Research And Design Of Strong Robustness ESD Protection Unit Based On SCR Structure

Electrostatic discharge(ESD)refers to the physical phenomenon of charge transfer between two objects with different potential.It exists in any link of people’s daily work and life.There are many ways to generate ESD,such as contact,friction,electromagnetic induction,etc.The characteristics of ESD include high voltage,low charge,short operation time,etc.ESD phenomena often occurs in the manufacturing,transportation and application of integrated circuits.Any personnel and equipment may have ESD events with IC,which is one of the prime reasons results in IC chip damage or failure.ESD protection has not attracted widespread attention because the large critical dimension of early integrated circuits is insensitivity to ESD.With the development of IC manufacturing technology,the critical dimension of the chip decreases continuously,which not only makes the chip more integrated,faster and less power consumption but also makes the chip more sensitive to ESD events.The commonly used ESD protection devices include diode,BJT,MOSFET and silicon controlled rectifier(SCR).SCR structure is one of the best-performing ESD protection devices as known at present.The intrinsic PNP and NPN transistors will provide base current to each other and form positive feedback when SCR turns on and releases ESD current.Hence,SCR has higher current release capability than other ESD protection devices.In other words,SCR structure can discharge more ESD current under the same layout area.But the serious snapback phenomenon will occur after triggering because of the strong positive feedback of SCR device structure.If traditional SCR devices are applied to power pins directly,serious Latch-up effect will occur,which will lead to power supply voltage clamped by SCR.Therefore,if we want to make full use of its strengths and avoid its weaknesses of SCR structure,we must improve the structure.In this paper,the latch-up problem of traditional SCR structure is studied.And several new SCR structures are proposed,which can be applied to power supply or I/O port directly.Before introducing the new device structure,this paper introduces the IV characteristics of traditional ESD protection devices firstly.And then studies the influence of parameters in SCR structure on IV characteristics by simulation,which provides simulation basis for subsequent design.Based on the high holding voltage design window of ESD protection,a new SCR structure with top layers and a high holding voltage SCR device with zp injection are proposed.Based on the high holding current design window of ESD protection,a two-way high holding current SCR device with zn injection is proposed.The IV characteristics of the proposed device are verified by using the simulation TCAD software.The proposed device is verified to be latch-up free by circuit hybrid simulation.Based on a domestic 6-inch 0.5μm process,the high holding voltage SCR device with zp injection and strong robustness is experimentally obtained,and the new device is under test and analyze.