Low-loss and wide-band acoustic delay lines using Z-cut lithium niobate piezoelectric thin films

A full-duplex radio comprising:

• an antenna to transmit a first radio frequency (RF) signal in a first frequency range and receive a second RF signal at the first frequency range;
• transmit (TX) chain circuitry coupled to the antenna;
• receive (RX) chain circuitry coupled to the antenna, wherein the RX chain circuitry receives the second RF signal and a reflected portion of the first RF signal;
• a directional coupler in the TX chain circuitry, the directional coupler to direct a portion of the first RF signal to the RX chain circuitry;
• and
• a plurality of acoustic delay lines (ADLs) coupled between the TX chain circuitry and the RX chain circuitry to provide a signal delay, wherein the portion of the first RF signal experiences the signal delay and destructively interferes with the reflected portion of the first RF signal, an insertion loss of the plurality of ADLs is no larger than that of free space, and wherein each ADL of the plurality of ADLs comprises:
• a piezoelectric thin film located above a carrier substrate, wherein the piezoelectric thin film is a Z-cut lithium Niobate (LiNbO3) thin film adapted to propagate an acoustic wave;
• a first interdigitated transducer (IDT) disposed on a first end of the piezoelectric thin film, the first IDT to convert a first electromagnetic signal, traveling in a longitudinal direction along a length of the piezoelectric thin film, into the acoustic wave;
• and
• a second IDT disposed on a second end of the piezoelectric thin film with a gap between the second IDT and the first IDT, the second IDT to convert the acoustic wave into a second electromagnetic signal, and the gap to determine a time delay of the acoustic wave before output of the second electromagnetic signal.

A method comprising:

• converting, by a first interdigitated transducer (IDT) disposed on a first end of a piezoelectric thin film, a first electromagnetic signal traveling in a longitudinal direction along a length of the piezoelectric thin film into an acoustic wave, wherein the piezoelectric thin film is a Z-cut lithium niobate (LiNbO3) thin film located above a carrier substrate;
• propagating the acoustic wave in at least one of:
• a first mode excited by an electric field oriented in the longitudinal direction;
• or
• a second mode excited by the electric field oriented at least partially in a thickness direction of the piezoelectric thin film;
• converting, by a second IDT disposed on a second end of the piezoelectric thin film, the acoustic wave into a second electromagnetic signal after a delay determined by a gap between the first IDT and the second IDT, wherein the first IDT and the second IDT are bi-directional transducers;
• and
• outputting the second electromagnetic signal.