{"id":3323,"date":"2011-07-19T20:24:47","date_gmt":"2011-07-19T20:24:47","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/?p=3323"},"modified":"2011-07-20T16:39:25","modified_gmt":"2011-07-20T16:39:25","slug":"gan-high-frequency-transistors-2","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/gan-high-frequency-transistors-2\/","title":{"rendered":"GaN High Frequency Transistors"},"content":{"rendered":"

GaN-based high electron mobility transistors (HEMTs) have great potential for high power\/frequency applications due to their outstanding combination of large breakdown voltage and high electron velocity. Among the different possible nitride structures, InAlN\/GaN heterostructures have attracted much attention recently because they enable an extremely high charge density with a thin barrier thickness [1<\/a>] <\/sup>. With the use of these advantages, outstanding progress in the frequency performance of InAlN\/GaN transistors has been recently achieved. Sun et al. reported a 55-nm gate length device with fT<\/sub> of 205 GHz (fmax <\/sub>= 191 GHz) [2<\/a>] <\/sup> and Lee et al.<\/em> demonstrated a 30-nm gate length device with fT<\/sub> of 245 GHz [3<\/a>] <\/sup>.<\/p>\n

In this study, we used an AlGaN back-barrier in InAlN\/GaN HEMT structures for the first time and studied its impact on the DC and RF characteristics of these devices [4<\/a>] <\/sup>. A maximum drain current of 1.49 A\/mm is obtained at Vgs<\/sub>=2 V in the device with the back-barrier, about 27 % lower than that of the standard device (2.05 A\/mm at Vgs<\/sub>=2 V). The smaller drain current in the device with the back-barrier mainly results from the lower sheet charge density and subsequent higher threshold voltage. However, the output conductance is significantly smaller in the device with the back-barrier, which shows an effective suppression of the \u00a0short-channel effects. In addition, in sub-100-nm-gate-length transistors, the back-barrier makes it possible to maintain a drain-induced barrier lowering (DIBL) near 50-60 mV\/V while preventing the degradation of the subthreshold swing (SS). Thanks to the reduced short-channel effects, 65-nm-gate-length devices with a back-barrier showed an fT<\/sub> of 210 GHz, which is higher than that of the standard device with the same gate length (195 GHz). Moreover, in a sub-30-nm-gate-length device with AlGaN back-barrier, an fT<\/sub> of 270 GHz, the highest fT<\/sub> ever reported in GaN transistors, was achieved.<\/p>\n\n\t\t