Vol. 36, No. 8
Journal of Semiconductors
August 2015
W-band GaN MMIC PA with 257 mW output power at 86.5 GHz
Xu Peng(徐鹏)Ž , Song Xubo(宋旭波), Lü Yuanjie(吕元杰), Wang Yuangang(王元刚),
Dun Shaobo(敦少博), Yin Jiayun(尹甲运), Fang Yulong(房玉龙), Gu Guodong(顾国栋),
Feng Zhihong(冯志红), and Cai Shujun(蔡树军)
National Key Laboratory of Application Specific Integrated Circuit (ASIC), Hebei Semiconductor Research Institute,
Shijiazhuang 050051, China
Abstract: A three-stage W-band GaN monolithic microwave integrated circuit power amplifier (MMIC PA) is
reported. In order to manage coupling effects between all the parts of the W-band MMIC, all matching and bias
networks have been first optimized using circuit simulating software and then systematically simulated on 3D
full-wave electromagnetic simulator. The fabricated MMIC PA achieves a 257 mW output power at 86.5 GHz in
continuous-wave mode, with an associated power added efficiency of 5.4% and an associated power gain of 6.1 dB.
The power density is 459 mW/mm. Moreover, the MMIC PA offers over 100 mW in the 83–90 GHz bandwidth.
Those performances were measured at drain bias of 12 V.
Key words: W-band; MMIC; GaN; power amplifier
DOI: 10.1088/1674-4926/36/8/085009
EEACC: 2560
1. Introduction
In recent years, the emergence of W-band (75–110 GHz)
applications such as high data rate communications, phased array radar and active imaging is driving growth in device technology. The monolithic microwave integrated circuit power
amplifier (MMIC PA) is one of the most important components
in the module for these systems. Although the technologies are
fairly mature, the GaAs and InP MMIC have reached their limit
in terms of maximum output power per MMIC chip. GaN based
high electron mobility transistors (HEMTs) are very attractive
for high power and high voltage RF applications due to the
larger band-gap of GaNŒ1 . The tremendous progress of GaN
devices has created a real possibility for W-band MMIC PA. In
2006, HRL demonstrated the first W-band GaN MMIC PAŒ2 .
By using Lange coupler techniques, QuinStar Technology reported a W-band GaN MMIC PA with an output power of 3.2 W
at 86 GHz in 2013Œ3 . However, the domestic research of GaN
MMIC PA is mainly restricted to the X-band and Ka-bandŒ4; 5 ,
and W-band GaN MMIC PA has not been reported.
In this paper, a three-stage W-band GaN MMIC PA is presented. At frequency of 84.3 GHz, the small signal gain of the
GaN MMIC PA is measured to be 6.4 dB. The output power
has achieved 24.1 dBm (257 mW) at 86.5 GHz in continuouswave (CW) mode, with an associated power added efficiency
(PAE) of 5.4% and an associated power gain of 6.1 dB. Moreover, the MMIC PA offers over 100 mW in the 83–90 GHz
frequency range. To the best of our knowledge, this is the first
demonstration of domestic W-band GaN MMIC PA.
substrate. The epitaxial structure consists of, from top to bottom, a 18 nm undoped AlGaN layer, a 1 nm AlN layer and a
2 m undoped GaN layer. The MMIC fabrication began with
mesa isolation which was performed using a Cl2 /BCl3 plasmabased dry etch. Source and drain ohmic metals of Ti/Al/Ni/Au
were evaporated and annealed to form good ohmic contact at
850 ıC for 30 s under Nitrogen atmosphere. Using transmission line method (TLM) patterns, the ohmic contact resistance
was measured to be 0.40 mm. Electron-beam lithography
was employed to define a 100 nm T-shaped Ni/Au gate in the
center of the source-to-drain space using a tri-layer photoresist.
The MMIC was passivated with 100 nm SiN using plasma enhanced chemical vapor deposition (PECVD) to reduce current
collapse. The SiC substrate was thinned down to 50 m for
W-band application. Grounded via holes were etched by inductively coupled plasma (ICP) to reduce parasitic source inductance.
Tradeoffs between operating bias conditions and device
geometries have been made to select a high power transistor
cell optimal for MMIC PA design. For W-band application, a
4 35 m wide device with gate length of 100 nm was used
as the basic unit cell. S-parameter measurements of the device demonstrate an intrinsic current gain cutoff frequency (fT /
exceeding 90 GHz and an intrinsic maximum oscillation frequency (fmax / exceeding 150 GHz at the bias of Vds D 12 V and
Vgs D 3:5 V. DC measurements demonstrate that the extrinsic
peak gm exceeds 330 mS/mm and Imax reaches 1.2 A/mm.
3. MMIC PA design
2. Device technology and fabrication process
The material structure used in the MMIC PA was grown
by metal organic chemical vapor deposition (MOCVD) on SiC
The three-stage GaN MMIC PA reported in this paper has
a 140 m wide input stage, a 280 m wide second stage (two
basic unit cells), and a 560 m wide output stage (four basic
* Project supported by the National Natural Science Foundation of China (No. 61306113).
† Corresponding author. Email: maxuanxupeng@126.com
Received 5 January 2015, revised manuscript received 10 March 2015
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© 2015 Chinese Institute of Electronics
J. Semicond. 2015, 36(8)
Xu Peng et al.
unit cells), resulting in a stage gate-width ratio of 1 : 2 : 4. This
ratio was used to ensure the driver stage has enough power.
