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. 2018 Oct 29;9(11):559.
doi: 10.3390/mi9110559.

A Temperature-Compensated Single-Crystal Silicon-on-Insulator (SOI) MEMS Oscillator with a CMOS Amplifier Chip

Mohammad S Islam  1 , Ran Wei  2 , Jaesung Lee  3 , Yong Xie  4 , Soumyajit Mandal  5 , Philip X-L Feng  6
Affiliations

A Temperature-Compensated Single-Crystal Silicon-on-Insulator (SOI) MEMS Oscillator with a CMOS Amplifier Chip

Mohammad S Islam et al. Micromachines (Basel). .

Abstract

Self-sustained feedback oscillators referenced to MEMS/NEMS resonators have the potential for a wide range of applications in timing and sensing systems. In this paper, we describe a real-time temperature compensation approach to improving the long-term stability of such MEMS-referenced oscillators. This approach is implemented on a ~26.8 kHz self-sustained MEMS oscillator that integrates the fundamental in-plane mode resonance of a single-crystal silicon-on-insulator (SOI) resonator with a programmable and reconfigurable single-chip CMOS sustaining amplifier. Temperature compensation using a linear equation fit and look-up table (LUT) is used to obtain the near-zero closed-loop temperature coefficient of frequency (TCf) at around room temperature (~25 °C). When subject to small temperature fluctuations in an indoor environment, the temperature-compensated oscillator shows a >2-fold improvement in Allan deviation over the uncompensated counterpart on relatively long time scales (averaging time τ > 10,000 s), as well as overall enhanced stability throughout the averaging time range from τ = 1 to 20,000 s. The proposed temperature compensation algorithm has low computational complexity and memory requirement, making it suitable for implementation on energy-constrained platforms such as Internet of Things (IoT) sensor nodes.

Keywords: MEMS-ASIC integration; application-specific integrated circuit (ASIC); micro/nanoelectromechanical systems (MEMS/NEMS); oscillator; programmable sustaining amplifier; real-time temperature compensation loop; resonator; silicon-on-insulator (SOI); single-crystal silicon (SC-Si).

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Conflict of interest statement

The authors declare no conflicts of interest regarding the publication of this paper.

Figures

Figure 1
Figure 1
Overview of the temperature-compensated oscillator.
Figure 2
Figure 2
Single-crystal Si-on-insulator (SOI) comb-drive MEMS resonator characteristics. (a) Scanning electron microscopy (SEM) image. The inset shows a partial zoom-in view of the comb drive and fingers. Scale bar: 20 μm; (b) Simulated vibration pattern and mode shape for the first in-plane resonance mode; (c) Optically measured transmission data and frequency response around the first resonance as temperature increases; (d) Open-loop resonance frequency dependence on temperature for the extraction of TCf from the data in (c); (e) Electrically measured transmission and frequency response when various values of the DC polarization voltage are applied to the shuttle. The responses in (c,e) have not been converted to dimensionless transfer functions since the measurement path includes both electrical and optical components, which makes it difficult to derive absolute calibration factors.
Figure 3
Figure 3
(a) Simplified system diagram illustrating the integration of the MEMS resonator chip with the CMOS sustaining amplifier chip; (b) Simplified block diagram of the programmable single-chip CMOS sustaining amplifier (corresponding to the same color-coded dashed-line box in (a)).
Figure 4
Figure 4
(a) Die micrograph of the CMOS sustaining amplifier; (b) Test board used for characterizing the amplifier and integrating with the MEMS resonator to build the oscillator.
Figure 5
Figure 5
Electrical characterization results of the single-crystal SOI MEMS resonator. (a) Measured transmission (dB) and frequency response of the resonance; (b) Open-loop phase (degrees) around the first mode for VDC = 20 V and an input power of −10 dBm.
Figure 6
Figure 6
(a) Measured single-sideband (SSB) phase noise of the single-crystal SOI MEMS oscillator for VDC = 20 V; (b) Measured electrical tuning of the oscillator frequency as a function of VDC (approximately −1 Hz/V for voltages >16 V).
Figure 7
Figure 7
Block diagram of the model calibration procedure, and the proposed real-time temperature compensation loop.
Figure 8
Figure 8
(a) Measured temperature variation (top) and fluctuation of oscillation frequency (bottom) for the uncompensated oscillator over 24 h; (b) Linear fit of the oscillation frequency versus temperature.
Figure 9
Figure 9
(a) Instantaneous frequency of the uncompensated and compensated oscillators over 24 h; (b) Measured Allan deviation σA (τ) with and without real-time temperature compensation.
Figure 10
Figure 10
Fractional frequency shift (in ppm) as the device temperature is varied, measured from both the temperature-compensated and uncompensated oscillators over a temperature range of 10 to 45 °C.
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