Research On The Self-heating Effect And Thermal Hot Carriers Effect Of VDMOS Device

Semiconductor power device is one of the most focuses since the development of integrated circuits.lt is the basis of the core technology to achieve industrial control intelligent and systematic.VDMOS is one of the most distinctive features of the mainstream power devices what has developed form the end of the 20th Century. It has series advantages,such as high withstand voltage、high switching speed, driving ability, good thermal stability and so on. It has widely been used in automotive electronics, motor driver, switching power supply and other fields.As the market share of VDMOS has increased year by year, people put forward higher requirements to the performance of the device.The reliability of VDMOS device is one of the hottest topics discussed at nowadays. The main aim of research the device reliability is to improve the stability through optimization.The domestic and abroad research situation of VDMOS is reviewed in this paper. The power devices brought great economic benefits to the market, but also caused a huge energy consumption and lots of reliability problems. Under this background, A deep research about reliability at high temperature of VDMOS device has be executed in this paper, and as follows:First, Starting from the basic structure and working principle of VDMOS, analyzes the performance parameters of the device. Learned about the device channel is formed by using the self-aligned double diffusion process.Through design P-well doping concentration rational can control channel length effectively what is conducive to improve the device switch speed, operating frequency, and also reduced the conduction resistance to enhance the drive ability at the same time. VDMOS has an epitaxial layer that is the key to having a higher withstand voltage characteristics than ordinary MOS.The Vth, Ron and breakdown voltage and other parameters are focus discussed.And shows the output and transmission characteristic curves.In this letter, the self-heating effect of VDMOS has been made in-depth discussion.Through analyzing the simulation results what obtained by using Silvaco-Atlas, can get to know the high temperature area concentrate distributed at the end of channel and accumulation layer. The output characteristic curve of VDMOS was simulated at the stress of self-heating effect, what come to downtrend after drain voltage reached the saturation point and more obvious at the conditions of large gate voltage. Combined with theoretical analysis reveals the inwardness that the electrical parameters of the device degradation were caused by self-heating effect.Finally, the injury mechanism of VDMOS hot carriers effect at high temperature environment has been discussed in this article. By establishing the substrate current model, the changing processes of substrate current with the bias voltage and temperature was analyzed at last.The results show that:(1) When the bias voltage is fixed, the substrate current decreases first and then increases with the increase of temperature. (2)At the condition of the same temperature, high bias voltage will result in a large of substrate current,while low bias voltage may result in a low substrate current. Combined with theoretical analysis, can establish that the electric field distribution, surface potential, current density degradation under thermal stress were the main factors which lead to substrate current increase. At the end, The degradation condition of threshold voltage, saturation drain current and transfer characteristic curve were showed.