{"id":5779,"date":"2012-07-12T14:28:43","date_gmt":"2012-07-12T14:28:43","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/?p=5779"},"modified":"2012-07-18T22:27:17","modified_gmt":"2012-07-18T22:27:17","slug":"use-of-in-situ-sinx-to-reduce-the-off-state-degradation-of-algangan-hemts","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2012\/use-of-in-situ-sinx-to-reduce-the-off-state-degradation-of-algangan-hemts\/","title":{"rendered":"Use of in-situ SiNx<\/sub> to Reduce the OFF-state Degradation of AlGaN\/GaN HEMTs"},"content":{"rendered":"

Thanks to their excellent electrical performance, AlGaN\/GaN high electron mobility transistors (HEMTs) are considered ideal devices for the next generation of high-power and high-frequency electronics [1<\/a>] <\/sup>. However, the limited understanding of their long-term reliability and degradation mechanisms is slowing down the insertion of these devices in actual systems [2<\/a>] <\/sup>.<\/p>\n

Recently, we have reported the formation of oxide particles next to the gate edge of GaN HEMTs after OFF-state step-stress degradation experiments [3<\/a>] <\/sup>. Underneath these particles, pits similar to the ones reported in previous papers [4<\/a>] <\/sup> are observed. In this work, we investigate the role of oxygen in the formation of these particles\/pits during OFF-state stress and use oxygen diffusion barriers to improve the reliability of AlGaN\/GaN HEMTs.<\/p>\n

Two different dielectrics have been used: Al2<\/sub>O3<\/sub> deposited by atomic layer deposition and in-situ SiNx<\/sub> deposited immediately after the growth of the AlGaN\/GaN epitaxial layer by metal organic chemical vapor deposition (MOCVD). Step-stress degradation experiments were performed in both samples in air and vacuum. No degradation was found in either sample during the experiments in vacuum, which shows that the oxygen necessary for the particle formation probably comes from air. In contrast, when the samples were stressed in air, a large degradation and particle\/pit formation were found in the Al2<\/sub>O3<\/sub>-passivated sample, while no structural or electrical degradation was found in the sample with in-situ SiNx<\/sub> (see Figures 1 and 2). The in-situ SiNx<\/sub> dielectric is believed to be a much better diffusion barrier for oxygen gas and water vapor than Al2<\/sub>O3<\/sub>, which significantly reduces device degradation.<\/p>\n

In summary, the in-situ deposition of a SiNx<\/sub> gate dielectric and passivation layer successfully eliminated the diffusion of oxygen from air and water vapor to the AlGaN surface, which improved the OFF-state reliability of AlGaN\/GaN HEMTs.<\/p>\n\n\t\t