The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 02, 1986
Filed:
Jul. 18, 1984
Peter E Cottrell, Essex Junction, VT (US);
William J Craig, South Burlington, VT (US);
Ronald R Troutman, Essex Junction, VT (US);
International Business Machines Corporation, Armonk, NY (US);
Abstract
Disclosed is an overvoltage protection structure which when used with CMOS circuits it protects them from overvoltage conditions while minimizing latch-up conditions in the structure. It consists of a well region of an opposite conductivity to that of the substrate defining a pocket region having a conductivity type which is similar to that of the substrate. A first PN junction diode is formed in a portion of the well region and a second PN junction diode is formed in the pocket region. The two diodes have opposite polarity and they both are connected to a signal line in such a way that one of the two diodes will be forward biased if the voltage on the signal line exceeds the bounds of the power supply voltages. The pocket region is connected to a V.sub.SS terminal which is normally grounded and the well region is connected to a power supply V.sub.DD. The doping concentration in the well region is predetermined to have a gradient so that minority carriers injected from one of the diodes in the well region will be repulsed and prevented from moving into the substrate region where they would be majority carriers and they could cause latch-up in the structure or at the very least adversely affect the voltage level of the substrate. Instead the injected carriers recombine in the well region or are collected by the adjacent isolated pocket region. When the second diode is forward biased, the minority carriers are injected into the isolated pocket region and are prevented from reaching the substrate by the underlying well region. This prevents these carriers from affecting the operation of adjacent circuits.