Silver Micro-Structures

About

Background: MEMS-based RF components are leading candidates for cellular front-end modules that need to support an increasing number of frequency bands and communication standards. Tunable MEMS LC filters offering very low insertion loss (IL), and high quality factor (Q) can be prime candidates for multi-band cellular application. This can be achieved by using high Q tunable capacitors and inductors. Silver devices show superior performance compared to the other metallic/semiconductor devices due to the high conductivity of silver. However, silver structures suffer from early failure due to the electromigration and formation of dendrites. These fatigues and failures occur in the presence of moisture and air. Hermetically sealing the silver structure would thus prevent silver fatigues. If hermetically sealed, silver structure outperforms other structures in terms of the ohmic loss.    Technology: Inventors at Georgia Institute of Technology have developed a method to obtain high performance silver microstructures that are hermetically sealed using thermally-released wafer level polymer packaging. This is achieved by electroplating thick silver into a thick photoresist mold. The conductivity of the electroplated silver can get close to the silver bulk conductivity. The polymer packaging is low-temperature and the process is post CMOS-compatible (If necessary, subsequent over-molding can provide additional strength and resilience, and ensures long-term hermeticity). Using this fabrication method, record high-Q inductor, tunable inductors and capacitors, and low-insertion loss filters have been successfully fabricated and tested. A tuning of 330% is measured for a 0.4pF tunable capacitor with an embedded Q>250 at 1 GHz. A 1nH inductor exhibits record high Q of >180 in 8-23GHz range. A third order elliptic filter shows an insertion loss of 0.9dB at 1.2GHz. A 1.0nH inductor was tuned to 0.60nH when both coils at the secondary side were switched on, which represents a maximum tuning of 40% at 5GHz. Measured embedded Q of this inductor when the secondary coils are both off is about 45.   Applications: This novel CMOS-compatible high-performance switched tunable inductor can be used to improve the tuning capability of the RF tunable filters and reconfigurable impedance matching networks by using low-loss metallic micro-machined switches, with applicability in electronically scanned sub-arrays (Phase shifters), and software defined radios (reconfigurable antennas, and band pass filters).   Advantages:  •High quality factor (Q) tunable inductors and capacitors •Low insertion loss (IL) filters