Prototype of micro ISFET for biomedical research

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Abstract
With a view to developing an ion sensor capable of simple measurement of ion concentration at the cell level, a micro ionsensitive FET (micro ISFET) has been studied. For this purpose, it is necessary that the micro ISFET be a probe structure whose tip size is smaller than the cell and that the ion‐sensitive gate be placed at the tip of the probe. Special micro fabrication techniques are required for such a micro ISFET. This paper describes a three‐dimensional processing technique to fabricate a microprobe from an Si wafer and a method for forming an ISFET on a Si probe. Based on these fabrication techniques, a fundamental design of the micro ISFET is performed. An Si3N4 gate micro ISFET for pH is fabricated that has a tip size of 10 μm and a gate area of 5 × 5 μm2. Its characteristics are evaluated.