US 5,374,844 A · Bipolar transistor structure using ballast resistor

Abstract

A transistor structure incorporates a polysilicon layer which is doped with N-type dopants and is used as an emitter ballast resistor in an array of NPN transistors. In one embodiment, the polysilicon layer is also used as a diffusion source to form N-type emitter regions within a deep and high resistivity P-well, which acts as a relatively high value base ballast resistor for the transistor. In another embodiment, a standard base is used, contributing little base ballast resistance. A buried collector region carries collector current. Preferably, the emitter regions are formed as oblong strips. P-type base contact regions, also generally formed as oblong strips, are formed in the surface of this P-well parallel to the emitter regions. The dimensions of the base contact regions may be varied in order to achieve a constant base-emitter voltage along the entire length of each emitter strip. An emitter metal layer overlies the polysilicon layer and contacts the polysilicon layer through openings in an insulating layer. The resulting three dimensional structure in one embodiment thus incorporates a stacked collector region, base ballast resistor, base region, emitter regions, emitter ballast resistors, and emitter metal layer. In another embodiment, the same three dimensional structure results except that there is no base ballast resistor. Dimensions of the emitter metal layer and other metal layers may be adjusted so that the transistor structure has a trapezoidal shape and requires less silicon real estate.

Claims27

Dependent claims

A bipolar transistor structure comprising:

a semiconductor substrate having a substrate surface of a first conductivity type;
a base region of a second conductivity type formed in said substrate surface, said base region acting as a base for said transistor;
a plurality of emitter regions of said first conductivity type formed in a top surface of said base region;
a first metal layer for conducting emitter current;
and
a plurality of polysilicon ballast resistors connected between associated emitter regions and said first metal layer, said polysilicon ballast resistors being doped with a dopant of said first conductivity type, said dopant in said polysilicon ballast resistors being diffused into said base region to form said associated emitter regions, wherein a first polysilicon ballast resistor connected between a first emitter region and said first metal layer has a resistance value which is greater than a resistance value of a second polysilicon ballast resistor connected between a second emitter region and said first metal layer, and wherein a resistance of said first metal layer between an emitter bias voltage source and said first polysilicon ballast resistor is less than a resistance of said first metal layer between said emitter bias voltage source and said second polysilicon ballast resistor.

3 more elements

A bipolar transistor structure comprising:

a semiconductor substrate having a substrate surface of a first conductivity type;
a base region of a second conductivity type formed in said substrate surface, said base region acting as a base for said transistor;
one or more emitter regions of said first conductivity type formed in a top surface of said base region;
a first metal layer for conducting emitter current;
one or more polysilicon ballast resistors connected between associated emitter regions and said first metal layer;
one or more oblong base contact regions formed in said base region, said base contact regions being of said second conductivity type and more highly doped than said base region, a portion of each of said base contact regions underlying said first metal layer and said polysilicon ballast resistors;
and
a second metal layer for conducting base current, said second metal layer contacting only ends of said oblong base contact regions,
wherein emitter current in said first metal layer flows in a direction substantially perpendicular to base current flowing in a longitudinal direction in said oblong base contact regions to or from said second metal layer.

6 more elements

A bipolar transistor structure comprising:

a semiconductor substrate having a substrate surface of a first conductivity type;
a base region of a second conductivity type formed in said substrate surface, said base region acting as a base for said transistor;
a plurality of oblong emitter regions of said first conductivity type formed in a top surface of said base region, each of said emitter regions being formed in said base region so as to form a linear array of emitter regions;
a plurality of oblong base contact regions of said second conductivity type formed in said top surface of said base region, each of said base contact regions being more highly doped than said base region, each of said oblong base contact regions being substantially parallel to said oblong emitter regions;
a doped polysilicon layer overlying and insulated from said base region and said base contact regions and contacting said emitter regions, said polysilicon layer having a resistance;
an emitter metal layer overlying said polysilicon layer and contacting said polysilicon layer at selected areas on said polysilicon layer, said emitter metal layer conducting emitter current, whereby emitter current flows between said emitter regions and said emitter metal layer through said polysilicon layer, said polysilicon layer providing emitter ballast resistance for each transistor formed with said transistor structure;
and
a base metal layer for conducting base current, said base metal layer contacting each of said oblong base contact regions only at ends of said base contact regions so as to energize said base contact regions with a base bias voltage.

5 more elements

Dependencies are inferred from the claim text.

Bipolar transistor structure using ballast resistor

Life of this patent

Bipolar transistor structure using ballast resistor

Life of this patent

Abstract

Claims27