Study of Recessed-SAW Devices Fabrication by Proton-Exchange Wet-Etching Technology

• Main Authors: Shih-Hung Tsai, 蔡世鴻
• Other Authors: Mau-Phon Houng
• Format: Others
• Language: en_US
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/50412551361655388442

博士 === 國立成功大學 === 微電子工程研究所碩博士班 === 93 === 　　Recently, the needs for piezoelectric devices have been greatly increasing with the rapid growth of mobile communication systems. The requirements for the devices have been widely spreading and becoming more critical. In order to satisfy these requirements, not only new designing methods but also new piezoelectric materials have to be brought into practice. For example, SAW-semiconductor coupled devices, such as convolvers and correlators, are promising for signal processing. However, the drawbacks of these bonding technologies would be a lack of mass productivity, reliability, tensile strength weakness, poor yield and complicated fabrication processes involved. In this dissertation, we have proposed the improved method to fabricate the Recessed-SAW device and then applied to integrate semiconductor device into one chip by the direct bonding technique. 　　At first, we created the design criterion of the SAW devices by using the coupling-of-modes model. The simulated results indicate that the device performances are appeared by changing several variable parameters such as overlaps, transfer distance, number of interdigital transducer (IDT) pairs and piezoelectric materials exactly. It is very helpful for us to shorten the cost and time-consuming in some specific researches. 　　Subsequently, an improved method for fabricating recessed-structure SAW filters is reported. Etch rates of normally slow-to-etch LiNbO3 are enhanced by proton exchange (PE) pretreatment. It was observed for PE times for a long time, substrate surface damage occurred during the subsequent etching step. Structures fabricated by the proposed method have been shown to have controllable groove depth, smooth etched surfaces and sharp edges. The fabricated SAW device was demonstrated to have a good performance. 　　After that, an optimal method for fabricating the Recessed-SAW device bonded with silicon substrate has been presented. Experimental results indicate that the hydrophilic surface can be obtained using the H2SO4-based solutions, and the heating processes about 100℃ are also effective to obtain the tight bonding force. The Si/Recessed-SAW device was demonstrated to perform as well as the original Recessed-SAW device and to be useful in fabricating integrated devices. 　　Based on the above studies, we have also investigated the propagation characteristics of the 64o Y-X recessed substrate. The calculated propagation loss increases with increasing electrode thickness. The internal reflection can be reduced to almost zero by controlling the metal film-thickness and groove depths. In our experiments, the 1000 A Al film-thickness needs 800-900 A groove depth. In addition, the surface skimming bulk wave can be found by sand-blasting treatment. The measured temperature coefficient of frequency of Recessed-SAW is -61.4 ppm/℃ which is better than the Non-Recessed-SAW with -85.5 ppm/℃. 　　Combining all the experimental results in this dissertation, this device with its good performance and suitability to needs of increased miniaturization in mixed-material ICs and hybrid devices makes significantly probable its expanded use.