Ming-Huang Li

A Monolithic CMOS-MEMS Oscillator Based on an Ultra-Low-Power Ovenized Micromechanical Resonator

A fully monolithic complimentary metal-oxide- semiconductor-microelectormechanical systems (CMOS-MEMS) oscillator comprised of an ovenized double-ended tuning fork resonator to enable ultra-low heater power operation of only 0.47 mW over entire temperature span (-40 °C to 85 °C) and a low noise sustaining circuit to achieve low phase noise has been demonstrated in a Taiwan Semiconductor Manufacturing Company (TSMC) 0.35-μm CMOS process. The combination of low thermal conductivity material and high thermal isolation design is the key to attaining ultra-low-power heater operation in a sub-mW level. Passive temperature compensation scheme is also conducted in the proposed CMOS-MEMS resonator by an oxide-metal composite structure, showing a low temperature coefficient of frequency (TC f ) of only +5.1 ppm/°C, which is suited for the use in ovenized oscillator systems. By implementing a constant-resistance temperature control scheme, the frequency drift of the resonator smaller than 120 ppm from -40 °C to 85 °C is demonstrated in this paper, indicating an equivalent TC f smaller than 1 ppm/°C, a record-low value against its CMOSMEMS counterparts. The CMOS-MEMS oscillator operating at 1.2 MHz demonstrates a phase noise of -112 dBc/Hz at 1-kHz offset and -120 dBc/Hz at 1-MHz offset while drawing less than 1.3 mW. The entire power consumption of the ovenized oscillator system is confirmed to be less than 1.8 mW (oscillator + micro-oven), verifying the great potential of low power oven-controlled MEMS oscillators realized in CMOS-MEMS technology.

Mechanically coupled CMOS-MEMS free-free beam resonator arrays with enhanced power handling capability

Integrated CMOS-MEMS free-free beam resonator arrays operated in a standard two-port electrical configuration with low motional impedance and high power handling capability, centered at 10.5 MHz, have been demonstrated using the combination of pull-in gap reduction mechanism and mechanically coupled array design. The mechanical links (i.e., coupling elements) using short stubs connect each constituent resonator of an array to its adjacent ones at the high-velocity vibrating locations to accentuate the desired mode and reject all other spurious modes. A single second-mode free-free beam resonator with quality factor Q >; 2200 and motional impedance Rm <; 150 kΩ has been used to achieve mechanically coupled resonator arrays in this work. In array design, a 9-resonator array has been experimentally characterized to have performance improvement of approximately 10× on motional impedance and power handling as compared with that of a single resonator. In addition, the two-port electrical configuration is much preferred over a one-port configuration because of its low-feedthrough and high design flexibility for future oscillator and filter implementation.

A Fully Differential CMOS–MEMS DETF Oxide Resonator With

A fully differential CMOS-MEMS double-ended tuning-fork (DETF) oxide resonator fabricated using a 0.18-μm CMOS process has been demonstrated with a Q greater than 4800 and more-than-20-dB stopband rejection at 10.4 MHz. The key to attaining such a performance attributes to the use of oxide structures with embedded metal electrodes, where SiO2 offers a Q enhancement (at least a 3-times-higher Q) as compared to other CMOS-MEMS-based composite resonators with similar structures and vibrating modes and where flexible electrical routing facilitates fully differential configuration to suppress capacitive feedthroughs. In addition, the resonators developed in this work possess a positive temperature coefficient of frequency (TCf) and mode-splitting capability, therefore indicating a great potential for temperature compensation and spurious-mode suppression, respectively. This technology paves a way to realize fully integrated CMOS-MEMS oscillators and filters which might benefit future single-chip transceivers for wireless communications.

Q > \hbox{4800}

Integrated CMOS-MEMS array resonators have been demonstrated that takes advantage of pull-in effect to surmount limitations of CMOS foundry process and attains electrode-to-resonator gap spacing at a deep-submicron range, leading to much smaller motional impedance compared to conventional CMOS-MEMS technologies, while possessing unique frequency tuning capability by modulating their mechanical boundary conditions. With the increase of applied dc-bias which simultaneously serves for functions of pull-in and resonator operation, the upward frequency shift of resonance caused by boundary condition (“BC”) change offers opposite tuning mechanism to well-known effect of electrical stiffness. As a result, frequency variation induced by BC-modulation and electrical-stiffness would yield a frequency-insensitive region under a certain dc-bias.

and Positive TCF

This letter presents the design of a low power, low phase noise monolithic oscillator with a back-end-of-line-embedded CMOS-MEMS resonator. The proposed CMOS-MEMS oscillator consists of a double-ended tuning fork resonator and a high gain (>138 dBQ) ultra-low input-referred current noise (<;25 fA/√Hz) integrator-differentiator transimpedance amplifier (TIA) with sub-150-μW power consumption. The 1.2-MHz CMOS-MEMS oscillator prototype shows the phase noise better than -120 dBc/Hz at 1-kHz offset and -122 dBc/Hz at 10-kHz offset with moderate dc-bias (VP = 22 V). The proposed oscillator can be operated with reduced MEMS dc bias (VP <; 7 V) and TIA power supply (VDD <; 1.3 V, 65 μW) while maintaining satisfactory performance. The frequency-power-normalized oscillator phase noise figure-of-merit (will be defined later) of 190 dB is achieved at 1-kHz offset with a resonator Q of 1900, which is comparable with the state-of-the-art using bulk-mode resonators possessing Q > 100 k.

