Chengliang Sun

Flow-driven triboelectric generator for directly powering a wireless sensor node.

A triboelectric generator (TEG) for scavenging flow-driven mechanical -energy to directly power a wireless sensor node is demonstrated for the first time. The output performances of TEGs with different dimensions are systematically investigated, indicating that a largest output power of about 3.7 mW for one TEG can be achieved under an external load of 3 MΩ.

Methods for improving electromechanical coupling coefficient in two dimensional electric field excited AlN Lamb wave resonators

An AlN piezoelectric Lamb-wave resonator, which is excited by two dimensional electric field, is reported in this paper. Rhombus-shape electrodes are arranged on AlN thin film in a checkered formation. When out-of-phase alternating currents are applied to adjacent checkers, two dimensional acoustic Lamb waves are excited in the piezoelectric layer along orthogonal directions, achieving high electromechanical coupling coefficient, which is comparable to film bulk acoustic resonators. The electromechanical coupling coefficient of the 285.3 MHz resonator presented in this paper is 5.33%, which is the highest among AlN based Lamb-wave resonators reported in literature. Moreover, the spurious signal within a wide frequency range is significantly suppressed to be 90% lower than that of the resonance mode. By varying the electrode dimension and inter-electrode distance, resonators having different resonant frequencies can be fabricated on a single wafer, making single-chip broadband filters, duplexers, and multi...

A High Coupling Coefficient 2.3-GHz AlN Resonator for High Band LTE Filtering Application

This letter reports an aluminium nitride (AlN)based micromechanical resonator with high-effective coupling coefficient (k2eff) and low insertion loss (IL), which are comparable with those of Film Bulk Acoustic Resonators (FBARs). The in-house-fabricated resonator comprises of lithographically patterned top and bottom molybdenum interdigitated electrode fingers and a layer of 1-μm-thick AlN sandwiched in between. Synergetic inter-mode coupling between the constituent thickness mode and the lateral mode can be realized within a wide frequency range, which can be treated as a subcategory of degenerated cross-sectional Lamé mode, enabling the capability of lithographic tuning of resonant frequency yet not compromising k2eff. Measurement results show that the designed 2.3-GHz resonator achieves a k2eff of 6.34% and an IL of 0.26 dB upon direct connection to a network with 50-Ω termination, making it a promising candidate for Wireless Local Area Network (WLAN) and high band Long Term Evolution (LTE) band selection filtering applications.

An Energy Autonomous 400 MHz Active Wireless SAW Temperature Sensor Powered by Vibration Energy Harvesting

An energy autonomous active wireless surface acoustic wave (SAW) temperature sensor system is presented in this paper. The proposed system adopts direct temperature to frequency conversion using a lithium niobate SAW resonator for both temperature sensing and high-Q resonator core in a cross-coupled RF oscillator. This arrangement simplifies the temperature sensor readout circuit design and reduces the overall system power consumption. A power conditioning circuit based on buck-boost converter is utilized to provide high efficiency power extraction from piezoelectric energy harvester (PEH) and dynamic system power control. The SAW resonator is fabricated in-house using a two-step lithography procedure while the RF oscillator as well as the PEH power conditioning circuit are implemented in standard 65-nm and 0.18- μm CMOS processes respectively. The measured RF transmitter output power is -15 dBm with a phase noise of -99.4 dBc/Hz at 1 kHz offset, achieving a figure of merit (FOM) of -217.6 dB. The measured temperature sensing accuracy is ±0.6 °C in -40 °C to 120 °C range. Fully powered by a vibration PEH, the proposed energy autonomous system has a self-startup voltage of 0.7 V and consumes an average power of 61.5 μW.

A Miniaturization Strategy for Harvesting Vibration Energy Utilizing Helmholtz Resonance and Vortex Shedding Effect

In this letter, we report a miniaturization strategy for harvesting a low-frequency random vibration energy with a piezoelectric energy harvesting (EH) system utilizing coupled Helmholtz resonance and vortex shedding effect. This is made possible by transferring the low-frequency vibration energy into a pressurized fluid, which is in turn converted into predefined, pressure-independent high-frequency energy harvested by the device. The vibration-pressurized fluid conversion extends the device sampling frequency band; enables efficient harvesting of broadband low vibration frequencies with small form factor. Proof of concept of the proposed strategy has been demonstrated with an AlN-based MEMS EH, which delivered an output power density of 95.5 mW/cm3 under a constant input airflow at 4.2 lbf/in2 pressure.

