The MOS-BI—A monolithic MOS-bipolar integrated structure

To combine the high packing density and high impedance of the MOSFETs and the high driving, surge protective capability of the bipolar transistor, it is most desirable to fabricate both devices in a monolithic structure called the MOS-BI structure. Various structures will be discussed involving different combinations of: enhancement or depletion mode MOSFETs, vertical npn or pnp bipolar transistors and vertical or lateral bipolar transistors. MOSBI structure can be most readily achieved with enhancement mode p-channel MOSFETs and n-p-n bipolar transistor. The p-type diffusion for forming the base of the n-p-n transistor is used also for forming the source and the drain of the MOSFET. The n-type epitaxial background resistivity is in the 2 to 5 Ω-cm range on p-type substrate of