Ultrahigh Energy Density in SrTiO3 Film Capacitors - ACS Publications

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Ultrahigh Energy Density in SrTiO Film Capacitors Chuangming Hou, Weichuan Huang, Wenbo Zhao, Dalong Zhang, Yuewei Yin, and Xiao-Guang Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 30 May 2017 Downloaded from http://pubs.acs.org on June 2, 2017

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ACS Applied Materials & Interfaces

1

Ultrahigh Energy Density in SrTiO3 Film Capacitors

2

Chuangming Hou, † Weichuan Huang, † Wenbo Zhao, † Dalong Zhang, † Yuewei Yin,*,†,‡

3

Xiaoguang Li*,†,§

4

†

Hefei National Laboratory for Physical Sciences at the Microscale and Department of

5

Physics, University of Science and Technology of China, Hefei 230026, China

6

‡

Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588,

7 8

USA §

Collaborative Innovation Center of Advanced Microstructures, Nanjing, 210093, China

9

ABSTRACT: Solid-state dielectric film capacitors with high energy-storage density will

10

further promote advanced electronic devices and electrical power systems toward

11

miniaturization, light weight, and integration. In this study, the influence of interface and

12

thickness on energy storage properties of SrTiO3 (STO) films grown on La0.67Sr0.33MnO3

13

(LSMO) electrode are systematically studied. The cross-sectional high resolution

14

transmission electron microscopy reveals an ion interdiffusion layer and oxygen

15

vacancies at the STO/LSMO interface. The capacitors show good frequency stability and

16

increased dielectric constant with increasing STO thickness (410-710 nm). The

17

breakdown strength (Eb) increases with decreasing STO thickness and reaches 6.8

18

MV/cm. Interestingly, the Eb under positive field is enhanced significantly and an

19

ultrahigh energy density up to 307 J/cm3 with a high efficiency of 89% is realized. The

20

enhanced Eb may be related to the modulation of local electric field and redistribution of

21

oxygen vacancies at the STO/LSMO interface. Our results should be helpful for potential

22

strategies to design devices with ultrahigh energy density.

23

KEYWORDS: dielectric capacitor; energy storage; ion interdiffusion; breakdown

24

strength; oxygen vacancy 1

ACS Paragon Plus Environment


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1. INTRODUCTION

2

Ever-increasing energy requirements and the exhaustion of fossil fuels demand an

3

improvement in the efficiency of energy usage, as well as the search for sustainable and

4

renewable resources.1 Solid-state dielectric capacitors store energy electrostatically2 and

5

possess the intrinsic fast charge–discharge capability offering the highest power density

6

among all currently available electrical energy storage devices,3 which is crucial in

7

portable electronics, medical defibrillators, hybrid electric vehicles, and power grids.4-6 In

8

principle, the maximum recoverable energy density (Umax) of linear dielectrics is

9

2 determined by breakdown strength (Eb) and dielectric constant (εr) as: U max = ε 0ε r Eb 2 .

10

Most composites with polymer matrix possess high Umax for their high Eb,5, 7-9 such as 20

11

J/cm3 at 6.46 MV/cm in PVDF with BaTiO3@TiO2 nanofibers,10 but are limited to the

12

relatively low working temperature.4 Inorganic dielectric ceramics can tolerate high

13

working temperature, but the Umax is less than 2 J/cm3 for their very low Eb.11-14 Although

14

Eb of ceramics can be improved by adding glass additions, the value of εr decreases

15

dramatically.15-16 Dielectric films possess much higher Eb than that of bulk ceramics,17-18

16

and inorganic dielectric films with good temperature stability are the suitable materials

17

for energy storage among all candidates.

