High-Îº Samarium-Based MetalâOrganic Framework for Gate Dielectric

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High‑κ Samarium-Based Metal−Organic Framework for Gate Dielectric Applications Abhishek Pathak,†,‡,¶ Guan Ru Chiou,⊥ Narsinga Rao Gade,⊥ Muhammad Usman,† Shruti Mendiratta,† Tzuoo-Tsair Luo,† Tien Wen Tseng,□ Jenq-Wei Chen,⊥ Fu-Rong Chen,‡ Kuei-Hsien Chen,*,§,∥ Li-Chyong Chen,*,∥ and Kuang-Lieh Lu*,† †

Institute of Chemistry, Academia Sinica, Taipei 115, Taiwan Department of Engineering and System Science, National Tsing Hua University, Hsinchu 300, Taiwan § Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 106, Taiwan ⊥ Department of Physics, National Taiwan University, Taipei 106, Taiwan ¶ Nano Science and Technology Program, Taiwan International Graduate Program, Academia Sinica, Taipei 115, Taiwan, and National Tsing Hua University, Hsinchu 300, Taiwan □ Department of Chemical Engineering, National Taipei University of Technology, Taipei 106, Taiwan ∥ Center for Condensed Matter Sciences, National Taiwan University, Taipei 106, Taiwan ‡

S Supporting Information *

ABSTRACT: The self-assembly of a samarium-based metal−organic framework [Sm2(bhc)(H2O)6]n (1) in good yield was achieved by reacting Sm(NO3)3·6H2O with benzenehexacarboxylic acid (bhc) in a mixture of H2O−EtOH under hydrothermal conditions. A structural analysis showed that compound 1 crystallized in a space group of Pnmn and adopted a 3D structure with (4,8) connected nets. Temperature dependent dielectric measurements showed that compound 1 behaves as a high dielectric material with a high dielectric constant (κ = 45.1) at 5 kHz and 310 K, which is comparable to the values for some of the most commonly available dielectric inorganic metal oxides such as Sm2O3, Ta2O5, HfO2, and ZrO2. In addition, electrical measurements of 1 revealed an electrical conductivity of about 2.15 × 10−7 S/ cm at a frequency of 5 kHz with a low leakage current (Ileakage = 8.13 × 10−12 Amm−2). Dielectric investigations of the Sm-based MOF provide an effective path for the development of high dielectric materials in the future. KEYWORDS: dielectric, high-κ, hydrothermal, metal−organic framework, samarium

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INTRODUCTION High-κ materials are the essential components of the gate dielectrics used in integrated circuits (ICs).1 Silicon dioxide (SiO2) has primarily been utilized as a gate dielectric in ICs. However, when the effective oxide thickness of SiO2 is below certain limits, large leakage currents develop as a result of quantum tunneling effects.2,3 To replace the SiO2 dielectric, new materials with high-κ dielectric constants and with better compatibility with other electronic components are required to ensure the production of highly efficient electronic devices. As a consequence, the search for new high dielectrics offers an effective approach to further improve the functioning of transistors as predicted by Moore’s law.4 Inorganic materials with high dielectric constant such as Si3N4, Al2O3, Sm2O3, Ta2O5, HfO2, ZrO2, and La2O3 have been used in the past as alternatives to SiO2 in microelectronics.5 Some organic compounds such as polydimethyl glutereate, cyanoethylpullulan, polyvinylphenol, and poly(vinyl alcohol) have also been reported as high dielectric. Nevertheless, these © 2017 American Chemical Society

organic molecules are incompatible as gate dielectrics due to their weak intermolecular interactions and low thermal stability.6−8 Moreover, the current inorganic and organic dielectric materials have major issues related to their reactivity with metallic substrates, thermal stability, mechanical flexibility, and leakage current. Metal−organic frameworks (MOFs) are a new family of inorganic−organic hybrid crystalline materials that represent an alternative choice for future high-κ materials due to their varying charge densities, uniform porosity, structural tunability, functionalization of organic linkers, presence of polar guest molecules, and thermal/mechanical stability.9,10 MOFs have been utilized in diverse applications, including catalysis, gas storage, separation, chemical sensing, luminescence etc.11−16 Expanding the dimensions of applications of MOFs toward electronics is in the initial stage of Received: March 21, 2017 Accepted: June 8, 2017 Published: June 8, 2017 21872

