Journal ArticleDOI

# Write-Once–Read-Many-Times Memory Based on ZnO on p-Si for Long-Time Archival Storage

12 Aug 2011--Vol. 32, Iss: 10, pp 1445-1447

AbstractWrite-once-read-many-times memory cells were fabricated using ZnO thin film on p-Si (111) substrate. The off- and on-state resistance ratio is over 104 and can be well sustained for more than 100 years and perfectly endure reading cycles of 108 . The conducting filaments consisting of oxygen vacancies are responsible for the switching mechanism.

Topics: Write once read many (56%)

### Summary

• Write-once–read-many-times memory cells were fabricated using ZnO thin film on p-Si (111) substrate.
• The OFFand ON-state resistance ratio is over 10 and can be well sustained for more than 100 years and perfectly endure reading cycles of 10.
• The conducting filaments consisting of oxygen vacancies are responsible for the switching mechanism.

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IEEE ELECTRON DEVICE LETTERS, VOL. 32, NO. 10, OCTOBER 2011 1445
ZnO on p-Si for Long-Time Archival Storage
Jing Qi, Qing Zhang, Jian Huang, Jingjian Ren, Mario Olmedo, and Jianlin Liu
ricated using ZnO thin ﬁlm on p-Si (111) substrate. The
OFF-and
ON-state resistance ratio is over 10
4
and can be well sustained
for more than 100 years and perfectly endure reading cycles of
10
8
. The conducting ﬁlaments consisting of oxygen vacancies are
responsible for the switching mechanism.
times (WORM), ZnO.
I. INTRODUCTION
W
ory devices, in which the data storage is permanent,
as required for archival storage of video images and for
noneditable database, have attracted a great deal of interest
[1], [2]. Even though some studies regarding the formation
and electrical properties of WORM memory devices using
organic materials [3], [4], inorganic/organic nanocomposites
[5], and inorganic/organic heterojunction [2] have been carried
out, studies on WORM memory devices fabricated using ZnO
ﬁlm have not been reported yet. ZnO material is a promis-
ing candidate for WORM memory application primarily due
to its environmental friendliness, abundant availability in na-
ture, highly evolved growth technologies, compatibility with
metal–oxide–semiconductor technology, and suitability for fab-
rication of small-size devices [6], [7]. This letter reports the
switching characteristics and mechanism of WORM memory
devices fabricated using ZnO on p-Si.
II. E
XPERIMENTAL PROCEDURE
ZnO (60 nm) was deposited on p-Si (111) substrate at 400
C
with a few atomic layers of MgO as buffer in a radio-frequency
Manuscript received June 6, 2011; revised July 5, 2011; accepted
July 11, 2011. Date of publication August 11, 2011; date of current version
September 28, 2011. This work was supported in part by the Microelec-
tronics Advanced Research Corporation and its Focus Center on Function
Engineered Nano Architectonics, by the Defense Advanced Research Projects
Agency/Defense Microelectronics Activity under Agreement H94003-10-2-
1003 (3-D Electronics), and by the National Natural Science Foundation of
China under Grant number 50902065. The review of this letter was arranged by
Editor T. Wang.
J. Qi is with the Quantum Structures Laboratory, Department of Electrical
Engineering, University of California, Riverside, CA 92521 USA, and also
with the Department of Physics, School of Physical Science and Technology,
Lanzhou University, Lanzhou 730000, China (e-mail: qijing@lzu.edu.cn).
Q. Zhang, J. Huang, J. Ren, M. Olmedo, and J. Liu are with the Quan-
tum Structures Laboratory, Department of Electrical Engineering, Univer-
sity of California, Riverside, CA 92521 USA (e-mail: zq2000@hotmail.
com; jian.huang002@email.ucr.edu; jren004@student.ucr.edu; molmedo@
ee.ucr.edu; jianlin@ee.ucr.edu).
Color versions of one or more of the ﬁgures in this letter are available online
at http://ieeexplore.ieee.org.
Digital Object Identiﬁer 10.1109/LED.2011.2162219
(RF) plasma-assisted molecular beam epitaxy system. An ex-
periment on a reference sample with only MgO layer indicated
that MgO is too thin to have similar memory performance (not
shown here). The Si substrates were cleaned using standard
RCA method to remove contamination and native oxide layer.
High-purity Mg (6 N) and Zn (6 N) sources were evaporated
from conventional low-temperature effusion cells. Atomic oxy-
gen was provided by an RF plasma source. Ti (10 nm)/Au
(90 nm) square-shaped metal patterns of different areas, which
act as top electrodes, were deposited on ZnO by electron-beam
evaporation after photolithography, followed by a standard
lift-off process. Al was evaporated also by electron-beam evap-
oration as back contact onto p-Si (111). The electrical charac-
teristics of the Au/Ti/ZnO/p-Si/Al structure were measured by
an Agilent 4155 C semiconductor analyzer. Current maps for
the surface of ZnO ﬁlm were measured by a conductive atomic
force microscope (C-AFM). A scanning electron microscope
(SEM) was utilized to observe surface morphology change of
top electrodes after electrical characterization.
III. R
ESULTS AND DISCUSSION
Fig. 1(a) shows a typical current–voltage (IV ) curve of a
memory cell [device structure with electrodes of different areas
shown as the bottom right inset in Fig. 1(a)]. First, an external
applied voltage (V
ext
) was swept from 1.5 to 1.5 V to obtain
the IV curve for high-resistance state (OFF), as shown in
Fig. 1(a) as black square curve. Then, as V
ext
(0 20 V) in
sweeping mode increased to approximately the writing voltage
(V
w
) of 14 V, the current increased suddenly, which switched
the memory cell to low-resistance state (ON), as shown in
the right inset of Fig. 1(a). This phenomenon is similar to an
electroforming process, which is a soft breakdown due to the
protection of current compliance, in resistive random access
memory (RRAM), where the sudden current increase is caused
by the formation of the conducting ﬁlaments [8]. Finally, V
ext
swept from 1.5 to 1.5 V again to obtain the IV curve for
ON state, as shown in Fig. 1(a) as red circle curve. Probability
of resistance ratio (R-ratio, R
OFF
/R
ON
voltage of 1 V from 100 devices with an area of 30 × 30 μm
2
[left inset of Fig. 1(a)] shows that the R-ratio for most devices
is between 10
5
and 10
6
. Fig. 1(b) shows the dependence of R-
ratio and writing power on the current compliance during the
writing process. A WORM memory effect can still be clearly
observed even if the writing power is lowered to be smaller
than 1 mW. Furthermore, R-ratio decreases to 10
3
with the
writing power lowered to 1 mW. This ratio is large enough to
distinguish two different states.

