A C/Ku Dual-Band Reconfigurable Baw Filter Using Polarization Tuning in Layered Scaln

This paper reports, for the first time, on the scandium-aluminum nitride (Sc
0.28
Al
0.72
N) bulk acoustic wave (BAW) bandpass C/K
u
dual-band filter with intrinsically reconfigurable center frequencies at 6.81 GHz and 13.29 GHz. The filter is created from electrical coupling of dual-mode BAW resonators with complementary-switchable operation in the first and second thickness-extensional modes (TE
1,2
), defined by spatial poling in a layered Sc
0.28
Al
0.72
N transducer. The transducer is created from alternate stacking of two ~150nm Sc
0.28
Al
0.72
N films with three ~50nm molybdenum electrodes to enable independent control over polarization direction across the thickness, using ferroelectric behavior. Poling Sc
0.28
Al
0.72
N layers in the same or opposite directions, through application of low-frequency pulses, enables complementary excitation of TE
1
and TE
2
BAW modes with similar electromechanical coupling but a frequency ratio nearing two. A filter prototype is presented with operating bands at 6.81 GHz and 13.29 GHz, bandwidths of 382MHz (≈ 5.6%) and 809MHz (≈ 6.1%), and insertion losses of 2.59dB and 2.62dB, respectively. The filter operation band is reconfigured through application of 79V triangular pulses at 20kHz to reverse polarization direction in one of the Sc
0.28
Al
0.72
N layers. On-off isolation of ~7dB and 5dB are measured for C- and K
u
-band filters, when switching between TE
1
and TE
2
operation modes of BAW resonators. The intrinsic reconfiguration of center frequency while sustaining similar fractional bandwidth, enabled by complementary ferroelectric poling in layered transducer, highlights the potential of C/K
u
dual-band scandium-aluminum nitride BAW filters for creation of compact multi-frequency spectral processors in C/K
u
bands.