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A new solid-state field-effect bipolar device designated the BICFET for bipolar inversion channel field-effect transistor is proposed. The device, which is bipolar in nature and relies upon the field-effect inducement of an inversion layer, that corresponds to the conventional neutral base of a bipolar transistor, features potentially very high current gain (105), very high current operation (106A/cm2) and thus high transconductance (4 × 107S/cm2) and low input capacitance. The BICFET has three terminals: a metallic emitter which makes ohmic contact to a semi-insulator (wide bandgap semiconductor); a source terminal which contacts an inversion layer formed at the interface between the semi-insulator and the semiconductor depletion region; and a collector which is the semiconductor bulk. An important feature of this bipolar device is the absence of the base layer and all of its associated problems. The principle of operation is based on controlling the flow of majority carriers through the semi-insulating region to the collector by the biasing action of charge in the inversion channel. A significant advantage of the BICFET structure is that it is not subject to the scaling limitations due to punchthrough as in the MOS or junction bipolar transistor. The problem of threshold control in the MOS transistor is avoided, so the requirement of very shallow junctions may be relaxed.
Date of Publication: Nov 1985