Abstract
A novel chemical-resistant ion-selective field-effect transistor (ISFET) array is introduced, using amorphous diamond-like carbon (DLC) films 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 produced by a low-temperature dual rf methane–helium gas mixture plasma. DLC thin films show complete chemical inert behaviour in aggressive aqueous electrolytes. The high film hardness in addition to the chemically inert behaviour makes DLC films more suitable as passivation layers for sensor devices than other materials (i.e. Si 3N 4, SiO 2, etc.). It is shown from the results of electrochemical and electronic characterization of ISFET devices with DLC thin films that DLC is suitable for sensor applications. A comparative characterization of DLC-coated ISFET with a Ta 2O 5-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 Ta 2O 5-coated ISFET. No redox cross-sensitivity was found for DLC-coated ISFET. The shift of the sensor response is only slightly dependant on temperature.
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