A Ultra High Ruggedness Performance of InGaP/GaAs HBT
for Multi-Mode / Multi-Band Power Amplifier Application
Shu-Hsiao Tsai, Rei-Bin Chiou, Tung-Yao Chou, Cheng-Kuo Lin, and Dennis Williams
WiN Semiconductors Corp.
No.69, Technology 7th Rd., Hwaya Technology Park, Kuei-Shan Hsiang, Taoyuan, Taiwan 333
E-mail: andytsai@winfoundry.com, Phone: +886-3-3975999#1512
Keywords: Multi-mode Multi-band (MMMB), Ruggedness
Abstract
InGaP/GaAs HBT has been widely used in power
amplifier (PA) design for wireless communications due to
its high linearity and high efficiency. In recent years
Multi-Mode / Multi-Band (MMMB) power amplifier
plays more important role with the strong growth of
smart phone. A MMMB power amplifier requires
applying for GSM, UMTS and LTE applications. One of
the requirements for GSM PA is the ruggedness of HBT
which can maintain the same performance after the
stress of high voltage standing wave ratio (VSWR)
mismatch. In this paper, we present an ultra high
ruggedness HBT technology which can pass the
ruggedness test under VCE is 5V and VSWR 50:1.
(SOA) [3]. The devices were fabricated by using WiN’s
latest HBT process which included two interconnection
metal layers (M1 and M2) and a thicker SiN layer as the
dielectric layer between M1 and M2. A thicker SiN film
instead of using Polyimide as dielectric film can provide
better mechanical and moisture protection. The thickness of
two metal interconnection layers are 1um evaporated and 4
um plated Au for M1 and M2 respectively. MIM capacitors
with unit capacitance of 570 pF/mm , stacked MIM
capacitors with unit capacitance of 870 pF/mm , and thin
film resistors with sheet resistance of 50 Ohm/sq can be used
for MMIC designs. Fig. 1 shows the SEM photo of HBT
cross-section.
2
2
INTRODUCTION
The growth of mobile internet and multimedia services
has been explosive in recent years [1]. Multimode multiband
(MMMB) power amplifiers have been developed in recent
years for next generation mobile handsets and tablets
applications. These mobile devices are required to support
higher data rates promised by 3G WCDMA/HSPA, and even
4G LTE standards with backward compatibility to the legacy
2G GSM and 2.5G GPRS/EDGE standards. In the meantime,
a combination of frequency bands will need to be supported
while reducing cost and die size of mobile devices [2].
Therefore, the requirement of ruggedness, efficiency, and
linearity will be needed simultaneously in HBTs for MMMB
PA design.
This paper will demonstrate a InGaP/GaAs HBT with
excellent ruggedness performance, qualified power and
linearity performance, and flexible device layout design for
applying into MMMB PA design and development.
Fig. 1 The Cross section photos of HBT unit cell.
Table 1
The illustration of horizontal and vertical orientation HBTs
Horizontal orientation HBTs
DEVICE FABRICATION AND FEATURES
The ultra high ruggedness performance InGaP/GaAs
HBTs were fabricated with WiN’s optimized epi-structure,
layout and latest HBT process. The collector was designed
to achieve not only high off-state breakdown voltage but
also on-state breakdown voltage for wide safe operation area
CS MANTECH Conference, April 23rd - 26th, 2012, Boston, Massachusetts, USA
Vertical orientation HBTs
In order to achieve the application of MMMB PA, more
flexible HBT design is supported in this work. Table 1
shows that two kinds of HBT unit transistor in both
horizontal and vertical orientations of emitter fingers are
presented in this work. As Fig. 2 shown, two orientations
HBTs can be implemented into a multi-band PA for
realizing two power stages of high band and low band in a
single die more easily and die size efficiently.
proper collector layer design.
