstra et al, "Miniaturized flow sensor with planar integrated sensor structures on semicircular surface channels," MEMS 2007, Kobe, Japan, January 2007, pp GERG Academic Network Event

11 Fabrication process GERG Academic Network Event

12 Making free hanging tubes GERG Academic Network Event

13 Typical measurement results P = 3 mw GERG Academic Network Event

14 Thermal flow sensors Extremely sensitive picoliter/minute resolution Relatively easy fabrication & readout Problem: Drift Drift in heating resistors: Use power control Drift in temperature sense resistors: Use a thermopile Use AC signals Problem: Sensitive to fluid parameters like density, thermal conductivity, viscosity. GERG Academic Network Event

15 Flow & viscosity sensor δx xfd,h J.J. van Baar, W.A. Verweij, et al, "Micromachined two dimensional resistor arrays for determination of gas parameters," Transducers 2003, vol. 2, pp , GERG Academic Network Event

16 Viscosity sensor May 27,

17 Micro Coriolis mass flow sensor r v r F = 2L ω M c f GERG Academic Network Event

18 Micro Coriolis mass flow sensor Advantages: Independent of: flow profile density temperature viscosity pressure homogeneity Less external mechanical influences due to low system mass/high resonance frequency Disadvantages: Higher stiffness + lower mass flow lower signal High manufacturing accuracy necessary GERG Academic Network Event

19 Processing results GERG Academic Network Event

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22 Mounted chip GERG Academic Network Event

23 Vibrometer measurements GERG Academic Network Event

24 Vibrometer measurements No flow Max. flow GERG Academic Network Event

25 Electronics GERG Academic Network Event

26 Mass flow measurements GERG Academic Network Event

27 Density measurements 1/f 2 [Hz -2 ] 3.25E E-07 water 3.15E E E E E E-07 white gas 2.85E E-07 ethanol 2.75E medium density [g/cm 3 ] GERG Academic Network Event

28 Accelerometers, gravity (gradient) sensors Basic accelerometer structure: Vibration sensing / seismology Gravity measurement in boreholes Two accelerometers: gravity gradient sensing GERG Academic Network Event

29 Accelerometer structure with large proof mass Thickness: Top layer: 25 um Proof mass: 450 um Proof mass: 4 x 4 mm 17 microgram Springs: Width: 3 um Length: mm Spring constant: N/m Capacitance: 20 pf Fixed frame Trench through wafer Proof-mass

30 Accelerometer structure with large proof mass ~30 µm Proof-mass 4 mm May 27, 2009 Wafer thickness ~500 µm Moving sensing finger Folded beam spring Fixed sensing fingers ~3 µm ~450 µm Fixed frame 30

31 Interested? Visit us at: University of Twente MESA+ Institute for Nanotechnology Research group: Transducers Science and Technology Enschede, The Netherlands Building: Carré The authors would like to thank the Dutch Technology Foundation STW, the Dutch MicroNed program, the Point-One project MEMSLand and the PIDON- HTF program for financial support. GERG Academic Network Event