UV-LIGA Microfabrication of a Power Relay Based on Electrostatic Actuation

1. UV-LIGA Microfabricationof a Power Relay Based on Electrostatic Actuation Ren Yang, Seok Jae Jeong, and Wanjun Wang Department of Mechanical Engineering Louisiana State University Baton Rouge, LA 70810 USA Louisiana State University

2. Introduction. • Design • Fabrication • Summary & Future work

3. 1. Introduction Different Types of Power Relays • Traditional Relay - Advantage: low on resistance, off-leakage, and big output capacitance - Disadvantage: large, noisy, slow, and difficult to integrate • Solid-state Relay - Advantage: much longer life time, fast response, low noisy, smaller size - Disadvantage: high on-resistance, low off-resistance, high power consumption, and poor electrical isolation • MEMS (Micro Electro Mechanical System) Relay - Takes advantages from traditional and solid-state relay

4. General Principle Commonly Used MEMS Design • Electrostatic force • Magnetomotive force • Piezoelectrical force

5. 2. Design Schematic diagram of the micro power relay

6. Differences Compared to Other MEMS Relays • Not silicon based • Metal/Alloy as basic materials such as Ni or Cu for conductivity • Thick metal/Alloy pads can be used instead of thin metal films as silicon based relay

7. Fundamental calculation for electrostatic force E:electrical energy stored by the capacitor C: capacitance P:power q:current x:gap ε:electric permittivity of free space E:voltage A:surface area

8. 3. Fabrication of micro-relay by UV-LIGA • What is UV-LIGA? ; Approach where a UV aligner is used with a thick resist in place of the synchrotron x-ray exposure step. After the lithography, electrodeposition and planarization are used to produce metal micropart. • Advantages - High aspect-ratio microfabrication - Broad selection of materials - Slightly lower quality and much lower fabrication cost compared to X-ray LIGA

9. Fabrication Method Bottom part Top part Assemble

10. Bottom part substrate photo resist(SU 8) Au/Cr seed layer UV light mask developing electroplating metal structure

11. Top part substrate photo resist Au/Cr seed layer UV light mask developing Insulation layer electroplating metal structure Separated structure

12. Top view picture of Bottom and top part Side view schematic diagram of relay Bottom part Top part Initial open position Closing operation Assembled top and bottom part

13. Adding an insulation layer on the bottom part Top part Bottom part Insulation layer

14. Top view picture of Bottom and top part Side view schematic diagram of relay Initial open position Bottom part Top part Closing operation Assembled top and bottom part

15. 4. Preliminary test of assembled relay Mechanical properties Measurement of deflection by applied weight

16. Electrical properties R=872kΩ R=Infinite

17. I 4. Summary • Design of a novel micro-relay for power applications based on electrostatic actuation • Fabrication by UV-LIGA • Preliminary test • Control voltage: 10V • Spring constant: 1.7510-3N/m

18. 5. Future Work • Improve fabrication process • Low stress plating condition • Easy way separate top structure from the substrate. • Measure physical properties • Spring constant • Strength of polymer connector • Test working properties of the assembled power relay • On/off resistance • Life time • reliability