Space-charge-controlled field emission model of current conduction through Al2O3 films

Atsushi Hiraiwa, Daisuke Matsumura, Hiroshi Kawarada

    Research output: Contribution to journalArticle

    10 Citations (Scopus)

    Abstract

    This study proposes a model for current conduction in metal-insulator-semiconductor (MIS) capacitors, assuming the presence of two sheets of charge in the insulator, and derives analytical formulae of field emission (FE) currents under both negative and positive bias. Since it is affected by the space charge in the insulator, this particular FE differs from the conventional FE and is accordingly named the space-charge-controlled (SCC) FE. The gate insulator of this study was a stack of atomic-layer-deposition Al2O3 and underlying chemical SiO2 formed on Si substrates. The current-voltage (I-V) characteristics simulated using the SCC-FE formulae quantitatively reproduced the experimental results obtained by measuring Au- and Al-gated Al2O3/SiO2 MIS capacitors under both biases. The two sheets of charge in the Al2O3 films were estimated to be positive and located at a depth of greater than 4 nm from the Al2O3/SiO2 interface and less than 2 nm from the gate. The density of the former is approximately 1 × 1013cm-2 in units of electronic charge, regardless of the type of capacitor. The latter forms a sheet of dipoles together with image charges in the gate and hence causes potential jumps of 0.4 V and 1.1 V in the Au- and Al-gated capacitors, respectively. Within a margin of error, this sheet of dipoles is ideally located at the gate/Al2O3 interface and effectively reduces the work function of the gate by the magnitude of the potential jumps mentioned above. These facts indicate that the currents in the Al2O3/SiO2 MIS capacitors are enhanced as compared to those in ideal capacitors and that the currents in the Al-gated capacitors under negative bias (electron emission from the gate) are more markedly enhanced than those in the Au-gated capacitors. The larger number of gate-side dipoles in the Al-gated capacitors is possibly caused by the reaction between the Al and Al2O3, and therefore gate materials that do not react with underlying gate insulators should be chosen in order to achieve a low leakage current by suppressing the current enhancement. Although the current conduction in this study is essentially limited by FE, neither the Fowler-Nordheim (FN) nor Poole-Frenkel (PF) plots of the I-V characteristics are fitted by a linear function. The failures of the FN and PF plot methods alert us to the inaccuracies of basing the investigation of current conduction on these traditional plots. Hence, the methodology of a current conduction analysis and the knowledge of Al2O3 charging in this study provide a solid foundation for investigating the current conduction in MIS capacitors.

    Original languageEnglish
    Article number064505
    JournalJournal of Applied Physics
    Volume119
    Issue number6
    DOIs
    Publication statusPublished - 2016 Feb 14

    Fingerprint

    space charge
    field emission
    capacitors
    conduction
    MIS (semiconductors)
    insulators
    plots
    dipoles
    atomic layer epitaxy
    electron emission
    charging
    margins
    leakage
    methodology
    augmentation
    causes
    electric potential
    electronics

    ASJC Scopus subject areas

    • Physics and Astronomy(all)

    Cite this

    Space-charge-controlled field emission model of current conduction through Al2O3 films. / Hiraiwa, Atsushi; Matsumura, Daisuke; Kawarada, Hiroshi.

    In: Journal of Applied Physics, Vol. 119, No. 6, 064505, 14.02.2016.

    Research output: Contribution to journalArticle

    @article{1106b9e223bf4d998c6552e2d3a54d32,
    title = "Space-charge-controlled field emission model of current conduction through Al2O3 films",
    abstract = "This study proposes a model for current conduction in metal-insulator-semiconductor (MIS) capacitors, assuming the presence of two sheets of charge in the insulator, and derives analytical formulae of field emission (FE) currents under both negative and positive bias. Since it is affected by the space charge in the insulator, this particular FE differs from the conventional FE and is accordingly named the space-charge-controlled (SCC) FE. The gate insulator of this study was a stack of atomic-layer-deposition Al2O3 and underlying chemical SiO2 formed on Si substrates. The current-voltage (I-V) characteristics simulated using the SCC-FE formulae quantitatively reproduced the experimental results obtained by measuring Au- and Al-gated Al2O3/SiO2 MIS capacitors under both biases. The two sheets of charge in the Al2O3 films were estimated to be positive and located at a depth of greater than 4 nm from the Al2O3/SiO2 interface and less than 2 nm from the gate. The density of the former is approximately 1 × 1013cm-2 in units of electronic charge, regardless of the type of capacitor. The latter forms a sheet of dipoles together with image charges in the gate and hence causes potential jumps of 0.4 V and 1.1 V in the Au- and Al-gated capacitors, respectively. Within a margin of error, this sheet of dipoles is ideally located at the gate/Al2O3 interface and effectively reduces the work function of the gate by the magnitude of the potential jumps mentioned above. These facts indicate that the currents in the Al2O3/SiO2 MIS capacitors are enhanced as compared to those in ideal capacitors and that the currents in the Al-gated capacitors under negative bias (electron emission from the gate) are more markedly enhanced than those in the Au-gated capacitors. The larger number of gate-side dipoles in the Al-gated capacitors is possibly caused by the reaction between the Al and Al2O3, and therefore gate materials that do not react with underlying gate insulators should be chosen in order to achieve a low leakage current by suppressing the current enhancement. Although the current conduction in this study is essentially limited by FE, neither the Fowler-Nordheim (FN) nor Poole-Frenkel (PF) plots of the I-V characteristics are fitted by a linear function. The failures of the FN and PF plot methods alert us to the inaccuracies of basing the investigation of current conduction on these traditional plots. Hence, the methodology of a current conduction analysis and the knowledge of Al2O3 charging in this study provide a solid foundation for investigating the current conduction in MIS capacitors.",
    author = "Atsushi Hiraiwa and Daisuke Matsumura and Hiroshi Kawarada",
    year = "2016",
    month = "2",
    day = "14",
    doi = "10.1063/1.4941547",
    language = "English",
    volume = "119",
    journal = "Journal of Applied Physics",
    issn = "0021-8979",
    publisher = "American Institute of Physics Publising LLC",
    number = "6",

