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High sensitivity of isopropyl alcohol gas sensor based on memristor device operated at room temperature

Abstract

In this paper, we present the high sensitivity of an isopropyl alcohol gas sensor, which is based on a memristor device that is operated at room temperature. We proposed the SnO2-based memristor to detect isopropyl alcohol and demonstrated the change in the current of the SnO2-based memristor that is monitored in real time depending on concentration of the isopropyl alcohol gas at room temperature. As a result, the current of the SnO2-based memristor is drastically decreased as we introduced isopropyl alcohol into the memristor based gas sensor. A change in current, which depends on the concentration of the isopropyl alcohol gas, was evaluated as the sensitivity and the sensitivity was 2.02 for 30 ppm isopropyl alcohol gas. In addition, in the proposed SnO2-based memristor, we observed an immediate response of < 4 s when exposed to isopropyl alcohol as well as an immediate recovery of < 6 s when flowing of the injected gas was stopped.

Introduction

The concern about air pollution has increased after the third industrial revolution, so gas sensor technologies, which are used to detect harmful gases have been extensively investigated. In addition, analyzing exhaled breath has been attracted attention in recent decades because exhaled breath contains a type of biological information, which is useful for the fast diagnosis of diseases without blood and urine analyses for diagnostics. One of developments in the medical diagnosis of diseases with respect to analyzing exhaled breath is the inflammatory diagnosis of patients with asthma using NO breath test because NO gas concentration in exhaled breath is increased by inflammation [1]. Detecting isopropyl alcohol in exhaled breath has recently been intensively studied due to its wide diagnosis capability. Hanouneh et al. reported isopropyl alcohol in the exhaled breath of patients who have liver disease shows higher concentrations than that the exhaled breath of healthy people [2], Phillips et al. informed that analyzing the concentration of isopropyl alcohol in exhaled breath is useful in order to predict breast cancer [3], and Rudnicka et al. demonstrated that concentration of isopropyl alcohol in the exhaled breath of patients who have lung cancer showed a high concentration than the breath of healthy patients [4].

Gas sensors for detecting isopropyl alcohol have been studied according to detection mechanisms, such as electrochemical-based, semiconductor-based, catalytic-based, and photoionization-based gas sensors. Electrochemical-based gas sensors measure the current, which is changed by a redox reaction between the anode and cathode during the gas flow, a semiconductor-based gas sensor operates by the adsorption and desorption of the gas molecules on the surface of semiconductor particles, a catalytic-based gas sensor measures the resistance, which is changed by the heat energy that is generated by the reaction between the oxygen and combustible gases, and the photoionization-based gas sensor converts the change of ultraviolet light energy that occurs by the gas molecules to an electrical signal. A semiconductor-based gas sensor, which first had its feasibility using a metal oxide demonstrated in 1962 by Seiyama and Taguch, has been widely used to detect gas after the commercialization of the metal oxide semiconductor-based gas sensor by Figaro in 1968 [5]. However, low power consumption and minimization are a huge significance for the gas sensor according to the development of wearable device and drones, so conventional gas sensors have limitations due to their high power consumptions, slow recovery speeds, and huge device sizes. Therefore, innovative gas sensor technologies that have low power consumptions, fast response/recovery times, small devices are required. A gasistor that is based on a memristor device has been proposed in several institutes due to its advantages, such as reusability, room temperature operating, and low power consumption [6,7,8,9,10]. However, the reported gasistors showed low sensitivity (0.1 for 1000 ppm of ethanol) and a slow response/recovery time (120/59 s). Therefore, a gasistor that is based on various metal oxides has to be intensively studied in order to detect several gases. In our previous study [11], we demonstrated the feasibility that was proposed by the SnO2, HfO2, and Ta2O5-based gasistors for detecting the NO, O2, and C2H6 gases, which obtained high sensitivity (118.9 for 50 ppm of NO gas) and fast response/recovery time (1 s/90 ns). However, the sensitivities for the NO, O2, and C2H6 gases were obtained using an SnO2-based gasistor, so the sensitivities for isopropyl alcohol have to be analyzed due to its application, which is mentioned above. In this paper, we demonstrated the feasibility of a SnO2-based gas sensor for detecting isopropyl alcohol and obtained a high sensitivity and a fast response/recovery time.