Realizing deep-submicron gap spacing for CMOS-MEMS resonators with frequency tuning capability via modulated boundary conditions

A cutting-edge ovenized micromechanical resonator circuit comprised of a double-ended tuning fork (DETF) resonator and serpentine-shaped heaters to enable ultra-low heater power of only 0.47 mW over the entire temperature range (-40°C to 85°C) has been reported for the first time in a low-cost, foundry CMOS-based fabrication platform. The combination of low thermal conductivity materials (i.e., SiO2 and poly-Si) and high thermal isolation designs is key to attaining low heater power consumption in a sub-mW level. An ovenized 1.2-MHz CMOS-MEMS oscillator with a phase noise lower than -103 dBc/Hz at 1-kHz offset and -110 dBc/Hz at 1-MHz offset was also demonstrated in this work, verifying the great potential of low power oven-controlled MEMS oscillators realized using the well-established CMOS-MEMS technology.

A Sub-150-

A foundry-oriented capacitively driven CMOS-MEMS resonator using differentially piezoresistive sensing is successfully demonstrated to enable effective feedthrough cancellation with more than 20-dB feedthrough floor reduction as compared to its capacitive readout. The resonator is mainly formed by high-Q SiO2 structure utilizing metal wet etching and XeF2 release processes, while the polysilicon layer (originally CMOS gate poly material) embedded inside the resonator structure serves as a piezoresistor for vibratory detection. In addition, such a composite structure enabling electrical isolation realizes decoupling of the capacitive and piezoresistive transductions, allowing the selection (or switching) of the preferred readout scheme using the same resonator device. The proposed resonator consists of only one single capacitor for driving and a simple beam structure for both vibration and detection, therefore greatly simplifying the device design and facilitating future CMOS-MEMS implementation. This paper achieves resonator , more than 28-dB signal-to-feedthrough ratio, and two-times smaller motional impedance than that of the single-ended piezoresistive detection using the same device and driving condition. Furthermore, the piezoresistive operation offers a simple temperature compensation scheme for CMOS-MEMS resonators via the adjustment of the dc current through the piezoresistor, therefore showing 1.4-times improvement on thermal stability as compared to their capacitive readout.

\mu \text{W}

This paper focuses on the design and development of a CMOS-MEMS resonator integrated with an on-chip amplifier with emphasis on its single-chip frequency reference oscillator implementation. A flexural-mode ring resonator with a desired mode shape featuring an inherent fully-differential mode of mechanical operation is designed using both analytical and finite element models. Two such resonators in low- and high-frequency domains, centered at 1.39 and 9.34 MHz respectively, are individually modeled using first principals, equations, and simulation tools to evaluate and improve device performance. In this paper, the device is also shown to offer a potential benefit of capacitive feedthrough cancelation up to 30 dB attributed to differential signaling scheme. Subsequently, both rapidly prototyped devices integrated with their on-chip transimpedance amplifiers are demonstrated using a commercially available TSMC 0.35-μm CMOS technology. A low-frequency resonator integrated with its on-chip amplifier exhibited decent overall performance capabilities in terms of much higher transmission spectra (closer to 0 dB), greater feedthrough suppression, higher signal-to-feedthrough ratio (35 dB), and exact phase shift (0°) at resonance frequency, therefore being a potential candidate for a single-chip oscillator system.

BEOL-Embedded CMOS-MEMS Oscillator With a 138-dB

This letter presents the design of a micromechanical oscillator based on a vertically coupled (VC) CMOS-microelectromechanical systems (MEMS) resonator pair for phase noise reduction. The prototyped resonator pair consists of two vibrating plates coupled with each other, thus providing enhanced power handling while keeping compact footprint. The proof-of-concept oscillator based on a 6.5-MHz, VC mode resonator achieves a phase noise of -97 dBc/Hz at 1-kHz offset and -118 dBc/Hz at 1-MHz offset from carrier with a resonator size of 30 × 30 μm2. Compared with its nonresonance-coupled saddle mode counterpart, the VC-mode-based oscillator features 10-dB phase noise reduction using the same oscillator circuit setup. The design concept of this letter can be extended to three dimensional (3-D) mechanically coupled resonator designs in the future.

\Omega

A novel complimentary metal-oxide-semiconductor-microelectormechanical systems (CMOS-MEMS) composite ring resonator capable of a dual-mode operation has been proposed to enable temperature coefficient of frequency (TCf