Microwave heterojunction bipolar transistors suitable for low-power, low-noise and high-power applications and method for fabricating same

Claim 2

A heterojunction bipolar transistor having an emitter, a base, and a collector, wherein said base is at least one island of semiconductor material, said island having a boundary that lies within, and is separate from, any boundaries of an active area of said transistor.

Claim 3

The microwave heterojunction bipolar transistor of claim 1 wherein said at least one base island is surrounded by a non-conductive area.

Claim 4

The microwave heterojunction bipolar transistor of claim 2 wherein said at least one base island is contacted by a conductive layer at least partially overlying said non-conductive area.

Claim 5

The microwave heterojunction bipolar transistor of claim 1 wherein said at least one base island is contacted by an air bridge.

Claim 6

The microwave heterojunction bipolar transistor of claim 1 wherein said collector and said base are GaAs and said emitter is Al x Ga 1-x As.

Claim 7

The microwave heterojunction bipolar transistor of claim 1 wherein said emitter is at least one island of semiconductor material, said at least one island not crossing any boundaries of said active area of said transistor.

Claim 8

A heterojunction bipolar transistor comprising: a semi-insulating semiconductor substrate; a collector layer of a first conductivity type disposed on said substrate; at least one base island of a second conductivity type disposed on said collector layer; an active area defined in said substrate and said collector layer and encompassing said at least one base island; an emitter of said first conductivity type disposed on said at least one base island and having a wider energy bandgap than said at least one base island; and conductive contacts disposed on said collector layer, said at least one base island and said emitter, wherein said at least one base island is disposed on said collector layer and has a boundary that lies within, and is separate from, any boundaries of said active area.

Claim 9

A heterojunction bipolar transistor comprising: a semi-insulating semiconductor substrate; a collector layer of a first conductivity type disposed on said substrate; at least one base island of a second conductivity type disposed on said collector layer; an active area defined in said substrate and said collector layer and encompassing said at least one base island; an emitter of said first conductivity type disposed on said at least one base island and having a wider energy bandgap than said at least one base island; and conductive contacts disposed on said collector layer, said at least one base island and said emitter, wherein said at least one base island is disposed on said collector layer and has a boundary that lies within, and is separate from, any boundaries of said active area.

Claim 10

The microwave heterojunction bipolar transistor of claim 7 wherein said active area is defined by ion implantation.

Claim 11

The microwave heterojunction bipolar transistor of claim 7 wherein said at least one base island is surrounded by a non-conductive area.

Claim 12

The microwave heterojunction bipolar transistor of claim 9 wherein said at least one base island is contacted by a conductive layer at least partially overlying said non-conductive area.

Claim 13

The microwave heterojunction bipolar transistor of claim 7 wherein said conductive contact disposed on said at least one base island is an air bridge.

Claim 14

The microwave heterojunction bipolar transistor of claim 7 wherein said substrate, said collector layer and said at least one base island are GaAs and said emitter is Al x Ga 1-x As.

Claim 15

The microwave heterojunction bipolar transistor of claim 7 wherein said conductive contacts are ohmic.

Claim 16

The microwave heterojunction bipolar transistor of claim 7 wherein said collector layer, said at least one base island and said emitter are deposited epitaxially.

Claim 17

The microwave heterojunction bipolar transistor of claim 14 wherein said collector layer, said at least one base island and said emitter are doped in situ.

Claim 18

The microwave heterojunction bipolar transistor of claim 7 wherein said first conductivity type is n-type and said second conductivity type is p-type.

Claim 19

The microwave heterojunction bipolar transistor of claim 7 wherein said emitter is at least one island of semiconductor material, said at least one island not crossing any boundaries of said active area of said transistor.

Claim 20

A monolithic microwave integrated circuit (MMIC) including a plurality of electrically interconnected heterojunction bipolar transistors disposed on a semi-insulating semiconductor substrate wherein each of said transistors comprises: a collector layer of a first conductivity type disposed on said substrate; at least one base island of a second conductivity type disposed on said collector layer; an active area defined in said substrate and said collector layer and completely encompassing said at least one base island; an emitter island of said first conductivity type disposed on said at least one base island and having a wider energy bandgap than said at least one base island; and conductive contacts disposed on said collector layer, said at least one base island and said emitter, wherein said at least one base island is disposed on said collector layer and has a boundary that lies within, and is separate from, any boundaries of said active area.

Claim 21

A monolithic microwave integrated circuit (MMIC) including a plurality of electrically interconnected heterojunction bipolar transistors disposed on a semi-insulating semiconductor substrate wherein each of said transistors comprises: a collector layer of a first conductivity type disposed on said substrate; at least one base island of a second conductivity type disposed on said collector layer; an active area defined in said substrate and said collector layer and completely encompassing said at least one base island; an emitter island of said first conductivity type disposed on said at least one base island and having a wider energy bandgap than said at least one base island; and conductive contacts disposed on said collector layer, said at least one base island and said emitter, wherein said at least one base island is disposed on said collector layer and has a boundary that lies within, and is separate from, any boundaries of said active area.

Claim 22

The monolithic microwave integrated circuit of claim 18 wherein said active area is defined by ion implantation.

Claim 23

The monolithic microwave integrated circuit of claim 18 wherein said at least one base island is surrounded by a non-conductive area.

Claim 24

The monolithic microwave integrated circuit of claim 20 wherein said at least one base island is contacted by a conductive layer at least partially overlying said non-conductive area.

Claim 25

The monolithic microwave integrated circuit of claim 18 wherein said conductive contact disposed on said at least one base island is an air bridge.

Claim 26

The monolithic microwave integrated circuit of claim 18 wherein said substrate, said collector layer and said at least one base island are GaAs and said emitter is Al x Ga 1-x As.

Claim 27

The monolithic microwave integrated circuit of claim 18 wherein said conductive contacts are ohmic.

Claim 28

The monolithic microwave integrated circuit of claim 18 wherein said collector layer, said at least one base layer and said emitter are deposited epitaxially.

Claim 29

The monolithic microwave integrated circuit of claim 25 wherein said collector layer, said at least one base island and said emitter are doped in situ.

Claim 30

The monolithic microwave integrated circuit of claim 18 wherein said first conductivity type is n-type and said second conductivity type is p-type.

Claim 31

The monolithic microwave integrated circuit of claim 18 wherein said emitter is at least one island of semiconductor material, said at least one island not crossing any boundaries of said active area.