In this paper, the sensing characteristics of Ni/Al2O3/Ni/n-Si devices as magnetic tunneling transistor (MTT) hydrogen gas sensors were investigated. The Ni/Al2O3/Ni/n-Si sensors were prepared using an electron beam deposition of Ni, Al2O3 and Ni layers, respectively with different tunnel barrier (Al2O3) thicknesses of 10, 15, 20 and 25 nm onto n-type Si substrates. An appropriate profile of magnetization was used to magnetize the ferromagnetic Ni layers of emitter and base. We measured current-voltage (I-V) characteristics of the sensors in absence and presence of 500 ppm hydrogen gas at room temperature. From I-V characteristics, we obtained the sensing response of the sensors with different tunnel barrier thicknesses when exposed to 500 ppm hydrogen gas. We have found that the MTT sensors showed an excellent response to hydrogen at room temperature so that the response was inversely related to the Al2O3 film thickness and a higher response was recorded for thinner tunnel barrier layers which exhibited an excellent agreement with the results obtained from the simulation of the device.
