Reduction of direct-tunneling gate leakage current in double-gate and ultra-thin body MOSFETs

The impact of energy quantization on gate tunneling current is studied for double-gate and ultra-thin body MOSFETs. The lower vertical electric field in the channel of these thin-body devices causes a reduction in gate leakage by as much as an order of magnitude. The additional effects of channel doping and high-k dielectrics are also investigated.

Introduction

Continued scaling of transistor gate lengths may require the adoption of novel transistor structures [1] such as the double-gate (DG) or ultra-thin body (UTB) MOSFET [2] (Fig.1). Such devices rely on the thickness of the silicon channel to control short-channel effects by eliminating any leakage paths far from the gate electrode. This may allow for scaling beyond the limitations of the standard bulk MOSFET design. Based on estimates of off-state drain leakage current, these advanced device structures could be scalable down to an ultimate limit of ~10 nm in gate length [3]. Figure 1: a) Bulk, b) Double-Gate (DG), and c) Ultra-Thin-Body (UTB) MOSFET structure cross-sections and energy band diagrams. A broader inversion charge distribution and reduced electric field away from the dielectric interface reduces gate leakage current.