SiO 2 /Ge nanocrystal/SiO2 structures have been fabricated by deposition of Ge film on a SiO2 layer and subsequent oxidation of the structure at a temperature between 800 °C and 1000 °C. Secondary ion mass spectrometry results indicate that the Ge precipitates into the bulk SiO2 at a density of 1×1012 cm−2. Raman spectra show a sharp peak at 300 cm−1 for the nanocrystallized Ge. The nanocrystal diameter is determined to be 5 nm on average. In the metal–insulator–silicon structure, electron storage occurs in the SiO2/Ge/SiO2 potential well via electron tunneling into the oxide film. Capacitance-voltage measurements indicate that flatband voltage (VFB) shifts to 0.91 V after the electron injection. The VFB shift is attributed to the charge storing for a single electron per potential well.
Titanium oxide (TiO 2 ) thin films were formed on a Si substrate by metalorganic decomposition at temperatures ranging from 600 • C to 1000 • C. As-deposited films were in the amorphous state and were completely transformed after annealing at 600 • C to a crystalline structure with anatase as its main component. During crystallization in oxygen atomosphere, a reaction between TiO 2 and Si occurred at the interface, which resulted in the formation of a thin interfacial SiO 2 layer. Capacitance-voltage measurement showed good dielectric properties with a maximum dielectric constant of 76 for films annealed at 700 • C. For the crystallized TiO 2 films, the interface trap density was 1 × 10 11 cm −2 eV −1 , and the leakage current was 1 × 10 −8 A/cm 2 at 0.2 MV/cm. The modified structure of TiO 2 /SiO 2 /Si is expected to be suitable for the dielectric layer in an integrated circuit in place of SiO 2 or Si 3 N 4 films.
Crystalline CeO2 films were formed on a Si (100) substrate by metalorganic decomposition at
temparatures ranging from 600°C to 800°C. As-deposited films were in the amorphous state
and were completely transformed to crystalline CeO2 above 600°C. However, during
crystallization in oxygen atomosphere, a reaction between CeO2 and Si occurred at the interface,
which resulted in the formation of a thin interfacial SiO2 layer. Capacitance-voltage
measurement on these films showed good dielectric properties with a dielectric constant of 15,
which is more than three times higher than that of SiO2. The modified structure of
CeO2/SiO2/Si is expected to be suitable for the dielectric layer in an integrated circuit, in place
of conventional dielectric films such as those of SiO2 or Si3N4.
Ta 2 O 5 -based composite thin films formed by metalorganic decomposition have been investigated with respect to their dielectric properties. The dielectric and insulating properties of composite (1−x)Ta2O5−xTiO2 and (1−x)Ta2O5−xWO3 thin films are found to be improved compared to those of pure Ta2O5 thin films. In particular, thin films with x=0.08 composition of additive TiO2 or WO3 to Ta2O5 exhibited superior dielectric and insulating properties. The maximum dielectric constant and charge storage density of composite films are about 20 and 53.6 fC/μm2, respectively, higher than those of pure Ta2O5 films (about 13 and 34.5 fC/μm2). The temperature coefficient of the dielectric constant of composite films dramatically decreases from 65 ppm/°C for pure Ta2O5 to less than 11 ppm/°C. The leakage current density of composite films is lower than 1×10−9 A/cm2 up to an applied electric field of 3 MV/cm. The dominant conduction is Poole–Frenkel conduction in the films according to the measurement temperature dependence of the I−V characteristics.
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