Multi-gate nor flash thin-film transistor strings arranged in stacked horizontal active strips with vertical control gates
First Claim
1. A NOR string array formed over a planar surface of a semiconductor substrate, comprising a first NOR string and a second NOR string, each NOR string comprising thin-film storage transistors formed along an active strip extending lengthwise along a first direction parallel to the planar surface, wherein the thin film storage transistors in each NOR string share a pre-charge device, a common drain terminal and a common source terminal, wherein a gate terminal of each storage transistor in the first NOR string is electrically connected to a gate terminal of a corresponding storage transistor in the second NOR string by a conductor that extends lengthwise along a second direction which is substantially perpendicular to the planar surface, and wherein the pre-charge device pre-charges the common source terminal to a voltage that is substantially held by virtue of a parasitic capacitance in the source terminal during a program, program-inhibit, reading or erasing operation on the NOR string, further comprising a third NOR string, wherein the first NOR string and the third NOR string are formed on a plane parallel the planar surface, wherein one or more storage transistors on the third NOR string are programmed to have reference threshold voltages, which are compared to threshold voltages of storage transistors in the first NOR string during programming or read operations.
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Accused Products
Abstract
Multi-gate NOR flash thin-film transistor (TFT) string arrays (“multi-gate NOR string arrays”) are organized as stacks of horizontal active strips running parallel to the surface of a silicon substrate, with the TFTs in each stack being controlled by vertical local word-lines provided along one or both sidewalls of the stack of active strips. Each active strip includes at least a channel layer formed between two shared source or drain layers. Data storage in the TFTs of an active strip is provided by charge-storage elements provided between the active strip and the control gates provided by the adjacent local word-lines. Each active strip may provide TFTs that belong to one or two NOR strings, depending on whether one or both sides of the active strip are used.
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Citations
16 Claims
- 1. A NOR string array formed over a planar surface of a semiconductor substrate, comprising a first NOR string and a second NOR string, each NOR string comprising thin-film storage transistors formed along an active strip extending lengthwise along a first direction parallel to the planar surface, wherein the thin film storage transistors in each NOR string share a pre-charge device, a common drain terminal and a common source terminal, wherein a gate terminal of each storage transistor in the first NOR string is electrically connected to a gate terminal of a corresponding storage transistor in the second NOR string by a conductor that extends lengthwise along a second direction which is substantially perpendicular to the planar surface, and wherein the pre-charge device pre-charges the common source terminal to a voltage that is substantially held by virtue of a parasitic capacitance in the source terminal during a program, program-inhibit, reading or erasing operation on the NOR string, further comprising a third NOR string, wherein the first NOR string and the third NOR string are formed on a plane parallel the planar surface, wherein one or more storage transistors on the third NOR string are programmed to have reference threshold voltages, which are compared to threshold voltages of storage transistors in the first NOR string during programming or read operations.
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16. A NOR string array formed over a planar surface of a semiconductor substrate, comprising a first NOR string and a second NOR string, each NOR string comprising thin-film storage transistors formed along an active strip extending lengthwise along a first direction parallel to the planar surface, wherein the thin film storage transistors in each NOR string share a pre-charge device, a common drain terminal and a common source terminal, wherein a gate terminal of each storage transistor in the first NOR string is electrically connected to a gate terminal of a corresponding storage transistor in the second NOR string by a conductor that extends lengthwise along a second direction which is substantially perpendicular to the planar surface, and wherein the pre-charge device pre-charges the common source terminal to a voltage that is substantially held by virtue of a parasitic capacitance in the source terminal during a program, program-inhibit, reading or erasing operation on the NOR string, wherein the first NOR string and the second NOR string are formed on first and second planes parallel to the planar surface, respectively, the NOR string array further comprising one or more reference NOR strings on each of the first and second planes, and wherein for each of the reference NOR strings, one or more storage transistors on the reference NOR string are programmed to have reference threshold voltages, which are compared during programming and read operations to threshold voltages of storage transistors in the corresponding NOR string on the same plane as the reference NOR string.
Specification