Mems accelerometer designing and fabrication

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Design,fabrication and Application of MEMS accelerometer.

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Mems accelerometer designing and fabrication

  1. 1. MEMS CAPACITIVE ACCELEROMETER (Design and Fabrication) Presented by:- PRASHANT SINGH
  2. 2. OUTLINE  Introduction  MEMS         Accelerometer Basic operation principle Capacitive Accelerometer   MEMS vs. IC’s Capacitance basics Sensing mechanism Structure analysis (spring stiffness) Advantages Accelerometer fabrication Applications
  3. 3. INTRODUCTION  MEMS    MEMS:    MEMS move and Sense Mass. MEMS act as transducer (Sensor & Actuator). IC    Micro-Electro-mechanical-system Integration of mechanical unit, electrical unit, sensor and actuator on a single substrate. IC’s move & sense electrons. IC’s acts as sensor not actuator. MEMS Advantage    Smaller Lighter Economical
  4. 4. ACCELEROMETER  Inertial sensor:   Device used to measure:      Newton’s 1st law (Mass of inertia). Acceleration Displacement Force Inclination Design Approach:     Piezoelectric Piezoresistive Tunneling Capacitive, etc. Basic capacitive Accelerometer.
  5. 5. BASIC OPERATION PRINCIPLE 
  6. 6. CAPACITIVE ACCELEROMETER     Based on Change in capacitance between Comb fingers. {Capacitance change} α {Force applied on Proof Mass} Comb structure Large capacitance value Advantages      High resolution Good DC response Linear output low power dissipation Easy incorporation with CMOS
  7. 7. CAPACITANCE BASICS 
  8. 8. SENSING MECHANISM  (a) Two types:  Out-of-Plane Sensing  Change  in overlapping width (w). In-Plane sensing  Lateral  sensing (a) Change in overlapping length (L)  Transverse  sensing (b) Change in finger gap (d) (b)
  9. 9. STRUCTURE ANALYSIS  Unguided and guided beam structure
  10. 10. CAPACITIVE ACCELEROMETER ADVANTAGES High sensitivity.  Easy readout circuitry.  Independent of temperature variation.  Easy fabrication (two level mask).  Large noise margin.  Fabrication on silicon.  Compatible with CMOS technology. 
  11. 11. FABRICATION PROCESS  Silicon on insulator(SOI) wafer(i) 15µm 2µm  Cleaning -RCA 1 -RCA 2  Oxidation(ii)   475 µm thickness of oxide layer ::7700 Å at 1050ºC Photolithography(iii) -1st level mask -prebaking -UV light exposer-15 sec -PR develop silicon oxide silicon oxide silicon oxide (i) (ii) silicon oxide photoresist Silicon oxide silicon oxide (iii)
  12. 12. FABRICATION PROCESS CONTD..  SiO2 etch (iv) –buffer HF -etch rate ≈ 1000Å/min.  Silicon etch(v) Silicon oxide silicon oxide (iv oxide -PR removal -Anisotropic Si etch -THAH solution used -V groove formation oxide silicon oxide (v
  13. 13. FABRICATION PROCESS CONTD..  SiO2 removal (vi) -Buffer HF -hanging structure  oxide (vi silicon Metallization (vii) -2nd level mask -Al deposited -temp. 650ºC oxide silicon (vi
  14. 14. ACCELEROMETER FABRICATION CONTD..  Accelerometer (1st level mask, PR developed) photoresist  Accelerometer (SiO2 etched) SiO2 Si SiO2 Si
  15. 15. APPLICATIONS  Automotive   Consumer Electronics     hard disk protection(laptops) screen rotation (mobile) Image stabilization (camera) Industrial    Crash detection & Air bag deployment. Vibration detection (machine) crack detection (pulley) Aerospace & Defence    Navigation Missile guidance Thrust detection Accelerometer application
  16. 16. THANK YOU

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