The Differential SiGe-HBT

A new fabrication method for SiGe-HBTs is presented using molecular beam epitaxy (MBE) for growing the device layers on SiO
2
patterned Si wafers. The epitaxial layers inside the SiO
2
windows are monocrystalline. The polycrystalline Si and SiGe on top of the surrounding SiO
2
is used for the base contact. This technique reduces the parasitic base-collector capacitances. The first differential SiGe-HBTs (DHBTs) show good DC-characteristics and cut-off frequencies f
T
of 65 GHz and f
max
of 38 GHz.