دانلود رایگان ترجمه مقاله ترانزیستور بدون پیوند گیت-دوبل دی الکتریک-گیت-گوناگون (نشریه IOP 2014)

ترانزیستور بدون پیوند گیت-دوبل دی الکتریک-گیت-گوناگون (HGJLT) با اثرات تونل باند-به-باند کاهش یافته در رژیم زیرآستانه

Hetero-gate-dielectric double gate junctionless transistor (HGJLT) with reduced band-to-band tunnelling effects in subthreshold regime

Abstract

We propose a hetero-gate-dielectric double gate junctionless transistor (HGJLT), taking high-k gate insulator at source side and low-k gate insulator at drain side, which reduces the effects of band-to-band tunnelling (BTBT) in the sub-threshold region. A junctionless transistor (JLT) is turned off by the depletion of carriers in the highly doped thin channel (device layer) which results in a significant band overlap between the valence band of the channel region and the conduction band of the drain region, due to off-state drain bias, that triggers electrons to tunnel from the valence band of the channel region to the conduction band of the drain region leaving behind holes in the channel.These effects of band-to-band tunnelling increase the sub-threshold leakage current, and the accumulation of holes in the channel forms a parasitic bipolar junction transistor (n–p–n BJT for channel JLT) in the lateral direction by the source (emitter), channel (base) and drain (collector) regions in JLT structure in off-state. The proposed HGJLT reduces the subthreshold leakage current and suppresses the parasitic BJT action in off-state by reducing the band-to-band tunnelling probability.

1 Introduction

Recently, junctionless transistors (JLT)Œ1, based on Lilienfeld’s device, are being studied to overcome the scaling limitation of MOSFETs due to the simple fabrication steps of JLTs compared with those in conventional MOSFETs. Junctionless transistors do not have any metallurgical p–n junction unlike MOSFETs. They have NCN CN C or PCP CP C structures with thin body and highly doped channel and the source, channel and drain have uniform doping. A JLT is turned off by the depletion of carriers in the channel by a suitable work function difference of gate material and channel and turned on by bulk conduction of current through the thin highly doped channel. Different types of structures for junctionless transistor have also been proposed and fabricated, such as, junctionless nanowire gate-all-around (GAA) architectures, multi-gated nanowire architectures with silicon-on-insulator (SOI) and with bulk substrate, planar junctionless transistor on bulk substrate, planar junctionless transistor with non-uniform doping etc.

Many research works explore the physics of the junctionless transistorŒ4; 5; 8; 9 and the effect of band-to-band tunnelling (BTBT) on their characteristics has been studied in Refs. [10– 15]. The effect of band-to-band tunnelling, in off-state of JLT, has been studied in detail in Ref. [10]. In off-state, the suitable off current is maintained by the depletion of carriers in the channel on applying the work function difference in between the gate metal and the channel (MS/ and on application of drain bias, the conduction band of drain overlaps the valence band of the channel that triggers the electron to tunnel from the valence band of the channel to the conduction band of the drain (n-channel JLT). When an electron tunnels from the valence band of the channel to the conduction band of the drain, it creates holes in the channel and due to accumulation of holes in the channel, a parasitic bipolar junction transistor (n–p–n BJT for channel JLT) is formed in the lateral direction by the source (emitter), channel (base) and drain (collector) regions in JLT structure in off-state.The accumulation of holes increases the potential of a floating-body channel (base of parasitic BJT) and turns on the parasitic BJT by forward biasing the base-emitter junction, resulting in a large drain current (collector current of the BJT) in off-state of JLT. In this context, large static power dissipation due to large leakage current in off-state, which increases with the decrease of gate length from one technological node to the next one, has become a big problem for low standby power (LSTP) applications. Here, band-to-band tunnelling (BTBT) in off-state significantly affects the sub-threshold leakage current, and has to be handled carefully to reduce the static power dissipation.

Recently, the hetero-gate-dielectric tunnel field effect transistors (HGTFETs) have been theoretically proposed16; 17 and also experimentally investigatedŒ18 to improve electrical characteristics. It has been shown that the hetero-gate-dielectric tunnel field effect transistors (HGTFETs) have higher on current, lower ambipolar leakage current and smaller subthreshold slope without sacrificing chip density. The physics of ambipolar leakage current in TFETs is the same as the effect of bandto-band tunnelling in JLTs. Hence, combining the advantages of the hetero-gate-dielectric structure and junctionless transistor, we propose a hetero-gate-dielectric double gate junction- less transistor (HGJLT) to optimize electrical characteristics by reducing the band-to-band tunnelling (BTBT) current in sub threshold regimes. It has been shown that HGJLT has lower sub threshold leakage current and it suppresses the parasitic BJT action.