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Sneak Path Elimination using Switching Heterojunction

IP.com Disclosure Number: IPCOM000076639D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Hovel, HJ: AUTHOR

Abstract

In fabricating memory arrays of negative resistance switching devices and, in particular, two-terminal switching devices such as the Ovshinsky, Niobium Oxide and Hovel heterojunction switching devices, it is often necessary to place a diode or other type rectifying device in series with the switch to prevent "sneak paths" during interrogation. A "sneak path". may be defined as a current path which acts to cause a false low-state reading when the switching or memory device being interrogated is in its high state. A typical "sneak path" is depicted in Fig. A by the dashed line. There, switching device S1 will appear to be in its low-impedance state because of the action of the sneak path, as shown.

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Sneak Path Elimination using Switching Heterojunction

In fabricating memory arrays of negative resistance switching devices and, in particular, two-terminal switching devices such as the Ovshinsky, Niobium Oxide and Hovel heterojunction switching devices, it is often necessary to place a diode or other type rectifying device in series with the switch to prevent "sneak paths" during interrogation. A "sneak path". may be defined as a current path which acts to cause a false low-state reading when the switching or memory device being interrogated is in its high state. A typical "sneak path" is depicted in Fig. A by the dashed line. There, switching device S1 will appear to be in its low- impedance state because of the action of the sneak path, as shown. However, by placing a diode or other type rectifying device in series with each of the switches sneak paths are eliminated, since in the paths at least one of the three series diodes would be reverse biased and, thus, represent a high enough impedance so that switching device S1 would be interrogated as exhibiting a high-impedance state, as it properly should.

There are several disadvantages to using such a diode arrangement, however. One particular disadvantage involves matching the characteristics of the bistable switch to that of the diode. Thus, in order for reliable, practical switching with well-defined high and low-impedance states to occur in, for example, the Hovel switching device, it is necessary that the voltage level at which Hovel switching occurs be greater than the voltage level at which reverse breakdown occurs in the rectifying diode, in the one direction, while in the other direction the voltage level at which the rectifying diode conducts in the forward direction be less than the other voltage level at which Hovel switching occurs. This is more particularly depicted in Fig. B, where it can be seen that the breakdown...