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

Louisiana State University

Ren Yang, Seok Jae Jeong, and Wanjun Wang

Department of Mechanical EngineeringLouisiana State University

Baton Rouge, LA 70810USA

1. Introduction.2. Design3. Fabrication 4. Summary & Future work

1. Introduction

Different Types of Power RelaysDifferent Types of Power Relays

1. Traditional Relay- Advantage: low on resistance, off-leakage, and big

output capacitance- Disadvantage: large, noisy, slow, and difficult to

integrate2. 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

3. MEMS (Micro Electro Mechanical System) Relay- Takes advantages from traditional and solid-state relay

General Principle Commonly Used MEMS Design

Electrostatic force

Magnetomotive force

Piezoelectrical force

Schematic diagram of the micro power relay

2. Design

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

Fundamental calculation for electrostatic force

VA

Fxe

NFmx

mAmF

datagiven

ex

Aq

Ax

EF

vFiV

dt

dx

x

E

dt

dq

q

E

dt

dEP

capacitoraforA

xqq

CE

25~2

107656.2,20

2000,/1085.8

;

22

1

22

1

2

12

7

12

22

2

22

Ax

E:electrical energy stored by the capacitorC: capacitance P:powerq:current x:gapε:electric permittivity of free spaceE:voltage A:surface area

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

Fabrication Method

Polymer connectorsInsulator to protect

short- circuit

Substrate (Si)

1st layer

Poles to support top part15 m

Substrate (Si)

1st layer

3rd layer2nd layer

Top partBottom part

Assemble

Poles to support top part15 m

Substrate (Si)

1st layer

3rd layer2nd layer

Substrate (Si)

Electrodes to be swithced on

Poles to support top part

10 m

1st layer

3rd layer

Bottom capacitor for electrostatic driving

Electrodes to be swithced on

Poles to support top part

55 m

Substrate (Si)

1st layer

Bottom part

substrate

Au/Cr seed layer

photo resist(SU 8)

UV light

mask

developing

electroplating

metal structure

Top part

Insulation layerPolymer connectors

Insulator to protect short- circuit

Substrate (Si)

1st layer

Polymer connectorsInsulator to protect

short- circuit

Substrate (Si)

1st layer

Suspension springs Switching connectorsTop capacitor plate

Substrate (Si)

1st layer

substrate

Au/Cr seed layer

photo resist

UV light

mask

developing

electroplating

metal structure

Separated structure

Top view picture of Bottom and top part Side view schematic diagram of relay

Initial open position

Closing operation

Bottom part Top part

Assembled top and bottom part

top plate

bottom plate supporting postelectorodes

suspension spring

polymer layerpolymer connector

substrate

electric connection made

deflectionelectrically isolated

substrate

Adding an insulation layer on the bottom part

Bottom part Top part

Insulation layerPoles to support top part15 m

Substrate (Si)

1st layer

3rd layer2nd layer

Substrate (Si)

Electrodes to be swithced on

Poles to support top part

10 m

1st layer

3rd layer

Bottom capacitor for electrostatic driving

Electrodes to be swithced on

Poles to support top part

55 m

Substrate (Si)

1st layer

Suspension springs Switching connectorsTop capacitor plate

Substrate (Si)

1st layer

Polymer connectors

Substrate (Si)

1st layer

Polymer connectors

Substrate (Si)

1st layer

top plate

bottom plate supporting postelectorodes

suspension spring

Insulation layerpolymer connector

substrate

Top view picture of Bottom and top part Side view schematic diagram of relay

Initial open position

Closing operation

Bottom part Top part

Assembled top and bottom part

electric connection made

deflectionelectrically isolated

substrate

4. Preliminary test of assembled relay

Mass Deflection

Mechanical properties

Measurement of deflection by applied weight

1.0x10-4

2.0x10-4

3.0x10-4

4.0x10-4

2.0x10-7

4.0x10-7

6.0x10-7

Slope(K)=1.75*10-3

Slope(K)=2.13*10-3

experiment simulation

For

ce (

N)

Deflection (m)

Experiment Calculation

Working voltage

~10V 8.5V

Spring constant 1.7510-3N/ 2.1310-

3N/m

Electrical properties

R=872kΩ

R=Infinite

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: 1.7510-3N/m

I

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