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Junjun Huan , George Xereas, Vamsy Chodavarapu
Department of Electrical EngineeringUniversity of Dayton, OH
Email: [email protected]
WAFER-LEVEL VACUUM-ENCAPSULATED ULTRA-LOW
VOLTAGE TUNING FORK MEMS RESONATOR
Integrated Microsystems Laboratoryiml
RESONATORS: TIMING & FREQUENCY REFERENCES
Today, we have stringent requirements of low cost, low complexity, compact system integration, low power consumption, and shock resistance in mobile, IoT and wearable applications that cannot be satisfied with Quartz devices.• High spectral purity (High Q > 10,000)• Low temperature sensitivity (<5 ppm/oC)• High Stability over lifetime (material, aging
issues)• MEMS Piezoelectric Vs MEMS Electrostatic (SiLabs/IDT/Sand9 Vs SiTime)• Small size (1mm3)
3 oscillators in Apple Watchiml
5 oscillators in Apple iPhone
SINGLE CHIP MULTI-FUNCTION INTEGRATION
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Single-band Multi-chip
Multi-band Single-chip
CDMA
GSM
PCS
MEMS ELECTROSTATIC RESONATORS
524 kHz MEMS tuning fork resonator with Q of 52,000 by SITIME [2]
32 kHz MEMS tunable capacitive-comb driven folded-beam resonator with Q of 57,000 by Dr. Clark T.-C. Nguyen’s Group [3]
10 MHz MEMS ring resonator with Q of 473000 by SITIME [1]
6.35 MHz MEMS LAME-MODE resonator with Q of 3240000[2]
[1] S. Wang, T.W. Kenny, "Nonlinearity of hermetically encapsulated high-Q double balanced breathe-mode ring resonator," 23rd IEEE International Conference on Micro Electro Mechanical Systems, Hong Kong, p. 715-718, 2010.
[2] G. Xereas and V. P. Chodavarapu, "Wafer-Level Vacuum-EncapsulatedLame Mode Resonator With f-Q Product of 2.23 x 10(13) Hz," Ieee Electron Device Letters, vol. 36, pp. 1079-1081, Oct 2015.
[3] S. Zaliasl, J. C. Salvia, G. C. Hill, L. Chen, K. Joo, R. Palwai, et al., "A 3 ppm 1.5 x 0.8 mm(2) 1.0 mu A 32.768 kHz MEMS-Based Oscillator," Ieee Journal of Solid-State Circuits, vol. 50, pp. 291-302, Jan 2015.
[4] H. G. Barrow, T. L. Naing, R. A. Schneider, T. O. Rocheleau, V. Yeh, Z. Y. Ren, et al., "A Real-Time 32.768-kHz Clock Oscillator Using a 0.0154-mm(2) Micromechanical Resonator Frequency-Setting Element," 2012 Ieee International Frequency Control Symposium (Fcs), 2012
MEMS INTEGRATED DESIGN FOR INERTIAL SENSORS (MIDIS)
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MIDIS process from Teledyne DALSA Semiconductor Inc.
CMOS Compatible with flip chip bonding
Vacuum Encapsulation at 10mTorr
Reproducible Transduction Gap: 1.5um Device Layer Thickness: 30um
World’s most ultra-clean MEMS vacuum cavity demonstrated to date (Leak rate of 4 to 45 molecules/second)
MIDIS FABRICATION PROCESS
3 wafer process. Top: Interconnect WaferMiddle: Membrane WaferBottom: Handle Wafer
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MIDIS FABRICATION PROCESS
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Material: silicon <100>Resonance Frequency:
32.77kHzOverall Dimension:700 µm × 550 µm × 30 µmShuttle Finger Number:
89Transduction Gap Size (1) Fabrication: 1.5 µm(2) Post-Fabrication
silicon fusing: 50 nm DC Polarization Voltage:
1V
LOW POWER WEARABLE APPLICATIONS: TUNING FORK
RESONATOR
imlStop Anchors
Anchors
Driving Electrode
Sensing Electrode
Serpentine Spring
Folded Beams
TUNING FORK RESONATOR
3D Resonator Schematic
1. A pull-in voltage of over 50V applied to stop anchors
2. A contact formed between the welding pads and isolated stop anchors
3. Using a strong current pulse generated through electrical discharge of a capacitor at 100V to melt the connection joints
4. The final locking (permanent fusion bond connection) realized with a deflection of Movable Electrodes of 1.45 µm (50 nm gap between fingers)
SILICON FUSING: TRANSDUCTION GAP REDUCTION TECHNIQUE
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TRANSDUCTION GAP REDUCTION TECHNOLOGY
@5V and 1.5µm gap on one side
iml@1V and 50nm gap on one
side
3D Animation
• k: spring constant of spring system• m: dynamic mass• Q: quality factor• : coupling factor• : DC polarization voltage• N: number of f inger gaps• : dielectric constant of free space• t: thickness of fingers• : transduction gap• : overlapping finger length
RESONATOR ELECTRICAL EQUIVALENT MODEL
iml[5]
[5] C. T.. Nguyen and R. T. Howe, "An integrated CMOS micromechanical resonator high-q oscillator," IEEE Journal of Solid-State Circuits, vol. 34, no. 4, pp. 440–455, Apr. 1999.
TRANSIMPEDANCE AMPLIFIER: BIASING CIRCUIT (GFUS 180NM
PROCESS)High Resistance
High DC Gain of CMOS OPAMP
Low Power Consumption of Oscillator Circuit
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SUSTAINING TRANSIMPEDANCE AMPLIFIER
Telescopic Differential Amplifier(high DC gain and low power
consumption) +
Push-pull Output Stage (low power consumption and
rail to rail output swing)
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OPERATIONAL AMPLIFIER SIMULATION RESULT
High DC Gain
Enough Bandwidth(minus 3dB frequency >>32kHz)
Good Phase Margin(60)
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CMOS OSCILLATOR CIRCUIT (180NM PROCESS)
A Colpitts oscillator configuration utilizinga capacitive voltagedivider as a feedbacksource with an overall loop phase shift of 360 between outputand input port of OPAMP (180 of OPAMP plus 180 of two capacitors )
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OSCILLATOR SIMULATION RESULTS
iml AC analysis(Bode Plot)
OSCILLATOR SIMULATION RESULTS
:=((M1a) +) =((4.63+6+352.7)5)W=1.86mW
Transient Analysis
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ULTIMATE GOAL: SINGLE CHIP IMPLEMENTATION
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MEMS Resonator
CMOS Amplifie
r
THANK YOU!