Correlation between Ni valence and resistance modulation on

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Correlation between Ni valence and resistance modulation on SmNiO chemical transistor 3

Daiki Kawamoto, Azusa N. Hattori, Mahito Yamamoto, Xin Liang Tan, Ken Hattori, Hiroshi Daimon, and Hidekazu Tanaka ACS Appl. Electron. Mater., Just Accepted Manuscript • DOI: 10.1021/acsaelm.8b00028 • Publication Date (Web): 18 Dec 2018 Downloaded from http://pubs.acs.org on December 19, 2018

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ACS Applied Electronic Materials

Correlation between Ni valence and resistance modulation on SmNiO3 chemical transistor Daiki Kawamoto1, Azusa N. Hattori1, 2, Mahito Yamamoto1, Xin Liang Tan3, Ken Hattori3, Hiroshi Daimon3, and Hidekazu Tanaka1,* AUTHOR ADDRESS 1Institute

of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047,

Japan 2JST-PRESTO,

3Graduate

Kawaguchi, Saitama 332-0012, Japan

School of Science and Technology, Nara Institute of Science and Technology, Ikoma,

Nara 630-0192, Japan KEYWORDS Nickelate.thin film, oxygen vacancy, redox reaction, nonvolatile, control resistance modulation

ABSTRACT

The resistance modulation under various gate voltage (Vg) application conditions was systematically studied for a chemical field effect transistor (FET) composed of a SmNiO3 (SNO)

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film channel and an ionic liquid gate insulator. The channel resistance of the SNO chemical FET changed nonlinearly over a wide range for different temperatures, Vg magnitudes, and Vg application durations. The correlation between the modulated resistance and the Ni valence state was quantitatively revealed using X-ray photoelectron spectroscopy. A model describing the resistance change with the Vg application conditions was proposed by considering the kinetics of the reduction reaction on the SNO channel. This model enables the resistance to be predicted for given Vg application conditions, and selective resistance modulation over a wide range of resistances has been demonstrated.

TEXT

INTRODUCTION

The combination of exotic materials, such as a strongly correlated electron material (SCEM) and an ionic liquid (IL), sometimes results in novel reactions.1 For example, a field effect transistor (FET) composed of an SCEM and IL as the channel and gate insulator, respectively, often shows a huge resistance change due to the chemical reaction between the channel and the IL interface.213

To realize new FETs beyond the conventional performance, an SCEM chemical FET has the

potential to introduce new functionalities.8,14,15 A chemical-FET with a channel of SmNiO3 (SNO), which is a typical SCEM, showed nonvolatile and multilevel analogue resistance states by control gating through an IL.7,8 The mechanism of resistance modulation on the IL gate layer has been proposed to be a redox reaction, where the creation or annihilation of oxygen vacancies generated on the SNO channel


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surface occurs depending on whether the gate voltage (Vg) is positive or negative, respectively.7,8,15 One of the advantages of chemical FETs is their analogue and multistate responses, which can lead to the evolution of new types of device such as those with biomimetic functionalities.7,8 Thus, precise control of the huge resistance modulation is indispensable for realizing a programmable fluidic response and opening up new possibilities for SCEM devices. In contrast to the electrostatic FET devices, the resistance modulation mechanism of chemical FET devices is still unclear because of the lack of quantitative understanding of the relationship between the redox reactions and the device performance, i.e., the resistance change. In this study, we systematically studied the magnitude of the Ni valence state modification through Vg application using X-ray photoelectron spectroscopy (XPS) and revealed the quantitative relationship between change in the Ni valence and the modulated resistance for different Vg application conditions, such as the operation temperature, Vg magnitude, and Vg application duration. Finally, we demonstrated accurate control of the resistance on a SNO chemical-FET with an IL on the basis of the quantitative relationship among the chemical state, resistance modulation, and Vg application conditions.