Table 2
Key device DC and RF characteristics
Parameters
Current Gain @ 1.25kA/cm2
Turn-on voltage @ 1.25kA/cm2
BVceo @ 0.05kA/cm2
BVcbo @ 0.05kA/cm2
BVebo @ 0.05kA/cm2
Ft @ 25kA/cm2
0.7
Unit
N/A
V
V
V
V
GHz
Typical Value
75
1.265
18.5
37
7.0
28
Device size: 3um x 40um x 3 fingers
Ambient Temp.: 25C
0.6
Ic(mA)
0.5
Fig. 2 The illustration of both horizontal and vertical orientation HBTs
applying to Multi-Band PA.
0.4
0.3
Device B
this work
0.2
0.1 Device A
as reference
Besides two orientations of emitter finger, this work
demonstrated two configurations of HBT unit transistor. As
Table 2 shown, Type-A HBTs was the conventional layout
which base metal finger surrounded emitter mesa to form the
B-E-B-E-B structures. In order to improve the power gain of
unit HBT transistors, Type-B HBTs were proposed.
Compare to conventional Type-A HBTs, Type-B HBTs
which was E-B-E structure removed the outer base metal
fingers to reduce the base-collector capacitance (Cbc) by
shrinking the base mesa area and further enhance the power
gain.
Table 2
The illustration of Type-A and Type-B HBTs
Type-A HBTs
0.0
0
5
10
15
20
VCE(V)
Fig. 3 The comparison results of safe operation area (SOA) between high
ruggedness version and conventional version of collector layer design.
Fig. 4 shows the comparison results of maximum
available gain (MAG) between Type-A and Type-B HBTs.
Type-B HBTs show higher MAG than Type-A HBTs due to
the lower Cbc capacitance. Therefore, Type-B HBTs can
provide better power performance under the frequency
below 3GHz for handset application.
*Device size : 2um X 20um X 2f
40
Type HBTs
Type-B
Type-A HBT
Type-B HBT
35
30
MAG (dB)
25
20
15
10
5
0
DEVICE DC & RF PERFORMANCE
1
The key device parameters are shown in Table 2. Fig. 3
shows the safe operation area of a single unit cell which the
emitter size is 3um*40um*3fingers. The wider safe
operation area (SOA) can be achieved in this work due to
10
freq. (GHz)
Fig. 4 The comparison results of Maximum Available Gain (MAG) between
Type-A and Type-B HBTs. Type-B HBTs show higher MAG than Type-A
HBTs for handset application.
CS MANTECH Conference, April 23rd - 26th, 2012, Boston, Massachusetts, USA
As the Fig. 5 shown, Gummel plot and I-V curves of both
vertical and horizontal orientations HBTs show identical
result.
0.1
0.01
160
Horizontal orientation HBT
Vertical orientation HBT
120
1E-3
Icq (mA)
100
1E-4
1E-5
80
60
1E-6
20
1E-7
40
Horizontal orientation HBT
Vertical orientation HBT
16
1E-9
8
0
4
0
1E-10
1E-11
0.8
20
12
0
1
2
3
4
5
6
-50
VCE (V)
0.9
1.0
1.1
1.2
1.3
1.4
Frequency: 900MHz
Constant Pout: 21.5dBm
0
50
100
150
200
250
300
350
400
Phase (degree)
1.5
Fig. 6. The variation of DC collector current during all phase rotation for
Device-B at 10:1 VSWR and 3 ~7.5V.
VBE (V)
Fig. 5 The comparison results of Gummel Plot measurement between
horizontal and vertical orientation HBTs. The DC characteristics between
horizontal and vertical orientation HBTs are identical.
DEVICE POWER AND RUGGEDNESS PERFORMANCE
30
70
28
65
26
60
24
55
Table 3 shows the results of the ruggedness test for single
unit cell which the emitter size is 3um*40um*3fingers. The
VSWR was fixed at 10:1 for 360 degree all phase rotation.
VCE was increased from 3.6V and stop until device failed.
Device-A was the reference device with the conventional
collector design and the proper collector design in this work
was implemented in Device-B. Device-A can only pass the
ruggedness test under VCE was 5V. However Device-B
started to fail until VCE went to 7.5V. According to the
SOA measurement and ruggedness test results, Device-B
showed not only wider SOA but also more robust
ruggedness performance. The detailed test results of DeviceB were shown in Fig.6.
