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Researchers use ink-jet to print MEMS switches

Posted: 09 Dec 2011     Print Version  Bookmark and Share

Keywords:display backplane  MEMS switch  ink-jet printing 

University of California Berkeley (UCB) researchers describe a process to print MEMS switches using an ink-jet printer that they say can be used to create flexible display backplanes. The low thermal process budget also makes inkjet-printed MEMS technology a potential candidate for large-area systems on glass, according to the researchers.

The switch is an electrostatically-operated cantilever beam type in which a voltage on a gate electrode attracts the beam to close with a contact. The removal of the voltage allows the beam to spring back breaking contact. The total area of the device is about 1 x 1mm although there is scope of scaling the manufacture.

Traditionally active-matrix switching for display backplanes has been done by amorphous silicon thin-film transistors, although recently organic polymers have also been applied to the task. Both types of TFT suffer from some leakage current in the off-state and some resistance in the on-state. The UCB researchers said their inkjet-printed MEMS switch has near ideal characteristics for the application of zero off-state leakage and on-state resistance of about 10Ω.

The switch is made by repeated inkjet printing passes to build up conductive and insulator layers. A layer of polymethylmethacrylate (PMMA) is used as a sacrificial layer to separate the cantilever from the gate contact below.

The gate, drain and source electrodes are printed on to an oxidized silicon wafer using a silver particle ink. Cross-linked poly-4-vinylphenol (PVP) is baked at 180°C for 30min to form an insulating gate dielectric layer. The drain electrode is thickened using in the contacting region by multiple print cycles. The PMMA thickness is about 2µ.

The source beam is about 100 x 550µ and printed on top of the PMMA. The thickness of the beam is also built up by repeated printing at about 450nm per printed later. The researchers report that they found the beam needed to be greater than 1.6µ thick to avoid failure. The last manufacturing step is the selective removal of the PMMA using acetone at 50°C.

The researchers concluded that the device has moderate switching delay of about 10µs and with dimensional scaling, the performance should be suitable for video-rate active-matrix display applications.

- Peter Clarke
  EE Times

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