SRAM with stacked bit cells
First Claim
1. A static random access memory (SRAM), comprising:
- a plurality of bit cells, each comprising;
a first inverter, comprising a first pull-up transistor and a first pull-down transistor;
a second inverter cross-coupled with the first inverter, comprising a second pull-up transistor and a second pull-down transistor;
a first pass gate transistor coupled between an input of the first inverter and a bit line; and
a second pass gate transistor coupled between an input of the second inverter and a complementary bit line,wherein the plurality of bit cells are divided into a plurality of top tier cells and a plurality of bottom tier cells, and each one of the plurality of bottom tier cells is disposed under a corresponding one of the plurality of top tier cells,wherein the first inverter of each one of the top tier cells is disposed over the second inverter of a corresponding bottom tier cell, and the second inverter of the top tier cell is disposed over the first inverter of the corresponding bottom tier cell; and
wherein drains of the transistors of each top tier cell of the plurality of top tier cells are disposed on a first layer of the substrate, gates of the transistors of the top tier cell are disposed on a second layer under the first layer of the substrate, sources of the transistors of the top tier cell and sources of the transistors of the corresponding bottom tier cell are disposed on a third layer under the second layer of the substrate, gates of the transistors of the corresponding bottom tier cell are disposed on a fourth layer under the third layer of the substrate, and drains of the transistors of the corresponding bottom tier cell are disposed on a fifth layer under the fourth layer of the substrate.
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Accused Products
Abstract
Static random access memories (SRAM) are provided. The SRAM includes a plurality of bit cells. Each bit cell includes a first inverter, a second inverter cross-coupled with the first inverter, a first pass gate transistor coupled between the first inverter and a bit line, and a second pass gate transistor coupled between the second inverter and a complementary bit line. The bit cells are divided into a plurality of top tier cells and a plurality of bottom tier cells, and each of the bottom tier cells is disposed under the individual top tier cell. The first inverter of the top tier cell is disposed on the second inverter of the corresponding bottom tier cell within a substrate, and the second inverter of the top tier cell is disposed on the first inverter of the corresponding bottom tier cell within the substrate.
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Citations
20 Claims
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1. A static random access memory (SRAM), comprising:
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a plurality of bit cells, each comprising; a first inverter, comprising a first pull-up transistor and a first pull-down transistor; a second inverter cross-coupled with the first inverter, comprising a second pull-up transistor and a second pull-down transistor; a first pass gate transistor coupled between an input of the first inverter and a bit line; and a second pass gate transistor coupled between an input of the second inverter and a complementary bit line, wherein the plurality of bit cells are divided into a plurality of top tier cells and a plurality of bottom tier cells, and each one of the plurality of bottom tier cells is disposed under a corresponding one of the plurality of top tier cells, wherein the first inverter of each one of the top tier cells is disposed over the second inverter of a corresponding bottom tier cell, and the second inverter of the top tier cell is disposed over the first inverter of the corresponding bottom tier cell; and wherein drains of the transistors of each top tier cell of the plurality of top tier cells are disposed on a first layer of the substrate, gates of the transistors of the top tier cell are disposed on a second layer under the first layer of the substrate, sources of the transistors of the top tier cell and sources of the transistors of the corresponding bottom tier cell are disposed on a third layer under the second layer of the substrate, gates of the transistors of the corresponding bottom tier cell are disposed on a fourth layer under the third layer of the substrate, and drains of the transistors of the corresponding bottom tier cell are disposed on a fifth layer under the fourth layer of the substrate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A static random access memory (SRAM), comprising:
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a plurality of bit cells, each comprising; a first inverter, comprising a first pull-up transistor and a first pull-down transistor; a second inverter cross-coupled with the first inverter, comprising a second pull-up transistor and a second pull-down transistor; a first pass gate transistor coupled between an input of the first inverter and a bit line; and a second pass gate transistor coupled between an input of the second inverter and a complementary bit line, wherein the bit cells are divided into a plurality of top tier cells formed in a first array and a corresponding plurality of bottom tier cells formed in a second array disposed under the first array, wherein the first pass gate transistor, the second pull-up transistor, and the second pull-down transistor of the top tier cell are disposed in a first column of the first array, and the second pass gate transistor, the first pull-up transistor, and the first pull-down transistor of the corresponding bottom tier cell are disposed in a second column of the second array parallel to and under the first column, wherein sources of the transistors of the top tier cell and sources of the transistors of the corresponding bottom tier cell are disposed between the first and second columns, wherein each top tier cell and corresponding bottom tier cell are coupled to a same bit line and different word lines. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A static random access memory (SRAM), comprising:
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a top tier bit cell coupled to a first word line, a bit line, and a complementary bit line of a metal layer, comprising six transistors in a substrate, wherein drains of the transistors of the top tier cell are disposed on a first layer of the substrate, gates of the transistors of the top tier cell are disposed on a second layer under the first layer of the substrate, and sources of the transistors of the top tier cell are disposed on a third layer under the second layer of the substrate; and a bottom tier bit cell disposed under the top bit cell and coupled to a second word line, the bit line, and the complementary bit line of the metal layer, comprising six transistors in the substrate, wherein sources of the transistors of the bottom tier cell are disposed on the third layer, gates of the transistors of the bottom tier cell are disposed on a fourth layer under the third layer of the substrate, and drains of the transistors of the bottom tier cell are disposed on a fifth layer under the fourth layer of the substrate, wherein the six transistors of the top tier bit cell and the bottom tier bit cell respectively comprise; a first pull-up transistor and a first pull-down transistor, wherein a first inverter is formed by the first pull-up and pull-down transistors; a second pull-up transistor and a second pull-down transistor, wherein a second inverter cross-coupled with the first inverter is formed by the second pull-up and pull-down transistors; a first pass gate transistor coupled between an input of the first inverter and the bit line; and a second pass gate transistor coupled between an input of the second inverter and the complementary bit line, wherein the first and second pass gate transistors of the top tier bit cell are controlled by the first word line, and the first and second pass gate transistors of the bottom tier bit cell are controlled by the second word line. - View Dependent Claims (18, 19, 20)
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Specification