Bias stress tests of extremely high doped base HBTs

Recently, there has been a great deal of interest in HBTs for ultra-high performance applications, such as low-noise oscillators at 77 GHz and power amplifiers at K-band and above. We have also demonstrated a 1 W amplifier with 65% PAE at 20 GHz. Such performance is extremely appealing for a number of applications, including satellite communications. However, to obtain the performance needed at these frequencies, device design must be extremely aggressive. This includes the use of heavily doped base layers to reduce base resistance. The purpose of this work is to describe what is to our knowledge the first set of bias-stress tests performed on ultra-high doped base HBTs (C⩾10²⁰ cm^-3)