Improvement in the sensing performance of SiGe pocket Si/Ge VTFET based biosensor using extended source electrode and nano-cavity length

In this work, the sensing speed and sensitivity of the dielectric modulated biosensors has been enhanced by incorporating novel approach of source over electrode extension and nano cavity length extension in the SiGe p+ pocket doped Si/Ge vertical TFET , which is named Hetero-Junction Extended Source Electrode Vertical TFET (HJ-ESE-VTEFT). In this regard, the limit of material solubility is overcome by depositing extended electrode over the Ge source and the band gap modulation at the source channel interface is performed by formation of hetero junction due to P+ pocket of SiGe material. Band gap modulation causes band narrowing and results in high speed. On the application of negative bias on the extended source electrode attracts holes from the P+ Ge source and work as add-on in the band narrowing by enhancing the abruptness at the interface. The cavity length, which was initially under the gate electrode is further extended under the source electrode provide larger area to accommodate larger bio-molecules in the cavity through the electrostatic behavior of the device can be changed. In combination, p+ SiGe pocket, Ge Source, Extended source electrode, and extended cavity length give significant improvement in the sensing speed and sensing capabilities of the device. The electrostatic characteristics and then device sensitivity of the conventional VTFET and proposed device are compared to prove the effectiveness of the proposed device. There is an increment of two-order in drain current for the neutral bio-molecules and three-order increment in the charged bio-molecule having dielectric constant of k = 5 has been noticed in the results. The proposed device produces 5.5 times higher bio-molecule sensitivity as compared to the conventional V-TFET device for neutral bio-molecules having dielectric constant of k = 7 and at Vgs = 0.9 V. Moreover, the transit time using the HJ-ESE-VTEFT is 50 % lower as compared to the C-VTFET means the proposed device is 2 times higher sensing speed as compare to the C-VTFET.