10 December 2010

IMEC reports ultra-thin AlGaN-on-Si solar-blind EUV imager

At the 56th annual IEEE International Electronic Devices Meeting (IEDM 2010) in San Francisco, CA, USA this week (6–8 December), the IMEC research center of Leuven, Belgium presented an ultra-thin hybrid AlGaN-on-Si-based extreme ultraviolet (EUV) imager with a pixel-to-pixel pitch of just 10µm.

The wide-bandgap aluminum gallium nitride (AlGaN) material provides insensitivity to visible wavelengths and enhanced UV radiation hardness compared to silicon. Backside illumination in a hybrid design was used to achieve the very small pixel-to-pixel pitch (10µm).

UV 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 infrared radiation.

IMEC’s backside-illuminated EUV imager is based on a hybrid design that integrates an AlGaN sensor on a silicon read-out chip. A submicron-thick AlGaN layer was grown on a Si(111) wafer using molecular beam epitaxy (MBE) and a focal plane array of 256x256 pixels with a pixel-to-pixel pitch of 10µm was processed. Each pixel contains a Schottky diode optimized for backside illumination.

A custom read-out chip, based on capacitance transimpedance amplifiers (TIAs), was fabricated in 0.35µm CMOS technology. The AlGaN wafer and read-out chip were post-processed with indium solder bumps with 10µm pixel-to-pixel pitch, achieving what is claimed to be excellent uniformity.

The focal plane array and read-out chip were assembled using flip-chip bonding, and subsequently the silicon substrate was locally removed to enable backside illumination of the active AlGaN layer. Finally, the imager was packaged and wire-bonded. Measurements on the imager demonstrated what is claimed to be excellent response down to a wavelength of 1nm.

The 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).

Tags: IMEC AlGaN-on-Si MBE

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