Gabriel Vidal-Alvarez

This paper reports on the design, fabrication, and characterization of $S_0$ mode X-cut Lithium Niobate Laterally Vibrating Resonators (LVRs) operating between 100 MHz and 1 GHz. In the first section of this work, analytical and numerical models are implemented to investigate the impact of topology and geometrical features on the Electromechanical Coupling ( $k_t^2$ ) and Quality Factor ( $Q_s$ ) of this class of devices. The models are used to define the design of experiments aimed at characterizing the resonator performance. The resonators are fabricated and tested in atmospheric, vacuum, and cryogenic ( $T$ = 10 K) conditions to assess their performance and identify the main sources of discrepancies in $k_t^2$ and $Q_s$ with respect to the analytical and numerical models. Under vacuum quality factors exceeding a few thousands are recorded across the investigated spectrum, with measured $k_t^2$ as high as 28.9 $\%$ . At 100 MHz, measured $Q_s$ and $k_t^2$ of 8,279 and 28.5 $\%$ , respectively, combine into a record-breaking Figure of Merit ( $FOM$ ) of 2,688, while cryogenic testing highlighted $Q_s$ as high as 26,511. In the last section, by analyzing the differences in $k_t^2$ and $Q_s$ between experiments and models, best design approaches to maximize the $FOM$ and minimize spurious modes responses are reported, with a focus on the 100 to 550 MHz range.2022-0081

This paper investigates the impact of resonant frequency (fₛ) mismatch on the quality factor (Qas) of large arrays of X-cut Lithium Niobate (LN) Laterally Vibrating Resonators (LVRs) operating around 50 MHz and 400 MHz. The statistical distributions of key device parameters, including resonant frequency, quality factor (Qₛ), electromechanical coupling (kt²), and static capacitance (C₀), are collected from replicas of identical resonators. A Monte Carlo approach is later implemented to simulate the impact of statistical variability on the quality factor of arrays of resonators. By including the effect of interconnects series resistance on the arrays, an excellent agreement between experimental and simulated Qas is achieved, demonstrating that frequency mismatch is the major mechanism of quality factor degradation in arrays of parallel resonators. The experimental validation of the model confirms that it can be used as a predictive tool to establish the frequency tolerance requirements in order to attain high Qas in arrays. [2019-0210]

This paper reports on the modeling, design, fabrication, and testing of high-performance X-cut Lithium Niobate (LN) Laterally Vibrating Resonators (LVR) operating around 50 MHz. The objective of this work is to exploit the high Figure of Merit (FoM) –product of quality factor at series resonance (Qs) and electromechanical coupling (kt2)– to provide for large passive voltage amplification in the front-end of emerging radio frequency (RF) applications –i.e., Wake-Up Radio Receivers (WuRx). Finite Element Analysis (FEA) is performed to optimize devices’ geometry and ensure simultaneous high Qs and kt2. Resonators exhibiting Qs > 5,300 and kt2 > 27% are demonstrated, with FoM > 1,650 –the highest recorded for resonators in the MHz range to the authors’ knowledge. Finally, passive voltage gains between 35 V/V and 57 V/V are showcased for capacitive loads ranging from 400 fF to 1 pF.

We present the conceptual approach, theoretical simulations, and experimental results of a novel device based on acoustic delay lines with different pitch between transmitter and receiver (dubbed pitch-asymmetric delay lines) for passive voltage amplification of radio frequency signals. The theoretical results show that it is possible to attain very high voltage gains in this new class of asymmetrical delay lines. The experimental results validate the ability to produce voltage gain, but significantly below theoretical predictions. We attribute this discrepancy to the high admittance at the nulls of the experimental response of the interdigital transducers. We investigate the maximum admittance at the nulls compatible with obtaining high voltage gains (>20 dB) and find that it is two order of magnitude lower than that achieved in this work. [2019-0209]

This work demonstrates a low-power wake-up receiver utilizing a MEMS resonant device followed by CMOS demodulator and rectifying trigger circuits. The MEMS device is a Lamb wave piezoelectric-based acoustic resonator utilizing a thin film of lithium niobate (LN) which possess the largest reported electromechanical coupling factors (kₜ²). This parameter, in conjunction with the high Q, is of paramount importance in providing for passive voltage amplification and filtering of the input signal. The CMOS demodulator is a 9-stage differential cross-coupled passive rectifier circuit designed with a differential output. It demodulates the signal from the MEMS resonator with the same gain as that could be achieved by a single-ended rectifier, but with half the charging time for double the single-ended bit-rate. The rectifier's output is AC-coupled and fed to a two-stage differential voltage amplifier. Finally, an active latch rectifier is used to trigger a wake-up signal. The wake-up receiver is tested with an on-off keying modulated signal with carrier frequency around 400 MHz achieving a bit rate up to 100 kbps. This newly proposed system exhibits a sensitivity of -47 dBm at 3 kbps while consuming a total power of 18 nW.

This paper reports a practical demonstration of a proposed resonant microelectromechanical receiver for low power wake-up receiver (WuRx) applications. The proposed system is made of three main components: a piezoelectric based acoustic resonator, an electrostatically-driven MEMS resonant demodulator, and a CMOS baseband trigger circuit. The filtering, amplification, and demodulation of the incoming signal are performed through the piezoelectric resonator and the resonant demodulator, ensuring zero power consumption for both the radio frequency (RF) and mixing stages. The only power consumption occurs at baseband by operating the CMOS circuit in deep subthreshold. This system utilizes a lithium niobate piezoelectric resonator possessing a figure of merit of around 650 and achieving voltage gain of 28 dB. A resonant demodulator fabricated in the Epi-Seal MEMS process is utilized to attain a conversion efficiency of 13.8 nA/V². In the trigger circuit, an amplifier with transimpedance >200 MΩ is utilized to sense the output current from the demodulator. An intermediate buffer and a multiple stage passive latch rectifier are utilized to generate the wake-up signal through a Schmitt trigger. The demonstrated system achieves -40.2 dBm sensitivity for a 44 kHz amplitude-modulated 50 MHz RF signal while consuming 38.75 nW. This architecture is a promising step toward a WuRx capable of achieving higher interference rejection, high sensitivity, and nW range power consumption at a high data rate. [2018-0261]

This letter reports on the design, fabrication, and testing of an X-cut lithium niobate laterally vibrating resonator operating around 50 MHz and exhibiting a record figure of merit-FoM = product of electromechanical coupling (kt²) and quality factor at a resonance (Qs)- of 1560. For practical applications, the individual resonator is arranged in a large array so as to achieve a static capacitance around 1 pF, while still preserving a high FoM of 570. Modeling of anchor losses through finite element analysis is used to guide the design of these resonators, which simultaneously exhibit high electromechanical coupling (kt² > 30%) and high quality factor (Qs > 5000) in vacuum.l [2018-0097]