EXPERIMENTAL

A 12-nm-thick SNO film was deposited on a LaAlO3(001) substrate by pulsed laser deposition (PLD) (ArF excimer, =193 nm). The base pressure in the PLD chamber was lower than 2×10−6 Pa. The film growth temperature and oxygen pressure were set to 948 K, and 30 Pa, respectively. After the deposition, the film was simultaneously annealed in situ for 1 hour at 1023 K under an oxygen pressure of 30 Pa. The SNO film was patterned into a Hall bar structure with a channel size of 30 m × 10 m × 12 nm by photolithography and Ar ion milling. Au/Ni were deposited


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by electron-beam evaporation at room temperature (RT) to form the source (S), drain (D), and gate (G) electrodes. The channel and gate electrodes were isolated by sputtered SiO2. The IL electrolyte N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis-trifluoromethylsulfonyl)imide was used as the gate dielectric. The channel SNO and the isolated gate electrodes were covered by the IL (Fig. S1(a)). Note that in this study the SNO films with certain amount of oxygen vacancies, that is, vacancies, a large part of which is counter part of Ni2+ with 20-30 % of all Ni at initial was employed as the channel on a chemical transistor to obtain the higher resistance modulation efficiency. The resistance modulation behavior for the SNO film channel with less oxygen vacancies is shown in Fig. S2. The resistance modulation was measured using a Physical Property Measurement System (Quantum Design). The resistance modulation of the SNO channel was performed as a function of the Vg magnitude (1.0–3.8 V), Vg application duration (0–105 sec), and temperature (300–400 K) at a drain voltage VD of 0.1 V. Here, the modulated resistance is defined as the value obtained by dividing the resistance after gating by the pristine resistance of the channel. The devices after resistance modulation by gating were placed in an XPS chamber after removing the IL from the channel surface. XPS spectra were obtained using monochromatic Al K X-rays (h = 1486.6 eV) at RT. The XPS system (PHI 5000 VersaProbe Ш, Ulvac-Phi) equipped with Ar+ sputtering equipment (0.5-2.0 kV, Ar pressure: ∼5 × 10−3 Pa) enabled the in-situ channel surface cleaning and the depth-profile investigation. The core-level spectra were obtained with a pass energy of 40 eV, an energy resolution of 0.8 eV, and an X-ray spot size of ∼50 m. The binding energy (BE) of the spectra was taken relative to the valence band maximum, which was measured with the Al K1 photon line. The background was subtracted using the Shirley method.17 Peaks in each spectrum were fitted by a Voight (i.e., convolution of Gaussian and Lorentzian) curves.


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RESULTS and DISCUSSION

The channel resistance on the SNO chemical-FET increased and decreased upon applying a positive and negative Vg, respectively. It exhibited a nonvolatile and reversible resistance change (Fig. 1(a) inset). Figure 1(a) shows the Vg dependence of the modulated resistance, which is defined as the resistance at Vg normalized by the initial resistance (R/Rint) at T = 380 K, when a positive Vg was applied for 30 sec. The resistance modulation was observed at Vg ≧1.0 V. The modulated resistance was small but significantly increased below 2.5 V in Vg and drastically increased above 2.7 V, namely, the modulated resistances were ~1.02, ~102, and ~103 at 1.0 V, 2.7 V, and 3.0 V, respectively. Figure 1(b) shows the dependence of the modulated resistance on the operation temperature (T) at Vg = 2.6 V (Vg = 1.0 in the inset); the modulated resistance increased from 1 to 103 (from 1 to 1.016) with increasing operation temperature from 300 K to 390 K. The modulated resistance as a function of Vg and T is shown in Fig. 1(c), which indicates the nonlinear response of the resistance modulation to both Vg and T. In order to elucidate the resistance modulation mechanism, the change in the valence state of Ni through the Vg application was investigated using XPS. The SNO chemical FET device showed a nonvolatile property and its electrical resistance was maintained for as long as 1 week under atmospheric conditions after removing the IL (Fig. S1(b)). Such a long retention time enables ex-situ XPS measurement to compare the electrical structure. Three samples (devices 13) with different modulated resistances were prepared by applying suitable values of Vg with reference to Fig. 1(c). Device 1 was pristine and not subjected to Vg application, and the modulated resistance was 1 (Fig. 2(a)). Devices 2 and 3 had modulated resistances of 102 and 105, respectively. Figure 2(b) shows the Ni 2p3/2 spectrum obtained from the SNO channel of


