Comparison of Si3N4–SiO2 and SiO2 Insulation Layer for Zero-Bias CMUT Operation Using Dielectric Charging Effects

Choi, Won Young; Lee, Chang Hoon; Kim, Young Hun; Park, Kwan Kyu

doi:10.1109/tuffc.2019.2950902

Cited by 8 publications

(7 citation statements)

References 15 publications

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“…The same parameters were used for all four devices to compare their charging capabilities. Other groups that investigated pre-charged CMUTs, charged their devices with voltages between 1.5 to 2.5 times the pull-in voltage [15]- [19], mostly resulting, except for one case [17], in out of collapse pre-charged CMUTs. In this work, the amplitude of the DC charging voltage was chosen to be about three times higher than the analytically calculated pull-in voltage out of the four devices, in order to initiate charge trapping in a deep collapsed state.…”

Section: Pre-charging the Cmutsmentioning

confidence: 99%

“…Dielectric charging is usually seen as a reliability issue in MEMS devices since it causes instability of the device characteristics up to the point at which the device fails [9]- [11]. On the other hand, the concept of dielectric charging is at the base of the semiconductor memory industry [12]- [14], and other groups have already experimentally applied it to CMUT devices to achieve reduced or zero-bias operation [15]- [19]. High-k materials such as Si 3 N 4 or HfO 2 could be used for this application [20], as investigated by Park et al [18] and Choi et al [15], who demonstrated the feasibility of pre-charged CMUTs with Si 3 N 4 as dielectric showing good charge retention over time, even at high temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, the concept of dielectric charging is at the base of the semiconductor memory industry [12]- [14], and other groups have already experimentally applied it to CMUT devices to achieve reduced or zero-bias operation [15]- [19]. High-k materials such as Si 3 N 4 or HfO 2 could be used for this application [20], as investigated by Park et al [18] and Choi et al [15], who demonstrated the feasibility of pre-charged CMUTs with Si 3 N 4 as dielectric showing good charge retention over time, even at high temperatures. Charge retention over time represents the major challenge for these devices and, depending on the application, the minimum lifetime can vary from hours in the case they are part of a disposable device, or a few months for acute applications, to years.…”

Section: Introductionmentioning

confidence: 99%

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Modeling and Characterization of Pre-Charged Collapse-Mode CMUTs

Saccher

Kawasaki

Klootwijk

et al. 2023

IEEE Open J. Ultrason., Ferroelect., Freq. Contr.

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Recently, the applications of ultrasound transducers expanded from high-end diagnostic tools to point of care diagnostic devices and wireless power receivers for implantable devices. These new applications additionally require that the transducer technology must comply to biocompatibility and manufacturing scalability. In this respect, Capacitive Micromachined Ultrasound Transducers (CMUTs) have a strong advantage compared to the conventional PZT based transducers. However, current CMUTs require a large DC bias voltage for their operation, which limits the miniaturizability of these devices. In this study, we propose a pre-charged collapse-mode CMUT for immersive applications that can operate without an external bias by means of a charge trapping Al 2 O 3 layer embedded in the dielectrics between the top and bottom electrodes. The built-in charge layer was analytically modeled and four layer stack combinations were investigated and characterized. The measurement results of the CMUTs were then used to fit the model and to quantify the amount and type of trapped charge. It was found that these devices polarize due to the ferroelectric-like behavior of the Al 2 O 3 , and the amount of charge stored in the charge-trapping layer was estimated to be approximately 0.02 C/m 2 . Their acoustic performance shows a transmit and receive sensitivity of 8.8 kPa/V and 13.1 V/MPa respectively. In addition, we show that increasing the charging temperature, the charging duration, and the charging voltage results in a higher amount of stored charge. Finally, results of ALT tests showed that these devices have a lifetime of more than 2.5 years at body temperature. CMUT, zero-bias CMUTs, collapse-mode CMUTs, ultrasound transducer INDEX TERMS

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Section: Pre-charging the Cmutsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modeling and Characterization of Pre-Charged Collapse-Mode CMUTs

Saccher

Kawasaki

Klootwijk

et al. 2023

IEEE Open J. Ultrason., Ferroelect., Freq. Contr.

