Patent ID: 7135757

Claim:
A bipolar transistor, comprising: a substrate; a first layer disposed on said substrate; a collector disposed in said first layer; a second layer disposed on said first layer, said second layer having a base cutout formed therein; a base disposed in said base cutout above said collector; a third layer disposed on said second layer, said third layer including a lead for said base; said lead and said base defining a transition region therebetween, said lead being in contact with said base at said transition region; said third layer having an emitter cutout formed therein, said emitter cutout being provided above said base; an emitter disposed in said emitter cutout; said second layer having an undercut formed therein, said undercut adjoining said base cutout and being disposed between said first layer and said third layer, said undercut having given regions, said base extending at least into said given regions of said undercut; an intermediate layer disposed between said first layer and said second layer, said intermediate layer being selectively etchable with respect to said second layer; a base terminal region provided at least at said undercut between said lead and said base, said base terminal region being in direct contact with said lead and said base; and said intermediate layer defining a contact region at said base and having a cutout formed therein at said contact region under said base terminal region such that said base terminal region is not in direct contact with said intermediate layer; said base extending into said cutout of said intermediate layer.