High-Dielectric Constant Thin Films for Dynamic Random Access Memories (Dram)

Scott, J. F.

doi:10.1146/annurev.matsci.28.1.79

Cited by 242 publications

(129 citation statements)

References 98 publications

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“…From the 2θ XRD data for the (002) peak, the out-of-plane (OOP) lattice parameters of BST and LSMO layer are determined as 3.956A • and 3.843A • , respectively. These are very close to the bulk lattice parameters of BST (3.965A • ) [1][2][3][4][5][6][7] and LSMO (3.870A • ) 12,13 layers. The estimated strain for BST and LSMO layers along the c-direction is ∼0.2% and 0.7%, respectively, which is attributed to unrelaxed thermal and defect-induced strain, and some additional unrelaxed lattice mismatch strain for the BST (delete LSMO and insert BST) layer grown on the LSMO (delete BST and insert LSMO).…”

Section: Resultssupporting

confidence: 74%

“…The magnetic response is not saturated under a 300 Oe field, hence, it is expressed only in magnetic moment (emu), not in emu/cc. [1][2][3][4][5][6][7] The enhancements in H c and H EB at low temperature appears to be directly related to the ferroelectric nature of BST layer, and the resulting strain (∼0.4%) and/or charge redistributions that take place as the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at low temperature (200K). 18 This may also be consistent with the number of previous reports [19][20][21][22] on the formation of an antiferromagnetic region or layer due to strong pinned spins and magnetic depletion layer observed at various ferromagnetic and ferroelectric interfaces.…”

Section: Fig 2 Magnetic Moment Vs Temperature (M-t) Curves Of Lsmomentioning

confidence: 99%

“…For this study a concentration of Ba 0.4 Sr 0.6 TiO 3 (BST) is chosen, which is cubic and paraelectric at the (delete) ambient temperature, and then transforms to a ferroelectric tetragonal phase upon cooling through the Curie temperature (T C ) at 200K. 4 Previous workers [1][2][3][4][5][6][7] have deposited BST thin films on oxide substrates such as MgO, LaAlO 3 , SrTiO 3 , and Al 2 O 3 . However, high single crystal cost and small size are their (delete) major drawbacks of such substrates.…”

Section: Introductionmentioning

confidence: 99%

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Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures

2017

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This work relates to the integration of the two-layer stack of the proposed multiferroic structure onto silicon substrates. Ba1-xSrxTiO3 is an excellent material for room-temperature voltage-tunable dielectric applications due to its high (ε=6000) dielectric constant. In this study we choose a composition of Ba0.4Sr0.6TiO3 (BST), which is cubic and paraelectric at 300K, and transforms to a ferroelectric tetragonal phase upon cooling through the Curie temperature (TC) at 200K. The main focus of the present work is to study what happens when BST is placed in contact with a room temperature ferromagnetic layer such as La0.7Sr0.3MnO3 (LSMO). In this study, the magnetic properties of a BST (200nm)/LSMO (63nm) heterostructure was compared to that of a single LSMO layer (63nm). Both films were deposited onto MgO/TiN buffered Si (100) using pulsed laser deposition (PLD) and a domain matching epitaxy (DME) paradigm. X-ray diffraction (XRD) measurements showed that these films were of single phase and epitaxial in nature, with an unrelaxed lattice strain of ∼0.2% that was predominately composed of thermal and defect-induced strain. The magnetic measurements showed that the Curie temperature (TC) of LSMO remained unchanged at 350K when the BST was in contact with the LSMO layer. Interestingly, at 4K both the coercive field (Hc) and the exchange bias (HEB) of the BST/LSMO heterostructure as compared to the lone LSMO film increased significantly from 400 to 800 Oe and from 155 to 305 Oe, respectively. These differences were found to disappear above 200 K, the ferroelectric TC of the BST over-layer. This strongly suggests that the observed changes in the magnetic behavior of the heterostructure was the result of stress and/or charge redistributions that resulted when the BST layer transformed from the cubic (paraelectric) to tetragonal (ferroelectric) phase at low temperature.

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Section: Resultssupporting

confidence: 74%

Section: Fig 2 Magnetic Moment Vs Temperature (M-t) Curves Of Lsmomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures

2017

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“…This was the main incentive to investigate both MOSD and MOCVD to deposit high dielectric constant BST films for DRAM applications, in order to build high density, non-planar capacitor geometries. 62,63 Similar to other vacuum techniques, MOCVD requires a large up-front capital investment for the equipment. However, when implemented in high volume production, MOCVD can provide low overall cost-of-ownership, due to its high throughput and high source material utilization.…”

Section: E Mocvdmentioning

confidence: 99%

Challenges and opportunities for multi-functional oxide thin films for voltage tunable radio frequency/microwave components

