capacitive pressure sensor
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capacitive pressure sensor






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capacitive pressure sensor Presentation Transcript

  • 1. 1
  • 3. This presentation includes , Figures included Process flow diagram. Photolithography. +ve & -ve photo resist. Fabricated sensor. Root principle. Exp. Setup. Relaxation oscillator. Results. 4
  • 4. Introduction PCBMEMS Technology. FR4. Photo resist. 5
  • 5. PCBMEMS Technology 1. Micro Electro Mechanical Systems (MEMS) The technology of very small mechanical devices Made up of components between 1-100 m in size Consist of a central unit, the P and Micro sensors. Basic techniques are Deposition, Patterning & Etching 6
  • 6. PCBMEMS Technology 2. Materials used Silicon Polymers Metals Ceramics 7
  • 7. PCBMEMS Technology Photo Exposed remaining Copper sensitive to materials covering uv rays etched off Process Block Diagram 8
  • 8. FR4 What is..? Popular And Versatile High Pressure Thermoset. With zero water absorption. Retains insulating qualities in dry & humid conditions. Made of woven fiberglass cloth with an epoxy resin binder 9
  • 9. FR4 Properties Parameter Value Specific gravity/Density 1850 kg/m³ Water Absorption -.125" < .10 % Temperature Index 140 °C Bond Strength > 1000 kg Dielectric strength 20 kV/mm 10
  • 10. FR4 Applications Printed circuit boards Relays Switches Transformers 11
  • 11. Photo resist What is..? A light sensitive material to form patterned coating on a surface. Classified as Positive and Negative Photo resist. 12
  • 12. Photo resist What is..? Positive photoresist: the light exposed portion becomes soluble while the unexposed remains insoluble. 13
  • 13. Photo resist What is..? Negative photoresist: the light exposed portion becomes insoluble while the unexposed is dissolved. 14
  • 14. Photo resist 15
  • 15. Photo resist CHARACTERISTIC POSITIVE NEGATIVE S Adhesion to Silicon Fair Excellent Relative Cost More expensive Less expensive Developer Base Aqueous Organic Minimum Feature <-0.5 m ± 2 μm Step coverage Better Lower Wet chemical Fair Excellent resistance 16
  • 16. Design Principle: Variation in capacitance b/w 2 PCB substrates. Solder paste applied keeps the 2 plates together. Small separation in between yields a large capacitance. Capacitance obtained is converted to frequency. 17
  • 17. Design Principle Substrates etched with copper. Applied pressure deforms the gap. The circuits provided, reads the capacitance. 18
  • 18. Design Capacitance-frequency conversion Capacitance is converted to frequency. Relaxation oscillator is used. Equation: Square wave obtained. Here R=1M 19
  • 19. Fabrication process Photolithography Selectively remove parts of a thin film. Uses light to transfer geometric pattern. Affords exact control of shape & size of the objects. 20
  • 20. Fabrication process Photolithography Cleaning Preparation Photo resist application Exposure and developing Etching Photo resist removal 21
  • 21. Fabrication process Step 1 22
  • 22. Fabrication process Step 2 23
  • 23. Fabrication process Step 3 24
  • 24. Fabrication process Step 4 25
  • 25. Experimental Results Fabricated sensor 26
  • 26. Experimental ResultsAIM : To obtain the relation b/w applied pressure & output frequency A metal chamber gas was glued on the top PCB. Connected it with a regulated pressure source through. A manometer is used to measure the applied pressure. Pressure was varied & the frequencies obtained were read on an oscilloscope 27
  • 27. Experimental Results Experimental Setup 28
  • 28. Experimental Results Pressure was varied & waiting time was given after each. The pressure was varied in the range from 0-3000 mbar. Result is plotted as a function of the applied pressure. 29
  • 29. Experimental Results Measured freq. vs applied pressure 30
  • 30. Experimental Results Calculated capacitance b/w the 2 electrodes as a fn. of applied pressure. 31
  • 31. Advantages Low cost. Ease of integration with electronics. Manufactured in large volumes. Wide range of applications. 32
  • 32. Conclusion Inexpensive fabrication. Relying only on PCB techniques & automated soldering. Applicable in industries. 33
  • 33. Future ScopeThis process along with some modifications may be usedto fabricate other sensors like accelerometers and microfluidic detectors. 34
  • 34. 35
  • 35. Photograph of a PCBMEMS Fabricated Accelerometer 36
  • 36. Cross sectional view 37
  • 37. References IEEE Electron Device Letters 2009, v.30 n.12, p.1293- 1295 A Thesis on Design, Fabrication, and Dynamic Modeling of a PCBMEMS Accelerometer by John E. Rogers. Soldering techniques-UNC Dept. of Chemistry An introduction to thermosets R.Bruce. Prime IBM (retired) / consultant 38
  • 38. References Mask less Lithographic PCB/Laminate MEMS for a Salinity Sensing System D. Fries et al. University of South Florida. Applications of High-Performance MEMS Pressure Sensors Based on Dissolved Wafer Process by Srinivas Tadigadapa and Sonbol Massoud-Ansari Integrated Sensing Systems (ISSYS) Inc.,387 Airport Industrial Drive, Ypsilanti, MI 48198 39
  • 39. References Soldering techniques for PCB-Min Chen, student member IEEE. Photolithography written by Scotten.W.Jones. Capacitive pressure sensor design Version 8/PC Part Number 30-090-101 March 2006 ©IntelliSense Software Corporation 2004, 2005, 2006 40
  • 40. References www.seminar Wikipedia 41
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  • 42. 43