According to an article at EETimes, IBM and Georiga Tech have demonstrated a 500 GHz Silicon-germanium (SiGe) chip, operating at 4.5 Kelvins.

The 'frozen chip' was fabricated by IBM on 200mm wafers, and, at room temperature, the circuits operated at approximately 350 GHz.

By comparison, 500 GHz is more than 250 times faster than today's cell phones, which typically operate at approximately 2 GHz, according to the organizations.

The experiments, conducted jointly by IBM and Georgia Tech, are part of a project to explore the ultimate speed limits of silicon germanium (SiGe) devices, which are said to operate faster at cold temperatures.

This news article was written on June 20, 2006, quoting EETimes.