Bipolar junction transistors with a wraparound base layer

A device structure for a bipolar junction transistor, the device structure comprising:

• a substrate;
• a trench isolation region in the substrate, the trench isolation region surrounding an active region of the substrate;
• a collector in the active region of the substrate;
• a base layer including a first section positioned on the active region and a second section oriented at an angle relative to the first section;
• an emitter positioned on the first section of the base layer;
• and
• an extrinsic base layer positioned over the trench isolation region and adjacent to the emitter, the extrinsic base layer including an opening that extends to the first section of the base layer,
• wherein the second section of the base layer is laterally positioned between the extrinsic base layer and the emitter.

A method of forming a device structure for a bipolar junction transistor, the method comprising:

• forming a trench isolation region in a substrate, wherein the trench isolation region surrounds an active region of the substrate;
• forming a collector in the active region of the substrate;
• forming an extrinsic base layer positioned over the trench isolation region;
• forming a base layer including a first section positioned on the active region and a second section oriented at an angle relative to the first section;
• and
• forming an emitter positioned on the first section of the base layer,
• wherein the extrinsic base layer is positioned adjacent to the emitter, the second section of the base layer is laterally positioned between the extrinsic base layer and the emitter, and the base layer includes a third section positioned adjacent to the emitter and over the extrinsic base layer.