The GaN MMIC PA is consisted of unit cell devices,
matched circuits and bias circuits, which are fabricated on one
wafer. The performance of the GaN MMIC is determined by
the GaN devices, circuit structure and process. All stages of the
GaN MMIC were power-matched in order to maximize output
power. Restricted by load pull measurement conditions, optimal load and source impedances at the W-band cannot be obtained. The large signal device model of the basic unit cell was
established by using small signal S -parameter datas, pulsed
I –V device characteristics, and large signal load pull measurements performed at X-band and Ka-band. Then, the computer
load pull simulation of the large signal model was performed to
determine power and efficiency load contours, and the required
optimized large signal impedances were obtained.
Since lumped components would produce more parasitic
effects at W-band, the impedance matching did not use lumped
components which were often employed in low frequency circuits. Fully distributed transmission lines were selected for
impedance matching networks to minimize the combiner loss.
The first designed part is the output matching network circuit. Taken the high output power into account, four devices
were carried out in the output stage. The output network circuit was designed to transfer maximum output power from the
devices to 50  system. Secondly, the interstage network was
designed. Corporate 2-way and 4-way combining/splitting networks were used in this network, which was utilized to change
the impedance to the optimum input level for power matching of the output devices and provided the DC current to all
the output devices. Finally, the input stage was designed using
distributed line impedance transformers, which provided input matching for the signal transferring to the next stage. Each
stage was designed to be matched into 50  system to minimize
potential mismatch. In order to prevent RF waves interacting
with each other, capacitors were designed and inserted at the
load and source in each stage.
After matching networks, the bias and stabilizing circuits
of the MMIC were designed. Gate and drain bias networks
were realized by high impedance transmission lines. The radial
stub was not selected, because it is not stability at W-bandŒ6; 7 .
The MIM bypass capacitors were used for RF grounding. In order to suppress instabilities, the series NiCr thin film resistors
was used in the gate bias networks to prevent low-frequency
oscillations.
Compared with low frequency circuit, a difficult aspect of
the W-band design is the discrepancy between circuit simulation and EM simulation. In this work, all matching and bias
networks have been first optimized using circuit simulating
software and then systematically simulated on 3D full-wave
electromagnetic (EM) simulator in order to manage coupling
effects between all the parts of the MMIC. The circuit was reoptimized as long as 3D EM simulation achieves required electrical performances. This approach is applied for all the parts
of the MMIC. Since W-band wave is particularly sensitive to
environment, the stability of the entire MMIC was further evaluated by the simulation of stability factor, which is higher than
1 from DC to 110 GHz. The photograph of the MMIC PA is
shown in Figure 1.
Figure 1. Photograph of the W-band GaN MMIC PA.
Figure 2. Small signal performance of three-stage W-band GaN
MMIC measured at a drain bias of 12 V, and gate bias of 3:5 V.
4. MMIC PA characterization
The small signal response of W-band MMIC PA was measured on wafer at Vd D 12 V and Vg D 3:5 V using vector
network analyzer. The drain current density is 252 mA/mm @
Vg D 3:5 V. The measured small signal gain and input/output
return loss versus frequency are shown in Figure 2. The MMIC
has a peak small signal gain of 6.4 dB measured at the frequency of 84.3 GHz. The gain of the MMIC drops with increasing frequency from the peak value down to 1.1 dB at 96 GHz
with a linear slope of 0.45 dB/GHz. The small signal gain drops
rapidly past the frequency of 96 GHz. The input/output return
loss is better than 10 dB from 83 to 87 GHz.
Figure 3 displays power performance of the MMIC PA.
Power performance was measured in CW mode in the 83–
90 GHz frequency range. The drain bias is 12 V, and the input RF power is 18 dBm (63 mW). The peak power of the
MMIC of 24.1 dBm (257 mW) was measured at the frequency
of 86.5 GHz. The drain current density is 297 mA/mm @ Vg D
3:5 V. Associated PAE of the MMIC at peak output power is
5.4% with associated gain of 6.1 dB. Due to restricted by measurement conditions, the minimum frequency step is 0.5 GHz.
The large frequency step results in the output power swing. The
output power exceeds 100 mW in the 83–90 GHz frequency
range.
The measured power-out (Pout /, gain and PAE of the
MMIC PA versus power-in (Pin / at frequency of 86.5 GHz
and drain bias of 12 V are shown in Figure 4. The Pout and
PAE rises with increasing Pin . The peak Pout of 24.1 dBm was
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J. Semicond. 2015, 36(8)
Xu Peng et al.
Figure 3. Output power versus frequency of W-band GaN MMIC measured in CW mode at a drain bias of 12 V and input RF power of
63 mW.
measured at the Pin of 18 dBm, which was corresponding to
Figure 3. The output stage is 560 m wide, which equates to
459 mW/mm power density. Due to restricted by the W-band
power measured conditions, the maximum output power at the
W-band was not obtained.
5. Conclusion
A three-stage W-band GaN MMIC PA was designed and
fabricated in this work. Each stage of the MMIC PA was designed to be matched into the 50  system by a transmission
line. The peak Pout of 24.1 dBm (257 mW) was measured at
the Pin of 18 dBm (63 mW). The associated PAE is 5.4%, and
the associated power gain is 6.1 dB. The MMIC output stage
width is 560 m, which equates to a 459 mW/mm power density. To the best of our knowledge, this is the first report of a
W-band GaN MMIC PA in the domestic field.
Figure 4. Power-out versus power-in performance of W-band GaN
MMIC measured at a frequency of 86.5 GHz and a bias of 12 V.
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