SILICON NITRIDE PASSIVATION WITH AMMONIA PLASMA PRETREAMENT FOR IMPROVING RELIABILITY OF AlGaN/GaN HEMTs

Abstract

This invention pertains to an electronic device and to a method for making it. The device is a heterojunction transistor, particularly a high electron mobility transistor, characterized by presence of a 2 DEG channel. Transistors of this invention contain an AlGaN barrier and a GaN buffer, with the channel disposed, when present, at the interface of the barrier and the buffer. Surface treated with ammonia plasma resembles untreated surface. The method pertains to treatment of the device with ammonia plasma prior to passivation to extend reliability of the device beyond a period of time on the order of 300 hours of operation, the device typically being a 2 DEG AlGaN/GaN high electron mobility transistor with essentially no gate lag and with essentially no rf power output degradation.

1 . A high electron mobility transistor, comprising: 
 a substrate;    a GaN buffer layer disposed on the substrate;    an AlGaN barrier layer disposed on the GaN buffer layer such that a 2 DEG channel is disposed at the interface of the AlGaN barrier layer and GaN buffer layer; and    a passivation layer disposed on the AlGaN barrier layer, wherein an upper surface of the AlGaN barrier layer has been pre-treated with an ammonia plasma prior to a deposition of the passivation layer.    
   
   
       2 . The transistor of  claim 1 , wherein the transistor has essentially no measurable drain current collapse for up to about 176 hours of dc bias stress.  
   
   
       3 . The transistor of  claim 1 , wherein the transistor has essentially no measurable gate lag for up to about 176 hours of dc bias stress.  
   
   
       4 . The transistor of  claim 2 , wherein the dc bias stress is characterized by a drain current of 100-300 mA/mm and a drain voltage of about 23-30 volts.  
   
   
       5 . The transistor of  claim 2 , wherein the dc bias stress is provided by a microwave signal having an input power P in  of 5-20 dBm at a frequency of 2-12 GHz.  
   
   
       6 . The transistor of  claim 1 , wherein the AlGaN barrier layer is about 150 A to 300 A thick.  
   
   
       7 . The transistor of  claim 1 , wherein the GaN buffer layer is about 5000 μm to 15,000 μm thick.  
   
   
       8 . The transistor of  claim 1 , wherein the transistor has experienced essentially no decrease in rf power output (P out ) up to about 70 hours.  
   
   
       9 . The transistor of  claim 1 , wherein the AlGaN barrier layer is made from Al x Ga 1-x N, wherein 0.15≦x≦0.40.  
   
   
       10 . The transistor of  claim 1 , wherein the rate of degradation of microwave power output, while under continuous microwave operation, is at least 100 times smaller than a conventional high electron mobility transistor that is not pre-treated with ammonia plasma.  
   
   
       11 . The transistor of  claim 1 , wherein the transistor has electron mobility in excess of 1000 cm 2 /V sec.  
   
   
       12 . The transistor of  claim 1 , further comprising a AlN buffer layer disposed between the GaN buffer layer and the substrate.