Devices Employing Piezoelectric Boundary Waves for Integration with Semiconductor Circuitry

报道了在高压电性LiNbO_3衬底和Si衬底之间的界面上存在一个边界波，它使我们能够实现与传统声表面波(SAW)器件相当的高性能模拟信号处理功能。本研究旨在通过对基片键合技术的发展来开发边界波器件。为了开发这种器件结构所需的非常精细的电极图形，研究了电子束光刻技术的应用。就这一点而言，升空方法总体上是有效的。然而，由于LiNbO_3衬底是绝缘体，直接电子束曝光会引起充电问题。为了克服这一困难，作者开发了基于水性抗静电涂料的新的剥离工艺。该工艺使我们能够实现线宽为0.2μm的Al-IDT图形。然后在f-…中制作了Si/LiNbO_3结构的边界波器件(1)采用电子束剥离技术在LiNbO_3衬底上制备了非常精细的异质结薄膜。(2)用射频溅射法沉积SiO_2中间层作为绝缘层；(3)用电子束蒸发法沉积硅的顶层。在2.09 GHz处可以清楚地观察到边界波的响应，但通过硅层沉积使器件插入增加了20分贝。此外，还研究了该粘结剂在制作边界波器件中的应用。首次对紫外光树脂的使用进行了研究。虽然在991 MHz处观察到了波响应，但所获得的插入损耗很大(30.8dB)。它包括由于电极布线造成的大约10dB的欧姆损耗，而其余的欧姆损耗是由于树脂中的吸附。然后对Kovar玻璃的使用进行了研究，成功地实现了硅与LiNbO_3的粘结。虽然由于玻璃层的厚度，目前无法检测到响应，但它可以用于实现高性能的边界涉水器件。较少

The authors reported that there exists a boundary wave at the interface between the highly piezo-electric LiNbO_3 substrate and the Si substrate, and the wave enables us to realize high performance analog signal processing function comparable to the conventional surface acoustic wave (SAW) devices. This research intended to develop boundary wave devices through the development of to the substrate bonding technology. In order to develop very fine electrode pattern needed for this device structure, use of the electron-beam (EB) lithography was studied. For the purpose, the lift-off method is effective in general. However, since LiNbO_3 substrate is insulator, the direct EB exposure causes the charge-up problem. So as to circumvent this difficulty, the authors developed new lift-off process based on the water-solvable anti-static coating. This process enables us to realize Al IDT pattern of 0.2 μm line widths. Then the boundary wave device with Si/LiNbO_3 structure was fabricated in the f … More ollowing step : (1) very fine IDT was developed on the LiNbO_3 substrate by the EB-based lift-off process. (2) the SiO_2 intermediate layer was deposited as an insulation layer by the RF sputtering method, and (3) the Si top layer was deposited by the electron beam evaporation. The response by the boundary wave was clearly observed at 2.09 GHz, though the device insertion was 20 dB increased by the Si layer deposition. In addition, use of the adhesive was also investigated for the fabrication of the boundary wave devices. First use of the UV resin was studied. Although the wave response was observed at 991 MHz, the attained insertion loss was rather large (30.8 dB). It includes the ohmic loss of about 10 dB due to the electrode routing, whereas the remaining is due to the absorption with in the resin. Then the use of the kovar glass was studied, and the adhesion of Si with LiNbO_3 was succeeded. Although the response could not be detected at this moment due to the thickness of the glass layer, it could be used for the realization of high performance boundary wade devices. Less