SAW/BAW acoustoelectronic technology for filters and communication systems

Abstract

Solid state acoustoelectronic technology has had a major impact on communications systems for almost 100 years. The quartz crystal resonator first provided a device for accurate and precise frequency control in oscillators, and then was adapted to produce small, stable filters. However, due to the physical nature of the embodiments, the operational frequency was limited to less than 100 MHz. Solid state surface acoustic wave (SAW) technology emerged in the 1970's to fill a vast number of applications in the 30 MHz to 1 GHz range. The manufacturing used integrated circuit techniques and the embodiments allowed RF frequency operation. Many of the IF SAW applications still exist for demanding military and base station applications, but the performance is greatly enhanced from the early filter development. When cellular phones began in high volume, the technology was adapted and refined to meet demanding low loss, small, and cheap RF filters in the 800 MHz bands. As the frequency of mobile phones increased into the 2GHz band, SAW technology was further challenged requiring enhanced processing and manufacturing techniques, and devices are currently produced. As the frequency increased, thin film bulk acoustic wave resonator (TFR) technology, which had been researched for decades, overcame many drawbacks and are now able to produce high quality filters in the 1–5 GHz range. The SAW and TFR devices compete in the 1–3 GHz range and each can win filter slots, depending on specifications. In addition, these filters are now being integrated into RF modules for multi-band cellular applications. The development of the acoustoelectronic technology continues, always with an eye to enhanced performance, lower cost, and smaller size. New materials, embodiments, wave modes and packaging are all being investigated. Beyond use as just filters, the technology has expanded to RFID tags and sensors. The devices offer advantages of passive, radiation hard and small volume operation. This paper will provide a view of the technology, some historical perspective, current performance and future trends.