Cost-effective and manufacturable route to the fabrication of high-density 2D micromachined ultrasonic transducer arrays and (CMOS) signal conditioning electronics on the same silicon substrate

Abstract

The ability to fabricate Capacitive Micromachined Ultrasonic Transducers (cMUTs) and signal conditioning electronics together on the same silicon substrate offers significant benefits to overall transducer performance, and simplifies connectivity within a dense 2D transducer array. This integration of cMUTs and electronics has been demonstrated utilising a lowtemperature silicon nitride membrane technology, postprocessed onto CMOS-ASIC substrates. Successful results from fabricated arrays of cMUTs and front-end analogue amplifiers confirm the integration to be relatively simple and highly manufacturable. optimum method of integrating transducers and electronics on the same substrate. This paper presents the fabrication of cMUTs using a low-temperature silicon nitride membrane technology, thus enabling transducers to be fabricated directly onto a silicon substrate containing prefabricated electronics. This results in an inherent lowparasitic connectivity to individual transducer elements within an array, whilst retaining full flexibility in controlling the fundamental device properties which determine the transducers' subsequent acoustical performance.

11D-3 MOSAIC: An Integrated Ultrasonic 2D Array System

“…One possible solution lies with the avoidance of cables. Previous solutions aimed at direct attachment of the transducer to the electronics have been implemented on the same silicon substrate, as with CMUTs [5], or in the case of piezoelectric transducers, via direct pin attachments from the transducer to the PCB. Both these cases see the transducer mounted physically parallel to the electronics, rather than perpendicular as in the case of the tiles.…”

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

“…Compared to general purpose ultrasound imaging systems, IVUS imaging system requirements are quite challenging and in particular the probe in IVUS imaging systems is based on a catheter with a diameter of the order of 1 mm or less. The combination of high frequency, small form factor, and good performance requires ultrasound transducers and interface electronics to be tightly integrated [2,3]. In such catheter based IVUS imaging systems, the latest ultrasound sensors, capacitive micro-machined ultrasound transducers (CMUTs), fit best compared to conventional piezoelectric transducers, as CMUTs are compatible with the well known CMOS process.…”

“…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].…”

Experimental characterization of collapse-mode CMUT operation

“…Batch manufacturing provides significant cost reduction compared to existing piezoelectric transducer fabrication technology, which relies on meticulous and labor-intensive steps, such as hand lapping, polishing, and high-precision dicing. CMUT technology also conveniently integrates the transducer array with supporting electronic circuits (either monolithically [6], [7] or in a flip-chip package [8]). …”