**3.2. Geometry**

*λ* = √

20 Design, Simulation and Construction of Field Effect Transistors

**Figure 1.** Energy band diagram of a p-i-n TFET showing the on and off states.

amount of ΔΦ at the tunnel junction.

*I*

*WT*,*min* decreases, and drain current increases.

rent as [49].

\_\_\_\_\_\_\_\_\_\_

*ox* (2)

*<sup>q</sup> Wt*,*min*) (3)

and *BK*

are material

(*εs* /*εox*) *t s t*

The dielectric modulation in a MOS-based device, and particularly TFETs is the alteration in the dielectric constant in the gate dielectric region of the device. Keeping other parameters constant, the effect of dielectric modulation in TFET is best explained by the parameters, *λ* and ΔΦ. A low dielectric constant decreases the gate-to-channel coupling as a result of which the tunnel width is more even at high gate voltages, as compared to the presence of higher gate dielectric constants at the tunnel junction [3, 47, 48]. This results in a low tunneling probability, and hence, low tunneling current. Lesser the gate-to-channel coupling, lesser is the

A 2-D Poisson's equation based model of TFET results in a closed form equation of drain cur-

where, *W* is the width of the device, *TSi*,*eff* is the effective Silicon body thickness, *EG* is the band

dependent constants. Equation (3) suggests the dependence of drain current on the minimum tunnel width which, in turn, is dependent on the dielectric constant of the gate insulator region near the tunnel junction. Therefore, as dielectric constant of the nanogap increases,

Another prospect of utilizing dielectric modulation for biosensing is by placing the embedded nanogap towards the channel-drain junction of the TFET, and exploit its ambipolarity [45]. For a conventional n-TFET, when the drain voltage is positive, and gate voltage is negative,

.*exp*(<sup>−</sup> *BK <sup>E</sup>* \_\_\_\_\_\_*<sup>G</sup>*

*E*\_\_\_\_\_ *<sup>G</sup> Wt*,*min* <sup>2</sup> . \_\_\_ *AK BK*

*DS* = *W TSi*,*eff*

gap of the semiconductor, *Wt,min* is the minimum tunneling width, *AK*

As evident from Section 3.1, the objective of utilizing dielectric modulation for biosensing requires a modified geometry with the following basic requirements

