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III-Nitride Transistors for High Linearity RF Applications

Sohel, Md Shahadat Hasan
http://orcid.org/0000-0001-9389-6982
http://rave.ohiolink.edu/etdc/view?acc_num=osu1599819098404026

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
This dissertation investigates new approaches to improve the linearity performance of III-Nitride high-frequency transistors. Next-generation communication technologies require significantly better linearity performance from power amplifiers, and new design approaches are necessary to achieve higher power amplifier linearity at high frequency. Currently, AlGaN/GaN high electron mobility transistor (HEMT) based power amplifiers are preferred choice for high power high frequency applications. However, they suffer from gain suppression resulting from non-linear transconductance characteristics. Transconductance (gm) drop-off at high currents is one of the major sources of non-linearity in HEMTs. A three-dimensional electron channel from compositional grading of the AlGaN is found to create a constant transconductance profile by enabling constant sheet charge density and saturation velocity of carriers in the channel over a wide range of gate bias conditions. Composite channels that combine 2-dimensional (2D) and 3-dimensional (3D) electron channels could also enable improved linearity performance. Large signal simulations to predict the power and linearity performance of transistors for arbitrary epitaxial design transistors were developed. The large signal simulations show significantly improved linearity performance in polarization-graded field effect transistors (PolFETs) and composite 2D-3D channel transistors when compared with conventional AlGaN/GaN HEMTs. Graded channel transistors were found to be limited by DC-RF dispersion resulting from poor surface passivation. To improve the DC-RF dispersion, low-pressure chemical vapor deposition (LPCVD)-based SiNx passivation was used, leading to significant improvement in the dispersion characteristics, and excellent linearity figure ore merit (OIP3/PDC) of 13.3 dB. In addition to dielectric passivation, to address the surface dispersion, epitaxial passivation of cap layers was also investigated, leading to nearly dispersion-free behavior for the graded channel transistors. As an alternative approach to achieve high linearity performance, III-Nitride bipolar junction transistors were investigated. A new device design is proposed based on a laterally patterned base that enables variable injection of current from emitter to the base in order to improve the base conductivity without sacrificing the injection efficiency. With this new technique, a high emitter current density of 55 kA/cm2 was achieved in an npn GaN bipolar transistor. The results presented in this thesis demonstrate an excellent potential for III-Nitride transistor as high linearity transistors required for next generation communication.
Siddharth Rajan (Advisor)
121 p.
Electrical Engineering
Power amplifier linearity; Graded AlGaN channel transistor; Passivation for AlGaN channel transistor; Nitride Heterojunction Bipolar Transistor

Recommended Citations

Citations

  • Sohel, M. S. H. (2020). III-Nitride Transistors for High Linearity RF Applications [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1599819098404026

    APA Style (7th edition)

  • Sohel, Md Shahadat Hasan. III-Nitride Transistors for High Linearity RF Applications . 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1599819098404026.

    MLA Style (8th edition)

  • Sohel, Md Shahadat Hasan. "III-Nitride Transistors for High Linearity RF Applications ." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1599819098404026

    Chicago Manual of Style (17th edition)

osu1599819098404026
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This open access ETD is published by The Ohio State University and OhioLINK.