Research On Tunneling Current Noise Characterization And Measurement Methods In MOSFETs

The scaled-down trend of CMOS devices has led to a dramatically reduce of equivalent gate oxide thickness, gate length and gate area. For conventional body MOSFET, when the oxide thickness is less than 2nm, a great number of carriers can form significant gate leakage current, which get through gate dielectric with different mechanisms. Gate leakage current appears not only in the channel region, but also in the overlap of gate and source / drain region. The current through the gate oxide increases the circuit leakage current, thus increasing the circuit static power consumption, impacting the conduction characteristics of MOS device and even leading to an abnormality. The increase of gate leakage current has become one of the major constraints of device size reduction.In this paper, the components of gate leakage current was discussed, at the same time, we focused on the tunneling process of the MOS structure, analyzed three types of tunneling mechanism, that is, direct tunneling, trap-assisted tunneling and FN tunneling, and gave the corresponding tunneling current model. The gate current in MOS devices are generally divided into three components, namely, gate to channel, gate to the substrate and the current of edge direct tunneling, the characteristics of each component, which changes with gate voltage, was discussed separately in this paper, based on that, at different bias range, the dominant component of tunneling current was discussed, and then the influencing factors of gate tunneling were analyzed.Model and experimental results indicate that gate leakage current fluctuation in ultra-thin gate oxide MOSFET, shows 1 / f noise and white noise components, white noise is close to shot noise (2qI_G ). For small-size device, 1 / f noise component almost is the quadratic function of gate current, power-law relationship exists between gate current noise spectrum density and gate-current. Therefore, two noise models were proposed, respectively based on the direct tunneling current component and non - elastic trap-assisted tunneling TAT, to explain the gate leakage current noise characteristics.Based on the research above, different components of gate leakage current and the corresponding noise measurement methods were proposed, the corresponding schematic diagram, measurement system and specific measurement programs were also given, and the problem which should be paid attention in measurement was discussed at last.