GB1326794A - Stored charge device - Google Patents

Abstract

1326794 Charge storage memory devices CALIFORNIA INSTITUTE OF TECHNOLOGY 11 Aug 1970 [11 Aug 1969] 38666/70 Heading H1M In a charge storage memory device a metal film 42 is deposited on an insulant substrate 40 and carries a first insulant film 44 of e.g. the oxide or nitride of the metal on which a metal e.g. Al film 46 is deposited. The latter is buried in an insulant film 48, e.g. of the metal oxide or nitride on which an outer metal electrode 50 is deposited; the insulant films 44, 48, not being identical but differing in substance and barrier energy to exhibit differential conductance in dependence on high fields with the thicker insulant having the smaller energy barrier (Fig. 1). Film 46 introduces a deep energy well trapping a large charge with high capture probability, and high voltage pulses between 42 and 50 add or remove electrons on negative or positive polarities, which electrons are retained due to insulant films 44, 48. The buried layer 46 may consist of a discontinuous layer assisting the rapid introduction of charge. The device operates as a two terminal memory. A random recess memory comprises an array of storage devices connected at the intersections of X wires 68 and Y wires 66 to X and Y access switches 62, 64 associated with a pulse generator 67 and a current detector 69 (Fig. 2) the array being deposited on a single insulant substrate with the lower electrode comprising the Y strip conductors overlain by oxidized or nitrided layers, a circular metal layer at intersections, a second insulant layer oxidized or nitrited thereon, and a strip conductor overlaying the insulant (Fig. 3, not shown). For write-in a pulse is applied of sufficient potential for the electrons to traverse the insulant and enter or leave the energy well formed by the buried metal layer so as to store a negative or positive charge; the pulse being derived from a generator between the appropriate X and Y access switches to affect the device situated at intersection while leaving other devices unaffected. For partially destructive readout either polarity pulse is applicable with lesser amplitude and the resultant current flow sensed by current detector 69 in series with the pulse generator; the flow amplitude being dependent (Fig. 4, not shown) on the polarity and charge previously stored. For non destructive readout; the array may be scanned by an optical or electron beam respectively effecting internal photoemission over the insulant film barrier light dependent on the stored charge and controlling the photoernission readout current, or sensing the stored charge surface potential for detection as in a scanning electron microscope.