Design A 150V Radiation Hardened Vdmos (Master Thesis)

Nowadays, the reliability and anti-harsh environment ability of power device have become considerable projects of either modern military or aerospace with the development of information technology industry. The electrical properties of radiation hardened power devices lag far behind commercial ones due to those poor demand as well as special process lines. In that case, it is significant to study on radiation effect and design those power devices with radiation hardened technology compatible with modern process.First, the physical models of VDMOS in different working conditions are analyzed with its structure and process. The breakdown voltage, threshold voltage and on-resistance of VDMOS are discussed in this paper. The application of terminal structure such as field limiting ring and field plate are introduced.Second, the relationship between CIA and breakdown characteristic of transistor is discussed depending on both analytical model and 2-D simulation model of SEB. The quasi light-triggered thyristor model along with new critical condition of SEB is put forward. Both bias effect and position effect are investigated with the help of MEDICI. In addition to the neck region, the most sensitive area to SEB is the border between channel and epitaxy layer. New SEGIB model is put forward due to the SEB Collapse near neck region, which illustrates the combined effect including traditional SEB and gate leakage current. An impact factor γSG is used to determine that effect.Third, a new evaluation method is put forward on the basis of the former determination through simulated quasi-stationary avalanche curves, which combines the quasi-stationary avalanche curves with current response of SEB. The intersection is highlighted to evaluate radiation harden ability precisely. The SOLA point and S parameter are put forward to evaluate the radiation harden ability based on radiation sensitive area after optimization of evaluation method. With the help of the method, different structures are evaluated, including partial SOI, super junction, trench, P+ diffusion and gradient epitaxy. As a result, even though super junction seems not to have significant effect on radiation harden, P+ diffusion and gradient epitaxy do show certain effects while partial SOI and trench reveal outstanding performances.At last, VDMOS and its layout are designed with gate-last process, gradient epitaxy and P" diffusion used as radiation harden process. The simulation results of VDMOS show that, the breakdown voltage is 155V, threshold voltage is about 3.2V, continuous drain current is over 20A, on-resistance is less than 0.05Ω and radiation harden performance is remarkable.