Joontaek Jung

Fabrication of a two-dimensional piezoelectric micromachined ultrasonic transducer array using a top-crossover-to-bottom structure and metal bridge connections

A new design methodology and fabrication process for two-dimensional (2D) piezoelectric micromachined ultrasonic transducer (pMUT) arrays using a top-crossover-to-bottom (TCTB) structure was developed. Individual sensing and actuation of pMUT elements from a small number of connection lines was enabled by the TCTB structure, and the parasitic coupling capacitance of the array was significantly reduced as a result. A 32 × 32 pMUT array with a TCTB structure was fabricated, resulting in 64 connection lines over an area of 4.8 × 4.8 mm2. The top electrodes for each pMUT element were re-connected by metal bridging after bottom-electrode etching caused them to become disconnected. A deep reactive ion etching process was used to compactify the array. Each pMUT element was a circular-shaped K31-type ultrasonic transducer using a 1 µm thick sol–gel lead zirconate titanate (PZT: Pb1.10 Zr0.52 Ti0.48) thin film. To characterize a single element in the 2D pMUT array, the resonant frequency and coupling coefficient of 20 pMUT elements were averaged to 3.85 MHz and 0.0112, respectively. The maximum measured ultrasound intensity in water, measured at a distance of 4 mm, was 4.6 µW cm−2 from a single pMUT element driven by a 5 Vpp sine wave at 2.22 MHz. Potential applications for development of a TCTB-arranged 2D pMUT array include ultrasonic medical imaging, ultrasonic communication, ultrasonic range-finding and handwriting input systems.

31-mode piezoelectric micromachined ultrasonic transducer with PZT thick film by granule spraying in vacuum process

A piezoelectric micromachined ultrasonic transducer (pMUT) is an ideal device for portable medical diagnosis systems, intravascular ultrasound systems, and ultrasonic cameras because of its favorable characteristics including small size, acoustic impedance matching with the body, low power consumption, and simple integration with the systems. Despite these advantages, practical applications are limited because of insufficient acoustic pressure of the pMUT caused by the thin active piezoelectric layer. Here, we report the fabrication of a thick piezoelectric Pb(Zr,Ti)O3 (PZT) film-based pMUT device having high deflection at low driving voltage using the granule spraying in vacuum (GSV) process. Pre-patterned high-density thick (exceeding 8 μm) PZT films were grown on 6-inch-diameter Si/SiO2/Ti/Pt silicon-on-insulator wafers at room temperature at a high deposition rate of ∼5 μm min−1. The fabrication process using the proposed GSV process was simple and fast, and the deflection of the pMUT exhibited a high...

Mechanosensitive channel stimulation system using low-intensity ultrasound by piezoelectric micromachined ultrasonic transducer array

In this research, piezoelectric micromachined ultrasonic transducer (pMUT) array was used for stimulation of mechanosensitive channel of HEK293T cells. The fabricated pMUT array was made by microelectromechanical system (MEMS) technology such as photo process, etching, sputtering, and sol-gel method. The resonance frequency and acoustic positive peak pressure were 2.07 MHz and 3.94 kPa, respectively. The proposed system can be used for ultrasonic stimulation and the result can be confirmed using fluorescence microscope by observing the cation changing in real-time. The cells were treated by fluorescence staining and transient receptor potential cation channel subfamily V member 1 (TRPV1) channel inserting. The Ca+ ion level of stimulated cell was changed by ultrasound. The result showed mechanosensitive channel was activated by ultrasound stimulation and observed influx of Ca+ ion in real-time.

A study on the beamforming system with reconfigurable focusing depth for ultrasound-enhanced thrombolysis

In order to dissolve clots within blood vessels located in various parts of the human body with one sonothrombolysis application, the device employed should be able to control the focal depth where acoustic energy is focused. This paper presents such an ultrasound beamforming system with reconfigurable focal depth. It consists of an annular piezoelectric micromachined ultrasonic transducer (pMUT) array of 1 cm radius, and a beamforming unit that is composed of an ARM processor and a driving circuit. The measured peak intensity at the focal point of 13 mm is 1.35 W/cm2, and the average intensity of the -3 dB focal dimension from the peak intensity is 933 mW/cm. The proposed system operating at 1.21 MHz could be used for ultrasound-accelerated thrombolysis with an intensity that is above typical diagnostic levels at the focusing point, and also with a reconfigurable focusing depth.

Energy and thermal distribution under the skin during ultrasound power transfer

Energy distribution under the human skin during ultrasound power transfer using a 15×15 MEMS transducer array with 2.2 MHz driving frequency is presented in this paper. When the surface pressure of the array element is 96 kPa, intensity at 2 mm under the skin is 0.96 W/cm2; intensity increases to 24 W/cm2 when the surface pressure increases to 0.48 MPa. In other words, the simulation results show that the larger the surface pressure, the larger the intensity. The simulated and the measured power density values at 7 mm in the vertical direction of the transducer surface in degassed water are 96.72 mW/cm2 and 94.08 mW/cm2, respectively. Temperature change due to ultrasound radiation on the skin is discussed, and the feasibility of ultrasonic power transfer for implantable medical devices specially implanted just underneath the skin is presented.