A GaAs MMIC Single-Chip RF-MEMS Switched Tunable LNA
1,2
Robert Malmqvist, 1,†Carl Samuelsson, 2,3Shakila Reyaz, 1Andreas Gustafsson, 4Seonho Seok,
4
Michel Fryziel, 4Paul-Alain Rolland, 5Brice Grandchamp and 6Rens Baggen
1
Swedish Defence Research Agency (FOI), 58330 Linköping, Sweden, +46 13 378353, rma@foi.se
2
Uppsala University, 751 05 Uppsala, Sweden
3
NED University of Engineering & Technology, Karachi 75270, Pakistan
4
CNRS-IEMN, 59652 Villeneuve d’Ascq, Cedex, France
5
OMMIC S.A.S, F-94453 Limeil-Brevannes, Cedex, France
6
IMST GmbH, D-47475 Kant-Lintfort, Germany
†Now with SAAB AB, SE-581 88 Linköping, Sweden
Abstract — This paper presents a novel compact circuit
design of an RF-MEMS frequency-agile LNA realized in a
GaAs MMIC process that also includes a BCB cap type of
wafer-level package. The uncapped/BCB capped single-chip
GaAs MEMS tunable LNA circuits which can be matched at
different frequency bands (e.g at X-band and Ku-/K-band)
present similar in-band gain, linearity and noise figure over
30-60% wide tuning ranges (the uncapped MEMS tunable
LNA has an NF≤3 dB at 14-21 GHz with ≤0.6 dB higher NF
at 9-13 GHz). The validated MMIC designs are first time
realizations of uncapped/0-level packaged MEMS tunable
(wide-band/narrow-band) LNAs in a GaAs foundry process.
Index Terms — Low noise amplifiers, MMIC, radio
frequency micro-electromechanical systems, switches
I. INTRODUCTION
Reconfigurable high-performance (low loss/DC power
and high isolation/linearity) ICs are key elements in RF
systems for wireless communication, space, defense and
security applications. Due to its superior RF properties
RF-MicroElectroMechanical Systems (MEMS) switches
have been proposed as an enabling technology in adaptive
front-end solutions (e.g. switches from RadantMEMS).
On-chip integration of RF-MEMS and Monolithic
Microwave Integrated Circuits (MMICs) could enable a
higher degree of functionality in reconfigurable (multiband/wideband) front-ends. Single-chip MEMS switched
low noise amplifiers (LNAs) based on GaAs and silicon
technologies reported a noise figure (NF) of 1-2 dB at 1020 GHz and 8 dB at 60-77 GHz, respectively [1-4].
The GaAs MEMS LNAs presented in [1-3] were
implemented as switched dual-amplifier designs where
two different amplifiers covering the same frequency
range could be selected depending on the requirements.
Packaging of RF-MEMS switches is also a critical part of
the manufacturing process and the MEMS active ICs
reported in [1-4] were not packaged. MEMS switches are
mechanical devices which need to be packaged (protected)
before the wafers are diced and to extend the life time of
such switches. Micro-strip ICs that use via holes require a
backend processing of the wafers that can also result in
destruction of the MEMS switches. Packaging of MEMS
switches is preferably made at the wafer-level (0-level) in
which case the MEMS switches can be released and
packaged after the backend process. Some recent studies
have focused on development of packaging solutions
using e.g. BenzoCycloButene (BCB) type of protective
caps with marginal effect on the packaged switch
performance up to the mm-wave range and also to
improve the reliability of MEMS switches fabricated in
III-V processes [5-6]. In this paper, we will present
uncapped/BCB capped GaAs frequency-agile (tunable)
LNAs that can be matched at different frequency bands
(e.g. close to 10 GHz and 20 GHz) using reconfigurable
impedance matching networks. Such highly integrated
adaptive (dual-band/multi-band) RF-MEMS enabled LNA
MMICs can be commercially very attractive since such
tunable devices can be useful for many different frequency
bands and applications.
