Semiconductor device with a wrapped finger element

A transistor die comprising:

• a semiconductor substrate;
• an input terminal integrally formed over the semiconductor substrate;
• an output terminal integrally formed over the semiconductor substrate;
• a source through-substrate via (TSV) integrally formed in the semiconductor substrate and positioned between the input and output terminals;
• a shared source contact integrally formed on the semiconductor substrate and electrically coupled to the source TSV with first side and an opposed second side extending longitudinally between the output terminal and the input terminal;
• a peripheral ancillary region of the semiconductor substrate located adjacent to the shared source contact and positioned between the shared source contact and the output terminal;
• first and second primary drain finger contacts integrally formed on the semiconductor substrate and electrically coupled to the output terminal, wherein the first primary drain finger contact extends from the output terminal toward the input terminal past the first side of the shared source contact and wherein the second primary drain finger contact extends from the output terminal toward the input terminal past the first side of the shared source contact;
• a wrapped drain finger contact integrally formed on the semiconductor substrate and electrically coupled to the output terminal, wherein the wrapped drain finger contact is positioned in the peripheral ancillary region to extend laterally between terminal ends of the first and second primary drain finger contacts;
• a primary transistor element comprising the first and second primary drain finger contacts, a first portion of the shared source contact, and a primary gate structure located outside of the peripheral ancillary region;
• and
• an ancillary transistor element comprising the wrapped drain finger contact, a second portion of the shared source contact, and an ancillary gate structure located within the peripheral ancillary region.

A method of forming a semiconductor device, comprising:

• providing a gallium nitride substrate;
• forming one or more passivation layers on the gallium nitride substrate;
• selectively etching the one or more passivation layers to define an elongated source contact opening, a U-shaped drain contact opening, and a U-shaped gate contact opening which expose the gallium nitride substrate;
• selectively depositing one or more metal layers into the elongated source contact opening, the U-shaped drain contact opening, and the U-shaped gate contact opening, thereby respectively forming:
• an elongated source contact with first and second opposed sides extending longitudinally between a first source end that is proximate to an output terminal layer and a second source end that is proximate to an input terminal;
• a U-shaped drain contact positioned to enclose the first source end and located to define a U-shaped channel region in the gallium nitride substrate between the elongated source contact and the U-shaped drain contact, where the U-shaped drain contact has a closed end located in a peripheral ancillary region between the first source end and the output terminal;
• and
• a U-shaped gate contact positioned over the U-shaped channel region and between the U-shaped drain contact and the elongated source contact, where the U-shaped gate contact has a closed end located in the peripheral ancillary region between the first source end and the output terminal.