1. Professor Richard S. MullerMichael A. Helmbrecht MEMS for Adaptive Optics Michael A. Helmbrecht Professor R. S. Muller

2. Professor Richard S. MullerMichael A. Helmbrecht MEMS for Adaptive Optics Adaptable-Mirror Section Mirror Substrate Solder-Bump Electrical Connections Movable Mirror Elements Scale ~10s to 100s  m Scale ~ mm to cm Current-Driver Electronics Array of Elevating Mirrors

3. Professor Richard S. MullerMichael A. Helmbrecht How Can We Elevate the Mirror Elements? Magnetic Actuation – Solenoidal structures Electrostatic Actuation – Vertical comb-drives Thermal Actuation – Thermal-bimorph structures – Our initial design approach

4. Professor Richard S. MullerMichael A. Helmbrecht Thermal-Bimorph Actuation  Large force  Low voltage  Long life 10 7 cycles without failure measured at BSAC  Actuators can be hidden under mirror - Heat dissipation Possible mirror distortions Possible electronics problems - Complicated linkage Must be compliant when bending Must result in pure translation of mirrors

5. Professor Richard S. MullerMichael A. Helmbrecht Actuator Design

6. Professor Richard S. MullerMichael A. Helmbrecht Mirror-Element Layout

7. Professor Richard S. MullerMichael A. Helmbrecht Thermal-Bimorph Actuators Tip deflects when     1  is the coefficient of expansion h  T-T 0 ), (  2 -  1 ), 1/w Theoretical plot shown for: T-T 0 =70°C (  2 -  1 )=23.4 ppm/°C w=1  m

8. Professor Richard S. MullerMichael A. Helmbrecht Bimorph Mechanical Model Mirror element size l Bimorph length l Au- or Al-film on 10  m- thick silicon (SOI) –Neglect bimorph mass Each bimorph layer thickness w Bimorph width b=20  m –Power scales with b

9. Professor Richard S. MullerMichael A. Helmbrecht Mechanical-Resonance Frequency (h=10  m) T-T (K)

10. Professor Richard S. MullerMichael A. Helmbrecht Bimorph Thermal Model Losses through the substrate dominate –Convection losses are negligible Mirror heats up to a fraction of the bimorph temperature (T - T 0 ) mirror = (0.33 down to 0.125) (T - T 0 ), for 100  m < l < 300  m

11. Professor Richard S. MullerMichael A. Helmbrecht Thermal-Time-Constant -3dB Frequency and Power Density

12. Professor Richard S. MullerMichael A. Helmbrecht Mirror Berkeley Bimorph Process Single-mask process Low-stress nitride (Si x N y ) and aluminum bimorph Other processes under consideration –Hidden actuators –Electrostatic actuators –Bonded mirrors Current path Mirror Die photo - actuated, released mirrors

13. Professor Richard S. MullerMichael A. Helmbrecht Conclusions Bimorph actuator is small and can be fabricated under the mirror –Fill factor > 98% Bimorph actuators can be tiled in an arrays to actuate large numbers of mirrors Bimorph actuator provides large tip deflection (h = 10  m) Models show frequency requirements are met (f>1 kHz) Bimorph actuators have been fabricated –Testing is underway