Accepted Manuscript Effect of adding a polymer and varying device size on the resistive switching characteristics of perovskite nanocubes heterojunction Young Jin Yang, Muhammad Muqeet Rehman, Ghayas Uddin Siddiqui, Kyoung Hoan Na, Kyung Hyun Choi PII:
S1567-1739(17)30270-5
DOI:
10.1016/j.cap.2017.10.001
Reference:
CAP 4597
To appear in:
Current Applied Physics
Received Date: 30 April 2017 Revised Date:
20 September 2017
Accepted Date: 2 October 2017
Please cite this article as: Y.J. Yang, M.M. Rehman, G.U. Siddiqui, K.H. Na, K.H. Choi, Effect of adding a polymer and varying device size on the resistive switching characteristics of perovskite nanocubes heterojunction, Current Applied Physics (2017), doi: 10.1016/j.cap.2017.10.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Effect of Adding a Polymer and Varying Device Size on the Resistive Switching Characteristics of Perovskite Nanocubes Heterojunction 1
Young Jin Yang†, 1Muhammad Muqeet Rehman†, 1Ghayas Uddin Siddiqui, 2Kyoung Hoan Na, 1 Kyung Hyun Choi* Department of Mechatronics Engineering, Jeju National University, 690-756, Republic Korea. 2 College of Engineering, Dankook University, Gyeonggi, Korea. * E-mail address:
[email protected] Both authors have equal contribution
†
SC
Abstract
RI PT
1
Emerging resistive switching devices are believed to play a vital role in realizing ultra-dense
M AN U
nanocrosbar arrays for the next generation mass storage memory. This work reports the resistive switching effect in organic-inorganic hybrid nanocomposite of perovskite oxide zinc stannite nanocubes (ZnSnO3 NCs) and a polymer Poly(methyl methacrylate) (PMMA). The functional layer was sandwiched between indium tin oxide (ITO) and silver (Ag) electrodes on a flexible PET substrate. The obtained electrical results clearly exhibited that the addition of PMMA in
TE D
ZnSnO3 NCs enhanced electrical endurance (500 biasing cycles), retention time (~ 104 s), switching ratio (~ 103) and repeatability of our memory device. Moreover the effect of device size on the resistive switching characteristics of this hybrid nanocomposite is also explored by
EP
varying the diameter of top electrode. The whole device fabrication except bottom layer was
AC C
done through all printed technology such as electrohydrodynamic atomization (EHDA) and inkjet reciprocating head. The developed memory device displayed characteristic bipolar, nonvolatile and rewritable memory behavior at a low operating voltage. The obtained results of chemical, structural, electrical and surface morphology are added to completely understand the impact of adding a polymer on the switching characteristics of perovskite NCs. Keywords Polymer; Perovskite oxide; PMMA-ZnSnO3 nanocomposite; All-printed; Flexible memory
ACCEPTED MANUSCRIPT
Introduction Storage of digital data has a huge demand among electronic device applications in modern world owing to its rapid increase in capacity that is expected to reach 44 ZB by 2020 [1]. Henceforth,
RI PT
resistive switching devices are extremely important in the context of replacing transistors as the digital data storage devices of the future owing to their extremely high scalability, simple
structure, cost effectiveness, small size, light weight, fast operating speed and easy device
SC
fabrication [2–6]. Moreover, other promising applications of this electronic device include logic gates [7], neuromorphic circuits [8], computing [9], and photo switches [10].
M AN U
The structure of a resistive switch is such that a functional layer of an insulator or a semiconductor is sandwiched between two metal electrodes. Choice of the sandwiched functional material is therefore particularly critical in realizing a memory device with promising switching characteristics. Various inorganic materials and their compounds such as metal and
TE D
pervoskite oxides have been proposed as the active material for resistive switching applications owing to their advantages of high conductivity, longer lifetime, resistance against atmospheric conditions, and enormous thermal stability [11–15]. Despite all such advantages, inorganic
EP
materials have certain disadvantages too as compared to organic polymers. Polymers are highly flexible, recyclable, solution processable, light weight, cost effective, environment friendly and
AC C
highly scalable [16–18]. Therefore, functional thin film of a hybrid nanocomposite consisting the superior qualities of both organic and inorganic materials has become a popular choice memory devices [19–21].
Hybrid nanocomposites have gained importance due to their distinct and tunable optical, chemical, mechanical and electrical characteristics [22]. Hybrid organic-inorganic nanocomposites have already been reported as the functional material for various other electronic
ACCEPTED MANUSCRIPT
devices such as solar cells [23], TFTs [24], light emitting diodes (LEDs) [25], and sensors [26]. These hybrid nanocomposites therefore seem to be an attractive choice for the next generation non-volatile memory device owing to combined advantages of organic and inorganic materials.
RI PT
Moreover, various types of metallic nanoparticles (NPs) such as silver (Ag), gold (Au),
aluminum (Al), and copper (Cu) have been reported to have great charge-trapping potential that is essential for a memory behavior [27]. However, such metallic NPs have the inherent
SC
limitations of being expensive and unstable at high temperatures making them an undesirable choice to be used specifically for low cost memory device. On the other hand, semiconducting
M AN U
NPs such as NCs of ZnSnO3 pervoskite oxide are cost effective and highly stable with a high probability of charge trapping owing to their quantum confinement and edge effects making them an attractive choice for memory device applications. ZnSnO3 NCs have well confined cubical shapes along with long carrier diffusion length and high specific surface area.
