Robot Leg Motion in a Planarized-SOI, 2-Poly Process Hilton Head 2002 Seth Hollar, Dr. Anita Flynn, Sarah Bergbreiter, Professor Kris Pister Berkeley Sensor and Actuator Center, UC Berkeley
Acknowledgements Dr. Chris Keller, MEMS Precision Instruments DARPA/ITO SDR NSF Berkeley Sensor and Actuator Center Sponsors UC Berkeley Microfabrication Facility, Robert Hamilton Dr. Azzam Yasseen James Wu, Lawrence Berkeley National Labs Dr. Dimitry Kousminov from Accurel Systems
Outline Microrobot History Inchworm Actuation Microrobot Assembly Robot Leg Design Fabrication Process Results Late News Conclusion
Previous Microrobot History Courtesy Richard Yeh No Motors No Legs 1988 Microrobot concepts Anita Flynn 1992 Poly-Si pin hinges Kris Pister 1995 Legs in MUMPS Richard Yeh 2001 Electrostatic Inchworm Motors in SOI Richard Yeh No one has shown large force electrostatic actuators combined with robot legs
Electrostatic Inchworm Actuators Large Force, Low Power, Large Displacement Actuation Single Mask SOI Process Courtesy Richard Yeh 80µm Displacement, ~100µN Force 4 Control Signals with 30 Volts Input
How an Inchworm Motor Works Clutch Clutch Drive Drive 0 V Shuttle Drive Clutch
Left Right Clutch Clutch Drive Drive 0 V
Left Right Clutch 0 V Clutch Drive 0 V Drive
Left Right Clutch Clutch Drive 0 V Drive
Left Right Clutch Clutch 0 V Drive Drive 0 V
Left Right Clutch Clutch Drive Drive 0 V
Left Right Clutch 0 V Clutch Drive 0 V Drive
Left Right Clutch Clutch Drive 0 V Drive
Left Right Clutch Clutch 0 V Drive Drive 0 V
Left Right Clutch Clutch Drive Drive 0 V
Left Right Clutch 0 V Clutch Drive 0 V Drive
Left Right Clutch Clutch Drive 0 V Drive
Left Right Clutch Clutch 0 V Drive Drive 0 V
Microrobots Three Processes The Brain - CMOS Digital Circuits Sequencer - generates digital signals to drive motors The Power Solar Cells Step-up converter from 3 volts to 30 volts Solar Cell Arrays The Actuation Hinges, Motors, Legs Planarized SOI / 2 Structural Poly Layers
Proposed Integration Method Solar Cell/High Voltage Chip CMOS Chip Inchworm Motors Leg Solar Cells/ High Voltage Assembly CMOS Legs and Motors Wire Bonds Substrate
Assembled Robot 4mm Legs of Robot Inchworm Motors Solar Cell High Voltage Chip Low Power Digital Chip
Worst Case Design Parameters Mass (mg) Die Area (mm 2 ) Efficiency Power Consumption Motors (+ Legs) 12 20 8% 500nW Step Up Converters 2 2 10% 5µW Solar Cells 2 2 5% Generates 50µW CMOS Controller 1 1-30nW Total 17 24 0.04% 5.5µW
Leg Schematic Hinges Flaps Leg Shuttle Substrate
Hinges Flaps Leg Shuttle Substrate
1mm Inchworm Motor Leg
SOI wafer Crys. Si ~ ~ Oxide Substrate
ASE Etch Crys. Si ~ ~ Oxide Substrate
A. Yasseen, J. Cawley, M. Mehregany Thick Glass Film Technology for Polysilicon Surface Micromachining. JMEMS 1999. Glass Slurry Glass Slurry Crys. Si ~ ~ Oxide Substrate
Organic Burnout Glass Frit Crys. Si ~ ~ Oxide Substrate
Celsius 1000 900 800 700 600 500 400 Glass Firing Profile 2Torr Softening Point 1ATM Transition Temperature 0 50 100 150 200 minutes Chris Keller http://www.memspi.com/
Reflow Glass in Vacuum Reflowed Glass Crys. Si ~ ~ Oxide Substrate
CMP to Si-Glass surface Crys. Si ~ ~ Oxide Substrate
Structural 2 layer poly-si Poly Si PSG Reflowed Glass Crys. Si ~ ~ Oxide Substrate
ASE Backside Etch Poly Si PSG Reflowed Glass Crys. Si Oxide ~ ~ ~ ~ Substrate
Timed HF/HCl release Poly Si Crys. Si Oxide ~ ~ ~ ~ Substrate
Fabrication Results Shuttle Leg 250 µm Leg Shuttle
Hinges Poly-Si Hinges 40 µm Device SOI Substrate Leg
Flaps Leg Shuttle Poly-Si Flaps Shuttle 12µm
Friction Sliding Tests Flaps Poly 9 8 7 Without Substrate With Substrate Substrate Number of Samples 6 5 4 3 2 SOI 1 0 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12 12-13 13-14 14-15 15-16 Force, µn
Surface Bubbles Crys. Si We Want Substrate We Got Bubbles
Float Away Structures Poly Si PSG Reflowed Glass Crys. Si Oxide Substrate During Release
Presetting Leg out of Plane Shuttle 140 µm
Leg Actuation Vertically preset to 360µm. Actuated to 580µm Angular deflection from 34 o to 63 o 200 µm Shuttle travel: 250 µm
Autonomous Inchworm Operation from 3 Chip Hybrid CMOS 1.8x0.4 mm 2 One Mask Inchworm Motor Solar Cells 3.0x1.0 mm 2 1.7x2.4 mm 2 Flashlight
Conclusion We have demonstrated all 3 key elements of a microrobot: Legs with motors Brains Power bsac.eecs.berkeley.edu/~shollar Integrated motors with hinges using glass reflow technology Microrobots are within reach!!!