Journal
IEEE TRANSACTIONS ON ELECTRON DEVICES
Volume 66, Issue 2, Pages 1107-1112Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TED.2018.2888598
Keywords
Charged impurity (CI) scattering; high-k encapsulation; mobility; MoS2 FET; trapped charges
Funding
- National Natural Science Foundation of China [61774064, 61404055]
- Fundamental Research Funds for the Central Universities [2015TS042]
- University Development Fund of the University of Hong Kong [00600009]
- RGC of HKSAR, China [PolyU 252013/14E]
- University Development Fund of the Hong Kong Polytechnic University
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The effects of trapped charges in gate dielectric and high-k encapsulation layer on the performance of MoS2 transistor are investigated by using SiO2 with different thicknesses as the gate dielectric and HfO2 as the encapsulation layer of the MoS2 surface. Results indicate that the positive trapped charges in SiO2 can increase the electrons in MoS2 for screening the scattering of charged impurity (CI) in SiO2 and at the SiO2/MoS2 interface to increase the carrier mobility. However, the CI scattering becomes stronger for thicker gate dielectric with more trapped charges and can dominate the electron screening effect to reduce the mobility. On the other hand, with the HfO2 encapsulation, the OFF-currents of the devices greatly increase and their threshold voltages shift negatively due to more electrons induced by more positive charges trapped in HfO2. Moreover, the screening effect of these electrons on the CI scattering results in a mobility increase, which increases with the magnitude of the CI scattering. A 51% improvement in mobility is obtained for the sample suffering from the strongest CI scattering, fully demonstrating the effective screening role of high-k dielectric on the CI scattering.
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