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postgraduate thesis: Amorphous InGaZnO thin-film transistor with La-based high-k gate dielectric

TitleAmorphous InGaZnO thin-film transistor with La-based high-k gate dielectric
Authors
Advisors
Advisor(s):Lai, PT
Issue Date2014
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Qian, L. [钱凌轩]. (2014). Amorphous InGaZnO thin-film transistor with La-based high-k gate dielectric. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5317022
AbstractIn general, La-based high-k gate dielectric owns superior properties to offer transistor excellent characteristics. Thus, amorphous InGaZnO thin-film transistor with La-based high-k gate dielectric has been investigated in this thesis. Different approaches have been adopted to improve the device performance. First of all, the influence of gate-dielectric annealing in oxygen for different times on the device characteristics of the amorphous InGaZnO thin-film transistor with HfLaO gate dielectric has been investigated. It is demonstrated that this annealing treatment can effectively suppress the negative oxide charges. Moreover, it is discovered that this annealing treatment can suppress the acceptor-like border and interface traps. Accordingly, a high saturation carrier mobility of 35.2 〖cm〗^2/V∙s is achieved for the 30’-annealed device. Then, the effects of dielectric-annealing gas (O2, N2 and NH3) for a fixed annealing time of 10 min on the device characteristics are studied, and improvements by the dielectric annealing are observed for each gas. Among the samples, the N2-annealed sample has a high saturation carrier mobility of 35.1 〖cm〗^2/V∙s, the lowest subthreshold swing of 0.206 V/dec and a negligible hysteresis. On the contrary, the O2-annealed sample shows poorer performance due to a decrease of electron concentration in InGaZnO. Furthermore, the NH3-annealed sample displays the lowest threshold voltage (1.95 V) due to increased gate-oxide capacitance and generated positive oxide charges. Next, the effects of fluorine incorporation in amorphous InGaZnO by ion implant on the characteristics of InGaZnO thin-film transistor have been investigated. The electrical characteristics can be improved by this treatment due to increase of carrier concentration and passivation of defects in the InGaZnO film. Consequently, the saturation carrier mobility can be increased to 34.0 〖cm〗^2/V∙s, and the output current can be nearly doubled. However, device degradation is observed for very high fluorine dose above 1.0×1015 /〖cm〗^2. Then, another method for fluorine incorporation has been studied by treating the amorphous InGaZnO film in a CHF3/O2 plasma. The saturation carrier mobility can be improved to as high as 39.8 〖cm〗^2/V∙s. Then, a new high-k material is proposed by investigating the effects of Ta incorporation in the La2O3 gate dielectric of amorphous InGaZnO thin-film transistor. Since the Ta incorporation is found to effectively enhance the moisture resistance of the La2O3 film, both the dielectric roughness and trap density at/near the InGaZnO/dielectric interface can be reduced, resulting in a significant improvement in the electrical characteristics of the device. Nevertheless, excessive incorporation of Ta can degrade the device characteristics due to newly-generated Ta-related traps. Finally, the proposed TaLaO is compared with Ta2O5 as the gate dielectric of amorphous InGaZnO thin-film transistor. It is found that the electrical characteristics of the device can be effectively improved by the incorporation of La in the Ta2O5 gate dielectric, which is ascribed to the fact that La incorporation can enlarge the band gap of Ta oxide and its conduction-band offset with InGaZnO, and also reduce the trap densities in the Ta2O5 gate dielectric and at the InGaZnO/gate-dielectric interface.
DegreeDoctor of Philosophy
SubjectDielectric devices
Thin film transistors
Dept/ProgramElectrical and Electronic Engineering
Persistent Identifierhttp://hdl.handle.net/10722/206467

 

DC FieldValueLanguage
dc.contributor.advisorLai, PT-
dc.contributor.authorQian, Lingxuan-
dc.contributor.author钱凌轩-
dc.date.accessioned2014-10-31T23:15:58Z-
dc.date.available2014-10-31T23:15:58Z-
dc.date.issued2014-
dc.identifier.citationQian, L. [钱凌轩]. (2014). Amorphous InGaZnO thin-film transistor with La-based high-k gate dielectric. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5317022-
dc.identifier.urihttp://hdl.handle.net/10722/206467-
dc.description.abstractIn general, La-based high-k gate dielectric owns superior properties to offer transistor excellent characteristics. Thus, amorphous InGaZnO thin-film transistor with La-based high-k gate dielectric has been investigated in this thesis. Different approaches have been adopted to improve the device performance. First of all, the influence of gate-dielectric annealing in oxygen for different times on the device characteristics of the amorphous InGaZnO thin-film transistor with HfLaO gate dielectric has been investigated. It is demonstrated that this annealing treatment can effectively suppress the negative oxide charges. Moreover, it is discovered that this annealing treatment can suppress the acceptor-like border and interface traps. Accordingly, a high saturation carrier mobility of 35.2 〖cm〗^2/V∙s is achieved for the 30’-annealed device. Then, the effects of dielectric-annealing gas (O2, N2 and NH3) for a fixed annealing time of 10 min on the device characteristics are studied, and improvements by the dielectric annealing are observed for each gas. Among the samples, the N2-annealed sample has a high saturation carrier mobility of 35.1 〖cm〗^2/V∙s, the lowest subthreshold swing of 0.206 V/dec and a negligible hysteresis. On the contrary, the O2-annealed sample shows poorer performance due to a decrease of electron concentration in InGaZnO. Furthermore, the NH3-annealed sample displays the lowest threshold voltage (1.95 V) due to increased gate-oxide capacitance and generated positive oxide charges. Next, the effects of fluorine incorporation in amorphous InGaZnO by ion implant on the characteristics of InGaZnO thin-film transistor have been investigated. The electrical characteristics can be improved by this treatment due to increase of carrier concentration and passivation of defects in the InGaZnO film. Consequently, the saturation carrier mobility can be increased to 34.0 〖cm〗^2/V∙s, and the output current can be nearly doubled. However, device degradation is observed for very high fluorine dose above 1.0×1015 /〖cm〗^2. Then, another method for fluorine incorporation has been studied by treating the amorphous InGaZnO film in a CHF3/O2 plasma. The saturation carrier mobility can be improved to as high as 39.8 〖cm〗^2/V∙s. Then, a new high-k material is proposed by investigating the effects of Ta incorporation in the La2O3 gate dielectric of amorphous InGaZnO thin-film transistor. Since the Ta incorporation is found to effectively enhance the moisture resistance of the La2O3 film, both the dielectric roughness and trap density at/near the InGaZnO/dielectric interface can be reduced, resulting in a significant improvement in the electrical characteristics of the device. Nevertheless, excessive incorporation of Ta can degrade the device characteristics due to newly-generated Ta-related traps. Finally, the proposed TaLaO is compared with Ta2O5 as the gate dielectric of amorphous InGaZnO thin-film transistor. It is found that the electrical characteristics of the device can be effectively improved by the incorporation of La in the Ta2O5 gate dielectric, which is ascribed to the fact that La incorporation can enlarge the band gap of Ta oxide and its conduction-band offset with InGaZnO, and also reduce the trap densities in the Ta2O5 gate dielectric and at the InGaZnO/gate-dielectric interface.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.subject.lcshDielectric devices-
dc.subject.lcshThin film transistors-
dc.titleAmorphous InGaZnO thin-film transistor with La-based high-k gate dielectric-
dc.typePG_Thesis-
dc.identifier.hkulb5317022-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplineElectrical and Electronic Engineering-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.5353/th_b5317022-

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