Dielectric relaxation and frequency dependence of Hf02 doped by lanthanide elements

Zhao, Chun
Dielectric relaxation and frequency dependence of Hf02 doped by lanthanide elements. Doctor of Philosophy thesis, University of Liverpool.

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The decreasing sizes in complementary metal oxide semiconductor (CMOS) transistor technology requires the replacement of SiO2 with gate dielectrics that have a high dielectric constant (k). When the SiO2 gate thickness was reduced below 1.4 nm, electron tunneling effects and high leakage currents occurred which presented serious obstacles for the reliability issue in terms of metal-oxide-semiconductor field-effect transistor (MOSFET) devices. In recent years, various alternative gate dielectrics have been researched. Following the introduction of HfO2 into the 45 nm process by Intel in 2007, the screening and selection of high-k gate stacks, understanding their properties, and their integration into CMOS technology has been a very active research area. Frequency dispersion of high-k dielectrics was commonly observed and classified into two parts: extrinsic and intrinsic causes. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such as the effects of the lossy interfacial layer (between the high-k thin film and silicon substrate) and the parasitic effects. The significance of parasitic effects (including series resistance and the back metal contact of the metal-oxide-semiconductor (MOS) capacitor) on frequency dispersion was studied. The effect of the lossy interfacial layer on frequency dispersion was investigated and modeled using a dual frequency technique. The effect of surface roughness on frequency dispersion is also investigated. Several mathematical models were discussed to describe the dielectric relaxation of high-k dielectrics. Some of the relaxation behavior can be modeled using the Curie-von Schweidler (CS) law, the Kohlrausch-Williams-Watts (KWW) relationship and the Havriliak-Negami (HN) relationship. Other relaxation models were also introduced. For the physical mechanism, dielectric relaxation was found to be related to the degree of polarization, which was dependent on the structure of the high-k material. The degree of polarization was attributed to the enhancement of the correlations among polar nano-scale size domain within the materials. The effect of grain size for the high-k materials' structure mainly originated from higher surface stress in smaller grain size due to its higher concentration of grain boundary.

Item Type: Thesis (Doctor of Philosophy)
Additional Information: Date: 2014-04 (completed)
Subjects: ?? TK ??
Divisions: Faculty of Science and Engineering > School of Electrical Engineering, Electronics and Computer Science
Depositing User: Symplectic Admin
Date Deposited: 05 Aug 2014 09:56
Last Modified: 17 Dec 2022 00:51
DOI: 10.17638/00017673
  • Zhao, Cezhou
URI: https://livrepository.liverpool.ac.uk/id/eprint/17673