MOSFET RF Characterization Using Bulk and SOI CMOS ...lib.tkk.fi/Diss/2007/isbn9789513870256/ RF, CMOS, modeling, MOSFET, measurement uncertainty ... design group as well as my present

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  • VTT PU

    BLICATIO

    NS 644

    MO

    SFET RF Characterization Using Bulk and SO

    I CMO

    S TechnologiesJan Saijets

    ESPOO 2007 VTT PUBLICATIONS 644

    Jan Saijets

    MOSFET RF Characterization UsingBulk and SOI CMOS Technologies

    This work deals with CMOS transistor characterization at radio-frequencies(RF). An accurate transistor model is the basis for circuit simulation anddesign. Previously MOS transistor models have been less accurate at RF andhave prevented the use of cheap CMOS circuitry in the radio parts of mobileterminals. In recent years a lot of research has been made to correct thisproblem. This thesis work has produced new knowledge and scientific resultsin the following areas: 1) RF measurement uncertainty effect on the transistorcharacterization; 2) the input impedance accuracy of MOS models comparedto experimental results; 3) the benefit of different modifications to the basicdigital CMOS model equivalent circuit. The equivalent circuit modificationsincludes different approaches to describe MOSFET bulk resistance network,absorption of the series resistances into the current description as well as twoapproaches of describing the distributed nature of gate polysilicon behavior.Both SOI CMOS and bulk CMOS technologies have been used in this work.

    ISBN 978-951-38-7024-9 (soft back ed.) ISBN 978-951-38-7025-6 (URL: http://www.vtt.fi/publications/index.jsp)ISSN 1235-0621 (soft back ed.) ISSN 1455-0849 (URL: http://www.vtt.fi/publications/index.jsp)

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  • VTT PUBLICATIONS 644

    MOSFET RF CharacterizationUsing Bulk and SOI CMOS

    Technologies

    Jan Saijets

    Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical Communications Engineering for public examination and debate in Auditorium S4 at the Helsinki University of

    Technology (Espoo, Finland) on the 18th of June, 2007, at 12 o'clock noon.

  • ISBN 978-951-38-7024-9 (soft back ed.) ISSN 1235-0621 (soft back ed.)

    ISBN 978-951-38-7025-6 (URL: http://www.vtt.fi/publications/index.jsp) ISSN 1455-0849 (URL: http://www.vtt.fi/publications/index.jsp)

    Copyright VTT Technical Research Centre of Finland 2007

    JULKAISIJA UTGIVARE PUBLISHER

    VTT, Vuorimiehentie 3, PL 1000, 02044 VTT

    puh. vaihde 020 722 111, faksi 020 722 4374

    VTT, Bergsmansvgen 3, PB 1000, 02044 VTT

    tel. vxel 020 722 111, fax 020 722 4374

    VTT Technical Research Centre of Finland, Vuorimiehentie 3, P.O. Box 1000, FI-02044 VTT, Finland

    phone. +358 20 722 111, fax + 358 20 722 4374

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    VTT Technical Research Centre of Finland, Tietotie 3, P.O. Box 1000, FI-02044 VTT, Finland

    phone internat. +358 20 722 111, fax +358 20 722 7012

    Technical editing Leena Ukskoski

    Edita Prima Oy, Helsinki 2007

    http://www.vtt.fi/publications/index.jsphttp://www.vtt.fi/publications/index.jsp

  • 3

    Saijets, Jan. MOSFET RF Characterization Using Bulk and SOI CMOS Technologies

    [MOSFETien radiotaajuuskarakterisointi bulk- ja SOI MOS -teknologioita kytten]. Espoo 2007.

    VTT Publications 644. 171 p. + app. 4 p.

    Keywords RF, CMOS, modeling, MOSFET, measurement uncertainty

    Abstract

    MOSFET radio-frequency characterization and modeling is studied, both with

    SOI CMOS and bulk CMOS technologies. The network analyzer measurement

    uncertainties are studied, as is their effect on the small signal parameter

    extraction of MOS devices. These results can be used as guidelines for designing

    MOS RF characterization layouts with as small an AC extraction error as

    possible. The results can also be used in RF model extraction as criteria for

    required optimization accuracy.

    Modifications to the digital CMOS model equivalent circuit are studied to

    achieve better RF behavior for the MOS model. The benefit of absorbing the

    drain and source parasitic series resistances into the current description is

    evaluated. It seems that correct high-frequency behavior is not possible to

    describe using this technique. The series resistances need to be defined

    extrinsically. Different bulk network alternatives were evaluated using scalable

    device models up to 10 GHz. Accurate output impedance behavior of the model

    requires a bulk resistance network. It seems that good accuracy improvement is

    achieved with just a single bulk resistor. Additional improvement is achieved by

    increasing the number of resistors to three. At this used frequency range no

    further accuracy improvement was achieved by increasing the resistor amount

    over three. Two modeling approaches describing the distributed gate behavior

    are also studied with different MOS transistor layouts. Both approaches

    improve the RF characteristics to some extent but with limited device geometry.

