High-speed and low-power differential non-volatile content addressable memory cell and array
View Patent ↗A differential non-volatile content addressable memory array has a differential non-volatile content addressable memory cell which uses a pair of non-volatile storage elements. Each of the non-volatile storage elements can be a split-gate floating gate transistor or a stack gate floating gate transistor having a first terminal, a second terminal, a channel therebetween and a floating gate over at least a portion of the channel to control the conduction of electrons in the channel, and a control gate. The floating gate storage transistor can be in one of two states: a first state, such as erase, in which current can flow between the first terminal and the second terminal, and a second state, such as programmed, in which substantially no current flows between the first terminal and the second terminal. A pair of differential compare data lines connects to the control gate of each of the pair of non-volatile floating gate transistors. A match line connects to the first terminal of each of the pair of non-volatile floating gate transistors to a first voltage. Finally, the second terminals of each storage element is connected to a second voltage, different from the first voltage. A current passing through the memory cell is indicative of a mis-match between the contents of the compare data lines and the contents of the storage elements.
1. A differential non-volatile content addressable memory cell comprising:
a pair of non-volatile storage elements, each having a first terminal, a second terminal, and a control terminal for controlling the flow of current between the first terminal and the second terminal; wherein each of said storage elements is characterized by capable of being in one of two non-volatile states: a first state in which a first current flows between said first terminal and said second terminal, and a second state in which a second current, less than said first current, flows between said first terminal and said second terminal;
a pair of differential data lines, each for connecting to the control terminal of one of said pair of non-volatile storage elements;
a match line connecting to the first terminals of each of said pair of non-volatile storage elements for connecting to a first voltage; and
said second terminals of each of said pair of non-volatile storage elements for connecting to a second voltage, different from said first voltage.
2. The memory cell of claim 1 wherein each of said non-volatile storage elements comprises:
a first terminal in a semiconductor substrate;
a second terminal in said semiconductor substrate;
a channel between said second terminal and said first terminal;
a floating gate disposed over a first portion of said channel and said second terminal and is insulated therefrom; and
a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom.
3. The memory cell of claim 1 wherein each of said non-volatile storage elements comprises:
a first terminal in a semiconductor substrate;
a second terminal in said semiconductor substrate;
a channel between said first and second terminals;
a floating gate disposed over said channel and is insulated therefrom; and
a control gate disposed over said floating gate and is insulated therefrom.
4. The memory cell of claim 2 wherein said second terminals of each of said storage elements in the same memory cell are connected together.
5. The memory cell of claim 1 wherein each of said storage elements comprises:
a first transistor having a first terminal, a second terminal and a gate for controlling the flow of current between the first terminal and the second terminal;
a storage transistor having a third terminal, a fourth terminal a channel between said third terminal and said fourth terminal; a floating gate disposed over a first portion of said channel and said fourth terminal and is insulated therefrom; and a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
wherein said third terminal is connected to said second terminal;
one of said pair of differential data lines is connected to said gate;
said fourth terminal of said storage transistor is said second terminal of said storage element for connection to a second voltage;
a word line connecting the control gates of said storage elements; and
a pair of differential bit lines for connecting to the second terminals of each of said storage elements.
6. The memory cell of claim 1 wherein each of said storage elements comprises:
a first storage transistor having a first terminal, a second terminal a channel between said first terminal and said second terminal; a floating gate disposed over a first portion of said channel and said second terminal and is insulated therefrom; a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
a second storage transistor having a third terminal, a fourth terminal a channel between said third terminal and said fourth terminal; a floating gate disposed over a first portion of said channel and said third terminal and is insulated therefrom; a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
wherein said first terminal is connected to said third terminal;
wherein one of said differential data lines is connected to the control gates of said first and second storage transistors;
wherein said second terminal of said first storage transistor is connected to said match line;
wherein said fourth terminal of said second storage transistor of one storage element is connected to the fourth terminal of said second storage transistor of another storage element; and
wherein said connection of said first and third terminals of each of said storage element is a node to program each of said first and second storage transistors.
7. The memory cell of claim 1 wherein each of said storage elements comprises:
a first storage transistor having a first terminal, a second terminal a channel between said first terminal and said second terminal; a floating gate disposed over a first portion of said channel and said second terminal and is insulated therefrom; a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
a second storage transistor having a third terminal, a fourth terminal a channel between said third terminal and said fourth terminal; a floating gate disposed over a first portion of said channel and said fourth terminal and is insulated therefrom; a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
a control transistor having a fifth terminal, a sixth terminal and a channel between said fifth terminal and said sixth terminal, a gate disposed over said channel and insulated therefrom for controlling the flow of current between said fifth terminal and said sixth terminal;
wherein one of said data lines is connected to the gate of said control transistor;
wherein said control gate of said first storage transistor of one storage element is electrically connected to the control gate of said first storage transistor of another storage element;
wherein said control gate of said second storage transistor of one storage element is electrically connected to the control gate of said second storage transistor of another storage element;
wherein said fifth terminal is connected to said second terminal;
wherein said sixth terminal is connected to said fourth terminal; and
wherein said connection of said fifth and second terminals and the connection of said sixth and fourth terminals of each of said storage element are nodes to program each of said first and second storage transistors.
