Sunday, June 04, 2006

US Patent 7053736 - MEMS Switch With Restoring Force Member

Micromechanical switches have some advantages over electronic switches including resistance to electrostatic shock, low leakage current, and higher power transmission. Often MEMS switches are in the form of a lever or cantilever that is bent from an open state, in which the cantilever is out of contact with an opposing electrode, to a closed state, in which the cantilever is in contact with the opposing electrode, by application of a voltage to a separate gate electrode. However, one of the problems of this configuration is that the the cantilever often sticks to the opposing electrode requiring excessive voltage for release. The inventors of this patent offer the solution of providing a second cantilever above the first to provide a restoring force and thus reducing the voltage necessary for releasing the cantilever to the open state.

The independent claims read:

1. A microelectromechanical device, comprising a beam configured to apply an opening force on a closed switch, wherein the opening force is substantially independent of a force stored in the closed switch.

6. A microelectromechanical device, comprising: a switch beam spaced above a closing gate and a contact structure; and an additional beam configured to apply a force on the switch beam in a direction away from the contact structure.

31. A method for opening a switch, comprising: reducing an attractive force between a switch beam and a closing gate; and externally applying a mechanical force on the switch beam in a direction away from the closing gate.

Reading the file history of this case I actually found a few disturbing things. First off the Examiner applied separate rejections based on two different prior art references under 35 USC 102e. The earliest of these references had a US priority date of November 9, 2001 whereas the filing date of this patent was Sept. 30, 2002. To counter these rejections the applicant provided an affidavit stating an earlier conception date prior to Sept.30,2002. However, in this affidavit the only proof of earlier reduction to practice was an Invention Disclosure Form without any signatures of the inventors or witnesses and with the conception date blacked out with a marker. I'm not sure whether this is common practice but I've never had a case like that when I was an Examiner. The rule covering swearing back a reference (37 CFR 1.131) requires a showing of facts rather than only an allegation of an earlier reduction to practice and the applicant didn't seem to provide such a showing. Nevertheless it appeared adequate to the Examiner handling this case.

Unfortunately, one of the applied anticipatory references (US 6720851) has a foreign priority date to an even earlier date so, while not applicable under 35 USC 102e I doubt the applicant could win an interference hearing.

Also unfortunately the Examiner missed even earlier anticipatory prior art such as