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Lead-free paraelectric SrTiO3, which has moderate εr (∼300) at room temperature,

19

low dielectric loss (tan δ), and good frequency stability,19 is a good candidate for energy

20

storage.20 In the last few years, researchers were trying to increase Umax of STO

21

ceramics.11,

22

improved by decreasing grain size via adding glass additions, but εr decreases from 300

23

to ∼160.24 By adjusting the Sr/Ti ratio to be 0.996, Eb of STO ceramics can be increased

24

from 0.21 MV/cm to 0.285 MV/cm without reducing εr, and thus Umax is increased from

25

0.7 J/cm3 to 1.2 J/cm3 as a result.11 Further increase of Umax to 1.95 J/cm3 can be attained

21-23

Similar to other inorganic ceramics, Eb of STO ceramics can be

2


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in Sr0.98Ca0.02TiO3 ceramics at 0.333 MV/cm by Ca doping.22 Rare earth elements doping

2

at A site will dramatically increase εr of STO ceramics, but the value of Umax is still less

3

than 4 J/cm3 due to the dramatically decreased Eb.13, 23 Compared with STO ceramics,

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STO films possess much higher Eb and are promising for energy storage. By using

5

artificial interfacial layer Al2O3 (∼6 nm) between electrode and dielectric layer, Umax can

6

be further increased to 17 J/cm3 in 400 nm (BiFeO3)0.6-(SrTiO3)0.4 thin film.25 Higher Eb

7

was also achieved in STO/Al2O3 laminated film capacitors because the naturally formed

8

anodic oxide Al2O3 automatically repairs the defects in the laminated film.26 Recently,

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Sun et al. report that the interface in Ba0.7Ca0.3TiO3-BaZr0.2Ti0.8O3 multilayer films may

10

act as the obstructers for the development of the electric trees, leading an increasing Eb

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with increasing number of interface.27 Besides, Eb of dielectric capacitors can be further

12

increased by improving the distribution of interfacial local electric field via structure

13

modulation in dielectric composites, especially in composites with high-κ dielectric

14

fillers.7-8 These demonstrate that interfacial modifications do enhance the energy density

15

of dielectrics. Moreover, the interfacial coupling between perovskite oxides and

16

manganite oxides will induce novel phenomena at interface,28-29 which may give us new

17

opportunities to further increase energy density of perovskite oxides dielectrics.

18

Here, we investigated the influence of interface and thickness on energy storage

19

properties of STO films grown on La0.67Sr0.33MnO3 (LSMO) bottom electrode, and

20

energy storage properties of STO films grown on Pt electrode were also studied for

21

comparison. Importantly, benefitting from the ion interdiffusion and redistribution of

22

oxygen vacancies at STO/LSMO interface, the Eb of Au/STO/LSMO capacitors under

23

positive field is significantly enhanced, leading to an ultrahigh Umax of 307 J/cm3 with a

24

high efficiency of 89% at 6.6 MV/cm, much higher than the currently highest energy

25

density

of

154

J/cm3

in

dielectric 3


capacitors

based

on


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(Bi1/2Na1/2)0.9118La0.02Ba0.0582(Ti0.97Zr0.03)O3 thin films.17

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2. EXPERIMENTAL DETAILS

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The STO films were fabricated by a magnetron sputtering technique on

4

La0.67Sr0.33MnO3/SrTiO3

5

Au/STO/LSMO capacitors, an LSMO layer with a thickness of 170 nm was first

6

deposited on (001) oriented STO single crystal substrate at 750 °C under a pressure of 4

7

Pa (Ar:O2=1:1), the DC sputtering power was 40 W, and the distance between the

8

substrate and target was 5.5 cm. Subsequently, a STO layer with a thickness of 710 nm

9

was deposited on the LSMO film at 670 °C under a pressure of 1 Pa (Ar:O2=9:1), the RF

10

(13.56 MHz) sputtering power was 60 W, and the distance between the substrate and

11

target was 5 cm. For Au/STO/Pt capacitors, a STO layer with a thickness of 643 nm was

12

grown in the same way on commercial Pt (111)/Ti/SiO2/Si substrate at 700 °C under a

13

pressure of 2 Pa (Ar:O2=9:1), the RF (13.56 MHz) sputtering power and the distance

14

between the substrate and target were 90 W and 5 cm, respectively. Then, different areas

15

of the STO films were etched into different thicknesses by Ar ion beam milling with an

16

acceleration voltage of 150 V. Circular Au electrodes with the same geometrical size (0.1

17

mm in diameter) and interval (0.5 mm) were sputtered on the film surface via a shadow

18

mask.

(001)

(LSMO/STO)

and

Pt/Ti/SiO2/Si

substrates.