DOI: 10.1021/acsami.7b03959 ACS Appl. Mater. Interfaces 2017, 9, 21872−21878

Research Article

ACS Applied Materials & Interfaces ⎛t⎞ σAC = ωC tan δ ⎜ ⎟ ⎝ A⎠

development, a number of porous MOFs with low dielectric properties have been reported.17−21 However, investigations of high dielectric behavior of MOFs are rare, and further study is highly desirable. There are only a few reports of MOFs with high dielectric constants at particular phase transitions due to the presence of solvent molecules.22−25 Moreover, a very high dielectric value is undesirable in complementary metal-oxidesemiconductors (CMOS) because a large fringing field occurs between the source and drain regions.26,27 Herein, we report the design and synthesis of a high-κ SmMOF (1), which can be potentially used as a gate dielectric by virtue of its high dielectric constant, low dielectric loss, and small leakage current. This Sm-based MOF consists of an electron-rich organic linker benzenehexacarboxylate, and its preparation is in environmentally friendly green solvents (H2O and EtOH). These results provide beneficial solutions toward achieving distinctive applications of MOFs as high-κ gate dielectrics in designing ICs for use in the area of microelectronics and will encourage researchers to utilize MOFs in capacitors, transistors, resonators, integrated circuits, etc., which are currently very rare.15,16,28

where C corresponds to the capacitance (F), t the thickness of the sample (cm), A the area of cross section (cm2), and ε0 the permittivity of the free space (ε0 = 8.854 × 10−14 F/cm). 2.2. Synthesis of [Sm2(bhc)(H2O)6]n (1). The Sm-based MOF [Sm2(bhc)(H2O)6]n (1) was hydrothermally synthesized at 170 °C for 72 h by reacting Sm(NO3)3·6H2O (67.0 mg, 0.20 mmol) and benzenehexacarboxylic acid (H6bhc) (34.2 mg, 0.10 mmol) in a mixture of EtOH and H2O (1:3 v/v) along with 1 drop of a 1.0 M KOH solution. Colorless hexagonal crystals of 1 were isolated on a filter, washed thoroughly with water, and further dried at room temperature. Compound 1 can also be synthesized in the absence of KOH under similar reaction conditions, but the product yields are lower. Yield: 55.1% (41.8 mg; 0.05 mmol). IR data (KBr, cm−1): 3468(m), 3372(m), 3176(m), 1602(m), 1553(s), 1443(s), 1341(s), 1049(w), 919(m), 722(m), 673(m), 595 (m), 534 (m). Anal. calcd for C12H12O18Sm2: C, 19.35%; H, 1.62%. Found: C, 19.33%; H, 1.60%.

3. RESULTS AND DISCUSSION 3.1. Synthesis of Compound 1. In this study, 1 was obtained by the reaction of Sm(NO3)3·6H2O with benzenehexacarboxylic acid (H6bhc) in an EtOH−H2O solvent system at 170 °C under hydrothermal conditions (Scheme 1). Com-

2. EXPERIMENTAL SECTION 2.1. Materials and Methods. The chemical reagents used in these studies were directly purchased and used without further purification. Single-crystal X-ray diffraction measurements were performed on a Bruker-Nonius Kappa CCD diffractometer with graphite monochromated Mo Kα radiation (λ = 0.7107 Å). The crystallographic data and refinement results are provided in Table S1 (Supporting Information). The direct method and the SHELXL-97 program with full-matrix leastsquares on F2 values were used to solve the structure and the refinement, respectively.29 All non-hydrogen atoms were refined anisotropically, while the hydrogen atoms were located in ideal, calculated positions, with isotropic thermal parameters riding on their respective carbon atoms. Infrared spectra (4000−400 cm−1) were collected in the solid state (KBr pellets) on a Perkin−Elmer FT-IR spectrometer (Model, Paragon 1000). Elemental analyses were performed on a Perkin−Elmer 2400 CHN elemental analyzer. Thermogravimetric analyses (TGA) were conducted under an atmosphere of nitrogen with a Perkin−Elmer TGA-7 TG analyzer. Experimental powder X-ray diffraction patterns were obtained on a Siemens D-5000 diffractometer at 40 kV, 30 mA using Cu Kα radiation with a wavelength of 1.5406 Å with a step size of 0.004° and scan speed of 0.15 s per step. The simulated powder diffraction pattern was obtained using the Mercury 1.4.1 software program. AC conductivity, capacitance (C), impedance (Z), and dielectric loss (tan δ) measurements were performed in the frequency range of 20 Hz−1 MHz on an Agilent Model HP-4284A LCR meter with a Lakeshore temperature controller. The measurements were carried out in the temperature range of 10−310 K under vacuum (0.1 Pa or 1 × 10−3 Torr). For each measurement, a constant temperature was maintained within an accuracy of ±0.05 K. For these measurements, the crystals were ground, and the resulting powder was pressed into pellets with a diameter of about 0.6 cm with a thickness between 0.04−0.08 cm. The measurements were taken using a circular pellet in which both sides had been coated with silver paste to allow them to function as electrodes. The experiments were repeated for samples with different thicknesses. Consistent experimental results were obtained within experimental errors. The dielectric permittivity (ε′) and loss (ε″) values along with AC conductivity (σAC) were determined using the following equations: ε′ =

Ct εoA

ε″ = ε′tan δ

(3)

Scheme 1. Synthesis of Compound 1

pound 1 was obtained as colorless hexagonal crystals. The choice of the appropriate organic ligand (H6bhc) with specific functional groups and geometry is crucial in attaining this special structure. The H6bhc ligand was chosen because it contains a hexa-carboxylate functionality and could provide multiple coordination modes, which would facilitate the formation of a 3D framework.30 An FTIR spectrum is included in the Supporting Information (Figure S1). 3.2. Crystal Structure. A structural analysis of 1 showed that the compound crystallized in an orthorhombic space group (Pnmn). Two Sm(III) centers, one bhc6− ligand, and three coordinated water molecules were found in the asymmetric unit. The coordination environment of the metal center and the bhc6− ligand are presented in Figures 1a and c. The Sm(III) center adopts a nine-coordinated {SmO9} tricapped trigonal prismatic geometry by coordinating to four oxygen atoms (O1, O2, O1′, and O2′) of two distinct bhc6− ligands in a chelating fashion, two oxygen atoms (O3″ and O4‴) of two other bhc6− ligands in a monodentate fashion, and three oxygen atoms (O5w, O5′w, and O6w) belonging to the three coordinated H2O molecules (Figure 1a). The lengths of the Sm−O bonds were in the normal range (2.340−2.580 Å). Each bhc6− ligand behaves as a μ8-bridge to connect eight Sm(III) centers in a monodentate and chelating fashion. Each {SmO6} unit is coordinated to four bhc6− ligands to form a 3D network. The Sm(III)···Sm(III) separation across the bhc6− bridges are in the range of 11.620−9.350 Å. The values of metal···metal separation distances are comparable to the previously reported values linked by the bhc6− ligands.31 When the network is viewed along the b-axis, 1D hexagonal channels with diagonal

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Figure 1. (a) Coordination mode of Sm(III) ion. (b) 3D framework in compound 1 viewed along the a-axis. (c) The coordination mode of the ligand. (Sm = blue; O = red; C = light gray).

Figure 2. (a) The as-synthesized and simulated PXRD patterns shown for compound 1. (b) Thermogravimetric analysis curve of compound 1 as a function of temperature.

(experimental: 14.9%, calculated: 14.5%), as shown in the TGA diagram (Figure 2b). No weight loss was observed in the temperature range of 180−455 °C. The decomposition process started at 455 °C. The high thermal stability of compound 1 makes it a suitable candidate for use as a high-κ dielectric material in high temperature applications. 3.4. Dielectric Investigation. The temperature dependent dielectric behavior in the range from 10 to 310 K was studied (Figure 3a). On heating compound 1, the dielectric constant (κ) increased from temperature 10 to 220 K, indicating that the polarization of water molecules increases with increasing temperature. The dielectric constant originates from the ionic and orientational polarization of the water molecules,33,34 hydrogen bonding between the solvents molecules (Figures S3), and the density of the framework.33 It shows high dielectric constant (κ = 45.1) at 310 K (5 kHz), which drops to (κ = 41.9) at 10 K (5 kHz). The frequency dependence permittivity [εr′(ω) + εr″(ω)] of compound 1 was measured from 10 to 310 K, in which εr′(ω) (dielectric constant) and εr″(ω) (dielectric loss) correspond to the real and imaginary parts of the permittivity, respectively. The εr′(ω) value gradually decreases from its highest value (κ = 45.1) at 5 kHz to 42.3 at 0.2 MHz and 300 K (Figure 3b). At low

metal separation distances of 8.30 and 7.11 Å can be observed. Every hexagonal channel along the b-axis is occupied by four water molecules. The one-dimensional hexagonal channels with coordinated water molecules show hydrogen bonding interactions between (H51)···(O2) [1.97 Å], (H52)···(O1) [2.06 Å], (H61)···(O1) [2.05 Å], and (H62)···(O6) [2.19 Å] (Figure S3). The crystallographic information and the crystal refinement parameters of compound 1 are listed in Table S1. If each μ8-bhc6− ligand is considered to be an 8-connected node and every Sm atom is considered to be a 4-connected node, then overall 3D framework structure can be reduced to give (4,8) nets, where a four membered ring is formed through the cooperation of two 4-connected and two 8-connected nodes (Figure S4). The value for N2 adsorption in compound 1 is 0.85 cm3/g at 1 bar, 298 K (Figure S8). Calculations using the PLATON software revealed the extra framework volume to be around 6.9% for compound 1, which confirms the low porosity and high density of the 3D Sm-based framework.32 3.3. Powder X-ray Diffraction and Thermogravimetric Analysis. The powder X-ray diffraction pattern of 1 is in good agreement with the simulated one, indicating the crystallinity of compound 1 (Figure 2a). The coordinated water molecules were eliminated at temperatures between 101 and 180 °C 21874


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Figure 3. (a) Temperature dependent relative permittivity (ε′) of compound 1 with different frequencies. (b) Log10 frequency dependent relative permittivity (ε′) of compound 1 with different temperatures. (c) Temperature dependent dielectric loss (tan δ) of compound 1 with different frequencies and the inset showing dielectric loss (100−150 K). (d) Log10 frequency dependent dielectric loss (tan δ) of compound 1 with different temperatures.

Figure 4. (a) Temperature dependent AC conductivity of compound 1 measured at different frequencies and the inset showing AC conductivity at low frequency (y-axis from 0 to 1.9 μS/cm). (b) Frequency dependent AC conductivity of compound 1 measured at different temperatures and the inset showing AC conductivity at low frequency (log10 0.56 to 0.64 μS/cm).

frequencies, the coordinated water molecules at the metal center were polarized along the applied electric field. At higher frequencies, the movement of the dipole cannot keep up with the alternating field, and the polarization mechanism drops to contribute to the polarization of the dielectric by coordinated water molecules. Hence, for compound 1, the permittivity gradually decreases with an increasing frequency. The dielectric loss (tan δ = 0.023) of compound 1 was low at 0.2 MHz and 310 K (Figure 3c). The dielectric loss remains constant at different temperatures and shows decaying behavior with different frequencies (Figure 3d).

The origin of the high dielectric of compound 1 at a low frequency (5 kHz) can be attributed to the high charge density associated with the Sm(III) ions and the presence of the benzene hexacarboxylate ligand. The dielectric constant of dehydrated compound 1′ (κ = 27.6) at 310 K and 0.2 MHz with low dielectric loss (tan δ = 0.024) was observed (Figures S6 and S7). This confirms the origin of high dielectric constant from the coordinated water molecule as well as high charge density of the samarium ion and the benzene hexacarboxylate ligand. The high dielectric constant originates from the 21875


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Figure 5. (a) Impedance plot of real impedance vs imaginary impedance with the equivalent circuit for compound 1. (b) Experimental results for impedance vs frequency at different temperatures are shown for compound 1.

