Biblio

This work reviews various methods which improve the effective coupling coefficient ( k2eff) of non-bulk acoustic wave (BAW) aluminum nitride (AlN) based RF MEMS resonators, mainly focusing on the innovative structural design of the resonators. k2eff is the key parameter for a resonator in communication applications because it measures the achievable fractional bandwidth of the filter constructed. The resonator's configuration, dimension, material stack and the fabrication process will all have impact on its k2eff. In this paper, the authors will review the efforts in improving the k2eff of piezoelectric MEMS resonators from research community in the past 15 years, mainly from the following three approaches: coupling lateral wave with vertical wave, exciting two-dimensional (2-D) lateral wave, as well as coupling 2-D lateral wave with vertical wave. The material will be limited to AlN family, which is proven to be manageable for manufacturing. The authors will also try to make recommendations to the effectiveness of various approaches and the path forward.

This paper reported the polymer coated film bulk acoustic resonators (FBAR) as a sensitive detector in micro chromatography for the detection of trace chemical warfare agents (CWA) simulants. The FBAR sensor was enclosed in a microfluidic channel and then coupled with microfabricated separation column. The subsequent chromatographic analysis successfully demonstrated the detection of parts per billion (ppb) concentrations of chemical warfare agents (CWAs) simulants in a five components gas mixture. This work represented an important step toward the realization of FBAR based handheld micro chromatography for CWA detection in the field.

This work investigates the electromechanical coupling coefficient (kt2) attained by two available piezoelectric acoustic resonator technologies relying on Aluminum Scandium Nitride (ScyAl1-yN) films to operate. In particular, by using a theoretical approach, we extracted the maximum kt2-value attainable, for different scandium-doping concentrations (from 0% to 40%), by Film-Bulk-Acoustic-Resonators (FBARs) and Cross-Sectional-Lamé-Mode Resonators (CLMRs). For the first time, we show how the use of higher scandium doping concentrations can render the kt2 of CLMRs higher (35%) than the one attained by FBARs (28%). Such a unique feature renders CLMRs as ideal candidates to form lithographically defined resonators and filters for next-generation wideband radiofrequency (RF) front-ends.

Emerging next generation wireless communication devices call for high-performance filters that operate at 3-10 GHz frequency range and offer low loss, small form factor, wide bandwidth and steep skirts. Bulk and surface acoustic wave devices have been long used in the RF front-end for filtering applications, however their operation frequencies are mostly below 2.6 GHz band. To scale up the frequency of the filters, the thickness of the piezoelectric material needs to be reduced to sub-micron ranges. One of the challenges of such scaling is maintaining high electromechanical coupling as the film thickness decreases, which in turn, determines the filter bandwidth.Aluminum Nitride (AlN) - popular in today's film bulk acoustic resonators (FBARs) and mostly deposited using sputtering techniques-shows degraded crystal quality and poor electromechanical coupling when the thickness of AlN film is smaller than 1 μm.In this work, we propose using high-quality single-crystalline AlN and Scandium (Sc)-doped AlN epi-layers grown on Si substrates, wherein high crystal quality is maintained for ultra-thin films of only 400 nm thickness. Experimental results verify improved kt2 for 3-10 GHz resonators, with quality factors of the order of 250 and kt2 values of up to 5%based on bulk acoustic wave resonators. The experimental results suggest that single-crystal Sc-AlN is a great material candidate for 5G resonators and filters.

Current BLE transmitters are susceptible to selective jamming due to long dwell times in a channel. To mitigate these attacks, we propose physical-layer security through an ultra-fast bit-level frequency-hopping (FH) scheme by exploiting the frequency agility of bulk acoustic wave resonators (BAW). Here we demonstrate the first integrated bit-level FH transmitter (TX) that hops at 1$μ$s period and uses data-driven random dynamic channel selection to enable secure wireless communications with additional data encryption. This system consists of a time-interleaved BAW-based TX implemented in 65nm CMOS technology with 80MHz coverage in the 2.4GHz ISM band and a measured power consumption of 10.9mW from 1.1V supply.