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Airbridges

Part of the Applications Notes Line
Photoresists & Specialty Chemicals

Airbridges use air as the dielectric between two conductors to extend the operating frequency. Fabricating microelectromechanical systems (MEMS) where airbridges or cantilevers are required has been done for many years using polymethylglutarimide (PMGI) as a sacrificial release layer.

PMGI: Benefits/Attributes

  • Spin-coatable from 10nm to 6µm in a single coat
  • No intermixing with imaging resist
  • High thermal stability <300 C (Tg~189C)
  • Strippable in NMP, DMSO and aqueous-based developers
  • Resistant to conventional semiconductor solvents
  • Excellent adhesion to various substrates

Process Flow


10 GHz GaAs Modulator with Airbridge. Image courtesy of Nortel.

Plate overlay layer
• 3μm – 5μm plated gold
• Strengthen bridge landings
• Compensate stress gradients


Remove PMGI sacrifical layer
• Wet release process
• All organic solvents
• End with acetone
• Boil off acetone in vacuum