DIAMOND-LIKE CARBON-GATE PH-ISFET

A novel chemical-resistant ion-selective field-effect transistor (ISFE T) array is introduced, using amorphous diamond-like carbon (DLC) film s for passivation and as pH-sensitive layer. A DLC coating technology is developed, useful for depositing and patterning final thin films on active and passive surfaces of ISFET devices. The DLC films are produ ced by a low-temperature dual rf methane-helium gas mixture plasma. DL C thin films show complete chemical inert behaviour in aggressive aque ous electrolytes. The high film hardness in addition to the chemically inert behaviour makes DLC films more suitable as passivation layers f or sensor devices than other materials (i.e. Si3N4, SiO2, etc.). It is shown from the results of electrochemical and electronic characteriza tion of ISFET devices with DLC thin films that DLC is suitable for sen sor applications. A comparative characterization of DLC-coated ISFET w ith a Ta2O5-coated ISFET on a single chip sensor is shown in this work . The pH response of the DLC ISFET shows lower drift than that of the Ta2O5-coated ISFET. No redox cross-sensitivity was found for DLC-coate d ISFET. The shin of the sensor response is only slightly dependant on temperature. (C) 1997 Elsevier Science S.A.