    Both distributed gate models describe well the high frequency device behavior

    of devices not commonly used at radio frequencies.

  • 4

    Saijets, Jan. MOSFET RF Characterization Using Bulk and SOI CMOS Technologies

    [MOSFETien radiotaajuuskarakterisointi bulk- ja SOI MOS -teknologioita kytten]. Espoo 2007.

    VTT Publications 644. 171 s. + liitt. 4 s.

    Avainsanat RF, CMOS, modeling, MOSFET, measurement uncertainty

    Tiivistelm

    MOSFETin radiotaajuuskarakterisointia ja mallitusta tarkastellaan sek SOI

    CMOS ett bulk CMOS -teknologioilla. Piirianalysaattorien mittaus-

    epvarmuutta tarkastellaan ja niiden vaikutusta MOS-transistorin piensignaali-

    parametrien ekstraktointiin. Nit tuloksia voidaan kytt ohjenuorana RF

    MOS -karakterisointiin kytettvien piirikuvioiden suunnittelussa, kun halutaan

    AC-ekstraktoinnin virhe mahdollisimman pieneksi. Tuloksia voidaan kytt

    mys RF-mallin ekstraktoinnissa halutun optimointitarkkuuden kriteerin.

    Digitaalisen CMOS-mallin vastinpiirimuunnelmia on tarkasteltu tarkoituksena

    saada MOS-mallille paremmat radiotaajuusominaisuudet. Kanavan kanssa

    sarjassa olevien parasiittisten vastusten vaikutusta on tarkasteltu, kun ne ovat

    joko erillisin tai suoraan virtayhtln sisllytettyin. Jlkimmisen tavan

    hyty on arvioitu. Nytt silt, ett oikeanlaatuisen suurtaajuuskyttytymisen

    kuvaaminen ei onnistu tll tekniikalla. Kanavan kanssa sarjassa olevat vastuk-

    set on mriteltv ulkoisiksi. Erilaisia substraattivastinpiirien vaihtoehtoja on

    arvioitu kytten skaalautuvia transistorimalleja 10 GHz:n taajuuteen asti.

    Tarkan ulostuloimpedanssin kuvaaminen edellytt transistorille substraatti-

    vastinpiiri. Nytt silt, ett merkittvn mallin tarkkuuden parantumiseen

    riitt yksi ainoa substraattivastus. Tarkkuus paranee tstkin listtess

    vastusten mr kolmeen. Kytetyll taajuusvlill ei saavutettu mallin

    tarkkuuden lisparannusta, kun yritettiin nostaa substraattiverkon vastusten

    mr yli kolmen. Erilaisilla MOS-transistorin piirikuvioilla tarkasteltiin mys

    kahta mallitustapaa, joilla voidaan kuvata jakautuneen hilan kyttytymist.

    Kummatkin lhestymistavat parantavat mallin radiotaajuusominaisuuksia

    johonkin rajaan asti, mutta vain tietyill transistorigeometrioilla. Molemmat

    jakautuneen hilan mallit kuvaavat hyvin sellaisten transistoreiden suurtaajuus-

    ominaisuuksia, joita ei yleens kytet radiotaajuuksilla.

  • Preface

    This work has been carried out in 19972004 at VTT, Technical ResearchCenter of Finland, in INWITE and SOIKARA projects funded by VTT, Tekes,Nokia Research Center, Okmetic, Micorans and VLSI Solutions. This workwould have been much harder without the help and support of my previous IC-design group as well as my present group. I would like to thank my supervisorand former group leader Prof. Markku berg for his guidance and support in mywork. His broad insight in electronics was crucial especially at the beginning ofthis work and helped along the later times as well. I am also grateful for all myother coworkers at VTT for providing me with an inspiring work environment,politeness days and other strange ideas not related to work at all.

    With the help of Dr. Mikael Andersson from Nokia Research Center I gotfamiliar with the challenging MOSFET modeling subject. The extraction toolsprogrammed by him were the basis of this work and examining these programstaught me to develop my own extraction tools. Im very grateful for his help,instructions and support. His comments on an early manuscript version of thisthesis were invaluable.

    I would like to thank Prof. Veikko Porra from TKK, Helsinki University ofTechnology, for improving my scientific approach in this thesis by commentingon an early manuscript version. I would like to thank Prof. Daniel Foty fromGilgamesh Associates for many fruitful discussions on commercial MOSFETmodels and their shortcomings. Im very grateful to Prof. Pekka Kuivalainenfrom TKK for his aid in improving one of my best papers.

    I thank Prof. Timo Rahkonen from Oulu University and Prof. Tor A. Fjeldlyfrom NTNU for carefully pre-examining the manuscript. I never expected theywould go through my equatio