Capacitive-coupled non-volatile thin-film transistor NOR strings in three-dimensional arrays
First Claim
1. A memory structure, comprising:
- a semiconductor substrate having a substantially planar surface, wherein the semiconductor substrate has circuitry formed therein;
a first stack of active strips and a second stack of active strips formed over the surface of the semiconductor substrate and separated by a predetermined distance along a first direction, wherein each stack of active strips comprises two or more active strips provided one on top of another on two or more isolated planes and being substantially aligned lengthwise with each other along a second direction substantially parallel to the planar surface, and wherein each active strip comprises a first semiconductor layer of a first conductivity type provided between a second semiconductor layer and a third semiconductor layer each of a second conductivity type, the first, second and third semiconductor layers each comprise polysilicon or silicon germanium;
a charge-trapping material; and
a plurality of conductors each extending lengthwise along a third direction that is substantially perpendicular to the planar surface, each conductor being within a group of the conductors that are provided between the first stack of active strips and the second stack of active strips and separated from each stack of active strips by the charge-trapping material, thereby forming in each active strip at least one NOR string, each NOR string including a plurality of thin film transistors, including two or more thin-film transistors, that are formed out of the first, the second and the third semiconductor layers of the active strip and their adjacent charge-trapping material and the conductors within the group, wherein (a) the first, second and third semiconductor layers in each active strip provide, respectively, channel, source and drain regions of the thin-film transistors, (b) the thin-film transistors of each active strip sharing source and drain regions in common, and (c) one of the shared source and shared drain regions is electrically isolated relative to the circuitry, except when one or more of a selected group of thin-film transistors formed in the active strip are rendered conducting to charge a parasitic or intrinsic capacitor of the electrically isolated shared region by a current through the other shared region to a predetermined voltage.
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Accused Products
Abstract
Multi-gate NOR flash thin-film transistor (TFT) string arrays are organized as three dimensional stacks of active strips. Each active strip includes a shared source sublayer and a shared drain sublayer that is connected to substrate circuits. Data storage in the active strip is provided by charge-storage elements between the active strip and a multiplicity of control gates provided by adjacent local word-lines. The parasitic capacitance of each active strip is used to eliminate hard-wire ground connection to the shared source making it a semi-floating, or virtual source. Pre-charge voltages temporarily supplied from the substrate through a single port per active strip provide the appropriate voltages on the source and drain required during read, program, program-inhibit and erase operations. TFTs on multiple active strips can be pre-charged separately and then read, programmed or erased together in a massively parallel operation.
110 Citations
101 Claims
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1. A memory structure, comprising:
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a semiconductor substrate having a substantially planar surface, wherein the semiconductor substrate has circuitry formed therein; a first stack of active strips and a second stack of active strips formed over the surface of the semiconductor substrate and separated by a predetermined distance along a first direction, wherein each stack of active strips comprises two or more active strips provided one on top of another on two or more isolated planes and being substantially aligned lengthwise with each other along a second direction substantially parallel to the planar surface, and wherein each active strip comprises a first semiconductor layer of a first conductivity type provided between a second semiconductor layer and a third semiconductor layer each of a second conductivity type, the first, second and third semiconductor layers each comprise polysilicon or silicon germanium; a charge-trapping material; and a plurality of conductors each extending lengthwise along a third direction that is substantially perpendicular to the planar surface, each conductor being within a group of the conductors that are provided between the first stack of active strips and the second stack of active strips and separated from each stack of active strips by the charge-trapping material, thereby forming in each active strip at least one NOR string, each NOR string including a plurality of thin film transistors, including two or more thin-film transistors, that are formed out of the first, the second and the third semiconductor layers of the active strip and their adjacent charge-trapping material and the conductors within the group, wherein (a) the first, second and third semiconductor layers in each active strip provide, respectively, channel, source and drain regions of the thin-film transistors, (b) the thin-film transistors of each active strip sharing source and drain regions in common, and (c) one of the shared source and shared drain regions is electrically isolated relative to the circuitry, except when one or more of a selected group of thin-film transistors formed in the active strip are rendered conducting to charge a parasitic or intrinsic capacitor of the electrically isolated shared region by a current through the other shared region to a predetermined voltage. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101)
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Specification