Effect of PECVD Gate SiO2 Thickness on the Poly-Si/SiO2 Interface in Low-Temperature Polycrystalline Silicon TFTs


This study investigates the effect of the gate SiO2 thickness (80, 100, and 130 nm) deposited by plasma enhanced chemical vapor deposition on the interface and reliability characteristics of low-temperature polycrystalline silicon thin film transistors. Field effect mobility is significantly degraded as the gate oxide thickness decreases. The border trap density (Nbt) extracted from capacitance–voltage hysteresis exhibits no trend with respect to the gate oxide thickness, indicating that field effect mobility is not governed by Nbt. The quantitative interface trap density (Nit) was obtained using a 3-terminal charge pumping method; results showed that Nit decreased as the gate oxide thickness increased. However, it was observed that the threshold voltage (Vth) shift during negative bias temperature stress is worse in the thicker SiO2 film, which has a low Nit. After activation annealing, the amount of hydrogen in the gate oxide increased as the thickness of the insulator was raised. This in turn caused a larger shift in Vth. To validate this mechanism, the amount of hydrogen with respect to the device depth was analyzed via secondary ion mass spectroscopy. It has been found that the presence of more hydrogen concentration in the SiO2 film and the interface to the thicker SiO2 results in more Vth shifts under bias temperature stress.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8


  1. 1.

    Tai Y-H et al (2005) A new pixel circuit for driving organic light-emitting diode with low temperature polycrystalline silicon thin-film transistors. J Disp Technol 1(1):100

    Article  Google Scholar 

  2. 2.

    Lee JH et al (2006) New current-scaling pixel circuit compensating non uniform electrical characteristics for active matrix organic light emitting diode. Jpn J Appl Phys 45(5S):4402

    Article  Google Scholar 

  3. 3.

    Sugimoto A et al (2004) Flexible OLED displays using plastic substrates. IEEE J Sel Top Quantum Electron 10(1):107–114

    Article  Google Scholar 

  4. 4.

    Sposili RS, Im JS (1996) Sequential lateral solidification of thin silicon films on SiO2. Appl Phys Lett 69(19):2864–2866

    Article  Google Scholar 

  5. 5.

    Jin GH, Kim M (2010) Characteristics of excimer laser-annealed thin-film transistors on the polycrystalline silicon morphology formed in the single and double (overlap) scanned area. Jpn J Appl Phys 49(4R):041301

    Article  Google Scholar 

  6. 6.

    Kimura M et al (2001) Device simulation of carrier transport through grain boundaries in lightly doped polysilicon films and dependence on dopant density. Jpn J Appl Phys 40(9R):5237

    Article  Google Scholar 

  7. 7.

    Boogaard A, Kovalgin AY, Wolters R (2011) Negative charge in plasma oxidized SiO2 layers. ECS Trans 35(4):259

    Article  Google Scholar 

  8. 8.

    Kim D-M et al (2004) Dopant-activation and damage-recovery of Ion-shower-doped poly-Si through PH3/H2 after furnace annealing. J Inf Disp 5(1):1–6

    Article  Google Scholar 

  9. 9.

    Ma WCY et al (2011) Oxide thinning and structure scaling down effect of low-temperature poly-Si thin-film transistors. J Disp Technol 8(1):12–17

    Article  Google Scholar 

  10. 10.

    Fortunato G et al (2005) Short channel effects in polysilicon thin film transistors. Thin Solid Films 487(12):221–226

    Article  Google Scholar 

  11. 11.

    Farmakis FV et al (2001) Anomalous turn-on voltage degradation during hot-carrier stress in polycrystalline silicon thin-film transistors. IEEE Electron Dev Lett 22(2):74–76

    Article  Google Scholar 

  12. 12.

    Fleetwood DM, Saks NS (1996) Oxide, interface, and border traps in thermal, N2O, and N2O-nitrided oxides. J Appl Phys 79(3):1583–1594

    Article  Google Scholar 

  13. 13.

    Lin TC, Young DR (1992) New methods for using the Q–V technique to evaluate Si-SiO2 interface states. J Appl Phys 71(8):3889–3893

    Article  Google Scholar 

  14. 14.

    Nicollian EH, Goetzberger A (1967) The Si-SiO, interface–electrical properties as determined by the metal-insulator-silicon conductance technique. Bell Syst Tech J 46(6):1055–1033

    Article  Google Scholar 

  15. 15.

    Nguyen MC et al (2018) Application of single-pulse charge pumping method on evaluation of indium gallium zinc oxide thin-film transistors. IEEE Trans Electron Dev 65(9):3786–3790

    Article  Google Scholar 

  16. 16.

    Jeppson KO, Svensson CM (1977) Negative bias stress of MOS devices at high electric fields and degradation of MNOS devices. J Appl Phys 48(5):2004–2014

    Article  Google Scholar 

Download references


This work was supported by the Industrial Human Resources and Skill Development Program (P0012453, Next-generation Display Expert Training Display Expert Training Project for Innovation Process and Equipment, Materials Engineers) funded by the Ministry of Trade, Industry, and Energy (MOTIE, Korea).

Author information




Conceptualization, methodology, writing—original draft preparation: [Jungmin Park], data curation, investigation: [Pyungho Choi], data curation, investigation: [Soonkon Kim], data curation, investigation: [Bohyeon Jeon], data curation, investigation: [Jongyoon Lee], supervision, writing—review and editing: [Byoungdeog Choi].

Corresponding author

Correspondence to Byoungdeog Choi.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Park, J., Choi, P., Kim, S. et al. Effect of PECVD Gate SiO2 Thickness on the Poly-Si/SiO2 Interface in Low-Temperature Polycrystalline Silicon TFTs. J. Electr. Eng. Technol. (2021). https://doi.org/10.1007/s42835-020-00648-7

Download citation


  • PECVD SiO2
  • Field effect mobility
  • 3-Terminal charge pumping
  • Grain boundary