    }

    TY - JOUR

    T1 - Space-charge-controlled field emission model of current conduction through Al2O3 films

    AU - Hiraiwa, Atsushi

    AU - Matsumura, Daisuke

    AU - Kawarada, Hiroshi

    PY - 2016/2/14

    Y1 - 2016/2/14

    N2 - This study proposes a model for current conduction in metal-insulator-semiconductor (MIS) capacitors, assuming the presence of two sheets of charge in the insulator, and derives analytical formulae of field emission (FE) currents under both negative and positive bias. Since it is affected by the space charge in the insulator, this particular FE differs from the conventional FE and is accordingly named the space-charge-controlled (SCC) FE. The gate insulator of this study was a stack of atomic-layer-deposition Al2O3 and underlying chemical SiO2 formed on Si substrates. The current-voltage (I-V) characteristics simulated using the SCC-FE formulae quantitatively reproduced the experimental results obtained by measuring Au- and Al-gated Al2O3/SiO2 MIS capacitors under both biases. The two sheets of charge in the Al2O3 films were estimated to be positive and located at a depth of greater than 4 nm from the Al2O3/SiO2 interface and less than 2 nm from the gate. The density of the former is approximately 1 × 1013cm-2 in units of electronic charge, regardless of the type of capacitor. The latter forms a sheet of dipoles together with image charges in the gate and hence causes potential jumps of 0.4 V and 1.1 V in the Au- and Al-gated capacitors, respectively. Within a margin of error, this sheet of dipoles is ideally located at the gate/Al2O3 interface and effectively reduces the work function of the gate by the magnitude of the potential jumps mentioned above. These facts indicate that the currents in the Al2O3/SiO2 MIS capacitors are enhanced as compared to those in ideal capacitors and that the currents in the Al-gated capacitors under negative bias (electron emission from the gate) are more markedly enhanced than those in the Au-gated capacitors. The larger number of gate-side dipoles in the Al-gated capacitors is possibly caused by the reaction between the Al and Al2O3, and therefore gate materials that do not react with underlying gate insulators should be chosen in order to achieve a low leakage current by suppressing the current enhancement. Although the current conduction in this study is essentially limited by FE, neither the Fowler-Nordheim (FN) nor Poole-Frenkel (PF) plots of the I-V characteristics are fitted by a linear function. The failures of the FN and PF plot methods alert us to the inaccuracies of basing the investigation of current conduction on these traditional plots. Hence, the methodology of a current conduction analysis and the knowledge of Al2O3 charging in this study provide a solid foundation for investigating the current conduction in MIS capacitors.

    AB - This study proposes a model for current conduction in metal-insulator-semiconductor (MIS) capacitors, assuming the presence of two sheets of charge in the insulator, and derives analytical formulae of field emission (FE) currents under both negative and positive bias. Since it is affected by the space charge in the insulator, this particular FE differs from the conventional FE and is accordingly named the space-charge-controlled (SCC) FE. The gate insulator of this study was a stack of atomic-layer-deposition Al2O3 and underlying chemical SiO2 formed on Si substrates. The current-voltage (I-V) characteristics simulated using the SCC-FE formulae quantitatively reproduced the experimental results obtained by measuring Au- and Al-gated Al2O3/SiO2 MIS capacitors under both biases. The two sheets of charge in the Al2O3 films were estimated to be positive and located at a depth of greater than 4 nm from the Al2O3/SiO2 interface and less than 2 nm from the gate. The density of the former is approximately 1 × 1013cm-2 in units of electronic charge, regardless of the type of capacitor. The latter forms a sheet of dipoles together with image charges in the gate and hence causes potential jumps of 0.4 V and 1.1 V in the Au- and Al-gated capacitors, respectively. Within a margin of error, this sheet of dipoles is ideally located at the gate/Al2O3 interface and effectively reduces the work function of the gate by the magnitude of the potential jumps mentioned above. These facts indicate that the currents in the Al2O3/SiO2 MIS capacitors are enhanced as compared to those in ideal capacitors and that the currents in the Al-gated capacitors under negative bias (electron emission from the gate) are more markedly enhanced than those in the Au-gated capacitors. The larger number of gate-side dipoles in the Al-gated capacitors is possibly caused by the reaction between the Al and Al2O3, and therefore gate materials that do not react with underlying gate insulators should be chosen in order to achieve a low leakage current by suppressing the current enhancement. Although the current conduction in this study is essentially limited by FE, neither the Fowler-Nordheim (FN) nor Poole-Frenkel (PF) plots of the I-V characteristics are fitted by a linear function. The failures of the FN and PF plot methods alert us to the inaccuracies of basing the investigation of current conduction on these traditional plots. Hence, the methodology of a current conduction analysis and the knowledge of Al2O3 charging in this study provide a solid foundation for investigating the current conduction in MIS capacitors.

    UR - http://www.scopus.com/inward/record.url?scp=84958818862&partnerID=8YFLogxK

    UR - http://www.scopus.com/inward/citedby.url?scp=84958818862&partnerID=8YFLogxK

    U2 - 10.1063/1.4941547

    DO - 10.1063/1.4941547

    M3 - Article

    AN - SCOPUS:84958818862

    VL - 119

    JO - Journal of Applied Physics

    JF - Journal of Applied Physics

    SN - 0021-8979

    IS - 6

    M1 - 064505

    ER -