II. GAAS RF-MEMS BASED TUNABLE LNA MMICS
A. RF-MEMS Switches made in a GaAs Foundry Process
The RF-MEMS switches used here (developed by the
GaAs foundry OMMIC) are ohmic contact switches (see
Fig. 2) and when the switch is closed the cantilever is in
down-state (ON) and a low contact resistance (RON) is
realized in the RF path (while COFF=10 fF in the up-state).
The cantilever contains several parallel so-called flex slots
to ensure a good contact is made between the four switch
beams and the contact bumps when the switch is pulled
down (the switch actuation voltage is typically 50-70 V).
Such GaAs MEMS serial switches show 15-60 dB of
isolation up to 40 GHz with 0.3-1 dB of transmission
losses up to 95 GHz [7]. The DC power consumption is
very low since only a small leakage current will flow (<10
µA). The on/off switch times are in the order of 1-10 µs
[7].
978-1-4799-0583-6/13/$31.00 ©2013 IEEE
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(a)
Fig. 1. Circuit schematic of a frequency-agile LNA with RFMEMS switched reconfigurable impedance matching networks.
B. Circuit Design
Figure 1 depicts the circuit schematic of a frequencyagile LNA consisting of an unmatched amplifier
combined with reconfigurable (switched) input and output
matching networks. Four MEMS switches (SW1, SW3,
SW4, SW6) are in a shunt configuration to ground via a
small on-chip capacitor C1 (0.13 pF) and in parallel with
an equally sized capacitor C2 (0.13 pF). Two switches
(SW2, SW5) are used to connect different transmission
lines (or on-chip inductors) TL1, TL2, TL3 and TL4. When
the shunt switches are in down-state (“1”) and the series
switches are in up-state (“0”) the load capacitance CL of
each matching network will be determined by 2(C1 + C2)
which together with TL1 and TL3 can be used to set the
resonance frequencies (f101) of the input/output impedance
matching (s11 and s22) for a specific frequency band. On the
other hand, when the shunt switches are in up-state (0) and
the series switches are in down-state (1) the corresponding
s11 and s22 resonance frequencies (f010) will be controlled by
CL=2C2 (COFF << C1) and the parallel combinations of
TL1//TL2 and TL3//TL4, respectively. Given certain
transmission line (or inductor) values f101 < f010 since
CL(101) > CL(010) (we will denote those frequencies or
bands as Low-band and High-band, respectively). The
frequency tuning range Δf = f010 – f101 is proportional to the
ratio between the load capacitances CL(101)/CL(010) =
2(C1 + C2)/2C2 = 2 when C1 = C2.
Figure 2a-c show micrographs of an RF-MEMS
reconfigurable matching network (break-out) and tunable
MEMS LNA MMICs that were fabricated on 100 μm
thick GaAs wafers using OMMIC’s 0.13 μm gate length
high electron mobility transistor (HEMT) technology.
Compared with the fabricated uncapped versions of those
circuits the BCB capped RF-MEMS tunable LNA design
was modified in order to fulfill the design rules for 0-level
2
packaging (circuit areas of both designs equal 1x3 mm ).
The following gate widths (Wgi, i=1, 2) were used in the
the uncapped/BCB capped tunable LNA designs: Wg1 =
6×35 µm, Wg2 = 4×35 µm and Wg1=4×50 µm, Wg2=4×35
µm. In the BCB capped LNA design C1=C2=0.1 pF.
(b)
(c)
Fig. 2. Micrographs of (a) a GaAs RF-MEMS reconfigurable
LNA matching network and (b-c) uncapped/BCB capped tunable
LNA MMICs with on-chip RF-MEMS matching networks.
