US Patent 7465995 Resistor structure for ESD protection circuits

A semiconductor device includes an ESD protection device on a substrate, and a resistor having a gate structure overlying a resistor well separating a first doped region coupled to the ESD protection device and a second doped region coupled to a supply voltage for passing an ESD current from the second doped region to the first doped region to turn on the ESD protection device for dissipating the ESD current during an ESD event. The resistor well has an impurity density lower than that of the first and second doped regions for increasing resistance therebetween.