Search

An IC flip-chip bonded to a 16 * 16-element capacitive micromachined ultrasonic transducer (CMUT) array is described for 3-D ultrasonic imaging. The IC flip-chip bonded to a CMUT array has shown that the IC can produce steered and focused ultrasound beams and the 2-D and 3-D images of a wire phantom and 2-D orthogonal cross-sectional images of a latex heart phantom are presented.

In real-time ultrasonic 3-D imaging, in addition to difficulties in fabricating and interconnecting 2-D transducer arrays with hundreds of elements, there are also challenges in acquiring and processing data from a large number of ultrasound channels. The coarray (spatial convolution of the transmit and receive arrays) can be used to find efficient array designs that capture all of the spatial frequency content (a transmit--receive element combination corresponds to a spatial frequency) with a reduced number of active channels and firing events. Eliminating the redundancies in the transmit--receive element combinations and firing events reduces the overall system complexity and improves the frame rate. Here we explore four reduced redundancy 2-D array configurations for miniature 3-D ultrasonic imaging systems. Our approach is based on 1) coarray design with reduced redundancy using different subsets of linear arrays constituting the 2-D transducer array, and 2) 3-D scanning using fan-beams (narrow in one dimension and broad in the other dimension) generated by the transmit linear arrays. We form the overall array response through coherent summation of the individual responses of each transmit--receive array pairs. We present theoretical and simulated point spread functions of the array configurations along with quantitative comparison in terms of the front-end complexity and image quality. Index Terms--Beamforming, biomedical ultrasonics, image reconstruction, phased arrays, ultrasonic imaging.

A commercial ultrasound imaging system is used for characterizing the capacitive micromachined ultrasonic transducer microlinear (CMUT ML) array integrated with the custom front-end electronics and also for evaluating the imaging results for the array assembly. The fabricated CMUT technology is used for designing even higher frequency arrays with other array geometries for catheter-based intracardiac and intravascular applications.

A multifunctional intracardiac imaging and electrophysiology (EP) mapping catheter is introduced for guiding diagnostic and therapeutic intracardiac EP procedures. Results suggest the excellent performance of the catheter in high frame rate imaging, color flow imaging and strain rate imaging of atrial and ventricular structures.

Flexible transducer arrays are desired to wrap around catheter tips for side-looking intravascular ultrasound imaging. We present a technique for constructing flexible capacitive micromachined ultrasonic transducer (CMUT) arrays by forming polymer-filled deep trenches in a silicon substrate. First, we etch deep trenches between the bottom electrodes of CMUT elements on a prime silicon wafer using deep reactive ion etching. Second, we fusion-bond a silicon-on-insulator (SOI) wafer to the prime silicon wafer. Once the silicon handle and buried oxide layers are removed from the back side of the SOI wafer, the remaining thin silicon device layer acts as a movable membrane and top electrode. Third, we fill the deep trenches with polydimethylsiloxane, and thin the wafer down from the back side. The 16 by 16 flexible 2-D arrays presented in this paper have a trench width that varies between 6 and 20 [micro]m; the trench depth is 150 [micro]m; the membrane thickness is 1.83 [micro]m; and the final substrate thickness is 150 [micro]m. We demonstrate the flexibility of the substrate by wrapping it around a needle tip with a radius of 450 [micro]m (less than catheter size of 3 French). Measurements in air validate the functionality of the arrays. The 250-[micro]m by 250-[micro]m transducer elements have a capacitance of 2.29 to 2.67 pF, and a resonant frequency of 5.0 to 4.3 MHz, for dc bias voltages ranging from 70 to 100 V. [2007-0078] Index Terms--Capacitive micromachined ultrasonic transducer (CMUT), fabrication, flexible arrays, intravascular ultrasound (IVUS), polydimethylsiloxane (PDMS), through-wafer interconnects, trench isolation.

A 3D ultrasound imaging device obtained by combination of a capacitive micromachined ultrasonic transducer (CMUT) array with an integrated circuit (IC) is described. The device exhibits wide bandwidth, excellent sensitivity, and high element yield and could be used in other ultrasound imaging applications.

The crosstalk performance of a one-dimensional (1-D) capacitive micromachined ultrasonic transducer (CMUT) array is analyzed by comparing the finite element calculations using a commercial package (LS-DYNA) and the experimental measurements in both conventional and collapsed modes. The results have shown that the LS-DYNA model can be used to accurately model the crosstalk in CMUT arrays under specific voltage bias and excitation conditions.

The experimental characterization of collapse-mode operation of capacitive micromachined ultrasonic transducers (CMUTs) is reported, which includes impedance measurements in air, pulse-echo experiments in immersion, and one-way optical displacement measurements in immersion for both conventional and collapse-mode operations. Experimental results show that a collapsed membrane can be used to generate and detect ultrasound more efficiently than a membrane operated in the conventional mode.

Two main approaches to the fabrication of capacitive micromachined ultrasonic transducers (cMUTs) namely the sacrificial release processes are reviewed and the new wafer-bonding method is described in detail. The findings suggest that wafer-bonded cMUT technology is superior in terms of process control, yield and uniformity, as the number of steps and consequent process time were reduced and turn-around time was improved significantly.

Finite element calculations for capacitive micromachined ultrasonic transducers (cMUTs) using LS-DYNA, a commercially available finite element package, DC bias mode, and other new cMUT operations are studied. Observations suggest that the finite element results for both conventional and collapse modes when compared to measurements made by an optical interferometer was good, proving it useful for designing cMUTs that operate in regimes where membranes make contact with the substrate.

The collapse-snapback operation of the capacitive micromachined ultrasonic transducers (cMUT), where in the membrane is collapsed onto the substrate in the collapsing cycle, and released in the snapback cycle. The collapse-snapback operation overcomes the above-mentioned limitations of the conventional operation.

Full-phased array (FPA), classical synthetic aperture (CSA) and phased sub-array (PSA) imaging of a resolution phantom are performed using both simulated and experimental data from a 3-MHz, 3.2-cm, 128-element capacitive micromachined ultrasound transducer (CMUT) array. The simulated and experimental test results validate theoretical expectations and illustrate the flexibility of PSA imaging as a way to exchange signal-to-noise ratio (SNR) and frame rate for simplified front-end hardware.

The design and testing of forward-viewing annular arrays fabricated using capacitive micromachined ultrasonic transducer (CMUT) technology is reported. The results demonstrate that CMUT annular array elements indeed have wide frequency bandwidth and a high dynamic range.

The first volumetric images, using a 2-D capacitive micromachined ultrasonic transducers(CMUT) is presented. The 2-D CMUT can be fabricated with high yield using silicon IC-fabrication process.

The viability of capacitive micromachined ultrasonic transducers (CMUT) for ultrasound imaging is examined and discussed.