The impact of the residual strain induced by the thermal strain on the dielectric tunability was systematically studied for rf sputtered ͑100͒-one-axis-oriented polycrystalline ͑Ba 0.5 Sr 0.5 ͒TiO 3 films. These films were grown on various substrates with different thermal expansion coefficients ͓␣ ͑sub͒ ͔ covered with a stack of ͑100͒ c SrRuO 3 / ͑100͒ c LaNiO 3 / ͑111͒Pt layers. The residual strain was ascertained to linearly increase with the increase in ␣ ͑sub͒ by enhancement of the surface-normal lattice spacing of ͑Ba 0.5 Sr 0.5 ͒TiO 3 and Pt. Dielectric tunability of the films also linearly increased with the increase in ␣ ͑sub͒. These results clearly demonstrate that dielectric tunability tailoring of the ͑Ba 0.5 Sr 0.5 ͒TiO 3 films can be achieved by using residual thermal strain.

The coronavirus 2019 (COVID-19) pandemic was caused by a positive sense single-stranded RNA (ssRNA) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, other human coronaviruses (hCoVs) exist. Historical pandemics include smallpox and influenza, with efficacious therapeutics utilized to reduce overall disease burden through effectively targeting a competent host immune system response. The immune system is composed of primary/secondary lymphoid structures with initially eight types of immune cell types, and many other subtypes, traversing cell membranes utilizing cell signaling cascades that contribute towards clearance of pathogenic proteins. Other proteins discussed include cluster of differentiation (CD) markers, major histocompatibility complexes (MHC), pleiotropic interleukins (IL), and chemokines (CXC). The historical concepts of host immunity are the innate and adaptive immune systems. The adaptive immune system is represented by T cells, B cells, and antibodies. The innate immune system is represented by macrophages, neutrophils, dendritic cells, and the complement system. Other viruses can affect and regulate cell cycle progression for example, in cancers that include human papillomavirus (HPV: cervical carcinoma), Epstein–Barr virus (EBV: lymphoma), Hepatitis B and C (HB/HC: hepatocellular carcinoma) and human T cell Leukemia Virus-1 (T cell leukemia). Bacterial infections also increase the risk of developing cancer (e.g., Helicobacter pylori). Viral and bacterial factors can cause both morbidity and mortality alongside being transmitted within clinical and community settings through affecting a host immune response. Therefore, it is appropriate to contextualize advances in single cell sequencing in conjunction with other laboratory techniques allowing insights into immune cell characterization. These developments offer improved clarity and understanding that overlap with autoimmune conditions that could be affected by innate B cells (B1+ or marginal zone cells) or adaptive T cell responses to SARS-CoV-2 infection and other pathologies. Thus, this review starts with an introduction into host respiratory infection before examining invaluable cellular messenger proteins and then individual immune cell markers.

Ba0.7Sr0.3TiO3 (BST) single and quadruple layer capacitors with Pt electrodes were fabricated together on polycrystalline alumina substrates with a SiO2-based multicomponent amorphous buffer layer (SiO2/Al2O3). This paper presents the results of the characterization of these capacitors, to demonstrate their suitability for application as decoupling (high value) capacitors and as components in tunable RF applications (e.g., phase shifters and filters). BST films of different compositions, (Ba0.7Sr0.3)TiO3 and (Ba0.5Sr0.5)TiO3, were grown by metal-organic decomposition (MOD) and RF magnetron reactive sputtering. The capacitance density of 90–140 nm thick BST films was in the range of 20 to 70 fF/μm 2. Parallel plate capacitors with areas from 16 μm2 to 2.25 mm2 were fabricated using photolithography and ion milling techniques. For large capacitors (0.125 to 2.25 mm2), capacitance and tanδ were measured at low frequencies (1 KHz - 1 MHz) using an LCR meter. Smaller capacitors (16 μm2 to 3600 μm2) were additionally characterized in the frequency range of 50 MHz - 20 GHz. In such case, capacitance, tanδ and equivalent series resistance (ESR) were extracted from two port scattering parameters obtained using a vector network analyzer (VNA). The relationship between dielectric loss, tunability and calculated figure of merit vs. BST composition and deposition temperature was outlined. In addition, loss and ESR at high frequencies was investigated. The typical achieved leakage current density of sputtered BST films for 2.25 mm2 capacitors fabricated on SiO2/Al2O3 was 7.3×10-9 A/cm2 at 300 kV/cm (65 fF/μm2), about 2 times lower than for (Ba0.7Sr0.3)TiO3 films deposited by MOD (1.4×10-8 A/cm2 at 300 kV/cm, 34.5 fF/μm2). Furthermore, the tunability of (Ba0.7Sr0.3)TiO3 deposited by both methods on SiO2/Al2O3 was ∼60% at 350 kV/cm.

Thin films of (Ba x Sr 1−x ) 1+y Ti 1−y and Zr, Gd codoped (Ba x Sr 1−x ) 1+y Ti 1−y were deposited on platinized sapphire substrates at 640 °C under constant flux of atomic oxygen or a mixture of atomic oxygen and nitrogen to synthesize perovskites of (Ba x Sr 1−x ) 1+y Ti 1−y O 3−δ (also referred to as BSTO), (Ba x Sr 1−x ) 1+y Ti 1−y O 3−z N z (also referred to as BSTON), and Zr, Gd codoped (Ba x Sr 1−x ) 1+y Ti 1−y O 3−z N z . Structural characterization was done via XRD and XPS, and electrical characterization was done via LCR (dielectric properties and tunability under DC bias) and P−E measurements. Although the levels of nitrogen incorporated within the perovskite structure appear to be very low as determined by XPS analysis, definite improvements in dielectric properties and tunability have been achieved by synthesis of the BSTON oxynitride films. For a composition of Ba 0.8 Sr 0.2 TiO 3−z N z an improvement by a factor of 1.72 for tunability and 1.44 for relative permittivity has been observed between the oxide and the oxynitride. The oxynitride achieved a tunability ratio of 6.78 to 1 (close to 7:1) under an applied electrical field of 34 kV/mm. The high throughput approach allowed us to highlight a compositional shift for the material with the best dielectric properties when comparing the oxide with the oxynitride thin films. Effects of codoping the perovskite structure with Zr and Gd have also been investigated and although the tunability and dielectric constant of the thin films were not improved, some improvements in dielectric losses were observed, along with a superparaelectric state as observed by P−E hysteresis measurements.

This paper presents a film transfer process to integrate barium strontium titanate (BST) metal-insulator-metal (MIM) structures with surface acoustic wave (SAW) devices on a lithium niobate (LN) substrate. A high-quality BST film grown on a Si substrate above 650 • C was patterned into the MIM structures, and transferred to a LN substrate below 130 • C by Ar-plasma-activated Au-Au bonding and the Si lost wafer process. Simple test SAW devices with the transferred BST variable capacitors (VCs) were fabricated and characterized. The resonance frequency of a one-port SAW resonator with the VC connected in series changed from 999 to 1018 MHz, when a dc bias voltage of 3 V was applied to the VC. Although the observed frequency tuning range was smaller than expected due to the degradation of BST in the process, the experimental result demonstrated that a tunable SAW filter with the transferred BST VCs was feasible.