TE D
Embedding these semiconducting NPs in a polymer would add a lot in the functionality of a thin film. A polymer like PMMA has several useful properties such as its high bandgap to restrict the trapped charge carriers after the removal of external power supply, weak chemical bonds,
EP
excellent transparency, biocompatibility and high bendability for flexible and wearable electronics [4]. A hybrid nanocomposite of semiconductive NCs embedded in a polymer is
AC C
therefore an attractive choice to test for a nonvolatile memory application. In this work, we have reported a solution-processed hybrid nanocomposite of PMMA-ZnSnO3 NCs as the functional layer of a nonvolatile and rewritable resistive switching memory device to study the effect of adding a polymer on the switching properties of ZnSnO3 NCs. Furthermore, the effect of changing device size has also been studied in this work by varying the top electrode size. The characteristic bipolar memory behavior in ZnSnO3 nanocubes has already been
ACCEPTED MANUSCRIPT
reported in our previous work [28]. We have verified that switching characteristics of this inorganic pervoskite oxide (ZnSnO3 NCs) are enhanced by the addition of PMMA polymer mainly due to its large bandgap and dielectric property. A complete comparison of both devices
RI PT
is illustrated in table 1. Furthermore PMMA polymer restricts the agglomeration of ZnSnO3 NCs in the solution that results in a stable spray to deposit uniform thin films.
The whole device was fabricated through a cost effective and highly controllable printed
SC
technology in ambient environment without any requirement of vacuum. Functional layer of hybrid nanocomposite (PMMA-ZnSnO3 NCs) was sprayed over ITO coated PET substrate
M AN U
through state of the art electrohydrodynamic atomization (EHDA) printing system. Top circular electrodes of three different sizes (100 µm, 200 µm and 300 µm) were patterned through a highly controllable and non-contact technique of inkjet reciprocating head printing system to study the effect of device size on the resistive switching characteristics of PMMA-ZnSnO3 NCs. Field
TE D
emission scanning electron microscopy (FESEM) was used to study the surface morphology of ZnSnO3 NCs and its hybrid nanocomposite with PMMA polymer. Atomic force microscope (AFM) was used to measure the average roughness of as deposited hybrid thin film layer. XRD
EP
and Fourier Transform Infra-Red (FTIR) spectroscopy were performed to record the crystalline nature and composition of nanocomposite materials. Moreover the optical transmittance of
AC C
hybrid functional thin film was carried out through UV-vis spectroscopy. 2. Experimental 2.1. Materials
Zinc sulfate heptahydrate (ZnSO4.7H2O) and sodium stannate trihydrate (Na2SnO3.3H2O) were used as precursors for the synthesis of ZnSnO3 NCs and they were purchased from Duksan Pure Chemicals, Korea and Junsei Chemical Co., Ltd. Japan respectively. The powder of polymer,
ACCEPTED MANUSCRIPT
PMMA [CH2C(CH3)(CO2CH3)]n with average Mw ~ 15000 by GPC, and its solvent toluene (C6H5CH3, anhydrous, 99.8%) were purchased from Sigma-Aldrich. Silver nanoparticles ink (Ag NPs) for patterning top electrodes was purchased from Paru Co., Ltd. Korea.
RI PT
2.2 Instrumentation and characterizations
Morphological analysis was carried out by field emission scanning electron microscope
(FESEM) using Zeiss Supra 55VP operating at 20 kV. Topography imaging at the nanoscale was
SC
conducted by using the Dimension 3100 atomic force microscope (AFM, Vecco). X-ray
diffraction (XRD) patterns were recorded by using Rigaku D/MAX 2200H diffractometer with
M AN U
Cu Kα radiation (k =1.5406 Å , 40 kV, 250 mA, 8 min-1) through a fixed glancing incidence angle (2°). Surface chemistry of PMMA-ZnSnO3 NCs nanocomposite thin film was investigated by Fourier Transform Infrared (FTIR) spectroscopy using Nicolet 6700 FTIR spectrophotometer. The UV/Vis spectrophotometer (Shimadzu UV 3150PC) was used to record the transmittance
TE D
spectra of hybrid thin film. The semiconductor device analyzer (Agilent B1500A) was used to measure the electrical characteristics of resistive switching device. 2.3. Synthesis of ZnSnO3 NCs and PMMA nanocomposite ink
EP
Highly crystalline ZnSnO3 nanocubes were synthesized through aqueous solution method using ZnSO4.7H2O and Na2SnO3.3H2O precursors as reported in our previous work [28]. The PMMA
AC C
solution (1 wt. %) was prepared in toluene by dissolving polymer powder in it and placed at a magnetic stirrer for 24 h to acquire a stable and homogeneous polymer solution. The as synthesized ZnSnO3 NCs were then dispersed in the PMMA solution with 2 wt. % concentration and sonicated for 30 min by probe sonication to get a uniform dispersion. Later, PMMA-ZnSnO3 NCs solution was placed on a magnetic stirrer for overnight. The as prepared PMMA-ZnSnO3 NCs ink was utilized to fabricate thin film for resistive switching device through EHDA. The
ACCEPTED MANUSCRIPT
formation of the polymer matrix interspersed perovskite ZnSnO3 NCs has been illustrated in
M AN U
SC
RI PT
schematic diagram of figure 1.
Figure 1. Chemical structures of used materials (ZnSnO3 NCs, PMMA) and final form of their hybrid nanocomposite
2.4. Device fabrication 2.4.1. Substrate cleaning
Polymer and perovskite oxide based hybrid memory device was fabricated on a transparent and
TE D
flexible ITO coated PET substrate. The substrate was thoroughly rinsed with ethanol, acetone and deionized water in a bath sonicator prior to fabrication for 10 min each followed by drying in ambient atmosphere. In order to disassociate the contaminant molecules from the surface,
EP
flexible ITO coated PET substrate was treated in a UV ozone cleaning system. Finally the
AC C
substrate was treated with oxygen plasma to further enhance the wettability of surface for better adhesion of thin film.
