U.S. patent application number 10/971387 was filed with the patent office on 2006-04-27 for method of affecting rram characteristics by doping pcmo thin films.
This patent application is currently assigned to Sharp Laboratories of America, Inc.. Invention is credited to David R. Evans, Sheng Teng Hsu, Fengyan Zhang, Wei-Wei Zhuang.
Application Number | 20060088974 10/971387 |
Document ID | / |
Family ID | 36147348 |
Filed Date | 2006-04-27 |
United States Patent
Application |
20060088974 |
Kind Code |
A1 |
Zhuang; Wei-Wei ; et
al. |
April 27, 2006 |
METHOD OF AFFECTING RRAM CHARACTERISTICS BY DOPING PCMO THIN
FILMS
Abstract
A method of fabricating a doped-PCMO thin film layer includes
preparing a PCMO precursor solution having a transition metal
additive therein; and spin-coating the doped-PCMO spin-coating
solution onto a wafer.
Inventors: |
Zhuang; Wei-Wei; (Vancouver,
WA) ; Evans; David R.; (Beaverton, OR) ;
Zhang; Fengyan; (Vancouver, WA) ; Hsu; Sheng
Teng; (Camas, WA) |
Correspondence
Address: |
SHARP LABORATORIES OF AMERICA, INC
5750 NW PACIFIC RIM BLVD
CAMAS
WA
98642
US
|
Assignee: |
Sharp Laboratories of America,
Inc.
|
Family ID: |
36147348 |
Appl. No.: |
10/971387 |
Filed: |
October 21, 2004 |
Current U.S.
Class: |
438/384 ;
257/E21.004; 257/E21.272; 257/E45.003; 438/3; 438/382; 438/385 |
Current CPC
Class: |
C23C 18/1295 20130101;
C23C 18/1225 20130101; H01L 45/1608 20130101; H01L 21/02282
20130101; H01L 45/04 20130101; H01L 21/02197 20130101; H01L 45/147
20130101; C23C 18/1216 20130101; H01L 28/20 20130101; H01L 45/1233
20130101; C23C 18/1283 20130101; H01L 21/31691 20130101; H01L
21/02205 20130101 |
Class at
Publication: |
438/384 ;
438/003; 438/382; 438/385 |
International
Class: |
H01L 21/20 20060101
H01L021/20; H01L 21/00 20060101 H01L021/00 |
Claims
1. A method of fabricating a doped-PCMO thin film layer comprising:
preparing a PCMO precursor solution, including: dehydrating
Ca(OAc).sub.2(H.sub.2O) and Mn(OAc).sub.3(2H.sub.2O); mixing
Pr(OAc).sub.3(H.sub.2O), Ca(OAc).sub.2(H.sub.2O) and
Mn(OAc).sub.3(2H.sub.2O); adding a transition metal additive to the
PCMO precursor solution; dissolving the PCMO chemicals and
transition metal additive in an organic solvent; heating the
doped-PCMO precursor solution at between about 90.degree. to
120.degree. for between about one hour to eight hours; filtering
the doped-PCMO through a 0.2 .mu.m filter; thereby forming
doped-PCMO spin-coating solution; spin-coating the doped-PCMO
spin-coating solution onto a wafer by: injecting the doped-PCMO
spin-coating solution onto a wafer surface; spinning the wafer at
about 2500 RPM for about 45 seconds; baking the coated wafer at
about 180.degree. for about one minute; ramping the baking
temperature up to about 230.degree., and baking for about one
minute; annealing the wafer in a RTA furnace at about 500.degree.
for about five minutes; repeating the spin-coating process at least
three times to fabricate a doped-PCMO layer; and annealing the
wafer at between about 500.degree. to 600.degree. for between about
one hour to six hours in dry, clean air.
2. The method of claim 1 wherein said adding includes selecting a
transition metal additive from the group of transition metal
additives consisting of V, Cr, Co, Fe, Ni, Ti, Zr, Hf, Nb, Ta, Mo W
and Zn.
3. The method of claim 2 wherein said adding includes adding a
transition metal additive in a ranges of between about 0.01 mol %
to 10 mol % of the transition metal additive to the PCMO.
4. The method of claim 1 wherein the organic solvent is acetic acid
to form a doped-PCMO precursor solution.
