Nanoelectronics research specialist, Imec, has developed a new platform based on its SiGe above-ic technology, which it claims improves the performance of state-of-the-art mems.
The new devices are a 15µm SiGe micromirror and a grating light valve for high resolution displays. The devices were developed with imec's generic cmos compatible mems process for the monolithic integration of mems devices directly on top of cmos metallisation.
The 15µm micromirror, designed for use in display systems, uses an innovative electrostatic actuation mechanism relying on six electrodes. According to imec, the design enables analogue pulse-width modulation (pwm) instead of the binary-weighed pwm of traditional mems-based micromirrors.
This actuation mechanism is said to allow display of a large range of greyscale values, while binary-weighed pwm depends on the number of sub-frames or bit-planes.
Imec says that by using analogue pwm, it can lead to higher response speed, less image processing hardware and less memory. As the analogue pwm is implemented on the mems level instead of on the cmos level, a simplified electronic circuit is enabled.
The second device is a grating light valve, a mems reflection grating producing bright and dark pixels in a display system by controlled diffraction of incident light due to electrostatic deflection of microbeams. The grating light valve uses clamped-clamped microbeams which are suspended over an electrode. It can modulate the intensity of the diffracted light when an actuation voltage is applied to half of the beams. Display systems using such a technology provide a high contrast ratio, high resolution and high brightness. Imec says that both the mirrors and grating light valves were realised with a 300nm thick SiGe structural layer.
The devices have been developed as part of the Flemish Strategic Basic Research project Gemini, a collaboration between imec, Ghent University and Katholieke Universiteit Leuven.
Imec's technology platform, set up in its 200mm fab, to integrate mems and its readout and driving electronics on one chip, has been used to design and process the devices.
The platform consists of a number of standard modules (cmos protection layer, mems via and poly-SiGe electrode, anchor and poly-SiGe structural layer and a thin-film poly-SiGe packaging module) which imec claims can be processed at 450
ºC above standard cmos. Optional modules can be added, depending on the functionality that is needed and, according to imec, this monolithic approach results in more compact systems - with a reduced assembly and packaging cost - and a higher performance than current hybrid systems.
