Yuan Xie

1.52-GHz micromechanical extensional wine-glass mode ring resonators

Vibrating polysilicon micromechanical ring resonators, using a unique extensional wine-glass-mode shape to achieve lower impedance than previous UHF resonators, have been demonstrated at frequencies as high as 1.2 GHz with a Q of 3,700, and 1.52 GHz with a Q of 2,800. The 1.2-GHz resonator exhibits a measured motional resistance of 1 MOmega with a dc-bias voltage of 20 V, which is 2.2 times lower than the resistance measured on radial contour- mode disk counterparts at the same frequency. The use of larger rings offers a path toward even lower impedance, provided the spurious modes that become more troublesome as ring size increases can be properly suppressed using methods described herein. With spurious modes suppressed, the high-Q and low-impedance advantages, together with the multiple frequency on-chip integration advantages afforded by capacitively transduced mumechanical resonators, make this device an attractive candidate for use in the front-end RF filtering and frequency generation functions needed by wireless communication devices.

Vibrating micromechanical resonators with solid dielectric capacitive transducer gaps

VHF and UHF MEMS-based vibrating micromechanical resonators equipped with new solid dielectric (i.e., filled) capacitive transducer gaps to replace previously used air gaps have been demonstrated at 160 MHz, with Qs ~ 20,200 on par with those of air-gap resonators, and motional resistances (Rxs) more than 8times smaller at similar frequencies and bias conditions. This degree of motional resistance reduction comes about via not only the higher dielectric constant provided by a solid-filled electrode-to-resonator gap, but also by the ability to achieve smaller solid gaps than air gaps. These advantages with the right dielectric material may now allow capacitively-transduced resonators to match to the 50-377 Omega impedances expected by off-chip components (e.g., antennas) in many wireless applications without the need for high voltages. In addition to lower motional resistance, the use of filled-dielectric transducer gaps provides numerous other benefits over the air gap variety, since it (a) better stabilizes the resonator structure against shock and microphonics; (b) eliminates the possibility of particles getting into an electrode-to-resonator air gap, which poses a potential reliability issue; (c) greatly improves fabrication yield, by eliminating the difficult sacrificial release step needed for air gap devices; and (d) potentially allows larger micromechanical circuits (e.g., bandpass filters comprised of interlinked resonators) by stabilizing constituent resonators as the circuits they comprise grow in complexity

60-MHz wine-glass micromechanical-disk reference oscillator

A reference oscillator utilizing a 60MHz, MEMS-based, wine glass disk vibrating micromechanical resonator with a Q of 48,000 and sufficient power handling capability to achieve a far-from-carrier phase noise of -130dBc/Hz is demonstrated. When divided down to 10MHz, this corresponds to an effective level of -145dBc/Hz.

UHF micromechanical extensional wine-glass mode ring resonators

Vibrating polysilicon micromechanical ring resonators, utilizing a unique extensional wine-glass mode shape to achieve lower impedance than previous UHF resonators, have been demonstrated at frequencies as high as 1.2-GHz with a Q of 3,700, and 1.47-GHz (highest to date) with a Q of 2,300. The 1.2-GHz resonator exhibits a measured motional resistance of 560 k/spl Omega/ with a dc-bias voltage of 20 V, which is 6/spl times/ lower than measured on radial contour mode disk counterparts at the same frequency, and which can be driven down as low as 2 k/spl Omega/ when a dc-bias voltage of 100 V and electrode-to-resonator gap spacing of 460 /spl Aring/ are used. The above high Q and low impedance advantages, together with the multiple frequency, on-chip integration advantages afforded by electrostatically-transduced /spl mu/mechanical resonators, make this device an attractive candidate for use in the front-end RF filtering and oscillator functions needed by wireless communication devices.

A Bonded-Micro-Platform Technology for Modular Merging of RF MEMS and Transistor Circuits

A technology has been demonstrated that uses compression bonding to modularly combine platform-supported jumechanical filters with integrated BiCMOS transistor circuits while attempting to preserve the Q of mounted resonators. In this process, jumechanical devices are first fabricated onto SOI platforms, which are then released (together with devices) and compression bonded onto a transistor circuit wafer, making electrical connections at the bonds. Prior to bonding, while mounted on unreleased platforms, 6 MHz and 40 MHz clamped-clamped beam jumechanical resonators exhibit Q’s of 2,000 and 300, respectively. After release and bonding to the circuit wafer, the Q’s are degraded to 520 and 120, respectively. Poor bonding quality is identified as a likely reason for the observed Q reductions.

Small percent bandwidth design of a 423-MHz notch-coupled micromechanical mixler

Notching and low-velocity coupling design strategies are described and demonstrated that yield the first UHF vibrating micromechanical hollow-disk ring mixer-filters with IF bandwidths down to 0.05%, while still retaining reasonable passband shapes. Specifically, a 423-MHz mixer-filter, comprised of two mechanically coupled resonators exhibiting Qs in excess of 10,000, has been successfully demonstrated with a flat passband bandwidth of only 202 kHz. Like a previous 34-MHz mixer-filter based on clamped-clamped beam resonators, the much higher frequency device of this work is capable of performing both mixing (via capacitive transducer nonlinearity) from an RF frequency down to its IF passband centered at 423 MHz, then very small percent bandwidth filtering, e.g., to remove unwanted interferers in the receive path of a communication handset. The percent bandwidths demonstrated here are small enough to make possible channel-selection much earlier in a receive path chain, which could then greatly enhance the robustness and battery lifetime of future wireless transceivers.

Frequency tolerance of RF micromechanical disk resonators in polysilicon and nanocrystalline diamond structural materials

A statistical evaluation of the absolute and matching tolerances of the resonance frequencies of surface-micromachined micromechanical 1-port disk resonators is conducted by fabricating and measuring a large quantity (>100) of devices in both polysilicon and nanocrystalline diamond structural materials. Through this analysis, respective average resonance frequency absolute and matching tolerances of 450 ppm and 343 ppm for polysilicon, and 756 ppm and 392 ppm for diamond, have been demonstrated on a measured set of 6 dies on 4-inch wafers fabricated using university facilities. The measured matching tolerance is sufficient to allow implementation of RF pre-select or image-reject filters for wireless communications with a confidence interval better than 99.7% over tested dies without the need for frequency trimming