2.4.2. Deposition of PMMA-ZnSnO3 nanocomposite through EHDA Thin film of hybrid nanocomposite was successfully deposited through a well-established printing technique of EHDA due to its high control, simplicity and ability to produce extremely uniform thin films in a short duration [18,19]. Stable mode of deposition was achieved for spraying the nanocomposite ink by applying electric field through an external power supply
ACCEPTED MANUSCRIPT
across the spraying nozzle and substrate holder. Various critical printing parameters of EHDA such as standoff distance, nozzle diameter, magnitude of applied voltage, flow rate and speed of stage were optimized for spraying the thin film of PMMA-ZnSNO3 NCs functional
RI PT
nanocomposite in atmospheric conditions. Stable cone jet was attained at a stand-off distance of 13 mm between 5.7 kV to 6.5 kV and at a flow rate of 320 ml/h. The as deposited functional thin film was sintered at 110 °C for 2h in the thermal furnace.
SC
2.4.3. Top electrode printed through inkjet reciprocating head system
Circular top electrodes of Ag metal were deposited on the surface of hybrid functional layer of
M AN U
PMMA-ZnSnO3 NCs through a glass needle to complete the device fabrication. A total of nine memory cells with three different sizes of 100 µm, 200 µm, and 300 µm respectively were deposited to observe the effect of device size on the resistive switching characteristics of our proposed hybrid nanocomposite. The working mechanism of this patterning technique is
TE D
explained in detail in our previous work [13] however, the optimized operating conditions are listed here for reproducibility. The diameter of the needle holder was 1mm while the glass needles with different diameters of 100 µm, 200 µm, and 300 µm respectively were selected for
EP
top electrode deposition of variable size. The standoff distance between the glass needle and functional layer was maintained at 100 µm for each memory cell while the pneumatic pressure
AC C
for patterning each top electrode was fixed at 0.2 kPa. This patterning technique was preferred over other methods of top electrode deposition such as screen printing, roll to plate etc. because it is a non-contact method that does not damage the functional thin film. Moreover, reciprocating inkjet system has a microscale precision with high resolution. Sintering of Ag top electrode was carried out at 110 °C for 1 h in the thermal furnace to complete the device fabrication. Flow
ACCEPTED MANUSCRIPT
diagram of complete fabrication process and schematic diagram of our memory device is shown
TE D
M AN U
SC
RI PT
in figure 2.
EP
Figure 2. (a) Process flow diagram for device fabrication of flexible memory device through EHDA and reciprocating inkjet printing systems (b) Schematic diagram of ITO/PMMA-ZnSnO3 NCs/Ag
3. Results and discussion
AC C
3.1. Structural and optical characterizations The surface chemistry of the PMMA-ZnSnO3 NCs nanocomposite thin film has been analyzed by the FTIR spectroscopy as shown in figure 3(a). The absorption band at 952 cm-1 is the characteristic peak for PMMA. The absorption bands at 2950 cm-1 and 2907 cm-1 are attributed to C-H asymmetric stretching vibrations whereas the band at 2877 cm-1 is assigned to C-H symmetric vibrations. The bands observed at 3396 cm-1 and 1512 cm-1 are assigned to –OH
ACCEPTED MANUSCRIPT
group stretching and bending vibrations of physisorbed moisture. The band at 1732 cm-1 is assigned to C=O stretching vibrations showing the presence of acrylate carboxyl group of PMMA. The other absorption bands at 1033 cm-1 and 1246 cm-1 are attributed to the C-O
RI PT
stretching vibration and wagging vibration of C-H bond respectively. The absorption peaks at 540 cm-1 and 668 cm-1 are attributed to the vibrations of M-O or M-O-M groups of ZnSnO3 NCs. These all recorded absorption peaks are in good agreement with already reported previous results
SC
[29].
X-ray diffraction patterns were recorded for the structural and compositional analysis of PMMA-
M AN U
ZnSnO3 NCs nanocomposite thin film as illustrated in figure 3(b). It is evident from the XRD patterns that both the materials of nanocomposite are present in the deposited thin film indicating the amorphous PMMA and crystalline ZnSnO3 NCs. Most of the XRD patterns belong to ZnsnO3 NCs and are in well agreement with the standard data of pure ZnSnO3 NCs powder
TE D
(JCPDS card, No. 11-0274) [30] while only one pattern at 2θ =13.37 belongs to PMMA. Figure 3(c) shows the transmittance spectra of PMMA-ZnSnO3 NCs nanocomposite thin film recorded by UV/vis spectroscopy showing the high transmittance up to 91 % of the film deposited through
AC C
cells and LEDs.
EP
EHDA verifying potential use of this hybrid nanocomposite in optical applications such as solar
Figure 3. (a) FTIR spectra showing the surface chemistry of PMMA-ZnSnO3 NCs nanocomposite thin film having characteristics absorption peaks of ZnSnO3 and PMMA (b) X-ray diffraction patterns of nanocomposite showing a
ACCEPTED MANUSCRIPT
small peak of amorphous PMMA at 13.37° while rest of the peaks belong to crystalline ZnSnO3 NCs (c) Transmittance spectrum of nanocomposite thin film showing high transmittance up to 91 %.
