Patent Application
20140269001
Not Applicable
The present invention is generally related to resistive switching devices. More particularly, embodiments according to the present invention provide a method and a structure for forming a resistive switching device coupled to a non-linear device. The present invention can be applied to non-volatile memory devices but it should be recognized that the present invention can have a much broader range of applicability.
The inventors of the present invention have recognized the success of semiconductor devices has been mainly driven by an intensive transistor down-scaling process. However, as field effect transistors (FETs) approach sizes less than 100 nm, physical problems such as short channel effect begin to hinder proper device operation. For transistor based memories, such as those commonly known as Flash memories, other performance degradations or problems may occur as device sizes shrink. With Flash memories, a high voltage is usually required for programming of such memories, however, as device sizes shrink, the high programming voltage can result in dielectric breakdown and other problems. Similar problems can occur with other types of non-volatile memory devices other than Flash memories.
The inventors of the present invention recognize that many other types of non-volatile random access memory (RAM) devices have been explored as next generation memory devices, such as: ferroelectric RAM (Fe RAM); magneto-resistive RAM (MRAM); organic RAM (ORAM); phase change RAM (PCRAM); and others.
A common drawback with these memory devices include that they often require new materials that are incompatible with typical CMOS manufacturing. As an example of this, Organic RAM or ORAM requires organic chemicals that are currently incompatible with large volume silicon-based fabrication techniques and foundries. As another example of this, Fe-RAM and MRAM devices typically require materials using a high temperature anneal step, and thus such devices cannot be normally be incorporated with large volume silicon-based fabrication techniques.
Additional drawbacks with these devices include that such memory cells often lack one or more key attributes required of non-volatile memories. As an example of this, Fe-RAM and MRAM devices typically have fast switching (e.g. “0” to “1”) characteristics and good programming endurance, however, such memory cells are difficult to scale to small sizes. In another example of this, for ORAM devices reliability of such memories is often poor. As yet another example of this, switching of PCRAM devices typically includes Joules heating and undesirably require high power consumption.
From the above, a new semiconductor device structure and integration is desirable.
The present invention is generally related to resistive switching devices. More particularly, embodiments according to the present invention provide a method and a structure for forming a resistive switching device coupled to a non-linear device. The present invention can be applied to non-volatile memory devices but it should be recognized that the present invention can have a much broader range of applicability.
In a specific embodiment, a non-volatile memory device is provided. The non-volatile memory device includes a resistive switching device. In a specific embodiment, the resistive switching device includes a first electrode, a second electrode, and a resistive switching element disposed in an intersection region between the first electrode and the second electrode. The resistive switching element can include a silicon material in a specific embodiment. In a specific embodiment, the second electrode includes at least a metal material physically and electrically in contact with the resistive switching material. In a specific embodiment, the non-volatile memory device includes a non-linear device disposed in between the first electrode and the resistive switching element and serially connected to the resistive switching element. The non-linear device is configured to conduct electric current when a voltage greater than a first voltage is applied to the second electrode. The first voltage causes the resistive switching device to change from a first state to a second state in a specific embodiment. Depending on the embodiment, the first state can be a high resistance state and the second state can be a low resistance state. Alternatively, the first state can be a low resistance state and the second state can be a high resistance state.
In a specific embodiment, a method of programming a memory cell in an array of non-volatile memory devices is provided. The method includes providing a plurality of memory cells arranged in an array. Each of the plurality of memory cells includes a resistive switching device and a non-linear device serially coupled to the resistive switching device. In a specific embodiment, the resistive switching device includes at least a first electrode, a second electrode, and a resistive switching material. The resistive switching material includes a silicon material in a specific embodiment. The first electrode includes at least a silver material in a specific embodiment. The non-linear device is disposed between the second electrode and the resistive switching material in a specific embodiment. In a specific embodiment, each of the memory cells has a first current flowing in the respective resistive switching device. The first current can be a dark current in each of the device in a specific embodiment. The method includes selecting a first memory cell and applying a first voltage to the first memory cell. The first voltage is configured to cause the non-linear device, e.g., punch-through diode, to conduct current and to cause the resistive switching device associated with the first memory cell to change from the first state to a second while the first current from other memory cells is blocked from flowing in the first memory cell by a second voltage drop across the respective non-linear device in other memory cells.