Experiments and discussion

First, to prepare the SnO2-based gasistor, the Si substrate was cleaned using acetone, methanol, and deionized water for 15 min in the same sequence. The Pt bottom electrode (BE), which was 50 nm thick, was deposited on the cleaned Si substrate using a radio frequency (RF) sputtering system. The SnO2, which was 50 nm, was then deposited on the Pt/Si substrate using an RF sputtering system. The SnO2 deposition was performed at a 100 W sputtering power in an Ar ambient at a base pressure of ~ 20 mTorr and a working pressure of ~ 5 mTorr. Subsequently, the Ti top electrode (TE) was deposited on SnO2/Pt/Si substrates using RF sputtering system. In order to evaluate the resistive switching (RS) characteristic, we measured the electrical characteristics of the SnO2-based gasistor using a Keithley 4200-Semiconductor Characterization Systems (SCS) and a high-frequency capacitance–voltage (C–V) meter. To demonstrate the gas sensing capability of the SnO2-based gasistor at room temperature, the current of the SnO2-based gasistor was monitored while inducing the isopropyl alcohol gas. The SnO2-based gasistor was placed onto the ground plate inside of the gas sensing chamber and electrically connected to a Keithley 4200-SCS. The humidity was maintained under a 65%RH. The isopropyl alcohol gas was injected through a pipe to the gasistor. The concentration of isopropyl alcohol gas was controlled to 10, 20, and 30 ppm. Then, the current at a read voltage of 0.13 V was measured while inducing the isopropyl alcohol gas.

A schematic of the fabricated SnO2-based gasistor with a Ti/SnO2/Pt/Si structure is described in Fig. 1a. the SnO2-based gasistor basically had a metal–insulator–metal structure in this paper. As shown in Fig. 1b, the Ti, SnO2, and Pt layers with a 50 nm thick were identified. So as to evaluate the material properties, we measured the X-ray diffraction (XRD) peaks, as shown in Fig. 1c. The pristine SnO2 films had amorphous characteristics, so the diffraction peaks of SnO2 were observed to be near 30° and 55°. To analyze the diffraction peaks in detail, we used JCPDS card to match the measured diffraction peaks of SnO2. As a result, the measured diffraction peaks were in a good agreement with the JCPDS card 41-1445. The diffraction peaks near 30° consisted of (110) and (101) planes of SnO2 and the diffraction peak near 55° was (220) plane of SnO2. The wide diffraction peaks were generally attributed with small crystal sizes [12]. The average crystal size of SnO2 was identified following the Debye–Sherrer equation, which is R = 0.9λ/βcosθ, where R = the average crystal size, λ = is the wavelength of the X-ray, β is the full width at half maximum of the peak, and θ is the Braggs angle. The average crystal sizes for the (110), (101), and (220) planes of SnO2 were estimated to be 0.51, 1.41, and 0.4 nm, respectively.

Fig. 1
figure 1

a Schematic illustration, b cross-section of the FE-SEM image, and c the XRD result of the SnO2-based gasistor

The pristine SnO2 was initially an insulator, whereby by following the conducting filaments (CFs) forming process with a positive bias sweep from 0 to 2.7 V to the TE of SnO2-based gasistor, in direct current (DC) mode, the oxygen ions migrated toward the TE and left the oxygen vacancies, which were manifested. As the concentration of oxygen vacancies around the BE of the SnO2-based gasistor was above the concentration of the oxygen vacancy accumulation, the oxygen vacancies were reconstructed, which showed the formation of the CFs between the BE and the TE of the SnO2-based gasistor. Therefore, according to the formation of CFs, abrupt increase in the current was observed at 2.67 V, as shown in the inset figure of Fig. 2a, and it represents that the CFs that consisted of oxygen vacancies were formed, which is consistent with the previous reports. [11, 13,14,15]. In order to investigate the RS characteristics of the SnO2-based gasistor that has a Ti/SnO2/Pt structure with a 50-nm-thick SnO2 layer, a DC bias sweep was applied in a sequence that followed: 0 → − 1.3 V → 0 V → 0.8 V → 0 V. As a result, the SnO2-based gasistor showed a typical current–voltage (I–V) characteristic, because a bipolar RS behavior was observed by the DC bias sweep, which is shown in Fig. 2a. As the DC bias swept to a negative direction to − 1.3 V, an abrupt decrease in the current was manifested close to − 1.24 V, because the CFs were partially disrupted, which indicated that the resistance was changed from a low resistance state (LRS) to a high resistance state (HRS), which is called the reset process, as shown in step 1 and 2 steps of Fig. 2a. Conversely, as the DC bias was swept in a positive voltage direction from − 1.3 V with a compliance current of 100 mA, the current was drastically increased, because the partially disrupted CFs were formed again at 0.72 V, which represented that the resistance was changed from the HRS to the LRS, which is called the CFs forming process, as shown in 3 step and 4 step of Fig. 2a. The current ratio between the HRS and the LRS was greater than 10.53 at a read voltage of 0.13 V. In order to evaluate the long-term stability of the resistance state on the SnO2-based gasistor, the resistance state was measured for 104 s at a read voltage of 0.13 V, as shown in Fig. 2b. As a result, LRS was stably maintained above 104 s, which indicated that the CFs were stably kept during the gas sensing without any degradation or reaction in the air at room temperature.

