Semiconductor device

Abstract

The reliability of a field effect transistor made of a nitride semiconductor material is improved. An ohmic electrode includes a plurality of unit electrodes isolated to be separated from each other. With this configuration, an on-state current can be prevented from flowing in the unit electrodes in a y-axial direction (negative direction). Further, in the respective unit electrodes, a current density of the on-state current flowing in the y-axial direction (negative direction) can be prevented from increasing. As a result, an electromigration resistance of the ohmic electrode can be improved.

What is claimed is: 
     
         1 . A semiconductor device including a field effect transistor, the field effect transistor comprising:
 (a) a gallium nitride semiconductor layer;   (b) a gate electrode formed over the gallium nitride semiconductor layer and extending in a first direction in a plan view;   (c) a first ohmic electrode arranged at one side of the gate electrode and including a plurality of first patterns, the plurality of first patterns being in ohmic contact with the gallium nitride semiconductor layer, being separated from each other, and being arranged in the first direction in a plan view;   (d) a second ohmic electrode arranged at the other side of the gate electrode and including a plurality of second patterns, the plurality of second patterns being in ohmic contact with the gallium nitride semiconductor layer, being separated from each other, and being arranged in the first direction in a plan view;   (e) an insulating film formed to cover the first ohmic electrode and the second ohmic electrode, the insulating film having a plurality of first openings to expose surfaces of the plurality of first patterns and having a plurality of second openings to expose surfaces of the plurality of second patterns;   (f) a source electrode pattern formed on the insulating film, the source electrode pattern being electrically and commonly connected to the plurality of first patterns of the first ohmic electrode; and   (g) a drain electrode pattern formed on the insulating film, the drain electrode pattern being electrically and commonly connected to the plurality of second patterns of the second ohmic electrode.   
     
     
         2 . The semiconductor device according to  claim 1 ,
 wherein the first ohmic electrodes and the second ohmic electrodes each include an aluminum film.   
     
     
         3 . The semiconductor device according to  claim 1 ,
 wherein each of the source electrode pattern and the drain electrode pattern is extended in the first direction.   
     
     
         4 . The semiconductor device according to  claim 1 ,
 wherein the source electrode pattern and the first patterns form a source electrode of the field effect transistor, and   wherein the drain electrode pattern and the second patterns form a drain electrode of the field effect transistor.   
     
     
         5 . The semiconductor device according to  claim 1 ,
 wherein the source electrode pattern and the drain electrode pattern each include an aluminum film.   
     
     
         6 . The semiconductor device according to  claim 1 ,
 wherein the first ohmic electrodes and the second ohmic electrodes each include a laminate film having an aluminum film sandwiched between titanium films.   
     
     
         7 . The semiconductor device according to  claim 1 ,
 wherein the source electrode pattern and the drain electrode pattern each include an aluminum alloy film.   
     
     
         8 . The semiconductor device according to  claim 7 ,
 wherein the aluminum alloy film includes one of an AlCu film and an AlSiCu film.   
     
     
         9 . The semiconductor device according to  claim 1 ,
 wherein the ohmic contact is a resistive contact having no rectification.