According to one aspect of the invention, a non-volatile memory device is described. One device includes a resistive switching device comprising a first electrode, a second electrode, and a resistive switching element, wherein the resistive switching element comprises a silicon material disposed in an overlapping region between the first electrode and the second electrode, wherein the second electrode comprises at least a metal material physically and electrically in contact with the resistive switching material, wherein the resistive switching element is characterized by a resistance depending on an electric field in the resistive switching element. A device may include a non-linear device coupled between the first electrode and the resistive switching element, wherein the non-linear device is configured to conduct electric current when a voltage greater than a first voltage is applied to the second electrode. In various embodiments, the resistive switching device is configured to change from a first state to a second state in response to the first voltage.
According to another aspect of the invention, a method of programming a memory cell in an array of non-volatile memory devices is described. One technique includes providing a plurality of memory cells arranged in an array, wherein each of the plurality of memory cells comprises a resistive switching device and a non-linear device serially coupled to the resistive switching device, wherein each of the memory cells have a first current flowing in respective resistive switching devices, wherein the resistive switching device comprise at least a first electrode, a second electrode, and a resistive switching material, wherein the resistive switching material comprises a silicon material, wherein the first electrode comprises at least a silver material, and wherein the non-linear device is disposed in between the second electrode and the resistive switching material. A process may include selecting a first memory cell, and applying a first voltage to the first memory cell, wherein the first voltage is greater than a voltage to cause the non-linear device to conduct a first current and to cause the resistive switching device associated with the first memory cell to change from a first state to a second state, while a first current from other memory cells is blocked from flowing in the first memory cell by a second voltage drop across respective non-linear devices associated with other memory cells.
Many benefits can be achieved by ways of present invention over conventional techniques. Embodiments according to the present invention provide a device structure and a programming method for a non-volatile memory device. The device structure includes a non-linear device to suppress leakage current from interfering with write, erase as well as read operations in a specific embodiment. Depending on the embodiment, one or more of these benefits may be achieved. One skilled in the art would recognize other variations, modifications, and alternatives.
In order to more fully understand the present invention, reference is made to the accompanying drawings. Understanding that these drawings are not to be considered limitations in the scope of the invention, the presently described embodiments and the presently understood best mode of the invention are described with additional detail through use of the accompanying drawings in which:
The present invention is directed to switching devices. More particularly, embodiments of the present invention provide a method and device structure for a resistive switching device coupled to a non-linear device, e.g., diode, to prevent leakage current for proper operations of the resistive switching device. Embodiments of the present invention have been applied to a crossbar array of non-volatile memory device using a silicon material as resistive switching material. But it should be recognized that embodiments of the present invention have a broader range of applicability.
High density and low cost storage devices are in ever increasing demand due to the growth in consumer devices common in the market place. Current non-volatile memory devices including Flash are probably approaching an end to further scaling due to fundamental limitations in the devices. It is predicted that current charge storage in a floating gate or a dielectric material in Flash may not be possible in device size less that about 10 nm. A new category of devices using an interconnected crossbar configuration that can be vertically integrated in a three dimensional manner provides a high device density not achievable in current memory devices.
However, leakage current from cells in an interconnected crossbar array can affect proper operations (read, write, or erase) of the device. To suppress the leakage current and to isolate a cell from the leakage current, certain rectifiers can be used. A conventional rectifier usually limits current to flow in a single direction, and can only work for a forward bias operation or a reverse bias operation and not for both. Thus conventional rectifiers are of limited applicability. Certain switching devices can have symmetrical current-voltage (IV) behavior, but such devices do not generally work well in a crossbar array. Other rectifying devices may have a low on-state current but can have poor data retention characteristics. Embodiments of the present invention provide a device structure that includes at least a non-linear device and related methods for a resistive switching device that is rectifying and yet allows current to flow in forward bias as well as in reverse bias operations.