was determined to be 1 × 105 Ω, as shown in Figure 5a. From this value for the resistance, the conductivity can be calculated to be 2.83 × 10−6 S/cm. This shows that the value for the conductivity of compound 1 can be attributed to an electron or bipolaron hopping mechanism.39−41 The impedance of compound 1 in Figure 5b drops with increasing frequency, indicating that the reactive part of the impedance was capacitive. 3.7. Leakage Current Measurement. The leakage current was measured as a function of the applied voltage (V) in a metal−insulator−metal (MIM) configuration to evaluate the quality of the dielectric material (Figure 6a and b). Both sides

different polarization mechanisms (electronic, atomic, interfacial and ionic, etc.) in the lower frequency region.35,36 According to the polarization theory of ionic crystal discussed by Qu et al., the distance between metal cation and anions from the ligand are responsible for high dielectric constant of desolvated metal−organic frameworks. The high dielectric constant of dehydrated compound 1′ can be attributed to the polarized interaction between the Sm metal center and the O atom of the ligand.37 3.5. Electrical Conductivity Measurements. The electrical conductivity (IAC) of 1 at different temperatures showed the linear increase with respect to frequency. The intercept and slope can be calculated from the equation σAC = AωS where σAC is the AC conductivity, A is the intercept and constant, ω is the frequency, and S is the slope. The calculated value of the slope was determined to be from 0.93 to 0.92, indicating that AC conductivity is derived from hopping (i.e. carrier jump from one moiety to another).38 The AC conductivity of compound 1 remains invariable at different temperatures for an individual frequency (Figure 4a) and increases from 2.15 × 10−7 S/cm (5 kHz) to 1.46 × 10−5 S/cm (0.5 MHz) with increasing frequency, as shown in Figure 4b. The increasing σAC at higher frequencies is attributed to charge carriers that can be transported by a hopping mechanism. 3.6. Impedance Behavior. The frequency dependent dielectric behavior of compound 1 was further investigated by impedance spectroscopy at room temperature. The impedance data can be fitted using the equivalent circuit in impedance analyzer. Both the experimental results and simulation data indicate that the high dielectric constant can be attributed to the intrinsic behavior of compound 1. As shown in Figure 5a, a large arc was modeled through two equivalent circuits that were connected in series. The first circuit, corresponding to the impedance arising from the crystal grain interface, consisted of two elements, the resistance (R1) in parallel with the constant phase element (CPE1). The second circuit, corresponding to the impedance from the bulk material, also contained two elements, the resistance (R2) and the constant phase element (CPE2), connected in parallel. The capacitance calculated from the impedance curve at room temperature was determined to be 0.44 pF, which can be attributed to the intrinsic behavior of the bulk compound. The crystal grains are largely responsible for the high dielectric. The equation σ = d/RA was used to calculate the conductivity of the material. In the equation, d corresponds to the thickness of the bulk phase; R corresponds to the resistance obtained from the impedance fitting curves, and A is the area of the electrode. The value of the resistance R

Figure 6. (a) Schematic diagram of leakage current measurements for compound 1. (b) Leakage current density vs applied voltage of compound 1.

of a pellet of compound 1 were coated with silver (Ag) to form an electrode. At 0 V, a very small leakage current of 8.13 × 10−12 A mm−2 was observed under ambient conditions. Such a low gate leakage current (Ileakage) for this high-κ Sm-based MOF (1) renders it a promising material for high-κ gate dielectrics in designing integrated circuits. 21876


