Elsevier

Microelectronics Reliability

Volume 47, Issues 2–3, February–March 2007, Pages 384-390
Microelectronics Reliability

Review
Performance trends of Si-based RF transistors

https://doi.org/10.1016/j.microrel.2006.05.015Get rights and content

Abstract

This paper discusses several aspects of the performance of advanced Si-based RF transistors. The RF performance of SiGe HBTs and Si RF MOSFETs is reviewed and compared to that of III–V RF transistors. The speed – breakdown voltage tradeoff which is typical for bipolar transistors is discussed with special emphasis on SiGe HBTs. On the field-effect transistor side, we review the performance of state-of-the-art Si RF MOSFETs and show that these devices are highly competitive in terms of speed and cutoff frequency.

Introduction

About 15 years ago, the field of RF transistors has clearly been dominated by III–V transistors. The only commercially available Si-based RF transistor was the conventional Si bipolar transistor for application in the lower GHz range. Since that time, the situation changed dramatically, and both SiGe HBTs and Si RF MOSFETs became widely accepted RF devices recently. To get an impression on how the frequency performance of Si-based RF transistors evolved and how it competes with that of III–V transistors, Fig. 1, Fig. 2 show the best reported cutoff frequencies, fT, and maximum frequencies of oscillation, fmax, of Si MOSFETs, SiGe HBTs, III–V FETs, and III–V HBTs versus time. The data shown in Fig. 1, Fig. 2 (as well as those in Fig. 3, Fig. 4, Fig. 7, Fig. 8, Fig. 9 to be shown later) have been taken from two comprehensive data collections on the performance of all relevant RF transistor types currently in use or under development [1], [2].

The fT and fmax data vs. time plots clearly indicate that the frequency limits of the Si-based and of the III–V RF transistor types have been enhanced continuously. A closer inspection of the shown data reveals, however, several additional interesting details which are worth mentioning. The record fT and fmax data for III–V FETs stem solely from InP HEMTs, while the record fTs of GaAs MESFETs, AlGaAs/GaAs HEMTs, and GaAs pHEMTs (pseudomorphic HEMTs) are below 200 GHz and the best reported fmaxs of these transistors are below 350 GHz. The record performance of III–V HBTs in terms of fT and fmax has also been obtained almost exclusively with InP transistors. The only exceptions are the fmax records from the 1990s which have been achieved with GaAs HBTs (open triangles in Fig. 2). The current record fT and fmax are:

  • fT 562 GHz [3] and fmax 600 GHz [4] for InP HEMTs,

  • fT 550 GHz [5] and fmax 687 GHz [6] for InP HBTs,

  • fT 380 GHz [7] and fmax 350 GHz [8] for SiGe HBTs,

  • fT 330 GHz [9] and fmax 320 GHz [9] for Si MOSFETs.

It should be noted that only III–V HBTs with rather conventional designs have been included in Fig. 1, Fig. 2. Not covered are HBTs fabricated with a sophisticated transferred substrate process. Laboratory InP transferred substrate HBTs showing an fmax around 1 GHz have been reported recently [10]. This is the highest fmax ever reported for a transistor.

We see that presently the frequency limits of Si-based RF transistors are well above 200 GHz. Only a few years ago, such a statement would have been considered as wishful thinking!

In the following sections, we shall take a closer look at some specific aspects of the performance of Si-based RF transistors. In particular, the performance of SiGe HBTs will be reviewed and compared to that of GaAs and InP HBTs. The tradeoff between cutoff frequency and breakdown voltage, BVCEO, of SiGe HBTs and options to optimize the collector design will be discussed. We present the results of a simulation study, where the fT, fmax, and BVCEO have been considered simultaneously. Finally, the frequency limits and noise figures of Si RF MOSFETs will be reviewed and compared to those of GaAs pHEMTs.

Section snippets

SiGe HBTs vs III–V HBTs

In many cases it is important that an HBT shows simultaneously high fT and high fmax, i.e., fT  fmax. To clarify to what extend high-performance SiGe, GaAs, and InP HBTs fulfill this requirement, Fig. 3 shows an fmax versus fT plot. Each data point indicates the fT and fmax obtained with one transistor. The best GaAs HBTs show maximum frequencies of oscillation in excess of 200 GHz, while the cutoff frequency is limited to about 150 GHz. The best reported SiGe HBTs reach both fmax and fT of around

Collector optimization for SiGe HBTs

We have shown that there exists a general tradeoff between speed and breakdown voltage for bipolar transistors and that especially high-speed SiGe HBTs suffer from low breakdown voltages. This leads us to the question whether the collector design can be optimized in order to improve the cutoff frequency without affecting the breakdown voltage.

