Integrated Biosensor and Interfacing Circuits

Driven by the demand of the bioelectronics market, many biosensors need to work in parallel or in a controllable way to achieve complicated biodetections, however the limited scale, speed, cost, complex signal processing, and bulky circuit routing problems prohibit the discrete biosensor solutions (Drummond et al., 2003). Nowaday biosensor are usually integrated on the same substrate to form biosensor array to improved the scale and efficiency, and solve the signal routing difficulties. CMOS technology emerges since the mid-1960s, and rapidly captured the IC market. The aggressive scaling of CMOS technology following the famous Moore’s Law enables the realization of high-speed digital circuits, analog and mixed-signal circuits, as well as radiofrequency (RF) communication circuits. A single chip monotonically integrating all components of a complex electronics systems or laboratory systems which contain digital, analog, mixed-signal, and RF communication, microelectromechanical systems (MEMS), and other experimental functions, i.e. lab-on-a-chip (LOC) is avidly to be implemented to possess the capabilities of high-efficiency characterization, high-speed complex signal processing and communication, mass production, large scale, low cost, and low power as well. Fortunately, most of the fabrication processes of biosensors are compatible with the standard CMOS technology either directly or via the post-CMOS processes, e.g. DNA sensors fabricated on Si-nanowire (Li et al., 2004) and gold surface (Cheng et al., 2005) etc, which makes it possible to integrate the biosneosr arrays and CMOS IC on a single chip as a CMOS integrated biosensing system (IBS) (Augustyniak et al., 2006; Prakash et al., 2006; Thewes et al., 2005; Han et al., 2007). The CMOS IBS usually composes of four parts in its system circuitry: integrated biosensor array, interfacing circuits, analog-to-digital (A/D) conversion, and digital signal processor (DSP), as shown in Fig. 1(a). In some system requiring feedback controlling during the characterization, digital-to-analog (D/A) converters are also included depending on the applications, as shown in Fig. 1(b). In the system architecture of CMOS IBS, the overall performance such as noise, bandwidth, sensitivity etc are mainly governed by the performances of interfacing circuits which controls the electrolyte potential and directly acquires signals from the integrated biosensor array. The three electrode system, as shown in Fig. 2, is the most popular electrode architecture of the integrated biosensor array in nowadays CMOS IBS. The system is composed of reference electrode, working electrode, and counter electrode (it is also called auxiliary electrode sometimes).