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METHOD FOR SENSOR SUBSTRATE BIAS

IP.com Disclosure Number: IPCOM000006351D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2001-Dec-27
Document File: 1 page(s) / 62K

Publishing Venue

Motorola

Related People

Ira Baskett: AUTHOR

Abstract

The substrate can be biased positive with respect to the P+ interconnects by an alternate method. By mak- ing contact to the small P+ diffusion area with the power supply metal and damaging this P+ to substrate junc- tion by suffGent reverse bias voltage, a low resistance path is formed to allow current to flow (see Figure 1). This starves the parasitic PNP of base current and decreases the back-gate bias of the parasitic MOSFET This technique is similar to the Zener diode zap trim method used in the manufacture of operational amplfi- ers. Further advantage can be gained by applying laser heat during the junction damaging or shorting process. The use of a lower current and voltage level will help to ensure that no other component on the chip is damaged or that no other voltage breakdown will occur, and that maximum productivity can be maintained. Implementing this junction-damage process at water probe will be most cost efficient.

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MOTOROLA INC. Technical Developments Volume 14 December 1991

METHOD FOR SENSOR SUBSTRATE BIAS

by Ira Basketi

THE SOLUTION:

  The substrate can be biased positive with respect to the P+ interconnects by an alternate method. By mak- ing contact to the small P+ diffusion area with the power supply metal and damaging this P+ to substrate junc- tion by suffGent reverse bias voltage, a low resistance path is formed to allow current to flow (see Figure 1). This starves the parasitic PNP of base current and decreases the back-gate bias of the parasitic MOSFET This technique is similar to the Zener diode zap trim method used in the manufacture of operational amplfi- ers. Further advantage can be gained by applying laser heat during the junction damaging or shorting process. The use of a lower current and voltage level will help to ensure that no other component on the chip is damaged or that no other voltage breakdown will occur, and that maximum productivity can be maintained. Implementing this junction-damage process at water probe will be most cost efficient.

Laser Heat Junction

(Optional)

THE PROBLEM:

  Bare element and temperature compensated piezo- resistive silicon pressure sensors do not utilize N+ ditTu- sions as do integrated circuits for emitter and collector contacts. As a result, the substrates are often left floating and are subject to parasitic PNP and MOSFET action between the P+ current conductors due to process varia- tions and media effects.

  A biased field...