Base diffusion isolation (BDI) for transistors

A new bipolar integrated circuit structure in which the conventional isolation diffusion is replaced by a diffusion performed at the same time as the base has been proposed (1). Such Base Diffusion Isolation (BDI) transistors without buried collectors have been built in 3µ thick, 0.6Ω2-cm, arsenic doped epitaxial layers on 10Ω-cm boron doped substrates. They require only four masking operations to first level metallization, i.e. they are of about the same complexity as p-channel IGFET circuits.