Capacitive-Piezoelectric Transducers for High-<inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> Micromechanical AlN Resonators

Abstract

A capacitive-piezoelectric (also known as, capacitive-piezo) transducer that combines the strengths of capacitive and piezoelectric mechanisms to achieve a combination of electromechanical coupling and Q higher than otherwise attainable by either mechanism separately, has allowed demonstration of a 1.2-GHz contour-mode aluminum nitride (AlN) ring resonator with Q > 3000 on par with the highest measured d 31 -transduced AlN-only piezoelectric resonators past 1 GHz, and a 50-MHz disk array with an even higher Q > 12 000. Here, the key innovation is to separate the piezoelectric resonator from its metal electrodes by tiny gaps to eliminate metal material and metal-to-piezoelectric interface losses thought to limit thin-film piezoelectric resonator Q, while also maintaining high electric field strength to preserve a strong piezoelectric effect. While Q increases, electromechanical coupling decreases, but the k 2 eff · Q product can still increase overall. More importantly, use of the capacitive-piezo transducer allows a designer to trade electromechanical coupling for Q, providing a very useful method to tailor Q and coupling for narrowband radio frequency (RF) channel-selecting filters for which Q trumps coupling. This capacitive-piezo transducer concept does not require dc-bias voltages and allows for much thicker electrodes that reduce series resistance without mass loading the resonant structure. The latter is especially important as resonators and their supports continue to scale toward even higher frequencies.[2013-0395]

Reliable Accessibility of Intermediate Polarization States in Textured Ferroelectric Al0.66Sc0.34N Thin Film

“…[16] Due to its superior thermal stability and high mechanical quality factor, the wurtzite AlN or Al 1-x Sc x N has been investigated as a piezoelectric and optoelectronic material. [17,18] Recently, Fitchner et al demonstrated ferroelectricity in Al 1-x Sc x N under a viable operation scheme with a P r value of 100 μC cm −2 and an E c value of 2-5 MV cm −1 . [19] Extensive research revealed that the Sc in Al 1-x Sc x N can cause the flattening of the ionic potential toward the metastable hexagonal structure with a decrease in the aspect ratio of the lattice constant, i.e., the c/a value.…”

Weakly Coupled Piezoelectric MEMS Resonators for Aerosol Sensing

“…Piezoelectric MEMS (Micro-Electro-Mechanical Systems) resonators have shown great potential for the development of high resolution and low power physical, chemical, and biological sensors [1][2][3]. Today, AlN (Aluminium Nitride) is the commonly employed material in RF (Radio Frequency) devices based on piezoelectric thin films, e.g., filters, duplexers, and other front-end modules [4,5]. Piezoelectric actuation and sensing of bulk acoustic modes of vibration in AlN-on-Si (Aluminium Nitride-on-Silicon) plate structures are made possible due to the high electromechanical coupling and high-quality factors achievable in these devices.…”

Effect of Sr and La co-doping on structural and electrical properties of RF sputtered PZT thin films

“…They possess higher electromechanical coupling coefficients, piezoelectric coefficients and dielectric constants than the other widely used materials, ZnO and AlN [1][2][3]. The composition, near morphotropic phase boundary (MPB), is the best choice for various MEMS such as accelerometer [4], hydrophone [5], acoustic imaging [6], RF MEMS [7] etc. Improvements in piezoelectric and ferroelectric properties of PZT are reported to further enhance the performance of MEMS by adding dopants in PZT thin films [8][9][10][11][12], particularly for acoustic devices, where higher piezoelectric charge coefficient and moderate dielectric constant are essential for getting better receiving sensitivity.…”