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show abstract

“…On the one hand, the insulating layer can prevent the membrane from collapsing or the cavity is broken down and the upper and lower electrodes contact and cause a short circuit. On the other hand, it can be used as a stop layer for sacrificial layer etching to protect the device from damage [20,21]. The sealed vacuum cavity is selected to prevent the CMUT element from being interfered by the external environment, causing energy loss and affecting the normal operation of the device.…”

Section: Cmut Basic Structure and Its Main Parametersmentioning

confidence: 99%

Hybrid Cell Structure for Wideband CMUT: Design Method and Characteristic Analysis

Wang¹,

Huang²,

Yu³

et al. 2021

Micromachines

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Capacitive micromachined ultrasonic transducer (CMUT) is an ultrasonic transducer based on the microelectromechanical system (MEMS). Wideband CMUT has good application prospects in ultrasonic imaging, ultrasonic identification, flow measurement, and nondestructive testing due to its excellent characteristics. This paper studies the method of increasing the bandwidth of the CMUT, proposes the structure of the wideband CMUT with a hybrid cell structure, and analyzes the design principles and characteristics of the wideband CMUT structure. By changing the cell spacing and the number of cells of different sizes composing the CMUT, we analyze the simulation of the effect of the spacing and number on the CMUT bandwidth, thereby optimizing the bandwidth characteristics of the CMUT. Next, the selection principle of the main structural parameters of the wideband CMUT is analyzed. According to the proposed principle, the CMUT in the air and water are designed and simulated. The results prove that both the air and water CMUT meet the design requirements. The design rules obtained in this paper can provide theoretical guidance for the selection of the main structural parameters of the wideband CMUT.

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“…Recently, other groups have performed long-term measurements of pre-charged CMUTs. However, their research aimed to study the stability of the trapped charges in the dielectric rather than estimating the duration of the charge retention [15,16].…”

Section: Introductionmentioning

confidence: 99%

The long-term reliability of pre-charged CMUTs for the powering of deep implanted devices

Saccher

Kawasaki

Dekker

2021

2021 IEEE International Ultrasonics Symposium (IUS)

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Recently, focused ultrasound has been proposed to power deeply implanted medical devices. Almost exclusively, lead zirconate titanate (PZT) transducers are used to convert acoustic energy into electrical energy. Unfortunately, these lead containing devices cannot be hermetically encapsulated since that would block the ultrasound. We propose the use of biocompatible Capacitive Micromachined Ultrasonic Transducer (CMUT) elements to replace traditional PZT transducers. In addition, to eliminate the external bias voltage, we introduced a charge trapping Al2O3 layer inside the CMUT to create a built-in bias voltage. These devices can be pre-charged and used as a receiver for US power. In this work, the viability of charged CMUTs to power deep implants was explored by investigating the effect of the charging parameters and by performing Accelerated Lifetime Tests (ALT). The estimated lifetime at body temperature ranges between 2.5 to 3.5 years at body temperature, which significantly depends on the charging parameters. Keywords-capacitive micromachined ultrasound transducers, pre-charged CMUT, zero-bias transducers, ultrasound power transfer, accelerated lifetime test

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Comparison of Si₃N₄–SiO₂ and SiO₂ Insulation Layer for Zero-Bias CMUT Operation Using Dielectric Charging Effects

Cited by 8 publications

References 15 publications

Modeling and Characterization of Pre-Charged Collapse-Mode CMUTs

Modeling and Characterization of Pre-Charged Collapse-Mode CMUTs

Hybrid Cell Structure for Wideband CMUT: Design Method and Characteristic Analysis

The long-term reliability of pre-charged CMUTs for the powering of deep implanted devices

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