5. A method of fabricating a doped-PCMO thin film layer comprising:
preparing a PCMO precursor solution, including: dehydrating
Ca(OAc).sub.2(H.sub.2O) and Mn(OAc).sub.3(2H.sub.2O); mixing
Pr(OAc).sub.3(H.sub.2O), Ca(OAc).sub.2(H.sub.2O) and
Mn(OAc).sub.3(2H.sub.2O); adding a transition metal additive to the
PCMO precursor solution, including selecting a transition metal
additive from the group of transition metal additives consisting of
V, Cr, Co, Fe, Ni, Ti, Zr, Hf, Nb, Ta, Mo W and Zn; dissolving the
PCMO chemicals and transition metal additive in an organic solvent;
heating the doped-PCMO precursor solution at between about
90.degree. to 120.degree. for between about one hour to eight
hours; filtering the doped-PCMO through a 0.2 .mu.m filter; thereby
forming doped-PCMO spin-coating solution; spin-coating the
doped-PCMO spin-coating solution onto a wafer by: injecting the
doped-PCMO spin-coating solution onto a wafer surface; spinning the
wafer at about 2500 RPM for about 45 seconds; baking the coated
wafer at about 180.degree. for about one minute; ramping the baking
temperature up to about 230.degree., and baking for about one
minute; annealing the wafer in a RTA furnace at about 500.degree.
for about five minutes; repeating the spin-coating process at least
three times to fabricate a doped-PCMO layer; and annealing the
wafer at between about 500.degree. to 600.degree. for between about
one hour to six hours in dry, clean air.
6. The method of claim 5 wherein said adding includes adding a
transition metal additive in a range of between about 0.01 mol % to
10 mol % of the transition metal additive to the PCMO.
7. The method of claim 5 wherein the organic solvent is acetic acid
to form a doped-PCMO precursor solution.
8. A method of fabricating a doped-PCMO thin film layer comprising:
preparing a PCMO precursor solution, including: dehydrating
Ca(OAc).sub.2(H.sub.2O) and Mn(OAc).sub.3(2H.sub.2O); mixing
Pr(OAc).sub.3(H.sub.2O), Ca(OAc).sub.2(H.sub.2O) and
Mn(OAc).sub.3(2H.sub.2O); adding a transition metal additive to the
PCMO precursor solution, including selecting a transition metal
additive from the group of transition metal additives consisting of
V and Cr; dissolving the PCMO chemicals and transition metal
additive in an organic solvent; heating the doped-PCMO precursor
solution at between about 90.degree. to 120.degree. for between
about one hour to eight hours; filtering the doped-PCMO through a
0.2 .mu.m filter; thereby forming doped-PCMO spin-coating solution;
spin-coating the doped-PCMO spin-coating solution onto a wafer by:
injecting the doped-PCMO spin-coating solution onto a wafer
surface; spinning the wafer at about 2500 RPM for about 45 seconds;
baking the coated wafer at about 180.degree. for about one minute;
ramping the baking temperature up to about 230.degree., and baking
for about one minute; annealing the wafer in a RTA furnace at about
500.degree. for about five minutes; repeating the spin-coating
process at least three times to fabricate a doped-PCMO layer; and
annealing the wafer at between about 500.degree. to 600.degree. for
between about one hour to six hours in dry, clean air.
9. The method of claim 8 wherein said adding includes adding the
transition metal additive in a range of between about 0.01 mol % to
10 mol % of the transition metal additive to the PCMO.
10. The method of claim 8 wherein the organic solvent is acetic
acid to form a doped-PCMO precursor solution.
Description
FIELD OF THE INVENTION
[0001] This invention relates to the preparation of a
P.sub.0.7Ca.sub.0.3MnO.sub.3 (PCMO) spin-coating, thin film
precursor and the doping of a PCMO layer, in order to modify the
PCMO thin film's reversible resistance switch properties.
BACKGROUND OF THE INVENTION
[0002] The reversible resistance switch properties of
Pr.sub.0.7Ca.sub.0.3MnO.sub.3 (PCMO) metal oxide thin films by
applying nanoseconds short electric pulses has been disclosed by
Liu et al., Electric-pulse-induced Reversible Resistance Change
Effect in Magnetoresistive Films, Applied Physics Letters, Vol. 76,
No. 19, pp2749-2751 (2000) and U.S. Pat. No. 6,204,139 B1, to Liu
et al., granted Mar. 20, 2001, for Method for Switching the
Properties of perovskite Materials Used in Thin Film Resistors. The
PCMO thin films described therein were grown on epitaxial
YBa.sub.2Cu.sub.3O.sub.7 (YBCO), or partial epitaxial Pt/LAO
(LaAlO.sub.3), substrates via pulsed laser abrasion (PLA)
techniques. XRD polar figures disclosed in the cited references
indicate conventional epitaxial properties of PCMO thin films, and
indicate that colossal magnetoresistance (CMR) materials have
reversible resistance change property at room temperature.
