High frequency bipolar transistor and method of forming the same
AssigneeMotorola, Inc.
InventorsKurt K. Sakamoto, Peter J. Zdebel, Michael G. Lincoln
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Abstract
A high frequency bipolar transistor (30, 60) having reduced capacitance and inductance is formed over a substrate (61). The substrate (61) is heavily doped to form a low resistance current path. A lightly doped epitaxial layer (62) isolates the substrate (61) from layers which form the transistor. The epitaxial layer (62) is the same conductivity type as the substrate (61). A topside substrate contact (73) couples an emitter of the transistor (60) to the substrate (61). The backside of the substrate (61) is metalized and conductively attached to a leaded flag of a leadframe (51) thereby eliminating wirebond inductance in the emitter of the transistor.
Claims24
A high frequency bipolar transistor, comprising:
- a substrate of a first conductivity type;
- a first epitaxial layer of said first conductivity type disposed over said substrate, wherein a doping concentration of said substrate is greater than approximately two orders of magnitude higher than a doping concentration of said first epitaxial layer;
- the bipolar transistor formed over said first epitaxial layer, the bipolar transistor having a collector region, a base region, and an emitter region;
- and
- a topside substrate contact coupled to one of the collector, base, and emitter regions.
A bipolar transistor, comprising:
- a substrate of a first conductivity type;
- a first epitaxial layer of said first conductivity type formed on said substrate, said first epitaxial layer having a doping concentration less than a doping concentration of said substrate;
- a buried layer of a second conductivity type formed on said first epitaxial layer;
- a second epitaxial layer of said second conductivity type formed on said buried layer, said second epitaxial layer forming a collector region of the bipolar transistor;
- a base region of said first conductivity type formed in said second epitaxial layer;
- an emitter region of said second conductivity type formed in said base region;
- and
- a topside substrate contact of said first conductivity type wherein one of a collector, a base, and an emitter of the bipolar transistor is coupled to said topside substrate contact.
A method of extending a frequency response of a bipolar transistor, the method comprising the steps of:
- providing a heavily doped substrate;
- isolating said heavily doped substrate from subsequently formed layers with a lightly doped epitaxial layer formed thereon, said lightly doped epitaxial layer being of similar conductivity type;
- forming the bipolar transistor over said heavily doped substrate;
- forming a topside substrate contact;
- coupling one of a collector region, a base region, and an emitter region to the topside substrate contact;
- and
- conductively attaching a backside of said heavily doped substrate to a leaded flag of a leadframe.
Dependencies are inferred from the claim text.