Robert Gideon Wodnicki

Reconfigurable arrays for portable ultrasound

A collaborative effort is aimed at the development of reconfigurable array technology. The goal is to enable innovative medical ultrasound imagers ideally suited for portable ultrasound and applications such as remote emergency medicine and combat casualty care. Success depends on developing several technologies, the first of which is capacitive micromachined ultrasound transducers (cMUTs). The monolithic nature of cMUTs facilitates close connection with microelectronics. Thus a second technology under development is a switch matrix application specific integrated circuit (ASIC) that will enable the changing of interconnect between cMUT cells. The reconfigurable array concept arises from this ability to dynamically combine cMUT cells to form ideal apertures for a given imaging target (e.g. annular and phased apertures of various ring widths) and to move these apertures across the reconfigurable array plane [1-4]. Two central hypotheses are being tested: (1) the reconfigurable array can acquire acoustic pulse-echo data in a manner equivalent or superior to today’s 1D piezoceramic arrays (2) reconfigurable array technology will enable highly portable ultrasound platforms. Keywords-reconfigurable; annular; array; cMUT; ASIC; switch matrix; dynamic; phased; real-time

Multi-row linear cMUT array using cMUTs and multiplexing electronics

A large area reconfigurable imaging array for research purposes is being developed with co-integrated cMUTs and control electronics. The goal is a 2.5cm 2D tileable module with ≫16,000 transducer sub-elements spaced at a pitch of 185um in X and Y dimensions. As a prototype demonstration of some of the goals of this effort, a multi-row linear array using cMUTs and external multiplexing electronics was designed and fabricated. In this paper the challenges of trenched cMUT attach to a laminate interposer as part of a tileable module will be discussed. The architecture of the tileable module build-up for manufacturability, reliability, acoustic planarity, and reduced spacing between tiles and cMUT chips will also be addressed. Finally, a first prototype will be shown and experimental acoustic results with the new cMUT-based probe will be presented.

5F-2 Packaging and Design of Reconfigurable Arrays for Volumetric Imaging

Recent advances in capacitive micromachined ultrasound transducers (cMUTs), piezoceramic acoustic stack design, and transducer-to-electronics integration are enabling the fabrication of highly integrated reconfigurable ultrasound arrays. Reconfigurability in this context refers to the ability to reorganize the array elements in any configuration deemed desirable. Attractive configurations are an annular array, which can be translated electronically along a 2D array surface, or a phased array whose element orientation and pitch can be varied to optimize an image [1-6]. Further, annular array configurations make possible 3D-stacked miniaturized systems by reducing channel count, system size, and power consumption. In addition to such benefits, the annular array also provides dynamic axisymmetric focusing for excellent image quality. Several methods of integration have been explored to realize stacked transducer arrays with low channel count. Key components of the design include advanced interconnect such as through silicon vias in cMUTs and z-axis backing stacks, switch matrix application specific integrated circuits (ASICs), and high density multi-layer flex.

Packaging of large and low-pitch size 2D ultrasonic transducer arrays

The successful packaging and electronics integration of large 2D array devices with small pitch-sizes, such as fully populated 2D ultrasonic transducer arrays, require a flexible, simple, and reliable integration approach. One example for such electronics integration is based on through silicon vias (TSVs) with under-bump metallization (UBM) stack for solder bumping. In this paper, we demonstrate such an approach by successfully integrating a fully populated 2D ultrasonic transducer array. Our integration is based on a previously reported TSV technology (trench-frame technology), based on trench-isolated interconnects with supporting frame. We successfully combined the trench-frame technology with a simple UBM preparation technique - electro plating or chemical plating techniques with passivation layers for UBM pad definition are not required. Our results show high shear strength (26.5 g) of the UBM, which is essential for successful flip-chip bonding. The yield of the interconnections is 100% with excellent solder-ball-height uniformity (¿ = 0.9 ¿m). As demonstrated in this paper, this allows for a large-scale assembly of a tiled array by using an interposer. A design guideline for finer element-pitch design was developed suggesting that fusion bonding strength and the length of pillars are the main design parameters.

Large Area MEMS Based Ultrasound Device for Cancer Detection.

We present image results obtained using a prototype ultrasound array which demonstrates the fundamental architecture for a large area MEMS based ultrasound device for detection of breast cancer. The prototype array consists of a tiling of capacitive Micro-Machined Ultrasound Transducers (cMUTs) which have been flip-chip attached to a rigid organic substrate. The pitch on the cMUT elements is 185 um and the operating frequency is nominally 9 MHz. The spatial resolution of the new probe is comparable to production PZT probes, however the sensitivity is reduced by conditions that should be correctable. Simulated opposed-view image registration and Speed of Sound volume reconstruction results for ultrasound in the mammographic geometry are also presented.