[0003] The structure of a PCMO thin film integrated with a silicon
wafer is known, and methods to achieve electrically reversible
resistance changes are also known. A method for the synthesis of a
stable spin-coating PCMO precursor solution through the pre-thermal
treatment of Mn(OAc).sub.3(2H.sub.2O) is disclosed in PCMO Spin
Coating Deposition, Ser. No. 10/759,468, filed Jan. 15, 2004.
SUMMARY OF THE INVENTION
[0004] A method of fabricating a doped-PCMO thin film layer
includes preparing a PCMO precursor solution, including:
dehydrating Ca(OAc).sub.2(H.sub.2O) and Mn(OAc).sub.3(2H.sub.2O);
mixing Pr(OAc).sub.3(H.sub.2O), Ca(OAc).sub.2(H.sub.2O) and
Mn(OAc).sub.3(2H.sub.2O); adding a transition metal additive to the
PCMO precursor solution; dissolving the PCMO chemicals and
transition metal additive in an organic solvent; heating the
doped-PCMO precursor solution at between about 90.degree. to
120.degree. for between about one hour to eight hours; filtering
the doped-PCMO through a 0.2 .mu.m filter; thereby forming
doped-PCMO spin-coating solution; spin-coating the doped-PCMO
spin-coating solution onto a wafer by: injecting the doped-PCMO
spin-coating solution onto a wafer surface; spinning the wafer at
about 2500 RPM for about 45 seconds; baking the coated wafer at
about 180.degree. for about one minute; ramping the baking
temperature up to about 230.degree., and baking for about one
minute; annealing the wafer in a RTA furnace at about 500.degree.
for about five minutes; repeating the spin-coating process at least
three times to fabricate a doped-PCMO layer; and annealing the
wafer at between about 500.degree. to 600.degree. for between about
one hour to six hours in dry, clean air.
[0005] It is an object of the invention to fabricate a doped-PCMO
layer in a single deposition step.
[0006] This summary and objectives of the invention are provided to
enable quick comprehension of the nature of the invention. A more
thorough understanding of the invention may be obtained by
reference to the following detailed description of the preferred
embodiment of the invention in connection with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 depicts steps in preparation of a doped PCMO
precursor and spin-coating process used in the method of the
invention.
[0008] FIG. 2 depicts properties of a Cr-doped PCMO thin film
resistance switch.
[0009] FIGS. 3-6 depict Cr-doped PCMO thin film
characteristics.
[0010] FIGS. 7 and 8 depict temperature dependent characteristics
of Cr-doped PCMO thin films.
[0011] FIG. 9 depicts the effect of Cr-doped PCMO thin film on
resistance measurements
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0012] The prior art, as described in the references of Liu et al.,
teaches that Pr.sub.0.7Ca.sub.0.3MnO.sub.3 (PCMO) thin films
exhibit reversible resistance change properties when electric
pulses are applied to the thin films at room temperature, wherein
the resistance change is controlled by the polarity of electric
pulses. The resistance increases by applying a short positive
pulse, and the resistance decreases by applying a short negative
pulse. The PCMO thin films were deposited on both epitaxial
YBa.sub.2Cu.sub.3O.sub.7 (YBCO) and partial epitaxial platinum
substrates by pulsed laser deposition method (PLD).
[0013] In U.S. patent application Ser. No. 10/759,468, filed Jan.
15, 2004, for PCMO Spin Coating Deposition, synthesis of a PCMO
precursor and application of the precursor by spin-coating is
described. The PCMO thin films thus formed exhibit reversible
resistance switching upon application of short electric pulses.
[0014] The method of the invention herein provides a method of
doping a PCMO thin film for use in RRAM devices, to adjust the
electrical properties thereof so that a doped-PCMO thin film may be
fabricated in a single step deposition.
