Leuven, Belgium--At the International Electron Devices Meeting (San Francisco, CA; December 6 to 8, 2010) the Interuniversity Microelectronics Centre (Imec) presented an ultra-thin hybrid aluminum gallium nitride on silicon (AlGaN-on-Si)-based extreme-ultraviolet (EUV) imager with a pixel-to-pixel pitch of only 10 µm.
The wide-bandgap AlGaN provides insensitivity to visible wavelengths and enhanced UV radiation hardness compared to Si devices. Backside illumination in a hybrid design was used to achieve a very small pitch. The novel imager shows an excellent detection down to a wavelength of 1 nm.
Ultraviolet detection is of particular interest for solar science, EUV microscopy, and advanced EUV lithography tools. Sensors using wide-bandgap materials overcome the drawbacks of Si-based sensors such as their sensitivity to UV radiation damage and the need for filters to block the unnecessary visible and IR radiation.
Imec's backside illuminated EUV imager is based on a state-of-the-art hybrid design integrating an AlGaN sensor on a silicon readout chip. A submicron-thick AlGaN layer was grown on a Si(111) wafer using molecular-beam epitaxy and a focal-plane array of 256 x 256 pixels was created. Each pixel contains a Schottky diode optimized for backside illumination. A custom readout chip, based on capacitance transimpedance amplifiers, was fabricated in 0.35 µm CMOS technology. The AlGaN wafer and readout chip were post-processed with indium solder bumps with a 10 µm pixel-to-pixel pitch.
The focal-plane array and readout chip were assembled using flip-chip bonding; the silicon substrate was then locally removed to enable backside illumination of the active AlGaN layer. Finally, the imager was packaged and wire-bonded.
These results were obtained in collaboration with CRHEA/CNRS (France) and the Royal Observatory of Belgium in the framework of the BOLD project of the European Space Agency (ESA).
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