Electric field-tunable Ba<i>x</i>Sr1−<i>x</i>TiO3 films with high figures of merit grown by molecular beam epitaxy

Mikheev, Evgeny; Kajdos, Adam P.; Hauser, Adam J.; Stemmer, Susanne

doi:10.1063/1.4773034

Cited by 45 publications

(25 citation statements)

References 31 publications

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“…At the same time, the curves for permittivity in Figure 7 b resemble the macroscopically measured ones for similar BST fi lms in terms of shape and tunability values. [ 3,5,37 ] In particular in ref., [ 5 ] Figure 7 b). Since the electric fi eld strength under the probe apex both in sMIM and PFM is larger when compared to the capacitor geometry, lower values for the normalized permittivity are expected at the same bias voltages for sMIM and PFM than for capacitors.…”

Section: Resultsmentioning

confidence: 98%

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Quantitative Nanometer‐Scale Mapping of Dielectric Tunability

Tselev

Klein

Gaßmann

et al. 2015

Adv Materials Inter

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usual approach to characterization of the thin fi lms dielectric properties assumes fabrication of sandwich (parallel-plate) or planar (interdigitated) capacitors or coplanar waveguides from micrometer to tens and hundreds of micrometers in dimensions. [5][6][7] Apparently, such approach is capable of delivering information only about fi lm properties averaged over a relatively large area. While this can be appropriate for single-crystalline epitaxial thin fi lms, the information about properties of single morphological elements of polycrystalline fi lms-such as fabricated by magnetron sputtering-cannot be obtained. Additionally, only macroscopic scale devices can be characterized. Fabrication of test devices is destructive for thin fi lms with a consequence that generally, characterized fi lms cannot be further used for fabrication of desired functional structures.Furthermore, a problem for polycrystalline fi lms are always pinholes leading to shorts in capacitor structures. The density of the pinholes increases with decreasing fi lm thickness, so that sample with a thicknesses of about 50 nm and below are hardly accessible to the measurements with lithographically fabricated capacitor structures since the electrodes should be made very small. On the other side, in general, thinner fi lms show worse performance than thicker fi lms, often related to "dead layers," i.e., layers with reduced permittivity and tunability at the electrode interfaces. A possibility to measure dielectric properties without top electrodes can help to discriminate between dead layers at bottom and at top electrodes as well as fi lm defects and, therefore, guide the development of improved bottom or top electrodes in the tunable devices. Therefore, noninvasive and nondestructive characterization methods capable of a high spatial resolution are required. The scanning probe techniques offer the opportunity of accessing the dielectric properties of nanoscale thin fi lms without the extensive effort of lithographically structured electrodes.In this paper, we used two scanning probe microscopy techniques-near-fi eld scanning microwave microscopy (SMM) and piezoresponse force microscopy (PFM)-to characterize and image tunability in a thin paraelectric fi lm. Using a polycrystalline Ba 0.6 Sr 0.4 TiO 3 (BST) fi lm as a model system, we prove that near-fi eld microwave imaging and PFM provide similar information about dielectric tunability with high spatial resolution in the 10's of nm regime. This is key to understand the origin of macroscopic material properties and its correlation to the underlying microstructure and defects as pathway for material Two scanning probe microscopy techniques-near-fi eld scanning microwave microscopy (SMM) and piezoresponse force microscopy (PFM)-are used to characterize and image tunability in a thin (Ba,Sr)TiO 3 fi lm with nanometer scale spatial resolution. While sMIM allows direct probing of tunability by measurement of the change in the dielectric constant, in PFM, tunability can be extracted via electrostrict...

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Section: Resultsmentioning

confidence: 98%

“…It is well established for the BST fi lms that fi lm properties, and in particular permittivity and tunability depend strongly on composition. [ 3,[37][38][39] We typically fi nd strong variations in the Ti/(Ba+Sr) ratio from sample to sample in fi lms fabricated in similar way. The samples are either Ti-rich or slightly Ti-defi cient.…”

Section: Resultsmentioning

confidence: 99%

Quantitative Nanometer‐Scale Mapping of Dielectric Tunability

Tselev

Klein

Gaßmann

et al. 2015

Adv Materials Inter

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“…Recently, BST films fabricated via MOMBE technique achieved device quality dielectric properties. 61 The MBE technique is also limited by low throughput/yield and is an expensive technique to use and sustain. However, if the cost of this technique becomes commensurate with that of CVD and PVD growth techniques, properly optimized MBE grown complex oxide thin films will become widespread and mainstream.…”

Section: Mbementioning

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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“…2,6 Q-factors exceeding 1000 and tunabilities up to 5:1 were reported in BST films that were grown by molecular beam epitaxy (MBE). 7 Further improving the performance requires understanding of the effects of key materials parameters on tunable device properties. For example, the hybrid MBE approach employed in Ref.…”

mentioning

confidence: 99%

“…BST films were grown by hybrid molecular beam epitaxy, described previously. 7,17 The hybrid MBE process uses a metal-organic source, titanium tetra isopropoxide (TTIP) to supply Ti and O, whereas Ba and Sr are supplied from effusion cells. Additional oxygen is supplied from an oxygen plasma source.…”

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confidence: 99%

Role of film stoichiometry and interface quality in the performance of (Ba,Sr)TiO3 tunable capacitors with high figures of merit

Freeze

Stemmer

2016

Applied Physics Letters

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Parallel plate capacitors with quality factors exceeding 1000 were fabricated using Ba0.3Sr0.7TiO3 (BST) thin films grown by hybrid molecular beam epitaxy on epitaxial Pt bottom electrodes. The influence of film stoichiometry was investigated by varying the (Ba + Sr)/Ti ratio around the stoichiometric composition. The quality factor is highest for stoichiometric films, but (Ba + Sr)-rich films can be biased to higher fields. Furthermore, two different processes were used to deposit the top electrodes of the parallel plate capacitors. While the quality of the top contact/BST interface did not strongly affect the device quality factor, an enhancement in the dielectric tunability was seen for capacitors with top electrodes deposited at high temperatures, which effectively removes interfacial contamination layers.

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Electric field-tunable BaxSr1−xTiO3 films with high figures of merit grown by molecular beam epitaxy

Cited by 45 publications

References 31 publications

Quantitative Nanometer‐Scale Mapping of Dielectric Tunability

Quantitative Nanometer‐Scale Mapping of Dielectric Tunability

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

Role of film stoichiometry and interface quality in the performance of (Ba,Sr)TiO3 tunable capacitors with high figures of merit

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