Micro-machined high-frequency (80 MHz) PZT thick film linear arrays

Abstract

This paper presents the development of a micro-machined high-frequency linear array using PZT piezoelectric thick films. The linear array has 32 elements with an element width of 24 μm and an element length of 4 mm. Array elements were fabricated by deep reactive ion etching of PZT thick films, which were prepared from spin-coating of PZT solgel composite. Detailed fabrication processes, especially PZT thick film etching conditions and a novel transferring-and-etching method, are presented and discussed. Array designs were evaluated by simulation. Experimental measurements show that the array had a center frequency of 80 MHz and a fractional bandwidth (−6 dB) of 60%. An insertion loss of −41 dB and adjacent element crosstalk of −21 dB were found at the center frequency.

New fabrication of high-frequency (100-MHz) ultrasound PZT film kerfless linear array [Correspondence]

“…This difference is mainly due to the ultrasound attenuation in the water at high frequency. After compensation for the attenuation caused by the water and reflection from the quartz, the insertion loss of the array element is determined to be −30 dB at 100 MHz, which is 11 dB better than that reported in [9] and [10]. At around the center frequency, the crosstalk of the adjacent elements was measured to be −15 dB.…”

“…Note that no substrate needs to be etched in this fabrication process. In our previous works [9], [10], there is a crucial but expensive step to etch Si substrate under the working area by XeF 2 . Thus, the new fabrication process is much simpler and cheaper.…”

“…At around the center frequency, the crosstalk of the adjacent elements was measured to be −15 dB. This relatively large cross talk is caused by the lack of isolation between elements, and we believe that it can be reduced by fabricating a kerfed array with a dry-etching process [10]. The performance of the transducer may be further improved by introducing matching layers to increase the bandwidth at the center frequency.…”

“…However, the piezoelectric coefficient and electromechanical coupling coefficient of ZnO materials ( d 33 ~ 7.5 pm/V, k t ~ 0.24) is very low [18], [19], and moreover, the element pitch produced is large (approximately 7λ in water at 100 MHz), making this array unsuitable for medical imaging. In our previous works, with lead zirconate titanate (PZT) thick films prepared by modified sol-gel method, an 80-MHz kerfed array and a 120-MHz kerfless linear array with 32 elements were fabricated using dry etching and photolithography, respectively [9], [10]. Compared with bulk PZT ceramic ( k t > 0.5), the obtained PZT thick film had a lower electromechanical coupling coefficient ( k t = 0.34).…”

High-frequency (>50 MHz) medical ultrasound linear arrays fabricated from micromachined bulk PZT materials

“…The dry-etching mechanism of PZT in chlorinated gas plasmas has been investigated in detail [15], [16], and measures have been proposed to minimize etching damage to the PZT material during the dry-etch process [17]. Using similar dry-etching techniques, researchers have successfully produced array transducers with PZT thick film [18]. …”