Lecture Outline Reading from reader Cohn M B Howe R T et al Microassembly Technologies for MEMS pp 2 16 Srinivasan U et al MEMS Some Self Assembly Required pp 20 24 56 Assembly Techniques for MEMS Dr Thara Srinivasan Lecture 26 Sign up for poster session Dec 11 or 12 today or e mail me Today s Lecture Serial Assembly pick place Parallel Assembly Processes Guided Transfer Self Assembly EE C245 EE C245 Assembly of Hinged MEMS Structures Assembly of MEMS With Other Microdevices U Srinivasan Picture credit Alien Technology Assembly and MEMS Assembling Hinged Structures This new technology originating in microelectronics offers the possibility of fabricating fully assembled lowcost mechanical devices and systems emphasis added 2 U Srinivasan Enable assembly of 3 D structures from surface micromachined parts Manual assembly fluidic agitation On chip MEMS actuators Parallel external methods Small Machines Large Opportunities NSF Workshop on MEMS Research 1987 1988 K Gabriel J Jarvis and W Trimmer eds U Srinivasan EE C245 EE C245 M S Rodgers and J Sniegowski Sandia National Labs Transducers 99 3 First hinge K Pister et al 1992 U Srinivasan Corner Cube Reflector V Hsu 1999 4 1 On chip Actuation Methods Using Beam Buckling Use actuators i e comb drives vibromotors scratch drives to push hinges into assembled position Fix hinges using ohmic heating friction Use in plane forces to buckle clamped clamped support beam out of plane Can generate few N displace few tens of m Vibromotor results EE C245 EE C245 Daneman et al BSAC Step size 0 27 0 16 m near resonance step size can change with small frequency variations Closed loop control necessary 5 U Srinivasan Challenges Real estate requirements Need closed loop control Parallel External Methods Garcia et al Sandia Labs U Srinivasan 6 Parallel External Methods Fluidic agitation Ultrasonic forces Magnetic deflection Polymer shrinkage Surface tension of droplets Polymer shrinkage Surface tension of droplets U Srinivasan Yi and Liu U of Illinois EE C245 EE C245 E Smela group Univ of MD 7 U Srinivasan Syms Imperial College 8 2 Closed Box Assembly Pop Up MEMS U Srinivasan E Hui Howe group EE C245 EE C245 Complex structures one simple assembly step Sandia SUMMiT 4 level process used to fabricate pop up MEMS 9 E Hui Howe group Lecture Outline Integration with Circuitry Assembly of Hinged MEMS Structures Assembly of MEMS With Other Microdevices Serial Assembly pick place Parallel Assembly Processes Guided Transfer Self Assembly U Srinivasan MEMS CMOS co fabrication MEMS CMOS mixed Boutique processes Analog Devices MEMS first CMOS last Need to own or control CMOS fab Sandia CMOS first MEMS last EE C245 Can use CMOS foundry thermal budget for MEMS is a challenge EE C245 10 U Srinivasan 11 Challenges CMOS and MEMS wafer sizes Material and process incompatibilities Yield losses from high mask counts MEMS specific dicing and packaging Microassemble finished components instead U Srinivasan 12 3 Motivation for Integration Smart Dust Mote Advantages increased functionality higher performance lower cost Brittle star on SEM of brittle star eyes EE C245 EE C245 Next generation of microsystems K Pister group BSAC now on leave at Dust Inc Berkeley 13 U Srinivasan MEMS microelectronic microoptical microfluidic components on a single substrate Why Microassembly Adapted from K B hringer 15 et al May 1998 EE C245 Technique requirements EE C245 Lecture Outline Avoid materials and process incompatibilities and optimize elements separately Reduce materials cost Reduce yield losses U Srinivasan 14 Assembly Classification Assembly vs co fabrication Massively parallel low cost high speed Microscale positioning precision Mechanical bonding and electrical interconnection available Joanna Aizenberg et al Nature 2002 U Srinivasan Assembly of Hinged MEMS Structures Assembly of MEMS With Other Microdevices Serial Assembly pick place Parallel Assembly Processes Guided Transfer Self Assembly Serial microassembly pick and place on the microscale Parallel microassembly multiple parts assembled simultaneously Guided Pre determined destination for parts ensured by guiding Self Assembling Parts initially in random positions energy minimization determines part destinations without active intervention U Srinivasan 16 4 Microassembly System Robotic Microassembly Serial robotic pick place assembly Hierarchy of adhesive forces must be established Commercial tooling advancing for high density consumer electronics e g cell phones 5 x 106 chip capacitors in a coffee mug Murata 2002 Suss MicroTEC bonder can achieve submicron accuracy in x y z Imaging optical mixing of two images Robotic bonding arm parts as small as 250 300 m2 range of bonding forces available 10 g to 200 kg 6 DOF motion temp up to 450 C C Keller and R T Howe MEMS 97 U Srinivasan SUSS FC 250 Production Device Bonder EE C245 EE C245 MEMS PI 17 18 U Srinivasan SUSS Microassembly MEMS Actuator Arrays Use MEMS cooperatively Regular grid of motion pixels move parts in parallel until they reach potential energy minima Challenges EE C245 EE C245 High cost low speed Surface effects do lead to unwanted adhesion Compromised electrical performance U Srinivasan 19 Microcilia arrays built on top of CMOS Bohringer et al 2000 Each actuator curls into out of substrate plane due to CTE differences of 2 polyimide layers Linear translation diagonal motion and vector field operations like centering and squeeze field manipulations possible U Srinivasan 20 5 Wafer to Wafer Transfer Parallel assembly Wafer to wafer transfer Self assembly Wafer to wafer transfer Microstructures held on donor wafer by break away tethers Transferred occurs between aligned donor and target wafers EE C245 Transfer of Hexsil actuator onto CMOS wafer Donor Wafer Hexsil Cap Hexsil Cap Pros and Cons Parallel assembly Smaller area electrical connections Inefficient use of materials Yield losses U Srinivasan Target Wafer Sandia IMEMS Cohn PhD 1998 Heck PhD 2001 Howe group BSAC EE C245 Transfer Results 21 Angad Singh et al Transducers 97 U Srinivasan Quality Factor Degradation 22 Recent Results Tuning fork resonator transferred Quality factor degradation observed Work by C Nguyen group U of Michigan Transducers 01 3000 1500 before transfer 1200 500 after In metal U Srinivasan EE C245 EE C245 Angad Singh et al Transducers 99 23 U Srinivasan 24 6 Alien Technology s Fluidic Self Assembly Self Assembly Complex structures form using information embedded in components without individual
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