High sensitivity NO2 sensors for environmental monitoring produced using laser ablated nanocrystalline metal oxides

An integrated CMOS sensing chip for NO2 detection

“…This task requires the development of both sensitive layers and sensor structures compatible with integrated circuit (IC) fabrication processes. Old and new materials such as polymers [1][2][3], thick and thin metal oxides [4][5][6], porous silicon (PS) [7][8][9], carbon nanotubes [10][11][12], and others are today under investigation.…”

NO2 adsorption effects on p+–n silicon junctions surrounded by a porous layer

“…For instance, as reported in ref. [12] for SnO 2 films, a variation of the relative humidity level from 0% to 30% produces a relative resistance variation of about 10, more than the variation produced by 100 ppb of NO 2 in dry air. Moreover, a degradation of the sensor response to NO 2 is observed when the RH level increases.…”

“…Thick and thin metal-oxides [12][13][14][15][16][17][18], porous silicon [3,[5][6][7][8][9][10][11], carbon nanotubes [19][20][21][22] have been used to detect NO 2 by monitoring changes in the material or device conductance, induced by gas adsorption. However, in spite of the many different materials and devices reported in literature, several problems related to the sensitivity, selectivity, transient times, reliability and time stability still exist for practical applications.…”

“…A number of both simple and mixed metal-oxides have been considered, in particular, SnO 2 [12], In 2 O 3 [13], In 2 O 3 -SnO 2 [14], MoO 3 -In 2 O 3 [15], YSZ [16], NASICON [17], WO 3 [18]. However, few of these materials are able to detect hundreds ppb of NO 2 in air, as required by the European legislation.…”

“…In ref. [12] it was demonstrated that laser ablated SnO 2 can detect NO 2 at hundreds ppb, with a relative resistance variation of about 3, using a moderatelylow operating temperature (134 • C). However, at this temperature the recovery time is in the order of tens minutes.…”