Browsing by Author "Cheng, Xiaoyang"

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A capacitive micromachined ultrasonic transducer array for minimally invasive medical diagnosis
(2008-06-01)
Chen, Jingkuang
;
Cheng, Xiaoyang
;
Chen, Chien-Chang
;
Li, Pai-Chi
;
Liu, Jian-Hung
A capacitive micromachined ultrasonic transducer (CMUT) array for minimally invasive medical diagnosis has been developed. Unlike traditional ultrasonic transducers, which generally use a bulky piece of substrate, this transducer array was integrated on a 40-mu m-thick micromachined silicon substrate into a probe shape with a typical shank width of 50-80 mu m and a shank length of 4-8 mm. For 1-D arrays, 24-96 CMUT devices were integrated on one such silicon probe and formed an accurately configured phase array. In addition to miniaturization, reduction of the substrate thickness also decreases the intertransducer crosstalk due to substrate Lamb waves. Due to its miniature size, this array can be placed or implanted close to the target tissue/organ and can perform high-resolution high-precision diagnosis and stimulation using high-frequency ultrasounds. The issue of conflict between resolution and penetration depth of ultrasonic diagnosis can therefore be resolved. A two-layer polysilicon surface micromachining process was used to fabricate this device. Suspended polysilicon membranes of diameters ranging from 20 to 90 mu ms and thicknesses from 1.0 to 2.5 mu m were used to generate and detect ultrasounds of frequencies ranging from I to 10 MHz. B-mode imaging using this transducer array has been demonstrated.
AN IMPLANTABLE ULIRASONIC DOPPLER BLOOD FLOWMETER
(2006)
Cheng, Xiaoyang
;
Chen, Jingkuang
;
Zhang, Tongsheng
;
Chen, Chien-Chang
;
Cheng, Yu-Ting
A miniature ultrasonic transducer array for minimally invasive blood flow measurement has been developed. Compare with laser Doppler flowmeter, this tool is much smaller in size and is capable of reaching deep inside the tissue to monitor blood flow not accessible by the laser beam. Compared with traditional ultrasound Doppler flowmeter, this miniature tool is able to achieve more accurate measurement by using high frequency ultrasounds. The silicon substrate of the transducers array was micromachined into a probe shape using double-sided dry etching. The typical cross-sectional dimension of the silicon probe is 40 mu mx80 mu m. Arrays comprising 24-32 transducers were prototyped and tested. The 46 mu m-diameter drum shaped ultrasound transducers operate at a voltage lower than 40 volts, generate and receive ultrasound at a central frequency of 5.8MHz, and has a bandwidth of about 80%. A new polysilicon surface micromachining process was developed for fabrication of the transducer. The new process separates all the conductors from the silicon nitride film and reduces the charging problem associated with nitride-conductor interface.