Yildiz Fikret, Matsunaga Tadao, Haga Yoichi
Graduate School of Engineering, Tohoku University, 6-6 Aza-Aoba, Aramaki Aoba-ku, Sendai 980-8579, Japan.
Faculty of Engineering, Hakkari University, Hakkari 30000, Turkey.
Micromachines (Basel). 2018 Oct 27;9(11):553. doi: 10.3390/mi9110553.
This paper presents fabrication and packaging of a capacitive micromachined ultrasonic transducer (CMUT) using anodically bondable low temperature co-fired ceramic (LTCC). Anodic bonding of LTCC with Au vias-silicon on insulator (SOI) has been used to fabricate CMUTs with different membrane radii, 24 µm, 25 µm, 36 µm, 40 µm and 60 µm. Bottom electrodes were directly patterned on remained vias after wet etching of LTCC vias. CMUT cavities and Au bumps were micromachined on the Si part of the SOI wafer. This high conductive Si was also used as top electrode. Electrical connections between the top and bottom of the CMUT were achieved by Au-Au bonding of wet etched LTCC vias and bumps during anodic bonding. Three key parameters, infrared images, complex admittance plots, and static membrane displacement, were used to evaluate bonding success. CMUTs with a membrane thickness of 2.6 µm were fabricated for experimental analyses. A novel CMUT-IC packaging process has been described following the fabrication process. This process enables indirect packaging of the CMUT and integrated circuit (IC) using a lateral side via of LTCC. Lateral side vias were obtained by micromachining of fabricated CMUTs and used to drive CMUTs elements. Connection electrodes are patterned on LTCC side via and a catheter was assembled at the backside of the CMUT. The IC was mounted on the bonding pad on the catheter by a flip-chip bonding process. Bonding performance was evaluated by measurement of bond resistance between pads on the IC and catheter. This study demonstrates that the LTCC and LTCC side vias scheme can be a potential approach for high density CMUT array fabrication and indirect integration of CMUT-IC for miniature size packaging, which eliminates problems related with direct integration.
本文介绍了一种使用可阳极键合的低温共烧陶瓷（LTCC）制造和封装电容式微机械超声换能器（CMUT）的方法。LTCC与带有金通孔的绝缘体上硅（SOI）进行阳极键合，已被用于制造具有不同膜半径（24 µm、25 µm、36 µm、40 µm和60 µm）的CMUT。在对LTCC通孔进行湿法蚀刻后，底部电极直接在剩余的通孔上进行图案化。CMUT腔和金凸块在SOI晶圆的硅部分上进行微加工。这种高导电性的硅也用作顶部电极。在阳极键合过程中，通过对湿法蚀刻的LTCC通孔和凸块进行金-金键合，实现了CMUT顶部和底部之间的电气连接。使用三个关键参数，即红外图像、复导纳图和静态膜位移，来评估键合是否成功。制造了膜厚度为2.6 µm的CMUT用于实验分析。在制造过程之后，描述了一种新颖的CMUT-IC封装工艺。该工艺能够使用LTCC的侧面通孔对CMUT和集成电路（IC）进行间接封装。侧面通孔通过对制造的CMUT进行微加工获得，并用于驱动CMUT元件。连接电极在LTCC侧面通孔上进行图案化，并且在CMUT的背面组装了一根导管。通过倒装芯片键合工艺将IC安装在导管上的键合焊盘上。通过测量IC和导管上焊盘之间的键合电阻来评估键合性能。这项研究表明，LTCC和LTCC侧面通孔方案可能是一种用于高密度CMUT阵列制造以及CMUT-IC间接集成以实现微型尺寸封装的潜在方法，它消除了与直接集成相关的问题。
