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A tunable third-order combline bandpass filter using thin-film barium-strontium-titanate varactors and fabricated on a sapphire substrate is reported. Application of 0-200-V bias varied the center frequency of the filter from 2.44 to 2.88 GHz (16% tuning) while achieving a 1-dB bandwidth of 400 MHz. The insertion loss varied from 5.1 dB at zero bias to 3.3 dB at full bias, while the return loss exceeded 13 dB over the range. The third-order intercept of the filter was found to be 41 dBm. Index Terms--Barium strontium titanate (BST), combline filter, ferroelectric films, intermodulation distortion, microstrip filters, resonators, thin-film devices, tunable filters, varactor.

Tunable lowpass and bandpass lumped-element filters employing barium--strontium-titanate (BST)-based capacitors are presented. A new metallization technique is used, which improves the quality factor of the tunable BST capacitors by a factor of two. The lowpass filter has an insertion loss of 2 dB and a tunability of 40% (120-170 MHz) with the application of 0-9-V dc bias. The bandpass filter (BPF) has an insertion loss of 3 dB and a tunability of 57% (176-276 MHz) with the application of 0-6 V dc. The third-order intercept point of the BPF was measured to be 19 dBm with the application of two tones around 170 MHz. Index Terms--Barium-strontium-titanate (BST), ferroelectric, intermodulation distortion, metalorganic chemical vapor deposition (MOCVD), multilayer ground plane, paraelectric, tunable bandpass filter (BPF), tunable lowpass filter (LPF).

Author(s): Angus I. Kingon (corresponding author) [1]; Jon-Paul Maria [1]; S. K. Streiffer [2] Over the past 30 years, astounding progress has been made in silicon technology, achieved through continual [...]

The spatial variation of ferroelectric properties with submicron lateral resolution is presented by using an AFM piezoelectric measurement technique. The phase images obtained through this technique represents the polarization direction, while contrast in the amplitude images shows the spatial variation in d33.

The polarization wake‐up process is demonstrated here for ferroelectric switching in epitaxial Al0.93B0.07N films on W coated c‐axis oriented Al2O3 (sapphire) substrates. During the wake‐up process, the remanent polarization grows from ≈0 to >100 µC cm−2. As it does so, both the reversible and irreversible Rayleigh coefficients rise substantially, suggesting that the concentration of mobile interfaces that separate regions of opposite dipole orientation is increasing. The irreversible Rayleigh coefficient is very small (≈3.5 × 10−4 cm kV−1), four to five orders of magnitude below those of perovskite ferroelectric films such as PbZr0.52Ti0.48O3. These small values are consistent with the high coercive fields observed in the nitride ferroelectrics. The temperature dependence of the Rayleigh coefficients suggests that the interface motion is thermally activated. On increasing frequency, the Rayleigh coefficients drop, suggesting time‐dependent pinning processes also occur in this family of materials. With information from anisotropic etching experiments upon field‐cycling, a self‐consistent model that describes a polar domain microstructure evolution process during wake‐up is proposed. [ABSTRACT FROM AUTHOR]

The thermal conductivity of n- and p-type doped gallium nitride (GaN) epilayers having thicknesses of 3-4 µm was investigated using time domain thermoreflectance. Despite possessing carrier concentrations ranging across 3 decades (1015-1018 cm-3), n-type layers exhibit a nearly constant thermal conductivity of 180W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110W/mK with increased doping. These trends--and their overall reduction relative to bulk--are explained leveraging established scattering models where it is shown that, while the decrease in p-type layers is partly due to the increased impurity levels evolving from its doping, size effects play a primary role in limiting the thermal conductivity of GaN layers tens of microns thick. Device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of 240 W/mK owing to their finite thickness. [ABSTRACT FROM AUTHOR]

This manuscript reports the temperature dependence of ferroelectric switching in Al0.84Sc0.16N, Al0.93B0.07N, and AlN thin films. Polarization reversal is demonstrated in all compositions and is strongly temperature dependent. Between room temperature and 300 °C, the coercive field drops by almost 50% in all samples, while there was very small temperature dependence of the remanent polarization value. Over this same temperature range, the relative permittivity increased between 5% and 10%. Polarization reversal was confirmed by piezoelectric coefficient analysis and chemical etching. Applying intrinsic/homogeneous switching models produces nonphysical fits, while models based on thermal activation suggest that switching is regulated by a distribution of pinning sites or nucleation barriers with an average activation energy near 28 meV. [ABSTRACT FROM AUTHOR]

Smooth, commensurate alloys of 〈111〉-oriented Mg0.52Ca0.48O (MCO) thin films are demonstrated on Ga-polar, c+ [0001]-oriented GaN by surfactant-assisted molecular beam epitaxy and pulsed laser deposition. These are unique examples of coherent cubic oxide|nitride interfaces with structural and morphological perfection. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100x reduction in leakage current density for the surfactant-assisted samples. HAADF-STEM images of the MCO|GaN interface show commensurate alignment of atomic planes with minimal defects due to lattice mismatch. STEM and DFT calculations show that GaN c/2 steps create incoherent boundaries in MCO over layers which manifest as two in-plane rotations and determine consequently the density of structural defects in otherwise coherent MCO. This new understanding of interfacial steps between HCP and FCC crystals identifies the steps needed to create globally defect-free heterostructures. [ABSTRACT FROM AUTHOR]

We demonstrate the use of anomalous x-ray scattering of constituent cations at their absorption edge, in a conventional Bragg-Brentano diffractometer, to measure absolutely and quantitatively the polar orientation and polarity fraction of unipolar and mixed polar wurtzitic crystals. In one set of experiments, the gradual transition between c+ and c- polarity of epitaxial ZnO films on sapphire as a function of MgO buffer layer thickness is monitored quantitatively, while in a second experiment, we map the polarity of a lateral polar homojunction in GaN. The dispersion measurements are compared with piezoforce microscopy images, and we demonstrate how x-ray dispersion and scanning probe methods can provide complementary information that can discriminate between polarity fractions at a material surface and polarity fractions averaged over the film bulk. [ABSTRACT FROM AUTHOR]