Thin film transistors for memory cell array layer selection
Abstract:
In memory devices where a memory cell includes a thin film cell select transistor, selection between layers of such memory cells may further comprise another thin film select transistor. Bitline and wordline encoding suitable for a memory device having a single layer of memory cells may be scaled up to a 3D memory device having two or more memory cell layers. In a DRAM device one layer of (1TFT-1C) cells may include a 2D array of metal-insulator-metal capacitors over an array of TFTs. Additional layers of such 1TFT-1C cells may be stacked monolithically to form a 3D array. Memory cells in each layer may be accessed through a wordline and local bitline. A local bitline of one cell layer may be coupled to global bitline applicable to all cell layers through a layer-selected TFT according to a voltage applied to a layer-select gate voltage.
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