Table 3
Ruggedness test results under VSWR 10:1 for Device-A and Device-B.
Device size is 3um*40um*3fingers.
VCE
Device A
Device B
3.6V
Passed
Passed
5V
Passed
Passed
6V
Failed
Passed
6.5V
7V
7.5V
Passed
Passed
Failed
As Fig.7 shown, the same test vehicle of SOA
measurement and ruggedness test which the emitter size is
3um*40um*3fingers is chosen for the load-pull
measurement under 900MHz. DUT was attached on an
evaluation board the power performance was measured on a
Focus load pull system. The device was biased at VCE was
3.6V and collector quiescent current was 10mA. The result
shows there is no significant difference of power
performance between Device-A and Device-B. Linear power
gain is around 22.5 dB, P1dB is around 20dBm and the
power added efficiency (PAE) under P1dB is around 57%
for both Device-A and Device-B.
Pout (dBm), Gain (dB)
22
50
20
45
18
40
16
35
14
30
12
25
10
20
Device-A
Device-B
8
6
15
4
10
2
5
0
-16
PAE(%)
1E-8
IC(mA) 25C
IC & IB (A) @ 25C
VCE= 3.6 V
VCE= 5 V
VCE= 6 V
VCE= 6.5 V
VCE= 7 V
VCE= 7.5 V
140
0
-14
-12
-10
-8
-6
-4
-2
0
2
4
6
8
Pin (dBm)
Fig. 7. Power performance comparison between Device-A and Device-B.
In order to further confirm the ruggedness performance of
Device-B. The ruggedness test of 8064um2 power cell which
was formed by Device-B is shown as Table 4. DUT power
cell was partially matched on an evaluation board and it can
deliver 35dBm output power at 900 MHz. VSWR varied
from 10:1 to 50:1 all phase rotation during ruggedness test at
VCE was 3.6V and 5V respectively. This work shows the
excellent ruggedness performance which can pass under
VSWR 50:1 for both VCE was 3.6V and 5V.
Table 4
Various VSWR from 10:1 to 50:1 ruggedness test results under 35dBm
output power for VCE was 3.6V and 5V. Power cell size is 8064um2.
VSWR
VCE=3.6V
VCE=5V
10:1
Passed
Passed
CS MANTECH Conference, April 23rd - 26th, 2012, Boston, Massachusetts, USA
20:1
Passed
Passed
30:1
Passed
Passed
40:1
Passed
Passed
50:1
Passed
Passed
CONCLUSIONS
In conclusion, we have demonstrated an InGaP/GaAs
HBT with excellent ruggedness performance and without
sacrificing its power performance. HBTs survived the
ruggedness test of 50:1 VSWR at 5V VCE under 35dBm
output power delivered. This device is excellent candidate
for GSM applications and it can be further implemented to
the MMMB PA as well, due to its flexible device designs
and qualified power performance.
ACKNOWLEDGEMENTS
The authors would like to thank the people that supported
the measurements and wafer processing of WiN’s device
characterization team and manufacturing team respectively.
REFERENCES
[1] N. Q. Bolton, “Mobile Device RF Front-End TAM Analysis
and Forecast,” CS Mantech Conf., May 16-19, 2011.
[2] N. Cheng, “Challenges and Requirements of Multimode
Multiband Power Amplifiers for Mobile Applications,” IEEE
CSICS Conf., 2011.
[3] S. Lee, “The Study of Heterojunction Bipolar Transistors for
High Ruggedness Performance,” CS Mantech Conf., May 1619, 2011.
ACRONYMS
HBT: Heterojunction Bipolar Transistor
MMMB: Multimode Multiband
SOA: Safe Operation Area
VSWR: Voltage Standing Wave Ratio
CS MANTECH Conference, April 23rd - 26th, 2012, Boston, Massachusetts, USA