3.2. Morphological characterization
RI PT
The morphological and structural characteristics of as synthesized ZnSnO3 NCs and PMMAZnSnO3 NCs nanocomposite thin film was analyzed through FESEM images as shown in figure 4(a). Shape and structure of ZnSnO3 NCs is perfectly cubic and their average size is less than 100 nm as shown in figure 4(b). These small size NCs were found to be very appropriable when
SC
making the nanocomposite with polymer because they can be infiltrated easily into the polymer
M AN U
matrix. Due to the small size of NCs, they were found to be useful in fabricating a uniform thin film through EHDA which has the key role in resistive switching device. Figure 4(c) showing the FESEM image of PMMA-ZnSnO3 NCs nanocomposite thin film as it can be seen that NCs are entirely covered by the polymer resulting in a smooth surface with low roughness as further examined by the AFM spectroscopy. The surface roughness of as deposited hybrid thin film was
TE D
measured through AFM as shown in the 3D topography image presented in figure 4(d). The average values of roughness (Ra) and root mean square (Rq) as measured from the roughness
AC C
EP
plot of figure 4(e) are 23 nm and 27 nm respectively.
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Figure 4. Morphological characteristics of as synthesized ZnSnO3 NCs and deposited thin film of hybrid nanocomposite (a,b) FESEM images of the as synthesized ZnSnO3 NCs showing clearly the uniformity in size and shape, their size is less than 100 nm and shape is perfectly cubic (c) FESEM image showing the surface morphology of PMMA-ZnSnO3 NCs nanocomposite thin film; indicating that nanocubes are covered by the PMMA due to their small size and film is very uniform. (d) AFM image of as deposited thin film illustrating its surface roughness with a 3D view (e) Surface roughness plot of as deposited thin film with average and root mean square roughness values.
TE D
3.3. Electrical characterization
Electric field was applied across the two terminals of the developed hybrid memory device by applying a voltage sweep of 0-4.5 V to perform electroforming process so that stability in
EP
electrical results could be attained as illustrated in figure 5(a). Electroforming is necessary to induce defects in the polymer resulting in pathways for current through soft breakdown. A
AC C
double voltage sweep from -3 V to +3 V was applied across the two electrodes to pass electric current through the sandwiched functional layer of PMMA-ZnSnO3 NCs. The value of current compliance was limited to 300 µA to avoid hard breakdown of memory device. The obtained I-V curves of each device size i.e. 100 µm, 200 µm, and 300 µm respectively displayed characteristic bipolar hysteresis behavior as illustrated in figure 5(b). It can be seen from the obtained characteristic I-V curves that initially the memory device was in a high
ACCEPTED MANUSCRIPT
resistive state (HRS) however transition from HRS to a low resistive state (LRS) known as ‘SET process’ occurred when the applied positive bias increased to a threshold voltage (Vth) of 2.3 V. The Vth provided enough energy to the charge carriers to switch the device from HRS to LRS by
RI PT
flowing freely through the hybrid functional thin film from one electrode to the other electrode in the form of electric current. This implies that data can be written or stored on this device at an applied bias of 2.3 V. The device was brought back to its original state of HRS by applying a
SC
voltage sweep of opposite polarity at a threshold voltage of -2.7 V. This is known as ‘RESET process’ during which stored data can be erased from the memory device. Both SET and RESET
M AN U
processes are represented by upward and downward arrows respectively. The read voltage (VREAD) of our memory device was 0.2 V. It is also evident from figure 5(b) that switching ratio
AC C
EP
TE D
is largest for smallest device size.
Figure 5. Electrical characterization results of as fabricated flexible memory device (a) Electroforming curve to achieve stability in further results (b) Typical bipolar I-V curves of memory device with each size (c) Changing values of switching at different values of applied voltage (d) Stability of bistable resistive states for each device size (e) Stability of threshold voltages (f) Dependence of switching ratio on device size.
ACCEPTED MANUSCRIPT
Figure 5(c) exhibits the trend of resistive switching ratio against the increasing value of applied bias voltage. Moreover, the stability of the developed memory device was tested by plotting the cumulative probability plots of both resistive states (HRS and LRS) and threshold voltages (VSET
RI PT
and VRESET) as illustrated in figure 5(d) and figure 5(e) respectively. These cumulative
probability plots exhibit the distribution of bistable resistive states and threshold voltages for random memory cells. Such results with very little deviation illustrate high uniformity and
SC
reproducibility of our device. Figure 5(f) shows the plot of bistable resistive states against increasing size of top electrode in which LRS is similar for all devices however HRS is
M AN U
decreasing with increasing top electrode size resulting in a smaller switching ratio. The switching ratio values for 100 µm, 200 µm, and 300 µm are 1.1 × 103, 1.3 × 102 and 4.6 × 101 respectively. This inverse relation between device size and switching ratio can be attributed to the formation of micro cracks on the electrode surface that causes current leakage in HRS resulting in reducing
TE D
the gap between bistable resistive states, hence decreasing the switching ratio [13]. It implies that the device with a size of 100 µm will have small cracks, 200 µm will have moderate cracks while 300 µm will have large number of resulting in more leakage current in HRS. The device
EP
size had no noticeable effect on the stability of bistable resistive states or threshold voltages
AC C
however the switching ratio changes significantly.
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Figure 6. Characteristic I-V curves illustrating the endurance and retention of obtained data (a-c) Endurance curves of memory cells with 100 µm, 200 µm and 300 µm device size for 500 biasing cycles (d-f) Retention time of memory cells with 100 µm, 200 µm and 300 µm device size for 104 s.
