Single-Pole Single-Throw RF Acoustic Phase Inversion Switch Leveraging Poled Ferroelectrics

This article marks the first demonstration of an integrated single-pole single-throw (SPST) radio frequency (RF) switch using ferroelectric thin films in acoustic wave devices. Polarization control via electric field application allows for selective acoustic phase inversion (API) to cause signal reflection via destructive interference. A specialized implementation of the modified Butterworth-Van Dyke (mBVD) model is presented to describe the<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> and<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> states of the switch. The equivalent circuit can accurately predict ferroelectric stacked crystal filter (SCF) S-parameters under various poling configurations and is also valid for the design of API RF switches. An integrated proof-of-principle device is presented using paraelectric barium strontium titanate, Ba0.5Sr0.5TiO3 (BST), SCFs. The switch has SCF-type response in the<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> state with insertion loss (IL) of under 1.8 dB and a notched<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> state response with an isolation of over 37 dB. The first thickness extensional mode occurs at 1.6 GHz, and the total area is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100\times 200~\mu $ </tex-math></inline-formula>m, including decoupling capacitor (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100\times 100~\mu $ </tex-math></inline-formula>m) and electrical connections. Moreover, total active area consumes less than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$26\times 52~\mu $ </tex-math></inline-formula>m, suggesting future miniaturization. With the increasing inclusion of ferroelectric materials, such as BST and scandium-doped aluminum nitride (ScAlN) in the next-generation acoustic wave devices, this novel switch provides an avenue to eliminate interconnects between RF switches and microwave acoustic filters in RF front ends.