Browse Prior Art Database

Floating Plate Protective Device

IP.com Disclosure Number: IPCOM000087996D
Original Publication Date: 1977-Apr-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 31K

Publishing Venue

IBM

Related People

Huang, YS: AUTHOR

Abstract

This input pad protective device for semiconductor chips protects integrated circuits from electrostatic discharge, especially for MOS metal-oxide semiconductor) integrated circuits having current carrying and/or low input capacitance input/output (I/O) pads and using a conductive field-shield for isolation.

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Floating Plate Protective Device

This input pad protective device for semiconductor chips protects integrated circuits from electrostatic discharge, especially for MOS metal-oxide semiconductor) integrated circuits having current carrying and/or low input capacitance input/output (I/O) pads and using a conductive field-shield for isolation.

Referring to Figs. 1 and 2, a semiconductor substrate 10 is provided with large and small oppositely doped diffusions 12 and 14. On the surface of substrate 10 and surrounding the diffused areas of the protective device is a field structure comprising thin oxide layer 16, polysilicon field shield layer 18 and oxide layer 20. Overlying the field structure is conductive metal line 22 connected at one end to I/O pad 24 and at the other end to the circuit to be protected. Metal line 22 passes over and contacts diffusion 12 to form a large normally reverse biased diode. Capacitively coupled to a large portion of diffusion 12 is a metal capacitor plate 26 having one end connected to the small diffusion 14. A portion of the field shield 18 overlies the edge of diffusion 14 to provide a gated diode to the substrate, since the field shield and substrate are held at the same potential.

When the input voltage on I/O pad 24 is less than the gated diode breakdown voltage, capacitor plate 26 is electrically floating and is serially connected to the substrate through the gated diode. When the input voltage exceeds the breakdown voltage, the...