Anming Gao

Harnessing Mode Conversion for Spurious Mode Suppression in AlN Laterally Vibrating Resonators

This paper reports on a spurious mode suppression technique for S0 mode aluminum nitride (AlN) laterally vibrating resonators. The technique utilizes a notch in the resonator body to convert spurious asymmetrical (A0) modes into the intended S0 mode vibration. Finite-element analyses were employed to theoretically investigate the mode conversion from A0 mode to S0 mode, and identify the optimal notch configuration. The technique has been experimentally validated to simultaneously eradicate the A0 spurious mode and enhance the S0 mode electromechanical coupling (kt2) for the monolithically integrated resonators over a wide frequency range (100~600 MHz). It is a crucial technology development, because the spurious modes are a major bottleneck obstructing the deployment of single-chip multi-frequency AlN resonators as a commercially viable solution for radio frequency front-end filtering.

Piezoelectric RF resonant voltage amplifiers for IoT applications

This paper reports the design and development of aluminum nitride (AlN) piezoelectric RF resonant voltage amplifiers for Internet of Things (IoT) applications. These devices can provide passive and highly frequency selective voltage gain to RF backends with a capacitive input to drastically enhance sensitivity and to reduce power consumption of the transceiver. Both analytical and finite element models (FEM) have been utilized to identify the optimal designs. Consequently, an AlN voltage amplifier with an open circuit gain of 7.27 and a fractional bandwidth (FBW) of 0.11 % has been demonstrated. This work provides a material-agnostic framework for analytically optimizing piezoelectric voltage amplifiers.

Eradication of asymmetric spurious modes in AlN MEMS resonators using mode conversion

This papers reports on a spurious mode suppression technique that converts the asymmetrical (A0) mode to the intended symmetrical (S0) mode vibrations by installing a notch in aluminum nitride (AlN) laterally vibrating resonators. The technique has been experimentally validated to simultaneously eradicate the A0 spurious mode and enhance the S0 mode electromechanical coupling (kt2) for the monolithically integrated resonators over a wide frequency range (100~600 MHz). The method described herein has overcome a major bottleneck obstructing the deployment of single-chip multi-frequency AlN resonators as a commercially viable solution for RF front-end filtering. It is also the first demonstration of complete A0 mode suppression in lamb-wave resonators with enhancement of kt2.

Deciphering intermodulation in AlN laterally vibrating resonators

This paper reports an analytical and quantitative method that, for the first time, precisely predicts the third-order intermodulation distortion (IMD3) in AlN laterally vibrating resonators (LVRs). The simulated IMD3 reaches an excellent agreement with the measurements for a fabricated 453.4 MHz AlN LVR. This method provides an unprecedented framework for enhancing the power handling and reducing the nonlinearity of AlN LVRs to meet the requirements of RF front-end filtering.

Parametric excitation in geometrically optimized AlN contour mode resonators

This work reports the first observation of parametric excitation in geometrically optimized Aluminum Nitride (AlN) contour mode resonators (CMRs). The concept of parametric excited AlN CMRs harnesses the fact that the resonant frequencies of extensional mode vibrations along transverse and longitudinal directions can both be determined by resonator dimensions. Therefore, by geometrically optimizing lateral dimensions, dual resonances can be engineered at f0 and 2f0 respectively for inputting parametric excitation and outputting fundamental oscillations. In operation, the parametric excitation amplifies an orthogonal oscillation at f0 by periodically modulating the stiffness constants of AlN piezoelectric thin film via straining the structure. The experimental results have shown quality factor (Q) enhancement from 50 ot 2708 for a parametrically excited resonance. Upon further scaling and optimizations, it is anticipated that this type of devices will lead to the development of GHz low noise frequency sources and nano-electro-mechanical logic.

A 150 MHz voltage controlled oscillator using lithium niobate RF-MEMS resonator

This paper presents the first radio frequency (RF) voltage controlled MEMS oscillator (VCMO) using a high Q Lithium Niobate (LiNbO3) micromechanical resonator. The resonator has a quality factor of 650 in air with a motional impedance of 262 Ω. The oscillators measured phase noise is −84.4 dBc/Hz and −146 dBc/Hz at 1 kHz and 1 MHz offsets respectively from a 149.13 MHz carrier with an output power of −8.6 dBm. The oscillator consumes less than 1 mA with a tuning range of 0.42 MHz. Such VCMOs are envisioned to enable low power, and low phase noise RF signal synthesis for Internet of Things applications.

High speed mid-infrared detectors based on MEMS resonators and spectrally selective metamaterials

This work reports the development of uncooled spectrally selective mid-infrared (IR) detectors based on the seamless integration of metamaterial (MM) structures with microelec-tromechanical AlN resonators. The complete coverage of the resonator surface with MM results in high mid-IR absorption (>80%) at an optimized spectral wavelength of 9.6 μm with a Full Width at Half Maximum (FWHM) of 1.02 μm without compromising resonator acoustic performance. A novel detector readout has also been implemented to linearly convert incident IR power to a DC voltage and to demonstrate the potential for expanding our single element detector to a focal plane array imager. The measurements of the detectors have shown a high temperature coefficient of impedance (TCZ) of 9.6% a fast thermal response time of 400 μs, and a responsivity of 33 V/W.

Simultaneous wireless power transfer and communication to chip-scale devices

This paper reports a 2.48 GHz tri-coil and rectifier design implemented in a system that demonstrates simultaneous wireless power transfer and communication to a 0.1 mm by 0.1 mm coil. The tri-coil link and rectifier successfully rectified and demodulated a 20 dBm amplitude-shift keyed (ASK) RF signal modulated at a rate of 1 Mb/s. Additionally, a 5.7 GHz tri-coil link was fabricated to validate the frequency scalability of this technology platform for other unlicensed bands and was measured in a customized experimental testbed to account for the effects of lateral misalignment between coils. The 5.7 GHz tri-coil design had a measured peak RF power transfer efficiency of −29 dB with a vertical separation of 1 mm, which is ten times the load coil diameter.

A 3.5 GHz AlN S1 lamb mode resonator

This paper presents a 3.5 GHz aluminum nitride (AlN) microelectromechanical system (MEMS) resonator. The high frequency resonance is attained by exploiting the high phase velocity S1 Lamb mode in an AlN thin film. Finite element analyses (FEA) are employed to show a high phase velocity larger than 50000 m/s and a large electromechanical coupling of 3.6% for S1 when h<inf>AlN</inf>=0.1λ. As predicted by the simulation, the fabricated resonator demonstrates a high frequency resonance at 3.5 GHz and a large electromechanical coupling (k<inf>t</inf>²) of 3.59%. Among the demonstrated S1 mode deviecs, this work has achieved the highest product of merit, f • k<inf>t</inf>² • Q, of 69.1.

A 3.5 GHz hybrid wideband RF filter using AlN S1 lamb mode resonator

High frequency bands such as LTE band 42 and band 43 require resonators and filters that can operate at frequencies higher than 3 GHz. However, existing lithium niobate fundamental symmetric (S0) lamb mode resonators and surface acoustic wave (SAW) resonators have operating frequency limitations (<2 GHz) due to their low phase velocities. High frequency AlN film bulk acoustic resonators (FBARs) suffer from the deteriorated crystallization and power handling issues due to the thin AlN film. High frequency AlN S0 lamb mode resonators encounter lithography and power handling challenges because of their narrow pitch. The first-order symmetric (S1) lamb mode in AlN shows a very high phase velocity and is promising in building high frequency resonators and filters. This work thoroughly investigates the S1 lamb mode resonator and extends its application to high frequency RF filters with a hybrid topology.