MEMS applications in electrical metrology

Microelectromechanical systems (MEMS) can offer a competitive alternative to conventional technologies for precision electrical measurements. This dossier reviews recent work on the development of microsystem solutions for electrical metrology. Voltage references, RMS voltage converters – (RMS-DC), high-frequency power detectors and reference oscillators are examined. The operating principle of these components is based on the balance between electrical and mechanical restoring forces in micro-machined silicon structures. In RMS voltmeters and RMS-DC converters, the quadratic relationship between voltage and force between the electrodes of a moving-armature capacitor is exploited; MEMS-based voltage reference operation is based on the pull-in phenomenon of a moving-armature capacitor.

The advantages of devices using microsystems over more conventional solutions are small size, low power consumption, low cost of mass production, stability and lower 1/f noise. Variations caused by electrostatic charge effects have proved to be a key problem. This problem has not yet been completely solved in DC applications, but can be avoided by using AC actuation and compensating for the component's internal DC potentials. In this way, an AC voltage reference with a relative stability of less than 2 × 10 ^–6 over a three-week measurement period was achieved. Much better stability was demonstrated with a microsystem-based reference oscillator: no change in resonant frequency was observed at a relative uncertainty level of 10 ^–8 in a measurement conducted over more than a month.

Microsystem-based components have also been developed for radio frequency and microwave power measurements, up to frequencies of around 40 GHz. Unlike conventional high-frequency power detectors (wattmeters), which measure absorbed power, microsystem devices measure the power transmitted through the detector.

This text was translated from English by Anne-Marie GAULIER.