A Study On The Turn Off Failure Mechanism In The Hign Voltage IGBT

A new generation of power device IGBT because of its high breakdown voltage,low forward voltage, was widely used in civilian fields, commercial fields, and othermany kinds of fields in the national economy. Its reliability is directly related to thesecurity and stability of the application system, so the reliability research in the IGBThas a very important role. The paper focuses on the research of high-voltage IGBT turnoff failure phenomena, explore the underlying mechanism, expected to play a valuablerole in the development of highly reliable IGBT. Meanwhile this paper I analyze theforward conductor characteristic and the blocking characteristic, propose new structureand optimize the corresponding characteristic. The main works of this paper are asfollows:1. This paper will focus on the three parts of IGBT: cell region, termination region,transition region to analyze and explore the turn off failure in high voltage IGBT. Basedon the scholar and own research, we can know the main factor affects the IGBT turn offfailure due to the transition region which combine the cell region and the terminationregion. With simulation tool, I research the current, potential, temperature and otherselectrical properties with the change of the turn off process in the transition zone, theresult show many holes will gather in the transition region make the current andtemperature rise sharply so it will lead to dynamic avalanche breakdown in thetransition zone and even burned. In this paper I propose two new IGBT structures,collector termination having a dielectric layer and termination zone having deep levelimpurity layer, they can reduce the gather phenomena in the transition, reduce the turnoff current. So they can improve the reliability of the IGBT. Meanwhile this paperanalyzes how to improve the reliability of the cell region and termination region,introduces emitter ballast resistors and deep P+structure in the cell, field plate and fieldlimiting ring combined structure and3D-RESURF structure in the termination. In the2500V NPT IGBT item, use the mentioned structure in the cell and termination, it caneffectively prevent the dynamic latch up in the cell region and field plate ignitionphenomena in the termination region. 2. Based on the trench IGBT, I propose a variable trench gate oxide CSTBTstructure which can improve the breakdown voltage，with the simulation，the breakdownvoltage of the conventional CSTBT is1068.7V, the proposed CSTBT is1424.8V. Thispaper also propose a less forward conduction voltage structure called a new carrierstored trench bipolar transistor, it proves this structure will not affect other characteristic,meanwhile it can reduce the10.3%forward conduction voltage when current density is100A/cm~2.