1. Field of the Invention
The disclosed method relates generally to use of multi-state materials, such as chalcogenide, in semiconductor devices and, more particularly, relates to formation of a three-dimensional container diode that may be used in conjunction with a multi-state material memory element to form an electrical memory cell.
2. Description of Related Art
Multi-state materials are materials that can be caused to change physical states in response to an input stimulus. The use of programmable variable resistance materials, such as chalcogenide, amorphous silicon, or antifuse in electronic memories is known in the art. By way of example, chalcogenides are materials that may be electrically stimulated to change states and resistivities, from an amorphous state to a crystalline state, for example, or to exhibit different resistivities while in a crystalline state. A chalcogenide material may be predictably placed in a particular resistivity state by running a current of a certain amperage through it. The resistivity state so fixed will remain unchanged unless and until a current having a different amperage within the programming range is run through the chalcogenide material. Because of these unique characteristics, chalcogenide materials may be used in memory cells for storing data in binary or higher-based digital systems.
A chalcogenide-based memory cell typically includes a chalcogenide memory element for storing data and an access element, coupled to the memory element, for use in programming and sensing the stored data. The access element may be, in one embodiment, a diode. A chalcogenide-based memory cell will typically be accessible to external circuitry by the selective application of voltages to address lines, as are conventionally used in semiconductor memories.
Because of the unique operating characteristics of chalcogenide-based memories, control of current flow is crucial to facilitate programming. Programming of chalcogenide requires large current densities. In this regard, it is desirable that a chalcogenide-based memory cell include a diode large enough to permit a large current flow in the forward direction, while allowing essentially no current flow in the reverse direction. Conventional junction diode structures large enough to supply the necessary current require so much space on the upper surface of the silicon substrate that they negate the space-saving advantages of using chalcogenide in memories. Accordingly, there is a need for a small, easily manufactured diode that can meet the performance requirements of chalcogenide-based memory cells.
This invention in one respect is a multi-state material-based memory cell having a first node and a second node, and including a diode container formed in a container layer. The diode container extends downward into the container layer and the first node is disposed in electrical communication with at least a portion of the perimeter of the container. A diode is disposed inside the container and a multi-state material memory element is electrically coupled between the diode and the second node of the memory cell.
This invention in another respect is a multi-state material-based memory matrix formed on a structure having a container layer and including a plurality of memory cells disposed between a plurality of first address lines and second address lines. Each memory cell includes a first node and a second node, with the first node being electrically connected to one of the first address lines and the second node being electrically connected to one of the second address lines. Each memory cell also includes a multi-state material memory element that is electrically coupled to the second node and a diode that is disposed in a container extending from the top surface of the container layer downward into the container layer. The diode is electrically coupled between the memory element and the first node of each memory cell.
This invention in another respect is a multi-state material-based memory cell having a first node and a second node, and including an oxide layer disposed above a substrate. A diode container extends downwardly into the oxide layer, and the first node is disposed in electrical communication with the perimeter of the container. A diode is disposed inside the container and a multi-state material memory element is electrically coupled between the diode and the second node of the memory cell.
This invention in another respect is a multi-state material-based memory matrix formed on a structure having an oxide layer disposed above a substrate and including a plurality of memory cells disposed between a plurality of first address lines and second address lines. Each memory cell includes a first node and a second node, with the first node being electrically connected to one of the first address lines and the second node being electrically connected to one of the second address lines. Each memory cell also includes a multi-state material memory element that is electrically coupled to the second node and a diode that is disposed in a container having a perimeter and extending from the top surface of the oxide layer downwardly into the oxide layer. The diode is electrically coupled between the memory element and the first node of each memory cell.
This invention in another respect is a method of making a multi-state material-based memory cell having first and second nodes on a substrate. In this method, a first node is formed on the upper surface of the substrate, an oxide layer is formed on the first node, and a diode container is formed by etching an opening into the oxide layer. The inner surface of the diode container is formed to extend from the top surface of the oxide layer downwardly into communication with the first node, and a diode is formed proximate to at least a portion of the inner surface of the container so that it is in contact with the first node. A multi-state material memory element is formed between the diode and the second node of the memory cell.
This invention in another respect is a multi-state material-based memory cell disposed on a substrate and having a first node and a second node. The memory cell includes a diode container having a side extending from the top surface of the substrate downwardly into the substrate, and a diode formed in the substrate in a region proximate to the side of the container. The diode is disposed between the first node and the side of the container, and a multi-state material memory element is electrically coupled between the diode and the second node of the memory cell.
This invention in another respect is a pair of first and second multi-state material-based memory cells disposed on a substrate, each memory cell having a first node and a second node. The pair of memory cells includes a diode container having two opposing sides extending from the top surface of the substrate downwardly into the substrate, and has first and second diodes disposed proximate to the two opposing sides of the container. A first multi-state material memory element is electrically coupled between the first diode and the second node of the first memory cell, and a second multi-state material memory element is electrically coupled between the second diode and the second node of the second memory cell.
This invention in another respect is a method of making a multi-state material-based memory cell having first and second nodes on a substrate. In this method, a diode container is formed by etching a trench into the substrate. The diode container is formed to have an inner surface extending from the top surface of the substrate downwardly into the trench in the substrate, and a diode is formed in the container proximate to at least a portion of the inner surface of the container so that the first node of the memory cell is disposed in contact with the diode. A multi-state material memory element is formed between the diode and the second node of the memory cell.