Micromachining techniques in developing high frequency piezoelectric composite ultrasound array transducers

Abstract

The Series of micromachining techniques have systematically been developed in this paper for fabrication of high frequency piezoelectric composite ultrasonic array transducers. According to the specific requirements in different stages of production of array transducers, different micromachining techniques are employed in fabricating piezoelectric active material, attaching backing material to the transducer, and making an electric interconnection board for array elements electric connection. To prove the feasibility, a PMN-PT/epoxy 1-3 composite array transducer, which includes 2-dimensional array elements and annular array elements, was designed and produced, which has 64 2-D elements and 5 ring elements with the frequency of 60 MHz. The experimental results of some key parameters proved that the developed processing methods can be applied in producing high frequency ultrasound array transducers. I. INTRODUCTIONThe need for higher image resolution in medical imaging for specific applications has attracted many researchers and companies to develop high frequency ultrasound transducers above 20 MHz, especially high frequency ultrasonic array transducers. However, high frequency array system development faces indeed several challenges, such as limitations in fabrication technology and equipment, and a lack of high quality high-frequency materials and electronics. From array transducer manufacturing perspective, these challenges are mainly related to the small dimensions, narrow pitches, and huge number of the array elements, which result in some major problems in developing all kinds high frequency ultrasonic arrays, such as, 1) what kind piezoelectric material should be selected, 2) how to fabricate these piezoelectric elements that are very small, and 3) how to construct an electric interconnection system for array elements with narrow pitches.Piezoelectric composite materials have many attractive characteristics for ultrasonic transducer applications, especially for high frequency array transducers. However, fabrication of composite materials for high frequency arrays requires that the pillars/kerfs have very small dimensions. For example, at 60 MHz, the pillar size should be less than 10 µm and a kerf width of ~ 5 µm. The traditional dicing-and-filling method [1, 2] and other precise machining methods, such as laser ablation [3], cannot accomplish the task.For high-frequency arrays, electrical connection to each element is preferentially made on the back side of the transducer, which simplifies the top surface topology. Current

The fabrication and integration of a 15 MHz array within a biopsy needle

“…Composite piezoelectric substrates are generally favoured as the active material for ultrasound imaging transducers owing to their higher electromechanical coupling and lower acoustic impedance than bulk material [10] [11]. For the 15 MHz array, the 1-3 composite development used the "dice and fill" method for creating the piezoelectric pillars.…”

The fabrication and integration of a 15 MHz array within a biopsy needle

“…Composite piezoelectric substrates are generally favoured as the active material for ultrasound imaging transducers owing to their higher electromechanical coupling and lower acoustic impedance than bulk material [10] [11]. For the 15 MHz array, the 1-3 composite development used the "dice and fill" method for creating the piezoelectric pillars.…”

Tunable high acoustic impedance alumina epoxy composite matching for high frequency ultrasound transducer

“…Ultrasound biomedical imaging contains three components including an ultrasound transducer, a computation system and a transmission/receiving electronic circuit. In recent decades, the ultrasound transducers have been mainly investigated for accomplishing higher performance including high sensitivity and image resolution, and among them, to increase the operation frequency of the ultrasound transducer to the regime of 20 to 200 MHz [6][7][8][9][10][11][12][13][14][15] is a general trend in either clinical application and biomedical research. Other than enhancing C.M.…”