Research On IC Electrical Overstress Protection Methods And TVS Device Design

With the rapid development of semiconductor process technology,the integration degree of integrated circuits(ICs)as well as the impact of electrical overstress(EOS)on ICs is becoming higher.The suitable EOS protection for IC products helps to improve the stability and reliability of IC products significantly.Transient voltage suppressors(TVS)can provide effective EOS protection for IC products and have become a research hotspot in the industry.However,most TVS devices on the current market are still unable to meet the requirements of high EOS robustness protection solutions for complicated IC products.Therefore,based on the typical TVS devices,this thesis proposes several unidirectional and bidirectional TVS devices to meet the corresponding EOS protection requirements in different IC products.By ultilizing the Sentaurus simulation and transmission line pulse(TLP)test system,the electrical characteristics and internal physical mechanisms of these novel TVS devices are investigated in detail.The electrical performance of the designed TVS devices are further improved through structure modification and layout optimization.The main research content of this thesis is summarized as follows.Firstly,the characteristics and typical protection methods of EOS are briefly described.The testing methods of EOS protection devices and the TCAD simulation software Sentaurus are introduced.The structure and working characteristics of typical single-direction TVS devices,such as diode and silicon controlled rectifier(SCR),and bidirectional TVS devices such as dual-direction SCR(DDSCR),are described in emphasis.The EOS protection characteristics of these conventional TVS devices are analyzed and verified by using Sentaurus simulation and TLP test system.Secondly,aiming to the single-direction EOS protection requirements of IC products,a variety of new TVS devices have been designed and fabricated,including low-trigger-voltage SCR(LVTSCR),dual-MOS-triggered SCR(DMTSCR)and diode-clamping low-trigger-voltage SCR(DC-LVTSCR).Sentaurus simulation and TLP test results show that the LVTSCR can reduce its trigger voltage effectively by introducing an NMOS in the traditional SCR.However,its low holding voltage increases the latch-up risk.By adding a PMOS in the LVTSCR,the DMTSCR is obtained,whose holding voltage is increased by 5.6 V.By further optimizing the device parameters,the holding voltage of DMTSCR is further increased to 12.6 V.Furthermore,the DMTSCR can pass the 8-V latch-up test,meeting the EOS protection requirements for high-voltage ICs.By embedding a clamping diode and optimizing the topological structure of layout,the obtained DC-LVTSCR shows an increase by 3.6 V in the holding voltage without increasing the device area.By further optimizing the key paramaters,the holding voltage of DC-LVTSCR can be further increased by 29%,making it suitable for EOS protection of ICs with an operating voltage of 8 V.Finally,due to the dual-drection EOS protection requirements of some special ports in IC products,three types of new bidrectional TVS devices,the modified-dual-direction SCR(MDDSCR),the dual-direction low-trigger-voltage SCR(DD-LVTSCR)and the modified-dual-direction low-trigger-voltage SCR(MDD-LVTSCR),are designed and fabricated.Sentaurus simulation and TLP test results show that,compared with the common DDSCR,the bridge injection in the MDDSCR helps to reduce the trigger voltage;compared with the MDDSCR,the PMOS in the DD-LVTSCR helps to further reduce the trigger voltage.However,the holding voltage of the above three devices is still low,leading to certain latch-up risk in some EOS protection applications.Therefore,by adding two floating Pwells inside the DD-LVTSCR,the optimized MDD-LVTSCR exhibits an obviously increased holding voltage and a reduced voltage snapback margin,which can provide a good EOS protection solution for IC products with a power domain of 6-7 V.