Study On The Electronic Properties Of IGBT Under Mechanical Strain

With the advantages of high working voltage and large working current,the Insulated Gate Bipolar Transistor(IGBT)plays an important role in high-power system applications.In order to make the use of the excellent electronic properties of IGBT,therefore,continuous improvement of its packaging module is required.On the other hand,press-pack IGBT model is widely used because of its qualities such as low thermal resistance,low parasitic inductance and double-sided heat dissipation.In addition,it works without bonding lead and welding point.However,the IGBT inside the module will be subjected to biaxial mechanical stress because the components inside the press-pack IGBT are connected by pressure.What's more,the heat generated by the device will aggravate the biaxial mechanical stress,thus,the electronic properties of IGBT will be affected by both of them.The influence of biaxial mechanical stress introduced by press-pack IGBT module on the electronic properties of IGBT has been studied by this thesis and a packaging structure of press-pack IGBT which can introduce biaxial mechanical compressive strain is proposed.The software of COMSOL is used firstly to analyze the press-pack IGBT module,and then,the stress of IGBT derived from the press-pack IGBT module under the condition of mechanical and thermal is studied.The IGBT will be subjected to biaxial mechanical compressive stress,which can reach 170 MPa under the condition of thermo mechanical coupling.Then,by bending the silicon chip,the electronic properties of IGBT chip which are subjected to biaxial mechanical stress are studied and the experiments show that the transconductance of IGBT chip can be increased by 4.5%,the on-voltage drop can be reduced by 0.13 V and the threshold voltage decreases slightly when the biaxial mechanical comprehensive stress of-100 MPa is applied.The turn-off loss can be reduced by 1.5% and the breakdown voltage can be increased by 2.2% when the biaxial mechanical tensile stress of 100 MPa is applied.In order to study how the electronic properties of IGBT can be influenced by stress,the simulation and theoretical analysis of the experiment results are carried out by semiconductor simulation software Sentaurus.It is concluded that the application of biaxial mechanical compressive stress will generally increase the electronic mobility of IGBT and decrease the band gap of silicon materials,which can improve the device transconductance,increase the forward conduction current and decrease the on-voltage drop of the device.Therefore,this thesis has accomplished its task.Based on the study that we have discussed above,a new packaging structure of press-pack IGBT has been proposed by this thesis.This new structure can introduce-500 MPa biaxial mechanical compressive stress into IGBT devices,which can reduce the on-voltage drop by 0.44 v and increase the transconductance by 25% with taking a small cost from the breakdown voltage.