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Proceeding Paper

SnO2-Pd as a Gate Material for the Capacitor Type Gas Sensor †

National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Kashirskoe higway 31, Moscow 115409, Russia
*
Author to whom correspondence should be addressed.
Presented at the 8th GOSPEL Workshop. Gas Sensors Based on Semiconducting Metal Oxides: Basic Understanding & Application Fields, Ferrara, Italy, 20–21 June 2019.
Proceedings 2019, 14(1), 10; https://doi.org/10.3390/proceedings2019014010
Published: 19 June 2019

Abstract

:
The article describes the result of the use SnO2-Pd thin films as a gate for structure measured ppb range of NO2 gas by the capacitive method. The technological aspects of fabrication SnO2-Pd gate and one comparison by metrological parameters with the classical Pd gate field effect sensor are discussed. The use of SnO2-Pd material allows improvement in sensitivity of NO2 by an order of magnitude compare the classical Pd based gate field effect sensors.

1. Introduction

Using of SnO2 material for fabrication field effect gas sensors based on Schottky diode effect firstly describing in work [1], somewhat later, a study of the sensitivity of field-effect sensors to NO2 began [2]. But still remains an important issue measurement of sub-ppb concentrations of NO2 in such areas as medicine, environmental control and explosives detection. Materials based on SnO2 are widely used to measure NO2 by resistive type MOX sensors, but MOX sensors margin of stable sensitivity is limited by sub-ppm range. The further increase in sensitivity to NO2 is possible in the technological combination of well proven material using nowadays in MOX sensors and high sensitivity of field-effect sensors.

2. Experimental

In [3] was shown that the characteristics of field-effect sensors strongly depend on the composition metal-dielectric transition layer, which is determined by the materials of metal gate and insulator dielectric and methods of their deposition. For a new capacity type sensor manufacturing n-type silicon substrate with a 0.1 μm SiO2 layer thickness was used. Layer of SnO2 is additionally deposited through the shadow mask on the SiO2 film by the method of magnetron sputtering. This method of deposition allows you to form films with a high effective surface area. The Pd film with a thickness of 100 nm was coated SnO2 film through the shadow mask by pulse laser deposition method. The Pd-SnO2-SiO2-Si structure was basis of capacitor type gas sensor which photo present on Figure 1 and cross-section scheme of structure on Figure 2, respectively. In parallel with the SnO2-Pd based sensor, a similar series of capacity sensors without SnO2 layer, only with a 100 nm Pd gate, was made for comparing changes of gas-sensitive characteristics.
Figure 3 presents the capacitance-voltage characteristic for Pd gate sensor at different heating temperatures. The capacitance-voltage characteristics for SnO2-Pd and Pd base sensors at temperatures of 170 °C, 140 °C and 100 °C was study and present in Figure 4. Also sensitivity to NO2 at different temperatures present on Figure 5 and Figure 6. On Figure 4 and Figure 5 can be seen that the slope of the characteristic decreases with increasing temperature, therefore, the sensitivity of the sensor should decrease; this effect is explained by the shift of C-V characteristic during exposed to gas. The Figure 5 shows the time responding capacity sensor with SnO2-Pd gate to 108 ppb NO2 at different temperature and possible to see decreasing response time and sensitivity during increasing working temperature of sensor. This behavior is standard for the field effect sensor.
The using of the new type SnO2-Pd gate in capacity type sensor gives possible to raise sensitivity by almost ten times but disadvantage for such approach is increasing response and relaxation times of the sensor. Possible approach for improving response and relaxation times is using pulse temperature mode increasing diffusion rate through the gate present in work [4]. Extrapolation of present measurement results suggests stable detection NO2 concentrations by the Pd-SnO2-SiO2-Si structure in the region of 1 ppb and less.

