Showing papers by "Arif Sanli Ergun published in 2002"

Capacitive micromachined ultrasonic transducers: next-generation arrays for acoustic imaging?

Abstract: Piezoelectric materials have dominated the ultrasonic transducer technology. Recently, capacitive micromachined ultrasonic transducers (CMUTs) have emerged as an alternative technology offering advantages such as wide bandwidth, ease of fabricating large arrays, and potential for integration with electronics. The aim of this paper is to demonstrate the viability of CMUTs for ultrasound imaging. We present the first pulse-echo phased array B-scan sector images using a 128-element, one-dimensional (1-D) linear CMUT array. We fabricated 64- and 128-element 1-D CMUT arrays with 100% yield and uniform element response across the arrays. These arrays have been operated in immersion with no failure or degradation in performance over the time. For imaging experiments, we built a resolution test phantom roughly mimicking the attenuation properties of soft tissue. We used a PC-based experimental system, including custom-designed electronic circuits to acquire the complete set of 128/spl times/128 RF A-scans from all transmit-receive element combinations. We obtained the pulse-echo frequency response by analyzing the echo signals from wire targets. These echo signals presented an 80% fractional bandwidth around 3 MHz, including the effect of attenuation in the propagating medium. We reconstructed the B-scan images with a sector angle of 90 degrees and an image depth of 210 mm through offline processing by using RF beamforming and synthetic phased array approaches. The measured 6-dB lateral and axial resolutions at 135 mm depth were 0.0144 radians and 0.3 mm, respectively. The electronic noise floor of the image was more than 50 dB below the maximum mainlobe magnitude. We also performed preliminary investigations on the effects of crosstalk among array elements on the image quality. In the near field, some artifacts were observable extending out from the array to a depth of 2 cm. A tail also was observed in the point spread function (PSF) in the axial direction, indicating the existence of crosstalk. The relative amplitude of this tail with respect to the mainlobe was less than -20 dB.

Fabrication of Capacitive Micromachined Ultrasonic Transducers (CMUTs) using wafer bonding technology for low frequency (10 kHz-150 kHz) sonar applications

Abstract: This paper introduces a new method for fabricating Capacitive Micromachined Ultrasonic Transducers (CMUT) that uses a wafer-bonding technique. The transducer membrane and cavity are defined separately on a Silicon-On-Insulator (SOI) wafer and on a prime quality silicon wafer, respectively. Using silicon direct bonding in a vacuum environment, the two wafers are bonded forming the transducer. Among the many advantages this wafer-bonding technique, and probably the most important for low frequency transducer applications, is the ability to define relatively large membranes and large gaps easily. The particular device reported in this paper is designed to operate in the 10 kHz - 150 kHz range as a transmitter only for a sonar application. In this paper, we describe the new fabrication process to build CMUTs, and present the first experimental results obtained from this particular device that demonstrate wide-band operation in the above mentioned frequency range.

Microfluidic channels with integrated ultrasonic transducers for temperature measurement and method

Abstract: There is described a method and apparatus for measuring temperature of a fluid in a microchannel of the type having spaced walls. An ultrasonic transducer transmits ultrasonic waves transmitted from one wall to the opposite wall. A processor determines the time-of-flight of the ultrasonic waves from the one wall and reflected to the opposite wall to the one wall. The processor converts the time-of-flight to velocity by dividing the distance between walls by the time-of-flight. The processor converts velocity to temperature from the relationship of velocity to temperature in the fluid.

Broadband capacitive micromachined ultrasonic transducers ranging from 10 kHz to 60 MHz for imaging arrays and more

Abstract: Capacitive micromachined ultrasonic transducers (CMUTs) have long been studied. Past research has shown that CMUTs indeed have remarkable features such as wide bandwidth and high efficiency. This paper introduces an inclusion to the CMUT technology that uses the wafer-bonding technique to fabricate membranes on silicon. This new technology enables the fabrication of large membranes with large gaps, and expands the frequency span of CMUTs to 10 kHz in the low end. CMUT devices with different frequency spans are fabricated using both technologies, and tested. Electromechanical coupling efficiency, k/sub T//sup 2/, value as high as 0.85 and fractional immersion bandwidth as wide as 175 % are measured.

