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. 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. 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. 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. 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. Accelerometer Design
•

7. Proposed Accelerometer Model
• Modeling on COMSOL Multiphysics
• Dual axis accelerometer
• Cantilever: Out-of-Plane
• Spring: In-plane
Proposed accelerometer model

8. Simulation Results (proof mass support modeling)
•
Parameters
Beam (um)
Spring (um)
Length
20
100
Width
10
5
Height
10
10

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. Spring support Modeling
•
Effect of Spring flexure height on free
point displacement
•
Effect of Spring flexure height on
Resonance frequency

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. Spring support Modeling
•
Effect of Beam flexure height on
free point displacement
•
Effect of Beam flexure height on
Resonance frequency

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. Accelerometer Modeling Contd..
•

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. Accelerometer Modeling Contd..
• Out-of-Plane Resonance frequency.
• Beam support in use.
• Fr= 0.32 MHz
• BW= 0.25 MHz

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. 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. Thank You