Funding

This work was supported by the Russian Science Foundation (Grant Agreement 18-79-10230 of 08.08.2018).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Shivaraman, M.S.; Lundström, I.; Svensson, C.; Hammarsten, H. Hydrogen sensitivity of palladium-thin-oxide-silicon schottky barriers. Electron. Lett. 1976, 12, 483–484. [Google Scholar] [CrossRef]
  2. Fogelberg, J.; Dannetun, H.; Lundström, I.; Petersson, L.-G. A hydrogen sensitive palladium metal-oxide-semiconductor device as sensor for dissociating NO in H2-atmospheres. Vacuum 1990, 41, 705–708. [Google Scholar] [CrossRef]
  3. Zhovannik, E.V.; Nikolaev, I.N.; Stavkin, D.G.; Shevlyuga, V.M.; Imamov, R.M.; Lomov, A.A. Studies of transient region between laser-deposited palladium and (111)Si. Kristallografiya 1996, 41, 935–939. [Google Scholar]
  4. Samotaev, N.; Litvinov, A.; Etrekova, M. Improving Detection Chlorine by Field Effect Gas Sensor with Using Temperature Pulse Mode. In Proceedings of the IMCS 2018, Vienna, Austria, 15–19 July 2018; pp. 474–475. [Google Scholar]
Figure 1. Capacitor sensor’s photo assembled with film resistive heater and thermistor. Package type is TO-8 (11 mm in diameter).
Figure 1. Capacitor sensor’s photo assembled with film resistive heater and thermistor. Package type is TO-8 (11 mm in diameter).
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Figure 2. Capacitor sensor: 1—SnO2/Pd gate; 2—SiO2 film; 3—Si substrate; 4—Al electrode; 5—insulator; 6—heater; 7, 8, 10—the electric contacts; 9—thermistor.
Figure 2. Capacitor sensor: 1—SnO2/Pd gate; 2—SiO2 film; 3—Si substrate; 4—Al electrode; 5—insulator; 6—heater; 7, 8, 10—the electric contacts; 9—thermistor.
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Figure 3. Scheme of capacitance-voltage characteristic for Pd gate sensor at different heating temperatures and shift C-V characteristic during exposed to gas.
Figure 3. Scheme of capacitance-voltage characteristic for Pd gate sensor at different heating temperatures and shift C-V characteristic during exposed to gas.
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Figure 4. The capacitance-voltage characteristics for capacity sensor at temperatures: 1—170 °С, 2—140 °С, 3—100 °С, 4—pure Pd gate at 100 °С.
Figure 4. The capacitance-voltage characteristics for capacity sensor at temperatures: 1—170 °С, 2—140 °С, 3—100 °С, 4—pure Pd gate at 100 °С.
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Figure 5. Responses capacitor sensor to 108 ppb NO2 concentration at temperatures: 1—170 °С, 2—140 °С, 3—100 °С, 4—pure Pd gate at 100 °С.
Figure 5. Responses capacitor sensor to 108 ppb NO2 concentration at temperatures: 1—170 °С, 2—140 °С, 3—100 °С, 4—pure Pd gate at 100 °С.
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Figure 6. The response of capacity sensors to108 ppb NO2 concentration at different temperatures.
Figure 6. The response of capacity sensors to108 ppb NO2 concentration at different temperatures.
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MDPI and ACS Style

Samotaev, N.; Oblov, K.; Litvinov, A.; Etrekova, M. SnO2-Pd as a Gate Material for the Capacitor Type Gas Sensor. Proceedings 2019, 14, 10. https://doi.org/10.3390/proceedings2019014010

AMA Style

Samotaev N, Oblov K, Litvinov A, Etrekova M. SnO2-Pd as a Gate Material for the Capacitor Type Gas Sensor. Proceedings. 2019; 14(1):10. https://doi.org/10.3390/proceedings2019014010

Chicago/Turabian Style

Samotaev, Nikolay, Konstantin Oblov, Arthur Litvinov, and Maya Etrekova. 2019. "SnO2-Pd as a Gate Material for the Capacitor Type Gas Sensor" Proceedings 14, no. 1: 10. https://doi.org/10.3390/proceedings2019014010

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