For

19

The thicknesses of STO films were measured by cross sectional scanning electron

20

microscope (SEM), as shown in Figures S1 and S2 (Supporting Information). The

21

structure of the films was characterized by scanning transmission electron microscopy

22

(STEM). The annular bright field (ABF) and high angle annular dark field (HAADF)

23

STEM were carried out at 200 kV on a JEOL JEM-ARM200F equipped with aspherical

24

aberration corrector on the condenser lens system. The surface chemical states of STO

25

films were examined by X-ray photoelectron spectroscopy (XPS), as shown in Figure S3 4


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(Supporting Information). The frequency-dependent dielectric constant and loss tangent

2

were measured from 200 Hz to 1 MHz by using an LCR meter (Agilent 4294A). The

3

electric hysteresis (P–E) loops of STO film capacitors were measured at a frequency of 2

4

kHz using monopolar mode by Radiant Technologies Precision Premier II (Radiant Tech.)

5

equipped with high voltage amplifier (TREK MODEL 609B). For a negative polarization,

6

the P–E loops were measured under negative fields by a step of 0.025 MV/cm until

7

catastrophic breakdown occurred. And we take the maximum negative electric field

8

before breakdown as the negative breakdown strength, namely EbN. For a positive

9

polarization, the P–E loops of another dot with the same thickness were measured using

10

the similar step, and the corresponding maximum positive electric field as the breakdown

11

strength EbP was obtained. Energy densities of capacitors were determined by the P–E

12

loops, and detailed calculation method was given in Section 3 of Supporting Information.

13

All the measurements were carried out at room temperature.

14

3. RESULTS AND DISCUSSION

15

Figures 1a-b show the cross section and elemental profile of La or Sr at STO/LSMO

16

interface, respectively, performed by atomically resolved images obtained via STEM

17

using a HAADF detector. It can be seen that the STO film is epitaxially grown on LSMO

18

with an interfacial layer of about 11 unit cells (~4 nm) at STO/LSMO interface as shown

19

in Figure 1b, which is different from the interfacial amorphous layer at the STO/Pt

20

interface (Figure S5a, Supporting information). Within the STO, the Sr atoms appear as

21

the brighter spots forming a square lattice with Ti located at the center of these squares. In

22

LSMO, La (Sr) columns are the brightest with Mn located at the center of their rectangles.

23

Figure 1c shows the DF image and electron energy loss spectrum (EELS) profiles of

24

Ti-L2,3, O-K, Mn-L2,3 and La-M4,5 edges of each layer in the selected interfacial area

25

(green rectangle of Figure 1a), respectively. The splits of L2 and L3 peaks of Ti-L2,3 edges 5



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EELS profiles induced by crystal field,30 is not clear in STO film, indicating a mixture of

2

Ti3+ and Ti4+, and O-K edges are similar to those of oxygen deficient STO,31

3

demonstrating the existence of oxygen vacancies (ܸை•• ) in STO films near the STO/LSMO

4

interface. Around the STO/LSMO interface, Ti-L2,3 peaks can be detected in regions

5

inside LSMO films, and Mn-L2,3 peaks can be also found in a few atom layers inside STO

6

films, while La-M4,5 peaks appear in deeper regions inside STO films. In the region of

7

LSMO films near the STO/LSMO interface, the energy separations of pre-peak a′ and

8

main peak of O-K spectrum are slightly increasing, and the intensities of the main O-K

9

peak decrease along the grown direction. Besides, as shown in Figure 1d, the intensity

10

ratios of Mn-L3 and L2 edges (IL3/IL2) decrease in the region adjacent to STO/LSMO

11

interface along the grown direction. These indicates an increasing tendency of Mn ion

12

chemical valence.32 The average chemical valence of Mn ions will be increasing from +3

13

to +4 with more Sr2+ diffusion into LSMO, which is analogy to more Sr2+ doping in

14

LSMO. Given these considerations, it can be concluded that there is severe interfacial

15

interdiffusion between La and Sr, and less interdiffusion between Mn and Ti at the

16

STO/LSMO interface, which is consistent with that reported by Wang et al..33 The

17

interfacial interdiffusion will consequently induce an interfacial layer mainly consists of

18

(Sr,La)TiO3-δ at the STO side and (La,Sr)(Mn,Ti)O3-δ at the LSMO side, indicated by the

19

region between two red lines in DF image of Figure 1c. The element fractions of La, Mn

20

and Ti are shown in Figure 1e, extracted from the EELS map of the region indicated by

