Micro electro-mechanical systems

A method of fabricating a micro electro-mechanical system device comprises: providing at least two layered wafers; selectively etching layers of said wafers and joining the etched wafers to form the device. One or more of said wafers comprises at least two material layers (eg. Si) which, when selectively etched, form a part of the assembled device, said material layers having a layer of a different material (eg. SiO2) therebetween which is resistant to an etchant of said material layers and wherein at least one of said material layers is of a re-selected thickness which is used to define a spacing member for determining a distance between layers of the etched wafers when they are joined. The MOEMS devices may be for example micro-machined tiltable mirrors for use in optical cross connects in optical telecommunications, wavelength tuneable filters in the form of single etalon structures for selecting wavelength channels within wavelength division multiplex (WDM) optical signals, optical switches and variable optical attenuators for use in WDM optical telecommunications systems. The layered wafers may be silicon on insulator (SOI) type.