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Random Access, Nonvolatile Memory Array

IP.com Disclosure Number: IPCOM000080915D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Chang, WH: AUTHOR [+2]

Abstract

This high-density random access nonvolatile memory array utilizes charge storage to control the conduction of junction field-effect transistors (FET's).

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Random Access, Nonvolatile Memory Array

This high-density random access nonvolatile memory array utilizes charge storage to control the conduction of junction field-effect transistors (FET's).

A typical memory array layout is shown in Fig. 1. Figs. 2 and 3 show sections of the array. Starting with an N+ semiconductor substrate 10, a P-type epitaxial layer 12 is grown over the substrate. Recessed oxide 14 is utilized to provide isolation pockets in P layer 12. A very thin, 15 to 50 angstrom unit thick layer of tunneling material 14, for example silicon dioxide, and a layer of trapping material 16, for example silicon nitride or aluminum oxide, is then deposited. Conductive metal word lines 18 are applied perpendicular to isolated pockets 12. This structure avoids the necessity of providing individual device diffusions within the array area of the memory and allows for increased density.

The memory operates as follows: 1. Write "0" or Erase. The selected word line (W/L) 20 is lowered to -Vw, for example -25 volts. The bit sense lines B/S remain at ground potential. Since the silicon surface under the selected bit is accumulated, the entire applied potential drops across the insulators and any trapped electrons at the dielectric interface are removed. The bits corresponding to unselected word lines are not disturbed, since no voltage is developed across the insulator material.

2. Write "1". After an erase cycle as in the previous paragraph, a selected word line is raised to +Vw and a selected B/S line is allowed to remain at ground potential, while unselected B/S lines are lowered to the negative potential -Vb/s. The depletion region under the selected bit extends all the way to the N+ subst...