Interfacing SiGe Technology with Nanoscale Magnetic Tunnel Junctions*

Silicon germanium heterojunction bipolar transistors (SiGe HBTs) have been tested at cryogenic temperatures and a theory of operation has been developed for the purpose of interfacing with nanomagnets for rapid magnetic readout and data storage. Magnetic tunnel Junctions have been fabricated by electron beam lithography and shadow evaporation. The magnetization dynamics of these junctions with resistance near the resistance quantum have been measured with a SiGe HBT in a bench-top room temperature test, but these initial measurements were limited by a rise time of approximately 10 microseconds. The next step involves SiGe technology incorporated physically next to the magnetic tunnel junction to increase the measurement bandwidth by effectively transforming the high source impedance of the junction to a lower apparent value. A summary of the measurement results will be discussed including: tunnel magnetoresistance at room temperature and 1.8K, magnetic reversal times at room temperature, and single domain switching times and switching precursors at 1.8K.