SiGe BiCMOS Technology and Circuits for Active Safety Systems
INVITED
Franz Dielacher, Marc Tiebout, Rudolf Lachner*), Herbert Knapp*), Klaus Aufinger*) Willy Sansen**),
Infineon Technologies Austria AG, Siemensstrasse 2, 9500 Villach Austria
Infineon Technologies AG, Am Campeon 1-12, 85579 Neubiberg, Germany
**)
KU Leuven, &*3%"*("$$($54 61<99: +,$1"+#
*)
ABSTRACT
This paper provides an overview of the features and capabilities of
state-of-the-art SiGe devices and BiCMOS technology for
applications such as high-data-rate communications and pro-active
safety systems like car-radar, identification and e-safety.
The capabilities offered by SiGe-BiCMOS and microwave packaging
enable the integration of complete transceivers on a chip or in a
package even including the antenna. The criteria and trade-off’s for
the technology selection and system partitioning are described in the
introduction. In addition to the electrical components performance,
major criteria are addressed such as high reliability, long lifetime and
high yield fabrication. Advanced packaging technologies are
addressed as well, including embedded passive components and
package co-design.
Existing circuit design examples and future solutions for 77 GHz
automotive radar are presented, followed by a multichannel receiver
and a multichannel transmitter for mm-wave people scanners for
airport security.
Keywords – Silicon-Germanium (SiGe), BiCMOS, Heterojunction
Bipolar Transistor (HBT), Automotive Radar, mm-Wave Security
Scanner, mm-Wave Imaging
ratio of gm over IC (gm over IDS in CMOS) of the SiGe bipolar
transistor is essential to save current.
The mm-wave bandwidth covers a frequency range from 30 GHz to
300 GHz. However the interest for application development is
concentrated in selected bands for worldwide communication. The
allocation of the ISM band around 60 GHz and the 70 GHz and 80
GHz bands are released worldwide mainly for wireless high-data-rate
communication and car-radar applications, with an operating range
that is limited to a few meters for indoor communications at 60 GHz,
whereas it is up to around 1 km for the outdoor applications. The
operating range has a direct impact on the transmitted power, which
is between 0 and 10 dBm within indoor networks, whereas it needs to
be much higher in the case of outdoor applications. A rough
estimation gives an output power level of around 15 dBm to
guarantee reliable 1-to-2-km link for data transmission in all weather
conditions or to achieve a distance of >200m for long-range
automotive radar [9].
As circuit design examples, a multichannel 77GHz automotive radar
transmitter a multichannel receiver and a multichannel transmitter for
mm-wave people scanners in the 70 to 80 GHz frequency band will
be presented.
INTRODUCTION
RF/microwave circuits are designed in advanced CMOS, SiGeBiCMOS, GaAs and InP technologies as shown in Figure 1. In terms
of RF performance InP is the best but other criteria like integration
complexity and cost have to be taken into consideration. As a general
rule we can say that “what can be done in silicon will be done in
silicon” and “what can be done in CMOS will be done in CMOS” [2].
Today almost all the designs up to about 10GHz are in CMOS
because of the multi-million volumes and SoC integration
requirements. For the frequency range from 10GHz to about 100GHz
where the volumes are still moderate, SiGe-BiCMOS is most
attractive because of the excellent performance and overall cost
trade-off. Beyond 100 GHz InP is needed but here we are talking
about volumes below one k pieces and therefore the high technology
cost is not an issue.
In the SiGe bipolar and BiCMOS process development good
progress was made [1,2,9]. Today technologies with fmax>400GHz
and fT >250GHz are available as shown in table 1. This excellent RF
performance is achieved with a 130nm process lithography.
Extended temperature range, high reliability and long process
lifetime are other important features of the SiGe technologies.
According to the ITRS roadmap the next SiGe-based bipolar
transistor generation will even achieve 700 GHz in a 65nm (or 90nm)
technology [4].
