Prepared by: Yashodhan Tarte Dept. of Electrical and Computer Engineering Utah State University

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Electrostatic Microactuators Prepared by: Yashodhan Tarte Dept. of Electrical and Computer Engineering Utah State University E: y.tarte@usu.edu ; T: (435)797-2845 3/11/2005

2. Outline • Reference list • To Explore Further • Major Applications • Types of Electrostatic MAs • Working • Fabrication • Some Pictures • A Typical Example • Limitations • Manufacturers ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • Travel Range Extension of a MEMS Electrostatic Microactuator by D Piyabongkarn, Y Sun, R Rajamani, A Sezen, and B J Nelson. IEEE Transactions on Control Systems Technology, Vol. 13, No. 1, January 2005 • A DRIE Comb-Drive Actuator With Large, Stable Deflection Range for Use as an Optical Shutter by John D. Grade, Kevin Y. Yasumura, and Hal Jerman, Iolon, Inc., San Jose, CA, USA • University of Minnesota, Minneapolis 4. Micromanipulation with Cilia Arrays 5. Mechatronics of Electrostatic Microactuators for Computer Disk Drive Dual-Stage Servo Systems by Yunfeng Li and Roberto Horowitz. IEEE/ASME Transactions on Mechatronics, Vol. 6, No. 2, June 2001 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To Explore Further • This presentation gives a brief idea about electrostatic microactuators. So if you want to know more about this topic, you can try searching IEEE Xplore where you can find about current research going in this field. • Another type of MEMS actuator is electromagnetic microactuators. You may also want to explore them. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Major applications • Optical switching • Hard disk drive head motion • Manipulation of subcellular structures within biological cells • Microassembly of hybrid MEMS devices • Manipulation of large molecules such as DNA or proteins ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Types of Electrostatic MAs • Comb-drive • Parallel-plate ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Working1 • The actuation principle behind parallel-plate electrostatic microactuators is the attractive force of two oppositely charged plates by applying a voltage between them. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Working (cont.)1 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Working (cont.)1 • The comb-drive-type electrostatic microactuator has a large numbers of fine interdigitated “fingers” to generate the actuated force. • A comb drive that is actuated by a parallel-plate field at each finger pair is called a “transverse” comb drive. • The movable plate and movable finger are suspended by mechanical elastic members. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Working (cont.)1 • Solid model of a two axis microactuator: ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Working (cont.)1 • One axis comb drive model (offset): ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Working (cont.)1 • In the above figure x is the displacement of the movable fingers from the equilibrium position. • This comb drive is said to be “offset” since the distance x1 is much smaller than the distance x2. • Each gap between adjacent fingers has a specific capacitance. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Working (cont.)1 • For instance, C1 and C2 can be calculated by the following: where Kd = dielectric constant for the material, ε = permittivity of free space, and A = overlapping area of each finger pair. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Working (cont.)1 • The electrostatic force on the movable comb fingers is given by where N = number of parallel capacitor pairs, and V = applied actuation voltage. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Fabrication2 • The following slides show the fabrication process of an electrostatic microactuator for optical shutter (shown below) application. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Fabrication (cont.)2 • Etch shallow cavity in carrier wafer to create future movable areas. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Fabrication (cont.)2 • Fusion bond device wafer to carrier; polish to final thickness. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Fabrication (cont.)2 • Oxidize; open contact holes; deposit and pattern pad holes. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Fabrication (cont.)2 • DRIE (deep reactive ion etching) etch through device wafer. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Some Pictures3 • A close up of an electrostatic microactuator ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. Some Pictures (cont.)4 • A cut section of an organic thermal and electrostatic microactuator: ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

22. A Typical Example5 • IBM’s electrostatic microactuator mounted on an integrated lead suspension of hard disk drive head: ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

23. A Typical Example (cont.)5 • IBM’s electrostatic microactuator parameters: Resonance frequency: 1.5 kHz +/-15% Damping coefficient: 0.015 Stroke limit: +/- 1 µm Gain: 2 G/V Maximum voltage: +/-40V ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

24. Limitations Apart from advantages of high performance and low cost, these microactuators have some limitations also: • In parallel-plate type microactuators, the force output is highly nonlinear over stroke range and may become unstable under large actuation voltages. • Electrical isolation is another problem in parallel-plate microactuators. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

25. Manufacturers The major manufacturers of electrostatic microactuators are: • IBM Corporation • ST Microelectronics • Agilent Technologies ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators