M S Giridhar
Articles written in Sadhana
Volume 34 Issue 4 August 2009 pp 625-631
Communication systems such as those used on satellite platforms demand high performance from individual components that make up the varoius systems and sub-systems. Switching and routing of RF signals between various modules is a routine and critical operation that determines the overall efﬁciency of the entire system. In this paper, we present the design and fabrication aspects of a direct contact RF MEMS switch designed to operate in the X band (8–12 GHz) with a target insertion of about 0·5 dB and isolation better than 30 dB. The actuation voltage is expected to be around 50 V. The die size is designed to be 3 mm (H) × 3 mm(W) × 2 mm(H). The switch is built from a low residual stress device layer of a highly conducting (0·005 Ohms-cm) silicon on insulator (SOI) wafer. After subsequent lithographic steps, the wafer is bonded to a Pyrex glass wafer which has been previously patterned with gold transmission lines and pull in electrodes. Being built from a single crystal silicon structure, the mechanical robustness of the actuator is much greater than the those in similar membrane-based devices. A 6 mask fabrication process utilizing Deep Reactive Ion Etching to achieve high aspect ratio stiction free structures was developed and implemented. Devices from the ﬁrst fabrication run are being analysed in our laboratory.
Volume 38 Issue 2 April 2013 pp 297-316
RF characterization and packaging of a single pole single throw (SPST) direct contact microelectromechanical (MEMS) series radio frequency (RF) switch is reported. Precise thickness of the silicon MEMS structure is achieved using a specially developed silicon Deep Reactive Ion Etching (DRIE) thinning process. A stress free release process is employed which ensures a high yield of released microstructures. The design of the device is based on stiffness equations derived from ﬁrst principles. Displacement of the actuator under applied ﬁeld is measured to conﬁrm electrostatic pull in, which occurs in the 30–50 V range. The variation of contact resistance with time has been measured and is found to have a power law decay, in agreement with theoretical models. At the bare die level the insertion loss, return loss and the isolation of the switch were measured to be −0.43 dB, −25 dB and −21 dB, respectively at 10 GHz. The devices were packaged in commercially available RF packages and mounted in alumina boards for post package characterization. Due to the presence of bond wires in the signal path of the packaged devices, the RF performance was found to degrade at high frequencies. However, losses were measured to be at acceptable levels up to 2 GHz. Factors contributing to insertion loss at the die and package device levels are discussed in detail with possible solutions.