Evaluation of a microsensor fabricated using VLSI technology and doped phthalocyanines for detecting nitrogen dioxide

An integrated circuit microsensor for detecting nitrogen dioxide was designed and fabricated. The microsensor combined conventional VLSI fabrication techniques along with the deposition of chemically sensitive membranes. The microsensor consisted of an array of nine discrete sensing elements with in situ amplifiers, a reference amplifier, and an analog multiplexer. The nine individual sensing elements were composed of an interdigitated gate electrode field-effect transistor which was coupled to a serially connected pair of inverting amplifiers realized with metal-oxide-semiconductor field-effect transistors. Thin films of cobalt (II) phthalocyanine (CoPc), copper (II) phthalocyanine (CuPc), lead phthalocyanine (PbPc), nickel (II) phthalocyanine (NiPc), and, as a control, undoped phthalocyanine (Pc) were evaluated as candidate chemically sensitive membranes, and their performance was compared with respect to sensitivity, specificity, and reversibility. The electrical response was evaluated upon exposure to parts-per-billion concentrations of nitrogen dioxide (NO₂) and diisopropyl methylphosphonate (DIMP) using dried filtered room air as the diluent