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The relatively less exploited terahertz band possesses great potential for a variety of important applications, including communication applications that would benefit from the enormous bandwidth within the terahertz spectrum. This paper overviews an approach toward terahertz applications based on SiGe heterojunction bipolar transistor (HBT) technology, focusing on broad-band communication applications. The design, characteristics, and reliability of SiGe HBTs exhibiting record [f.sub.T] of 375 GHz and associated [f.sub.max] of 210 GHz are presented. The impact of device optimization on noise characteristics is described for both low-frequency and broad-band noise. Circuit implementations of SiGe technologies are demonstrated with selected circuit blocks for broad-band communication systems, including a 3.9-ps emitter coupled logic ring oscillator, a 100-GHz frequency divider, 40-GHz voltage-controlled oscillator, and a 70-Gb/s 4:1 multiplexer. With no visible limitation for further enhancement of device speed at hand, the march toward terahertz band with Si-based technology will continue for the foreseeable future. Index Terms--BiCMOS integrated circuits, communication systems, heterojunction bipolar transistors (HBTs), high-speed integrated circuits.

SiGe HBT transistoprs achieving over 200 GHz f[subscript gamma] and f[subscript MAX] are examined and reported.

A terahertz (THz) CMOS detector array based on multiple chips stitched together is reported. The proposed multichip detector is scalable as the total number of subarray chips is flexible and can be controlled as needed with the help of the modular scheme adopted. Based on the presented multichip technique, a $3\times $ 3 multichip detector array composed of nine subarray chips has been implemented in this work for operation at 300 GHz. With the subarray chips, each with $7\times $ 7 pixels, the complete multichip array comprises $21\times21$ physical pixels. By employing virtual pixels, which are included to compensate for the chip interface area consumed for interchip wire-bonding in this work, THz real-time images with $23\times23$ pixels have been successfully acquired. The distribution of the responsivity and noise equivalent power (NEP) over the multichip array is presented. The responsivity distribution shows the effect of the series resistance of the long bias lines stretched over the multichip array, while the effect is not apparent for NEP. The distribution due to series resistance, as well as other nonuniformities over the pixels and chips due to various causes, can be suppressed with a proper calibration for the images acquired with the multichip array. [ABSTRACT FROM AUTHOR]

P-type SiGe temperature-dependent minority electron mobilities have been measured.

A double mesa-structure Si/SiGe heterojunction bipolar transistor (HBT) and novel micromachined lumped passive components have been developed and successfully applied to the fabrication of X- and Ku-band monolithic amplifiers. The fabricated 5 x 5 [[[micro]meter].sup.2] emitter-size Si/SiGe HBT exhibited a dc-current gain [Beta] of 109, and [f.sub.T] and [f.sub.max] of 28 and 52 GHz, respectively. Micromachined spiral inductors demonstrated resonance frequency of 20 GHz up to 4 nil, which is higher than that of conventional spiral inductors by a factor of two. Single-, dual-, and three-stage X-band amplifiers have been designed, based on the extracted active- and passive-device model parameters. A single-stage amplifier exhibited a peak gain of 4.0 dB at 10.0 GHz, while dual- and three-stage versions showed peak gains of 5.7 dB at 10.0 GHz and 12.6 dB at 11.1 GHz, respectively. A Ku-band single-stage amplifier has also been designed and fabricated, showing a peak gain of 1.4 dB at 16.6 GHz. Matching circuits for all these amplifiers were implemented by lumped components, leading to a much smaller chip size compared to those employing distributed components as matching elements. Index Terms - Amplifier, HBT, micromachining, MMIC, resonance frequency, SiGe.

Embedding magnetic layers in inductors is an attractive option for increasing inductance density, which is a critical issue for radiofrequency applications. In this letter, we develop a magnetostatic model for square spiral inductors incorporating a magnetic layer. In our model, we assume that the permeability of the magnetic layer is isotropic and infinite. The model provides a fast and effective numerical calculation of the inductance of inductors incorporating a magnetic layer. We show the derivation of the model and provide calculation results for various inductor structures. Index Terms--inductors, magnetic films, magnetostatics.

This paper presents a comprehensive study on the high-Q island-gate varactor (IGV), which includes a comparison with the conventional multifinger varactors (MFVs) and analyses on the effect of structural variations on the varactor performance. The study shows that the IGV exhibits smaller Rs and larger Q factor compared to the MFV, while its capacitance tuning ratio is smaller. The effect of the dimension variation and shape of the gate island, as well as the gate thickness, is substantial and the observed trends can be exploited for IGV optimization. This work indicates that the IGV is a highly promising option for millimeter-wave applications. [ABSTRACT FROM PUBLISHER]

The current characteristics of SiGe heterojunction bipolar transistors (HBTs) operating in the reverse active mode are investigated. It is experimentally shown that the IC is identical for the reverse and the forward modes for arbitrary doping and Ge profiles across the base to first order. In contrast, the impact of VBE and VCB, modulation Oil IC is opposite for the two modes, leading to a smaller Early voltage but more Ideal collector current for the reverse mode. [ABSTRACT FROM AUTHOR]

Deals with the measurement of temperature-dependent minority electron mobilities in p-type SiGe. Fabrication of npn SiGe/Si heterojunction bipolar transistors; Mobility measurement by magnetotransport technique; Mobility measurement by cut-off frequency technique; Conclusion.