Flutter Phenomenon in Flow Driven Energy Harvester–A Unified Theoretical Model for “Stiff” and “Flexible” Materials

Here, we report a stable and predictable aero-elastic motion in the flow-driven energy harvester, which is different from flapping and vortex-induced-vibration (VIV). A unified theoretical frame work that describes the flutter phenomenon observed in both “stiff” and “flexible” materials for flow driven energy harvester was presented in this work. We prove flutter in both types of materials is the results of the coupled effects of torsional and bending modes. Compared to “stiff” materials, which has a flow velocity-independent flutter frequency, flexible material presents a flutter frequency that almost linearly scales with the flow velocity. Specific to “flexible” materials, pre-stress modulates the frequency range in which flutter occurs. It is experimentally observed that a double-clamped “flexible” piezoelectric P(VDF-TrFE) thin belt, when driven into the flutter state, yields a 1,000 times increase in the output voltage compared to that of the non-fluttered state. At a fixed flow velocity, increase in pre-stress level of the P(VDF-TrFE) thin belt up-shifts the flutter frequency. In addition, this work allows the rational design of flexible piezoelectric devices, including flow-driven energy harvester, triboelectric energy harvester, and self-powered wireless flow speed sensor.

GHz spurious mode free AlN lamb wave resonator with high figure of merit using one dimensional phononic crystal tethers

This letter reports a spurious mode free GHz aluminum nitride (AlN) lamb wave resonator (LWR) towards high figure of merit (FOM). One dimensional gourd-shape phononic crystal (PnC) tether with large phononic bandgaps is employed to reduce the acoustic energy dissipation into the substrate. The periodic PnC tethers are based on a 1 μm-thick AlN layer with 0.26 μm-thick Mo layer on top. A clean spectrum over a wide frequency range is obtained from the measurement, which indicates a wide-band suppression of spurious modes. Experimental results demonstrate that the fabricated AlN LWR has an insertion loss of 5.2 dB and a loaded quality factor (Q) of 1893 at 1.02 GHz measured in air. An impressive ratio of the resistance at parallel resonance (Rp) to the resistance at series resonance (Rs) of 49.8 dB is obtained, which is an indication of high FOM for LWR. The high Rp to Rs ratio is one of the most important parameters to design a radio frequency filter with steep roll-off.

Effectiveness of oxide trench array as a passive temperature compensation structure in AlN-on-silicon micromechanical resonators

This Letter presents the effectiveness of an oxide trench array (OTA) as a passive temperature compensation structure for aluminum nitride on silicon (AlN-on-Si) quasi-surface acoustic wave (SAW) micromechanical resonators over a wide temperature range. Two types of devices, namely, those with OTA and their reference counterparts without OTA, are designed, fabricated, and characterized over a wide temperature range of 360 °C. Experimental results show that the resonator with OTA has a first-order temperature coefficient of frequency (TCf1) at room temperature (20 °C) of 6.66 ppm/°C, which is lower than that of the reference device without OTA by 72% in magnitude. A high turnover temperature of 197 °C is achieved. Furthermore, the second-order temperature stability of the device has also improved. OTA is experimentally demonstrated to be an effective structure for passive temperature compensation, hence paving the way for using AlN-on-Si resonators as ultrasonic sensors or timing devices in ruggedized envi...

High-Band AlN Based RF-MEMS Resonator for TSV Integration

This paper reports two types of in-house fabricated aluminium nitride (AlN) based piezoelectric resonators, namely the thickness mode resonator and the Lamb-wave mode resonator, which are capable to be integrated with Through Silicon Via (TSV) technology, forming the basis of advanced filters, duplexers and multiplexers. Both types of the resonators, which are fabricated using a CMOS compatible platform, consist of a layer of 1 µm thick piezoelectric layer and two layers of molybdenum (Mo) electrodes covering the top and the bottom surface of the AlN layer. Resonant frequencies above 2GHz, as well as motional impedance less than 10Ω, are obtained when the fabricated resonators are connected directly to the 50Ω terminations of a network analyzer, making both types of resonators suitable for high-band LTE applications. Furthermore, negligible performance drift was observed for both types of resonators fabricated upon undergoing accelerated thermal cycling test, indicating the superior reliability and long-term stability of the fabricated AlN based MEMS resonators and showing their great potential for communications applications in the automotive industry, where reliability and long-term stability is a key requirement for device performance.

Wafer-Level Vacuum-Packaged Piezoelectric Energy Harvesters Utilizing Two-Step Three-Wafer Bonding

This paper reports on the successful implementation of a wafer-level vacuum-packaged, CMOS-compatible aluminum nitride (AlN) based microelectromechanical system (MEMS) energy harvester (EH). The reported EH features high Q-factor (709.3) and high-g survivability (harmonic at 20g), achieved through wafer-level vacuum-package scheme which reduces the air damping effect and increases the Q-factor, overcoming the tradeoff between vibration amplitude and output power density for EHs operated in air. A power of 468.77µW, bandwidth of 71Hz (3.66%) is delivered by a ~0.119cm3 footprint (1×0.7×0.1705cm3) EH at 20g sinusoidal input vibration, equates to a record power density of ~3.93mW/cm3. This novel packaging and design scheme, which utilizes two-step three-wafer wafer level eutectic bonding, allows size reduction and shock-resilience improvement of future EH. The ability to harvest broad spectrum mechanical vibration energy with small footprint and high-g survivability, makes the reported EH one step closer towards powering the next generation battery-less Smart Tire Pressure Monitoring System (TPMS). Furthermore, the whole integration process, including the wafer-level vacuum-packaging process, is CMOS compatible, making the reported EH viable for mass production with low fabrication cost.