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微波電路 /期中報告
A Novel Manufacturing Process of AlGaN/GaN
HEMT for X-Band High-Power Application on Si
(111) Substrate
Cong Wang, Ram Krishna Maharjan, Sung-Jin Cho, and
Nam-Young Kim
Proceedings of APMC 2012
報告人:
碩研電子一甲 MA130224 李堅誌
Southern Taiwan University
Department of Electronic Engineering
Abstract

In this paper, successful operation at 10 GHz of 0.5 μm gamma
gate AlGaN/GaN high electron mobility transistor (HEMT) is
demonstrated on Si (111) substrate.

Various material and processing approaches regarding double
surface passivation and post-gate annealing processes are
evaluated in terms of device performances.

In order to achieve better immunity to current collapse effects, we
conducted experiments that investigate the relationship between
the HEMTs electrical characteristics and different passivation films
(SiNx or SiO2) using plasma-enhanced chemical vapor deposition
(PECVD).
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Double Surface Passivation Process


Fig. 1. (a) I-V characteristics with varying gate biases,
and (b) the transfer characteristics of the SiNX/SiNXpasssivated HEMT and SiO2/SiO2-passivated HEMT
compared to the unpassivated HEMT.
The typical I-V output and
transfer characteristics of these
three AlGaN/GaN HEMTs are
shown in Fig. 1 (a) and (b),
respectively. Samples A and B
exhibit better saturation and pitchoff characteristics than the
unpassivated HEMT.
They yielded a maximum
saturation current density (IDS
max) of 643 and 540 mA/mm,
respectively, showing 40% and
17% increases relative to that
found for the unpassivated
HEMT.
2
Fig. 2. (a) I-V characteristics with varying gate biases, (b)
transfer characteristics

The I-V output and transfer
characteristics of the two type
AlGaN/GaN HEMTs are shown
in Fig. 2 (a) and (b). An increase
in the IDS max (16%) from 643
mA/mm to 750 mA/mm and the
gm max (10%) from 200 mS/mm
to 220 mS/mm can be observed
after the post-gate N2 RTA
treatment.

enhancement of these DC
characteristics is primarily cause
by the RTA process, which
reduces the electrically active
states at the Schottky
metal/AlGaN interfaces.
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(c) the gate-drain breakdown voltage of the SiNX/SiNXpasssivated HEMT using post-gate N2 RTA treatment
compared to the as-fabricated HEMT, (d) the cross-sectional
FIB image of the proposed HEMT, and (e) the enlarged
gamma gate with the proposed double passivation structure.

After the N2 annealing treatment,
the gate-drain breakdown voltage
of the HEMTs increased from 113
V to 141 V. increase in the
breakdown voltage.

This increase of breakdown
voltage is due to the decrease of
the gate leakage current. An
increase of the forward gate
threshold voltage to 2 V has been
verified in Sample D. The focused
ion beam (FIB) photographs of
the cross-sectional gamma gate
with double surface passviation
structure are shown in Fig. 2 (d)
and (e).
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Results And Discussions

Fig. 3 (a) shows an optical micrograph
of a fabricated 200 μm twofinger
freestanding HEMT with a gate length
of 0.5 μm, a drain-gate space of 2.5 μm,
and a gate-source space of 1 μm.

Fig. 3 (b) shows the short circuit
current gain (|h21|) and the maximum
stable gain (MSG) for the device with 2
× (200 × 0.5) μm2 gate periphery. The
fT and fMAX are determined by the
|h21| and the MSG, respectively. The
extrinsic fT and fMAX are 24.6 GHz and
45.4 GHz respectively at VDS = 10 V
and VGS = -3 V.
5

Large signal measurements have
been performed using a load-pull
system at 10 GHz. The device was
biased at a drain bias of 30 V.

The measured input power (Pin)
against the output power (Pout)
responses of the device is
illustrated in Fig. 3 (c), which
illustrates an output power density
of 5.8 W/mm, a peak PAE of 51%
at 21 dBm Pin with a linear gain of
14.4 dB and a power gain of about
13.68 dB.
Conclusion

This paper presents the state-of-the-art results obtained by 0.5 μm gammagate AlGaN/GaN HEMTs fabricated on Si (111) substrates.

In order to meet the performance improvement requirements needed for
high power applications, these optimized solutions which enhance the
characteristics and reduce the cost of HEMTs on Si substrates are
proposed.

Excellent performances have been achieved for 0.5 μm gate-length
HEMTs. The maximum output power density of 5.8 W/mm is achieved,
with an associated power gain of 13.68 dB and a maximum PAE of 51%.
Due to these results, this manufacturing process is shown to be an optimal
solution for fabricating HEMTs in X-band high-power applications.
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心得:
看完這篇ppt後發現跟我目前在做的薄膜有些許相同，不
過我們是利用氧化物。這則是一種新製程利用氮化矽，它
還利用退火使他的輸出電流電壓，傳輸特性更好，目前我
也是利用退火來觀察我的薄膜特性，提高他的耐久。