MEMS Capacitor Sensor Laboratory

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1 ROCHESTER INSTITUTE OF TEHNOLOGY MICROELECTRONIC ENGINEERING MEMS Capacitor Sensor Laboratory Dr. Lynn Fuller, Dr. Ivan Puchades Webpage: 82 Lomb Memorial Drive Rochester, NY Tel (585) Fax (585) Department webpage: capacitor_lab.ppt Page 1

2 OUTLINE Parallel Plate Capacitors Force/Position Sensor Water Level Sensor RC Oscillator Capacitance to Analog to Digital Output Resonant LC Wireless Capacitor Sensor Bluetooth Wireless Capacitor Sensor Page 2

3 CAPACITORS Capacitor C = eo er Area/d where eo is the permitivitty of free space er is the relative permitivitty Area is the overlap area of the two conductor separated by distance d d Area eo = 8.85E-14 F/cm er air = 1 er SiO 2 = 3.9 Page 3

4 CAPACITOR CALCULATIONS Page 4

Calculate capacitance and measure capacitance, compare results to theoretical.

5 CAPACITANCE BETWEEN TWO PLATES Design and build capacitors made of two metal plates separated by a thin foam insulator that can be compressed for various applied forces. Calculate capacitance and measure capacitance, compare results to theoretical. er air < er foam < er rubber 1 Microelectronic < er foam Engineering < 3 Capacitance of two wires 3 long Capacitance of 2 x 2 plates ½ gap Capacitance of 1 x 1 plates ¼ gap Page 5

6 CAPACITIVE FORCE SENSOR Page 6

7 LIQUID LEVEL CAPACITOR SENSOR Calculate Capacitance, 3 x 3 plates 1/32 gap Measure Capacitance Immersed in Water at ½, 1, 1 ½ and 2 er = ~80 for water Page 7

8 CAPACITIVE WATER LEVEL SENSOR Page 8

9 COMPARATOR Vin - + +V Vo +V Vo Theoretical Vref -V -V Vref +V Vin -V Measured Page 9

10 BISTABLE CIRCUIT WITH HYSTERESIS R1 R2 +V +V Vo Theoretical Vin + - -V Vo V TL V TH Vin -V Measured Sedra and Smith pg 1187 Page 10

11 RC INTEGRATOR +Va -Va Vin t1 Vin t R C Vout Vout +Va -Va Smaller RC t Vout = (-Va) + [2Va(1-e -t/rc )] for 0<t<t1 If R=1MEG and C=10pF find RC=10us so t1 might be ~20us Page 11

12 OSCILLATOR (MULTIVIBRATOR) R1 V T + - R2 +V Vo Vo +V -V t1 t C -V R Period = T = 2RC ln 1+Vt/V 1-Vt/V Bistable Circuit with Hysteresis and RC Integrator Page 12

13 OSCILLATOR OUTPUT 1.2 Mohm No Force Applied C ~50pf 1.2 Mohm with Force Applied C~100pf Page 13

14 CAPACITIVE SENSOR AND RC OSCILLATOR RC Oscillator movie Page 14

15 External Electronics MEMS Capacitor Laboratory BASIC IDEA Resonant Frequency = wo = 1/(LC) 0.5 Antenna I L Short Distance (few feet) I C R ~ MHz fo = wo/2p f Page 15

16 INVESTIGATE RESONANT LC CIRCUIT Network Analyzer I vs. Frequency Page 16

17 PICKUP COIL CURRENT WITHOUT RESONANT CIRCUIT Page 17

18 PICKUP COIL CURRENT WITH RESONANT CIRCUIT Resonant Frequency wo = 1/(LC) 0.5 Due to, fo = wo/2p Page 18

19 ZOOM IN ON RESONANCE DUE TO LC Resonant Frequency wo = 1/(LC) 0.5 fo = wo/2p Frequency at Which this Dip Occurs Changes with Change in C Page 19

20 RESONANT LC SENSOR FOR TEMPERATURE BATMON movie Page 20

21 CAPACITANCE TO ANALOG VOLTAGE TO DIGITAL Square Wave Generator RC Integrator Peak Detector C to Analog Voltage LED Bar Display Voltage Divider And Comparators A to D Page 21

22 CAPACITOR SENSOR ELECTRONICS R1 R2 +V + - +V -V R C - + C C R + - Square Wave Generator RC Integrator Buffer Peak + Detector Voltage Divider & Comparators Page 22

23 CAPACITANCE SENSOR AND SIGNAL CONDITIONING Page 23

24 BLUETOOTH WIRELESS CAPACITOR SENSOR 2.4 khz 5 Hz 3 V CTS TX RX RTS o/p 9 SCLK RCLK 10-bit (Left) Shift Register i/p 0 BT: Serial Port Profile (RS232) Packet Specification : Bluetooth Serial RF Link Baud rate: CCKEN RCO CCLK 2 8-bit Binary Counter 1 0 RCLK CCLR 5 Hz Data bits: 8 Parity: None Stop bits: 1 Page 24

25 BLUETOOTH WIRELESS CAPACITOR SENSOR Capacitor Sensor Bluetooth Radio Wireless Platform Breadboard Page 25

26 REFERENCES 1. Mechanics of Materials, by Ferdinand P. Beer, E. Russell Johnston, Jr., McGraw-Hill Book Co.1981, ISBN Electromagnetics, by John D Kraus, Keith R. Carver, McGraw- Hill Book Co.1981, ISBN Fundamentals of Microfabrication, M. Madou, CRC Press, New York, Mechanics of Materials, by Ferdinand P. Beer, E. Russell Johnston, Jr., McGraw-Hill Book Co.1981, ISBN Switched Capacitor Circuits, Phillip E. Allen and Edgar Sanchez- Sinencio, Van Nostrand Reinhold Publishers, Page 26

27 HOMEWORK - CAPACITOR SENSOR LAB 1. Calculate the capacitance of the two parallel plate sensors with foam between the plates. Let the plates be 1 inch x 1 inch and 2mm foam thickness. 2. Write and expression for a parallel plate analog capacitive oil level sensor as a function of oil height (Hoil). Let the plates be 0.5 inch wide and 2 inch tall with a gap of 2 mm. 3. Calculate the capacitance for a silicon diode at 25, 50, 75, and 100 C. Use values for doping and reverse bias that gives large changes in capacitance. Page 27

28 INSTRUCTORS NOTES: CAPACITOR SENSORS 1. Calculate the capacitance of a parallel plate capacitor. 2. Measure it. 3. Move the plate spacing, measure it. 4. Measure height of water. 5. Build RC Oscillator for measuring C. 6. Other ways to measure Capacitance 6.1 Resonant Frequency 6.2 Peak Detector 6.3 Blue Tooth Wireless Page 28

MEMS Capacitor Sensors and Signal Conditioning

ROCHESTER INSTITUTE OF TEHNOLOGY MICROELECTRONIC ENGINEERING MEMS Capacitor Sensors and Signal Conditioning Dr. Lynn Fuller Dr. FullersWebpage: http://people.rit.edu/lffeee Electrical and 82 Lomb Memorial