Fig. 2
figure 2

a The RS characteristic and b the maintain time of LRS on the SnO2-based gasistor

Then, in order to evaluate the isopropyl alcohol gas sensing capability of the SnO2-based gasistor at room temperature, the current of the SnO2-based gasistor was monitored at a read voltage of 0.13 V while inducing the isopropyl alcohol gas. Figure 3a shows the change of the current density on the SnO2-based gasistor before the CFs forming process when 30 ppm of the isopropyl alcohol gas was induced into the gasistor. As a result, the resistance was not changed by the isopropyl alcohol gas. However, as CFs were formed in SnO2-based gasistor, the resistance change according to the concentration of isopropyl alcohol gas was observed. Figure 3b shows the transient response current against concentration of isopropyl alcohol. The pristine current in the air was about 4.05 mA, whereas the currents were decreased to 3.47, 2.4, and 2 mA for the concentration of 10, 20, and 30 ppm, respectively. To evaluate the gas sensing characteristics in detail, the sensitivity (S) was calculated as S = Rgas/Rair, where Rgas is the resistance of the SnO2-based gasistor in the target gas, and Rair is the resistance of the SnO2-based gasistor in the air. As shown in Fig. 3c, the sensitivities were 1.17, 1.69, and 2.02 for 10, 20, and 30 ppm of isopropyl alcohol, respectively.

Fig. 3
figure 3

a The transient response of the SnO2-based gasistor at HRS for 30 ppm of isopropyl alcohol gas. The transient response of the SnO2-based gasistor at LRS against b the concentrations of isopropyl alcohol, c the sensitivity against the concentration of isopropyl alcohol gas on the SnO2-based gasistor, and d the response/recovery time of the SnO2-based gasistor for 30 ppm of isopropyl alcohol gas

On the other hand, the fast response/recovery time for the high concentration of isopropyl alcohol gas was essential for the gas sensor. The proposed SnO2-based gasistor represented a relatively fast response time that was below 4 s against all concentrations of the isopropyl gas sensor, whereas the response time for 30 ppm was relatively slower than the others. As shown in Fig. 3d, the recovery time for 30 ppm was above 6 s.

The decrease in the current with an increase in the concentration of isopropyl alcohol gas was caused by the reaction between the CFs consisted of the oxygen vacancies and the adsorbed isopropyl alcohol gas [11]. Before inducing isopropyl alcohol gas into the SnO2-based gasistor, the resistance state of the SnO2-based gasistor showed LRS, because the CFs provided conductive paths for the electrons to flow, which is described in Fig. 4a. As 10 ppm of isopropyl alcohol gas was induced into the SnO2-based gasistor, the isopropyl alcohol gas was adsorbed at the surface of the SnO2 particles and the adsorbed isopropyl alcohol gas had negative charge because the adsorbed isopropyl alcohol was a reducing gas [16,17,18]. The adsorbed isopropyl alcohol gas, which had a negative charge, was then reacted with the oxygen vacancies, Vo2+, which resulted in the broken CFs that are shown in Fig. 4b. Therefore, the reaction was attributed to the broken CFs, so a decrease of the current was observed as isopropyl alcohol was induced. As the concentration of isopropyl alcohol was increased to 30 ppm, the current of the SnO2-based gasistor decreased more than 10 ppm of the isopropyl alcohol gas. A current decrease against the increased concentration of isopropyl alcohol was due to the destructed CFs being increased as the quantity of the adsorbed isopropyl gas was increased, which is shown in Fig. 4c. When the isopropyl gas flow was stopped, the adsorbed isopropyl alcohol that occupied the CFs was automatically removed, which resulted in a recovery to the original state. In particular, the proposed SnO2-based gasistor showed fast recovery/response time because the nano-sized CFs were changed even with a minor change in concentration of isopropyl gas, which resulting in a change of the gasistor.

Fig. 4
figure 4

Schematic description of the gas response mechanism of the SnO2-based gasistor a without isopropyl alcohol gas, b at 10 ppm of isopropyl alcohol gas, and c at 30 ppm of isopropyl alcohol gas

Conclusion

In this paper, we proposed the SnO2-based gasistor for isopropyl alcohol gas sensing due to its wide application. The RS characteristics against the set (0.72 V) and reset (− 1.24 V) voltage was manifested depending on the CFs status. The LRS state was maintained for 104, which indicated that the CFs were stably kept during the gas sensing, without any degradation or reaction in the air at room temperature. In order to evaluate the capability of the isopropyl alcohol gas sensing on the SnO2-based gasistor, 10, 20, and 30 ppm of isopropyl alcohol gas were induced into SnO2-based gasistor. As a result, the current was decreased from 4.05 mA to 3.47, 2.4, and 2 mA for 10, 20, and 30 ppm of the isopropyl alcohol gas, respectively. The calculated sensitivity of the SnO2-based gasistor for the isopropyl alcohol gas showed 1.17, 1.69, and 2.02 for 10, 20 and 30 ppm of isopropyl alcohol gas, respectively. The response time was below 4 s against all concentration of isopropyl alcohol gas, whereas the recovery time for 30 ppm was below 6 s. Therefore, we demonstrated the feasibility of detecting isopropyl alcohol gas on the SnO2-based gasistor, which had a fast response/recovery time below 6 s.

