Methods for Forming Nickel Oxide Films for Use With Resistive Switching Memory Devices
Methods for forming a NiO film on a substrate for use with a resistive switching memory device are presenting including: preparing a nickel ion solution; receiving the substrate, where the substrate includes a bottom electrode, the bottom electrode utilized as a cathode; forming a Ni(OH)2 film on the substrate, where the forming the Ni(OH)2 occurs at the cathode; and annealing the Ni(OH)2 film to form the NiO film, where the NiO film forms a portion of a resistive switching memory element. In some embodiments, methods further include forming a top electrode on the NiO film and before the forming the Ni(OH)2 film, pre-treating the substrate. In some embodiments, methods are presented where the bottom electrode and the top electrode are a conductive material such as: Ni, Pt, Ir, Ti, Al, Cu, Co, Ru, Rh, a Ni alloy, a Pt alloy, an Ir alloy, a Ti alloy, an Al alloy, a Cu alloy, a Co alloy, a Ru alloy, and an Rh alloy.
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This application is a divisional claiming priority to U.S. patent application Ser. No. 11/963,656 filed on Dec. 21, 2007, now issued as U.S. Pat. No. 8,283,214, which is incorporated herein by reference in its entirety for all purposes.
BACKGROUNDNon-volatile memory devices based on the resistivity switching of transition-metal oxide materials has become a major focus for developing the next generation universal RAM devices. As may be appreciated, non-volatile memory does not require a constant power supply to retain stored information in contrast to volatile memory, which does require a constant power supply to retain stored information. Thus, non-volatile memory may have advantages for long term storage of critical data.
Many types of materials have been utilized to create non-volatile memory elements. Nickel oxide thin films are one such material. Conventionally, nickel oxide thin films have been prepared through physical-vapor deposition (PVD) methods by reactive sputtering of Ni targets in an O2 enriched environment. In addition, in some examples, conventional methods have generated reproducible resistance switching in an appropriate metal-insulator (NiO thin film)-metal structure with superior performances both in terms of reliability and speed.
Research of nickel oxide thin films has demonstrated that the defect chemistry of those films can play a role in determining the switching performance of the associated memory devices derived from those films. For example, according to some research, the atomic elemental ratio between nickel and oxygen must be carefully controlled to within certain ranges to obtain a desired resistance switching. Current deposition techniques may not provide sufficiently precise control over chemical defects in oxide materials.
As such, methods for forming nickel oxide films for use with resistive switching memory devices are presented herein.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
The present invention will now be described in detail with reference to a few embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.
The illustrative examples presented herein are for clarifying embodiments of the present invention. Theses illustrations are not scale representations of embodiments and should not be construed as so limiting with respect to scale and proportion. In addition, the illustrations provided may, in some examples, represent only a portion of an integrated memory device for clarity. Thus, substrates, dielectric materials, conductive materials, semiconductor features, semiconductor devices, or other associated elements or devices may be specifically excluded for the sole purpose of presenting simplified embodiments.
Non-volatile memory devices based on the resistivity switching of transition-metal oxide materials has been a major focus for developing the next generation universal RAM devices. NiO-based oxide thin films prepared from physical-vapor deposition (PVD) methods by reactive sputtering of Ni targets in O2-containing environments have been demonstrated to be able to generate reproducible resistance switching in an appropriate metal-insulator (NiO thin film)-metal structure. Further, it has been established that the defect chemistry of NiO may play a role in determining the switching performance of NiO thin films. In particular, the atomic elemental ratio between Ni and O can be controlled within certain ranges to obtain the resistance switching. However, in some implementations PVD exhibits poor control over the chemical defects in oxide materials. In addition, PVD can be an expensive deposition method due to the complexity of the PVD equipment and associated consumable parts. Therefore, low-cost chemical deposition methods that can generate NiO films with well-controlled chemical defect levels for the non-volatile memory application may be desirable.
It may be appreciated that electrodes 102 and 106 may be formed in any manner well-known in the art without departing from the present invention including: PVD, CVD, ALD, ECP, and Electroless deposition techniques. In general, memory device 100 forms a memory element equal to one bit. The memory element may have a value of 0 or 1 depending on the resistance across the element. For example, when the resistance across the element is high (e.g., 10 kOhm), the element has a value of 0, and when the resistance is low (e.g., 1 kOhm), the element has a value of 1. The resistance of the element can be changed by changing the resistance of the NiO film 104, which can be changed by applying a voltage across the element (e.g., one voltage to change to a 0, and another voltage to change to 1). The element's value (i.e., resistance) may be determined by using a read voltage that does not disturb the state of the element.
At a next step 304, a substrate is received. A substrate may be received by any configuration capable of performing wet processes without departing from the present invention. As such, in embodiments, a substrate may be immersed in a bath, or may be sprayed in some fashion. Notably, a substrate may include a bottom electrode that may be utilized as a cathode for a subsequent electrochemical deposition step. Referring briefly to
In some embodiments, an electrochemical cleaning may be performed that includes performing an in-situ cathodic reduction in a deposition bath at a potential of −0.4 to −0.7 volts (V) vs. Ag/AgCl (sat. KCl) for 10 to 60 s. In some embodiments, an electrochemical cleaning may be performed that includes performing a cathodic reduction in an H2SO4 solution at a potential of approximately −0.4 to −0.7V vs. Ag/AgCl (sat. KCl) for 10 to 60 s where the H2SO4 solution has a concentration of 0.1 to 1.0 M. As may be appreciated, selection of a chemical cleaning or an electrochemical cleaning may be made on the basis of compatible chemistries without departing from the present invention.