8. A differential non-volatile content addressable memory array comprising:
a plurality of non-volatile content addressable memory cells arranged in a plurality of rows and columns;
each non-volatile content addressable memory cell comprising a pair of non-volatile storage elements, each having a first terminal, a second terminal, and a control terminal for controlling the flow of current between the first terminal and the second terminal; wherein each of said storage elements is characterized by capable of being in one of two non-volatile states: a first state in which a first current flows between said first terminal and said second terminal, and a second state in which a second current, less than said first current flows between said first terminal and said second terminal;
a pair of differential data lines in each column, each for connecting to the control terminal of one of said pair of non-volatile storage elements in each memory cell of said column;
a match line in each row for connecting to the first terminals of the non-volatile content addressable memory cells in said row; and
said second terminals of each of said pair of non-volatile storage elements for connecting to a second voltage, different from said first voltage.
9. The memory cell of claim 8 wherein each of said non-volatile storage elements comprises:
a first terminal in a semiconductor substrate;
a second terminal in said semiconductor substrate;
a channel between said second terminal and said first terminal;
a floating gate disposed over a first portion of said channel and said second terminal and is insulated therefrom; and
a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom.
10. The memory cell of claim 8 wherein each of said non-volatile storage elements comprises:
a first terminal in a semiconductor substrate;
a second terminal in said semiconductor substrate;
a channel between said first and second terminals;
a floating gate disposed over said channel and is insulated therefrom; and
a control gate disposed over said floating gate and is insulated therefrom.
11. The memory cell of claim 9 wherein said second terminals of each of said storage elements in the same memory cell are connected together.
12. The memory cell of claim 8 wherein each of said storage elements comprises:
a first transistor having a first terminal, a second terminal and a gate for controlling the flow of current between the first terminal and the second terminal;
a storage transistor having a third terminal, a fourth terminal a channel between said third terminal and said fourth terminal; a floating gate disposed over a first portion of said channel and said fourth terminal and is insulated therefrom; and a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
wherein said third terminal is connected to said second terminal;
one of said pair of differential data lines is connected to said gate;
said fourth terminal of said storage transistor is said second terminal of said storage element for connection to a second voltage, wherein said corresponding second terminal of corresponding storage elements in the same row are connected together;
a word line extending in the row direction for connecting the control gates of said storage elements of memory cells in the same row together; and
a pair of differential bit lines extending in the column direction for connecting to the second terminals of each of said storage elements in the same column together.
13. The memory cell of claim 8 wherein each of said storage elements comprises:
a first storage transistor having a first terminal, a second terminal a channel between said first terminal and said second terminal; a floating gate disposed over a first portion of said channel and said second terminal and is insulated therefrom; a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
a second storage transistor having a third terminal, a fourth terminal a channel between said third terminal and said fourth terminal; a floating gate disposed over a first portion of said channel and said third terminal and is insulated therefrom; a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
wherein said first terminal is connected to said third terminal;
wherein one of said differential data lines is connected to the control gates of said first and second storage transistors;
wherein said second terminal of said first storage transistor is connected to said match line;
wherein said fourth terminal of said second storage transistor of one storage element is connected to the fourth terminal of said second storage transistor of another storage element and extends in the row direction connecting to the corresponding fourth terminal of corresponding storage transistors in the same row together; and
wherein said connection of said first and third terminals of each of said storage element is a node to program each of said first and second storage transistors and connecting to the corresponding node in the column direction of memory cells in the same column.
14. The memory cell of claim 8 wherein each of said storage elements comprises:
a first storage transistor having a first terminal, a second terminal a channel between said first terminal and said second terminal; a floating gate disposed over a first portion of said channel and said second terminal and is insulated therefrom; a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
a second storage transistor having a third terminal, a fourth terminal a channel between said third terminal and said fourth terminal; a floating gate disposed over a first portion of said channel and said fourth terminal and is insulated therefrom; a control gate having a first section disposed over a second portion of said channel and insulated therefrom, and having a second section over said floating gate and is insulated therefrom;
a control transistor having a fifth terminal, a sixth terminal and a channel between said fifth terminal and said sixth terminal, a gate disposed over said channel and insulated therefrom for controlling the flow of current between said fifth terminal and said sixth terminal;
wherein one of said data lines is connected to the gate of said control transistor;
wherein said control gate of said first storage transistor of one storage element is electrically connected to the control gate of said first storage transistor of another storage element extending in the row direction connecting to the corresponding control gate of corresponding first storage transistors in the same row direction;
wherein said control gate of said second storage transistor of one storage element is electrically connected to the control gate of said second storage transistor of another storage element extending in the row direction connecting to the corresponding control gate of corresponding second storage transistors in the same row direction;
wherein said fifth terminal is connected to said second terminal;
wherein said sixth terminal is connected to said fourth terminal; and
wherein said connection of said fifth and second terminals and the connection of said sixth and fourth terminals of each of said storage element are nodes to program each of said first and second storage transistors and connecting the corresponding node of memory cells in the same column.