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each device. The observed Ni 2p3/2 spectra were fitted with four symmetric Voigt components: Ni2+, Ni3+, and two La Auger peaks.18 The peak intensity of the Ni2+ component (BE = 852.4 eV) relative to that of Ni3+ (BE = 854.5 eV) increased from device 1 to device 3. The profile measurements of the Ni2+ concentration along the depth direction showed that the reduction reaction occurred at the SNO surface ranging from a depth of 7-9 nm. Figure 2(c) shows the quantitative relationship between the modulated resistance for the devices and the Ni2+ ratio (right axis). The Ni2+ ratio is defined as Ni2+/(Ni2+ + Ni3+)×100 [%], which was estimated from the peak area intensity in Fig. 2(b). The Ni2+ ratio increases with increasing modulated resistance. This clearly indicates that the creation of Ni2+, that is, the progress of the reduction reaction on the SNO channel, namely Ni3+ → Ni2+ results in the increased resistance on the SNO chemical FET device (inset of Fig. 2(c)). This is also consistent with the tendency for the film resistance to increase with the annealing temperature and duration under a reductive N2 atmosphere (Fig. S3).16 Therefore, the higher Ni2+ ratio on devices 2 and 3 than on device 1 means that a reduction reaction occurred upon positive Vg application. The number of generated Ni2+: ∆[Ni2+] was calculated using the change of the Ni2+ ratio.19 From Fig. 2(c), the quantitative relationship between the modulated resistance and the number of generated Ni2+ on the SNO channel ∆[Ni2+] is simply expressed as 𝑅

∆[𝑁𝑖2 + ] = K･log(𝑅𝑖𝑛𝑡) ···(1). Here, K is a constant parameter of 1.66 × 1013 cm-2. Equation (1) shows the degree of progress in the reduction reaction on the channel, which can indicate how much Ni2+ is required to obtain the corresponding resistance value. For example, to obtain the modulated resistance of 10 the amount of Ni2+ required is 1.66 × 1013 cm-2, which corresponds to 1.6% of the Ni in the SNO.


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The origin of eq. (1) is considered as percolation behavior which is reported for the SmNiO3 FET having Ni2+ and Ni3+ distribution8 and lithium ion conductivity in perovskite-type oxides.20 Namely, three dimensional percolation behavior in low resistance region (𝑝 is volume fraction of low resistance state) is express as 𝜎/𝜎𝐿𝑅 = (𝑝 ― 𝑝𝑐)2 ···(2). Our experimental relationship of eq. (1) can be derived from eq.2 (see supporting information), so that microscopic kinetics in resistance modulation is dominated by Ni2+ and Ni3+ percolation via oxygen diffusion. In the SNO chemical FET, the redox reaction rate at the interface between the SNO channel and the IL determines the resistance modulation (Ni2+ generation) speed. In the previous section, the temperature and Vg magnitude dependences (Figs. 1) are discussed for a fixed Vg application duration of 30 sec. To reveal the kinetics of the reduction reaction on the SNO channel, the relationship between the reaction time and Vg, i.e., the Vg dependence of the resistance modulation speed, is further investigated. Figure 3(a) shows the time dependence of the change in resistance for various Vg at T = 390 K. Initially, the resistance hardly increased, then it abruptly increased after a certain incubation time, namely 2 sec for Vg = 2.6 V and 40000 sec for Vg = 1.0 V. The required incubation time for the abrupt jump obviously depends on the magnitude of Vg. In order to discuss the resistance modulation speed, we define the time required to induce a one decade change in resistance as 𝑡𝑅/𝑅𝑖𝑛𝑡 = 10. Since the resistance modulation speed accelerates as reaction proceeds, this definition would be suitable for initial operation in chemical FET. Figure 3(b) shows 𝑡𝑅/𝑅𝑖𝑛𝑡 = 10 against Vg.


