Patent Application
20100283025
Not Applicable.
Not Applicable.
Not Applicable.
1. Field of the Invention
The invention relates to phase-change devices and, in particular, to their architecture and processes for manufacturing.
2. Description of Related Art
The electric resistance of a phase change device varies in wide range under programming pulses. Resistance of phase-change devices can be read and programmed very quickly and do not require power to maintain their value. Therefore, phase change devices are very useful for non-volatile memories.
Other electrical properties of a phase change device (such as threshold switching voltage or capacitance) can be also altered by programming current pulses and values of these properties do not significantly change after programming. Therefore, phase change devices are very useful for reconfigurable electronics.
The high programming current is the main problem of phase change devices. It is possible to decrease the programming current by
Several patents and publications address the problem of high programming current. The only closest prior art documents are described here.
Breakdown device with insulator layer between two phase-change alloy layers is proposed in US Patent Application 20070200202 “Phase change memory structure having an electrically formed constriction” by Nowak and Lu. This device has small programming current but has pure yield (because phase change alloy sometimes not fill the electrically formed aperture) and relatively small endurance and programming current stability (because strong thermal mismatch of insulator and phase change alloy).
Double phase change alloy layer device is proposed in US Patent Application 20080186762 “Phase-change memory element”. This device has small programming current that is very sensitive to ill-controlled slope of pore between two phase change alloy layers and, as the result, different devices have different programming currents, hence it is difficult to create an apparatus that consist of several such devices.
The phase change devices should have small cost and good performance for all applications of these devices.
What is needed in the art is a phase change device with low-energy programming, high endurance, stability and retention and a simple method for such devices manufacturing.
Broadly speaking, the embodiments of the present invention fill industry needs by providing robust and low-energy consuming phase change devices methods for their manufacturing.
New constructions of phase change devices are described in some embodiments of the present invention. A phase change device has native oxide that serves as breakdown layer between two phase change alloy(s) layers in one or more embodiments of the present invention. Methods of the phase change device with native oxide manufacturing are described in some embodiments of the present invention.
The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” embodiment in this disclosure are not necessarily to the same embodiment, and they mean at least one.
Several exemplary embodiments of the invention will now be described in details with reference to the accompanying drawings.
For the sake of simplicity only simplest phase change device and process of its fabrication are described in details below, although one or more embodiments of the invention are applicable for other types of phase change device and manufacturing processes.
A phase change device 100 (
The electrodes 110 and 120 can be made from metals, doped or degenerate semiconductors, superconductors. Electrodes 110 and 120 can be made from the same material or from the different materials, e.g., from TiSiN or carbon.
The layers 120 and 140 can be made from the same or from different phase change alloys based on a chalcogene such as Te or Se or pnictide such as Sb or As, e.g. from Ge—Sb—Te and from In—Sb—Te.
At least one of the first 110 and second 150 electrodes has electrical conductivity equal or large than an electrical conductivity of at least one of the first 120 and second 140 phase change alloys. At least one of the first 110 and second 150 electrodes has thermal conductivity equal to or larger than a thermal conductivity of at least one of the first 120 and second 140 phase change alloys.
The phase change alloy 120 (or 140) has low viscosity above it glass transition temperature and can easily fill the aperture forming during the first electrical pulse that breaks the native oxide 130. In some embodiment the viscosity of the alloy 120 (or 140) is below 5 Poise at the melting temperature.
The native oxide 130 selected from the group consisting germanium oxide, silicon oxide, tellurium oxide, antimony oxide, indium oxide, gallium oxide has thickness below 20 nm, preferably below 3 nm.
The native oxide 130 has the thermal expansion coefficient close (or the same as) to the thermal expansion coefficient of phase change alloy 120 (or 140). The native oxide 130 has a small thermal conductivity close (or the same as) to the thermal expansion coefficient of phase change alloy 120 (or 140). The native oxide 130 has a small thermal boundary resistivity with phase change alloy 120 (or 140).
The breakdown voltage for native oxide 130 is smaller than 20V, preferably smaller than 1V. The breakdown current for native oxide 130 is smaller than 1 mA, preferably smaller than 10 uA. The duration of pulse that break the native oxide 130 is shorter than 1 ms, preferably shorter than 10 ns.
The native oxide 130 blocks electrical current flow between the electrodes 110 and 150 until a breakdown pulse is applied to the electrodes. The breakdown pulse opens an aperture 160 in the native oxide 130 as shown in
Electrical programming of the device 100 by a programming circuit coupled with the phase change device 100 brings a part 170 of at least one of the first and second phase change alloys 120 or/and 140 to a new state. The part 170 shown in
Phase change devices compromise at least K electrodes (K>2), at least L phase change alloy layers (L>2), at least M native oxides of phase change alloys formed on the layers' surfaces (1<M≦L), and at least two of phase change alloy layers are electrically connected with at least two electrodes in some embodiments of this invention.
A flowchart for the device 100 manufacturing is shown in
In order to create the native oxide 130 the chamber for a phase change alloy deposition is filled with oxygen or oxygen-contained gases that contact the upper surface of the first alloy 120 at temperatures between 20 deg. C. and 900 deg. C. in some embodiments.
Electron or ion beam creates a weak spot in native oxide 130 before the second layer 140 deposition during the device fabrication in some embodiments.
The formation method for at least one of the first 110 and second 150 electrodes selected from the group consisting thermal evaporation, spin-on a liquid, vacuum sputtering, chemical vapor deposition, atomic layer deposition, electrolyze. The deposition method for at least one of the first 120 and second 140 phase change alloys selected from the group consisting thermal evaporation, spin-on a liquid, vacuum sputtering, chemical vapor deposition, atomic layer deposition, electrolyze, sol-gel deposition. The deposition material for the first and second phase change alloys can be the same or different, and selected from the group consisting a chalcogenide (e.g. tellurium), a pnictide (e.g. antimony), germanium, silicon, indium, gallium.
At least one of the first and second phase change layers 120 or/and 140 is compromising more than one alloy in some embodiments. The group consisting germanium oxide, silicon oxide, tellurium oxide, antimony oxide, indium oxide, gallium oxide can be formed on the surface of the layer 120 during the native oxide 130 growth in some embodiments.
The electrodes 110 and 150 are formed from the group consisting metals, doped semiconductors, superconductors in some embodiments. The materials for electrodes 120 and 140 can be the same or different in some embodiments. Because the programming part 170 does not contact electrodes 120 and 140, the requirements to these electrodes are not so tight as the requirements for electrodes of phase change devices known in prior art.
The main advantage of some embodiments of this invention is the phase change devices with low programming current that can be manufactured in simple process with high yield. Proposed in some embodiments of this invention devices have high stability of the programming current during device functioning, high endurance and good performance. One skilled in the art can easily produce the phase change devices according to their architecture and manufacturing methods described in embodiments of this invention.
The foregoing description of an example of the preferred embodiment of the invention and the variations thereon have been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description.
This application claims priority to and the benefit of, and incorporates herein by reference in its entirety, U.S. Provisional Patent Application No. 61/215,452 which was filed on May 6, 2010.
| Number | Date | Country | |
|---|---|---|---|
| 61215452 | May 2009 | US |