7 citations

### Cites background from "Write-Once–Read-Many-Times Memory B..."

• ...ZnO on Si was found to exhibit WORM characteristics, and further inclusion of a MgO thin layer between ZnO and Si led to enhanced memory performance [24], [25]....

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• ...In previous publication [24], it is reported that the conduct-...

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Journal ArticleDOI
Abstract: TaN/ZrTiOx/Pt metal-insulator-metal structure was employed as the platform to evaluate the eligibility for antifuse one-time programmable (OTP) memory applications, and the impact of O2 plasma on device performance was also discussed. Owing to the oxygen radicals that enhance the dielectric integrity, the voltage for state switching increases with O2 plasma treatment. Memory cells without plasma treatment demonstrate promising characteristics for OTP memory applications in terms of a low dc switching voltage of 2 V, high programming speed of 60 ns, high read endurance up to 106 reading cycles, and desirable retention time and low switching power density of 6.4 mW/cm2. The memory cell technology not only exhibits the prominent performance which is advantageous over other dielectrics reported in the literature, but it also possesses the capability to from stackable 3-D architecture.

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• ...Although these newly developed dielectrics exhibit promising characteristics, there is still plenty of room to improve their performance since most dielectrics show dc program voltage higher than 4 V [10], [11] and program speed longer...

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• ...Recently, dielectrics such as SiNx [6], Ta2O5 [7], Al2O3 [8], ZrO2 [9], ZnO [10], and BZN [11] have also been explored to investigate their feasibility for use in antifuse applications....

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• ...This result compares favorably to other dielectrics [6]–[8], and [10], [11] in terms of low programming voltage along with high operation speed....

[...]

Journal ArticleDOI
Abstract: Write-onceread-many-times memory (WORM) devices were fabricated using Ti/Au and Au as top contacts on ZnO thin films on Si. Electrical characterization shows that both types of WORM devices have large resistance OFF/ON ratio (R ratio), small resistance distribution range, long retention and good endurance. WORM devices with Au top contact have better performance of higher R ratio because of a larger work function of Au compared to Ti. ((c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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Ümit Özgür
Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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TL;DR: A coarse-grained classification into primarily thermal, electrical or ion-migration-induced switching mechanisms into metal-insulator-metal systems, and a brief look into molecular switching systems is taken.
Abstract: Many metal–insulator–metal systems show electrically induced resistive switching effects and have therefore been proposed as the basis for future non-volatile memories. They combine the advantages of Flash and DRAM (dynamic random access memories) while avoiding their drawbacks, and they might be highly scalable. Here we propose a coarse-grained classification into primarily thermal, electrical or ion-migration-induced switching mechanisms. The ion-migration effects are coupled to redox processes which cause the change in resistance. They are subdivided into cation-migration cells, based on the electrochemical growth and dissolution of metallic filaments, and anion-migration cells, typically realized with transition metal oxides as the insulator, in which electronically conducting paths of sub-oxides are formed and removed by local redox processes. From this insight, we take a brief look into molecular switching systems. Finally, we discuss chip architecture and scaling issues.

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• ...the effective cell area is attributed to the conducting filament density and diameter rather than to the geometrical size of the electrode [12]....

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TL;DR: It is demonstrated that the switching behaviour is an intrinsic feature of naturally occurring dislocations in single crystals of a prototypical ternary oxide, SrTiO3, and to be related to the self-doping capability of the early transition metal oxides.
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TL;DR: The results indicate that the hybrid organic/inorganic memory device is a reliable means for achieving rapid, large-scale archival data storage for ultralow-cost permanent storage of digital images, eliminating the need for slow, bulky and expensive mechanical drives used in conventional magnetic and optical memories.
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Abstract: Recently, films created by incorporating metallic nanoparticles into organic or polymeric materials have demonstrated electrical bistability, as well as the memory effect, when subjected to an electrical bias. Organic and polymeric digital memory devices based on this bistable electronic behavior have emerged as a viable technology in the field of organic electronics. These devices exhibit fast response speeds and can form multiple-layer stacking structures, demonstrating that organic memory devices possess a high potential to become flexible, ultrafast, and ultrahigh-density memory devices. This behavior is believed to be related to charge storage in the organic or polymer film, where devices are able to exhibit two different states of conductivity often separated by several orders of magnitude. By defining the two states as “1” and “0”, it is now possible to create digital memory devices with this technology. This article reviews electrically bistable devices developed in our laboratory. Our research has stimulated strong interest in this area worldwide. The research by other laboratories is reviewed as well.

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• ...and electrical properties of WORM memory devices using organic materials [3], [4], inorganic/organic nanocomposites [5], and inorganic/organic heterojunction [2] have been carried...

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