Adjustable Bipolar SCR holding voltage for ESD protection circuits in high speed Bipolar/BiCMOS circuits

摘要

The invention provides a Bipolar structure such as a silicon controlled rectifier (SCR) that exhibits advantageously low triggering and holding voltages for use in high speed (e.g., 900 MHz- 2 GHz) submicron ESD protection circuits for Bipolar/BiCMOS circuits. The Bipolar structure features a low shunt capacitance and a low series resistance on the input and output pins, allowing for the construction of ESD protection circuits having small silicon area and little to no impedance added in the signal path. In a preferred aspect of the invention, the SCR is assembled in the N-well of the Bipolar/BiCMOS device, as opposed to the P-substrate, as is customary in the prior art. A preferred aspect of the invention utilizes a Zener diode in combination with a resistor to control BSCR operation through the PNP transistor. The turn-on voltage of the Zener is selected so as to be comparable to the emitter-base breakdown voltage of the NPN structure, which is only slightly higher than the power supply voltage to ensure that the ESD protection circuit will not be triggered under normal circuit operation. During an ESD event, when pad voltage exceeds Zener breakdown voltage, the Zener breaks down, and current flows through an associated (polysilicon) resistor to trigger the PNP of the Bipolar SCR and thus activate the BSCR to conduct the High ESD current from the associated, protected circuit. BSCR resistance and Zener diode breakdown voltage values are selected which permit scaling of ESD protection circuit holding and trigger voltages for optimum compatibility with the power supply voltage.