Enabling Higher Order Lamb Wave Acoustic Devices With Complementarily Oriented Piezoelectric Thin Films

Abstract

In this work, we present a new paradigm for enabling gigahertz higher-order Lamb wave acoustic devices using complementarily oriented piezoelectric (COP) thin films. Acoustic characteristics are first theoretically explored with COP lithium niobate (LiNbO 3) thin films, showing their excellent frequency scalability, low loss, and high electromechanical coupling (k 2). Acoustic resonators and delay lines are then designed and implemented, targeting efficient excitation of higher-order Lamb waves with record-breaking low loss. The fabricated resonator shows a 2 nd-order symmetric (S2) resonance at 3.05 GHz with a high quality factor (Q) of 657, and a large k 2 of 21.5% and a 6 th-order symmetric (S6) resonance at 9.05 GHz with a high Q of 636 and a k 2 of 3.71%, both among the highest demonstrated for higher-order Lamb wave devices. The delay lines show an average insertion loss (IL) of 7.5 dB and the lowest reported propagation loss of 0.014 dB/µm at 4.4 GHz for S2. Notable acoustic passbands up to 15.1 GHz are identified. Upon further optimizations, the proposed COP platform can lead to gigahertz low-loss wideband acoustic components.

Acoustic Loss in Thin-Film Lithium Niobate: An Experimental Study

“…It would be interesting to study the damping in other orientations and potentially establish the correlation between PL and K 2 (causal or otherwise). Third, higher-order modes in the thickness directions [58], e.g., A1, whose frequencies are determined mainly by the stack thickness, need to be studied in future works. The current bottleneck is to build higher-order mode ADLs in different thickness LiNbO 3 , while still maintaining the same operating frequency.…”

Microwave Acoustic Devices: Recent Advances and Outlook

“…One can directly extract acoustic propagation loss [86] with the identical transducer design but different waveguide lengths [87]. Low-loss and wideband ADLs at GHz have been built using S0 in AlN thin films [82], S0 [87], SH0 [88], A1 [89], and higher-order Lamb waves [90] in LN thin-films, and SH-SAW in solidly mounted LN thin-films [91], [92]. The propagation loss reported for GHz acoustic waves in LN is around 0.005 dB/λ and 0.03 dB/λ [90], and S0 shows the lowest loss.…”

“…Low-loss and wideband ADLs at GHz have been built using S0 in AlN thin films [82], S0 [87], SH0 [88], A1 [89], and higher-order Lamb waves [90] in LN thin-films, and SH-SAW in solidly mounted LN thin-films [91], [92]. The propagation loss reported for GHz acoustic waves in LN is around 0.005 dB/λ and 0.03 dB/λ [90], and S0 shows the lowest loss. Such propagation loss is equivalent to maximum Qs between 6000 and 1000 for GHz thin-film LN devices.…”

“…In one example [Fig. 5(g)-(h)], one can use a bi-layer complimentarily oriented device to double or triple the resonant frequency with no or little loss of k 2 [90]. In the other instance, one uses bimorph of piezoelectric on insulator to scale to third order, beating the pace of k 2 loss in conventional overmode and attaining temperature compensation in the process.…”

On the Finite-Element Analysis of Resonance MEMS Structures based on Acoustic Lamb Waves

“…Values f and Q calculated for resonators with contour modes (according to results from[13][14][15][16][17][18][19][20][21][22][23]. Size of "bubbles" reflects resonator's level of quality f•Q.…”