C. Experimental Results
Figure 3 shows measured and simulated s-parameters
and noise figure of a two-stage unmatched wideband LNA
break-out circuit (chip photo not shown). The unmatched
LNA shows 15-20 dB of gain and NF=2 dB at 6-26 GHz
with |s11| and |s22| below 0 dB and –4 dB. The DC power
consumption (PDC) of the unmatched GaAs LNA was 56
mW. Figure 4 shows measured |s21|, |s11| and |s22| of a
GaAs MMIC 1-bit RF-MEMS input matching network
shown in Fig. 2a when the two shunt MEMS switches
used were first in up-state and the series switch in downstate and vice versa. The two possible tuning states (010
and 101) result in an f010 that occurs at 23.6 GHz for |s11|
and |s22| (High-band) whereas f101 occurs at 11.7/12.8 GHz
(Low-band) thus a factor two in tuning range. At those
resonance frequencies, |s21|, |s11| and |s22| equal -0.9/-2.6
dB, -15/-9 dB and -22/-41 dB, respectively. The measured
results are found to agree relatively well with simulations
(simulated |s21|, |s11| and |s22| equal -0.8/-1.6 dB, -15/-12
dB and -26/-26 dB at 24.3 GHz and 12.7 GHz,
respectively). The higher in-band transmission loss of the
GaAs MEMS matching network for the 101 state is
explained by additional losses of the two shunt switches in
down-state (simulations indicate it may be possible to
achieve lower losses for the Low-band case if the contact
resistance can be made sufficiently small).
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(a)
Fig. 3. Measured and simulated s-parameters and noise figure of
a two-stage unmatched LNA MMIC (break-out circuit).
(b)
Fig. 4. Measured s-parameters of a 1-bit GaAs MMIC RFMEMS based reconfigurable impedance matching network.
In Figs. 5a-c, measured s-parameters of the
uncapped/BCB capped GaAs RF-MEMS tunable LNA
MMICs are given for the two tuning states (101 and 010)
when PDC=21/40/60 mW (tunable LNA noise figure results
are shown in Figs. 6a-c). For the High-band state the
uncapped GaAs MEMS tunable LNA design achieve
s21|=11-13 dB at 7-21 GHz with NF=3 dB at 14-21 GHz
(|s11|, |s22| ≤ –10 dB at 16-21 GHz) whereas for the Lowband state |s21|=12-14 dB at 8-12 GHz and NF>4 dB (|s11|,
|s22| ≤ –10 dB at 10-12 GHz). The gain and NF improve
with PDC=40 mW (with similar -10 dB bandwidths for |s11|,
|s22|). The High-band NF=2.5-3.3 dB at 14-21 GHz and
Low-band NF is up to 0.6 dB higher at 9-13 GHz. The
GaAs MEMS tunable (wide-band/narrow-band) LNA
MMICs demonstrate dual-band impedance matching over
30-60% wide tuning ranges with similar in-band LNA
gain, noise figure and linearity (OIP3=13-17 dBm).
(c)
Fig. 5. Measured s-parameters of RF-MEMS tunable (wideband/narrow-band) LNA GaAs MMICs: (a-b) uncapped (PDC=21
mW/40 mW) and (c) BCB capped (PDC=60 mW).
The reduced tuning range of the BCB capped MEMS
tunable LNA may be explained by a denser circuit layout.
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VII. CONCLUSION
Uncapped and BCB capped (wafer-level packaged)
frequency tunable RF-MEMS switched GaAs LNA
2
MMICs with compact chip dimensions (1x3 mm ) were
presented in this paper. Such single-chip MEMS tunable
(wide-band/narrow-band) LNA circuits demonstrate dualband impedance matching over relatively wide (30-60%)
tuning ranges together with similar in-band gain, noise
figure and linearity. The experimentally validated RFMEMS reconfigurable GaAs LNA MMICs could enable
more cost-effective ways to realize highly adaptive (e.g.
wide-band/narrow-band/multi-band) single-chip frontends for wireless applications up to the mm-wave range.
(a)
ACKNOWLEDGMENT
The authors wish to acknowledge the European Union
for the funding and support of the FP7 project MEMS-4MMIC (grant agreement no. 224101).
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