Electrical Engineering
      and Computer Sciences

Electrical Engineering and Computer Sciences

COLLEGE OF ENGINEERING

UC Berkeley

   

2008 Research Summary

Manufacturing Repeatability of the Frequency and Q of Micromechanical Disk Resonators

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Yang Lin

With Q's over 150,000 at VHF [1] and over 15,000 into the GHz range [2], plus demonstrated aging and drift stabilities suitable for low-end timing products that are now entering consumer electronics markets [3], 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
Figure 1: SEM of a fabricated radial mode disk resonator

Figure 2
Figure 2: Single wafer resonance frequency distribution

[1]
Y.-W. Lin et al., "Low Phase Noise Array-Composite Micromechanical Wine-Glass Disk Oscillator," Tech. Dig., IEEE Int. Electron Devices Mtg., Washington, DC, December 5-7, 2005, pp. 287-290.
[2]
J. Wang et al., "1.51-GHz Polydiamond Micromechanical Disk Resonator with Material-Mismatched Isolating Support," Proc. IEEE MEMS Conf., Maastricht, The Netherlands, January 25-29, 2004, pp. 641-644.
[3]
W.-T. Hsu et al., "Reliability of Silicon Resonator Oscillators," Proc. IEEE Int. Frequency Control Symp., Miami, Florida, June 5-7, 2006.