TE D
Electrical endurance of each memory cell with a different device size was tested against multiple biasing cycles with excellent stability. Fig 6 (a-c) illustrates the robustness of our device against 500 voltage sweeps. The retention time of each device size was also studied and its obtained
EP
results are shown in Fig 6 (d-f). All the three devices with variable size (100 µm, 200 µm, and
AC C
300 µm) displayed appreciably stable and repeatable characteristic I-V curves for ~ 104 s. The developed memory device contained an array of nine memory cells. I-V characteristic curves for each memory cell is plotted in figure 7 (a-c) to show high reliability and repeatability of our proposed device. The resistive switching characteristics of our proposed device are superior to already reported memory device based on ZnSnO3 NCs and several other hybrid nanocomposite devices that are reported earlier as shown in table 1.
RI PT
ACCEPTED MANUSCRIPT
SC
Figure 7. Illustration of device repeatability by displaying the I-V curve for each memory cell of every device size (a) Repeatability of 100 µm memory cells (b) Repeatability of 200 µm memory cells (c) Repeatability of 300 µm memory cells.
Active Layer PMMA-ZnSnO3 NCs
Voltage Sweep -2.7 to +2.4 V
M AN U
Table 1. Comparison of hybrid PMMA-ZnSnO3 NCs nanocomposite based memory device with already reported memory devices based on ZnSnO3 NCs alone and other nanocomposites of polymers. C.C 300 µA
Off/On ratio ~103
Endurance 500 cycles
Retention 104 s
Ref This
Work 4
-2 to +2
100 nA
10
100 cycles
~ 10 s
[28]
GNF–PVA
-7 to +2 V
1 mA
~ 102
100 cycles
104 s
[31]
AgNW-PVA
-10 to +10 V
10 mA
~ 10
160 cycles
-
[32]
PVA-PbS
-30 to +30 V
30 µA
< 10
-
-
[33]
TE D
ZnSnO3 NCs
-3 to +3 V
Graphene-PVP PMMA:CdSe/ZnS QD
-2 to +4 V
20-200 nA 30 mA
~ 35 4
~ 10
200 cycles
3
[15]
4
[34]
4
10 s 10 s
-1.5 to + 1.5 V
2 mA
~ 10
1000 cycles
10 s
[4]
PMMA-MAPOM
-2 to +1.5 V
1 mA
~ 10
50 cycles
104 s
[35]
EP
PMMA-HfOx
AC C
3.4. Nonvolatile memory mechanism Conduction mechanism of resitive switching devices is a debatable point with various suggested theories such as filament formation, Ohmic conduction model, interface-type switching, electric field induced charge transfer, Poole-Frenkle (PF) conduction, thermionic emission, Schottky emission, Simmons and Verderber (SV) model etc [36]. However, the conduction mechanism observed in our hybrid memory device can be explained with the combination of two well established conduction models such as trap controlled space charge limited (TCSCLC) current
ACCEPTED MANUSCRIPT
model in HRS based on the two different gradient values of double logarithmic I-V curves (I α V and I α V2) and Ohmic conduction model (I α V) in LRS as illustrated in figure 8(a) and 8(b) respectively.
RI PT
At a low applied bias, ohmic conduction behavior was observed due to the thermally generated charge carriers at the interface of electrode and PMMA polymer. As the magnitude of applied voltage bias was increased, number of free charge carriers injected from the electrode into the
SC
PMMA polymer embedded with ZnSnO3 NCs layer were also increased that resulted in the formation of space charges near the interface of PMMA polymer and electrode. TCSCLC model
M AN U
is closely related to the trapping and detrapping of charge carriers that is highly appropriate to describe the conduction mechanism of a memory device composed of a hybrid functional layer with inorganic NCs embedded in a polymer matrix. ZnSNO3 NCs act as the charge trapping sites because their energy levels lies between the highest occupied molecular orbital (HOMO) and
TE D
lowest unoccupied molecular orbital (LUMO) of PMMA polymer. The wide bandgap of PMMA polymer act as a charge blocking material. The conduction in the low voltage range of applied positive bias can be associated to thermionic emission conduction model that allows only a small
EP
number of charge carriers to cross the potential barrier successfully due to the difference in workfunction of electrode and LUMO of PMMA. The energy band diagram of our device is
AC C
illustrated in figure 8(c).
For the applied positive bias of less than Vth, low magnitude current passes through the functional layer due to the insulating property of PMMA polymer corresponding to the OFF state of our memory device. The induced charge carriers from the metallic electrode are trapped inside the ZnSnO3 NCs owing to their quantum confinement and edge effect. These conductive NCs act as the linker of conductive path between the two electrodes. The electric field will be intense at
ACCEPTED MANUSCRIPT
the corners edges of NPs owing to the point effect and also due to density of nanocrystals in the nanocomposite. High magnitude of electric field would ease the transportation of charge carriers. These captured charge carriers fill all the traps and form an internal electric field strong enough
RI PT
to produce conducting channels throughout the PMMA polymer thin film. The trapping of
charge carriers reduce the available traps but increase the density of free electrons [36]. Once these conductive channels are formed, an abrupt increase in the value of current passing through
SC
the functional layer of PMMA-ZnSnO3 NCs is observed that switches the device to ON state. The current increases exponentially with respect to voltage (I α Vn) during this part of
M AN U
conduction. This is further verified by the presence of Ohmic conduction in the ON state where current abruptly increases after the writing Vth to switch the device from HRS to LRS. It is difficult to clearly determine the energy barrier heights of ZnSnO3 NCs however, these traps are deep enough to restrict the charge carriers from moving back to their original energy states even
TE D
when no external power supply is used to push them. High retention time and nonvolatile memory behavior (keeping charge carriers in trap sites even after the removal of external bias) observed in electrical characterization results for our device is mainly due to the large potential
EP
barrier offered by PMMA polymer owing to its insulating property that restricts the charge carriers from moving back to their original energy states even at zero applied bias. At a micro
AC C
scale, even a small operating voltage has the ability to produce very strong electric field that encourages electrons from the HOMO of PMMA to gain enough energy and tunnel through the capped ZnSnO3 NCs. This charge transfer results in the generation of more charge carriers that results in a higher conductivity by assisting charge carrier between electrodes. The value of HRS is also higher for our device due to the addition of PMMA polymer as compared to the HRS value of ZnSnO3 NCs memory device that results in higher switching ratio as the gap between
ACCEPTED MANUSCRIPT
LRS and HRS increases. A negative potential bias with high enough magnitude must be applied to the device in order to provide enough energy to the trapped charge carriers to leave those deep traps and bring the device back to its original resistive state of HRS. The electrons are detrapped
RI PT
from ZnSnO3 NCs resulting in the destruction of conductive pathways due to empty trap sites
AC C
EP
TE D
M AN U
SC
and high potential barrier of PMMA.
