In future space missions for Universe and Earth Observation, scientific return could be optimized using MOEMS devices. Large micromirror arrays (MMA) are used for designing new generation of instruments. In Universe Observation, multi-object spectrographs (MOS) are powerful tools for space and ground-based telescopes for the study of the formation and evolution of galaxies. This technique requires a programmable slit mask for astronomical object selection; 2D micromirror arrays are perfectly suited for this task. In Earth Observation, removing dynamically the straylight at the entrance of spectrographs could be obtained by using a Smart Slit, composed of a 1D micro-mirror array as a gating device. We are currently engaged in a European development of micro-mirror arrays, called MIRA, exhibiting remarkable performances in terms of surface quality as well as ability to work at cryogenic temperatures. MMA with 100 × 200 μm2 single-crystal silicon micromirrors were successfully designed, fabricated and tested down to 162 K. In order to fill large focal planes (mosaicing of several chips), we are currently developing large micromirror arrays to be integrated with their electronics. 1D and 2D arrays are built on wafer with Through Wafer Vias in order to allow routing of the device on wafer backside, foreseeing integration with dedicated ASICs. The yield of these devices as well as contrast enhancement have been successfully implemented.
We have designed, fabricated and tested narrow-band Fabry-Perot filters in the infrared using gold porous mirrors and a silicon spacer layer. The filter peaks at 10 μm and 15 μm have approximately 10% transmission and a 1.5% linewidth. A Fabry-Perot structure with plane metal layers having a similar linewidth would have a transmission of only 0.2%. Thus, for the same linewidth we have improved the transmission by a factor of 50. Apart from the optical enhancements, these filters also have the advantage that they can be made inexpensively in a standard silicon MEMS technology and that their resonances can be finely tuned through post processing.
An integrated position sensor for a dual-axis electromagnetic tilting mirror is presented. This tilting mirror is composed of a silicon based mirror directly assembled on a silicon membrane supported by flexible beams. The position sensors are constituted by 4 Wheatstone bridges of piezoresistors which are fabricated by doping locally the flexible beams. A permanent magnet is attached to the membrane and the scanner is mounted above planar coils deposited on a ceramic substrate to achieve electromagnetic actuation. The performances of the piezoresistive sensors are evaluated by measuring the output signal of the piezoresistors as a function of the tilt of the mirror and the temperature. White light interferometry was performed for all measurement to measure the exact tilt angle. The minimum detectable angle with such sensors was 30µrad (around 13bits) in the range of the minimum resolution of the interferometer. The tilt reproducibility was 0.0186%, obtained by measuring the tilt after repeated actuations with a coil current of 50mA during 30 min and the stability over time was 0.05% in 1h without actuation. The maximum measured tilt angle was 6° (mechanical) limited by nonlinearity of the MEMS system.
Heated tips offer the possibility to create arbitrary high-resolution nanostructures by local decomposition and
evaporation of resist materials. Turnaround times of minutes are achieved with this patterning method due to the high-speed
direct-write process and an in-situ imaging capability. Dense features with 10 nm half-pitch can be written into
thin films of organic resists such as self-amplified depolymerization (SAD) polymers or molecular glasses. The
patterning speed of tSPL has been increased far beyond usual scanning probe lithography (SPL) technologies and
approaches the speed of Gaussian shaped electron beam lithography (EBL) for <30 nm resolution. A single tip can write
complex patterns with a pixel rate of 500 kHz and a linear scan speed of 20 mm/s. Moreover, a novel scheme for
stitching was developed to extend the patterning area beyond the ≤100 μm range of the piezo stages. A stitching
accuracy of 10 nm is obtained without the use of markers. Furthermore, the patterning depth can be controlled
independently and accurately (~1 nm) at each position. Thereby, arbitrary 3D structures can be written in a single step.
Finally, we demonstrated an all-dry tri-layer pattern transfer concept to create high aspect ratio structures in silicon.
Dense fins and trenches with 27 nm half-pitch and a line edge roughness (LER) below 3nm (3σ) have been fabricated.
A high-resolution probe based patterning method is presented using organic resists that respond to the presence of a hot
tip by local material desorption. Thereby arbitrarily shaped patterns can be written in the organic films in the form of a
topographic relief. The patterning process is highly reproducible and repeatable enabling the creation complex relief
structures with arbitrary texture also in the vertical dimension. The patterns can be readily transferred into silicon using
standard RIE technology. The new technique offers a cost-effective and competitive alternative to high-resolution electron-beam lithography in terms of both resolution and speed.