The implanted zener diode (IZD) as an input protection device for MOS integrated circuits

Phosphorus implantation, performed prior to the major standard process steps in p-channel technology, is used for a well controllable reduction of the breakdown voltage of planar diodes down to values which makes them suited as protection devices. In these devices the walk-out of the breakdown voltage, which is characteristic for the field-plated types of protective devices is almost completely eliminated. The dynamic resistance of the implanted diodes can be considerably reduced by providing a second p⁺diffusion which gives rise to parasitic bipolar transistor operation during breakdown. The dynamic resistance is found to be linearly dependent on the width of the space charge layer which is ascribed to microplasma phenomena occuring during breakdown. The overvoltages against which the new devices can offer protection when used in a distributed resistance configuration of 200-µm width, are shown to be in the 10-60-kV range.