Method cuts MEMS inspection times

Presently MEMS, or MicroElectro Mechanical Systems, must be tested one at a time, which is a time-consuming and expensive process.

The EU’s SMARTIEHS (SMART InspEction systems for High Speed and multifunctional testing of MEMS and MOEMS) project is developing a better and cheaper testing method for industry.

Kay Gastinger of SINTEF ICT, the Scandinavian research organisation co-ordinating the project, said: ‘Today, tyre pressure sensors are only electrically tested during production, and these tests do not guarantee full functionality.’

The SMARTIEHS method involves an array of interferometers that can accurately identify an object’s shape, changes in shape and vibration.
The idea of the project is to produce a specially designed glass wafer that contains as many as 100 interferometers, and then use this to test 100 circuits on a MEMS wafer in one go.

The scientists will be able to measure the shape, deformation and resonant frequency of the MEMS chips and thus identify manufacturing faults.

Gastinger added: ‘We have already produced a prototype measurement station capable of measuring five chips at a time.’

The prototype consists of a lens wafer, mirror wafer and beam-splitter wafer. The top layer contains 25 tiny lenses, which in principle resemble little microscopes and have an imaging function. Micromirrors at the centre of the lenses produce the interference effect.

When the project is complete, at the end of 2011, the research team expects the demonstrator to be expanded to 50 channels. It is believed this design will enable the number to be easily increased to 100.