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Fabrication of Enhancement-mode AlGaN/GaN MOSHEMTs Integrating Isolation and Gate-recess in
One Process Step Using Self-terminating Thermal Oxidation Assisted Wet Etching Method
Jingqian Liu, Jinyan Wang，Hongyue Wang, Lin Zhu, Huaiyin Guo, Mengjun Li, Wengang Wu
Institute of Microelectronics, Peking University, Beijing 100871, China
Email:[email protected]
Enhancement-mode (E-mode) GaN-based high electron mobility transistors (HEMTs) have attracted
significant attention due to simple circuit configuration for power switch application [1]. Metal oxide
semiconductor HEMTs (MOSHEMTs) with gate-recess have been widely used to realize E-mode operation
[2-4]. A simplified fabrication process is crucial for mass production. Recently, we demonstrated a selfterminating thermal oxidation assisted wet etching technique (STOAWET) [5-6] for AlGaN/GaN. In this
work, E-mode AlGaN/GaN MOSHEMTs were fabricated with integration of gate-recess and isolation in one
process step using STOAWET by thermal oxidization at 650°C for 45min and etching in KOH solution at
70°C for 45min with GaN cap layer as process mask. Optical microscope image after etching is shown in
Figure 1 and schematic cross-section of the fabricated E-mode device is shown in Figure 2. Figure 3 shows
transfer characteristics of E-mode MOSHEMT by this work. Threshold voltage (Vth) is 1.5V defined as
linear extrapolation. Maximum drain current (Idmax) is 212mA/mm and maximum transconductance (Gmmax)
is 42mS/mm. Idmax is comparable with our previous ICP isolated E-mode MOSHEMTs (~200mA/mm) [5-6]
and Gmmax is a little lower than that in [5] (53 mS/mm) but higher than that in [6] (33 mS/mm). Off-state
drain current (Ioff) is ~10-7mA/mm, much lower than that in [5] (~0.01mA/mm) and a little higher than that
in [6] (~10-8mA/mm), but still at the same level as recent reported values [2-4]. Transfer characteristics of Dmode HEMTs are shown in Figure 4. Idmax, Gmmax and Ioff of HEMTs isolated by STOAWET are 505mA/mm,
119mS/mm and ~10-7mA/mm respectively, while those of HEMTs isolated by ICP are 492mA/mm,
112mS/mm and ~10-6mA/mm respectively, indicating comparable performances of D-mode HEMTs isolated
by two methods. Leakage current at a bias of 10V between two mesas with separation of 40µm and width of
80µm by STOAWET is measured as 4.8pA, as good as that isolated by ICP (24pA), implying the
applicability of STOAWET in AlGaN/GaN isolation. By the method in this work, a simplified fabrication
process of E-mode AlGaN/GaN MOSHEMTs is achieved, manifesting itself in concision and low cost.
Fig1. Optical microscope image after
etching gate-recess and isolation regions
simultaneously by STOAWET.
Fig2. Schematic cross-section of the
fabricated E-mode device.
Fig3. Transfer characteristics of E-mode MOSHEMT fabricated in this
work at Vds=10V where Vgs swept from -3V to 7V. Left: in linear scale.
Right: in semi-log scale.
Fig4. Transfer characteristics of D-mode HEMTs in semi-log scale at Vds
of 10V where Vgs swept from -7V to 1V. Left: isolated by STOAWET.
Right: isolated by ICP.
1. R. Chu, IEEE Electron Device Letters 32, 5 (2011).
2. C. Liu, IEEE Electron Device Letters 36, 4 (2015).
3. S. Liu, IEEE Electron Device Letters 35, 7 (2014).
4. S. Lin, IEEE Electron Device Letters 37, 4 (2016).
5. Z. Xu, IEEE Electron Device Letters 34, 7 (2013).
6. Z. Xu, IEEE Electron Device Letters 35, 12 (2014).
Presentation Method (Poster/ Invited Oral 15/20/25/30minutes): Oral 20minutes