Bragg Reflector Type Shear Mode BAW Transformer Based on c-Axis Zig-Zag ScAlN Multilayer for Rectifying Antenna

Radio frequency (RF) signals can be converted to dc signals using an antenna and diode (which is so called rectenna). In a long-distance wireless transfer, weak RF signals cannot exceed the threshold voltage of the diodes in the rectenna, making RF-DC conversion very inefficient. This letter proposes resonator type GHz piezoelectric transformer based on
c
-axis zig-zag ScAlN films. Solidly mounted resonator (SMR) type transformer using an acoustic Bragg reflector enables a wider bandwidth operation than film/substrate type transformer we reported previously. As a result, zig-zag multilayers which was oriented 180° symmetrically on the acoustic Bragg reflector was fabricated by oblique RF magnetron sputtering. In addition, voltage gain of 2.7 and the fractional bandwidth of 3.2% which was 46 times wider than that of film/substrate type transformer were observed.