Research And Design Of ESD Protection Based On SCR Structure

With the rapid development of high-voltage integrated circuits(IC)such as power management chips,LED/LCD drivers,and automotive electronics,strong electrostatic interference has become one of the key reasons affecting the stable operation of the internal circuits of the chip.Therefore,the design is suitable for High-voltage electrostatic discharge(Electrostatic Discharge,ESD)protection devices have become an inevitable requirement.The research focus of this thesis is the design of on-chip ESD protection scheme under high-voltage operating environment.Due to their own conductance modulation effect and many other reasons,the traditional dual-directional SCR(DDSCR)and laterally-diffused metal oxide semiconductor(LDMOS)devices all show the characteristics of low holding voltage and cannot be used in practical protection.In this thesis,the following work is mainly done to optimize the ESD design window of traditional devices:(1)Based on the LDMOS-SCR structure of unidirectional high-voltage protection,in view of the problem of low holding voltage of the device,this thesis proposes a SP-LDMOS-SCR structure with a shunt path,which suppresses the conductance modulation effect by reducing the proportion of the current flowing through the SCR path.The simulation results verify that the trigger voltage of the novel device is 27.8V and the holding voltage is 13.8V,which is 8.2V lower than that of the traditional device,and the holding voltage is increased by 10.6V.(2)Based on the DDSCR structure of bidirectional high voltage protection,in view of the problem that the ESD design window of this device is too wide,this thesis proposes two devices to optimize the ESD design window.The BD-DDSCR device suppresses the conductance modulation effect and current flow of the SCR path by introducing a reverse-biased diode in the conventional DDSCR;The GD-DDSCR device reduces the conductance modulation effect by adding an additional gate structure and forming a reverse-biased diode in the P well,forming another bleeder path on the surface of the device and extending the SCR path.Compared with the DDSCR device,the holding voltage of the two devices is improved to±10.1V and ±14.3V from ±2.4V.(3)Based on the LDMOS-DDSCR structure of bidirectional high voltage protection,this thesis aimed at the problems of high trigger voltage and low holding voltage of the device,which proposes two optimization schemes.The first scheme is to recombine electrons and holes in the well by introducing an electron recombination region,which reduces the carrier concentration in the well and suppresses the gain of the transistor;the second scheme is reducing the electron-hole recombination rate in the well by forming a new shunt path,which reduces the positive feedback effect of the device through this method.Through simulation verification,compared with the traditional device that the trigger voltage of±66.8V and the holding voltage of ±8.9V,the trigger voltage and maintenance voltage of the first scheme are ±49.0V and±17.2V respectively,and the trigger voltage and holding voltage of the second scheme are±33.9V and ±19.3V.