Tunable threshold voltage of a thick field oxide ESD protection device with a N-field implant

摘要

A structure and a process for manufacturing semiconductor devices with improved ESD protection for high voltage applications is described. A thick field gate oxide N channel field effect transistor (FET) device with a tunable threshold voltage (Vt) is developed at the input/output to the internal active circuits for the purpose of providing ESD protection for applications in the 9 volt and higher range. The FET threshold voltage determines the ESD protection characteristics. A N-field implant is used to provide a dopant region under the thick oxide gate element which has the effect of modifying the threshold voltage (Vt) of this device enabling the device turn-on to be "tuned" to more closely match the application requirements of the internal semiconductor circuits. The gate electrical contact is completed by using either a metal gate electrode or polysilicon gate element. The gate and drain of the thick oxide FET device are connected to the input/output connection pad of the internal semiconductor circuits which also enhances ESD protection. The FET source element is connected to another voltage source, typically ground, providing a path to shunt the current from an ESD incident thereby protecting the internal circuitry from damage.