A 17.6-MHz 2.5V ultra-low polarization voltage MEMS oscillator using an innovative high gain-bandwidth fully differential trans-impedance voltage amplifier

Abstract

This paper reports on the design and characterization of a low phase noise MEMS oscillator with ultra-low polarization voltage. An innovative oscillation circuitry is also proposed by a high gain-bandwidth, low-power TIVA (trans-impedance voltage amplifier) which is composed of two stages: the I-to-V stage and voltage gain stage. The TIVA is fabricated using 1P6M 0.18 m CMOS technology and has been demonstrated with gain of 110dBΩ, 3-dB bandwidth of 60MHz, and power consumption of only 5.9mW, achieving the highest figure of merit (FOM) among reported literatures. Moreover, the input referred noise is less than 2.5 pA/√Hz in the 10 kHz to 100 MHz range. In order to reduce the motional impedance of capacitive MEMS resonators, a 50 nm-gap process together with vacuum capping technology is implemented. The TIVA chip is wire-bonded to a 17.6-MHz high-Q (Q unloaded ~ 8,000) silicon-based capacitive MEMS resonator and perform the phase noise of -121 dBc/Hz @1kHz offset and -131 dBc/Hz @10kHz offset, respectively, at polarization voltage of 6.8V. At 2.5V polarization voltage, the phase noise can reach -116 dBc/Hz @1kHz offset and -125 dBc/Hz @10kHz offset, respectively.

A Novel High Q Lamé-Mode Bulk Resonator with Low Bias Voltage

“…The motional current is given by [ 19 ]: and the maximum displacement at resonance can be expressed as [ 20 ]: …”

“…A typical Lamé-mode resonator with an extremely high Q factor of 7.5 × 10 5 at a resonance frequency of 12.9 MHz requires a driving voltage of 100 V [ 10 ]. Increasing the capacitive area, shrinking the air gap between the resonator and the electrodes or utilizing different detection methods were effective in reducing the bias voltage, but these routines were often restricted by the fabrication technology [ 19 , 20 ]. A Lamé-mode resonator with thin air gap of 50 nm was excited with a low voltage of 2.5 V into vibration at 17.6 MHz, but its Q factor was only 8000 in vacuum [ 19 ].…”

“…Increasing the capacitive area, shrinking the air gap between the resonator and the electrodes or utilizing different detection methods were effective in reducing the bias voltage, but these routines were often restricted by the fabrication technology [ 19 , 20 ]. A Lamé-mode resonator with thin air gap of 50 nm was excited with a low voltage of 2.5 V into vibration at 17.6 MHz, but its Q factor was only 8000 in vacuum [ 19 ]. Additionally, a capacitively actuated and piezoresistively detected Lamé-mode resonator can vibrate at 2.2 MHz with low bias voltage of 3 V, yet its Q factor is 6771 at atmosphere [ 20 ].…”

A Sub-mW 18-MHz MEMS Oscillator Based on a 98-dBΩ Adjustable Bandwidth Transimpedance Amplifier and a Lamé-Mode Resonator

“…This can be accounted for by either enhancing the transduction, e.g., sub-micron gaps realized by complex fabrication processes [11,12,13], high voltages [1,2,3,4,5,6,7,14], added transducer combs [15,16], movable electrodes for gap closing [17,18], or increasing the gain for the transimpedance amplifier (TIA) in order to sustain oscillation. Several transimpedance topologies have been reported in the literature for MEMS-based oscillator applications [19,20,21,22,23,24,25,26]. Designs proposed in [19,20,21] use an automatic gain control circuit to regulate the oscillation amplitude and reduce the resonator mechanical non-linearity effect.…”

“…Designs proposed in [19,20,21] use an automatic gain control circuit to regulate the oscillation amplitude and reduce the resonator mechanical non-linearity effect. Furthermore, while differential TIAs allow for better performance, the power consumption of fully differential transimpedance amplifier designs in [19,22] are higher than single-ended TIAs in [20,21,23,24,25].…”