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Информатика Искусствоведение История Культурология Медицина Педагогика Политология Право Психология Религиоведение Социология Техника Филология Философия Экология Экономика
A. V. Kharkavyy, undergraduate,
K. T. Ashurova, undergraduate,
Tomsk state university of control systems and radioelectronics,
Porous dielectric thin films of silicon dioxide have become widely used as a base for creating gas detectors. The main advantage of sensors based on porous silicon dioxide is low power usage compared with gas detectors based on metal oxides. Moreover, it can be used in optoelectronics, biology, and medicine as material for sensors for diagnostics and treatment of diseases and drugs screening because of specific optical and electrical properties. Isolation layers made of porous silicon dioxide allow decreasing permittivity and signals’ passing time in a microcircuit .
During the formation of metal-insulator-metal (M-I-M) structure, silicon dioxide in different modifications took the role of an insulator. By using thermal evaporation, aluminum electrodes with a thickness of 100 nm were formed. Silicon dioxide (SiO2) layer was made by sputter deposition of a silicon target in the environment of oxygen (operating pressure (4-6)·10-3 Torr, discharge current 200 mA, accelerating potential difference 400 V). The film of modified silicon dioxide (SiO2М) was formed by sputter deposition of composite target silicon-carbon (Si+C) with materials’ ratio 70/30 in an oxygen environment under the same conditions. In order to get a holistic layer of both insulators the thickness 100 nm was chosen .
During the experiment, it was found that average capacity decreased by 23 % which might be related to the presence of a low permittivity gas phase in the SiO2М film. Consequently, it could be suggested that there is a porous structure in the SiO2М film. The loss tangent reduction by a half is the evidence of this. As the loss tangent is the ratio of active to reactive current parts, it means the decrease of the active current part leading the increasing of film resistance. The high electrical resistance of modified silicon dioxide film is due to catching charge carriers on the border of pores .
A number of pores in the structure can be defined by using capacitive porometry method :
The parameter showing porosity of the film is 0,296, that is why pore volume fraction in SiO2М structure is approximately 30 %.
The results obtained during the investigation of M-I-M structures with different modifications were statistically processed (table 1).
Statistical analysis results
In order to make sure that distribution matches to the normal distribution was used Pearson's chi-squared test (Table 2).
Pearson's chi-squared test
Critical value of χ2
From the data shown in Table 2 follows that distribution of capacities of both films is near to normal distribution, which means the results are relevant and reproducible. It’s clearly seen from Table 1 that the difference between a sample and general variances is lower than 5% which makes possible the mass-production of the structures with the given parameters.
By modification of a silicon dioxide film with carbon, its structure becomes porous. Thus, the research results represent that the silicon dioxide films modified by carbon can be used as gas detectors.
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