Other SiGe-bipolar features as a 4 times higher breakdown voltage
compared to CMOS (for identical fmax) are most useful for circuits
like power-amplifiers and to achieve a very low phase-noise in
VCO’s. For practical applications the collector base breakdown
voltage (BVCBo or BVCEs) is most relevant and is about 5V in a SiGe
bipolar transistor with fmax >400GHz. Further the four times better
FIGURE 1. TECHNOLOGY CHOICE
TABLE 1. SIGE PROCESS FOUNDRIES
978-1-4799-2217-8/14/$31.00 ©2014 IEEE
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SIGE TECHNOLOGY OVERVIEW
Modern SiGe and deep sub-µm CMOS processes both provide
transistors with fT/fmax well above 200/250 GHz, thus making mmwave transceivers feasible in either technology as is widely
documented in the literature. Usually the choice of the fabrication
process will be strictly linked to the final application specifications
and to technical implementation trade-offs such as the desired level
of integration, frequency bandwidth and distance operating ranges. In
addition to the required fT/fmax capability this relates to output signal
power, quality of on-chip passive components, noise issues,
robustness to process and temperature variations, antenna cointegration, and so on.
Current state of the art SiGe bipolar/BiCMOS technologies are
shown in table 1. The B7HF200 process from Infineon is a bipolar
SiGe HBT process featuring cut-off frequencies of 200 GHz (fT) and
250 GHz (fmax) and the next generation B11HFC achieves 250 GHz
(fT) and 435 GHz (fmax) with scaled HBT geometries as shown in
table 2 [1,2,3,4]. Beside the SiGe HBT key devices, both processes
offer poly-silicon and metal film resistors, MIM capacitors, a hyper
abrupt pn varactor diode and laser fuses. The SiGe HBT uses a
classical DPSA emitter/base structure (double-poly-silicon selfaligned structure, although one of the two poly-silicon contacts – the
emitter - actually is now made of mono crystalline Silicon) and a
selective epitaxially grown (SEG) Silicon Germanium base layer.
Shallow and deep trench isolation minimize internal parasitic
capacitances and allow for dense device packing. A cross-section of
the B7HF200 and the B11HFC fmax=435 GHz HBT device is shown
in figure 2 in a comparison. Measured fmax and fT characteristics as a
function of collector current IC for B11HFC are shown in figure 3.
The metallization system of B7HF200 consists of 4 copper layers
and one aluminum layer and a gold pad. The new B11HFC process is
using 6 copper and one aluminum layer and it incorporates 130nm
CMOS devices.
Currently the B7HF200 process is extensively used for products like
car-radars, mm-wave transceivers for data-links and airport security
scanners. Volume production started in 2007 and B7HF200 is
automotive qualified and fulfills all the extended reliability and
operating conditions requirements like extended temperature range.
In the future the new B11HFC BiCMOS with the improved HBT
performance and the additional CMOS devices will be used.
FIGURE 3: fmax AND fT VERSUS IC FOR B11HFC
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high amplification in the RF/mm-wave front-end
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more than 10 dBm output power at mm-wave frequencies
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passive devices with good high-frequency behaviour,
including top thick metal layers and a thick oxide from this
metal towards the substrate
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the oxide thickness of SiGe processes is usually around
twice the oxide thickness of CMOS
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both modern SiGe and CMOS transistors offer good noise
performance behaviour in the mm-wave range, but SiGe
devices are still superior and
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technology reliability in terms of process and temperature
PACKAGING OF MM-WAVE ICS
TABLE 2. DEVICE PARAMETERS OF SIGE HBTS
FIGURE 2: SIGE HBT CROSS SECTION
To simplify the fabrication of microwave systems and to reduce
production costs, the development of surface mountable devices
(SMD) was very important. A fan-out embedded wafer level ball grid
array package technology (eWLB) proved to be suited and most
useful [7]. Like shown in figure 3, the significant advantage
compared to the standard BGA-wirebond and BGA flip-chip
packages are the significantly reduced parasitic. A cross section of a
packaged device is shown in figure 4. eWLB is suited for)/)*#%$
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FIGURE 3: PACKAGE PARASITICS
FIGURE 5: THREE CHANNEL TRANSMITTER
FIGURE
4: eWLB PACKAGE
CROSS SECTION
DESIGN
EXAMPLE
: AUTOMOTIVE
RADAR
AUTOMOTIVE RADAR TRANSMITTER
The market for driver assistance systems based on millimeter-wave
radar sensor technology is gaining momentum. Radar is robust
against environmental influences and therefore has been identified as
the most promising technology for many driver assistance functions
for active comfort and active safety. For the radar transceivers
performance, integration, power consumption and cost are key
factors. Chip sets and MMICs in GaAs technology are used in the
2nd generation of radars but for the 3rd generation highly integrated
SiGe transceivers are the favorites.
