An 18-GHz 300-mW SiGe power HBT

Abstract

An 18-GHz, 300-mW SiGe power heterojunction bipolar transistor (HBT) is demonstrated. The optimization of SiGe HBT vertical profile has enabled this type of devices to operate with high gain and high power at this high frequency. In the common-base configuration, a continuous wave output power of 24.73 dBm with a power gain of 4.5 dB was measured from a single 20-emitter stripe SiGe (2×30 μm² of each emitter finger) double HBT. The overall performance characteristics represent the state-of-the-art SiGe power HBTs operating in the K-band frequency range.

Full text

Page 1

IEEE ELECTRON DEVICE LETTERS, VOL. 26, NO. 6, JUNE 2005381
An 18-GHz 300-mW SiGe Power HBT
Zhenqiang Ma, Ningyue Jiang, Guogong Wang, and Samuel A. Alterovitz
Abstract—An 18-GHz, 300-mW SiGe power heterojunction
bipolar transistor (HBT) is demonstrated. The optimization of
SiGe HBT vertical profile has enabled this type of devices to
operate with high gain and high power at this high frequency. In
the common–base configuration, a continuous wave output power
of 24.73 dBm with a power gain of 4.5 dB was measured from a
single 20-emitter stripe SiGe (?
double HBT. The overall performance characteristics represent
the state-of-the-art SiGe power HBTs operating in the K-band
frequency range.
??
m?of each emitter finger)
IndexTerms—Common-base,heterojunctionbipolartransistors
(HBTs), SiGe.
I. INTRODUCTION
I
integrating RF/microwave circuits and CMOS on a single chip
for future communication units. While the high-frequency per-
formance of low-power SiGe HBTs has increased dramatically
in the past few years [1], [2], high power SiGe HBTs operating
at high frequencies (K-band and higher), however, have not
been successfully developed. As the 20–30-GHz frequency
range is of growing interest for wireless communications, the
development of SiGe power HBTs for these applications has
thus reached the high-level urgency. In this letter, we report
the design and performance characteristics of SiGe HBTs
developed for K-band power amplifications. Under continuous
wave (CW) operation at 18 GHz, a device RF output power of
300 mW with 4.5-dB power gain has been achieved.
N COMPARISON to III-V device technologies, a SiGe
BiCMOS technology platform offers a low-cost solution for
II. DEVICE DESIGN AND FABRICATION
In order to achieve a high
large-area SiGe power HBTs such that sufficient power gain
is available in the 20–30-GHz frequency range, while main-
taining high breakdown voltages and relaxing the lithography
restriction to lower the fabrication cost of these devices, the
most efficient measure is to reduce the base resistance
by increasing the base doping concentration. However, in most
high-speed SiGe HBTs a low base doping concentration in con-
junction with a low Ge content of a trapezoid shape is employed
in order to maintain a high current gain
(–GHz) value for
(the doping profile is
Manuscript received November 30, 2004; revised March 17, 2005. This work
was supported by the National Science Foundation under Grant ECS 0323717.
The review of this letter was arranged by Editor E. Sangiorgi.
Z.Ma,N.Jiang,andG.WangarewiththeDepartmentofElectricalandCom-
