Search

This paper introduces a novel nondestructive wafer scale thin film thickness measurement method by detecting the reflected picosecond ultrasonic wave transmitting between different interfacial layers. Unlike other traditional approaches used for thickness inspection, this method is highly efficient in wafer scale, and even works for opaque material. As a demonstration, we took scandium doped aluminum nitride (AlScN) thin film and related piezoelectric stacking layers (e.g. Molybedenum/AlScN/Molybdenum) as the case study to explain the advantages of this approach. In our experiments, a laser with a wavelength of 515 nm was used to first measure the thickness of (1) a single Molybdenum (Mo) electrode layer in the range of 100–300 nm, and (2) a single AlScN piezoelectric layer in the range of 600–1000 nm. Then, (3) the combined stacking layers were measured. Finally, (4) the thickness of a standard piezoelectric composite structure (Mo/AlScN/Mo) was characterized based on the conclusions and derivation extracted from the aforementioned sets of experiments. This type of standard piezoelectric composite has been widely adopted in a variety of Micro-electromechanical systems (MEMS) devices such as the Piezoelectric Micromachined Ultrasonic Transducer (PMUT), the Film Bulk Acoustic Resonator (FBAR), the Surface Acoustic Wave (SAW) and more. A comparison between measurement data from both in-line and off-line (using Scanning Electron Microscope) methods was conducted. The result from such in situ 8-inch wafer scale measurements was in a good agreement with the SEM data. [ABSTRACT FROM AUTHOR]

This letter reports the first implementation of a new class of laterally coupled alternating thickness (LCAT) mode resonators operating above 2 GHz, realised by replacing the bottom interdigitated electrodes of the conventional LCAT mode resonator with an electrically floating plate. Besides saving one mask process and relaxing the tight resolution and alignment requirements for defining small features, the flat unpatterned bottom electrode metal is also more favorable for the growth of highly oriented piezoelectric thin film, which results in an improved resonator quality factor ( $Q$ ). A group of 8% scandium doped aluminium nitride-based modified LCAT mode resonators with frequency difference over 100 MHz by varying the top interdigitated electrode pitches are fabricated achieving coupling coefficient ( {k}_{\textit {eff}}^{\textit {2}}) of up to 6.45% and figure of merit of up to 54, making them promising candidates for integrated band selection filter banks. [ABSTRACT FROM AUTHOR]

In this paper we demonstrate a novel acoustic wave pressure sensor, based on an aluminum nitride (AlN) piezoelectric thin film. It contains an integrated vacuum cavity, which is micro-fabricated using a cavity silicon-on-insulator (SOI) wafer. This sensor can directly measure the absolute pressure without the help of an external package, and the vacuum cavity gives the sensor a very accurate reference pressure. Meanwhile, the presented pressure sensor is superior to previously reported acoustic wave pressure sensors in terms of the temperature drift. With the carefully designed dual temperature compensation structure, a very low temperature coefficient of frequency (TCF) is achieved. Experimental results show the sensor can measure the absolute pressure in the range of 0 to 0.4 MPa, while the temperature range is from 20 °C to 220 °C with a TCF of −14.4 ppm/°C. Such a TCF is only about half of that of previously reported works. [ABSTRACT FROM AUTHOR]

This paper presents a piezoelectric layered structure composed of Mn-doped PIN-PMN-PT thin film combined with diamond for high electromechanical coupling factor (K 2) and improved quality factor (Q) SAW devices. Comprehensive theoretical analysis of SAW resonator on the proposed structure is performed to calculate its SAW characteristics including K 2, V (phase velocity) and Q. The influence of the Euler angle, Mn-doped PIN-PMN-PT layer's thickness and the electrode's thickness as well as electrode's materials on the SAW properties are investigated. It is shown that the maximum electromechanical coupling factor of the proposed structure has been theoretically shown up to be 79.5 % for the main mode called shear-horizontal (SH)-type SAW. The FOM(K 2· Q) is enhanced to 868.5, which is more than two times larger than that of the previously reported work using pure PIN-PMN-PT. Such enhancement of FOM makes such structure has great potential application in ultra-wide band and high Q SAW filters operating at 1GHz–3GHz. [Display omitted] • A new layered structure composed of Mn-doped PIN-PMN-PT thin film combined with diamond for high performance SAW devices. • Theoretical analysis of SAW resonator on the proposed structure is performed to calculate its SAW characteristics. • Both velocity and electromechanical coupling factor are calculated for different Euler angles, film thickness and electrode thickness. • The proposed layered structure is proved to have large electromechanical factor and dramatically enhanced quality factor. [ABSTRACT FROM AUTHOR]