A beryllium chip was a component of some types of atomic clocks.
The clock designed by Professor Wagg used a beryllium chip. (TV: Doctor Who)
Around August 1999, Dieter Allegro stole the chip. Bill Bishop was sent to retrieve it. (PROSE: The Danger Men)
The Eighth Doctor stole the chip to repair a malfunction in the TARDIS which had been caused by the Master. The chip's installation closed the Eye of Harmony which the Master had opened. (TV: Doctor Who) Daniel Joyce gave Wagg a new beryllium chip. (PROSE: Unnatural History)
When the Doctor arrived in a hotel in Singapore in 2008, the receptionist told him that the clocks couldn't be wrong because they had beryllium chips. (AUDIO: The Girl Who Never Was)
The timecode on the holo-prints of Lexy's body was made with a beryllium chip. (AUDIO: Square One)