Analysis And Design Of Low-voltage Low-power Halo MOSFET

The mainstream of future ULSI technology is toward low-voltage and low-power. Besides optimization of circuit design technology, the structural design of devices is an another important factor. As device dimensions are continually scaled down, undesirable short-channel effects, such as hot carrier effect, DIBL effect and punchthrough are becoming more and more important. To overcome the problems above-mentioned, a compromise between low-voltage and high-speed must be taken for low-power devices.Halo MOSFET is naturally suitable for low-voltage and low-power ULSI, owing to its virtues such as reduced short-channel effect, reduced drift of threshold voltage, sharp subthreshold slope and high switch ratio. But to exert the Halo structural advantages and potential sufficiently, there is much work to be done no only on modeling of Halo MOSFET but numerical simulation. The modeling of Halo MOSFET, including surface potential distribution, threshold voltage, drain current characteristics, as well as breakdown characteristic, are analyzed and investigated.This paper analyzes the structural design requirement in low-voltage and low-power device at first. At present, Halo ion implantation is widely used in low-voltage and low-power MOSFET technologies. For different performance of the deep submicron MOSFET, this work introduces the characteristics of several typical Halo structures and their applications. The processing technique of Halo structure has also be described.Based on the surface potential model of the conventional short-channel devices and the channel characteristics of Halo implantation, the expression of minimum surface potential is obtained by solving 2D Poisson's equation. According to the strong inversion criterion, the threshold-voltage analytical model is derived. The calculation results from this model agree perfectly with simulation results of Medici. Moreover, it is found that LDD devices havesmaller Vth roll-off than convention devices.Taking into account the effects of the regionally distinctive channel dopingconcentration, the analytical drain current models of Halo MOSFET are presented both for strong and weak inversion operation. The models give special considerations for mobility and velocity saturation. The calculation results from the models are shown to agree well with 2D simulation. Meanwhile, the output characteristics of Halo MOSFET and conventional MOSFET are simulated by Medici. From the results, Halo MOSFET are found to have stronger drive current and lower subthreshold current compared to the conventional MOSFET, which satisfies the design requirements for low voltage and low power devices.The breakdown characteristics of Halo LDD MOSFET are simulated, which is compared with other devices. According to breakdown surface electric field, the physical mechanism is analyzed that the breakdown voltage of Halo LDD MOSFET is higher than other devices. Because of the thin gate oxide, the characteristics of gate current versus gate voltage are simulated with Medici in this paper. The breakdown theory is also investigated for the gate oxide. At last, the best thickness of gate oxide is designed by simulation results.The relation between DC resistance and drain voltage is proposed to judge whether the breakdown is happened. When MOSFET is breakdown, the current rises rapidly, DC resistance will drop accordingly. According to the breakdown characteristics of numerical simulation, the drain voltage corresponding to peak point is proposed as breakdown voltage. This method can reduce subjectivity of standards, while it is experience that is used as the criterion to get the breakdown voltage in the past.In a word, this paper presents systemic research on the threshold-voltage analytical model, the drain current analytical model and breakdown characteristics of Halo LDD MOSFET. The calculation results from the models agree perfectly with the simulation results of Medici. The models are of theoretical and apply values to the device modeling in EDA and the research on physical characteristics of Halo MOSFET.