2B-1 Solutions for Reconfigurable Arrays in Ultrasound

A reconfigurable array may involve a relatively large 2D array of transducer sub-elements and a layer of electronics which uses switches to connect certain sub-elements together, to a single system channel [Fischer et al., 2005 and Thomenius et al., 2005]. An annular array pattern, consisting of ring-shaped element groups, may be electronically scanned, or stepped, across the surface of such a reconfigurable array. The array could use 20 to 32 system channels and provide image quality comparable to a 128 channel linear array [Hazard et al., 2003 amd Dietz et al., 1979], This paper discusses some of the unique challenges and solutions pertaining to reconfigurable two-dimensional ultrasound arrays. Size constraints of the electronics result in some non-ideal aspects to the switch array; namely, there are constraints on the distribution of system channel access points across the array, and that these switches have a certain on-resistance which introduces non-ideal signal propagation delays. Some solutions will be discussed in this paper which aim to reduce the effect of these non-ideal constraints, and may suggest certain design tradeoffs which can be made in the design of future reconfigurable switch arrays

Reconfigurable mosaic annular arrays

Mosaic annular arrays (MAA) based on reconfigurable array (RA) transducer electronics assemblies are presented as a potential solution for future highly integrated ultrasonic transducer subsystems. Advantages of MAAs include excellent beam quality and depth of field resulting from superior elevational focus compared with 1-D electronically scanned arrays, as well as potentially reduced cost, size, and power consumption resulting from the use of a limited number of beamforming channels for processing a large number of subelements. Specific design tradeoffs for these highly integrated arrays are discussed in terms of array specifications for center frequency, element pitch, and electronic switch-on resistance. Large-area RAs essentially function as RC delay lines. Efficient architectures which take into account RC delay effects are presented. Architectures for integration of the transducer and electronics layers of large-area array implementations are reviewed.

Packaging and modular assembly of large-area and fine-pitch 2-D ultrasonic transducer arrays

A promising transducer architecture for largearea arrays employs 2-D capacitive micromachined ultrasound transducer (CMUT) devices with backside trench-frame pillar interconnects. Reconfigurable array (RA) application-specified integrated circuits (ASICs) can provide efficient interfacing between these high-element-count transducer arrays and standard ultrasound systems. Standard electronic assembly techniques such as flip-chip and ball grid array (BGA) attachment, along with organic laminate substrate carriers, can be leveraged to create large-area arrays composed of tiled modules of CMUT chips and interface ASICs. A large-scale, fully populated and integrated 2-D CMUT array with 32 by 192 elements was developed and demonstrates the feasibility of these techniques to yield future large-area arrays. This study demonstrates a flexible and reliable integration approach by successfully combining a simple under-bump metallization (UBM) process and a stacked CMUT/interposer/ASIC module architecture. The results show high shear strength of the UBM (26.5 g for 70-μm balls), high interconnect yield, and excellent CMUT resonance uniformity (s = 0.02 MHz). A multi-row linear array was constructed using the new CMUT/interposer/ASIC process using acoustically active trench-frame CMUT devices and mechanical/ nonfunctional Si backside ASICs. Imaging results with the completed probe assembly demonstrate a functioning device based on the modular assembly architecture.

An Integrated 90V Switch Array for Medical Ultrasound Applications

An integrated 90V 16-channel CMOS analog switch array has been designed and fabricated for next generation medical ultrasound systems. The array was implemented in AMIS I2T100 technology; the die area is 14.72mm2. Measurement results show that the static power consumption is 110 W. The on resistance of the switch is 200, and the switch off-state isolation is -30dB

PIN-PMN-PT single crystal composite and 3D printed interposer backing for ASIC integration of large aperture 2D array

High channel count, large area ultrasound arrays at fine pitch require close integration of transducer elements and ASIC electronics. Composites of single crystal material and non-conducting epoxy filler can be used to increase bandwidth. Direct bonding of the composite to the ASIC leads to acoustic mismatch and excessive ringing. A collimated connection block (i.e. an interposer) between the array elements and their respective ASIC connections can provide both acoustic attenuation and electrical interconnection. Here we present the implementation of an interposer backing using additive manufacturing processes and demonstrate integration of the interposer with a PIN-PMN-PT single crystal composite transducer array.