Jinying Zhang

Numerical and experimental investigation of kerf depth effect on high-frequency phased array transducer.

BACKGROUNDnHigh-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the structure design and fabrication of the kerfed ultrasonic array is quite challenging when very high frequency (≥100MHz) is required.nnnOBJECTIVE AND METHODnHere we investigate the effect of kerf depth on the performances of array transducers. A finite element tool, COMSOL, is employed to simulate the properties of acoustic field and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance. Furthermore, Inductively Coupled Plasma (ICP) deep etching process is used to etch 36°/Y-cut lithium niobate (LiNbO(3)) crystals and the limitation of etching aspect ratio is studied. Several arrays with different profiles are realized under optimized processes. At last, arrays with a pitch of 25μm and 40μm are fabricated and characterized by a network analyzer.nnnRESULTSnKerf depth plays an important role in the performance of the transducer array. The crosstalk is proportional to kerf depth. When kerf depth is more than 13μm, the array with crosstalk less than -20dB, which is acceptable for the real application, could provide a desired resolution. Compared to beam focusing, kerf depth exhibits more effect on the beam steering/focusing. The lateral pressure distribution is quantitatively summarized for four types of arrays with different kerf depth. The results of half-cut array are similar to those of the full-cut one in both cases of focusing and steering/focusing. The Full-Width-at-Half-Maximum (FWHM) is 55μm for the half-cut array, and is 42μm for the full-cut one. The 5-μm-cut array, suffering from severe undesired lobes, demonstrates similar behaviors with the no-cut one. ICP process is used to etch the 36°/Y-cut LiNbO(3) film. The aspect ratio of etching profile increases with the kerf width decreasing till it stops by forming a V-shaped groove, and the positive tapered profile angle ranges between 62° and 80°. If the mask selectivity does not limit the process in terms of achievable depth, the aspect ratio is limited to values around 1.3. The measurement shows the electrical impedance and crosstalk are consistent with the numerical calculation.nnnCONCLUSIONnThe numerical results indicate that half-cut array is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays. In fact, the minimum pitch that could be obtained is around 25μm, equivalent to a pitch of 1.6λ, with a kerf depth of 16μm under the optimized ICP parameters.

Modelling and simulation of high-frequency (100 MHz) ultrasonic linear arrays based on single crystal LiNbO3

BACKGROUNDnHigh-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the fabrication of conventional backing-layer structure, which requires a pitch (distance between the centers of two adjacent elements) of half wavelength in medium, is really a great challenge.nnnOBJECTIVE AND METHODnHere we present an alternative buffer-layer structure with a silicon lens for volumetric imaging. The requirement for the size of the pitch is less critical for this structure, making it possible to fabricate high-frequency (100MHz) ultrasonic linear array transducers. Using silicon substrate also makes it possible to integrate the arrays with IC (Integrated Circuit). To compare with the conventional backing-layer structure, a finite element tool, COMSOL, is employed to investigate the performances of acoustic beam focusing, the influence of pitch size for the buffer-layer configuration, and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance.nnnRESULTSnFor a 100MHz 10-element array of buffer-layer structure, the ultrasound beam in azimuth plane in water could be electronically focused to obtain a spatial resolution (a half-amplitude width) of 86μm at the focal depth. When decreasing from half wavelength in silicon (42μm) to half wavelength in water (7.5μm), the pitch sizes weakly affect the focal resolution. The lateral spatial resolution is increased by 4.65% when the pitch size decreases from 42μm to 7.5μm. The crosstalk between adjacent elements at the central frequency is, respectively, -95dB, -39.4dB, and -60.5dB for the 10-element buffer, 49-element buffer and 49-element backing arrays. Additionally, the electrical impedance magnitudes for each structure are, respectively, 4kΩ, 26.4kΩ, and 24.2kΩ, which is consistent with calculation results using Krimholtz, Leedom, and Matthaei (KLM) model.nnnCONCLUSIONnThese results show that the buffer-layer configuration is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays dedicated to volumetric imaging.

Dielectric microwave properties of Si-integrated pulsed laser deposited (Ba, Sr)TiO3 thin films up to 110 GHz

Ba0.6Sr0.4TiO3 thin films with a thickness of 339u2009nm are deposited directly on the high resistivity silicon through pulsed laser deposition. Coplanar waveguides with a slot width of 4.5u2009μm are designed to extract the complex permittivity of ferroelectric thin film in the frequency range from 1 GHz to 110u2009GHz. A fast three-dimensional (3D) finite element method (FEM) model is proposed to implement the permittivity extraction based on the propagation-constant matching, i.e., narrowing the difference between measured and simulated propagation-constants by adjusting the changeable permittivity in the fast 3D FEM model. In order to reduce the calculation overhead, the quasi transverse electromagnetic mode and conformal mapping analysis are introduced to realize the adjusting. The relative difference between measured and simulated propagation-constants is defined to describe the precision of the result. Experimental results show that the relative difference is less than 1.1%. The relative dielectric permittivit...

Power recovery from data line in avionic applications

In this paper, we propose a novel power recovery approach to reduce the mass of the cables installed in aircrafts. The power recovery unit harvests energy from data field bus which is recently presented to modify classical Avionics Full Duplex Ethernet (AFDX) networks, to power up the Smart Sensor Interface (SSI) module entirely. A top-down modeling approach in Verilog-A is used to build complex modules in the Power Conversion Chain (PCC) which makes power transfer and distribution possible. The effects of frequency and the size of capacitor reservoir on settling time and output voltage ripple are studied. Simulation results in system level prove that the proposed power recovery scheme could procure and deliver significant amount of power to SSI which makes the structure self-powered and therefore additional power lines are saved.

