**Abstract**

Tunnel Field Effect Transistors (TFETs) have appeared as an alternative candidate of "beyond CMOS" due to their advantages like very low leakage current and steep sub-threshold slope i.e. <60 mV/dec., etc. From past decades, researchers explored TFETs in terms of high ON current and steep subthreshold slope at low supply voltage i.e. < VDD = 0.5 V. The reliability issues of the device have profound impact on the circuit level design for practical perspectives. Noise is one of the important parameters in terms of reliability and very few research papers addressed this problem in comparison to other parameter study. Therefore, in this chapter, we discussed the impact of noise on Tunnel FET devices and circuits. The detail discussion has been done for the random telegraph noise, thermal noise, flicker noise, and shot noise for Si/Ge TFET and III-V TFETs. Recent research work for both low frequencies as well high frequency noise for different TFET device design has been discussed in details.

**Keywords:** Band-to-Band Tunneling, Flicker noise, Shot noise, Thermal noise, Random Telegraph Noise

#### **1. Introduction**

The semiconductor industry has been on a continuous run to search for miniaturized devices without compromising the electrical parameters [1]. Scaling down the device dimensions of *metal–oxide–semiconductor field-effect transistor* (MOSFET) has been very challenging due to the short channel effects like high subthreshold slope, high leakage current, and threshold voltage roll-off, etc. [2]. Tunnelingfield-effect-transistor (TFET) has appeared as a potential substitute to replace already existing MOSFET because of small leakage current and steep Subthreshold Swing (SS) [3, 4]. The basic difference between the MOSFET and TFET is the working principle. In MOSFET the current through the channel is set by an energy barrier and the height of the barrier determines the amount carriers injected into the channel thermionically. But in TFET, the charge carriers tunnel through the barrier to reach the channel [5]. TFET is gated reverse-biased pin diodes that operate on Band to Band (BTBT) tunneling principle [6, 7]. In the miniaturized devices operating on low voltages, the electrical noise has a serious effect on the device performance [8, 9]. The non-white noises like flicker noise and burst noise become more vigorous as we scale down the device dimensions, which degrades the performance of semiconductor memories [10] and analog circuits [11]. Also, highfrequency white noise sources like shot noise and thermal noise are desirable in

analog/Radio-frequency (RF) applications [12]. In the literature, the effect of electrical noise on the performance of TFETs has not been reported much and still under exploration. In the presence of noise, it is quite difficult to comprehend the behavior of TFETs. In the literature, very few works related to the modeling of the impact of high-frequency noise and low-frequency noise on the performance of TFETs have been reported [13, 14]. This paper provides a detail study of types of electrical noise in TFET structures and the modeling of electrical noise in various TFET structures. This paper also elaborates on the basic working principle of TFET along with the device operation.

## **2. Tunnel field effect transistors**

TFET is gated reverse-biased pin diodes that operate on BTBT) tunneling principle [15]. **Figure 1** shows the cross-sectional view of double gate TFET and energy band diagram of TFET for ON and OFF state, in which p-type silicon substrate of length *Lch* is taken. The source and drain regions have lengths of *Ls* and *Ld* with heavily doped p-type and n-type materials. Also, gate oxide of thickness Tox is deposited over a p-type silicon substrate.

When no voltage is applied at the gate terminal, no current flows through the channel. In TFETs, the off-current/leakage current is very small that makes it an energy-efficient device. When a positive bias is applied at the gate terminal, it pushes the conduction band down in the channel region. Thus, a tunneling path is formed between the source band and channel conduction bands.

In heterojunction TFET (HTFET), high ON current and low leakage current can be achieved. The source and channel may have large band gaps in the case of HTFET but at the source-channel interface, the tunneling barrier reduces significantly [16]. The energy band diagram of homojunction and heterojunction TFET is shown in **Figure 2**. In homojunction TFET, the same material is used for the source,

#### **Figure 1.**

*(a) Cross-sectional view of double gate TFET (b) energy band diagram of TFET for ON and OFF state.*

channel, and drain. The barrier height and the bandgap of material are the same. In heterojunction TFET, at the source-channel junction, the barrier height reduces significantly.