Figure 8. Conduction mechanism of a nonvolatile hybrid memory device (a) Double logarithmic I-V graph of OFF state showing TCSCLC conduction (b) Double logarithmic I-V graph of ON state showing Ohmic conduction (c) Energy band diagram of the as fabricated memory device.
ACCEPTED MANUSCRIPT
4. Conclusion In summary, we have fabricated a rewritable, nonvolatile, and flexible memory device based on a hybrid nanocomposite of PMMA-ZnSnO3 NCs. Entire device fabrication was carried out by
RI PT
using printing technology. The demonstrated memory device showed low VSET, large electrical endurance and long retention time of 2.3 V, 500 voltage sweeps, and 104 s respectively. The switching ratio of this hybrid nanocomposite was as high as ~103 to easily distinguish HRS from
SC
LRS. Electrical characterization results clearly exhibited that the addition of PMMA polymer into the perovskite oxide, ZnSnO3 NCs, had a definite effect on its resistive switching
M AN U
characteristics. TCSCLC and Ohmic conduction models satisfied the transportation mechanism of charge carriers in HRS and LRS as verified by the magnitude of slope values of double logarithmic I-V plots. Furthermore, the effect of device size on the switching ratio of the proposed hybrid nanocomposite was also examined by fabricating three different device sizes of
TE D
100 µm, 200 µm and 300 µm respectively that exhibited an inverse relation. The switching ratio values for 100 µm, 200 µm, and 300 µm were 1.1 × 103, 1.3 × 102 and 4.6 × 101 respectively. We believe that the hybrid nanocomposites of PMMA-ZnSnO3 NCs has a vast scope in various
AC C
EP
electronic devices specifically as a functional layer of a memory device for the future.
ACCEPTED MANUSCRIPT
Acknowledgement This work was supported by the Global Leading Technology Program funded by the Ministry of
AC C
EP
TE D
M AN U
SC
RI PT
Trade, Industry and Energy, Republic of Korea (10042477).
ACCEPTED MANUSCRIPT
References [1]
C. Pan, Y. Ji, N. Xiao, F. Hui, K. Tang, Y. Guo, X. Xie, F.M. Puglisi, L. Larcher, E. Miranda, L. Jiang, Y. Shi, I. Valov, P.C. McIntyre, R. Waser, M. Lanza, Coexistence of
RI PT
Grain-Boundaries-Assisted Bipolar and Threshold Resistive Switching in Multilayer Hexagonal Boron Nitride, Adv. Funct. Mater. 27 (2017) 1604811. doi:10.1002/adfm.201604811.
K. Yang, F. Li, C.P. Veeramalai, T. Guo, A facile synthesis of CH 3 NH 3 PbBr 3
SC
[2]
perovskite quantum dots and their application in flexible nonvolatile memory, Appl. Phys.
[3]
M AN U
Lett. 110 (2017) 83102. doi:10.1063/1.4976709.
M.N. Kozicki, H.J. Barnaby, Conductive bridging random access memory—materials, devices and applications, Semicond. Sci. Technol. 31 (2016) 113001. doi:10.1088/02681242/31/11/113001.
J. Lee, W. Cho, Fabrication of resistive switching memory based on solution processed
TE D
[4]
PMMA-HfO x blended thin films, Semicond. Sci. Technol. 32 (2017) 25009. doi:10.1088/1361-6641/aa5133.
M.M. Rehman, G.U. Siddiqui, S. Kim, K.H. Choi, Resistive switching effect in the planar
EP
[5]
structure of all-printed, flexible and rewritable memory device based on advanced 2D
AC C
nanocomposite of graphene quantum dots and white graphene flakes, J. Phys. D. Appl. Phys. 50 (2017) 335104. doi:10.1088/1361-6463/aa798a.
[6]
K.S. Karimov, Z. Ahmad, F. Touati, M. Mahroof-Tahir, M. Muqeet Rehman, S. Zameer Abbas, Surface-type nonvolatile electric memory elements based on organic-on-organic CuPc-H 2 Pc heterojunction, Chinese Phys. B. 24 (2015) 116102. doi:10.1088/16741056/24/11/116102.
ACCEPTED MANUSCRIPT
[7]
Y. Li, Y.-X. Zhou, L. Xu, K. Lu, Z.-R. Wang, N. Duan, L. Jiang, L. Cheng, T.-C. Chang, K.-C. Chang, H.-J. Sun, K.-H. Xue, X.-S. Miao, Realization of Functional Complete Stateful Boolean Logic in Memristive Crossbar, ACS Appl. Mater. Interfaces. 8 (2016)
[8]
RI PT
34559–34567. doi:10.1021/acsami.6b11465.