At a next step 310, the method continues to form a Ni(OH)2 film on a substrate. In some embodiments, a Ni(OH)2 film may be formed on a substrate by electrochemically depositing the film on the substrate. As noted above, a substrate may include a bottom electrode that may be utilized as a cathode for a subsequent electrochemical deposition step. Referring briefly to
In other embodiments, an electrochemical deposition may further include utilizing a reference electrode for use with a potential control waveform. In some embodiments, a potential control waveform proceeds under a set of operational parameters including: an applied potential selected to induce a current flow of approximately 50.0 1-A/cm2 to 2.0 mA/cm2; and a potential scan range selected to induce a current flow of approximately 0.05 to 2.00 mA/cm2. In some embodiments, the set of operational parameters more preferably includes: an applied potential selected to induce a current flow of approximately 0.1 to 0.5 mA/cm2. Furthermore, in some embodiments, the reference electrode may include: a hydrogen reference electrode, an Ag/AgCl reference electrode, and a Pt wire pseudo reference electrode. The method then continues to anneal the Ni(OH)2 film.
In some embodiments, co-depositing other materials utilizing techniques described above may be performed. For example, in one embodiment, a Co salt may be co-deposited to form a mixed layer of Co(OH)2/Ni(OH)2. The mixed layer of Co(OH)2 /Ni(OH)2 may then be annealed to form a mixed cobalt oxide and nickel oxide layer. Other mixtures are possible as well without departing from the present invention.
An anneal process may be utilized to convert the Ni(OH)2 film to an NiO film by thermal decomposition of the Ni(OH)2 film 406 as illustrated in
Returning to
While this invention has been described in terms of several embodiments, there are alterations, permutations, and equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. Furthermore, unless explicitly stated, any method embodiments described herein are not constrained to a particular order or sequence. Further, the Abstract is provided herein for convenience and should not be employed to construe or limit the overall invention, which is expressed in the claims. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.
Claims
1. A resistive switching memory element, comprising:
- a first conductive layer;
- a nickel oxide layer formed on the first conductive layer; and
- a second conductive layer formed above the nickel oxide layer;
- wherein the first and second conductive layers are operable as electrodes;
- wherein a resistance of the nickel oxide layer is switchable between two different values by applying a voltage across the electrodes; and
- wherein the nickel oxide layer is formed by electrochemical deposition.
2. The resistive switching memory element of claim 1, wherein the first conductive layer comprises at least one of nickel, platinum, iridium, titanium, aluminum, copper, cobalt, ruthenium, rhenium, or their alloys.
3. The resistive switching memory element of claim 1, wherein the first conductive layer is formed by at least one of physical vapor deposition, chemical vapor deposition, atomic layer deposition, electrochemical plating, or electroless deposition.
4. The resistive switching memory element of claim 1, wherein the nickel oxide layer is formed by electrochemical deposition using the first conductive layer as a cathode.
5. The resistive switching memory element of claim 4, wherein the first conductive layer is chemically or electrochemically cleaned before the nickel oxide layer is formed.
6. The resistive switching memory element of claim 1, wherein the nickel oxide layer is deposited as Ni(OH)2 and converted to NiO by thermal decomposition.
7. The resistive switching memory element of claim 6, wherein the thermal decomposition results from annealing at a temperature between 250 and 800 C.
8. The resistive switching memory element of claim 1, wherein the nickel oxide layer is formed by electrochemical deposition from a Ni(NO3)2 solution.
9. The resistive switching memory element of claim 8, wherein the Ni(NO3)2 solution further comprises an additional nitrate salt.
10. The resistive switching memory element of claim 9, wherein the additional nitrate salt comprises at least one of Co(NO3)2, LiNO3, Mg(NO3)2, or Cr(NO3)3.
11. The resistive switching memory element of claim 10, wherein the Co(NO3)2, LiNO3, Mg(NO3)2, or Cr(NO3)3 is co-deposited with the Ni(NO3)2 to form a mixed layer of Co(OH)2/Ni(OH)2, LiNO3/Ni(OH)2, Mg(NO3)2/Ni(OH)2, or Cr(NO3)3/Ni(OH)2.
12. The resistive switching memory element of claim 11, wherein the mixed layer is converted to a mixed oxide layer by thermal decomposition.
13. The resistive switching memory element of claim 12, wherein the thermal decomposition results from annealing at a temperature between 250 and 800 C.
14. The resistive switching memory element of claim 1, wherein the nickel oxide layer further comprises at least one dopant or at least one alloying element.
15. The resistive switching memory element of claim 1, wherein the nickel oxide layer further comprises at least one of cobalt, lithium, magnesium, or chromium.
16. The resistive switching memory element of claim 1, further comprising a buffer layer between the nickel oxide layer and the second conductive layer.
17. The resistive switching memory element of claim 16, wherein the buffer layer is operable to enhance adhesion.
18. The resistive switching memory element of claim 16, wherein the buffer layer is operable as a diffusion barrier.
19. The resistive switching memory element of claim 1, wherein the second conductive layer comprises at least one of nickel, platinum, iridium, titanium, aluminum, copper, cobalt, ruthenium, rhenium, or their alloys.
20. The resistive switching memory element of claim 1, wherein the second conductive layer is formed by at least one of physical vapor deposition, chemical vapor deposition, atomic layer deposition, electrochemical plating, or electroless deposition.
Type: Application
Filed: Aug 21, 2013
Publication Date: Dec 19, 2013
Applicant: Intermolecular Inc. (San Jose, CA)
Inventors: Zhi-Wen Wen Sun (Sunnyvale, CA), Tony P. Chiang (Campbell, CA), Chi-I Lang (Cupertino, CA), Jinhong Tong (Santa Clara, CA)
Application Number: 13/972,515
International Classification: H01L 45/00 (20060101);