puter Engineering University of Wisconsin, Madison, WI 53706 USA (e-mail:
mazq@engr.wisc.edu).
S. A. Alterovitz is with the NASA Glenn Research Center, Cleveland, OH
44135 USA.
Digital Object Identifier 10.1109/LED.2005.848619
analogous to that of traditional Si BJTs). Alternatively, the de-
couplingofbase Gummelnumberfrom intrinsicbaseresistance
due to SiGe induced bandgap narrowing permits a high base
doping concentration (higher than emitter region) with more Ge
content to be employed in the base region [3]. In this way, the
reduction of current gain due to high base doping concentration
can be effectively restored with a large valence band offset be-
tween emitter and base that can be obtained by incorporating a
high Ge content in the base.
In addition, the high-speed characteristics (e.g.,
performance SiGe HBTs are generally obtained with the sac-
rifice of breakdown voltages [1], [2]. In contrast to these low-
breakdown voltage devices for which emitter transit time
the dominant component in
charge layer delay
is instead the dominant time delay
component in
for high breakdown voltage (BV
HBTs [3]. As a result, for such high breakdown voltage SiGe
HBTs, although such parameters as Ge content and Ge profile
in the base region will affect
of these two parameters will not have a major influence on the
values. Since
component in
for high breakdown voltage devices, the in-
crease of
due to the increase of base doping concentration
in the base region will have minimal impact on
. However, the reduction of
doping concentration can significantly enhance the
without involving substantial scaling of the emitter widths. As a
result, a high power gain can be achieved at higher frequencies
by employing a heavily doped base region.
In the heterostructure design of the SiGe power HBTs, the
collector epilayer is made thick (nominal thickness: 0.45
and lightly doped (
cm
breakdown voltage. A high Ge content (24%) with a box-shape
profile is used to maintain a large valence band offset between
the emitter and the base. Such a high Ge content thus permits
a high doping concentration (
in a thin (30 nm) base region while still maintaining reason-
able current gain values. In order to reduce boron outdiffusion
during the chemical vapor deposition (CVD) growth and pro-
cessing, 0.2 atom% carbon was added during the epi-growth of
the SiGe base. The SIMS analysis results of the heterostructure
are shown inFig. 1(a).TheSiGe basesheet resistance measured
from TLM patterns is only 705
ported values, which is directly resulted from using heavy base
doping concentration. With a mesa-type structure used for de-
vice fabrication for which both the intrinsic and the extrinsic
base regions are made on the same SiGe layer [6], such a small
sheet resistance hence directly results in a small total base re-
sistance. A uniformly distributed subcell structure (with two
m emitter stripes in each subcell) is used in this power
) of high-
is
, [4], [5], the collector space
SiGe
(as well as ), the variation
is also not a dominant
and thus on
resulting from a heavy base
values
m)
) in order to realize a high
cm) to be employed
, much lower than any re-
0741-3106/$20.00 © 2005 IEEE

