Defect Tolerance for a Capacitance Based Nanoscale Biosensor

A capacitance based nanoscale biosensor and its defect tolerance are explored. The sensor consists of a microchamber that can be filled with the fluid under test. In a two step procedure the capacitance is measured between the upper plate and the lower plate first for (a) benign fluid, and then for (b) the test fluid, potentially containing the antigens. In each of these tests, an on-chip oscillator provides a test signal of selectable frequency. As shown in the paper the output signal can be processed by on-chip digital modules to estimate the capacitance values. A decision is then made not only on the presence/absence of the antigens, but also on the level of concentration in the medium. We describe the fabrication steps for the sensor plane, the 3-D architecture and the detection methodology, efficient circuits on the analog plane, and the J-platform on the digital plane. However, due the confluence of diverse technologies involved, the probability of defects is higher than that encountered in the usual 2-D device. Therefore, we propose defect tolerance for the planes of this 3-D biosensor. For example, on the sensor plane multiple chambers for the test fluid of defect resistant design are provided, rather than just one, and their measurements used for reliable estimates.