21

green rectangle of Figure 1a. Higher doping content of Sr and Ti dopant in the LSMO

22

adjacent to STO/LSMO interface, will weaken the double exchange interaction between

23

Mn3+ and Mn4+ compared with that of La0.67Sr0.33MnO3,34-35 which will lead to a poor

24

conductivity and a longer charge screening length in LSMO electrode,36 and result in a

25

larger electric field penetration into LSMO.37 6


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1

In order to investigate the thickness-dependent energy storage properties of STO

2

films, the STO films (4mm×5mm) were etched into different thicknesses, as

3

schematically indicated by Figure 2a, ensuring the same bottom interface conditions for

4

different Au/STO/LSMO capacitors. Figure 2b shows the frequency dependencies of εr

5

and tan δ in Au/STO/LSMO capacitors from 200 Hz to 1 MHz. STO films have a little

6

higher εr than that of STO single crystal, which may be ascribed to the existence of ܸை•• .38

7

It can be seen that for all capacitors, εr decreases slightly with increasing frequency and

8

the tan δ increases a little at high frequency band, demonstrating a good frequency

9

stability of Au/STO/LSMO capacitors. Good frequency stability of dielectric constant

10

means that the devices could be used over a wide frequency range, showing advantages in

11

actual applications.39 Similar to that reported by Boesch et al.,40 the value of εr increases

12

with increasing film thickness (d). Compared with that of bulk crystal, the smaller εr of

13

STO films was commonly observed in thin film capacitors owing to a low permittivity

14

interfacial layer.41-44 In our case, the low permittivity interfacial layer could come from

15

incomplete screening in LSMO electrode.37,

16

dipolar field generates a surface charge density on both sides of the slab. A realistic

17

electrode like LSMO is able to screen this perturbation partially for the screening charges

18

distribute over a small region, and the residual unscreened surface charges generate a

19

depolarizing field,43 preventing further development of polarization.42 Especially the

20

bottom LSMO electrode near the interface with additional Sr and Ti doping content

21

induced by ion interdiffusion, possesses relatively poor conductivity and worse ability to

22

screen charges.35-36 In other words, such screening charges in LSMO electrode occupy a

23

finite spatial extent, which can lead to a depolarizing field and a finite capacitance in

24

LSMO electrode adjacent to interface, inducing an interfacial layer with apparently low εr

25

at STO/LSMO interface.37, 42 If a film is thin enough, the measured εr will be much lower

42-43

When a dielectric is polarized, the

7



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1

than the bulk value and close to that of the interfacial layer. With increasing d, the

2

contribution of interfacial layer decreases and εr increases towards the bulk value.

3

The P–E loops of Au/STO/LSMO capacitors with applying the highest positive and

4

negative electric field before breakdown are shown in Figures 3a-b, respectively, and

5

those of Au/STO/Pt capacitors are given in Figures S6a-b (Supporting information).

6

Together with the P-E curves in Figure S7 in Supporting information, one can see that the

7

polarization increases with increasing E until breakdown occurs. The corresponding

8

recoverable energy densities (U) at different electric fields in Figure 3c are calculated by

U =∫

9

Pr

Pmax

E ⋅ dP

(1)

10

where Pmax and Pr are the maximum and remanent polarizations of STO films,

11

respectively. It is clearly observed that the P–E loops of Au/STO/LSMO capacitors

12

depend on the STO film thickness, e.g., at the same E a thicker film has a higher P due to

13

the larger εr, thus the corresponding U becomes higher. Figure 3d shows the electric field

14

dependences of energy storage efficiencies η (the ratio of U and total energy density

15

schematically shown in Figure S8 and calculated using Equation (S1) in Supporting

16

information). Because the P–E loops are slim, especially the ones under positive field,

17

such slim loops will lead to high energy storage efficiencies. The η ranging from 85% to

18

90% for Au/STO/LSMO capacitors is higher than that of most composites and lead-based

19

materials,6, 45-46 which can be attributed to the suppressed carrier injection into STO films,

20

which will be discussed later.