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(2) Chau, R.; Datta, S.; Doczy, M.; Doyle, B.; Kavalieros, J.; Metz, M. High-k/Metal−Gate Stack and its MOSFET Characteristics. IEEE Electron Device Lett. 2004, 25, 408−410. (3) Ha, Y. G.; Everaerts, K.; Hersam, M. C.; Marks, T. J. Hybrid Gate Dielectric Materials for Unconventional Electronic Circuitry. Acc. Chem. Res. 2014, 47, 1019−1028. (4) Moore, G. E. Progress in Digital Integrated Electronics. IEEE Int. Electron Devices Meet., Technol. Dig. 1975, 21, 11−13. (5) Singh, R.; Ulrich, R. K. High and Low Dielectric Constant Materials. Electrochem. Soc. Interface. 1999, 8, 26−30. (6) Baldwin, A. F.; Ma, R.; Mannodi-Kanakkithodi, A.; Huan, T. D.; Wang, C.; Tefferi, M.; Marszalek, J. E.; Cakmak, M.; Cao, Y.; Ramprasad, R.; Sotzing, G. A. Poly(Dimethyltin Glutarate) as a Prospective Material for High Dielectric Applications. Adv. Mater. 2015, 27, 346−351. (7) Facchetti, A.; Yoon, M. H.; Marks, T. J. Gate Dielectrics for Organic Field-Effect Transistors: New Opportunities for Organic Electronics. Adv. Mater. 2005, 17, 1705−1725. (8) Dimitrakopoulos, C. D.; Purushothaman, S.; Kymissis, J.; Callegari, A.; Shaw, J. M. Low-Voltage Organic Transistors on Plastic Comprising High−Dielectric Constant Gate Insulators. Science 1999, 283, 822−824. (9) Li, H.; Eddaoudi, M.; O’Keeffe, M.; Yaghi, O. M. Design and Synthesis of an Exceptionally Stable and Highly Porous Metal− Organic Framework. Nature 1999, 402, 276−279. (10) Kitagawa, S.; Kitaura, R.; Noro, S. I. Functional Porous Coordination Polymers. Angew. Chem., Int. Ed. 2004, 43, 2334−2375. (11) Féreya, G. Hybrid Porous Solids: Past, Present, Future. Chem. Soc. Rev. 2008, 37, 191−214. (12) Li, J. R.; Kuppler, R. J.; Zhou, H. C. Selective Gas Adsorption and Separation in Metal−Organic Frameworks. Chem. Soc. Rev. 2009, 38, 1477−1504. (13) Murray, L. J.; Dinca, M.; Long, J. R. Hydrogen Storage in Metal−Organic Frameworks. Chem. Soc. Rev. 2009, 38, 1294−1314. (14) Allendorf, M. D.; Schwartzberg, A.; Stavila, V.; Talin, A. A. A Roadmap to Implementing Metal−Organic Frameworks in Electronic Devices: Challenges and Critical Directions. Chem. - Eur. J. 2011, 17, 11372−11388. (15) Stavila, V.; Talin, A. A.; Allendorf, M. D. MOF-Based Electronic and Optoelectronic Devices. Chem. Soc. Rev. 2014, 43, 5994−6010. (16) Mueller, U.; Schubert, M.; Teich, F.; Puetter, H.; Schierle-Arndt, K.; Pastre, J. Metal−Organic Frameworks-Prospective Industrial Applications. J. Mater. Chem. 2006, 16, 626−636. (17) Usman, M.; Lee, C. H.; Hung, D. S.; Lee, S. F.; Wang, C. C.; Luo, T. T.; Zhao, L.; Wu, M. K.; Lu, K. L. Intrinsic Low Dielectric Behaviour of a Highly Thermally Stable Sr-Based Metal−Organic Framework for Interlayer Dielectric Materials. J. Mater. Chem. C 2014, 2, 3762−3768. (18) Usman, M.; Mendiratta, S.; Lu, K. L. Metal−Organic Frameworks: New Interlayer Dielectric Materials. ChemElectroChem 2015, 2, 786−788. (19) Mendiratta, S.; Usman, M.; Luo, T. T.; Chang, B. C.; Lee, S. F.; Lin, Y. C.; Lu, K. L. Anion-Controlled Dielectric Behavior of Homochiral Tryptophan-Based Metal−Organic Frameworks. Cryst. Growth Des. 2014, 14, 1572−1579. (20) Hendon, C. H.; Walsh, A.; Dinca, M. Frontier Orbital Engineering of Metal−Organic Framework with Extended Inorganic Connectivity: Porous Alkaline-Earth Oxides. Inorg. Chem. 2016, 55, 7265−7269. (21) Eslava, S.; Zhang, L.; Esconjauregui, S.; Yang, J.; Vanstreels, K.; Baklanov, M. R.; Saiz, E. Metal−Organic Framework ZIF-8 Films As Low-κ Dielectrics in Microelectronics. Chem. Mater. 2013, 25, 27−33. (22) Zhou, B.; Kobayashi, A.; Wang, Z. M.; Long, L. S.; Kobayashi, H. Anomalous Dielectric Behaviour and Thermal Motion of Water Molecules Incorporated in Porous Crystals. Phys. Status Solidi C 2012, 9, 1216−1218. (23) Ye, Q.; Song, Y. M.; Wang, G. X.; Chen, K.; Fu, D. W.; Hong Chan, P. W.; Zhu, J. S.; Huang, S. D.; Xiong, R. G. Ferroelectric

4. CONCLUSION To summarize, we successfully synthesized a novel Sm-based 3D MOF that exhibits a high dielectric constant (κ = 45.1) at 310 K and 5 kHz. Polarized coordinated water molecules, high density, and hydrogen bonding in the hexagonal channels are responsible for the high dielectric behavior of compound 1. The Sm-based MOF was synthesized in green solvents through a single step self-assembly process. Impedance results showed that the origin of the dielectric properties is from the intrinsic properties of the crystal grain. The high dielectric constant with an incredibly low electrical conduction (IAC) and low leakage current (Ileakage) along with its having a highly thermal stable framework makes compound 1 a potential material for use in high-κ gate dielectric applications. The results presented here indicate the potential utility of MOFs as ideal gate dielectrics which stimulate us to develop new MOFs for advanced microelectronics.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.7b03959. Crystal information and the structural refinement of compound 1 (Table S1); intercept and slope data as calculated from the AC conductivity vs frequency plot of compound 1 (Table S2); fitting values from the equivalent circuit drawn for compound 1 (Table S3); FTIR spectra of mellitic acid and Sm-MOF-1 (Figure S1); 3D framework of 1, (Figures S2 and S3); 3D network showing (4,8) connected network (Figure S4); optical image of the Sm-MOF-1 (Figure S5); temperature dependent relative permittivity (ε′) of compound 1 without water with different frequency after annealing at 200 °C (Figure S6); temperature dependent dielectric loss (tan δ) of the dehydrated sample of Sm-MOF-1 with different frequency after annealing at 200 °C (Figure S7); N2 adsorption and desorption of Sm-MOF-1 at different pressures (Figure S8); energy dispersive X-ray spectrum of Sm-MOF-1 by scanning electron microscopy (Figure S9) (PDF) Crystallographic data for C6H6O9Sm (CIF); CCDC = 1528426 (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. ORCID

Kuang-Lieh Lu: 0000-0002-5529-7126 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to Academia Sinica, Taiwan International Graduate Program, and the Ministry of Science and Technology, Taiwan for financial support.

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REFERENCES

(1) Jaeger, R. C. Introduction to Microelectronic Fabrication; Prentice Hall: NJ, 2002; Vol. 5, Chapter 2. 21877


