IMEC touts silicon-germanium MEMS and gallium-nitride-on-silicon technologies

Rick Nelson, Editor-in-Chief -- EDN, August 26, 2010

The MEMS capability centers on the development of a 15-micron silicon-germanium micromirror and a grating light valve for high-resolution displays. IMEC realized the devices with its generic CMOS-compatible MEMS process for the monolithic integration of MEMS devices directly on CMOS metallization. The micromirror, targeting use in display systems, uses an electrostatic actuation mechanism relying on six electrodes. The design enables analog PWM (pulse-width modulation) instead of the binary-weighted PWM of current MEMS-based micromirrors. IMEC’s novel actuation mechanism allows display of a large range of gray-scale values, whereas binary-weighted PWM depends on the number of subframes or bit planes. The use of analog PWM thus leads to higher response speed, less image-processing hardware, and less memory. Moreover, IMEC implements the analog PWM on the MEMS level instead of on the CMOS level.

The grating light valve employs MEMS-reflection grating and produces bright and dark pixels in a display system. Diffraction of incident light due to electrostatic deflection of microbeams in suspension over an electrode controls the display system. The display system can modulate the intensity of the diffracted light when you apply an actuation voltage to half of the beams. Display systems using such a technology provide a high contrast ratio, high resolution, and high brightness. IMEC realized both the mirrors and the grating light valves with a 300-nm-thick silicon-germanium structural layer.

IMEC developed the devices within the framework of the Flemish SBO’s (Strategic Basic Research’s) Project Gemini, a collaboration among IMEC, Ghent University, and Katholieke Universiteit Leuven. Micron Technology, Applied Materials, and Ultratech have also joined the IIAP (IMEC Industrial Affiliation Program) on gallium-nitride-on-silicon technology. This multipartner R&D program focuses on the development of gallium-nitride-on-silicon-process and -equipment technologies for manufacturing solid-state lighting, such as LEDs, and next-generation power electronics components on 8-in. silicon wafers.

Manufacturers currently build state-of-the-art LED processes on expensive 4-in. sapphire substrates. Depositing the gallium-nitride material on 8-in. silicon substrates could boost the productivity of gallium-nitride-based device-manufacturing processes.

IMEC also announced 70-cm² epitaxial solar cells with efficiency as great as 16.3% on highly doped, high-quality substrates.

Efficiencies reached as much as 14.7% on large-area, low-cost, UMG (upgraded metallurgic grade) multicrystalline silicon substrates, showing the potential for the industrial manufacturing of thin-film epitaxial solar cells.

IMEC