Engineering systems based on integrated circuits (IC) and microsystem technologies (MST) increasingly rely on materials whose behaviour is governed by coupled thermal, mechanical, and transport processes. Among these materials, borophosphosilicate glass (BPSG) thin films deposited by chemical vapor deposition (CVD) exhibit distinctive low-temperature flow characteristics that critically influence device-level performance. This study aims to provide a physically grounded synthesis of the mechanisms governing the flow behaviour of low-temperature BPSG thin films and to examine their functional roles across IC, MST, and optical device technologies. The analysis integrates reported experimental observations and process data to interpret BPSG behaviour in terms of thermo-viscous flow, compositional dependence, and surface evolution under thermal treatment. The results show that the reduced glass transition temperature induced by boron and phosphorus incorporation enables controlled viscous flow at temperatures as low as approximately 700–800 ℃, leading to effective surface planarization, void elimination, and geometry reconfiguration in complex device reliefs. The interaction between thermal activation, film composition, and structural constraints governs key performance outcomes, including planarization efficiency, gap-filling capability, and stress evolution. In MST and optical applications, the same flow mechanisms enable the formation of sealed cavities, microfluidic channels, and optically functional structures such as microlenses and waveguide cladding layers. It is concluded that the engineering functionality of BPSG films arises from the coupled interaction between thermal processes, material composition, and geometrical confinement. This work provides a unified interpretation of these mechanisms and highlights their implications for process optimisation and device design in integrated and multiphysics engineering systems.
The dynamic behavior of nanoscale beam structures is strongly influenced by material gradation, geometric discontinuities, foundation characteristics, and small-scale effects, all of which play critical roles in the performance of advanced multiphysics nano-engineering systems. In the present study, the free vibration characteristics of a perforated non-homogeneous nanobeam resting on a variable elastic foundation were investigated under sliding-end boundary conditions. Particular attention was devoted to applications involving resonators of microelectromechanical and nanoelectromechanical systems, nano-sensors, smart structural components, and coupled electromechanical nano-devices, where precise control of dynamic response is essential. Spatial variations in Young’s modulus and material density were incorporated to represent non-homogeneous material properties, while perforation effects were introduced through modified geometric and mechanical characteristics. Size-dependent nanoscale behavior was captured using Eringen’s nonlocal elasticity theory. Based on Euler-Bernoulli beam theory, the governing differential equation of motion was derived. The resulting eigenvalue problem was solved using the Galerkin method in conjunction with shifted Legendre polynomial admissible functions, enabling high numerical stability, rapid convergence, and computational efficiency. Validation of the proposed formulation was performed through comparisons with available benchmark results reported in the literature, and additional convergence studies were conducted. Investigations were carried out to evaluate the effects of perforation characteristics, non-homogeneity parameters, and spatially varying foundation stiffness on the natural frequencies and mode shapes of the nanobeam. It was demonstrated that significant alterations in dynamic response may be induced by the combined interaction of material gradation, perforation geometry, and foundation variability. The developed model provides an efficient and reliable computational framework for the dynamic characterization of perforated nanoscale structures and offers valuable insights for the design, optimization, and vibration control of next-generation multifunctional nano-engineering systems operating under coupled multiphysics environments.
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