21

Figures 4a-b show the thickness dependences of the maximum recoverable energy

22

densities (Umax) and breakdown strengths (Eb) of Au/STO/LSMO and Au/STO/Pt

23

capacitors, respectively. Here, we denote the maximum recoverable energy density under

24

positive and negative fields as UPmax and UNmax, respectively. The value of UPmax of

8


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1

Au/STO/LSMO capacitors is much higher than that of Au/STO/Pt capacitors.

2

Furthermore, the UPmax is higher than the corresponding UNmax because of the higher EbP

3

in Au/STO/LSMO capacitors. With increasing STO thickness, the variations of Umax of

4

Au/STO/LSMO capacitors are simultaneously affected by increasing εr and decreasing Eb

5

(see Figure 4b). It can be seen from Figure 4b that Au/STO/Pt capacitors have an average

6

Eb of 4.26 MV/cm with d ranging from 347 nm to 643 nm, consistent with that reported

7

by I. Manabu et al.,47 while Eb of Au/STO/LSMO capacitors decreases with increasing d.

8

The EbN of Au/STO/LSMO capacitors ranges from 5.2 MV/cm to 4.3 MV/cm, while EbP

9

ranges from 6.8 MV/cm to 5.5 MV/cm with d ranging from 410 nm to 710 nm.

10

Importantly, EbP of Au/STO/LSMO capacitors is higher than that of most films and

11

composites, such as 4.5 MV/cm in Ba0.7Ca0.3TiO3-BaZr0.2Ti0.8O3 multilayer films (100

12

nm),27 and 6.5 MV/cm in P(VDF-TrFE-CFE) with 12 wt% of h-BN nanosheets.6 The

13

high EbP leads to the highest Umax so far, namely 307 J/cm3 in Au/STO(610 nm)/LSMO

14

capacitor, much higher than the Umax of most composites (20-40 J/cm3),7, 10, 46 even the

15

currently highest Umax of 154 J/cm3 in (Bi1/2Na1/2)0.9118La0.02Ba0.0582(Ti0.97Zr0.03)O3 film.17

16

As for the thickness dependence of Eb, earlier researches have demonstrated that a higher

17

electric field is required to cause breakdown in a thinner film, which can be explained

18

based on different breakdown mechanisms, such as avalanche breakdown,48

19

trapping-detrapping breakdown49 and electromechanical breakdown.50 With further

20

decreasing the thickness d to below a critical thickness (dc), the Eb will be equal to the

21

intrinsic breakdown strength (Ei) of a material.49 Commonly, the relationship between Eb

22

and dielectric thickness d follows an empirical formula as:51

23

Eb = Ei (d − dc )−α

(2)

24

where α is a constant. If d is below dc, Eb becomes thickness-independent and is equal to

25

Ei.51 The solid lines in Figure 4b are the fitting results for Au/STO/LSMO capacitors 9



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1

using Equation (2), which reveals that the values of Ei under positive and negative

2

polarizations are 16.0 MV/cm and 15.1 MV/cm, respectively, the corresponding dc values

3

are about 78 nm and 222 nm, and the α values are about 0.15 and 0.20, lower than the

4

theoretical value (~0.5).52 A lower α value can suppress the steep decrease of Eb with

5

increasing d,53 which would be favorable for practical applications.

6

For the STO films thinner than 500 nm, the Eb of Au/STO/LSMO capacitors are

7

much higher than that of Au/STO/Pt capacitors and most composites, this may be related

8

to the following two aspects. On the one hand, there exists an abrupt change of εr at

9

STO/Pt interface due to the existence of the interfacial amorphous layer (see Figure S1a,

10

Supporting information) with lower εr.41 As we know, there will be considerable

11

polarization charges residing at the interface between two dielectrics with different εr,

12

which will induce excessive high local E in regions of low εr, and thus the values of Eb of

13

composites and ceramics degrade obviously as a result.3, 54-55 The interfacial amorphous

14

layer at STO/Pt interface with relatively high defect density, will suffer high local E, thus

15

the initial hot spots for degraded breakdown will tend to form in these regions.54 On the

16

other hand, there exists an interfacial ion interdiffusion layer which mainly consists of

17

(Sr,La)TiO3-δ and (La,Sr)(Mn,Ti)O3-δ at STO/LSMO interface (see Figures 1a and 1e).

