High-temperature processes, such as packaging and annealing, are challenges for Radio-Frequency Micro-Electro-Mechanical-Systems (RF MEMS) structures, which could lead to device failure. Coefficient of thermal expansion (CTE) mismatch and the material’s creep effect affect the fabrication and performance of the MEMS, especially experiencing the high temperature. In this paper, the Thermal–Mechanical-Stress-Creep (TMSC) effect during thermal processes from room temperature (RT) to 200 °C is modeled and measured, in which an Au-cantilever-based RF MEMS switch is selected as a typical device example. A novel Isolation-Test Method (ITM) is used to measure precise TMSC variation. This method can achieve resolutions of sub-nanometer (0.5 nm) and attofarad (1 aF). There are three stages in the thermal processes, including temperature ramping up, temperature dwelling, and temperature ramping down. In different stages, the thermal–mechanical stress in anchor and cantilever, the grain growth of gold, and the thermal creep compete with each other, which result in the falling down and curling up of the cantilever. These influencing factors are decoupled and discussed in different stages. The focused ion beam (FIB) is used to characterize the change of the gold grain. This study shows the possibility of predicting the deformation of MEMS structures during different high-temperature processes. This model can be extended for material selection and package temperature design of MEMS cantilever in the further studies.

Cantilevers are widely used as actuators and sensors in microelectromechanical system (MEMS) devices. The creep behavior of cantilevers is an important factor in the lifetime of a MEMS device. This study examines the creep phenomenon in metal-based MEMS cantilever devices and deformations of the cantilever were investigated at different temperatures. A Generalized-Accumulated-Temperature (GAT) parameter is introduced into the MEMS field for characteristic prediction, particularly for high-temperature storage lifetime prediction. Simplified radio frequency (RF) MEMS devices were designed, fabricated, and measured to investigate thermal creep. The devices were fabricated by surface micromachining processes at room temperature, strictly without any extra thermal effect before testing. The devices were tested with nanometer accuracy using the in-situ co-test method with three-dimensional (3D) optical microscope and RF probe station. The test results of the device with a gold-alloy cantilever showed that the deformation rate increased with temperature raising, and the logarithm of the rate exhibited a linear relationship with the temperature. A mathematical relation between the GAT parameter and cantilever deformation was established by which the lifetime of the cantilever can be predicted at different temperatures. The performances of pure gold and gold alloy were compared, and the alloy shows better thermal stability. This study shows that the gold alloy is more suitable on lifetime than pure gold for use as cantilevers. The GAT parameter introduced in this paper can enable the realization of metal-cantilever-based MEMS devices. It can also be widely used in other MEMS devices as a generic time–temperature parameter. 2023-0054

A high-sensitivity pH sensor based on an AlGaN/GaN high-electron mobility transistor (HEMT) with a 10 nm thick Au-gated sensing membrane was investigated. The Au nanolayer as a sensing membrane was deposited by electron-beam evaporation and patterned onto the GaN cap layer, which provides more surface-active sites and a more robust adsorption capacity for hydrogen ions (H⁺) and hydroxide ions (OH⁻) and thus the sensitivity of the sensor can be significantly enhanced. A quasi-reference electrode was used to minimize the sensing system for the measurement of the microliter solution. The measurement and analysis results demonstrate that the fabricated sensor exhibits a high potential sensitivity of 58.59 mV/pH, which is very close to the Nernstian limit. The current sensitivity is as high as 372.37 μA/pH in the pH range from 4.0 to 9.18, under a 3.5 V drain-source voltage and a 0 V reference-source voltage. Comparison experiments show that the current sensitivity of the Au-gated sensor can reach 3.9 times that of the SiO₂-gated sensor. Dynamic titration experiments reveal the pH sensor’s ability to promptly respond to immediate pH variations. These findings indicate that this pH sensor can meet most application requirements for advanced medical and chemical analysis.

Design, fabrication, and measurement of a single-pole-twelve-throw radio frequency (RF) micro-electro-mechanical systems switch are presented in this letter. A switch with specially designed parallel dual-cantilevers is used to improve the RF matching. Pure Au-Au contacts are applied to maintain the low insertion loss and verify the high linearity of the switch. A least square method is introduced to remove the uncertainty from the measurement of the third-order intermodulation intercept point (IIP3). The measurement results show that the insertion loss and isolation of each channel of the switch are better than 0.94 and 30 dB from dc to 8 GHz, respectively. The measured IIP3 of each channel is higher than 60 dBm. The switch works over 1 million cycles under cold-switching condition with 200-mA dc power.

With the booming development of satellite applications, the giant constellations of low Earth orbit (LEO) satellites have introduced challenges for the data relay service. The multi-beam satellite not only offers concurrent access to a large number of objects, but can also meet the high data requirements toward specific coverage of the LEO constellation. However, the multi-beam satellite often faces the mismatch problem of spot allocation and data requirements, which can cause an overload traffic jam or a waste of resources. An optimization algorithm on spot beam allocation is necessary to automatically place the spot centers with appropriate beam widths in line with the density of the traffic demands and to realize the uniformity of the beam occupation. Compared with the conventional K-means algorithm, two adjustable parameters α and β are introduced: one for tuning the ratio of two components making up the distance matrix, and the other for setting the obligatory minimum number of objects per beam. In this paper, the whole process of the proposed method is demonstrated, including the establishment of the low-orbit satellite constellation model, the extraction of the distribution features, and the implementation and evaluation of the modified K-means algorithm. The results prove the validity of the proposed algorithm. A larger value of β with a relative smaller value of α tends to obtain the uniformity of beam occupation; the minimum standard deviation of objects per beam is achieved when α is 0.2 and β is 0.8. This demonstrates that the uniformity of objects per beam can be realized by adjusting the parameters of the distance determination matrix and the obligatory minimal number of objects in each beam. The impact of parameter range on the results is also analyzed.

This paper proposes a series of optimized scalable contact-capacitive radio frequency micro- electro-mechanical systems (RF MEMS) switches for millimeter wave applications. Due to the contact-capacitive topology, the ON-state and OFF-state of the switch can be designed separately to obtain smaller $C_{ON}$ and larger $C_{OFF}$ , which results in high capacitance ratio ( $C_{r}$ ). The $C_{ON}$ is defined by capacitance of the contacts, and it is optimized for low insertion loss ( $IL_{ON}$ ). The $C_{OFF}$ is defined by the metal-insulator-metal (MIM) capacitor, and it is designed for working band and scalable performance. The measurements of the fabricated devices show acceptable agreements with design and simulation. The optimized switches perform well with $IL_{ON}$ better than 1.5dB and capacitive ratio about 124. The switches follow scaling rules from 20GHz to 110GHz. Linearity (IIP3) of the switches are tested to be higher than 60dBm, and calculated to be higher than 80dBm. Performances of the switch can be further improved and optimized in the future study.