Current-voltage (I-V) characteristics of the graphene field effect transistors (GFETs) are measured by the dc, fast I-V (FIV), and pulsed I-V (PIV) methods and analyzed. The hysteresis and conductance in the dc measurement are affected by the sweeping bias range and direction. The I-V curves measured by the FIV method show reduced hysteresis and enhanced conductance at a faster sweeping rate, but are still affected by the sweeping bias range. By applying the PIV method, the hysteresis can be suppressed significantly while the conductance is improved by controlling turn-on, turn-off times (t on and t off ) and the gate bias during t off (V base ) regardless of the sweeping bias range. With short t on , long t off , and V base of 0 V, the hysteresisfree characteristics of GFETs are obtained.

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We report a label-free field-effect sensing array integrated with complementary metal-oxide semiconductor (CMOS) readout circuitry to detect the surface potential determined by the negative charge in DNA molecules. For real-time DNA quantification, we have demonstrated the measurements of DNA molecules without immobilizing them on the sensing surface which is composed of an array of floating-gate CMOS transistors. This nonimmobilizing technique allows the continuous monitoring of the amount of charged molecules by injecting DNA solutions sequentially. We have carried out the real-time quantitative measurement of 19bp oligonucleotides and analyzed its sensitivity as a function of pH in buffer solutions.

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