Physical origin of colossal dielectric constant in CaCu 3 Ti 4 O 12 thin film by Pulsed Laser Deposition
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1073-H05-04
Physical origin of colossal dielectric constant in CaCu3Ti4O12 thin film by Pulsed Laser Deposition Guochu Deng, Tomoaki Yamada, and Paul Muralt Ceramics Laboratory, Ecole Polytechnique Federale de Lausanne, Station 12, Lausanne, CH1015, Switzerland ABSTRACT The (001) preferentially oriented CCTO thin film was grown on Pt/Ti/TiO2/Si (100) substrate by pulsed laser. I-V and C-V relationships of the CCTO thin film showed characteristics typical of a tunnel metal-insulator-semiconductor (MIS) structure and its capacitance response is the origin of the high apparent dielectric constant observed in CCTO thin films. The very thin insulating layer on top of the film can be reduced in thickness by treatment in HCl acid, as shown by smaller threshold voltages in the I-V curves. The overall behavior is compatible with a conduction activation energy of ~80 to 100 meV in the bulk of the film, and a diffusion potential at the interface of 500 to 800 meV. The acceptor concentration is of the order of 1019cm-3. INTRODUCTION The colossal dielectric constant (CDC) phenomenon in CCTO1-6 has been intensively researched in recent years due its potential applications in the microelectronic industry.3 From the discovery of CDC in CCTO,1 numerous research has been carried out to explore its properties and to probe the origin of the CDC3-5. An intrinsic origin for the CDC mechanism such as a structural phase transition linked to a dramatic change in dielectric constant had been ruled out7, and due to the electrically heterogeneous microstructures commonly observed in CCTO ceramics3, it is widely accepted that the CDC mechanism is extrinsic in origin. Namely, the CDC in CCTO can be attributed to a Maxwell Wagner (MW) mechanism in the material, which normally takes place in a material matrix composed of conductive grains separated by insulating grain boundaries (or other insulating interfaces)3,5. On the basis of the MW model, the measured ultrahigh dielectric constant and the relaxation process in the permittivity as a function of frequency can be easily understood. It should be mentioned, however, that the MW model is only a simplified model of interfacial polarization based on an equivalent circuit, and does not provide a physical explanation for the underlying polarization.8 In CCTO ceramics, the micro mechanisms contributing to the CDC can be the grain boundaries, planar defects (twin boundaries), insulating surface layers, electrode/sample contacts, etc.4,8 Which one causes the intriguing dielectric properties in CCTO is still an open question and indeed, the dominant mechanism may be different for different forms of CCTO samples, eg single crystals, thin films and ceramics. For example, a grain boundary-type mechanism may be primarily responsible for the CDC observed for ceramics, however, this mechanism cannot be responsible for the CDC observed in single crystals9 and epitaxial thin films10,11 where there are no grain boundaries present. The type of electrode contacts can also be a contributing factor5 and this raises t
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