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Isolated Buried Reference Zener Diode

IP.com Disclosure Number: IPCOM000043415D
Original Publication Date: 1984-Aug-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Ward, WA: AUTHOR

Abstract

As presently designed in bipolar technologies, Buried Reference Zener Diode anodes are contacted through the substrate using the bottom isolation diffusion (Fig. 1). As a result, the device is sensitive to substrate noise, as well as to substrate voltage shifts. In addition, the anode is electrically common with the substrate, so it can only be biased at the substrate voltage, limiting the circuit applications where it can be used and preventing the use of series Zener diodes. These problems force many designers to use surface Zener diodes, which have a higher Zener voltage and have been shown in some instances to be less stable with time and temperature.

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Isolated Buried Reference Zener Diode

As presently designed in bipolar technologies, Buried Reference Zener Diode anodes are contacted through the substrate using the bottom isolation diffusion (Fig. 1). As a result, the device is sensitive to substrate noise, as well as to substrate voltage shifts. In addition, the anode is electrically common with the substrate, so it can only be biased at the substrate voltage, limiting the circuit applications where it can be used and preventing the use of series Zener diodes. These problems force many designers to use surface Zener diodes, which have a higher Zener voltage and have been shown in some instances to be less stable with time and temperature. The device disclosed here takes advantage of two of the low resistance boron processes to create a Buried Reference Zener Diode whose anode is electrically isolated from the substrate (Fig. 2). The Buried Reference Zener Diode (Fig. 1) uses the available top isolation/PNP emitter diffusion (75 L/sq) as the anode, with contact being made through the substrate. The surface zener diode uses the NPN emitter-base junction in avalanche mode, with a base Rs of 560 L/sq. As shown in Fig. 2, the disclosed device uses the buried Zener diode of Fig. 1, with the 75 L/sq anode, but makes contact through the NPN base (pinch) resistor. The result is an isolated buried Zener diode in parallel with a surface Zener diode. However, because the surface Zener diode, voltage is 1 volt higher (6 v...