M. Prezioso, F. Merrikh-Bayat, B.D. Hoskins, G.C. Adam, K.K. Likharev, D.B. Strukov, Training and operation of an integrated neuromorphic network based on metal-oxide
[9]
SC
memristors, Nature. 521 (2015) 61–64. doi:10.1038/nature14441.
J.J. Yang, D.B. Strukov, D.R. Stewart, Memristive devices for computing, Nat.
[10]
M AN U
Nanotechnol. 8 (2012) 13–24. doi:10.1038/nnano.2012.240.
S. Nau, C. Wolf, S. Sax, E.J.W. List-Kratochvil, Organic Non-Volatile Resistive PhotoSwitches for Flexible Image Detector Arrays, Adv. Mater. 27 (2015) 1048–1052. doi:10.1002/adma.201403295.
D. Ielmini, Resistive switching memories based on metal oxides: mechanisms, reliability
TE D
[11]
and scaling, Semicond. Sci. Technol. 31 (2016) 63002. doi:10.1088/02681242/31/6/063002.
C. Ye, T. Deng, J. Zhang, L. Shen, P. He, W. Wei, H. Wang, Enhanced resistive switching
EP
[12]
performance for bilayer HfO 2 /TiO 2 resistive random access memory, Semicond. Sci.
[13]
AC C
Technol. 31 (2016) 105005. doi:10.1088/0268-1242/31/10/105005.
G.U. Siddiqui, M.M. Rehman, Y.-J. Yang, K.H. Choi, A two-dimensional hexagonal boron nitride/polymer nanocomposite for flexible resistive switching devices, J. Mater. Chem. C. 5 (2017) 862–871. doi:10.1039/C6TC04345C.
[14]
G.U. Siddiqui, M.M. Rehman, K.H. Choi, Resistive switching phenomena induced by the heterostructure composite of ZnSnO 3 nanocubes interspersed ZnO nanowires, J. Mater.
ACCEPTED MANUSCRIPT
Chem. C. 5 (2017) 5528–5537. doi:10.1039/C7TC01105A. [15]
M.M. Rehman, G.U. Siddiqui, Y.H. Doh, K.H. Choi, Highly flexible and electroforming free resistive switching behavior of tungsten disulfide flakes fabricated through advanced
RI PT
printing technology, Semicond. Sci. Technol. 32 (2017) 95001. doi:10.1088/13616641/aa77db. [16]
P.C. Ooi, J. Lin, T.W. Kim, F. Li, Tristable switching of the electrical conductivity
SC
through graphene quantum dots sandwiched in multi-stacked poly(methyl methacrylate) layers, Org. Electron. 38 (2016) 379–383. doi:10.1016/j.orgel.2016.09.010. V.C. Nguyen, P.S. Lee, Resistive Switching Memory Phenomena in PEDOT PSS:
M AN U
[17]
Coexistence of Switchable Diode Effect and Write Once Read Many Memory, Sci. Rep. 6 (2016) 19594. doi:10.1038/srep19594. [18]
M.M. Rehman, B.-S. Yang, Y.-J. Yang, K.S. Karimov, K.H. Choi, Effect of device
TE D
structure on the resistive switching characteristics of organic polymers fabricated through all printed technology, Curr. Appl. Phys. 17 (2017) 533–540. doi:10.1016/j.cap.2017.01.023.
M.M. Rehman, G.U. Siddiqui, J.Z. Gul, S. Kim, J.H. Lim, K.H. Choi, Resistive Switching
EP
[19]
in All-Printed, Flexible and Hybrid MoS2-PVA Nanocomposite based Memristive Device
[20]
AC C
Fabricated by Reverse Offset, Sci. Rep. 6 (2016) 36195. doi:10.1038/srep36195.
E.J. Yoo, M. Lyu, J. Yun, C.J. Kang, Y.J. Choi, L. Wang, Resistive Switching Behavior in
Organic-Inorganic Hybrid CH 3 NH 3 PbI 3 −x Cl x Perovskite for Resistive Random Access Memory Devices, Adv. Mater. 27 (2015) 6170–6175. doi:10.1002/adma.201502889.
[21]
M. V Jacob, D. Taguchi, M. Iwamoto, K. Bazaka, R.S. Rawat, Resistive switching in
ACCEPTED MANUSCRIPT
graphene-organic device: Charge transport properties of graphene-organic device through electric field induced optical second harmonic generation and charge modulation spectroscopy, Carbon N. Y. 112 (2017) 111–116. doi:10.1016/j.carbon.2016.11.005. G.U. Siddiqui, M.M. Rehman, K.H. Choi, Enhanced resistive switching in all-printed,
RI PT
[22]
hybrid and flexible memory device based on perovskite ZnSnO3 via PVOH polymer, Polymer (Guildf). 100 (2016) 102–110. doi:10.1016/j.polymer.2016.07.081.
J.H. Heo, S.H. Im, J.H. Noh, T.N. Mandal, C.-S. Lim, J.A. Chang, Y.H. Lee, H. Kim, A.
SC
[23]
Sarkar, M.K. Nazeeruddin, M. Grätzel, S. Il Seok, Efficient inorganic–organic hybrid
M AN U
heterojunction solar cells containing perovskite compound and polymeric hole conductors, Nat. Photonics. 7 (2013) 486–491. doi:10.1038/nphoton.2013.80. [24]
W. Hu, Z. Zheng, J. Jiang, Vertical organic-inorganic hybrid transparent oxide TFTs gated by biodegradable electric-double-layer biopolymer, Org. Electron. 44 (2017) 1–5.
