The effects of radiation on 1/f noise in complementary (npn+pnp) SiGe HBTs

We present the first study of the effects of radiation on low-frequency noise in a novel complementary (npn+pnp) silicon-germanium (SiGe) HBT BiCMOS technology. In order to manipulate the physical noise sources in these complementary SiGe HBTs, 63.3 MeV protons were used to generate additional (potentially noise-sensitive) trap states. The base currents of both the npn and pnp SiGe HBTs degrade with increasing proton fluence, as expected, although in general more strongly for the npn transistors than for the pnp transistors, particularly in inverse mode. For the pnp SiGe HBTs, irradiation has almost no effect on the 1/f noise to proton fluence as high as 5.0×10¹³ p/cm², while the npn SiGe HBTs show substantial radiation-induced excess noise. In addition, unlike for the pnp devices, which maintain an I_B² bias dependence, the 1/f noise of the post-irradiated npn SiGe HBTs change to a near-linear dependence on I_B at low base currents following radiation. That suggests a fundamental difference in the noise physics between the two types of devices.