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With increasing Vg from 1.0 V to 2.5 V, 𝑡𝑅/𝑅𝑖𝑛𝑡 = 10 logarithmically decreases from 7 × 104 sec to 7 sec. From Fig. 3(b), the relationship between 𝑡𝑅/𝑅𝑖𝑛𝑡 = 10 and Vg is described as 𝑙𝑜𝑔10(𝑡𝑅/𝑅𝑖𝑛𝑡 = 10) = ―𝐴𝑉𝑔··· (3), that is, 𝑡𝑅/𝑅𝑖𝑛𝑡 = 10 = Bexp( ― A’Vg)··· (3)’, where A and B are constant parameters at a fixed temperature T. Then, we calculate the creation speed of Ni2+ (𝑣𝑁𝑖2 + ) using eqs. (1) and (3)’ as

𝑣𝑁𝑖2 + =

𝑑[𝑁𝑖2 + ] 𝑑𝑡

=

𝑑[𝐾 ∙ log (𝑅/𝑅𝑖𝑛𝑡 = 10)] 𝑑𝑡

~𝑡𝑅/𝑅

𝑘 𝑖𝑛𝑡 = 10

𝑘

= 𝐵exp [A’𝑉𝑔] = Cexp[A’𝑉𝑔]··· (4).

Equation (4) shows the dependence of Vg on the reaction speed to Ni2+ on the SNO channel. In a chemical reaction, the reaction speed is often dominated by an Arrhenius type thermal activation process. Our SNO chemical-FET shows similar behavior (eq. (4)). Figure 3 (c) shows the dependence of Vg on the Ni2+ creation speed. Here, the parameter k was estimated to be Klog(10) = 1.66 × 1013. Because the relationship between Vg and the Ni2+ creation speed obeys eq. (4), the time development enables us to estimate the amount of generated Ni2+. When we assume a constant reaction speed 𝑣𝑁𝑖2 + , ∆Ni2+ is calculated using the relationship ∆[Ni2+] is 𝑣𝑁𝑖2 + ∙ t. Then, we obtain the following equation, which can give the resistance as a function of Vg, T, and t. The voltage-, temperature-, and time-dependent resistance of the SNO chemical transistor is able to be expressed as 𝑅 𝑅𝑖𝑛𝑡

= exp[

∆[Ni2 + ] K

] = exp[E ∙ exp[A’ ∙ Vg] ∙ t] ···(5).


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The parameter A’ corresponds to the slope in Fig. 3(c) and the parameter E is the Ni2+ creation speed without Vg application, which are experimentally obtained. A’ is the acceleration parameter and is temperature-dependent. When T = 390 K (black line), A’ = 5.706, and when T = 360 K (red line), A’ = 3.567 (Fig. 3(c)). The reduction of the slope with decreasing temperature means that the reduction reaction is suppressed at lower temperatures. Equation (5) allows us to calculate the time development of the resistance value under various Vg application conditions. Figure 4 shows a comparison between the experimental time evolution of the modulated resistance (blue circles) and values calculated from eq. (5) (green triangles) under various Vg application conditions (lower panel). The calculation of the modulated resistance shows good agreement with the experimental values at Vg of 2.6 V (left) and 3.2 V (middle). However, at Vg = 3.6 V (right), the experimentally obtained resistance value (~104) was 2 orders smaller than the calculated one (~106). This difference seems to be caused by the simplified model, where the Ni2+ creation speed is assumed to be constant during Vg application. At the actual SNO surface, the speed of Ni2+ creation (Ni3+ consumption) may decrease with the passage of time due to the exhaustion of Ni3+ on the SNO surface. The discrepancy between the experimental and calculated values should increase with Vg. Additionally, at Vg of more than 3.0 V, the leak current (the current between the G and D electrodes) became large, suppressing the operation of the FET. Since the threshold Vg for the reduction reaction was 1.0 V, thus, we confirmed the validity of our model in the ranges of 1.0 ≤ Vg ≤ 3.0 and 1 < R/Rint ≤ 103. We finally show the demonstration of wide range resistance modulation using the proposed model based on the kinetics of the reduction reaction on the SNO channel under Vg application. Figures 5 show the modulated resistance evaluated as a function of the Vg magnitude and


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duration time. With increasing Vg and t, the resistance nonlinearly increases. Although the function representing the modulated resistance is a simple function (eq. (4)), this model can explain the resistance modulation behavior over a wide range of Vg magnitudes and times.