The resistive switching material 104 can include a suitable insulator material having a resistance that can be altered upon application of an electric field to the insulator material. In a specific embodiment, the resistive switching material can include a silicon material. For example, the silicon material can be an amorphous silicon material, a microcrystalline silicon material, a macro crystalline silicon material, a silicon germanium material including any combination of these materials, or the like. In an embodiment, the silicon material includes an amorphous silicon material.
The second electrode 106 can comprise a second conductive material and can have a portion that includes a second metal material. The second metal material can be aluminum, nickel, silver, gold, palladium, platinum, or another similar metal or combination of metals. The second metal material typically is characterized by a suitable diffusivity into the resistive switching material in a specific embodiment. In a specific embodiment, the second electrode 106 is elongated in shape and extends in a second direction that is orthogonal to the first direction, as illustrated in
In certain embodiments, the resistive switching device further includes a contact material 108 disposed between the metal material of the first electrode 102 and the amorphous silicon material 104. The contact material is believed to provide a suitable interfacial defect characteristic for desirable switching behavior for the resistive switching device. For amorphous silicon material as the resistive switching material, the contact material can be p+ polysilicon material, p+ silicon germanium material, or the like. In certain embodiments, the contact material can be optional. The resistive switching device can be disposed in an N by M crossbar array with pillars of resistive switching material 104 located at the crossings of the array, to form a high density interconnected array of non-volatile memory cells.
As shown in
As illustrated in
Due to the interconnectivity of a crossbar structure, when an operating voltage (e.g. e.g. the second positive bias voltage 406) is applied to a selected cell, leakage current from un-selected cells can form a leakage path, that affects operations of the selected cell. Leakage current from the selected cell can also affect the states of unselected cells in the leakage path. As an example of this, in a situation where a selected cell is at a high conductance state, leakage current from the high conductance cell can erase an unselected cell also in the high conductance state in the leakage path.
An example of a programming operation of an embodiment will now be described with respect to
In various embodiments, to prevent or reduce the incidence of the leakage current from affecting operations of the selected cell or to maintain a state of an unselected cell, a rectifier or a diode may be incorporated into the design.
Embodiments according to the present invention provide a device coupled to a resistive switching device, as described above, that addresses this breakdown issue. In various embodiments, the non-linear device is a two terminal device configured to prevent leakage current from unselected cells to interfere with proper operation of a selected cell under conditions of forward bias as well as reversed bias. The non-linear device also prevents leakage current from a selected cell during, for example programming, from unintentionally erasing one or more unselected cells or unintentionally programming one or more unselected cells. In various embodiments, the non-linear device is serially connected to the resistive switching device and can be disposed between the first electrode (
Referring to
In operation, the non-linear device 800 is configured to conduct electric current when a voltage greater than a first voltage, or “punch-through” voltage, is applied. This type of diode may be referred to as a punch-through diode. The first voltage further causes the resistive switching device to change from a first state (e.g. non-conductive) to a second state (e.g. conductive). For example, the first state can be an off state or a high resistance state and the second state can be a programmed state or a low resistance state. In various embodiments, the first voltage can be a programming voltage or a read voltage depending on the embodiment. Embodiments according to the present invention can be applied to a one-time programmable memory device configured in an array, for example in a crossbar array.
Referring again to
Other embodiments of the present invention may include variations to what is illustrated and described above. For example, the non-linear device can have an insulator material sandwiched between a first metal and a second metal or having a metal-insulator-metal (MIM) configuration. The non-linear device can also have a first insulator material and a second insulator material sandwiched between the first metal and the second metal or a metal-insulator-insulator-metal (M-I-I-M) configuration depending on the application. Again, the diode having MIM or MIIM configuration can be disposed between the resistive switching element and the first electrode. And alternatively, the non-linear device having MIM or MIIM configuration can be disposed between the resistive switching element and the second electrode, depending on the application.
The present invention has been exemplified using silver electrode and amorphous silicon material as resistive switching material. The non-linear device can be applied to any two terminal devices to prevent leakage current from proper operation of the two terminal device. Therefore though the present invention has been described using various examples and embodiments, it is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or alternatives in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
The present application claims priority to and is a continuation of U.S. application Ser. No. 13/174,264, filed Jun. 30, 2011, which is herein incorporated by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13174264 | Jun 2011 | US |
| Child | 14106288 | US |
