Next generation MOS for space as well as ground-based instruments, including NIRSpec for JWST, require a
programmable multi-slit mask. A promising solution is the use of MOEMS-based devices such as micromirror arrays
(MMA) or micro-shutter arrays (MSA). Both configurations allow remote control of the multi-slit configuration in real
time. Engaged in the design studies for NIRSpec, we have developed different tools for the modelling and the
characterization of these devices. Since, we have continued our studies with commercial TI MMA and we show that in
a 20° ON-OFF configuration, the 3000 contrast requirement is fulfilled for any F# of 8m-class telescopes as well as
Within the framework of the JRA on Smart Focal Planes, micro-mirrors have been selected in order to get a first
demonstrator of a European MOEMS-based slit mask. We have fixed several key parameters: one micromirror per
astronomical object, high optical contrast of at least 3000, tilting angle of 20°, fill factor of more than 90%, size of a
micro-element around 100 × 200 μm2, driving voltage below 100V. The MMA would also work in a wide range of
temperature down to cryogenic temperatures.
Based on these parameters, we have designed a new MMA architecture, using a combination of bulk and surface
micromachining. A first small test array of micro-mirrors was successfully fabricated and shows the desired mechanical
tilting angle of 20° at a driving voltage of about 100V. Preliminary measurements show a surface quality better than
lambda/20. Assembly of small test arrays with their electrode chips and design of larger arrays are under way.