CONCLUSION

In conclusion, the magnitude of the modulated resistance was systematically investigated under different Vg application conditions for a SmNiO3 chemical FET. An XPS study quantitatively revealed the correlation between the Ni valence state and the electrical resistance in terms of the three parameters of the gate voltage, gate voltage application time, and operation temperature. The device operation mechanism is well explained by the redox reaction of the SmNiO3 channel surface, where the chemical kinetics depends on the applied Vg with Arrhenius behavior and the Ni2+ creation speed. The model was able to quantitatively describe the resistance modulation behavior in the SmNiO3 chemical FET, and wide range resistance control was demonstrated. The control of a chemical FET with flexible and nonlinear responses, which are absent in a conventional FET, is expected to contribute to the generation of new properties, such as biomimetic switches and/or sensors behaving similarly to the human brain.


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4

2

10

Modulated Resistance

3

10

(a) (a) 2 10 10

1

10

0

T=380 K

20 0 -2

Vg (V)


10

0

1

10

50

100 150 200

50 100 150 200 Time (sec)

0

10

1.0

1.5

4

3

10

2

10

2.5

(b) (b) 1.020 Modulated Resistance


10

2.0 Vg (V)

3.0 Vg=2.6 V

Vg=1.0 V 1.015 1.010 1.005 1.000

1

10

300 320 340 360 380 400 Temperature (K)

0

10

300

320 340 360 Temperature (K)

380

400

(c) Modulated Resistance

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


+

l pp

Temperature (K)

d

ie

Vg

(V

)

A

Figure 1. (a) Vg and (b) temperature dependences of modulated resistance for t = 30 sec. The temperature was maintained at 380 K in (a). The applied Vg in (b) was 2.6 V (1.0 V in the inset). The inset in (a) shows the resistance changes (upper panel) and the response to Vg application profile (bottom panel). (c) Modulated resistance as function of temperature and Vg.


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Device1 Device2 Device3

(a)

9

10

R (Ohm)

8

10

7

10

6

10

5

10

4

10

3

10

280

Normalized Intensity

0.8

360

400

Device3

0.4 0.0 860

858

856

854

852

850

848

846

858 856 Experimental Fitting 3+ Ni

854

852

850

848

846

0.8 0.4

Ni La

0.8

Device2

0.4 0.0860

7.5

Device1

2+

856

852 BE (eV)

848

(c)

32

28

6.0

26

5.5

24

2+

5.0

0

10

1

2

3

4

5

10 10 10 10 10 Modulated Resistance

2+

6.5

Ni

30

14

7.0

ratio (%)

-2

cm )

320 T (K)

(b) (b)

0.0 860

[ΔNi ] (10

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

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22 6 10

Figure 2. (a) Temperature dependence of resistance for device 1 (pristine), device 2 (modulated resistance = 102), and device 3 (modulated resistance = 105). (b) XPS spectra of Ni2p3/2 for each device at RT. Measured Ni2p3/2 spectra (black curves) are fitted with the Voigt functions of four components: Ni2+ (blue), Ni3+ (pink), and two La MNN Auger satellite (green dots) peaks. (c) Relationship between the ∆[Ni2+] (left axis) and the modulated resistance, corresponding to the change of the Ni2+ ratio (right axis). The inset is a schematic illustration of the resistance modulation mechanism in a chemical FET structure corresponding to the reduction reaction between the SNO channel and the IL.


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2

(a) Vg=+2.6 V Vg=+1.8 V Vg=+1.4 V Vg=+1.0 V

10 7 6 5 4 3 2

1

-1

10

5

10

0

10

1

2

3

4

10 10 10 Time (sec)

10

(b) (b)

5

10

T=390K

4

(sec)

10

3

tR/R

int=10

10

2

10

1

10

0

10

-1

10

0.5

1.0

1.5

2.0

2.5

3.0

Vg (V) 14

10

(c) T = 390 K T = 360 K

13

10

12

10

-2

-1

VNi2+ (cm ＊sec )

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


11

10

10

10

9

10

8

10

1.0

1.5

2.0

2.5

3.0

3.5

Vg (V)

Figure 3. (a) The resistance changes in response to Vg application at 390 K. The time at modulated resistance =10 (dashed line) was defined as 𝑡𝑅/𝑅𝑖𝑛𝑡 = 10. (b) Vg dependence of the time for required a 1 digit resistance modulation 𝑡𝑅/𝑅𝑖𝑛𝑡 = 10 at 390 K. (c) Vg dependence of Ni2+ creation speed at 390 K (black circles) and 360 K (red dots).


