Impedace spectroscopy

|R. Domínguez Domínguez, J.Guzmán Medoza, M.A. Aguilar Frutis. |
|Centro de Investigación en Ciencia Aplicada y Tecnología Avanzada, Instituto Politécnico Nacional, Legaria # 694, Miguel Hidalgo 11500,México D.F, |
|México.|
| |
[Asbtract]
Structural, morphology and composition properties of Hafnium Oxide (HfO2) films are reported. The films were prepared by spray pyrolysis deposition process,using chlorides as raw materials in deionised water as solvent. Corning glass was used as substrates at temperatures from 300°C to 600°C. X ray analysis shows an amorphous structure at low temperatures, while substrate temperatures higher than 400°C monoclinic phase of HfO2 appear. This result is confirmed by TEM. Scanning electron microscopy was use to observe the microstructure of the films; roughsurface with spherical particles are appreciated. The chemical composition was obtained by Energy Dispersive Spectroscopy (EDS), a rate Hf / O close to ideal (0.5) was obtained.

[Introduction]
Hafnium dioxide HfO2 films are widely used in optical coatings [1, 2], in gas sensors [3], and in tunnel junctions [4] for magnetic field sensors and magnetic random access memories and luminescentcoatings [5]. In the last few years, Hafnium oxide has been under intense investigation recently for remplacing conventional SiO2 in complementary metal oxide semiconductor (CMOS) devices. The requirements for these materials are: reduce tunneling current and borron penetration, high dielectric constant (k) value, chemical stability at high temperatures, large band gap and structural homogeneity.Even though many high-k materials are currently being studied, poor short channel effects due to the finging field induced barried lowering effect [6] and the thermal instability due to the formation of silicides or interfacial layers impede the effectiveness of these materials when directly in contact with silicon [7]. An HfO2 films has a high dielectric constant (~25), high heat offormation (271 kcal/mol), and a large bad gap (5.68 eV) [8, 9], and is thermally stable.
Various methods, such atomic layer deposition [10], evaporation whit ion-assisted [11], sputtering [12], in situ rapid thermal chemical vapor deposition [13], reactive electron bean evaporation [14] and spray pyrolysis technique [5] have been explored to deposit reliable and high-quality HfO2 films. Theproperties of the grow films show pronounced dependence upon the deposition process and the precise deposition parameters chosen each technique has its own set of advantages and disadvantages. The pyrosol (ultrasonic spray pyrolysis) process has proved to be very efficient to synthesize films [5]. This technique has advantages such as: low cost, a high deposition rate, ease of operation and capacity todeposit layers on big areas. HfO2 films can be synthesized using a wide range of precursor: chlorides [15], nitrates [16], alkoxides [17] and amino complexs [18].

[Experimental details]
Hafnium chloride (HfCl4) in deionized water with molar of 0.05 M was used as source of the precursor solution for HfO2 films. Cornning glass and SnO2 coated glass were used as substrates with dimensions of1.0x1.0 cm2. The substrates were cleaned first by extran solution whit ultrasonically cleaned to remove the dust and then they were ultrasonically cleaned in methanol, ethanol for at least 15 min. Finally they were soaked in distilled water and dried with nitrogen N2. The carrier gas flow (air) was 10 liter/min. The deposition temperatures for HfO2 films were taken in the range 300-600°C. The...