Abstract
Development of surface acoustic wave (SAW) devices has been getting attention to achieve next fifth generation (5G) mobile communications. We had previously proposed a temperature compensated SAW substrate, LiTaO 3 (LT: lithium tantalate)/ST-cut quartz (ST-quartz), with which directly combined piezoelectric single crystals using amorphous intermediate bonding (AIB) method. In this paper, we investigate bonding characteristics using different amorphous layers with the object of improving bonding of piezoelectric single crystals for future SAW devices. We applied amorphous Al 2 O 3 (α-Al 2 O 3 ) as intermediate layers as well as previously reported amorphous SiO 2 (α-SiO 2 ) to the bonding interface of LT and ST-quartz, since a-Al 2 O 3 has high water corrosion resistance against to the hydrophilic treatment. The substrates with both of the amorphous intermediate layers were successfully bonded assisted with vacuum ultraviolet irradiation in the presence of oxygen gas (VUV/O 3 ). Especially, the substrate with the a-Al 2 O 3 layer achieved the dominant highest bonding strength of 10.5 MPa, which is approximately three times stronger than the substrate with the α-SiO 2 layer. These results indicate that the α-Al 2 O 3 layer is preferable to improve effects of VUV/O 3 hydrophilic treatment and fabricate LT/ST-quartz substrate. To investigate the amorphous interlayers can be promising for making piezoelectric single crystals bonding enough strong to fabricate the future SAW devices.
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