Vertical gallium nitride Schottky diode
A vertical conduction nitride-based Schottky diode is formed using an insulating substrate which was lifted off after the diode device is encapsulated on the front side with a wafer level molding compound. The wafer level molding compound provides structural support on the front side of the diode device to allow the insulating substrate to be lifted off so that a conductive layer can be formed on the backside of the diode device as the cathode electrode. A vertical conduction nitride-based Schottky diode is thus realized. In another embodiment, a protection circuit for a vertical GaN Schottky diode employs a silicon-based vertical PN junction diode connected in parallel to the GaN Schottky diode to divert reverse bias avalanche current.
1. A vertical conduction nitride-based Schottky diode, comprising:
a nitride-based semiconductor body of a first conductivity type;
a first metal layer formed on a front side of the nitride-based semiconductor body forming a Schottky junction therewith, the first metal layer forming an anode electrode of the Schottky diode;
a second metal layer formed on the first metal layer;
a third metal layer formed on a backside of the nitride-based semiconductor body, the third metal layer forming an ohmic contact with the semiconductor body and forming a cathode electrode of the Schottky diode;
a termination structure formed at an edge of the first metal layer, the termination structure being configured to reduce electric field crowding at the edge of the anode electrode, wherein the termination structure comprises a guard ring comprising a nitride-based epitaxial layer of a second conductivity type, opposite the first conductivity type, formed on the front side of the nitride-based semiconductor body at the edge of the first metal layer, the nitride-based epitaxial layer having a step recess where the part of the epitaxial layer having a thinner thickness is disposed towards the Schottky junction of the Schottky diode; and a dielectric field plate formed on a top surface of the nitride-based epitaxial layer, the dielectric field plate extending up to the step recess of the nitride-based epitaxial layer;
a solder ball formed on the second metal layer; and
a wafer level molding layer formed on the front side of the nitride-based semiconductor body, the wafer level molding layer encapsulating the second metal layer and at least part of the solder ball,
wherein the Schottky diode has a vertical current path from the solder ball, through the anode electrode and the Schottky junction to the cathode electrode.
2. The vertical Schottky diode of claim 1 , wherein the solder ball is planarized to a top surface of the wafer level molding layer.
3. The vertical Schottky diode of claim 1 , wherein the nitride-based semiconductor body of the first conductivity type comprises:
a heavily doped gallium nitride (GaN) layer of the first conductivity type; and
a lightly doped gallium nitride (GaN) layer of the first conductivity type formed on the heavily doped GaN layer,
wherein the first metal layer is formed on a top surface of the lightly doped GaN layer and the third metal layer is formed on a back surface of the heavily doped GaN layer.
4. The vertical Schottky diode of claim 1 , wherein the nitride-based epitaxial layer comprises a gallium nitride layer of the second conductivity type and the dielectric field plate comprises a silicon nitride layer.
5. The vertical Schottky diode of claim 1 , wherein the first conductivity type comprises N-type conductivity and the second conductivity type comprises P-type conductivity.
6. The vertical Schottky diode of claim 1 , further comprising a passivation layer formed on the second metal layer to cover at least edges of the second metal layer.
7. The vertical Schottky diode of claim 1 , wherein the wafer level molding layer is formed from a molding compound for integrated circuits.