| 摘要 |
An electrostatic discharge (ESD) protection clamp (61) for I/O terminals (22, 23) of integrated circuits (ICs) (24) comprises an NPN bipolar transistor (25) coupled to an integrated Zener diode (30). Variations in the break-down current-voltage characteristics (311, 312, 313, 314) of multiple prior art ESD clamps (31) in different parts of the same IC chip is avoided by forming the anode (301) of the Zener (30) in the shape of a base-coupled P+ annular ring (75) surrounded by a spaced-apart N+ annular collector ring (70) for the cathode (302) of the Zener (30). Even though an angled implant (51, 86, 98) used to form the N+ annular collector ring (70) causes location dependent variations in the width (531, 532) of the Zener space charge (ZSC) region (691, 692), the improved annular shaped clamp (61) always has a portion that initiates break-down at the design voltage so that variations in the width (531, 532) of the ZSC region (691, 692) do not cause significant variations in the clamp's current-voltage characteristics (611, 612, 613, 614).
|
