Smart system based on silicon carbide semiconductor technology for detection combustible gas leakage in security applications

摘要

For high temperature sensing applications, metal/oxide/semiconductor (MOS) devices based on SiC show great promise, particularly above 200 ℃, which represents an upper bound for MOS devices based on silicon (Si) semiconductor. This paper presents an investigation of a smart system based on silicon carbide technology used as hydrogen sensor at high temperature. The (Pd/SiO_2/SiC) sensor was fabricated using microelectronics technology. The semiconductor used was 4H-SiC wafer, with two epitaxial layers: a buffer layer with a thickness of 0.5 μm and an active doped layer (N_D=2.07×l0~(16) cm~(-3)) with a thickness of 8 μm. The silicon oxide (SiO_2)layer, with 30 nm thickness was thermally grown by dry oxidation. The electrode of the capacitor was a catalytic metal, obtained by D.C. sputtering deposition of a palladium (Pd) thin film with 50 nm thickness. A chip structure with 400 μm diameter was obtained by photolithographic process. The experiments were aimed at the electrical behavior of the M/O/SiC device at gas concentrations from 0 ppm to 2000 ppm H_2 in argon (Ar). The C-V characteristics of the H_2 sensor shift to smaller voltages with increasing gas concentration. The bias voltage shift is caused by hydrogen adsorption in metal-oxide and oxide-semiconductor interfaces. The flat band voltage has an important decrease when H_2 concentration increases and reaches a -4.05 V shift at 2000 ppm H_2 in Ar. These results show that the Pd/SiO_2/SiC sensors are suitable for detection of small H_2 concentrations (10-200 ppm H_2), particularly for detection of H_2 leakages.