|
 |
DOWNLOAD |
|
| Development of a SiGeC Heterojunction
Bipolar Transistor for |
| Ultra-high-speed/High-frequency Communication
LSIs |
|
- Ultra-high maximum oscillation frequency of 174
GHz - |
| |
Tokyo
Japan, December 5, 2001 - Hitachi, Ltd. (NYSE:HIT)has developed
a prototype SiGeC heterojunction bipolar transistor (HBT) by using selective
epitaxial growth of a mixture of silicon (Si), germanium (Ge) and carbon
(C), and has achieved the world's fastest device performance; cutoff
frequency 1) of 124 GHz and a maximum oscillation
frequency 2) of 174 GHz. As SiGeC HBT features
little change in performance after high temperature processing, it is
well suited to application in bipolar CMOS (combination of HBT and CMOS)
device technology, which is expected to be the most promising candidate
for next generation communication LSIs. The high-speed performance developed
is expected to accelerate the application of the bipolar CMOS to transmitter/receivers
in ultra-high-speed communication systems.
The demand for large-capacity data transmission in optical and mobile
communication systems is increasing with the rapid proliferation of
the Internet and cellular phones. Thus, a significant improvement in
high-speed performance is being required of LSIs (Large Scale Integrated
Circuits) embedded in transmitters and receivers for communication systems.
Bipolar CMOS (BiCMOS), a combination of the ultra-high-speed HBT and
the mid-to-low speed signal processing CMOS (Complementary Metal-Oxide
Semiconductor), is currently considered a viable solution to the above-mentioned
requirement, and research is being focused on this device. Although,
SiGe HBTs can operate at a high speed alone, a rapid deterioration in
performance occurs due to heat-treatment when integrated with the CMOS,
resulting in the lower performance than expected. Thus, SiGeC has been
receiving much attention as a new material suitable for BiCMOS due to
its high tolerance to heat treatment 3). Until
now, however, it was not possible to fabricate a SiGeC HBT with a self-aligned
structure 4) by using selective epitaxial growth,
and thus high-speed performance could not be obtained.
Given this background, Hitachi developed a high-speed SiGeC HBT technology
suitable for BiCMOS and achieved the world's fastest performance. The
two technology developed are as follows:
| (1) |
Formation of a SiGeC base using
selective epitaxial growth: A selective epitaxial growth technology
to form a SiGeC single crystal only on a Si substrate, by using
UHV/CVD (ultra-high-vacuum chemical vapor deposition) method,
was developed. |
| (2) |
Self-aligned SiGeC HBT technology:
A self-aligned fabrication process technology using SiGeC selective
epitaxial growth was developed, and the active area of the transistor
was formed without mask alignment. |
As a result, the following performances were achieved:
| (1) |
Improvement in transistor operating
speed: A self-aligned SiGeC HBT with low parasitic resistance
and low parasitic capacitance was fabricated using a high-quality
base layer of SiGeC containing 0.4% carbon, and high-speed high-frequency
performances of 124-GHz cutoff frequency and 174-GHz maximum oscillation
frequency were achieved. |
| (2) |
Achievement of ultra-high-speed circuit
performance: Using these transistors, an ultra-high-speed
circuit performance of a 5.7-ps propagation gate delay in a ECL
circuit 5) was obtained. |
Using this technology, it will now be possible to integrate high-speed
HBT and 0.1 m CMOS. This
ultra-high-speed high-functional device technology is expected to play
an important role in supporting next-generation information technology
such as multi-media services offered by next-generation backbone transmission
systems, large-capacity radio communication systems, and intelligent
traffic control systems using millimeter-wave bands.
<Definitions & Explanations of Terms>
| (*1) |
Cutoff frequency: Frequency at which
current gain of a transistor becomes unity; that is, the highest
frequency that a transistor can amplify current. It is used as
a figure of merit for high-speed characteristics in digital circuits.
|
| (*2) |
Maximum oscillation frequency: Frequency
at which the maximum power gain of transistor becomes unity; that
is, the highest frequency that a transistor can amplify power.
It is used as a figure of merit for high-frequency characteristics
in analog circuits. |
| (*3) |
High heat-treatment tolerance of SiGeC
HBT: Diffusion of the impurity (boron) in the base can be suppressed
by adding C to the base layer of the bipolar transistor, and the
thickness of the base layer can be reduced even though high-temperature
heat treatment is conducted. Therefore, both HBT and scaled-down
CMOS can be integrated on the same substrate, and a high-performance
LSI realized. |
| (*4) |
Self-aligned structure: Fabrication
of transistor active regions using only one photo lithography
process permits a device design, without the need to consider
tolerance of mask alignment. As a result, the extrinsic regions,
which increase the parasitic capacitance and parasitic resistance,
can be reduced, and device performance (high-speed operation)
can be improved. |
| (*5) |
ECL circuit: Emitter-coupled logic circuit.
|
|
WRITTEN BY Corporate Communications Division
 |
|