Subramanyam¹,

Cole²,

Sun³

et al. 2013

Journal of Applied Physics

147

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There has been significant progress on the fundamental science and technological applications of complex oxides and multiferroics. Among complex oxide thin films, barium strontium titanate (BST) has become the material of choice for room-temperature-based voltage-tunable dielectric thin films, due to its large dielectric tunability and low microwave loss at room temperature. BST thin film varactor technology based reconfigurable radio frequency (RF)/microwave components have been demonstrated with the potential to lower the size, weight, and power needs of a future generation of communication and radar systems. Low-power multiferroic devices have also been recently demonstrated. Strong magneto-electric coupling has also been demonstrated in different multiferroic heterostructures, which show giant voltage control of the ferromagnetic resonance frequency of more than two octaves. This manuscript reviews recent advances in the processing, and application development for the complex oxides and multiferroics, with the focus on voltage tunable RF/microwave components. The over-arching goal of this review is to provide a synopsis of the current state-of the-art of complex oxide and multiferroic thin film materials and devices, identify technical issues and technical challenges that need to be overcome for successful insertion of the technology for both military and commercial applications, and provide mitigation strategies to address these technical challenges. V C 2013 AIP Publishing LLC.

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“…1,2 The large electric field-depended dielectric constant can be used for devices such as tunable oscillators, filters, and phase shifters. In such devices, it is desirable to have a high dielectric tunability in a certain electric field range and low dielectric loss.…”

mentioning

confidence: 99%

Effect of CaRuO3 interlayer on the dielectric properties of Ba(Zr,Ti)O3 thin films prepared by pulsed laser deposition

Tang

Tian

Wang

et al. 2006

Applied Physics Letters

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Ba͑Zr 0.2 Ti 0.8 ͒O 3 ͑BZT͒ thin films on Pt͑111͒ / Ti/ SiO 2 /Si͑100͒ substrates without and with CaRuO 3 ͑CRO͒ buffer layer were fabricated at 650°C in situ by pulsed laser deposition. The BZT thin films showed a dense morphology, many clusters are found on the surface images of BZT/Pt films, which are composed by nanosized grains of 25-35 nm; the average grain size of BZT/CRO films is about 80 nm, which lager than that of BZT/Pt thin film. The dielectric constants and dissipation factors of BZT/Pt and BZT/CRO thin films were 392 and 0.019 and 479 and 0.021 at 1 MHz, respectively. The dielectric constant of BZT/Pt and BZT/CRO thin films changes significantly with applied dc bias field and has high tunabilities and figures of merit of ϳ70% and 37 and 75% and 36, respectively, under an applied field of 400 kV/ cm. The possible microstructural background responsible for the high dielectric constant and tunability was discussed. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2360177͔ Barium strontium titanate ͑Ba, Sr͒TiO 3 ͑BST͒ thin films have currently become very attractive for applications in decoupling capacitors, storage capacitors, dynamic randomaccess memory, and tunable microwave devices. 1,2 The large electric field-depended dielectric constant can be used for devices such as tunable oscillators, filters, and phase shifters. In such devices, it is desirable to have a high dielectric tunability in a certain electric field range and low dielectric loss. Ba͑Zr y Ti 1−y ͒O 3 ͑BZT͒ is a possible choice as an alternative to BST in the fabrication of ceramic capacitors 3,4 because Zr 4+ is chemically more stable than Ti 4+ . The ferroelectric phase transition at the Curie temperature ͑T C ͒ in BZT bulk ceramics is known to change significantly with Zr content. BZT ceramics exhibit a diffuse phase transition and have high tunability in compositions with y ജ 0.20. [3][4][5][6] The fabrication of BZT thin films by rf-magnetron sputtering, 7 sol-gel method, 8 and pulsed laser disposition ͑PLD͒, 9 and their dielectric properties have been reported recently. Many efforts have been made to improve the dielectric properties of the BST thin film capacitors, including using conductive oxide electrodes such as ͑Ba, Sr͒RuO 3 , 10 ͑La 0.7 Sr 0.3 ͒MnO 3 , 11 LaNiO 3 , 12 and yttrium barrium copper oxide ͑YBCO͒. 13 The effects of CaRuO 3 buffer layer on the dielectric properties and tunability of BZT films have not yet been reported. In this work, Ba͑Zr 0.2 Ti 0.8 ͒O 3 thin films growth on Pt/ Ti/ SiO 2 / Si substrate without and with CaRuO 3 buffer layer were prepared by pulsed laser disposition. The orientation characteristics of grains, dielectric properties, tunability, and figure of merit of the columnar-grained Ba͑Zr 0.2 Ti 0.8 ͒O 3 thin films on Pt/ Ti/ SiO 2 / Si substrate without and with CaRuO 3 buffer layer are also reported.CaRuO 3 ͑CRO͒ bottom electrode layer was grown on Pt/ Ti/ SiO 2 / Si substrates at 750°C by rf-magnetron sputtering and using a CRO target. Ba͑Zr 0.2 Ti 0.8 ͒O 3 ͑BZT͒ thin films were gr...

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High-Dielectric Constant Thin Films for Dynamic Random Access Memories (Dram)

Cited by 242 publications

References 98 publications

Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures

Exchange bias in Ba0.4Sr0.6TiO3/La0.7Sr0.3MnO3 heterostructures

Challenges and opportunities for multi-functional oxide thin films for voltage tunable radio frequency/microwave components

Effect of CaRuO3 interlayer on the dielectric properties of Ba(Zr,Ti)O3 thin films prepared by pulsed laser deposition

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