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Reverse Diode NOSR Memory Cell

IP.com Disclosure Number: IPCOM000078310D
Original Publication Date: 1972-Dec-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Herrell, DJ: AUTHOR

Abstract

Fig. 1 shows a typical current-voltage characteristic for a niobium oxide switchable resistor (NOSR). If the negative applied voltage V(m) exceeds some 1 - 1.2 volts, the device rapidly degrades into a nonswitchable avalanche state, indicated by the broken line in Fig. 1. In order to reform a switchable NOSR, a larger pulse than V(+) must thereafter be applied.

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Reverse Diode NOSR Memory Cell

Fig. 1 shows a typical current-voltage characteristic for a niobium oxide switchable resistor (NOSR). If the negative applied voltage V(m) exceeds some 1 - 1.2 volts, the device rapidly degrades into a nonswitchable avalanche state, indicated by the broken line in Fig. 1. In order to reform a switchable NOSR, a larger pulse than V(+) must thereafter be applied.

Previous memory cells employing NOSR devices have used a diode in series with the bistable resistor. The reverse bias breakdown of the diode is V(r). Such a structure is shown in Fig. 2B, while Fig. 2A shows the current-voltage diagram for this memory cell. Because there is typical scattering in value for the voltages V(r),V(-), and V(m) it is very difficult to design an array such that the negative fail threshold is not exceeded by (V(r) + V(f)).

Fig. 3B shows an improved cell design, while Fig. 3A shows the current- voltage characteristic for this improved memory cell. The cell is characterized in that the diode is reversed with respect to the structure shown in Fig. 2B. V' is now the forward voltage drop of the diode and is << V(r). Further, Delta V' << Delta V(r). Therefore, the design problem which occurs when V(f) is exceeded is no longer present.

The device can be formed in a negative quadrant in which the niobium base electrode is at a positive potential rather than the bismuth counter electrode, if this is followed by a small positive current to drive the avalanche s...