Low temperature capacitive micromachined ultrasonic transducers (cMUTs) on glass substrate

Bahette, Emilie; Michaud, Jean-François; Certon, Dominique; Gross, D.; Perroteau, Marie; Alquier, Daniel

doi:10.1088/0960-1317/26/11/115023

Cited by 3 publications

(4 citation statements)

References 29 publications

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“…Besides the first investigations reported in [14] , where infrared transparency was achieved by thinning the silicon microfabrication substrate down to 100 μm, the successful microfabrication of CMUTs on an optically transparent substrate (i.e. glass), was shown in [26] , [27] . Furthermore, CMUT with through-glass-via interconnects fabrication was reported in [28] , possibly enabling the access to 3D-integration technologies.…”

Section: Discussionmentioning

confidence: 95%

Quantitative comparison of PZT and CMUT probes for photoacoustic imaging: Experimental validation

et al. 2017

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Photoacoustic (PA) signals are short ultrasound (US) pulses typically characterized by a single-cycle shape, often referred to as N-shape. The spectral content of such wideband signals ranges from a few hundred kilohertz to several tens of megahertz. Typical reception frequency responses of classical piezoelectric US imaging transducers, based on PZT technology, are not sufficiently broadband to fully preserve the entire information contained in PA signals, which are then filtered, thus limiting PA imaging performance. Capacitive micromachined ultrasonic transducers (CMUT) are rapidly emerging as a valid alternative to conventional PZT transducers in several medical ultrasound imaging applications. As compared to PZT transducers, CMUTs exhibit both higher sensitivity and significantly broader frequency response in reception, making their use attractive in PA imaging applications. This paper explores the advantages of the CMUT larger bandwidth in PA imaging by carrying out an experimental comparative study using various CMUT and PZT probes from different research laboratories and manufacturers. PA acquisitions are performed on a suture wire and on several home-made bimodal phantoms with both PZT and CMUT probes. Three criteria, based on the evaluation of pure receive impulse response, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) respectively, have been used for a quantitative comparison of imaging results. The measured fractional bandwidths of the CMUT arrays are larger compared to PZT probes. Moreover, both SNR and CNR are enhanced by at least 6 dB with CMUT technology. This work highlights the potential of CMUT technology for PA imaging through qualitative and quantitative parameters.

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Section: Discussionmentioning

confidence: 95%

Quantitative comparison of PZT and CMUT probes for photoacoustic imaging: Experimental validation

et al. 2017

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“…The optimized membrane thickness in bandwidth of interest is 2.2-um, and the gap (95-nm) is optimized to obtain ~1–2MPa peak-to-peak pressure with 30–60V pulses when operated in the non-collapsed mode [19]. Due to the residual stress and atmospheric pressure [9, 20, 21] on the Si x N y membrane, the static deflection of about 15–18 nm is observed and as a result, the sacrificial layer (Cu) thickness which forms the CMUT’s gap is designed to be around 110-nm.…”

Section: Cmut Designmentioning

confidence: 99%

“…The key for monolithic integration is the low temperature CMUT fabrication process. Although low temperature wafer bonding [5, 6] is demonstrated, sacrificial layer based processes are also widely used [3, 7, 8, 9]. Sacrificial layer process does not need large areas for reliable bonding which can reduce the active area of the transducer element, and hence can be especially suitable for high frequency applications with smaller lateral membrane dimensions.…”

Section: Introductionmentioning

confidence: 99%

Low temperature CMUT fabrication process with dielectric lift-off membrane support for improved reliability

Pirouz

Degertekin

2018

J. Micromech. Microeng.

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This paper reports an improved CMOS compatible low temperature sacrificial layer fabrication process for Capacitive Micromachined Ultrasonic Transducers (CMUTs). The process adds the fabrication step of silicon oxide evaporation which is followed by a lift-off step to define the membrane support area without a need for an extra mask. This simple addition improves reliability by reducing the electric field between the top and bottom electrodes everywhere except the moving membrane without affecting the vacuum gap thickness. Furthermore, the parasitic capacitance which degrades the CMUT receive performance is reduced. A 1-D CMUT array suitable for Intracardiac Echocardiography (ICE) imaging with 9MHz center frequency is fabricated using this method. Detailed electrical and acoustic testing indicates adequate performance of the devices for ICE in agreement with simulations. Long term output pressure testing with more than 2×10 pulsing cycles and environmental testing demonstrate the efficacy of the approach for improved reliability as compared to devices without the additional membrane support layer.

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“…To adress this aim, there many attemps to increase CMUT output performance (Bayram et al 2005;Olcum et al 2005Olcum et al , 2011F. Y. Yamaner KSÜ Mühendislik Bilimleri Dergisi, 21(4):280-285, 2018 281 KSU Journal of Engineering Sciences, 21(4): 280-285, 2018280-285, F. Yıldız et al 2012) Determination of fabrication process related stress on vibrating membrane is one of these attemps because it affects CMUT membrane performance in terms of collapse voltage, resonance frequency and gap distance (Bahette et al 2016;Yaralioglu et al 2001) . It is known that membrane formation using surface micromachining induces stress on membrane due to variety deposition processes (Ergun et al 2005).Similar to surface micromachining, CMUT fabrication with wafer bonding technology has cause stress on membrane due to high bonding temperature.…”

Section: Introductionmentioning

confidence: 99%

Capacitive Micromachined Ultrasonic Transducer (CMUT): Analytical Evaluation of Membranes Performance Under Fabrication Related Stress

Yildiz

2018

Kahramanmaraş Sütçü İmam Üniversitesi Mühendislik Bilimleri Dergisi

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High power transmission from CMUT (capacitive micromachined ultrasonic transducer) surface depends on output pressure and membrane displacement. Moreover, fabrication process related stress on membrane should also be considered because it affects CMUT performance in terms of collapse voltage, resonance frequency and gap distance. Therefore, stress on membrane becomes important criteria for CMUT modelling and fabrication. Surface micromachining and wafer bonding technologies are widely used for CMUT fabrications. These fabrication processes include several depositions and etching steps that those induce stress on CMUT membrane. Fabrication process related stress are classified as compressive or tensile. In this study, three common CMUT membranes, Si3Ni4, Poly-Si and SiC, were selected for analytic calculations and displacement and output pressure of these CMUT membranes were evaluated under built in stress. It was shown that stress on membrane has significant effect on membrane deflection and pressure from device surface for three membranes. As a result, stress on vibrating membrane should be minimized and optimized for reliable and high performance device fabrication when considering wide range of CMUT applications.

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Low temperature capacitive micromachined ultrasonic transducers (cMUTs) on glass substrate

Cited by 3 publications

References 29 publications

Quantitative comparison of PZT and CMUT probes for photoacoustic imaging: Experimental validation

Quantitative comparison of PZT and CMUT probes for photoacoustic imaging: Experimental validation

Low temperature CMUT fabrication process with dielectric lift-off membrane support for improved reliability

Capacitive Micromachined Ultrasonic Transducer (CMUT): Analytical Evaluation of Membranes Performance Under Fabrication Related Stress

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