Fabrication and characterization of 1-dimensional and 2-dimensional Capacitive Micromachined Ultrasonic Transducer (CMUT) arrays for 2-dimensional and volumetric ultrasonic imaging

Abstract: Capacitive Micromachined Ultrasonic Transducers (CMUTs) were introduced about a decade ago as an alternate method of generating and detecting ultrasound. Since their introduction, considerable research has been done to characterize CMUTs. They have been shown to have broad frequency bandwidth and very good sensitivity. Besides, CMUTs are built on silicon using standard surface micromachining techniques, and therefore have all the advantages of 1C processing, such as parallel production, batch fabrication and very high level of integration. All these qualities made CMUTs and CMUT arrays an alternative to their piezoelectric counterparts. In this paper, we focus on the CMUT fabrication process and present recent advances which made it possible to achieve very high process yields (practically 100%) leading to the fabrication of fully functional one-dimensional (ID) and two-dimensional (2D) CMUT arrays. Because of limitations on the element size, the fabrication of 2D CMUT arrays involves the use of electrical through-wafer interconnects (ETWI) which brings the electrical connection of each element from the transducer side to the backside of the wafer. In this paper, we also present ETWIs that have parasitic capacitance as low as 0.25 pF integrated with a 2D CMUT array of 128 by 128 elements. These arrays are characterized and tested in real imaging cases. The paper concludes with the presentation of the sample imaging results that demonstrate the viability of the CMUT process for array fabrication.

Underwater acoustic imaging using capacitive micromachined ultrasonic transducer arrays

Abstract: Capacitive micromachined ultrasonic transducers (CMUTs) have recently emerged as an alternative technology to piezoelectric transducers, offering advantages such as wide bandwidth, ease of fabricating large arrays and potential for integration with electronic circuits. In this paper, we present 2D and 3D pulse-echo imaging results using ID linear and 2D rectangular CMUT arrays, respectively. The aim of this paper is to demonstrate the viability of CMUTs for underwater acoustic imaging. For imaging experiments, we have fabricated ID and 2D CMUT arrays, and built an experimental setup allowing us to transmit and receive ultrasound signals from individual transducer elements. The image quality obtained shows that CMUTs are a strong alternative to conventional piezoelectric transducer arrays for the design of future generations of underwater acoustic imaging systems.

Capacitive micromachined ultrasonic transducer based integrated actuator for atomic force microscope cantilevers

Abstract: The atomic force microscope (AFM) is a versatile tool for imaging and modifying surfaces on atomic scales. The core of the device is a cantilever beam with a sharp tip. The cantilever usually measures a few hundred microns in length and tens of microns in width. Many imaging or surface modification applications require actuation of this micron scale beam. In this paper, a novel actuation mechanism is introduced. The method uses radiation pressure generated by capacitive micromachined ultrasonic transducers (cMUT). The cMUTs are fabricated on top of the cantilever beams and they operate in the megahertz range generating a DC radiation pressure in the immersion medium such as water or air. The integrated cMUT cantilever system compares favorably with piezoelectric film activated and with non-integrated ultrasonic actuation schemes. The cMUT cantilever does not require any alignment of the actuator to the cantilever. Moreover, it works in air as well as in water and is readily used with parallel cantilever probes. Finally, it is an IC compatible technology solution.

Lamb wave devices based on capacitive micromachined ultrasonic transducers

Abstract: This paper describes the theory, design, and realization of a new type of Ultrasonic Lamb Wave Transducer. The excitation mechanism of this device is unlike any other as it relies on the Capacitive Micromachined Ultrasonic Transducer (CMUT). Built using fundamental integrated circuit techniques, this device has an insertion loss of 20 dB at an operating frequency of 2.1 MHz. The dominant propagating mode in the device is that of the lowest order antisymmetric flexural wave (A/sub 0/). The substrate upon which the device rests is 18 /spl mu/m thick and is almost entirely made up of crystalline silicon. When configured as a delay line oscillator, the transducer functions well as a sensor to changes in environmental conditions.