18

The composition gradient ensures εr gradually varies from the value of STO films to that

19

of the region near LSMO electrode. Compared with the situation without dielectric buffer

20

layer induced by ion interdiffusion,56 such a continuous distribution of εr may smooth the

21

distribution of interfacial electric field, and relax the electric field aggregation at

22

STO/LSMO interface. Benefitting from this feature, Au/STO/LSMO capacitors can

23

tolerate much higher E.

24

The difference of Eb between positive and negative polarizations in Au/STO/LSMO

25

capacitors may be closely related to the voltage-driven redistribution of ܸை•• at the 10


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1

STO/LSMO interface. Under a positive field pointing from STO to LSMO, the positively

2

charged ܸை•• will migrate from STO side into LSMO side as illustrated by Figure 5. In

3

this case, STO films will show higher Eb because of the suppressed leakage current with

4

less ܸை•• .38, 47 While the increase of the ܸை•• density of LSMO electrode would enhance

5

the Mn3+/Mn4+ ratio and lead to weaker double-exchange interactions in LSMO, thus, the

6

LSMO electrode adjacent to STO/LSMO interface will have a higher resistivity.36 This

7

may lead to a relatively higher barrier at STO/LSMO interface.28 Such a barrier will act

8

as a charge-blocking layer and suppress the carrier injection into STO films, as proposed

9

by McMillen et al.25 and Kim et al.,46 which can further increase the Eb of

10

Au/STO/LSMO capacitors. For a negative polarization, the ܸை•• will migrate from

11

LSMO electrode into STO films, there will be more ܸை•• in STO films, and the resistivity

12

of both STO films and LSMO electrode decreases. Therefore, STO films should possess a

13

lower Eb in this circumstance, namely, the value of EbP of Au/STO/LSMO capacitors will

14

be larger than that of EbN. According to Figure 4b, the EbP of Au/STO/LSMO capacitors

15

is still much higher than Eb of Au/STO/Pt capacitors when d is larger than 700 nm,

16

meaning this interfacial effect makes great contributions at a wide range, which benefits

17

high energy density.

18

Furthermore, we propose a STO/LSMO multilayer film capacitor, and calculate the

19

energy density of such multilayer film capacitor based on the corresponding data of

20

Au/STO/LSMO capacitors (see Figure S10, Supporting information). The result shows

21

that the STO(610 nm)/LSMO multilayer film capacitor is of a higher energy density

22

(12-13 Wh/kg) than that of current commercial electrochemical supercapacitors (≤8

23

Wh/kg),57 demonstrating the promising future of energy storage devices.

24

4. CONCLUSIONS

25

In summary, we fabricated Au/STO/LSMO film capacitors with different STO film 11



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1

thicknesses, and found that the interfacial ion interdiffusion layer plays a key role in the

2

enhancement of breakdown strength and recoverable energy density via modifying the

3

dielectric constant distribution. Due to the modulation of local electric field and

4

redistribution of oxygen vacancies at STO/LSMO interface, the breakdown strength of

5

Au/STO/LSMO capacitors is greatly enhanced, leading to the highest energy density (307

6

J/cm3 at 6.6 MV/cm with efficiency of 89 %) so far, much higher than the currently

7

highest record of 154 J/cm3 in (Bi1/2Na1/2)0.9118La0.02Ba0.0582(Ti0.97Zr0.03)O3 thin film.17

8

These findings will provide a new strategy to design next generation micro energy

9

storage devices.

10

ASSOCIATED CONTENT

11

Supporting Information. The cross sectional SEM images of STO films, the

12

photoemission spectra of surface layer of STO films, the detailed calculation method of

13

energy density, the cross section of STO/Pt interface, the P-E loops and energy density of

14

Au/STO/Pt capacitors, the P-E curves of Au/STO/LSMO and Au/STO/Pt capacitors, the

15

calculation method of energy storage efficiency of STO film capacitors, the energy

16

storage density and efficiency of Au/STO/LSMO capacitors under negative fields, the

17

schematic diagram and energy density of the STO/LSMO multilayer film capacitor are

18

included. This material is available free of charge via the Internet at http://pubs.acs.org.

19

AUTHOR INFORMATION

20

Corresponding Author

21

*Email: [email protected] (XGL)

22

*Email: [email protected] (YWY)

23

Author Contributions 12


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1

The manuscript was written with contributions from all of the authors. All authors have

2

approved the final version of the manuscript.

