Silver nitrate (AgNO3) solution with different concentrations (0.003M, 0.006M, 0.009M and 0.012M), used on the surface modification for the effective sensing layer of tin dioxide (SnO2) sensor film, to study the effecting of Ammonia gas sensitivity for (SnO2) film sensor at room temperature, where the impurities effects on semiconductor gas sensor parameters are briefly interpreted. It has been found that the characteristics of impact(AgNO3) concentration on the value of gas sensitivity was as the following :Maximum sensitivity(Sg) was (35%) which occurs at the concentration ratio (0.006M) of (AgNO3) solution where the decreasing of the sensitivity was very small, in addition the sensitivity (Sg) decreased from (6-7) with increases of (AgNO3) concentration, at the rates (0.009M, 0.012M). The sensitivity of gas sensor depend on the gas concentration of the Ammonia in the range(500-5000) ppm. Results also showed that the best concentration of (AgNO3) result from the ratio (0.006 M) which consequently identified the threshold of (SnO2) film sensor.
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