[0015] Referring now to FIG. 1, the method of the invention is
depicted generally at 10. Raw chemicals used for the PCMO synthesis
are Pr(OAc).sub.3(H.sub.2O), Ca(OAc).sub.2(H.sub.2O) and
Mn(OAc).sub.3(2H.sub.2O), where OAc is OOCCH.sub.3, 12. Both
Ca(OAc).sub.2(H.sub.2O) and Mn(OAc).sub.3(2H.sub.2O) are subjected
to a pre-thermal, dehydration treatment. A doping element 14, which
is a transition metal additive, such as V, Cr, Co, Fe, Ni, Ti, Zr,
Hf, Nb, Ta, Mo W and Zn, is mixed with the PCMO chemicals. The
amount of doping ranges from between about 0.01 mol % to 10 mol %
of the transition metal additive to the PCMO. The organic solvent
used in the method of the invention is acetic acid HOAc, 16. The
dopant-bearing PCMO precursor and acetic acid solvent are heated at
between about 90.degree. to 120.degree. for between about one hour
to eight hours, 18. The solution is filtered through a 0.2 .mu.m
filter, 20, resulting in doped-PCMO spin-coating solution, 22. A
doped PCMO thin film is formed by spin-coating the doped-PCMO
spin-coating solution onto a Pt/Ti/SiO.sub.2/wafer substrate. The
PCMO spin-coating solution is injected onto a wafer surface, 24,
wherein the wafer is spinning at about 2500 RPM, 26, which spin
rate is maintained for about 45 seconds. The coated wafer is baked
at about 1800 for about one minute, 28, then the temperature is
ramped up to about 230.degree. for about one minute, 30. The wafer
is the annealed in a RTA furnace at about 500.degree. for about
five minutes, 32. The spin-coating process is repeated at least
three times, to fabricate a doped-PCMO layer. Once the doped-PCMO
layer is complete, the wafer is annealed at between about
500.degree. to 600.degree. for between about one hour to six hours
in dry, clean air, 34.
[0016] The initial doping experiments indicated the influence of
doping on PCMO thin film RRAM properties as described in the
following examples:
EXAMPLE 1
[0017] Spin-coating solution 22 includes a 0.1 mol % Cr metal
additive in the form of chromium(III) acetate hydroxide
(CH.sub.3CO.sub.2).sub.7Cr.sub.3(OH).sub.2. Three-layers of
Cr-doped PCMO thin film were deposited on a Pt/Ti/SiO.sub.2/Si
wafer substrate via spin-coating. A platinum the top electrode
having a thickness of about 200 .mu.m was formed on the Cr-doped
PCMO film. After post-annealing at 525.degree. C. for about 40
minutes, the resistance of the thin film dropped from 300 k.OMEGA.
to 20 k.OMEGA., however, no resistance switches were observed
regardless of the kind or duration of applied electrical pulse.
EXAMPLE 2
[0018] Following the results of the first test, the Cr metal
additive was reduced to about 0.05 mol % in the PCMO thin film.
Again, chromium(III) acetate hydroxide was used as the chromium
additive. Three-layers of Cr doped PCMO thin film were deposited on
a Pt/Ti/SiO.sub.2/Si wafer substrate via spin-coating. A platinum
top electrode having a thickness of about 200 .mu.m was formed on
the Cr-doped PCMO thin film. After post-annealing at 525.degree. C.
for about 40 minutes, the resistance of the thin film was dropped
from 300 k.OMEGA. to 20 k.OMEGA., and reversible resistance switch
characteristics were observed, as shown in FIG. 2.
[0019] The doped PCMO thin film of Example 2 required a 5V/100 ns
electric pulse for write operations, and a 3V/10 ms pulse for reset
operations. The Cr-doped PCMO thin film resistance switch
efficiencies are shown in FIGS. 3-6, wherein FIG. 3 depicts a write
pulse voltage dependency; FIG. 4 depicts a write pulse width
dependency; FIG. 6 depicts the reset pulse voltage dependency; and
FIG. 7 depicts the reset pulse width dependency. The write
threshold voltage is 3.5V, and the pulse threshold width is 75 ns.
For the reset process, the threshold voltage and pulse width are
2.5V and 3 .mu.s, respectively.
[0020] FIG. 7 depicts PCMO high temperature dependency, while FIG.
8 depicts the high temperature dependency of a Cr-doped PCMO thin
film. Comparing FIGS. 7 and 8, the Cr-doped PCMO thin film
exhibited a much lower temperature dependency. The effect of
Cr-doping vs. un-doped PCMO on resistance is shown in FIG. 9. The
Cr-doped PCMO thin film exhibits a much smaller resistance
measurement voltage influence than does the un-doped PCMO thin
film.
EXAMPLE 3
[0021] In this example, a 0.05 mol % of vanadium was introduced
into the PCMO thin film. Vanadyl acetylacetonate,
[CH.sub.3COCHCOCH.sub.3].sub.2VO, was used as the vanadium additive
compound. As in previous examples, three-layers of V-doped PCMO
thin film were deposited on a platinum substrate via spin-coating,
and a platinum top electrode formed on the V-doped PCMO. After
post-annealing at about 525.degree. C. for about 40 minutes, the
thin film exhibited the requisite RRAM properties, however, the
number of switch cycles proved to be limited, after which the
V-doped PCMO thin film layer appeared to suffer irreparable
damage.
[0022] Thus, a method for doping a PCMO thin film to enhance
reversible resistance properties thereof has been disclosed. It
will be appreciated that further variations and modifications
thereof may be made within the scope of the invention as defined in
the appended claims.
* * * * *