Residual stress and Young's modulus measurement of capacitive micromachined ultrasonic transducer membranes

2001-01-01
Yaralioglu, GG
Ergun, AS
Bayram, Barış
Marentis, T
Khuri-Yakub, BT
Membranes supported by posts are used as vibrating elements of capacitive micromachined ultrasonic transducers (CMUTs). The residual stress built up during the fabrication process determines the transducer properties such as resonance frequency, collapse voltage, and gap distance. Hence, it is important to evaluate and control the stress in thin film CMUT membranes. The residual stress in the membrane causes significant vertical displacements at the center of the membrane. The stress bends the membrane posts, and the slope at the membrane edges result in amplified displacement at the center by the radius of the membrane. By measuring the center displacement, it is possible to determine the stress provided that Young's modulus of the thin film is known accurately. Usually, in thin film structures Young's modulus differs from that of bulk materials and it depends on thin film deposition technique. In this paper, we propose a novel technique for the measurement of stress and Young's modulus of CMUT membranes. The technique depends on the measurement of membrane deflection and resonance frequency. We modeled the stress and Young's modulus dependence of membrane deflection and resonance frequency using finite element analysis. We used the atomic force microscope (AFM) to measure the membrane deflection and the laser interferometer to determine the resonance frequency of the membrane. The technique is tested on a CMUT membrane. We found that our LPCVD deposition technique yields residual stress of around 100 MPa and Young's modulus of around 300 GPa.

Suggestions

Diamond-based capacitive micromachined ultrasonic transducers
Bayram, Barış (2012-02-01)
Capacitive micromachined ultrasonic transducers (CMUTs) employing diamond membranes are demonstrated. The design, finite element modeling, microfabrication, and experimental characterization of diamondbased CMUTs are reported. Ultrananocrystalline diamond having a chemical mechanical polished silicon dioxide interlayer deposited via high temperature oxide (HTO) process at 850 degrees C in a low pressure chemical vapor deposition (LPCVD) furnace is employed as the membrane to form vacuum sealed cavities usin...
Experimental characterization of collapse-mode CMUT operation
Oralkan, Omer; Bayram, Barış; Yaralioglu, Goksen G.; Ergun, A. Sanli; Kupnik, Mario; Yeh, David T.; Wygant, Ira O.; Khuri-Yakub, Butrus T. (2006-08-01)
This paper reports on the experimental characterization of collapse-mode operation of capacitive micromachined ultrasonic transducers (CMUTs). CMUTs are conventionally operated by applying a direct current (DC) bias voltage less than the collapse voltage of the membrane, so that the membrane is deflected toward the bottom electrode. In the conventional regime, there is no contact between the membrane and the substrate; the maximum alternating current (AC) displacement occurs at the center of the membrane. I...
Analytical calculation of collapse voltage of CMUT membrane
Nikoozadeh, A; Bayram, Barış; Yaralioglu, GG; Khuri-Yakub, BT (2004-01-01)
Because the collapse voltage determines the operating point of the capacitive micromachined ultrasonic transducer (CMUT), it is crucial to calculate and control this parameter. One approach uses parallel plate approximation, where a parallel plate motion models the average membrane displacement. This usually yields calculated collapse voltage 25 percent higher than the actual collapse voltage. More accurate calculation involves finite element method (FEM) analysis. However, depending on the required accurac...
ACOUSTIC CROSSTALK REDUCTION METHOD FOR CMUT ARRAYS
Bayram, Barış; Kupnik, Mario; Khuri-Yakub, Butrus T. (2006-01-01)
This paper reports on the finite element analysis (FEA) of crosstalk in capacitive micromachined ultrasonic transducer (CMUT) arrays. Finite element calculations using a commercial package (LS-DYNA) were performed for an immersed I-D CMUT array operating in the conventional and collapsed modes. LS-DYNA was used to model the crosstalk in CMUT arrays under specific voltage bias and excitation conditions, and such a modeling is well worth the effort for special-purpose CMUT arrays for ultrasound applications s...
Influence of the electrode size and location on the performance of a CMUT
Bayram, Barış; Ergun, AS; Khuri-Yakub, BT (2001-01-01)
The collapse voltage of micromachined capacitive ultrasonic transducers (CMUT) depends on the size, thickness, type, and position of the metal electrode within the membrane. This paper reports the result of a finite element study of this effect. The program (ANSYS 5.7) is used to model a circular membrane on top of a Si substrate covered by a Si3N4 insulation layer. We find that the collapse voltage increases in proportion to the metal thickness for constant membrane thickness. The collapse voltage of a mem...
Citation Formats
G. Yaralioglu, A. Ergun, B. Bayram, T. Marentis, and B. Khuri-Yakub, “Residual stress and Young’s modulus measurement of capacitive micromachined ultrasonic transducer membranes,” 2001, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/54960.