Novel Phased Array Piezoelectric Micromachined Ultrasound Transducers (pMUTs) for Medical Imaging

Abstract

Two kinds of 128 channels pMUT-based phased array ultrasound transducers are described in this paper, one with a high frequency of around 6 MHz and another with a low frequency of around 1.5 MHz. The active area of the transducer is around 25 mm long and 10 mm wide. There are in total 6270 pMUT elements in the reported arrays. For the transducer with a center frequency of 6 MHz, each pMUT has a membrane diameter of 85 µm and the pitch between every two channels is 200 µm. The transducer benefits from a high transmission and receive sensitivity of 44 kPa / V / Channel @ 3 cm and 204 mV / MPa, respectively. For the transducer with a center frequency of 1.5 MHz, each pMUT has a membrane diameter of 160 µm and the pitch between every two elements is 214 µm. The proposed transducer obtained a transmit and receive sensitivity of 430 Pa / V / Channel @ 3 cm and 190 mV / MPa, respectively. The transducer has a -3dB and -6dB bandwidth of 118% and 184%, respectively. The bandwidth is higher than any previously reported transducer in any technology, such as bulk-PZT, pMUT, or capacitive MUT (cMUT). The functionality of the transducer arrays is confirmed by obtaining B-mode images in water medium.

Polyimide-On-Silicon 2D Piezoelectric Micromachined Ultrasound Transducer (PMUT) Array

“…However, with impedance matching, it is possible to generate even higher pressures. Still, the response can be considered to be on the lower side [ 14 ]. The lower response can be explained as follows: (1) It is the pressure generated by a single PMUT element and hence a very small vibrating aperture, resulting in a lower response.…”

“…For medical imaging applications using ultrasound transducer arrays, resonance frequencies of several MHz and a fractional bandwidth from 40 to 80% are used [ 38 ]. Sadeghpour et al tabulated the specifications of state-of-the-art PMUT arrays designed for imaging, which show pressure levels of about a few kPa to perform imaging in several mm ranges [ 14 ]. To use our wide-bandwidth PMUT array for medical imaging, focused ultrasound, and impedance matching are required to improve the transmit response.…”

“…By using polyimide, vibrations generated by the PZT layer are damped, which helps in widening the bandwidth. Additionally, the mass of the medium can effectively dampen the membrane vibration (thus improving fractional bandwidth) when the lateral dimension of the membrane is smaller than the wavelength; thus, 100 µm was chosen as the diameter of the PMUT membrane [ 14 ].…”

“…This can result in lower bandwidth and hinder their applicability in applications requiring high bandwidth, such as medical imaging. We have previously shown that using polyimide in the PMUT membrane improves the bandwidth and tends to widen it [ 14 , 15 ]. Likewise, this paper uses polyimide to introduce damping and improve the bandwidth.…”

PMUT and CMUT Devices for Biomedical Applications: A Review

“…The experimental setup used for the imaging tests includes in vitro sector scan of a portion of the phantom and in vivo linear scan of a human carotid artery. In [75], high frequency (6 MHz) and low frequency (1.5 MHz) PMUT arrays with 128 channels for medical imaging applications are proposed. In particular, the proposed high frequency array has a transmission sensitivity of 45 kPa/V at 3-cm distance and a receive sensitivity of 204 mV/MPa.…”