Tuesday, October 03, 2006

US Patent 7114397 - MEMS Parallel Plate Pressure Sensor


Parallel plate capacitive sensors are commonly employed to MEMS sensors to detect changes in pressure or as motion sensors. As the displacement between the plates changes due to pressure or motion, the capacitance formed by the plates also changes. This patent teaches forming such a pressure sensor so that it may fit in a smaller area by forming the capacitive plates perpendicular to a base substrate, rather than in parallel to the substrate which is more typical. Claim 1 reads:

1. An apparatus, comprising: a substrate defining a plane; a first conducting plate substantially normal to the substrate; and a second conducting plate substantially normal to the substrate and deformable in response to a pressure.

Speaking as a registered patent agent (and former patent examiner), I find claims such as the above kind of disturbing. On the one hand, given the full context and advantages of the invention (i.e. a MEMS sensors requiring less substrate area) and given the difficulty of fabrication of vertical plates on a substrate, I can see why the invention may be patent worthy. However, the attorney or agent who drafted the above claim clearly did not phrase the claim in such a context and instead opted for a much broader scope. In my opinion, this is bad practice and a failure of common sense on the part of the attorney/agent leading to a claim that is begging to be invalidated or ridiculed for undue breadth. I mean c'mon. Two metal plates held perpendicular to a support. I don't know whether to laugh or cry.