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# Dual axis accelerometer paper 157

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• for designing capacitive accelerometer in comsol should i place a layer on above and below the proof mass?or any one side?

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• okk .. and like in some papers mass of proof mass is given then how can we add that mass in proof mass using comsol.

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• @taniachauhan By proof mass displacement calcutaion and substituting its value in the capacitance formula we can get the value of change in capacitance.
and the capacitance is always maximum in the stationary position. Capacitance always decreases with movement (If the movement is out of plane).

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• how can you add the proof mass and compute the capacitance in comsol.. reply asap.

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### Dual axis accelerometer paper 157

1. 1. A Novel Approach to Design Dual Axis MEMS Capacitive Accelerometer Authors: Prashant Singh, Pooja Srivastava Student, Dept. of Microelectronics Indian Institute of Information Technology-Allahabad Presented by: Prashant Singh
2. 2. Outline • Definition • MEMS • Accelerometer • Accelerometer classification • Capacitive Accelerometer • Accelerometer design • Proposed Accelerometer Model • Simulation Results • Proof Mass Support Modeling • Accelerometer Modeling • Results and Conclusion • References
3. 3. Definition • MEMS • Micro-Electro-mechanical-system • Integration of mechanical unit, electrical unit, sensor and actuator on a single substrate. • Accelerometer • Inertial sensor • Newton’s 1st law (Mass of inertia) • Used to measure: (i) Acceleration, (ii) Displacement, (iii) Force (iv) Inclination angle
4. 4. Accelerometer Classification • Fabrication Technique: • Surface Micromachining- additive process • Bulk Micromachining- subtractive process • Sensing Technique • Read out principle • Displacement based: Capacitive Tunneling Optical Hall effect Thermal Magnetic • Stress based: Piezoelectric Piezoresistive
5. 5. 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
6. 6. Accelerometer Design •
7. 7. Proposed Accelerometer Model • Modeling on COMSOL Multiphysics • Dual axis accelerometer • Cantilever: Out-of-Plane • Spring: In-plane Proposed accelerometer model
8. 8. Simulation Results (proof mass support modeling) • Parameters Beam (um) Spring (um) Length 20 100 Width 10 5 Height 10 10
9. 9. Resonance Frequency for Spring support • Resonance frequency depends only on Spring parameters. • Beam has no effect on resonance frequency. • Resonance frequency=1.75 MHz • Bandwidth= 1 MHz
10. 10. Spring support Modeling • Effect of Spring flexure height on free point displacement • Effect of Spring flexure height on Resonance frequency
11. 11. Resonance Frequency for Beam support • Resonance frequency depends on beam as well as Spring parameters. • Resonance frequency=1.1 MHz • Bandwidth= 1 MHz
12. 12. Spring support Modeling • Effect of Beam flexure height on free point displacement • Effect of Beam flexure height on Resonance frequency
13. 13. Accelerometer Modeling • Accelerometer Parameters Parameters Comb Proof mass Length(µm) - 200 Width(µm) - 100 Finger length(µm) 50 - Finger width(µm) 5 - Finger overlap(µm) 2.5 - Finger gap(µm) 40 - Capacitor pair 52 - Height 10 10
14. 14. Accelerometer Modeling Contd.. •
15. 15. Accelerometer Modeling Contd.. • Frequency domain analysis • To determine accelerometer resonance frequency. • In-Plane resonance frequency- Transverse motion. • Spring support in use. • Fr=0.3 MHz • BW= 0.4 MHz
16. 16. Accelerometer Modeling Contd.. • Out-of-Plane Resonance frequency. • Beam support in use. • Fr= 0.32 MHz • BW= 0.25 MHz
17. 17. Results and Conclusion • Dual Axis accelerometer is designed. • In-Plane operation • Spring support in use. • Fr= 0.3 MHz • BW= 0.4 Mhz • Out-of-Plane operation • Cantilever beam support in use • Fr= 0.32 MHz • BW= 0.25 MHz • Application • Moderate frequency operation • Military
18. 18. References • G.M. Rebeiz, J.B. Muldavin, "RF MEMS switches and switch • • • • • circuits“, Microwave Magazine, IEEE , vol.2, no.4, pp.59-71, 2001. S. Pacheco, et al., Microwave and Optoelectronics Conference, pp. 770-777, 2007. http://www.memsnet.org/mems/what-is.html. B.V. Amini, F. Ayazi, “A 2.5-V 14-bit CMOS SOI capacitive accelerometer”, IEEE Solid-State Circuits 39(12):2467–2476, 2004. G. Kovacs, Micromachined Transducers Sourcebook; New York: McGraw Hill, 1998. Chi Yuan Lee, Guan Wei Wu, Wei Jung Hsieh, “Fabrication of micro sensors on a flexible substrate”, Sensors and Actuators,(2008).
19. 19. Thank You