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MEMS Design & Fab

Microassembly – deterministic• Sequential: pick and place

• Keller• Yeh

• Wafer scale• On-wafer (Magnetic, triboelectric, motorized,

residual stress, …)• Wafer-to-wafer (Howe, Cohn, Bright)

• Micro-packaging

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Micro-Tweezers (memspi.com)

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Tweezers holding optical fiber

Design: Chris KellerFab: Sandia

Courtesy: MEMS Precision Instruments

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Tweezer gripping Hexsil gear

Courtesy: MEMS Precision Instruments

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Comparison with Commercial subretinal tweezer (Storz)

Photos courtesy Chris Keller,MEMS Precision Instrumentswww.memspi.com

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Synthetic Insects(Smart Dust with Legs)

Goal: Make silicon walk.

•Autonomous•Articulated•Size ~ 1-10 mm•Speed ~ 1mm/s

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Actuating the Legs

1st LinkMotor

2nd LinkMotor

1mm

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Magnetic Parallel Assembly

Solid-State Sensor and Actuator WorkshopHilton Head 1998

Figure 1. (a) An SEM micrograph of a Type I structure. The flap is allowed to rotate about the Y- axis. (b) Schematic cross-sectional view of the structure at rest; (c) schematic cross-sectional view of the flap as Hext is increased.

Figure 2. (a) SEM micrograph of a Type II structure. (b) Schematic cross-sectional view of the structure at rest; (c) schematic cross-sectional view of the structure when Hext is increased.

Parallel assembly of Hinged Microstructures Using Magnetic Actuation

Yong Yi and Chang LiuMicroelectronics Laboratory

University of Illinois at Urbana-ChampaignUrbana, IL 61801

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Sequential parallel assembly

Solid-State Sensor and Actuator WorkshopHilton Head 1998

Parallel assembly of Hinged Microstructures Using Magnetic Actuation

Yong Yi and Chang LiuMicroelectronics Laboratory

University of Illinois at Urbana-ChampaignUrbana, IL 61801

Figure 8. Schematic of the assembly process for the flap 3-D devices. (a) Both flaps in the resting position; (b) primary flap raised to 90º at Hext = H1; (c) full 3-D assembly is achieved at Hext = H2 (H2 > H1 ).

Figure 9. An SEM micrograph of a 3-D device using three Type I flaps. The sequence of actuation is not critical to the assembly of this device.

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Assembly via Residual Stress

Low Insertion Loss Packaged and Fiber-Connectorized SiSurface-Micromachined Reflective Optical Switch

V. Aksyuk, B. Barber, C. R. Giles, R. Ruel, L. Stulz, and D. BishopBell Laboratories, Lucent Technologies, 700 Mountain Ave.

Murray Hill, NJ 07974

Figure 2. Self-Assembling optical shutter. High tensile residual stress metal is deposited on a polysilicon beam anchored at one end. Upon release the metal-poly sandwich structure deforms, moving the free end of the beam upward. The lifting structure engages the cut in the hinged-plate shutter causing it to rotate 90 degrees into tits operating position.

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MEMS Design & Fab

Parallel Assembly via Triboelectricity

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MEMS Design & Fab

OMM 16x16 switch• From www.omminc.com

• 256 hinged mirrors!

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Parallel Assembly via Surface Tension

• Compact, parallel process assembly

• Accuracy and reliability ?

Silicon substrate Silicon substrate

Reflow

Syms, then Bright

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Solder-assembly (Rich Syms)

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Taxonomy of Microassembly

• Parallel microassembly• Multiple parts assembled simultaneously• Deterministic: pre-determined destination for

parts• Stochastic: random process determines

part destinations

• Serial microassembly• “Pick and place” on a microscale

Courtesy: Roger Howe, UCB

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Parallel Microassembly Processes

K. Böhringer, et al, ICRA, Leuven, Belgium, May 1998

Courtesy: Roger Howe, UCB

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Stochastic Parallel Microassembly

• Agitated parts find minimum energy state via an annealing process• Gravitational well: J. S. Smith, UC Berkeley and

Alien Technology Corp., Morgan Hill, Calif.• (video)• Patterned chemical “binding sites”

G. M. Whitesides, Harvard: hydrophobic surfaces formed by self-assembled monolayers define the binding site

Courtesy: Roger Howe, UCB

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MEMS Design & Fab

Biomimetic Approach

• Pattern part surfaces with hydrophobic and hydrophilic regions using self-assembled monolayers (SAMs).