Figure 5 shows the block diagram of a three-channel 77 GHz radar
transmitter [5]. The circuit is manufactured in Infineon’s B7HF200
SiGe process and mounted in a eWLB package.
The transmitter contains a push-push VCO for the 76 – 77 GHz radar
band with a phase noise of -76 dBc/Hz. Three independent output
channels are available. The output power of each channel can be
controlled over a wide range via a digital interface.
In order to simplify the implementation of frequency control schemes,
the circuit contains a versatile frequency divider block which can be
configured to provide output signals in the range from 19 GHz to 50
kHz. An additional low-noise 18 GHz VCO allows the
implementation of offset PLLs.
Figure 6 shows a photograph of the transmitter chip in the eWLB
package. The package size is 6x6 mm2 with a ball pitch of 0.5 mm.
With additional balls for thermal management a thermal resistance
from chip to board of less than 10 K/W was achieved.
The circuit operates from a single supply voltage of 3,3 V and
consumes between 205 mA and 710 mA, depending on the
configuration. Measured performance data is shown in table 3.
FIGURE 6: CHIP/PACKAGE PHOTOGRAPH
TABLE 3: TRANSMITTER PERFORMANCE SUMMARY
WIDEBAND CHIPSET FOR MM-WAVE IMAGING
In this section a four channel receiver and transmitter chipset for high
resolution real-time imaging systems for people screening
applications operating near the W-band will be described [6, 10]. The
center frequency of operation is 78GHz with a 3-dB bandwidth of at
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least 7GHz for optimal image resolution and depth of focus.
Specifications are listed in Table 4.
CONCLUSION
It can be concluded that the potential of SiGe bipolar and BiCMOS
technology is excellent to push emerging mm-wave applications to
broader acceptance and market penetration. SiGe is an optimal
technology choice for „medium“ volume RFIC applications like carradar, mm-wave security scanners and high data-rate transceivers.
The strive for higher fT/fmax is driven by power saving needs and
new applications at even higher frequencies. New SiGe BiCMOS
with fmax > 400 GHz will be in volume production soon and research
projects with the goal to achieve fmax= 700 GHz have been initiated.
REFERENCES
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TABLE 4: CHIPSET SPECIFICATIONS
Figure 7 shows the block diagram of the four-channel receiver, Fig. 8
the block diagram of the four channel transmitter. The circuits are
manufactured in Infineon’s B7HF200 SiGe process, die size is
2x2.2mm².
The frequency generation consists of a frequency quaddrupler
consisting of 2 cascaded active Gilbert mixers. The receiver RFIC
contains 4 channels including LO generation and distribution. The
measured receiver conversion gain is 23dB with a SSB NF below
10dB over a wide frequency range from 70GHz up to 82GHz.
Transmitter output power is 5dBm over a 3dB bandwidth ranging
from 72GHz to 84GHz. The chip is supplied from a single 3,3V
supply voltage and the power consumption per channel is below
180mW/channel for the receiver and below 145mw/channel for the
transmitter.
The analog front ends are built of custom made four-channel receiver
and transmitter chips, which are connected to aperture-coupled patch
excited horn antennas. Those elements are embedded in a RF
multilayer PCB. The chips are mounted in multilevel cavities, as the
antenna’s differential feed lines run on an inner layer of the PCB, and
for RF performance reasons, vias and longer bond wires have been
avoided.
FIGURE 7: RECEIVER BLOCK DIAGRAM
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FIGURE 8: TRANSMITTER BLOCK DIAGRAM
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