We present the electrical characteristics of the first 90nm SiGe BiCMOS technology developed for production in IBM's large volume 200mm fabrication line. The technology features 300 GHz f T and 360 GHz f MAX high performance SiGe HBTs, 135 GHz f T and 2.5V BV CEO medium breakdown SiGe HBTs, 90nm Low Power RF CMOS, and a full suite of passive devices. A design kit supports custom and analog designs and a library of digital functions aids logic and memory design. The technology supports mm-wave and high-performance RF/Analog applications.
Development of SiGe HBTs in BiCMOS technology with both high f
T and f
MAX faces significant challenges. To increase f
T, thinning the base and collector thickness is generally the first step to reduce the carrier transit times, but this increases the base resistance and the collector-base capacitance, which impacts f
MAX negatively. Increasing collector doping is also often employed to increase f
T, but this increases collector-base capacitance, which drives f
MAX down. To overcome these limits, millisecond anneal techniques, low temperature silicide and low temperature contact processes are employed to reduce the base resistance. Concurrently a novel approach to reduce the extrinsic collector-base capacitance is developed, without affecting the manufacturability and integration with CMOS. The simultaneous reduction of both base resistance and collector capacitance enables high performance SiGe HBT devices in 90nm BiCMOS Technology with operating frequencies of 285/475GHz f
T/f
MAX.
We report the results of an extensive study of band-to-band optical transitions in Si-Ge (n:m) superlattices and alloys where nϷm. Our samples were grown by molecular-beam epitaxy on ͑001͒ silicon using symmetrically strained layers and characterized by high-resolution x-ray diffraction and transmission electron microscopy. This growth procedure permits the synthesis of continuous Si-Ge superlattices with a thickness of several thousand Å. Optical absorption was studied by photocurrent spectroscopy at 300, 77, and 4.2 K. These results were analyzed to determine the dependence of the photocurrent on the photon energy. The energy dependence of absorption was also measured by optical transmission spectroscopy. Analysis of these experiments gives approximate agreement with photoconductivity experiments on the value of the energy gap, but also shows that the energy dependence of the absorption coefficient varies linearly with the photon energy, while photoconductivity experiments show that the photocurrent increases with the fourth power of the energy. The absorption coefficient, and its dependence on the photon energy, are calculated directly from the joint density of states which is extracted from the electronic band structure. Our calculations show that the dependence of optical absorption on photon energy is linear for perfect superlattices: ␣(ប)ϭA 0 (បϪE g ) x , where xϭ1, with the exponent increasing above 1 in the presence of disorder such as from atomic steps, interface roughness, and similar defects. ͓S0163-1829͑98͒06715-0͔ PHYSICAL REVIEW B 15 APRIL 1998-I VOLUME 57, NUMBER 15 57 0163-1829/98/57͑15͒/9128͑13͒/$15.00 9128
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