• free energy cost of SAM-water interface is high

• hydrophobic regions act as binding sites

Terfort, A. et al. Nature, 386, 162-4 (1997).

Courtesy: Roger Howe, UCB

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Application to Microassembly

• Pattern complementary hydrophobic shapes onto parts and substrates using SAMs.• no shape constraints on parts• no bulk micromachining of

substrate• submicron, orientational alignment

• Uthara Srinivasan, Ph.D. thesis,UC Berkeley Chem.Eng., May 2001

Courtesy: Roger Howe, UCB

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Mirrors onto Microactuators

• Self-assemble mirrors onto microactuator arrays• Si (100) mirrors• Nickel-polySi bimorph

actuators

U. Srinivasan, M. Helmbrecht, C. Rembe, R. T. Howe, and R. S. Muller, IEEE Opto-MEMS 2000 Workshop, Kawai, Hawaii, Aug. 21-24, 2000

Courtesy: Roger Howe, UCB

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Unreleased Mirrors

• Si(100) mirror array with binding sites, fabricated from SOI wafer

oxide

Si mirror

binding site

Courtesy: Roger Howe, UCB

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Mirrors in Solution

Courtesy: Roger Howe, UCB

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Moore’s Law, take 2

• Nanochips on a dime (Prof. Steve Smith, EECS)

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Mirror on Released Actuator

assembled mirror

binding site

Courtesy: Roger Howe, UCB

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Mirrors on Microactuators

assembled mirror

Courtesy: Roger Howe, UCB

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Mirror Curvature

• Heat-cured acrylate adhesive

• Mirror curvature less than 30 nm

Courtesy: Roger Howe, UCB

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Research Challenges for Self-Assembly Processes

• Assembly extensions: • multi-pass and multi-part simultaneous assembly• Reduce area consumed by binding site, in order to

achieve:

• “High quality” mechanical interconnects

• “High density” electrical interconnects

Courtesy: Roger Howe, UCB

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Post-Assembly Processes

• Polymer adhesives are not sufficient for many MEMS applications

• Good interfaces require high temperatures (> 450o C), which can damage micro-components• Potential solutions:

Local heating through laser

Local resistive heating (Prof. Liwei Lin, UC Berkeley)

Courtesy: Roger Howe, UCB

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Chip-to-chip and wafer-wafer assembly

Flat, thin gold mirror with a thick Copper frame transferred from sourceSubstrate to MUMPS die. Maharbiz, Howe, Pister, Transducers 99MUMPS part by M. Helmbrecht

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MEMS Design & Fab

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MEMS Design & Fab

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Remove substrate!

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Could be 2-axis

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Packaging• IC Packaging extremely well developed

• Reliability• Thermal conductivity• Cost• Size

• Not well addressed• Packaging with unfilled volumes• Packaging in non-standard ambients

• Vacuum• Dry N2• Moist N2• 100 mTorr +/- 1%

• Fiber feedthroughs

• Somewhat addressed• Optical I/O• Packaging induced stresses

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MEMS Design & Fab

2x2 MEMS Fiber Optic Switches

2x2 MEMS Fiber Optic Switches with Silicon Sub-Mount for Low-Cost Packaging

Shi-Sheng Lee, Long-Sun Huang, Chang-Jin “CJ” Kim and Ming C. WuElectrical Engineering Department, UCLA

63-128, engineering IV Building, Los Angeles, California 90095-1594Mechanical and Aerospace Engineering Department

Figure 1. SEM of the 2x2 MEMS fiber optic switch.

Figure 3. SEM of the torsion mirror device.

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2x2 MEMS Fiber Optic SwitchesIntroduction to MEMS

Solid-State Sensor and Actuator WorkshopHilton Head 1998

2x2 MEMS Fiber Optic Switches with Silicon Sub-Mount for Low-Cost Packaging

Shi-Sheng Lee, Long-Sun Huang, Chang-Jin “CJ” Kim and Ming C. WuElectrical Engineering Department, UCLA

63-128, engineering IV Building, Los Angeles, California 90095-1594Mechanical and Aerospace Engineering Department

Figure 4. SEM of the vertical torsion mirror.

Figure 10. SEM of the fiber and ball lens assembly.

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Assembly - Summary• Pick-and-place assembly is the standard of

the IC industry!• Chips, passives into lead frames• Bond wires• Cost is ~1 penny/operation

• Parallel assembly is coming• Wafer-wafer transfer (deterministic)• Fluidic self-assembly (stochastic)