References

  1. P.P.R. Rosias, E. Dompeling, M.A. Dentener, H.J. Pennings, H.J.E. Hendriks, M.P.A. Van Iersel, Q. Jöbsis, Pediatr. Pulmonol. 38, 107 (2004)

    Article  Google Scholar 

  2. I.A. Hanouneh, N.N. Zein, F. Cikach, L. Dababneh, D. Grove, N. Alkhouri, R. Lopez, R.A. Dweik, Clin. Gastroenterol. Hepatol. 12, 516 (2014)

    Article  Google Scholar 

  3. M. Phillips, R.N. Cataneo, B.A. Ditkoff, P. Fisher, J. Greenberg, R. Gunawardena, C.S. Kwon, O. Tietje, C. Wong, Breast Cancer Res. Treat. 99, 19 (2006)

    Article  Google Scholar 

  4. J. Rudnicka, M. Walczak, T. Kowalkowski, T. Jezierski, B. Buszewski, Sens. Actuators B Chem. 202, 615 (2014)

    Article  Google Scholar 

  5. T. Seiyama, A. Kato, K. Fujiishi, M. Nagatani, Anal. Chem. 34, 1502 (1962)

    Article  Google Scholar 

  6. M. Strungaru, M. Cerchez, S. Herbertz, T. Heinzel, M. El Achhab, K. Schierbaum, Appl. Phys. Lett. 106, 143109 (2015)

    ADS  Article  Google Scholar 

  7. A.A. Haidry, A. Ebach-Stahl, B. Saruhan, Sens. Actuators B Chem. 253, 1043 (2017)

    Article  Google Scholar 

  8. R. Zhang, W. Pang, Z. Feng, X. Chen, Y. Chen, Q. Zhang, H. Zhang, C. Sun, J.J. Yang, D. Zhang, Sens. Actuators B Chem. 238, 357 (2017)

    Article  Google Scholar 

  9. N. Dehghani, E. Yousefiazari, Mater. Res. Express 5, 046304 (2018)

    ADS  Article  Google Scholar 

  10. M. Vidiš, T. Plecenik, M. Moško, S. Tomašec, T. Roch, L. Satrapinskyy, B. Grančič, A. Plecenik, Appl. Phys. Lett. 115, 093504 (2019)

    ADS  Article  Google Scholar 

  11. D. Lee, M.J. Yun, K.H. Kim, S. Kim, H.-D. Kim, ACS Sensors (2021).

  12. V. Bonu, A. Das, Mapan 28, 259 (2013)

    Article  Google Scholar 

  13. Y. Dai, Z. Pan, F. Wang, X. Li, AIP Adv 6, 085209 (2016)

    ADS  Article  Google Scholar 

  14. Q. Hou, J. Buckeridge, T. Lazauskas, D. Mora-Fonz, A.A. Sokol, S.M. Woodley, C.R.A. Catlow, J. Mater. Chem. C 6, 12386 (2018)

    Article  Google Scholar 

  15. J.-H. Hur, Sci. Rep. 9 (2019).

  16. H.C. Wang, Y. Li, M.J. Yang, Sens. Actuators B Chem. 119, 380 (2006)

    ADS  Article  Google Scholar 

  17. T. Akamatsu, T. Itoh, N. Izu, W. Shin, Sensors 13, 12467 (2013)

    ADS  Article  Google Scholar 

  18. S.-H. Li, Z. Chu, F.-F. Meng, T. Luo, X.-Y. Hu, S.-Z. Huang, Z. Jin, J. Alloys Compd. 688, 712 (2016)

    Article  Google Scholar 

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Acknowledgements

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (no. NRF-2020R1F1A1048423) and by Korea Institute for Advancement of Technology (KIAT) grant funded by the Korea Government (MOTIE) (P0012451, The Competency Development Program for Industry Specialist).

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Lee, D., Bae, D., Chae, M. et al. High sensitivity of isopropyl alcohol gas sensor based on memristor device operated at room temperature. J. Korean Phys. Soc. 80, 1065–1070 (2022). https://doi.org/10.1007/s40042-022-00470-6

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  • DOI: https://doi.org/10.1007/s40042-022-00470-6

Keywords

  • Isopropyl alcohol
  • Gas sensor
  • Memristor
  • SnO2