Design and Characterization of Wafer Level SAW Filter Package Using LT-LT Wafer Structure

Miniaturization is one of the driving design goals for large number of wireless applications, especially mobile phones. These market trends call for more thin and small size components with high reliability performance. In this paper, we describes the wafer level surface acoustic wave (SAW) filter package, 1.0 times 0.8 mm², which is applicable for radio frequency (RF) stage in mobile phones. The SAW filter is reduced in size and thickness by using a 4" wafer level package process technique. The technique uses interconnection via and LiTaO₃ (LT)-LiTaO₃ (LT) wafer bonding structure. The interconnection via is formed through LT wafer by using sand blasting or laser drilling method. The AuSn eutectic bonding enables the connection of the signal pad on the SAW chip, with gold metallized LT wafer package. This eutectic bonding ensures that the SAW chip is protected mechanically and connected electrically, with the package. In order to simulate and optimize the structure and characteristics of wafer level SAW filter package, we used HFSS and ADS software. Frequency responses of measurement and simulation are compared with wafer level SAW filter package. The results of reliability tests for wafer level SAW filter package was discussed.