Mechanical interlocking provides a simple and effective means of improving adhesion between dissimilar materials in micro-electro-mechanical systems (MEMS). Following successful implementation in hybrid Si-polymer systems (Larsson, Syms and Wojcik 2005 J. Micromech. Microeng. 15 2074–82), it was established that maximum interface strengthening does not necessarily rely on the presence of overhang between interlocking lobes. Instead, careful design of the lobe profile is advised in order to balance the opposing actions of physical restraint and lobe pull-out and to obtain optimal interface strength. When an interlocked interface is immersed in aggressive liquid media, however, the situation is clearer: chemical bonds are degraded or completely destroyed and lobe overhang provides the only source of physical restraint. Generating overhanging features in Si substrates is possible through reactive ion etching (RIE), but in the case of glass, the situation is more problematic. A straightforward, robust process is now described that extends mechanical interlocking to generic MEMS substrates, avoiding the need for RIE. By using inexpensive and established processes such as electroplating and wet etching, interlocking features with an overhanging profile are generated in glass substrates. Peel tests on cured strips of SU-8 confirm an increase in average peel strength by a factor of 3.5, compared with strips peeled from smooth substrates. The method can readily be applied to a number of substrates, including Si, providing a low-cost route towards attaining mechanical interlocking.

This article presents a new wafer-bonding fabrication technique for Capacitive Micromachined Ultrasonic Transducers (CMUTs) using polymethyl methacrylate (PMMA). The PMMA-based single-mask and single-dry-etch step-bonding device is much simpler, and reduces process steps and cost as compared to other wafer-bonding methods and sacrificial-layer processes. A low-temperature (< 180 ∘ C ) bonding process was carried out in a purpose-built bonding tool to minimize the involvement of expensive laboratory equipment. A single-element CMUT comprising 16 cells of 2.5 mm radius and 800 nm cavity was fabricated. The center frequency of the device was set to 200 kHz for underwater communication purposes. Characterization of the device was carried out in immersion, and results were subsequently validated with data from Finite Element Analysis (FEA). Results show the feasibility of the fabricated CMUTs as receivers for underwater applications.

Purpose This paper aims to Separation and sorting of biological cells is desirable in many applications for analyzing cell properties, such as disease diagnostics, drugs delivery, chemical processing and therapeutics. Design/methodology/approach Acoustic energy-based bioparticle separation is a simple, viable, bio-compatible and contact-less technique using, which can separate the bioparticles based on their density and size, with-out labeling the sample particles. Findings Conventionally available bioparticle separation techniques as fluorescence and immunomagnetic may cause a serious threat to the life of the cells due to various compatibility issues. Moreover, they also require an extra pre-processing labeling step. Contrarily, label-free separation can be considered as an alternative solution to the traditional bio-particle separation methods, due to their simpler operating principles and lower cost constraints. Acoustic based particle separation methods have captured a lot of attention among the other reported label-free particle separation techniques because of the numerous advantages it offers. Practical implications This study tries to briefly cover the developments of different acoustic-based particle separation techniques over the years. Unlike the conventional surveys on general bioparticles separation, this study is focused particularly on the acoustic-based particle separation. The study would provide a comprehensive guide for the future researchers especially working in the field of the acoustics, in studying and designing the acoustic-based particle separation techniques. Originality/value The study insights a brief theory of different types of acoustic waves and their interaction with the bioparticles is considered, followed by acoustic-based particle separation devices reported till the date. The integration of acoustic-based separation techniques with other methods and with each other is also discussed. Finally, all major aspects like the approach, and productivity, etc., of the adopted acoustic particle separation methods are sketched in this article.

Capacitive Micromachined Ultrasonic Transducers (CMUTs) are the prospective alternative to the traditional piezoelectric ultrasonic transducers. CMUTs are essentially parallel plate capacitors produced using Microelectromechanical Systems (MEMS) technology. The production of CMUTs is broken down into sacrificial underetching and wafer bonding methods. The sacrificial release-based techniques are complex and require several adjustments in terms of optimizing fabrication steps and material selections. Further, the sacrificial release-based processes need ultimate control over the gap height and membrane thickness. On the contrary, the wafer bonding fabrication processes are not only simpler than the sacrificial release methods but also provide a very good parametric control over the membrane thickness and gap height. Besides its advantages, the wafer bonding methods are very sensitive to contamination and surface roughness. The surface roughness problems are addressed by either using the costly Silicon-on-Insulator (SOI) wafers or by using complex Chemical Mechanical Polishing (CMP) method. This article presents a simple and economical CMUTs wafer bonding fabrication method. A thermocompression based metal bonded technique is adopted to successfully fabricate low frequency CMUTs to be used for underwater applications.

Mechanical integrity of interlayer and intralayer dielectric films and its impact on interconnect reliability has become more important as critical dimensions in ultralarge-scale integrated circuits are continuously reduced and Cu interconnect, low-k dielectrics (Cu/low-k) are widely adopted for the new technology nodes. Mechanical integrity of the dielectric films and reliability of interconnect can be affected by the film deposition process, stresses from chip-packaging interaction (CPI) and environmental factors such as moisture and temperature exposure.In this study attention has been focused on understanding the moisture and temperature effects on reliability of dielectric films in plastic encapsulated silicon devices. Sensitivities to moisture and temperature induced damage in the dielectric films of the silicon devices were first evaluated using accelerated temperature and humidity stress conditions. Multiple stress conditions were used so the testing results could be applied to validate a physical acceleration model for the combined temperature and humidity stresses. Moisture diffusion in the silicon devices and their packages was then modeled using commercial Finite Element Analysis (FEA) software. Moisture sorption and diffusion properties of the packaging materials were also characterized to support the moisture diffusion modeling. Moisture distribution in the plastic package was analyzed for both the accelerated stress conditions and the product use or storage environmental conditions. The effectiveness of the peripheral seal ring on the silicon device as a moisture barrier was also investigated. Finally, reliability of the silicon devices under typical and extreme product use or storage environment conditions was assessed using the moisture distribution results and the validated acceleration model.