IC MEMS Accelerometer in Standard CMOS Process

1
IC MEMS Accelerometer in Standard CMOS Process

• Carlos Amaya
• Dept. of Electrical Engineering
• Carleton University
• Prof. Tait

2
Outline

• Introduction
• CMOS Micromachining
• Accelerometer Background
• Sensor Design
• Sensor Implementation
• Future Work
• Conclusion

3
Introduction

• Problem
• Design a transducer for a single axis
  accelerometer sensor similar to the ADXL50
• Possible solutions
• MEMS Accelerometers
• Capacitive configurations
• Fabrication technologies available
• My solution
• Capacitive transverse comb transducer using
  surface IC MEMS with standard 0.35?m CMOS process

4
CMOS Micromachining

• Parallel fabrication
• Interface connections
• CMOS materials
• Processes optimization / SoC

CMOS Foundry Fabricates ICs
CMOS MEMS
Si µ-machining (post-process)
IC Design
5
Accelerometer Background
ADXL50
Ref Analog Devices ADXL50

• Measurement range ? 50g
• Sensitivity 19 mV/g

• Fresonant 24 KHz
• Co 100 fF
• Vo 1.8 V

6
Sensor Design
Ref B. Boser, Surface Micromachined
Accelerometers
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Sensor Design
Ref Analog Devices ADXL50
8
Sensor Design
9
Sensor Design
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Sensor Design

• Km 0.76 N/m
• Ke -0.1 N/m
• Kt Km Ke
• 0.66 N/m
• Lanchor-anchor 95 ?m
• Total Mass 28 ng
• Fr 24.3 KHz
• Sensitivity 0.061 mV/g
• Displacement
• 0.021 ?m _at_ 50g
• 0.84 ?m _at_2000g

• Gap Xo 2.25?m
• Thickness 0.3?m
• Overlap 282?m
• No. of fingers 300
• Area 580?m920?m

Ref Analog Devices ADXL50
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Sensor Implementation
LAYOUT
Ref Analog Devices ADXL50
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Sensor Implementation
13
Future Work

• Consider
• Post-process steps
• Pores on the proof mass
• Curling effect
• Parasitic capacitance
• Test set up

Ref G. Fedder, Structured Design of Integrated
MEMS
14
Conclusion

• Initial design of the transducer is complete
• IC MEMS with CMOS process is possible