[25]
TE D
doi:10.1016/j.orgel.2017.02.001.
Y.-K.S. and R.-T.C. Ming-Lung Tu, Hybrid light-emitting diodes from anthracenecontained polymer and CdSeZnS coreshell quantum dots, Nanoscale Res. Lett. 9 (2014)
[26]
EP
1–5. doi:10.1186/1556-276X-9-611.
K.-S. Sohn, S. Timilsina, S.P. Singh, J.-W. Lee, J.S. Kim, A Mechanoluminescent
AC C
ZnS:Cu/Rhodamine/SiO 2 /PDMS and Piezoresistive CNT/PDMS Hybrid Sensor: RedLight Emission and a Standardized Strain Quantification, ACS Appl. Mater. Interfaces. 8 (2016) 34777–34783. doi:10.1021/acsami.6b12931.
[27]
C.H. Bok, C. Wu, T.W. Kim, Operating mechanisms of highly-reproducible write-onceread-many-times memory devices based on graphene quantum dot:poly(methyl silsesquioxane) nanocomposites, Appl. Phys. Lett. 110 (2017) 13301.
ACCEPTED MANUSCRIPT
doi:10.1063/1.4973358. [28]
G. Siddiqui, J. Ali, Y.-H. Doh, K.H. Choi, Fabrication of zinc stannate based all-printed resistive switching device, Mater. Lett. 166 (2016) 311–316.
[29]
RI PT
doi:10.1016/j.matlet.2015.12.045.
M. Reyes-Acosta, A. Torres-Huerta, M. Domínguez-Crespo, A. Flores-Vela, H. DorantesRosales, J. Andraca-Adame, Thermal, Mechanical and UV-Shielding Properties of
SC
Poly(Methyl Methacrylate)/Cerium Dioxide Hybrid Systems Obtained by Melt
Compounding, Polymers (Basel). 7 (2015) 1638–1659. doi:10.3390/polym7091474. G. Ma, R. Zou, L. Jiang, Z. Zhang, Y. Xue, L. Yu, G. Song, W. Li, J. Hu, Phase-
M AN U
[30]
controlled synthesis and gas-sensing properties of zinc stannate (ZnSnO3 and Zn2SnO4) faceted solid and hollow microcrystals, CrystEngComm. 14 (2012) 2172. doi:10.1039/c2ce06272k.
Y.-C. Lai, D.-Y. Wang, I.-S. Huang, Y.-T. Chen, Y.-H. Hsu, T.-Y. Lin, H.-F. Meng, T.-C.
TE D
[31]
Chang, Y.-J. Yang, C.-C. Chen, F.-C. Hsu, Y.-F. Chen, Low operation voltage macromolecular composite memory assisted by graphene nanoflakes, J. Mater. Chem. C.
[32]
EP
1 (2013) 552–559. doi:10.1039/C2TC00010E. K. Oh, W. Jeon, S.-S. Lee, One-Dimensional TiO 2 @Ag Nanoarchitectures with
AC C
Interface-Mediated Implementation of Resistance-Switching Behavior in Polymer Nanocomposites, ACS Appl. Mater. Interfaces. 4 (2012) 5727–5731. doi:10.1021/am301362f.
[33]
S. Sarma, B.M. Mothudi, M.S. Dhlamini, Unipolar resistive switching behaviour of copper doped polyvinyl alcohol/lead sulphide quantum dot device, J. Mater. Sci. Mater. Electron. 27 (2016) 3785–3790. doi:10.1007/s10854-015-4223-5.
ACCEPTED MANUSCRIPT
[34]
Z. Ma, C. Wu, D.U. Lee, F. Li, T.W. Kim, Carrier transport and memory mechanisms of multilevel resistive memory devices with an intermediate state based on double-stacked organic/inorganic nanocomposites, Org. Electron. 28 (2016) 20–24.
[35]
RI PT
doi:10.1016/j.orgel.2015.10.002.
B. Hu, C. Wang, J. Wang, J. Gao, K. Wang, J. Wu, G. Zhang, W. Cheng, B.
Venkateswarlu, M. Wang, P.S. Lee, Q. Zhang, Inorganic–organic hybrid polymer with
SC
multiple redox for high-density data storage, Chem. Sci. 5 (2014) 3404. doi:10.1039/C4SC00823E.
M AN U
D. Wang, F. Ji, X. Chen, Y. Li, B. Ding, Y. Zhang, Quantum conductance in MoS 2 quantum dots-based nonvolatile resistive memory device, Appl. Phys. Lett. 110 (2017)
EP
TE D
93501. doi:10.1063/1.4977488.
AC C
[36]
ACCEPTED MANUSCRIPT
Effect of Adding a Polymer and Varying Device Size on the Resistive Switching Characteristics of Perovskite Nanocubes Heterojunction 1
Young Jin Yang†, 1Muhammad Muqeet Rehman†, 1Ghayas Uddin Siddiqui, 2Kyoung Hoan Na, 1 Kyung Hyun Choi* Department of Mechatronics Engineering, Jeju National University, 690-756, Republic Korea. 2 College of Engineering, Dankook University, Gyeonggi, Korea. * E-mail address:
[email protected] Both authors have equal contribution
†
M AN U
TE D EP
• • • •
A hybrid organic-inorganic nanocomposite of PMMA and ZnSnO3 nanocubes is proposed. Resistive switching behavior of ZnSnO3 is remarkably enhanced by adding PMMA. All printed approach was adopted to fabricate the suggested memory device. Effect of device size on the switching properties was also measured. Memory device showed high electrical and mechanical endurance with large repeatability.
AC C
•
SC
Highlights
RI PT
1
