Bio/CMOS Interfaces for Capacitance Sensing

This is the fourth chapter of the book where we learn about Complementary Metal-Oxide Semiconductor (CMOS) architectures. This chapter proposes methods for realizing capacitance biosensing. Two different methods are presented here. In both cases, the aim is to ensure a reliable estimation of the capacitance at the Bio/CMOS interface. In the first method, the average current supplied to the interface is measured by driving the interface with a square signal at a certain frequency. By changing this frequency, the interface capacitance is then estimated by the slope of the relationship between the measured current and the frequency of the driving signal. The limits of this method are deeply investigated, with special reference to the case of capacitance detection of DNA. With the second method, the interface capacitance is instead estimated by measuring the frequency of a signal that corresponds to cycles of charge and discharge of the interface capacitance. Again, the application of this second method to capacitance detection of DNA is discussed as well. Returning to what we learned in Chap. 8 , the chapter also shows that the capacitance detection of DNA is of a much higher quality if we use such methods by also integrating precursor films to prevent charge transfer at the interface. Finally, the chapter closes by briefly mentioning alternative methods for estimating DNA hybridization at the interface.