A comparison between bipolar transistor and nanowire field effect transistor biosensors
Important performance metrics, such as sensitivity and signal to noise ratio (SNR) of bipolar transistor based biosensors, are compared to those for nanowire field effect transistor (FET) sensors. The sensor consists of a heterojunction bipolar transistor (HBT) with silicon germanium base connected to a sensing surface in contact with the solution. The measured sensitivity is ≥2 times and SNR is >20 times higher in comparison to those for nanowire FET sensors. More importantly, the HBT biosensor sensitivity is constant over the sensing range of ∼5 decades and depends only on the temperature. In comparison, the nanowire FET sensor sensitivity varies in a complex manner over the sensing range and exhibits significant fabrication induced sensor to sensor variations. Consequently, HBT sensors would require minimal calibration for quantitative sensing studies. Furthermore, the bipolar transistor SNR is not only significantly higher but is also constant over the sensing range. In comparison, the nanowire FET sensor SNR varies with the peak value confined over a narrow sensing range. Hence, HBT sensor has <20 times lower detection limit that remains constant over the sensing range. In summary, HBT sensors are demonstrated to have superior performance metrics and are better suited for quantitative studies. Lastly, these HBT sensors also provide simultaneous temperature measurement.