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Reducing Series Resistance of a Schottky Barrier Diode Clamp for a NPN Transistor

IP.com Disclosure Number: IPCOM000082277D
Original Publication Date: 1974-Nov-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 2 page(s) / 72K

Publishing Venue

IBM

Related People

Knepper, RW: AUTHOR

Abstract

A method is described for reducing the series resistance of a Schottky barrier diode, used for clamping the collector-base junction of an NPN transistor. An N-type ion implantation (such as arsenic) is used to increase the conductivity of the epitaxial layer deep beneath the metal semiconductor interface. The improved Schottky diode is a more effective clamp preventing transistor saturation at high currents where the Schottky clamp effectiveness is ordinarily limited, due to a large voltage drop across the diode series resistance.

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Reducing Series Resistance of a Schottky Barrier Diode Clamp for a NPN Transistor

A method is described for reducing the series resistance of a Schottky barrier diode, used for clamping the collector-base junction of an NPN transistor. An N-type ion implantation (such as arsenic) is used to increase the conductivity of the epitaxial layer deep beneath the metal semiconductor interface. The improved Schottky diode is a more effective clamp preventing transistor saturation at high currents where the Schottky clamp effectiveness is ordinarily limited, due to a large voltage drop across the diode series resistance.

A cross section of the device structure is shown in Fig. 1. The doping concentration profile is indicated in Fig. 2. The N-type ion implanted region 1 is formed during the process sequence, sometime after the epitaxial layer 2 is grown and before the metal layer 3 is evaporated. One additional masking step is used to define the implanted region 1, so as to prevent intersection with the isolation 4 and the base region 5.

The energy (depth) of the implant and the subsequent thermal cycle are appropriately adjusted causing intersection of the implanted region with the subcollector 6, but preventing extension entirely to the Schottky barrier metal semiconductor interface 7. The doping concentration (conductivity) is, therefore, increased by an order of magnitude or greater throughout the major portion of the epitaxial region under the Schottky contact. However...