3

ACKNOWLEDGMENTS

4

This work was supported by the Natural Science Foundation of China, and the National

5

Basic

6

2012CB922003), and this work was partially carried out at the USTC Center for Micro

7

and Nanoscale Research and Fabrication.

8

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1

TOC graphic

2

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Figure captions

2

Figure 1. (a) Cross-sectional HAADF image of STO/LSMO interface, the insets show

3

the magnifying images of STO and LSMO, where the azury, orange, violet, navy and

4

green spheres refer to La, Sr, Mn, Ti and O atoms, respectively. (b) Element profile of La

5

or Sr along the yellow line in (a). (c) DF image and EELS profiles of Ti-L2,3, O-K,

6

Mn-L2,3 and La-M4,5 edges at the STO/LSMO interface taken from the green box of (a).

7

(d) The IL3/IL2 ratios of Mn-L2,3 EELS profiles in LSMO adjacent to the STO/LSMO

8

interface. (e) Normalized EELS intensities of Ti, La, and Mn calculated from EELS map

9

in the region indicated by green box of (a), and the intensity of La inside LSMO is

10

normalized to be 0.67.

11

Figure 2. (a) Schematic illustration of capacitors with different thicknesses. (b) Dielectric

12

constant and dielectric loss of Au/STO/LSMO capacitors.

13

Figure 3. P–E loops of Au/STO/LSMO capacitors under (a) positive fields and (b)

14

negative fields, the insets show the orientation of E. Variations of (c) recoverable energy

15

density and (d) energy storage efficiency under positive electric fields of Au/STO/LSMO

16

capacitors. Those under negative electric fields are shown in Figure S9 (Supporting

17

information).

18

Figure 4. (a) UPmax and UNmax of Au/STO/LSMO and Au/STO/Pt capacitors as a function

19

of film thickness at room temperature. (b) EbP and EbN of Au/STO/LSMO and Au/STO/Pt

20

capacitors. Black and blue solid lines refer to the fitting results of EbP and EbN of

21

Au/STO/LSMO capacitors, respectively. The cyan region indicates the average

22

breakdown strength of Au/STO/Pt capacitors.

23

Figure 5. Schematic of the migration of oxygen vacancies at STO/LSMO interface. 20


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Figure 1. (a) Cross-sectional HAADF image of STO/LSMO interface, the insets show the magnifying images of STO and LSMO, where the azury, orange, violet, navy and green spheres refer to La, Sr, Mn, Ti and O atoms, respectively. (b) Element profile of La or Sr along the yellow line in (a). (c) DF image and EELS profiles of Ti-L2,3, O-K, Mn-L2,3 and La-M4,5 edges at the STO/LSMO interface taken from the green box of (a). (d) The IL3/IL2 ratios of Mn-L2,3 EELS profiles in LSMO adjacent to the STO/LSMO interface. (e) Normalized EELS intensities of Ti, La, and Mn calculated from EELS map in the region indicated by green box of (a), and the intensity of La inside LSMO is normalized to be 0.67. 161x121mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. (a) Schematic illustration of capacitors with different thicknesses. (b) Dielectric constant and dielectric loss of Au/STO/LSMO capacitors. 71x28mm (300 x 300 DPI)


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Figure 3. P–E loops of Au/STO/LSMO capacitors under (a) positive fields and (b) negative fields, the insets show the orientation of E. Variations of (c) recoverable energy density and (d) energy storage efficiency under positive electric fields of Au/STO/LSMO capacitors. Those under negative electric fields are shown in Figure S9 (Supporting information). 133x99mm (300 x 300 DPI)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. (a) UPmax and UNmax of Au/STO/LSMO and Au/STO/Pt capacitors as a function of film thickness at room temperature. (b) EbP and EbN of Au/STO/LSMO and Au/STO/Pt capacitors. Black and blue solid lines refer to the fitting results of EbP and EbN of Au/STO/LSMO capacitors, respectively. The cyan region indicates the average breakdown strength of Au/STO/Pt capacitors. 76x32mm (300 x 300 DPI)


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Figure 5. Schematic of the migration of oxygen vacancies at STO/LSMO interface. 89x37mm (300 x 300 DPI)


Ultrahigh Energy Density in SrTiO3 Film Capacitors - ACS Publications

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