Nano Pt-decorated transparent solution-processed oxide semiconductor sensor with ppm detection capability

Abstract

In this study, we fabricated a transparent Pt-decorated indium gallium zinc oxide (IGZO) thin film based on a solution process to demonstrate a portable, low-cost volatile organic compound (VOC) based real-time monitoring system with the detection capability at as low as 1 ppm. The Pt/IGZO sensor shows remarkable response characteristics upon exposure of isobutylene (2-methylpropene) gas down to 1 ppm while also maintaining the reliability and reproducibility of the sensing capability, which is almost comparable to a commercial VOC sensor based on a photoionization detector (PID) method. For 1 ppm of isobutylene gas, the response and recovery time of the sensor estimated were as low as 25 s (S ₉₀) and 80 s (R ₉₀), respectively. The catalytic activity of Pt nanoparticles on an IGZO nano-thin film plays a key role in drastically enhancing the sensitivity and dynamic response behaviour of the VOC sensor. Furthermore, the solution-processed IGZO thin film decorated with Pt nanoparticles also represents a highly transparent (in visible region, ∼90%) and low-cost fabrication platform, thereby, facilitating the optical visibility and disposability for future applications in the field of electronics. Therefore, we believe that the nano-Pt/IGZO hybrid material for VOC sensor developed by us will pave a way to detect any harmful chemical gases and VOCs in various environments.

Fig. 1. (a) The schematic of the final device structure magnified the sensing layer (1 × 1 mm²). The width and length are 10 mm and 50 μm, respectively. (b) The transparent Pt/IGZO gas sensors on a glass substrate (5 × 5 cm²). The sample size of the single Pt/IGZO is 1 × 1 cm² (red dot square).

Fig. 2. The block diagram of the gas sensing test system with a parameter analyzer and MFC control system.

Fig. 3. The AFM images of the surface morphologies for (a) the pristine IGZO (RMS = 0.12) and (b) Pt/IGZO (RMS = 0.49). The scale of the AFM images is 1 × 1 μm². (c) The transmittance spectrum of a glass substrate (blue solid) and the Pt/IGZO gas sensor (red solid). (d) I–V characteristics of the Pt/IGZO sensor. (e) The current level of the pristine IGZO (red solid line, left-y-axis) and the Pt layer (blue solid line, right-y-axis). The exposure time of isobutylene gas is 3 min.

Fig. 4. (a) The illustration of the sensing mechanism between isobutylene molecules and Pt/IGZO film. More atomic-oxygen species reside near Pt particles, withdrawing electrons from the IGZO film. When the oxygen species are desorbed, the trapped electrons are released to the IGZO film. (b) The energy band diagram when isobutylene gas molecules react with adsorbed oxygen species. (c) and (d) The response and recovery characteristics for isobutylene detection of (c) 100 ppm and (d) 1 ppm.

Fig. 5. (a) The reliability and reproducibility of the VOC detection characteristics for 100, 10 and 1 ppm. The on/off interval is 3 minutes. (b) The response to isobutylene as a function of gas concentrations; 11,541; 11,611; 67,843; and 114,561 for 1, 10, 100, and 500 ppm, respectively. (S = R₀/R_g).

Fig. 6. (a) The block diagram of the portable real-time VOC monitoring system that can be operated by a portable power bank. (b) The photographs of the monitoring result in real-time. The 100 steps of VOC concentrations are displayed with 0.1 resolution, including the calibration points; pristine, 1, 5, and 10 ppm.