Transistor

Abstract

A field effect transistor includes an active layer and a capping layer sequentially stacked on a substrate, and a gate electrode penetrating the capping layer and being adjacent to the active layer. The gate electrode includes a foot portion adjacent to the active layer and a head portion having a width greater than a width of the foot portion. The foot portion of an end part of the gate electrode has a width less than a width of the head portion of another part of the gate electrode and greater than a width of the foot portion of the another part of the gate electrode. The foot portion of the end part of the gate electrode further penetrates the active layer so as to be adjacent to the substrate.

What is claimed is: 
     
         1 . A field effect transistor comprising:
 an active layer and a capping layer sequentially stacked on a substrate;   a source ohmic electrode and a drain ohmic electrode spaced apart from each other on the capping layer; and   a gate electrode disposed on the substrate between the source and drain ohmic electrodes, the gate electrode penetrating the capping layer and adjacent to the active layer,   wherein the gate electrode includes a foot portion adjacent to the active layer and a head portion disposed on the foot portion and having a width greater than a width of the foot portion;   wherein the gate electrode includes both end parts in an extending direction of the gate electrode;   wherein the foot portion of each of the both end parts of the gate electrode has a width less than a width of the head portion of another part of the gate electrode and greater than a width of the foot portion of the another part of the gate electrode; and   wherein the foot portion of each of the both end parts of the gate electrode further penetrates the active layer so as to be adjacent to the substrate.   
     
     
         2 . The field effect transistor of  claim 1 , wherein the foot portion of a center part of the gate electrode in the extending direction of the gate electrode has a width less than the width of the head portion of the another part of the gate electrode and greater than the width of the foot portion of the another part of the gate electrode; and
 wherein the foot portion of the center part of the gate electrode further penetrates the active layer so as to be adjacent to the substrate.   
     
     
         3 . The field effect transistor of  claim 1 , wherein the head portion of the gate electrode laterally extends toward the drain ohmic electrode. 
     
     
         4 . The field effect transistor of  claim 1 , further comprising:
 an insulating layer disposed between the gate electrode and the active layer and/or between the gate electrode and the capping layer.   
     
     
         5 . The field effect transistor of  claim 4 , wherein the insulating layer includes silicon nitride, silicon oxide, porous silicon oxide, or benzocyclobutene. 
     
     
         6 . The field effect transistor of  claim 1 , wherein the substrate is an insulating substrate. 
     
     
         7 . The field effect transistor of  claim 6 , wherein the insulating substrate includes gallium nitride, silicon, silicon carbide, semi-insulating gallium arsenide, or sapphire. 
     
     
         8 . The field effect transistor of  claim 1 , wherein the active layer includes a first layer including gallium nitride and a second layer including aluminum gallium nitride (AlGaN). 
     
     
         9 . The field effect transistor of  claim 1 , wherein the capping layer includes gallium nitride.