Recent experimental results on permeable base transistors

Permeable base transistors (PBTs) having an fmaxof 30 GHz have been fabricated and an amplifier using these devices has yielded a noise figure of 2.5 dB at 8 GHz with 10 dB associated gain. Detailed low frequency and microwave measurements of representative devices have been used to determine element values for a device equivalent circuit. In particular the devices with an fmaxof 30 GHz have a lower base resistance than previous devices which results in a net improvement in performance in spite of their lower transconductance. The transconductance and collector currents have been generally lower than predicted and have not been reproducible. We believe that a major source of this problem is due to tungsten debris in the openings of the tungsten grating. The data from the numerical simulations indicate that the devices which we are presently fabricating should have an fmaxabove 200 GHz.