Page 2

382IEEE ELECTRON DEVICE LETTERS, VOL. 26, NO. 6, JUNE 2005
Fig. 1.
heterostructure. (b) Photomicrograph of a fabricated 20-emitter stripes (each of
size ? ? ?? ?m ) SiGe power HBT. The total emitter area is 1200 ?m .
(a) Measured SIMS profile for a CVD-grown Si–SiGe–Si double
Fig. 2.
different configurations. MAGs are 4.7 dB for the common–emitter
configuration and 10 dB for the common–base configuration at 18 GHz
with the respective extrapolated ?
??? dB/decade degradation trend.
?
versus frequency measured for power SiGe HBTs in two
’s of 31 and 70 GHz, if assuming a
device layout and detailed structure can be found in elsewhere
[6]. The total emitter area of a 20-finger device is 1200
The mesa-type power devices were fabricated from heterostruc-
tures grown on 0.5-mm-thick Si substrates using CVD using
an in-house research double-mesa process [6]. The photomicro-
graph of a fabricated power SiGe HBT is shown in Fig. 1(b).
m .
III. DEVICE PERFORMANCE
High breakdown voltages are measured from the SiGe
power HBTs with
The measured small-signal RF characteristics for both the
CE and the CB configurations are shown in Fig. 2. The CE
configuration demonstrates an
BVGHz V, comparable to the reported SiGe
HBTs [7] having a similar BV
are4.7dBfortheCEand10dBfortheCBconfiguration,which
V and BV V.
of 28 GHz, resulting in an
. The values at 18 GHz
Fig.3.
AB operation (?
and load is optimized for maximum ?
gain with a peak PAE of 11% were obtained.
Powerperformance ofthecommon–base SiGeHBTbiased underclass
? ????? V and ?
. 24.73-dBm ?
? ? V). The matching for source
and 4.5-dB power
can be extrapolated to an
tively, if assuming a
relationship of
in Fig. 2 agrees well with the behavior predicted by our recent
theoreticalstudies[8].
Since a higher
(MAG) value is available from the CB
than from the CE configuration at 18 GHz, the CB configura-
tion was then used for source/load pull power characterization.
The large-signal performance of the device was tested on
wafer at 18 GHz using a Focus CCMT1816 source/load pull
system. Under CW operation and biased at class AB mode
(
V, V), the device was matched for
maximum output power,
. No oscillation was observed
at any matching points during the test. Fig. 3 shows the mea-
sured output power
, power gain (G), power added
efficiency (PAE) and collector current as a function of input
power
. The measured maximum
with a peak PAE value of 11% and an associated power gain
of 4.5 dB. The corresponding dc power
the device is 1.26 mW/ m
0.25 mW/ m . The power performance of the same device was
also measured at lower frequencies. At 8 GHz, the measured
highest RF power density is 0.56 mW/ m with a PAE of 34%
(
mW). The lowered RF power density at 18 GHz
is ascribed to the power gain degradation with the increase of
operation frequency. The degradation of power gain results in
a degraded PAE
portion of the DC power being converted into RF power at
the high frequency. At the two different operation frequencies,
the heating power
974 mW at 8 GHz to 1351 mW at 18 GHz. The increased
heating power thus raises the device junction temperature and
further degrades the power performance of the devices. It is
thus speculated that, by reducing the emitter finger width, the
power gain and thus PAE values can be substantially improved.
The improvement of PAE will in turn enhance the RF power
levels. In spite of the large emitter width (2
device, the overall power performance values achieved in this
study are, to our knowledge, still the best among those reported
SiGe power HBTs [9] and power amplifiers [7], [10] operated
nearby this frequency point. For comparison, a summary of
the reported RF power levels versus frequency for SiGe power
value of 31 and 70 GHz, respec-
/dB/decade degradation trend. The
between the two configurations shown
is 24.73 dBm
density of
and the RF power density is
, which causes a smaller
increased from
m) used in the

