Research On The Turn-on Speed And Temperature Characteristics Of ESD Protection Devices Of ICs

With the rapid development of integrated circuit(IC)technology,the integration degree of IC chips increases continuously,resulting in the decreasing resistance to electrostatic discharge(ESD).The harm of ESD to ICs has thus attracted more and more intensive attention.Although some ESD protection solutions have been applied in high-precision and high-reliability IC products,they may not be suitable for ICs used in high speed and high temperature application areas,where the ESD protection devices require quicker turn-on speed and more stable temperature characteristics.This thesis focuses on making a series of improvements on some important ESD protection devices based on the special IC process features,and studies their turn-on speed and temperature characteristics based on theoretical analyses,experimental tests and Technology Computer Aided Design(TCAD)simulations,which are helpful for improving the reliability of IC products.Major content of this thesis can be summarized as follows.Firstly,the ESD protection test models,the classification of ESD protection levels,the design rules and the transmission line pulse(TLP)test method are introduced.Then the internal current density distribution and working mechanisms of fundamental ESD protection units,such as diode,bipolar transistor(BJT),metal oxide semiconductor(MOS)transistor,silicon controlled rectifier(SCR)and laterally diffused metal oxide semiconductor-SCR(LDMOS-SCR),are analyzed and studied by TCAD simulations.Secondly,the turn-on and operation characteristics of some ESD protection devices are studied under the TLP pulse,and the corresponding improvement methods are proposed.1)For P+ type SCR devices,the turn-on time and principle of P+ grounded SCR device are analyzed under the ESD stress.By structure optimization and improvement,the turn-on speed of P+ floating SCR device increases by 17.70%.2)For cross-bridge SCR devices,the turn-on time and principle of P+ bridge SCR device are analyzed under the ESD stress.The optimized N+ bridge SCR device shows shorter turn-on time through structure improvement.By further replacing the N+ bridge with the NMOS in the device,the turn-on speed of improved device increases by 50.00%.3)For N-well type SCR structures,the turn-on time and principle of the floating N-well SCR device are analyzed under the ESD stress.The turn-on speed of the optimized non-floating N-well SCR increases by 21.43% through structure improvement and gate length optimization.Thirdly,the temperature characteristics of ESD protection devices are studied.1.For the improved SCR devices,the P+ floating SCR exhibits uniform internal current distribution and good temperature characteristics,while the trigger voltage of the cross-bridge SCR increases with increasing temperature.2.For the gate structure ESD protection devices,the current of the gate-controlled diode is mainly concentrated under the gate,resulting in local temperature increasing and easy failure.For the improved LDMOS devices,the threshold voltage decreases and the leakage current increases with increasing temperature.Finally,the dual-directional SCR(DDSCR)triggered by embedded gate-controlled diode and the LDMOS-SCR triggered by embedded NMOS are designed.By introducing two embedded gate-controlled diodes and NMOS in DDSCR and LDMOS devices,respectively,on one hand,the turn-on speed can be increased and the trigger voltage can be reduced;on the other hand,the hold voltage can be increased,and the ESD robustness and temperature characteristics can be improved.The triggering mechanisms and temperature characteristics of the two devices are also analyzed and studied under the ESD stress by TCAD simulations.