Greg Freeman

Record RF performance of 45-nm SOI CMOS Technology

We report record RF performance in 45-nm silicon-on- insulator (SOI) CMOS technology. RF performance scaling with channel length and layout optimization is demonstrated. Peak fTs of 485 GHz and 345 GHz are measured in floating- body NFET and PFET with nearby wiring parasitics (i.e., gate- to-contact capacitance) included after de-embedding, thus representing FET performance in a real design. The measured fTs are the highest ever reported in a CMOS technology. Body- contacted FETs are also analyzed that have layout optimized for high-frequency analog applications. Employing a notched body contact layout, we reduce parasitic capacitance and gate leakage current significantly, thus improving RF performance with low power. For longer than minimum channel length and a body-contacted NFET with notched layout, we measure a peak fT of 245 GHz with no degradation in critical analog figures of merit, such as self-gain.

Half-terahertz operation of SiGe HBTs

This letter presents the first demonstration of a silicon-germanium heterojunction bipolar transistor (SiGe HBT) capable of operation above the one-half terahertz (500 GHz) frequency. An extracted peak unity gain cutoff frequency (f/sub T/) of 510 GHz at 4.5 K was measured for a 0.12/spl times/1.0 /spl mu/m/sup 2/ SiGe HBT (352 GHz at 300 K) at a breakdown voltage BV/sub CEO/ of 1.36 V (1.47 V at 300 K), yielding an f/sub T//spl times/BV/sub CEO/ product of 693.6 GHz-V at 4.5 K (517.4 GHz-V at 300 K).

Avalanche current induced hot carrier degradation in 200 GHz SiGe heterojunction bipolar transistors

SiGe heterojunction bipolar transistors (HBTs) have been investigated under accelerated avalanche stress conditions, where the base-emitter junction is forward biased, while the collector-base junction is reverse biased under avalanche conditions. The high energy avalanche carriers (hot carriers) introduce damage at Si-SiO/sub 2/ interfaces and degrade the characteristics of the SiGe HBTs. A new model has been developed to predict the damage at the Si-SiO/sub 2/ interface. The DC degradation of the base current is shown to correlate with the injected charge total and corresponding energy. The change of base current dependence on avalanche charges and applied voltage is shown, and a model is used to predict the parameter degradation within a typical digital switching application. The impact of this degradation mechanism to f/sub T/ has also been studied and found not to be significant.

40 Gbit/sec circuits built from a 120 GHz f/sub T/ SiGe technology

Product designs for 40 Gbit/sec applications fabricated from SiGe BiCMOS technologies are now becoming available. This paper will briefly discuss technology aspects relating to HBT device operation at high speed, acting to dispel some common misconceptions regarding SiGe HBT technology applicability to 40 Gbit/sec circuits. The high speed portions of the 40 Gbit/sec system are then addressed individually, demonstrating substantial results toward product offerings, on each of the critical high speed elements.

SiGe heterojunction bipolar transistors and circuits toward terahertz communication applications

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.

Transistor design and application considerations for >200-GHz SiGe HBTs

SiGe HBT transistors achieving over 200 GHz f/sub T/ and f/sub MAX/ are demonstrated in this paper. Techniques and trends in SiGe HBT design are discussed. Processing techniques available to silicon technologies are utilized to minimize parasitic resistances and capacitances and thereby establish raw speeds exceeding III-V devices despite the higher mobility in those materials. Higher current densities and greater avalanche currents, which are required for establishing such high performance, are discussed as they relate to device self-heating and reliability and the degradation of the devices. Simple circuit results are shown, demonstrating 4.2-ps ring-oscillator delays.

Structure optimization of trench-isolated SiGe HBTs for simultaneous improvements in thermal and electrical performances

The current level in the modern high-speed SiGe heterojunction bipolar transistors (HBTs) continues to increase for operation speed enhancement, but the resultant self-heating and elevated junction temperature emerge as a growing concern for device reliability as well as performance. To address such thermal issues, the optimization of SiGe HBT structures to achieve simultaneous improvements in thermal and electrical performance is carried out in this study. As a foundation for the study, an R/sub th/ measurement method and a geometry-based fast analytic thermal model were first developed for trench-isolated SiGe HBTs. Based on the method and model, a set of device design points for lowered R/sub th/ without compromising the RF performance have been successfully proposed and experimentally verified on IBMs 200-GHz SiGe HBTs. The details of the proposed structures and acquired results will be described in detail in the paper. The results obtained in this study shed a light on the possibility of the simultaneous optimization of thermal and electrical performance of SiGe HBTs.

Product applications and technology directions with SiGe BiCMOS

In this paper we highlight the effectiveness and flexibility of SiGe BiCMOS as a technology platform over a wide range of performance and applications. Examples include high speed device design, power amplifiers, integrated VCOs and very high level integration.

Cryogenic operation of third-generation, 200-GHz peak-f/sub T/, silicon-germanium heterojunction bipolar transistors

We present a comprehensive investigation of the cryogenic performance of third-generation silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) technology. Measurements of the current-voltage (dc), small-signal ac, and broad-band noise characteristics of a 200-GHz SiGe HBT were made at 85 K, 120 K, 150 K, 200 K, and 300 K. These devices show excellent behavior down to 85 K, maintaining reasonable dc ideality, with a peak current gain of 3800, a peak cut-off frequency (f/sub T/) of 260 GHz, a peak f/sub max/ of 310 GHz, and a minimum noise figure (NF/sub min/) of approximately 0.30 dB at a frequency of 14 GHz, in all cases representing significant improvements over their corresponding values at 300 K. These results demonstrate that aggressively scaled SiGe HBTs are inherently well suited for cryogenic electronics applications requiring extreme levels of transistor performance.

Proton tolerance of fourth-generation 350 GHz UHV/CVD SiGe HBTs

We report, for the first time, the impact of proton irradiation on fourth-generation SiGe heterojunction bipolar transistors (HBTs) having a record peak unity gain cutoff frequency of 350 GHz. The implications of aggressive vertical scaling on the observed proton tolerance is investigated through comparisons of the pre-and post-radiation ac and dc figures-of-merit to observed results from prior SiGe HBT technology nodes irradiated under identical conditions. In addition, transistors of varying breakdown voltage are used to probe the differences in proton tolerance as a function of collector doping. Our findings indicate that SiGe HBTs continue to exhibit impressive total dose tolerance, even at unprecedented levels of vertical profile scaling and frequency response. Negligible total dose degradation in /spl beta/ (0.3%), f/sub T/ and f/sub max/(6%) are observed in the circuit bias regime, suggesting that SiGe HBT BiCMOS technology is potentially a formidable contender for high-performance space-borne applications.