Use of boron heavily doped silicon slabs for gas sensors based on free-standing membranes

Heavily doped silicon regions using boron solid sources, compatible with wet bulk micromachined free-standing membranes, have been successfully used as heat spreaders and infrared absorbers, making their incorporation advantageous in several devices involved in different gas sensing schemes, such as microhotplates and thermopiles. Moreover, good thermal conduction and infrared absorption of the doped silicon slabs have been combined in the fabrication of a thermopile array where ribs and absorbers have been simultaneously built in a single membrane. The good response homogeneity of all elements of the fabricated arrays confirms the results of the simulations performed in order to assess the thermal behaviour of the structure. The intrinsic free-standing membrane robustness was also improved by the addition of the silicon ribs.