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Fabrication of Switchable Resistor/Schottky Barrier Memory Cell

IP.com Disclosure Number: IPCOM000075979D
Original Publication Date: 1971-Dec-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Anacker, W: AUTHOR [+3]

Abstract

When memory cells are formed using switchable resistors, such as niobium oxide devices, and series connected diodes or Schottky barriers, a problem arises if diffusions into a silicon substrate are to be used for the Y lines of the memory. The doping level required for the Y lines is higher than that required for the Schottky barriers and, therefore, problems arise in trying to use the diffused lines for both functions. The methods shown above, illustrate two approaches for providing regions of controlled doping level in the diffused lines for fabrication of the Schottky barriers. Fig. 1 shows the basic memory cell configuration having a plurality of X drive lines X1, X2, X3... and a plurality of intersecting Y drive lines Y1, Y2,... .

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Fabrication of Switchable Resistor/Schottky Barrier Memory Cell

When memory cells are formed using switchable resistors, such as niobium oxide devices, and series connected diodes or Schottky barriers, a problem arises if diffusions into a silicon substrate are to be used for the Y lines of the memory. The doping level required for the Y lines is higher than that required for the Schottky barriers and, therefore, problems arise in trying to use the diffused lines for both functions. The methods shown above, illustrate two approaches for providing regions of controlled doping level in the diffused lines for fabrication of the Schottky barriers. Fig. 1 shows the basic memory cell configuration having a plurality of X drive lines X1, X2, X3... and a plurality of intersecting Y drive lines Y1, Y2,... . Intersecting each X and Y line is a memory cell comprising diode 1 and bistable resistor 2. These bistable resistors are usually made from an insulator having two stable resistance states, such as niobium oxide. The insulator is contacted by electrodes connected to voltage sources, in this case the drivers associated with the X and Y lines.

Figs. 2A-2C illustrate an etch-back method for fabricating each memory cell comprising diode 1 and bistable resistor 2. In this case, the structures are fabricated using Nb-Si as the Schottky barriers and Nb-Nb(2)O(5)-Bi as the bistable elements. Whereas diode 1 in Fig. 1 could be a PN junction diode or a zener diode, Schottky barriers are preferable and it is this type of diode which is illustrated in Figs. 2A-2C.

In Fig. 2A, a silicon substrate 3 has a diffused N+ region 4 located therein. There will be a plurality of these diffusions 1 extending across substrate 3 in stripes which will serve as the diffused Y lines (Fig. 1). Located over substrate 3 are SiO(2) layers 5 which serve as a mask for the N+ diffusion 4.

Fig. 2A-1 illustrates the doping level of diffusion 4 measured from the surface of substrate 3. The doping level is maximum at the surface of diffusion 4 and decreases in a Z direction (as the depth of the diffusion into the substrate 3 increases). Although high-doping densities are required if the diffusions 4 are to be used as Y drive lines, the doping level at the surface of diffusion 4 is...