Noise Characteristics in Integrated Biosensing Devices

Recently, there has been much interest in using modified mainstream semiconductor devices for new biological, chemical and environmental applications. One example of such a device (BioFET) being developed is for detection of specific single‐stranded DNA (oligonucleotides) related to identifying pathogens such as E‐coli or campylobacter jejuni. The term “BioFET” is used to describe a FET device whose gate contact and polysilicon are replaced by an electrolyte and a reference electrode. On the surface of the exposed insulator, single‐stranded DNA probes are attached using a functionalization layer. Hybridization of target DNA strands to the probes can be detected as a shift in the threshold voltage of the FET. Noise processes within this system can severely limit the amount of discernable signal from DNA hybridization and this becomes especially true for low density DNA sensing. An optimum biasing point for signal‐to‐noise ratio is given, and the effects of varying different device parameters on the signal‐to‐noise ratio (SNR) performance are demonstrated.