Chemical response of Si/sub 3/N/sub 4//SiO/sub 2//Si structures used in pH microelectronic sensors

Abstract
The effects of processing parameters such as annealing treatment and gas flow ratio on the chemical response of Si/sub 3/N/sub 4//SiO/sub 2//Si electrodes used in ISFET (ion-sensitive FET) pH sensors were studied. Experimental results based on capacitance-voltage measurements show that the voltage response and pH sensitivity depend on the gas flow ratio n=NH/sub 3//SiH/sub 4/ during the nitride deposition and the preoxidation anneal prior to thermal oxidation of the Si wafers. The results are interpreted in terms of chemical and physical properties of nitride and oxide layers. It is concluded that optimum performance of ISFET pH sensors requires better control and characterization of the gate insulator fabrication process.

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