Zeying Ren

1.156-GHz self-aligned vibrating micromechanical disk resonator

A new fabrication methodology that allows self-alignment of a micromechanical structure to its anchor(s) has been used to achieve vibrating radial-contour mode polysilicon micromechanical disk resonators with resonance frequencies up to 1.156 GHz and measured Qs at this frequency >2,650 in both vacuum and air. In addition, a 734.6-MHz version has been demonstrated with Qs of 7,890 and 5,160 in vacuum and air, respectively. For these resonators, self-alignment of the stem to exactly the center of the disk it supports allows balancing of the resonator far superior to that achieved by previous versions (in which separate masks were used to define the disk and stem), allowing the present devices to retain high Q while achieving frequencies in the gigahertz range for the first time. In addition to providing details on the fabrication process, testing techniques, and experimental results, this paper formulates an equivalent electrical circuit model that accurately predicts the performance of these disk resonators.

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.

Low phase noise array-composite micromechanical wine-glass disk oscillator

A reduction in phase noise by 13 dB has been obtained over a previous 60-MHz surface-micromachined micromechanical resonator oscillator by replacing the single resonator normally used in such oscillators with a mechanically-coupled array of them to effectively raise the power handling ability of the frequency selective tank. Specifically, a mechanically-coupled array of nine 60-MHz wine-glass disk resonators embedded in a positive feedback loop with a custom-designed, single-stage, zero-phase-shift sustaining amplifier achieves a phase noise of -123 dBc/Hz at 1 kHz offset and -136 dBc/Hz at far-from-carrier offsets. When divided down to 10 MHz, this effectively corresponds to -138 dBc/Hz at 1 kHz offset and -151 dBc/Hz at far from carrier offset, which represent 13 dB and 4 dB improvements over recently published work on surface-micromachined resonator oscillators, and also now beat stringent GSM phase noise requirements by 8 dB and 1 dB, respectively

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

1.14-GHz self-aligned vibrating micromechanical disk resonator

Micromechanical radial-contour mode disk resonators featuring new self-aligned stems have been demonstrated with record resonance frequencies up to 1.14 GHz and measured Qs at this frequency >1,500 in both vacuum and air. In addition, a 733-MHz version has been demonstrated with Qs of 7,330 and 6,100 in vacuum and air, respectively. For these resonators, self-alignment of the stem to exactly the center of the disk it supports allows balancing of the resonator far superior to that achieved by previous versions (where separate masks were used to define the disk and stem), allowing the present devices to retain high Q while achieving frequencies in the GHz range for the first time. In addition to providing measured results, this paper formulates an equivalent electrical circuit model that accurately predicts the performance of this disk resonator.

An MSI Micromechanical Differential Disk-Array Filter

A medium-scale integrated (MSI) vibrating micromechanical filter circuit that utilizes 128 radial-mode disk and mechanical link elements to achieve low motional resistance while suppressing unwanted modes and feedthrough signals has been demonstrated with a 0.06%-bandwidth insertion loss less than 2.5 dB at 163 MHz. The ability to attain an insertion loss this small for such a tiny percent bandwidth on chip is unprecedented and is made possible here by the availability of Qs >10,000 provided by capacitively transduced resonators. In particular, the MSI mechanical circuit is able to harness the high Q of capacitively transduced resonators while overcoming their impedance deficiencies via strategic mechanical circuit design methodologies, such as the novel use of wavelength-optimized resonator coupling to effect a differential mode of operation that substantially improves the stopband rejection of the filter response while also suppressing unwanted modes.

Fully monolithic CMOS nickel micromechanical resonator oscillator

A fully monolithic oscillator achieved via MEMS-last integration of low temperature nickel micromechanical resonator arrays over finished foundry CMOS circuitry has been demonstrated with a measured phase noise of -95 dBc/Hz at a 10-kHz offset from its 10.92-MHz carrier (i.e., output) frequency. The use of a side-supported flexural-mode disk resonator-array to boost the power handling of the resonant tank is instrumental to allowing adequate oscillator performance despite the use of low-temperature nickel structural material. Because the fabrication steps for the resonator-array never exceed 50degC, the process is amenable to not only MEMS-last monolithic integration with the 0.35 mum CMOS of this work, but also next generation CMOS with gate lengths 65 nm and smaller that use advanced low-k dielectric material to lower interconnect capacitance.

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.

Third-order intermodulation distortion in capacitively-driven VHF micromechanical resonators

Substantial increases by more than 22 dB in the third-order input intercept points (IIP3) of capacitively trans- duced MEMS-based vibrating micromechanical resonators have been attained by using contour-mode disk geometries to replace previous clamped-clamped beam versions. Specifically, a 156-MHz contour-mode disk resonator with Q = 20,500 exhibits a measured IIP3 = 19.49 dBm, which is substantially better than the -3 dBm previously measured for a 10-MHz clamped-clamped beam resonator, and which now erases any lingering skepticism regarding the linearity of micro-scale mechanical resonators. Indeed, with IIP3s about 20 dBm, high Q communication filters using the micromechanical resonators of this work should now be able to replace present-day receive path filters with little degra- dation (only 0.11 dB) in cumulative receiver IIP3.