Integration of 2D CMUT arrays with front-end electronics for volumetric ultrasound imaging

Abstract

For three-dimensional (3D) ultrasound imaging, connecting elements of a two-dimensional (2D) transducer array to the imaging system's front-end electronics is a challenge because of the large number of array elements and the small element size. To compactly connect the transducer array with electronics, we flip-chip bond a 2D 16 x 16-element capacitive micromachined ultrasonic transducer (CMUT) array to a custom-designed integrated circuit (IC). Through-wafer interconnects are used to connect the CMUT elements on the top side of the array with flip-chip bond pads on the back side. The IC provides a 25-V pulser and a transimpedance preamplifier to each element of the array. For each of three characterized devices, the element yield is excellent (99 to 100% of the elements are functional). Center frequencies range from 2.6 MHz to 5.1 MHz. For pulse echo operation, the average - 6-dB fractional bandwidth is as high as 125%. Transmit pressures normalized to the face of the transducer are as high as 339 kPa and input-referred receiver noise is typically 1.2 to 2.1 mPa/pHz. The flip-chip bonded devices were used to acquire 3D synthetic aperture images of a wire-target phantom. Combining the transducer array and IC, as shown in this paper, allows for better utilization of large arrays, improves receive sensitivity, and may lead to new imaging techniques that depend on transducer arrays that are closely coupled to IC electronics.

Integrated differential three-level high-voltage pulser output stage for CMUTs

“…Using (5) and the energies in table I and II the power consumption P T,Nj [mW] as a function of the period, T [µs], and the number of transitions per period, N j , is shown in (6) and (7) for the single-ended and differential output stages respectively. Using these equations, the power consumption of any pulse shape can be found for both topologies.…”

“…2. As it can be seen, three voltage levels correspond to six different voltage transitions, tr j (j ∈ [1,6]). From now on any pulse shape is characterized by its total period, T , and the number of each tr j transitions, N j .…”

A Scalable Organization of 2-D Ultrasonic Sensor Array

“…However, improvement in MEMS technologies enables us to make very small micro-machined ultrasonic sensors. One of them is capacitive micro-machined ultrasonic transducer (CMUT) (3) . CMUT enables the frontend to be small with integrated circuits(IC) and many receive elements can be placed.…”

Inverter-based 1 V analog front-end amplifiers in 90 nm CMOS for medical ultrasound imaging

“…These CMUTs are replacing the long-established piezoelectric transducers in high frequency and high resolution ultrasound imaging due to their attractive features of micro-fabrication, wide bandwidth, very high level of integration, and batch fabrication [4][5][6]. CMUTs can easily be integrated with CMOS front-end electronics either through flip-chip bonding [7][8][9] or monolithically through CMUTs on the CMOS process [2,3,10,11]. The integration of CMOS electronic circuits with CMUTs will greatly cut down the cost of ultrasound imaging systems as the mass production of CMOS electronic integrated circuits is very cheap.…”

“…Such integration of CMUTs with CMOS front-end electronics fits best with the requirements of IVUS imaging system probes. All these best features of CMUTs along with low-cost high-performance CMOS interface electronic circuits enable us to make a very cost effective integrated ultrasound system [2][3][4][5][6][7][8][9][10][11].…”