Page 3

MA et al.: 18-GHz 300-mW SiGe POWER HBT383
Fig. 4.
(square) or power amplifiers (open triangle) for SiGe HBTs. The performance
results of state-of-the-art AlInAs–InGaAs–InP [11] and AlGaAs–GaAs HBTs
[12] are also shown for reference.
Total output power versus frequency from single-chip discrete devices
HBTs and power amplifier modules is shown in Fig. 4 with ref-
erence to the performance of state-of-the-art InP-based [11] and
GaAs-based HBTs [12]. The high performance of SiGe HBTs
demonstratedhereresultsfromalowbase(sheet)resistanceand
high device breakdown voltages. These characteristic values
are realized by optimizing the device heterostructure with the
goal of achieving a high
value. These optimizations also
permit the CB configuration to be favorably employed at the
operation frequency [8].
IV. CONCLUSION
In conclusion, an 18-GHz, 300-mW SiGe power HBT em-
ploying a box-type Ge (24%) profile and a heavily doped (
cm) base region has been developed with the highest
performance. The high
value (70 GHz), achieved by using
theoptimizedheterostructure,enablesahigherpowergainvalue
at 18 GHz and the lightly doped collector region enables high
breakdown voltages (BV
operations. The heavy doping concentration in the base region,
resulting ina low baseresistance, favorsthecommon–base con-
figuration for power amplifications.
V), permitting high power
REFERENCES
[1] J.-S. Rieh, B. Jagannathan, D. R. Greenberg, M. Meghelli, A. Rylyakov,
F. Guarin, Z. Yang, D. C. Ahlgren, G. Freeman, P. Cottrell, and D.
Harame, “SiGe heterojunction bipolar transistors and circuits toward
terahertz communication applications,” IEEE Trans. Microw. Theory
Tech., vol. 52, no. 10, pp. 2390–2408, Oct. 2004.
[2] M. Racanelli, P. Ma, and P. Kempf, “SiGe BiCMOS technology for
highly integrated wireless transceivers,” in Gallium Arsenide Integrated
Circuit Tech. Dig., Nov. 2003, pp. 183–186.
[3] K. D. Hobart, F. J. Kub, N. A. Papanicoloau, W. Kruppa, and P. E.
Thompson, “Si–Si
Ge heterojunction bipolar transistors with high
breakdown voltage,” IEEE Electron Device Lett., vol. 16, no. 5, pp.
205–207, May 1995.
[4] R. J. E. Hueting, J. W. Slotboom, A. Pruijmboom, W. B. de Boer, C. E.
Timmering, and N. E. B. Cowern, “On the optimization of SiGe-base
bipolar transistors,” IEEE Trans. Electron Devices, vol. 43, no. 9, pp.
1518–1524, Sep. 1996.
[5] D. M. Richey, J. D. Cressler, and A. J. Joseph, “Scaling issues and Ge
profile optimization in advanced UHV/CVD SiGe HBTs,” IEEE Trans.
Electron Devices, vol. 44, no. 3, pp. 431–440, Mar. 1997.
[6] Z.Ma,S.Mohammadi,P.Bhattacharya,L.P.B.Katehi,S.A.Alterovitz,
and G. E. Ponchak, “A high power and high gain X-band Si/SiGe/Si
heterojunction bipolar transistor,” IEEE Trans. Microw. Theory Tech.,
vol. 50, no. 4, pp. 1101–1108, Apr. 2002.
[7] A. J. Joseph, J. Dunn, G. Freeman, D. L. Harame, D. Coolbaugh, R.
Groves,K.J.Stein,R.Volant,S.Subbanna,V.S.Marangos,S.St.Onge,
E. Eshun, P. Cooper, J. B. Johnson, J.-S. Rieh, B. Jagannathan, V. Ra-
machandran, D. Ahlgren, D. Wang, and X. Wang, “Product applications
andtechnologydirectionswithSiGeBiCMOS,”IEEEJ.Solid-StateCir-
cuits, vol. 38, no. 9, pp. 1471–1478, Sep. 2003.
[8] Z.MaandN.Jiang,“OntheoperationconfigurationofSiGeHBTsbased
on power gain analysis,” IEEE Trans. Electron Devices, vol. 52, no. 2,
pp. 248–255, Feb. 2005.
[9] S. Mohammadi, Z. Ma, J. Park, P. Bhattacharya, L. P. B. Katehi, G. E.
Ponchak, S. A. Alterovitz, K. M. Strohm, and J.-F. Luy, “SiGe/Si power
HBTs for X- to K-band applications,” in IEEE MTT-S Int. Microwave
Symp. Dig., vol. 1, Jun. 2002, pp. 289–292.
[10] W. Bakalski, A. Vasylyev, W. Simbürger, R. Thüringer, H. Wohlmuth,
A. L. Scholtz, and P. Weger, “A fully integrated 7–18 GHz amplifier
with on-chip output balun in 75 GHz-?
Bipolar/BiCMOS Circuits Technology Meeting, Sep. 2003, pp. 61–64.
[11] R. S. Virk, M. Y. Chen, C. Nguyen, T. Liu, M. Matloubian, and D.
B. Rensch, “A high-performance AlInAs/InGaAs/InP DHBT K-band
power cell,” IEEE Microw. Guided Wave Lett., vol. 7, no. 10, pp.
323–325, Oct. 1997.
[12] D. Hill, R. Yarborough, T. Kim, and H.-F. Chau, “Low thermal
impedance MMIC technology,” IEEE Microw. Guided Wave Lett., vol.
7, no. 2, pp. 36–38, Feb. 1997.
SiGe-bipolar,” in Proc.