Electrically switchable multi-frequency piezoelectric micromachined ultrasonic transducer (pMUT)

Working frequency is a key parameter for ultrasonic applications. For the ultrasonic diagnostic imaging, the frequency determines the imaging resolution, i.e. higher frequency results in better resolution. However, higher frequency also leads to smaller detecting range due to the higher attenuation. Users have to carefully choose the frequency between resolution and detecting range for different situations. Conventionally the piezoelectric micromachined ultrasonic transducer (pMUT) works at one frequency (the fundamental mode), and such transducer needs to be physically changed to meet the different frequency requirements. In this paper, an innovative electrically frequency switchable pMUT is proposed. The switchable pMUT, however, can switch among three frequencies, i.e. 2.01 MHz, 3.19 MHz, and 5.84 MHz, by activating different top electrode sets. The displacement sensitivity is achieved as 42.5 nm/V, 45 nm/V and 28 nm/V for each frequency. Such sensitivities are better than or comparable to the reference sensitivity of a conventional pMUT. The electrically frequency switching feature is realized by the same device for the first time.