Analysis of the charging problem in capacitive micro-machined ultrasonic transducers

Machida, Shinjiro; Migitaka, Sonoko; Tanaka, Hisatoshi; Hashiba, Kunio; Enomoto, H.; Tadaki, Yoshitaka; Kobayashi, Takashi

doi:10.1109/ultsym.2008.0094

Cited by 19 publications

(9 citation statements)

References 8 publications

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“…After charging for two minutes, the line was shifted to the right (positive direction), and the x-intercept was moved to −1.7V . The direction of the voltage shift was consistent with what was reported in [2]. This experiment shows that the proposed method can detect a change of trapped charges in the correct direction.…”

Section: Methodssupporting

confidence: 89%

A novel method for measuring dielectric charging of CMUT arrays

Wong

Chen

et al. 2014

2014 IEEE International Ultrasonics Symposium

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A novel method to detect the bias voltage shift caused by dielectric charging in immersed CMUT arrays is proposed. The proposed method uses acoustic crosstalk as a means of coupling ultrasonic signal from the transmitting element to the receiving element, thus no additional equipment is required except the standard driving circuits and amplifiers in CMUT systems. Continuous sinusoid waves with and without dc offset were used in experiments and output signals caused by acoustic crosstalk with peak to peak amplitudes in the range of 100-200mV were observed. The calculation of bias voltage shift was illustrated graphically. The array was then intentionally charged and a change of voltage shift in the correct direction was observed using the same method. The proposed method can be modified to use unipolar square pulses, thus enabling real time monitoring and automatic calibration of CMUT arrays.

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Section: Methodssupporting

confidence: 89%

A novel method for measuring dielectric charging of CMUT arrays

Wong

Chen

et al. 2014

2014 IEEE International Ultrasonics Symposium

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“…Hence the amplitude of the negative pressure cycle increases quadratically with the increasing pulse amplitude. The positive pressure cycle is generated by the restoring force of the deformed plate 2 . Since the collapsed state benefits greatly from higher voltages, the excitation voltage should be as high as possible.…”

Section: A Pulse Amplitudementioning

confidence: 99%

“…A thinner insulation layer is preferable to increase electrical force applied on the plate. However, a thin dielectric layer may pose a charge trapping problem when it is subject to high electric fields [2]. The charge trapped in the insulation layer may degrade the device performance by creating a counter-force.…”

Section: Introductionmentioning

confidence: 99%

CMUT array element in deep-collapse mode

Ölçüm

Yamaner

Bozkurt

et al. 2011

2011 IEEE International Ultrasonics Symposium

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Abstract-Collapse and deep-collapse mode of operations have boosted the pressure outputs of capacitive micromachined ultrasonic transducers (CMUTs) considerably. In this work, we demonstrate a CMUT element operating in the deep-collapse mode with 25 V pulse excitation and without the effects of charge trapping. The fabricated CMUT element consists of 4 by 4 circular cells with 20 µm radius and 1 µm thick plates suspended over a 50 nm cavity. The overall size of the element is 0.190 mm by 0.19 mm. The collapse voltage of the plates is measured to be approximately 3V. By driving the CMUTs with 25V pulses in the deep-collapse mode without any bias, we achieved 1.2 MPa peak-to-peak pressure output on the surface of the CMUT element with a center frequency of 9 MHz and 100% fractional bandwidth. We applied 1000 consecutive electrical pulses with alternating polarity to the element and witnessed no change in the transmitted acoustic pulse.

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“…There is same problem in the radio frequency (RF) MEMS switches and the MEMS mirrors . This electric charge injection will result in capacitance‐voltage (CV) characteristics drift and an imaging performance changes . In the CMUT, the gap changes between the top and bottom electrodes cause decreases in the transmitting strength and receiving sensitivity of ultrasonic waves and affect the ultrasonic diagnostic images.…”

Section: Introductionmentioning

confidence: 99%

“…10 This electric charge injection will result in capacitance-voltage (CV) characteristics drift and an imaging performance changes. [11][12][13] In the CMUT, the gap changes between the top and bottom electrodes cause decreases in the transmitting strength and receiving sensitivity of ultrasonic waves and affect the ultrasonic diagnostic images. The objective of this paper is to find a reasonable design of CMUTs (the size of top electrode and the gap diameter) for suppressing the electric charge injection drift.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of capacitance changes of capacitive micromachined ultrasonic transducers for ultrasonic diagnoses by charge‐injection

Aono

Yoshimura

Machida

2018

Elect Comm in Japan

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This research reports capacitance–voltage (CV) changes of capacitive micromachined ultrasonic transducers (CMUT) for ultrasonic diagnoses. The CMUT constitutes an electrostatically vibrating film, which is fabricated by deposition processes of SiO2 and SiN films as insulator and TiN and Al films as top electrode on a Si substrate. The ultrasonic waves are transmitted by addition of AC voltage between the top electrode and the Si substrate, whereas the reflective ultrasonic wave are received with the vibrating film and converted to the electrical signals for ultrasonic diagnostic images. There is a problem that the CV changes of CMUT occur due to charge‐injection into the insulator, since a high AC and DC voltages are applied for driving the vibrating film. Thus, it is necessary to suppress the change in CV characteristics of the CMUT due to charge‐injection. It is clarified that the CV drift due to charge‐injection can be decreased by forming the top electrode so as to cover the vibrating film. Also, the CV drift is able to be suppressed by setting the driving voltage to be equal to or less than the collapse voltage.

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Analysis of the charging problem in capacitive micro-machined ultrasonic transducers

Cited by 19 publications

References 8 publications

A novel method for measuring dielectric charging of CMUT arrays

A novel method for measuring dielectric charging of CMUT arrays

CMUT array element in deep-collapse mode

Evaluation of capacitance changes of capacitive micromachined ultrasonic transducers for ultrasonic diagnoses by charge‐injection

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