Design and Fabrication of Hemispherical Shell Resonator by Glass Blowing Method

The Hemispherical Resonator Gyroscope (HRG) has been a valuable choice for the aerospace industry due to its low noise, good performance, and long lifetime. Its main part consists of a hemispherical shell resonator (HSR). Recently, with the idea of using MEMS technology and using materials such as Pyrex in the construction of HSR, a significant reduction in the size, weight, and power consumption of this gyroscope along with the special gyroscopic characteristics of HRG, Today, the Micro-HRG has been introduced as a sensor in the strategic class. Micro-HSR can be implemented in three ways: micromachining, blowtorching, and glass blowing. In this paper, after a brief introduction and comparison of possible approaches to make an HSR, the glass blowing method is selected and the sub-processes of this method are introduced and the results of its implementation are presented. The proposed sensor is made by performing the glass blowing method, with a radius of 1.536 mm, a middle base radius of 252 µm, and a shell height of 355 µm. Also, the most important fabrication parameters for achieving the desired geometrical shell were as follows: The appropriate initial thickness of Pyrex is 200 µm and the depth of the cavity under the silicon layer is 532 µm. The bonding process to create a stable connection between Si and Pyrex must be performed at a voltage of 800 V at a temperature of 550 °C for the 30s. And the blowing process with a heating rate of 4 °C/s and a cooling rate of 9.5 °C/s has been evaluated as a suitable thermal profile. By optimally controlling the temperature process in the blowing sub-process, the crystallization phenomenon is prevented, which will lead to the improvement of the HSR quality factor. Achieving the technology of making this hemispherical glass shell in sub-millimeter dimensions, which plays the role of the resonator in an HRG, due to the superior features of this gyroscope such as low noise, good performance, and long lifetime and its application in strategic industries, like navigation and smart weapons, it is of particular importance.