Wide-range humidity sensing and monitoring applications including instrumentation, agriculture, meteorology, biomedicine, and food processing have attracted long-standing interests, where recently substantial progress is made in both sensing-material science and microfabrication technologies to achieve portable, reliable and low-cost humidity sensing instruments. Due to their high sensitivity, enormous miniaturization potential, and well-developed high-volume microfabrication technologies, microelectromechanical systems (MEMS)-based piezoresistive cantilever devices covered by large-surface-area nanostructures of hygroscopic materials offer an ideal platform for highly sensitive humidity detection. Since resonant gravimetric sensing is the dominant humidity sensing technique in recent research works, in this paper, resonant actuation principles for microcantilevers (i.e. the dynamic operation mode) are addressed and compared with respect to the quality of the amplitude and phase signals, as required for on-line frequency tracking using a phase-locked loop circuit. Parasitic feedthrough effects are considered between the resonance-mode ( f ₀ ) excitation element and the piezoresistive detection circuit, which can lead to a reduction of stop-band attenuation, the generation of a parallel resonance in close vicinity of f ₀ , a hardly detectable 90° phase jump, and a long-term drift of resonance frequency and phase shift. Methods for eliminating these parasitic feedthrough effects have been considered, including de-embedding of the motional signal by later data processing and the integration of a reference cantilever or circuit. Then, different concepts of environmental sensing using microcantilevers are described, including detection of particulate matter and gas molecules/volatile organic compounds. Depending on the condition of the cantilever during sensing operation, two different modes have been used to sense the target analyte (i.e. static and dynamic modes). In a static operation mode, mass change of the cantilever, surface stress, or swelling of a layer on top related to the uptake and binding of particles or molecules on the cantilever are detectable via a deformation of the cantilever (i.e. by deflection or strain), which can be sensed by an integrated piezoresistive strain gauge. Quasistatic bending of the cantilever as well as frequency down-shift of an excited resonance mode are normally used for detection. Humidity adsorption/desorption characteristics of such piezoresistive microcantilevers can be modified using hygroscopic layered materials deposited on the cantilever, among which we address metal oxides, ceramics, organics, or organic/inorganic composites. These thin layers comprise preferentially concave or convex nanostructures (e.g. pores, particles, colloids, rods, or fins), which provide a sensing surface of large surface-to-volume ratio and thus a large number of binding sites for highly efficient adhesion of water molecules. Finally, fabrication processes of integrated piezoresistive microcantilever-based humidity sensors, including micromachining/MEMS technology, integration of nanostructures and their combination with deposited hydrophilic materials are described. Lastly, their humidity sensing performance is compared with competing state-of-the art and advanced MEMS devices, e.g. capacitive micromachined ultrasonic transducers, quartz crystal microbalance, thin-film bulk acoustic resonator, surface acoustic wave resonator and complementary metal oxide semiconductor-MEMS for gravimetric sensing with respect to, e.g. sensitivity, hysteresis, and response time.

First steps are taken toward a low-cost alternative to silver sintering as a highly reliable die attach technology for deep drilling applications and future power electronic modules. In this feasibility analysis, we evaluate sintering of copper particles for die attach. Particulate copper pastes are pretreated in H₂ atmosphere (50 mbar) in order to gain oxide-free particles. Subsequently, particles are sintered at a pressure of 40 N/mm² and a temperature of 350°C for 2 min. Porosity, Young's modulus as well as electrical and thermal conductivities of sintered layers are analyzed. Moreover, shear tests at ambient temperature are performed for evaluating the adhesion of monometallic as well as Cu-Au bonds according to the American military standard for chip-substrate contacts (MIL-STD-883H, method 2019.8).