Current memory technologies such as DRAM (dynamic random access memory), SRAM (static RAM), and HAND flash are approaching their scalability limits. There is a growing need for new memory technologies that can meet increasing performance requirements of future memory applications. Memristor technology has the potential to satisfy this need. Memristors rely on drift of mobile charges upon application of an electric field. A memristor comprises a conducting channel disposed between two contacts. A large number of memristors may be fabricated in a crossbar configuration. Memristors offer con-volatile and multiple-state data storage. They are stackable in three dimensions and compatible with CMOS technology. Memristors fabricated of materials such as oxides of tantalum have shown high endurance, in some eases exceeding 1012 on-off cycles.
The figures are not drawn to scale. They illustrate the disclosure by examples.
Illustrative examples and details are used in the drawings and in this description, but other configurations may exist and may suggest themselves. Parameters such as voltages, temperatures, dimensions, and component values are approximate. Terms of orientation such as up, down, top, and bottom are used only for convenience to indicate spatial relationships of components with respect to each other, and except as otherwise indicated, orientation with respect to external axes is not critical. For clarity, some known methods and structures have not been described in detail. Methods defined by the claims may comprise steps in addition to those listed, and except as indicated in the claims themselves the steps may be performed in another order than that given. Accordingly, the only limitations are imposed by the claims, not by the drawings or this description.
Memristor fabrication has suffered from relatively low yields and great variability at small dimensions. This has adversely impacted scalability and controllability of fabrication of these devices.
“Thermal equilibrium” means the channel, region and the containing region are thermodynamically stable with respect to each other. In other words, they do not react with each other chemically even at elevated temperatures.
The channel region may be formed of any material that works as a conducting channel in a memristor system. The channel region may comprise a core and a gradient region. In some examples the channel region comprises a bistable metal-oxide solid solution and an amorphous oxide phase.
The containing region may consist of any insulating phase that is in thermal equilibrium with the channel region.
In an example of a memristor comprising tantalum, the channel region 101 comprises a metal-oxide solid solution of Ta(O) and an amorphous oxide TaOx, and the containing region comprises stoichiometric crystalline Ta2O5. Other material systems may be used. An example of a memristor fabricated, of hafnium includes a channel region of a metal-oxide solid solution of Hf(O) and an amorphous oxide HfOx, and, in thermal, equilibrium with the channel region, a containing region of stoichiometric crystalline HfO2.
In some examples the substrate 305 comprises silicon and the insulating layer 307 comprises silicon dioxide. The first contact 309 may comprise platinum and the second contact 311 may comprise tantalum. If an adhesion layer 313 is used, it may comprise titanium.
Dimensions are not critical and may be selected as appropriate for a device under fabrication. In one example the memristor is about 100 micrometers across. The contacts are each about 100 to 400 nanometers thick, the containing region and channel region are between less than 7 up to about 18 nanometers thick, the insulating layer is about 200 nanometers thick, and the adhesion layer (if used) is about one nanometer thick.
As noted above, the shapes of the examples depicted in the drawings are not critical. The containing region need not be rectangular, and the channel region need not be circular.
An example of a method of fabricating a memristor having a channel region in thermal equilibrium with a containing region is shown in
Memristors with channel regions protected by containing regions with which they are in thermal equilibrium offer improved scalability, endurance, and controllability. Such memristors will better realize the potential of vastly improved memory systems compared with existing memories fabricated with other technologies.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2012/027101 | 2/29/2012 | WO | 00 | 7/10/2014 |
Publishing Document | Publishing Date | Country | Kind |
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WO2013/130064 | 9/6/2013 | WO | A |
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Number | Date | Country | |
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20140346426 A1 | Nov 2014 | US |