Presentation on "Ambipolar Si-Junctionless Nanowire Transistor for NO2 and NH3 sensing" for EUROSENSORS XXXVI
Creators: name: Vardhan, Vaishali
name: Biswas, Subhajit
name: Ghosh, Sayantan
name: Hellebust, Stig
name: M. Georgiev, Yordan
name: Tsetseris, Leonidas
name: D. Holmes, Justin
Publisher: name: Zenodo
Year: 2024
Subjects: subject: Air pollution engineering
subject: Environmental sciences
subject: Pollution
subject: si-jnts
subject: NO2 sensor
subject: ambipolar device
subject: silicon nanowires
subject: air pollution
subject: free radicals
subject: electronic sensors
subject: air chemistry
subject: air quality
subject: atmospheric chemistry
subject: atmospheric radicals
subject: air quality monitoring
subject: gas sensor
subject: environmental monitoring
subject: junctionless nanowire transistor
subject: radical

description: ABSTRACT:

Summary:

We demonstrate highly effective ambipolar Si-junction less nanowire transistors (Si-JNTs) with a distinct dual reaction to oxidative pollutant NO2. Different Si-JNT characteristics including on-current (Ion), threshold voltage (Vth) and mobility (µ) shows dynamic change on both the p- and n-sides of the ambipolar transistor devices upon exposure to NO2 in a wide mixing ratio (250 ppb-50 ppm).

Keywords: Silicon nanowire, Junction less transistor, Ambipolar device, NO2 sensor 

Background

Due to their high surface-to-volume ratio, the ability to interact chemically with analytes on the surface, and operation at ambient temperature, Si NWs offer unique opportunities as efficient sensor material [1], [2]. Si NW-FET sensors are well recognized for their high sensitivity with exposed ultrathin (diameter 30–70 nm) Si NW channels under the control of back gate [3]–[6] In this regard, Si NW JNT; a nanowire transistor without any gate junction [7]; are interesting proposition as NO2 sensor. Incidentally, ambipolar transistors, a type of transistors that allow for simultaneous transit of both positive (holes) and negative (electrons) charge carriers within the semiconducting channel[8], can provide a dual response to a single analyte using a single device[8].In this paper, we show how NO2 can alter different device properties by acting as a pseudo dopant for ambipolar Si JNTs. Thus, a variety of electrical parameters could be explored for a single ambipolar Si-JNT upon analyte (NO2 in our case) interaction, offering variety of sensing properties and potentially extremely selective gas detection.  

Experimental

Si-JNTs were fabricated following a top-down approach using electron beam lithography (EBL) and reactive ion etching (RIE). Flash lamp annealing (FLA), which leads to form Nickel Silicide at the interface of Silicon and Nickel and controls the unipolar or ambipolar nature. Fig. 1.a shows top-view SEM image of the representative Si-JNT device. Electrical and sensor characterization of Si-JNTs was performed by using an electrical analysis system (two Keithley 2450 Source Meter) interfaced with the Nextron.

Results and discussion

The transfer curve of the Si NW JNT measured under ambient conditions exhibits typical ambipolar characteristics. The observed V-shape curves indicate that the number of free carriers can be controlled by externally applied gate voltage (Vg), resulting in a gate-tuneable hole and electron charge transport characteristics A clear change in on-current (Ion) is observed upon NO2 exposure to the Si-JNTs (Fig. 1. b). An increase in the drain current has been observed with increasing mixing ratios of NO2 in the p-side (from 25 ppm to 50 ppm) whereas a decrease in the n-type current was observed with NO2 exposure of same concentrations.   This is classified as dual interaction.   Being as an oxidizing gas, NO2 acts as electron’s acceptor. Therefore, NO2 can be directly adsorbed onto the Si NW surface trapping electrons or interact with the chemisorbed oxygen species. This adsorption induced charge transfer affect the electrical properties of the Si-JNT.To demonstrate the sensing performance of the ambipolar Si-JNTs, we tested and compared the interaction of Si-JNTs towards four gases, NO2, NH3, CH4, and SO2, at a low concentration regime (0.25-2 ppm). All different JNT parameters shows distinct response upon exposure to different mixing ratios of NO2 and binary, tertiary, and quaternary combination of all the gases. For example, as compared to oxidative NO2, reductive NH3 causes an inverse response in all Si-JNT electrical characteristics (Fig. 1.c). The significant different response for each JNT parameters easily distinguishes the target analyte, NO2.

Conclusion

In conclusion, we have demonstrated the potential of ambipolar Si-JNTs with dual response (up to 250 ppb) to target gas NO2. The information about the different influences that different gas mixtures have on different measured parameters will be used to create a multivariate calibration model for the target gas NO2. Future plan is to decorate Si-JNTs with organic molecules and utilize the resulting calibration model for the detection of gas short lived atmospheric radicals (e.g., OH·, NO3·) at atmospheric relevant concentration.  

AcknowledgementThis work is funded by the European Union’s Horizon 2020 research and innovation programme (Grant agreement 899282).

References

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description: Vaishali Vardhan delivered this presentation for the Eurosensor XXXVI Conference in Debrecen, Hungary.

RADICAL represents a 'Fundamental Breakthrough in Detection of Atmospheric Free Radicals'.

Find out more on the RADICAL project website: radical-air.eu

The RADICAL project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement number 899282.