Design of CMOS Readout Circuits for ISFET Aptasensor

We present the design and integration of ISFET aptasensor readout circuits on a single silicon substrate, integrated into a 1.2-μm 5V complementary metal oxide semiconductor process. The ISFET is based on a MOSFET with its gate connected to a metal pad brought to the surface of the chip through passivation opening. The ISFET design was determined by the ratio of the areas of the MOSFET and the sensitive surface of the floating gate. An aluminum oxide film was formed as the sensitive surface. Readout circuits based on differential measurements have been developed to implement a differentiation circuit into the chip using an instrumentation amplifier and due to processing by an external device using a repeater circuit and a transimpedance amplifier. For all circuits, an amplifier with a calculated gain of more than 1000 and a phase margin of 60.4 degrees at a frequency of 5.77 MHz and a gain margin of 7 dB at a frequency of 10.3 MHz with a load of 15 pF and 50 kOhm was used. DC measurements of the manufactured circuits were carried out and their operability was shown in direct contact with a metal probe and in contact with a buffer solution biased using platinum reference electrode. For the repeater and instrumentation amplifier circuits, the linearity of the characteristics is close to 1, and for the transimpedance amplifier circuit more than 0.98. The developed device provides a basis for the development of aptasensors for biomarkers detection.