To investigate this issue, we carried out a simulation study using the commercial device simulator ATLAS [12]. The DC and small-signal characteristics of

Si RF MOSFETs vs GaAs pHEMTs

Traditionally, the Si MOSFET has been considered a slow device not suitable for RF applications. Several reasons contributed to this conviction. First, the electron mobility in Si is by nature lower than in III–V compounds. Second, the current in a MOSFET flows in an inversion channel close to the Si/SiO2 interface where the carriers are subjected to the effects of interface roughness, interface traps, and crystal imperfections. As a result, the mobility is further degraded. Thanks to the

Conclusion

In recent years, the RF performance of Si-based RF transistors has been enhanced considerably. Meanwhile SiGe HBTs with frequency limits (fT and fmax) in excess of 300 GHz and Si RF MOSFETs with frequency limits well above 200 GHz have been realized. The RF noise behavior of Si-based RF transistors has also been improved considerably. Thus, Si-based RF transistors are successfully invading frequency ranges that had been the domain of III–V devices in the past.

Aside from the breakdown voltage,

Acknowledgement

This work has been supported by the Federal State of Thuringia under TMWTA contract No. B0509-03006.

References (26)

  • F. Schwierz et al.

    Modern microwave transistors – theory, design, and performance

    (2003)
  • Schwierz F. Microwave transistors: state of the art in the 1980s, 1990s, and 2000s – a compilation of 1000 top...
  • Y. Yamashita et al.

    Pseudomorphic In0.52Al0.48As/In0.7Ga0.3As HEMTs with an ultrahigh fT of 562 GHz

    IEEE Electron Dev Lett

    (2002)
  • P.M. Smith et al.

    W-band high efficiency InP-based power HEMT with 600 GHz fmax

    IEEE Microwave Guided Wave Lett

    (1995)
  • W. Hafez et al.

    0.25 μm emitter InP SHBT with fT = 550 GHz and BVCEO > 2 V

    IEDM Tech Dig

    (2004)
  • D. Yu et al.

    Ultra high-speed 0.25-μm emitter InP–InGaAs SHBTs with fmax of 687 GHz

    IEDM Tech Dig

    (2004)
  • B. Heinemann et al.

    A low-parasitic collector construction for high-speed SiGe:C HBTs

    IEDM Tech Dig

    (2004)
  • M. Khater et al.

    SiGe HBT technology with fmax/fT = 350/300 GHz and gate delay below 3.3 ps

    IEDM Tech Dig

    (2004)
  • S. Lee et al.

    Record RF performance of sub-46 nm Lgate NFETs in microprocessor SOI CMOS technologies

    IEDM Tech Dig

    (2005)
  • M. Rodwell et al.

    Submicron scaling of HBTs

    IEEE Trans Electron Dev

    (2001)
  • D.R. Greenberg et al.

    Noise performance of a low base resistance 200 GHz SiGe technology

    IEDM Tech Dig

    (2002)
  • ATLAS User’s Manual – Device Simulation Software, Silvaco International,...
  • K. Katayama et al.

    A new hot carrier simulation model based on full 3D hydrodynamic equations

    IEDM Tech Dig

    (1989)
  • Cited by (22)

    • Effect of localised charges on nanoscale cylindrical surrounding gate MOSFET: Analog performance and linearity analysis

      2012, Microelectronics Reliability
      Citation Excerpt :

      Adan et al. [7] reported experimental RF performance of SOI MOSFET including linearity study of single gate SOI MOSFET. There are several papers reported on analog and RF performance of SOI MOSFET [8–11] and DG MOSFET [12–14]. Surrounding Gate (SRG) MOSFET is one of the most promising device structure to extend the scaling of the CMOS device as it provides the best electrostatic control of the channel which further improves with the reduction of the gate length and gate oxide thickness [15–18].

    • Nanoscale FETs

      2012, Advances in Imaging and Electron Physics
      Citation Excerpt :

      Therefore, one shall expect that the minimum noise figure (NFmin) for the CMOS would perform much better than, for example, the GaAs-pHEMT technology (currently the most commercially used GaAs-based RF FET), whose state-of-the-art fT reported is only 150 GHz at LG = 100 nm (NFmin is inversely proportional to fT). However, this is not the case, as even though a larger fT is achievable in CMOS, results summarized in Schwierz & Schippel (2007) and Barnes et al. (2005) still claimed that NFmin in GaAs-based pHEMT performs similarly or even better than in CMOS. Using simple noise theory, an explanation to this phenomenon is given here, where the fundamental differences between the HF noise performances, in particular the correlation coefficient (C) for CMOS and III-V HEMT (pHEMT) technologies, are explained in detail.

    • Hot-carrier reliability and breakdown characteristics of multi-finger RF MOS transistors

      2009, Microelectronics Reliability
      Citation Excerpt :

      The continuous downsizing of MOS transistor to deep submicron range has enabled the application of MOS device in radio-frequency range and the applications of CMOS devices in radio-frequency (RF) integrated circuit (IC) designs have become increasingly important in recent years because of the rapid advancement of mobile communication technology, system integration considerations, and explosive expending markets [1–6].

    • Microwave electronics

      2017, Microwave Electronics
    • Guest editorial for the special issue on modeling of high-frequency silicon transistors

      2014, International Journal of Numerical Modelling: Electronic Networks, Devices and Fields
    View all citing articles on Scopus
    View full text