Packageless SAW Devices with Isolated Layer Acoustic Waves (ILAW) and Waveguiding Layer Acoustic Waves (WLAW)

P3I-2 Cavityless Wafer Level Packaging of SAW Devices

“…After patterning the Au electrode layer, the series resonance frequency was about 0.975 GHz and it decreased to about 0.8 GHz with SiO 2 layer deposited and annealed. The deposition of Al 2 O 3 coating with response monitoring [8] resulted in increase of this frequency to about 0.94 GHz as shown in figure 4. The application of the absorbing materials on the upper surface (in these experiments we have used a drop of photoresist) mainly impacts the modes that are related to this surface, while the useful part of the response becomes cleaner.…”

“…In [8] two approaches based on deposition of thin film isolating layers were described, one of which utilizes a Waveguiding Layer Acoustic Wave (WLAW) that is based on wave propagation in a relatively low acoustic velocity layer confined from one side by a substrate (for example LiTaO 3 or LiNbO 3 ) and from the other side by a deposited thin film layer with high acoustic velocity (Al 2 O 3 , AlN etc) thus being more or less analogue to dielectric waveguides or optical fibers. The second approach utilizes an Isolated Layer Acoustic Wave (ILAW) and uses Bragg mirror-like isolation principles more or less analogous to phononic crystal principles.…”

Monitored vacuum deposition of dielectric coatings over surface acoustic wave devices

“…The amplitude of the acoustic displacement on the top surface is greatly reduced by a high impedance layer with a thickness near a quarter of the shear acoustic wave wavelength in the material. For further reduction of this amplitude and consequently for better acoustical isolation additional layers with different acoustical impedance can be added to form a multiple layer acoustical mirror [2]. An example of the monitored deposition of a relatively soft and dense Yb 2 O 3 over a 1-micron SiO 2 layer on top of a resonator is shown in Fig.…”

“…A layer of silicon dioxide (SiO 2 ) has a lower shear acoustic wave velocity than some common piezoelectric substrates such as LiTaO 3 and LiNbO 3 and thus can serve as a waveguiding layer for a wave excited in piezoelectric media. To ensure the formation of top isolating layer for a WLAW several materials with high acoustic velocity can be used and alumina (Al 2 O 3 ) is one of them [2]. A 1-micron thick SiO 2 layer was pre-deposited by PECVD over a synchronous resonator with 20 electrodes in the IDT and in each grating (80 nm gold on 5 nm Ti; with metallization ratio 60%) on 36 Y-X cut of LiTaO 3 with electrode pitch of 2 microns (IDT period e 4 microns).…”

“…Indeed constitutive components of standard sealed boxes can withstand a temperature up to about 250 C. Thus, new packaging approaches need to be found. Coatings may serve for formation of acoustically isolated waves and thus they may replace additional packages for hermetically sealing the sensitive surface from the aggressive environment [2]; on the contrary, sensitivity-enhancing coatings work in chemical, biological and physicals sensors [3]. In some cases, very thin dielectric coatings can be used for monitored trimming of the working frequency of a SAW device [4].…”