Enhanced performance of 17.7 GHz SAW devices based on AlN/diamond/Si layered structure with embedded nanotransducer

Surface acoustic wave (SAW) devices using embedded interdigital transducers (IDTs) on an AlN/diamond/Si layered substrate are fabricated, and their performances are investigated. The Sezawa mode is the dominant resonance with the highest resonant frequency up to 17.7u2009GHz, a signal amplitude of 20u2009dB, and an electromechanical coupling coefficient of 0.92%. Comparing these SAW devices with those having the conventional IDTs on the same layered structure, the output SAW power and resonant frequency of devices are improved by 10.7% and 1.1%, respectively, for the embedded IDT devices. This is because the different field distribution leads to the different Bragg reflection and phase velocity for the two types of IDTs. The radiation frequency characteristics indicate that the advantages of the embedded IDTs would be useful for high frequency, high power applications such as monolithic integrated millimeter-wave integrated circuit and high speed communications.

A novel power harvesting scheme for sensor networks in advanced Avionic applications

In this paper, we propose a novel power recovery approach to procure power required for sensor networks and reduce the mass of the cables installed in aircrafts. The power scheme harvests energy from data field bus which is recently presented to modify classical Avionics Full Duplex Ethernet (AFDX) networks, to power up the position sensors entirely. A top-down modeling approach in Verilog-A is used to build complex modules in the power conversion chain which makes power transfer and distribution possible. The effects of frequency and the size of the charge reservoir on settling time and output voltage ripple are studied. Simulation results in system level prove that the proposed power recovery scheme could procure and deliver significant amount of power to the position sensors and/or the intefacing circuits to the network. This makes the structure self-powered and may lead to significant saving in the mass of power distribution wiring throughout the plane.

A self-aligned mask-free fabrication process for high-frequency ZnO array transducer

High-frequency ultrasonic array transducers are essential for high resolution imaging in clinical analysis and Non Destructive Evaluation (NDE). However, the fabrication of piezoelectric array transducers is a great challenge due to the small features in elaborating piezoelectric array films. This paper describes a MEMS based self-aligned mask-free process for fabrication of ZnO linear array transducers of more than 100MHz. A four-step-rotation deposition approach is proposed and investigated, that improves the lateral growth in ZnO array deposition. The ratio of vertical to lateral growth is improved by 40% compared to one-step deposition method. The results prove that the reduction of the lateral growth helps to achieve full-kerfed ZnO array with smaller pitch.

Photonic crystal biosensors based on surface plasmons

Surface plasmon photonic crystals can couple the incident light with surface plasmons by the periodic array of holes on the metal film. In this paper, surface plasmon photonic crystals with periodic square array of hexagon holes were fabricated. The infrared optical properties in transmittance and reflectance of the devices were tested. A sharp peak of surface plasmon resonance was observed at the incident angles of 30° and 90°. The optical wavenumber shift at 30° incident angle was used to detect the reaction of antigen and antibody, and the line correlation between protein concentrations and wavenumber shifts were investigated. By the comparison of the results between 4 ¿m and 8 ¿m periodic arrays, the 4 ¿m periodic structure has better performance. Based on the results, the surface plasmon photonic crystals can be used as biosensors.

Development of Microcantilever Sensors for Liver Cancer Detection

Recently, microcantilever-based technologies are playing more and more important roles in early diagnosis of cancer due to their high sensitivity, fast response, low cost, small reagent consumption, portability, real-time, labelfree detection, and so on. However, in conventional cantilever sensors working on mass-loading principle, the change of stiffness coefficient k is neglected. This results in distinct error for mass detection. Some researchers tried a local immobilization method to eliminate the undesired effect of k. But the change of k in this method still brings unexpected error. An accurate theoretical model is needed to take the effect of k change into account in the local immobilization approach. A micro-cavity was designed in the free end of the cantilever for local antibodyimmobilization in our work, thus the adsorption-induced variation of k can be dramatically reduced compared to that caused by adsorption of the whole lever. In addition, an analytical model has been established to eliminate the effect of adsorption-induced lever stiffness change and has been applied to precise mass detection of cancer biomarker AFP, the detected AFP antigen mass (7.6 pg/ml) is close to the calculated one (5.5 pg/ml), two orders of magnitude better than the value by the fully antibody-immobilized cantilever sensor. These approaches will promote clinical application of the cantilever sensors in early diagnosis of cancer.

Embedded nanotransducer for ultrahigh-frequency SAW utilizing AlN/diamond layered structure

In this work, we report the development and realization of ultrahigh-frequency, high-performance nano interdigital transducers (n-IDTs) for generation of surface acoustic wave (SAW) on aluminum nitride (AlN)/diamond/Si substrates, where the metal fingers are embedded in the AlN film. The well-defined n-IDTs resolution down to 200 nm were obtained using electron beam lithography, inductively coupled plasma (ICP) etching and lift-off processing. The fabricated SAW resonators exhibit response at a ultrahigh-frequency range, as high as 9.94 GHz, with stronger intensities of S11 peaks compared with normal transducer devices. The good high-frequency characteristics of the embedded n-IDTs and compatibility with existing fabrication technologies pave the way for the realization of advanced sensors and monolithic integrated MMICs on AlN/diamond/Si substrates for the high frequency and high power applications.