Manufacturing Repeatability of the Frequency and Q of Micromechanical Disk Resonators
With Q's over 150,000 at VHF  and over 15,000 into the GHz range , plus demonstrated aging and drift stabilities suitable for low-end timing products that are now entering consumer electronics markets , vibrating micromechanical resonator technology has garnered considerable momentum and now targets higher-end markets, such as communication-grade filters and oscillators for wireless handsets. Applications like these, however, tend to rely more heavily on the sheer performance of the resonators they use. Since resonator performance is a statistical quantity, the success of a higher-end product often depends more on the degree to which the manufacturing process can consistently achieve a specific frequency and maintain a Q above a certain threshold.
This project aims to study the statistical repeatability of the resonance frequencies, quality factors and circuit behaviors of surface-micromachined micromechanical resonators of various geometries. To date, a decent volume of center supported radial mode disk resonators, as shown in Figure 1, have been tested with the results showing that the standard deviations for both frequency and Q of this resonator type are well within values needed to achieve the ~3% percent bandwidth requirements for filters presently used in the RF front-ends of wireless communication devices without trimming. Figure 2 shows the frequency distribution of a single wafer. The long-term goal of this project is to devise methods for improving the untrimmed repeatability of micromechanical resonators so as to widen the breadth of applications addressable by such devices, e.g., to include a small percent bandwidth filter.
Figure 1: SEM of a fabricated radial mode disk resonator
Figure 2: Single wafer resonance frequency distribution
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