Design and Sensitivity Analysis of a Vertical TFET with Dielectric Pocket for its use as Label Free Biosensor

A comprehensive analysis of a dielectrically modulated vertical tunnel field effect transistor (VTFET) as a label free biosensor is presented in this article. The proposed structure considers an n+ pocket at the source /channel interface and a dielectric pocket at channel/drain interface. The sensitivity of the VTFET biosensor has been investigated, introducing neutral and charged biomolecules of different dielectric constants at the nanogap cavity. The n+ doped pocket introduced at the source/channel junction improves the output characteristics of the proposed VTFET due to its conduction mechanism in both lateral and vertical directions, thereby improving the sensitivity of VTFET biosensor as well. The proposed VTFET biosensor gains the sensitivity in the order of 105 for a fully filled cavity. Moreover, the HfO2 dielectric pocket at the channel/drain interface suppresses the deteriorating ambipolar behaviour and also enhances the ambipolar current sensitivity compared to a VTFET biosensor without dielectric pocket. Thus, it is perceived that the main drawback of TFET, ambipolar nature, has evolved as an advantage for sensing applications. The VTFET biosensor has been analyzed with regards to variations in dielectric constant of cavity, density of charge, length and height of cavity, mole fraction and also operating temperature at a particular bias condition to judge its sensing capability. A status map has been presented where the proposed VTFET biosensor has been compared with some of the significant works reported in literature in terms of sensitivity and selectivity.