A Monolithic Three-Dimensional Ultrasonic Transducer Array for Medical Imaging

Abstract

This paper presents the first monolithic multidirection-looking ultrasonic imager for minimally invasive medical diagnosis. In contrast to the traditional planar ultrasonic imagers that can only view in one direction, this 3-D array is able to view in multiple directions by using seven planar imagers integrated on a hexagonal silicon prism. Each facet on the prism is integrated with a planar 1-or 2-D capacitive-micromachined ultrasonic-transducer imager array for viewing in a specific direction. Each facet is connected by a flexible dielectric membrane, which is monolithically fabricated with the transducers. The dielectric membranes also support the thin-film electrical interconnects between the arrays on different facets. The substrate is folded into a hexagonal prism after completion of the transducer microfabrication process. With this architecture, a one flip-chip bonded or monolithically integrated front-end electronic circuit will be able to manage all the imagers on the 3-D array. The number of bonding wires for a connection to external electronics can therefore be reduced. Imager prisms, which are ranging from 1 to 4 mm in diameter and 2 to 4 mm in length, and positioned to view in seven directions, have been prototyped. Preliminary testing shows that the imager transducers behaved consistently before and after the assembly process. Applications of this 3-D imager array include capsule ultrasound endoscope, intravascular ultrasound, and other internal imaging needs.[ 2006-0269]Index Terms-Acoustic transducers. I. INTRODUCTIONE VOLVED from sonar technology, ultrasound imaging[1]-[3] has been widely used for medical diagnosis since the early 1970s. In this imaging process, high-frequency acoustic waves interact with biological tissue, so that the images of anatomical structures inside the body can be revealed in real time from the reflected ultrasonic pulses. Compared with other medical imaging techniques (X-ray, MRI, CT, etc.) [4], [5], the advantages of ultrasonic imaging include nonradioactivity, real-time acquisition, affordable equipment cost, and feasibility for the miniaturization in minimally invasive applications. In Manuscript

Capacitive micromachined ultrasonic transducer arrays for minimally invasive medical ultrasound

“…The CMUT devices showed consistent device characteristics before and after the prism assembly process [24]. The preliminary ultrasound imaging experiment with this device has been demonstrated [45].…”

“…Wong [44] proposed a curved CMUT array by thinning the silicon substrate from 650 μm to less than 150 μm suitable for mounting on a curved mounting block. Using a different approach, Chen [45] integrated multiple CMUT arrays on a regular-thickness silicon substrate and cut deep trenches between the arrays to form a flexible interconnect between arrays. The multiple arrays, monolithically integrated on a flexible silicon substrate, were then folded into a miniature 3D hexagonal prism capable of panoramic viewing.…”

A microfabricated platform for three-dimensional microsystems

“…For example, a 3-D ultrasonic imaging platform has been demonstrated by using planar, micromachined, capacitive array transducers wrapped around a hexagonal silicone structure to simultaneously image in seven directions as shown inFig. 1.3[35]. Each of the (total) 1240 transducer elements are independently controlled via a dedicated bond pad with no integrated support electronics.…”

“…D ultrasonic transducer array for multidirectional ultrasonic imaging[35].Another application is for next generation deep brain stimulation (DBS) electrodes. Within the past 15 years, DBS has been used clinically to treat many types of neurological conditions.…”