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ACS Applied Materials & Interfaces Metal−Organic Framework with a High Dielectric Constant. J. Am. Chem. Soc. 2006, 128, 6554−6555. (24) Fu, D. W.; Dai, J.; Ge, J. Z.; Ye, H. Y.; Qu, Z. R. Synthesis, Structure and Dielectric Properties of the First 1D Ba-Tetrazole Complex [Ba(4-TPA)2(H2O)4·3.5(H2O)]n. Inorg. Chem. Commun. 2010, 13, 282−285. (25) Chen, Q.; Guo, P. C.; Zhao, S. P.; Liu, J. L.; Ren, X. M. A Rhombus Channel Metal−Organic Framework Comprised of Sr2+ and Thiophene-2,5-Dicarboxylic Acid Exhibiting Novel Dielectric Bistability. CrystEngComm 2013, 15, 1264−1270. (26) Plummer, J. D.; Griffin, P. B. Material and Process Limits in Silicon VLSI Technology. Proc. IEEE 2001, 89, 240−258. (27) Houssa, M.; Pantisano, L.; Ragnarsson, L. Å.; Degraeve, R.; Schram, T.; Pourtois, G.; De Gendt, S.; Groeseneken, G.; Heyns, M. M. Electrical Properties of High-κ Gate Dielectrics: Challenges, Current Issues, and Possible Solutions. Mater. Sci. Eng., R 2006, 51, 37−85. (28) Li, W. J.; Liu, J.; Sun, Z. H.; Liu, T. F.; Lü, J.; Gao, S. Y.; He, C.; Cao, R.; Luo, J. H. Integration of Metal−Organic Frameworks into an Electrochemical Dielectric Thin Film for Electronic Applications. Nat. Commun. 2016, 7, 11830−11838. (29) Sheldrick, G. M. SHELXL-97, Program for Structure Refinement; University of Göttingen: Germany, 1997. (30) Wu, L. P.; Munakata, M.; Kuroda-Sowa, T.; Maekawa, M.; Suenaga, Y. Synthesis, Crystal Structures and Magnetic Behavior of Polymeric Lanthanide Complexes with Benzenehexacarboxylic Acid (Mellitic Acid). Inorg. Chim. Acta 1996, 249, 183−189. (31) Rodrigues, M. O.; Paz, F. A. A.; Freire, R. O.; de Sá, G. F.; Galembeck, A.; Montenegro, M. C.; Araújo, A. N.; Alves, S., Jr Modeling, Structural, and Spectroscopic Studies of Lanthanide− Organic Frameworks. J. Phys. Chem. B 2009, 113, 12181−12188. (32) Spek, A. L. Single-Crystal Structure Validation with the Program PLATON. J. Appl. Crystallogr. 2003, 36, 7−13. (33) Cui, H. B.; Takahashi, K.; Okano, Y.; Kobayashi, H.; Wang, Z.; Kobayashi, A. Dielectric Properties of Porous Molecular Crystals that Contain Polar Molecules. Angew. Chem., Int. Ed. 2005, 44, 6508−6512. (34) Zhou, B.; Kobayashi, A.; Cui, H. B.; Long, L. S.; Fujimori, H.; Kobayashi, H. Anomalous Dielectric Behavior and Thermal Motion of Water Molecules Confined in Channels of Porous Coordination Polymer Crystals. J. Am. Chem. Soc. 2011, 133, 5736−5739. (35) Cardarelli, F. Materials Handbook: A Concise Desktop Reference; Springer: London, 2008. (36) Patil, D. R.; Lokare, S. A.; Devan, R. S.; Chougule, S. S.; Kanamadi, C. M.; Kolekar, Y. D.; Chougule, B. K. Studies on Electrical and Dielectric Properties of Ba1−xSrxTiO3. Mater. Chem. Phys. 2007, 104, 254−257. (37) Qu, B. T.; Lai, J. C.; Liu, S.; Liu, F.; Gao, Y. D.; You, X. Z. Cuand Ag-Based Metal−Organic Frameworks with 4-Pyranone-2,6Dicarboxylic Acid: Syntheses, Crystal Structures, and Dielectric Properties. Cryst. Growth Des. 2015, 15, 1707−1713. (38) Ghosh, A. Frequency-Dependent Conductivity in BismuthVanadate Glassy Semiconductors. Phys. Rev. B: Condens. Matter Mater. Phys. 1990, 41, 1479−1488. (39) Sánchez-Andújar, M.; Yáñez-Vilar, S.; Pato-Doldán, B.; GómezAguirre, C.; Castro-García, S.; Señarís-Rodríguez, M. A. Apparent Colossal Dielectric Constants in Nanoporous Metal−Organic Frameworks. J. Phys. Chem. C 2012, 116, 13026−13032. (40) Sinclair, D. C.; Adams, T. B.; Morrison, F. D.; West, A. R. CaCu3Ti4O12: One-Step Internal Barrier Layer Capacitor. Appl. Phys. Lett. 2002, 80, 2153−2155. (41) Pato-Doldán, B.; Sánchez-Andújar, M.; Gómez-Aguirre, L. C.; Yáñez-Vilar, S.; Lopez-Beceiro, J.; Gracia-Fernández, C.; SeñarísRodríguez, M. A. Near Room Temperature Dielectric Transition in the Perovskite Formate Framework [(CH3)2NH2][Mg(HCOO)3]. Phys. Chem. Chem. Phys. 2012, 14, 8498−8501.

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