A 1.0nm silicon nitride (SiN) layer can prevent reaction between HfO2 and Si completely. In this case, the interface state spectra obtained from x-ray photoelectron spectroscopy measurements under bias have two peaks above and below the midgap, attributable to Si dangling bonds interacting weakly with an atom in SiN, indicating a high atomic density of the SiN layer. When a HfO2 layer is deposited on a 1.0nm SiO2 layer, the SiO2 thickness increases to 1.6nm. For this structure, one interface state peak is present near the midgap, attributable to isolated Si dangling bonds, indicating a low atomic density.
This paper described the development of a small and low cost biosensor consisting of a smartphone-based electrochemical biosensor device and a paper-based biosensor. The device harvested power from the smartphone and transferred data through audio jack. We designed CMOS circuits including a power supply circuit, a potentiostat, and a ΔΣ modulator. The fabrication of a paper-based biosensor was simple: the three electrodes were directly drawn on chromatography paper using a carbon pencil. The paper-based biosensor was low cost, disposable, portable and friendly to the environment. The sensing system was designed to perform the chronoamperometry measurement, and the glucose concentration in a liquid specimen was detected. Results showed that the sensing system was capable of measuring the glucose concentration as precisely as expensive equipments.
In this work, we demonstrated that enhancement of electrochemical current due to redox cycling could be accomplished by paper-based biosensor without any expensive microfabrication process. The paper-based sensor had layered structure to generate higher current than a conventional one. We took advantage of the fact that the paper thickness was micrometer-sized (180um), and it defined the distance between two electrochemical electrodes on both sides of the paper. Experimental results showed signatures of the redox cycling, where the electrochemical current from low concentration molecules could be arbitrarily increased by decreasing the distance between electrodes. Such a structure was advantageous for detecting target molecules at very low concentration, proposing a low-cost highly-sensitive biochemcal sensor.
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