ERL MEMS Interconnect Design

The ability to create microelectro-mechanical systems, dubbed MEMS, on the same surface and with the same fabrication process as integrated circuits will give future chip makers an explosion of options in their designs. MEMS, by itself, enables designers to create motors, sensors, and actuators on the micron scale. Nevertheless, the real benefits of this technology will be realized as a result of manufacturability. Because MEMS designs can be implemented in the same thin-film and doped silicon that make up IC's, designers can easily integrate this technology into VLSI and ULSI, creating designs for a broader range of applications without a major increase in technology cost.

We are investigating MEMS design for applications in high bandwidth optical routing, optical scanners and laser radar, and high speed digital switching and RF electrical signal routing.

Current Students working on these projects

• Bruce Duewer. PhD student working on Applications of MEMS to High Speed Interconnect.
• Umut Eksi. PhD student working on Novel Interconnect Circuits.
• Som Palchuadhury. MS student working on Optical Interconnect.
• John Tucker. MS student working on Applications of MEMS to High Speed Interconnect.
• John Wilson. PhD student working on Applications of MEMS to RF and Microwaves.
• David Winick. PhD student working on Applications of MEMS to Laser Radar.

Overview of Research Chips

Here are our first two chip designs:

HC1 HoloChip1 (or HC1, for short) is the name we gave to the first of this series of MEMS chips exploring high-speed signal routing and display applications. The chip includes MEMS structures for both electrical and optical interconnect.	HC2 HoloChip2 (or HC2, for short) is the name we gave to the second of this series of MEMS chips exploring high-speed signal routing and display applications. The chip includes MEMS structures for both electrical and optical interconnect.

These chips include elements for study in the following domains:

• Optical Interconnect
  • Optical Alignment
  • Reconfigurable Interconnect
  • Realignable Interconnnect
• Electrical Interconnect
  • Sliding Switches
  • Rotating Switches
  • Levered Switches
  • Scraping Switches
  • Latching Switches

Of the many micro-actuation methods available, we chose to study the following:

• Electrostatic (Capacitive) Deformation
• Electrostatic Actuation of Free-moving Structures
• Electromagnetic Coils

Fabrication Process

Our first two chips were fabricated via the MUMPs process, which consists of the following layers:

Layer	Size	Description	Notes
Metal	500nm	Cr-Pt	Evaporation deposited, liftoff patterned
Poly2	1.5um	2nd structural layer	Doped just as Poly1 through annealing *
Oxide2	500nm	PSG	Thin & Thick etched **
Poly1	2.0um	1st structural layer	Annealed/Phosphorus doped above & below
Oxide1	2.0um	PSG	LPCVD/RIE Dimpled 750nm deep/RIE
Poly0	500nm	0-layer polysilicon	LPCVD/masked/Reactive Ion Etched
SiN	500nm	Isolation layer	LPCVD -unetchable-
Wafer	100mm	Isolated substrate	Heavily doped n-type(100) w/ Phosphorus

* creates fine-grain size and low internal stress; poly is undoped initially.
** thick etch goes through oxides until it reaches nitride or substrate.

Other known facts about the process:

Smallest distinguishable feature size	2um
Young's Modulus for polysilicon layers	155.0E12 Pascals ***
Polysilicon resistivity	1e-3 Ohm*cm

*** assuming structures are sufficiently large that surface tensions do not play a significant factor.

3-D Visualization Demo!

For those with browsers configured to view VRML files (Virtual Reality Modeling Language):

• An on-line 3-D model of the device pictured above and to the left is available; and also two others: hinge, flawed-hex-piston.
  (For those sites with `vrweb' installed, I would suggest first switching to the Wireframe display mode for quicker redraws.)
• The cif2vrml package was used to generate this directly from the layout.

Related Information

• A Guide for Designing Microelectromechanical Systems in MUMPs (MCNC's multi-user process).
• MCNC Facility is where we have submitted some designs for fabrication
• MEMS Interchange, on the Semiconductor Subway, contains links to many other sites involved in this technology
• SPIE (The International Society for Optical Engineering) has information on all the goings on in the world of optics
• The Optical Society of America has information on this and many other areas of optical research