Details

Autor(en) / Beteiligte

• Tomita, R.
• Ueda, S.
• Kawada, T.
• Mitsuzono, H.
• Horio, K.

Titel

Analysis of Dependence of Breakdown Voltage on Gate-Drain Distance in AlGaN/GaN HEMTs With High-k Passivation Layer

Ist Teil von

• IEEE transactions on electron devices, 2021-04, Vol.68 (4), p.1550-1556, Article 1550

Ort / Verlag

New York: IEEE

Erscheinungsjahr

2021

Quelle

IEEE/IET Electronic Library

Beschreibungen/Notizen

• A 2-D analysis of OFF-state breakdown characteristics of AlGaN/GaN HEMTs with a high-<inline-formula> <tex-math notation="LaTeX">{k} </tex-math></inline-formula> passivation layer is performed as a function of gate-to-drain distance <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} </tex-math></inline-formula>. The relative permittivity of the passivation layer <inline-formula> <tex-math notation="LaTeX">\varepsilon _{\text {r}} </tex-math></inline-formula> is changed from 1 to 60, and <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} </tex-math></inline-formula> is changed from 1.5 to <inline-formula> <tex-math notation="LaTeX">10~\mu \text{m} </tex-math></inline-formula>. It is shown that, in all cases with different <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} </tex-math></inline-formula>, the breakdown voltage <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> increases as <inline-formula> <tex-math notation="LaTeX">\varepsilon _{\text {r}} </tex-math></inline-formula> increases. When a deep-acceptor density in an Fe-doped buffer layer <inline-formula> <tex-math notation="LaTeX">{N} _{\text {DA}} </tex-math></inline-formula> is <inline-formula> <tex-math notation="LaTeX">10^{{17}} </tex-math></inline-formula> cm<inline-formula> <tex-math notation="LaTeX">^{-{3}} </tex-math></inline-formula> and the gate length is <inline-formula> <tex-math notation="LaTeX">0.3~\mu \text{m} </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> is determined by buffer leakage current at <inline-formula> <tex-math notation="LaTeX">\varepsilon _{\text {r}} \ge30 </tex-math></inline-formula> before impact ionization dominates. Hence, <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> is similar at <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} =3 </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">10~\mu \text{m} </tex-math></inline-formula>, and the increase rate in <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> from <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} = 1.5\,\,\mu \text{m} </tex-math></inline-formula> is about 50% even at <inline-formula> <tex-math notation="LaTeX">\varepsilon _{\text {r}} =60 </tex-math></inline-formula>. However, when <inline-formula> <tex-math notation="LaTeX">{N} _{\text {DA}} </tex-math></inline-formula> is <inline-formula> <tex-math notation="LaTeX">2\times 10^{{17}} </tex-math></inline-formula> cm<inline-formula> <tex-math notation="LaTeX">^{-{3}} </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> is determined by impact ionization of carriers even at <inline-formula> <tex-math notation="LaTeX">\varepsilon _{\text {r}} \ge30 </tex-math></inline-formula> because the buffer leakage current is reduced. <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> becomes about 500, 930, 1360, and 1650 V for <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} =1.5 </tex-math></inline-formula>, 3, 5, and <inline-formula> <tex-math notation="LaTeX">7~\mu </tex-math></inline-formula> m, respectively, at <inline-formula> <tex-math notation="LaTeX">\varepsilon _{\text {r}} =60 </tex-math></inline-formula>. These voltages correspond to gate-to-drain average electric fields of about 3.3, 3.1, 2.7, and 2.3 MV/cm, respectively. Particularly, for short <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} </tex-math></inline-formula>, the electric field profiles between the gate and the drain are rather uniform. However, in the case of <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} = 10\,\,\mu \text{m} </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> is about the same as that (1650 V) of <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} = 7\,\,\mu \text{m} </tex-math></inline-formula>, suggesting that the electric field at the drain edge of the gate becomes a critical value before the high electric field region extends to the drain enough. This may be a limitation to increase <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> by using a high-<inline-formula> <tex-math notation="LaTeX">{k} </tex-math></inline-formula> passivation layer in this case. However, it can be said that, to improve <inline-formula> <tex-math notation="LaTeX">{V} _{\text {br}} </tex-math></inline-formula> further at long <inline-formula> <tex-math notation="LaTeX">{L} _{\text {GD}} </tex-math></inline-formula>, such as <inline-formula> <tex-math notation="LaTeX">10~\mu \text{m} </tex-math></inline-formula>, the combination of field plate or using a higher <inline-formula> <tex-math notation="LaTeX">\varepsilon _{\text {r}} </tex-math></inline-formula> material may be effective because both of them decrease the electric field at the drain edge of the gate.