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Figure 4. Resistance modulation (upper panel) for different Vg application conditions (bottom panel). Green triangles are the resistance values predicted from eq. (5).


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(a)

Tim

e( se c)

Vg

) (V

(b) Modulated Resistance

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


Tim

Vg

e( se

) (V

c)

Figure 5. Operation mapping for the resistance modulation as a function of Vg magnitude and duration (a) at 390 K, and (b) at 360 K. The resistance calculated using eq. (5) is expressed as a color. The black dots represent observed resistance values.


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ASSOCIATED CONTENT Supporting Information. The SNO chemical FET structure and its retention property, the resistance modulation for the SNO chemical FET with the SNO channel whose Ni2+ concentration was 10-15%, the resistance trend for SNO film after annealing under N2 atmosphere, and the relationship between the percolation (eq. (2)) and eq. (1) are provided in support of the results presented above. The Supporting Information are available free of charge.

AUTHOR INFORMATION Corresponding Author E-mail: [email protected]

ACKNOWLEDGMENT The authors are grateful to S. Tonda for her helpful assistance. The authors are also thankful to L. N. Pamasiand and S. Takemoto for their support in XPS measurements. This work was partially supported by a Grant-in-Aid for Scientific Research B (No. 16H06011) and a Grant-in-Aid for Scientific Research A (No. 26246013); the MEXT Elements Strategy Initiative to Form a Core Research Center from the Ministry of Education, Culture, Sports, Science and Technology (MEXT); and the Futaba Research Grant Program of the Futaba Foundation. Part of this work was also supported by the Nanotechnology Platform Project (Nanotechnology Open Facilities in Osaka University) of the MEXT, Japan (Nos. F-16-OS-0012 and F-16-OS-0016).


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(15) Yuan, H.; Shimotani, H.; Ye, J.; Yoon, S.; Aliah, H.; Tsukazaki, A.; Kawasaki, M.; Iwasa, Y. Electrostatic and Electrochemical Nature of Liquid-Gated Electric-Double-Layer Transistors Based on Oxide Semiconductors. J. Am. Chem. Soc. 2010, 132, 18402–18407. (16) Wang, L.; Dash, S.; Chang, L.; You, L.; Feng, Y.; He, X.; Jin, K. J.; Zhou, Y.; Ong, H. G.; Ren, P. Oxygen Vacancy Induced Room-Temperature Metal-Insulator Transition in Nickelate Films and Its Potential Application in Photovoltaics. ACS Appl. Mater. Interfaces 2016, 8, 9769– 9776. (17) Shirley, D. A. High-Resolution x-Ray Photoemission Spectrum of the Valence Bands of Gold. Phys. Rev. B 1972, 5, 4709–4714. (18) Galicka, K.; Szade, J.; Ruello, P.; Laffez, P.; Ratuszna, A. The Photoemission Study of NdNiO3/NdGaO3 Thin Films, through the Metal-Insulator Transition. Appl. Surf. Sci. 2009, 255, 4355–4361. (19) The total number of Ni ions (Ni2+ and Ni3+) was calculated from the channel volume (30 m × 10 m × 12 nm) and the unit cell volume of SmNiO3 (a=5.34 Å, b=5.43 Å, c=7.57 Å). (20) Inaguma, Y.; Mitsuru, I. Influences of Carrier Concentration and Site Percolation on Lithium Ion Conductivity in Perovskite-type Oxides. Solid State Ionics. 1996, 86-88, 257–260.


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Table of Contents

SNO Gate channel S 200 mm

IL

D D Modulated Resistance

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

+Vg

(b)


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Correlation between Ni valence and resistance modulation on

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