Coupling p+n Field-Effect Transistor Circuits for Low Concentration Methane Gas Detection

Abstract

Nowadays, the detection of low concentration combustible methane gas has attracted great concern. In this paper, a coupling p+n field effect transistor (FET) amplification circuit is designed to detect methane gas. By optimizing the load resistance (RL), the response to methane of the commercial MP-4 sensor can be magnified ~15 times using this coupling circuit. At the same time, it decreases the limit of detection (LOD) from several hundred ppm to ~10 ppm methane, with the apparent response of 7.0 ± 0.2 and voltage signal of 1.1 ± 0.1 V. This is promising for the detection of trace concentrations of methane gas to avoid an accidental explosion because its lower explosion limit (LEL) is ~5%. The mechanism of this coupling circuit is that the n-type FET firstly generates an output voltage (VOUT) amplification process caused by the gate voltage-induced resistance change of the FET. Then, the p-type FET continues to amplify the signal based on the previous VOUT amplification process.

Transilient Response to Acetone Gas Using the Interlocking p+n Field-Effect Transistor Circuit

“…Then, an n-type and a p-type FETs are added into the circuit, forming the interlocking p+n circuit as shown in Figure 1 . It is found that this circuit is different from the coupling or synergetic p+n circuits in Figure S1 in the supporting information according to our previous reports [ 28 , 29 ]. Similarly, the V OUT is still low in air using the same R L due to the negligible resistance of FET (R FET ) at ON state (~100 Ω).…”

“…The working curve of the interlocking p+n FET circuit in the third stage is estimated. It starts with the point (0.11 μA, 11 MΩ) and then increases almost vertically, very similarly to the coupling p+n FET circuit previous [ 29 ], followed by arriving at the ending point (1.7 × 10 −4 μA, 3.9 × 10 4 MΩ) along the blue dash line. The working curve of this interlocking p+n FET circuit including three stages is the red solid line in Figure 6 and Figure S4 , where the resistance jump of FET is the basic reason why this interlocking circuit can produce the transilient response.…”

“…Then the commercial MP-4 and TGS 2602 MOX sensors were utilized to detect the methane and toluene by using the interlocking p+n FET circuit respectively. More details of their sensing property measurements are seen in the references [ 28 , 29 ]. For the traditional circuit and the interlocking p+n FET circuit, the voltage signal is defined as voltage difference in acetone and in air and the response time is defined as the time needed to reach the maximum voltage from baseline voltage.…”

“…Our earlier reports [ 27 , 28 , 29 ] provided useful methods to enhance the response of MOX gas sensors. An n-type field effect transistor (FET) circuit has been proposed to amplify the apparent response of commercial sensor TGS 2602 (Figaro, Japan) [ 30 ] to toluene by around five times [ 27 ].…”

“…An n-type field effect transistor (FET) circuit has been proposed to amplify the apparent response of commercial sensor TGS 2602 (Figaro, Japan) [ 30 ] to toluene by around five times [ 27 ]. Besides this, the other commercial sensor, MP-4 sensor (Winsen, China) [ 31 ], in a coupling p+n FET circuit exhibits a ~14-fold higher apparent response to 150 ppm methane than that in the traditional circuit [ 29 ]. In this paper, a novel interlocking p+n FET amplification circuit is designed for Mn-doped ZnO nanoparticles (MZO) in order to detect acetone at low concentrations, especially at 2 ppm.…”