Search

In this work we demonstrate high values of electromechanical coupling coefficient ( $k_{t}^{2}$ ) exceeding 4.9% in 1- $\mu \text {m}$ thick Aluminum Nitride (AlN) two-dimensional-mode resonators (2DMRs) operating around 3.2 GHz. Such a high $k_{t}^{2}$ -value, which is attained thanks to the transduction of the resonators through both the $d_{33}$ and $d_{31}$ piezoelectric coefficients of AlN, enables low-power oscillators and low insertion-loss filters, operating in the Super-High-Frequency (SHF) range.

This paper presents an apodization technique to suppress spurious modes in aluminum nitride (AlN) lamb wave resonators. The apodization pattern proposed is a 5-vertex irregular polygon shape. Three dimensional (3D) simulations based on finite element methods (FEM) show that the presented apodization shape can effectively suppress both transverse and longitudinal spurious modes. To validate the concept, a lamb wave resonator operating at 2.1 GHz with the apodization applied is fabricated in house. The measured impedance response of the resonator with apodization demonstrates complete removal of the spurious modes with frequencies higher than the series resonant frequency (fs), and negligible spurs at the lower side of fs, though the effective coupling coefficient $(\mathbf{k}^{2}_{eff})$ is slightly degraded.

This work presents the implementation of two 4thorder ladder type integrated filters consisting of modified laterally coupled alternating thickness (LCAT) mode resonators. These modified LCAT resonators based on aluminum nitride (AIN) thin film achieve the coupling coefficient $(k_{eff}^{2})$ ranging from 2.8% to 3.8%. The two filters operate at 2.47GHz and 2.52GHz, and achieve average insertion losses of 2.64dB and 2.3dB within 40MHz passband bandwidth, respectively. The resonators composing the two filters share the same material stack and the frequency difference is achieved by patterning the electrodes into different pitches, thus integrating these two filters on the same wafers requires 2 masks less as compared with fabricating one discrete FBAR filter whose frequency is tuned by additional layer of mass loading. Such features render this technology a competitive candidate for integrated duplexers and filters for high frequency band filtering applications.

In a checker patterned lamb wave resonator, electrode patches with the square, diamond or round shape are usually arranged in the way that one electrode is surrounded by a group of four patches with an opposite electrical polarity to excite two-dimensional (2D) lamb waves. This arrangement of the electrodes makes the signal routing quite challenging. The existing approach is to supply the electrical signal from a thin anchor, then go to a long and narrow wire at the edge of the resonator plate before it is distributed to multiple rows/columns of the electrode patches. The drawback of this approach is firstly high resistive loss of the long wire which degrades the $\text{Q}$ factor and secondly the distorted acoustic field excitation due to the non-uniform distribution of the electric signal. This work presents a novel distributed anchor design which does not only improve the mechanical strength of the thin film resonator, but also reduce the resistive loss by embedding the electrical routing in each anchor. This concept is applied to a checker patterned resonator operating at 2.4GHz. The measurement results show the reduction of series resistance from 16Ω for the corner anchor design to 5.6Ω for the distributed anchor design, corresponding to a significant quality factor improvement.

This work reports a spurious mode free AlN plate mode resonator with high figure-of-merit (FoM) operating at 3.5GHz. The reported resonator, which comprises of two sets of $0.27\ \mu \text{m}$ -thick top molybdenum (Mo) interdigitated electrodes (IDE) fingers attached to a layer of $1\ \mu \text{m}$ -thick AlN, has an IDE pitch $(p)$ of 1m and a finger width $(w)$ of $0.5\ \mu \text{m}$ defined by optical photolithography. Besides reducing the fabrication process complexity, having only IDE on the top surface of AlN in the fabrication process also increases the acoustic phase velocity $(v_{p})$ as a result of the exclusion of bottom Mo IDE which has a lower acoustic phase velocity than AlN, thus relaxing the lithographic and etching requirement of IDE pitch. Measurement results show that the resonant frequency $(f)$ is around 3.5GHz, with a spurious mode free frequency response over a 1GHz frequency range from $3GHz$ to $4\text{GHz}$ . The effective electromechanical coupling coefficient $(k_{eff^{2}})$ is 3.15% and the Q factor $(Q)$ is 1000, yielding an $f\cdot Q$ product of $3.5\times 10^{12}$ and $k_{eff^{2}}\cdot Q$ of 31.5, respectively. Together with the series resistance of $3.11\Omega$ and the parallel resistance of $874\Omega$ , the proposed plate mode resonator is a promising candidate for mobile Band 42 applications.

The silicon probe with highly P-doped Si electrodes was realized on 8 inch SOI wafer through standard CMOS process. After additional coatings of nano-composite (CNTs + Au nanoparticles) on silicon electrodes, the functionality of neural recording was verified with a low noise level (< 20 μV) during in vivo recording on rat brain. With built-in silicon nanowires (SiNWs) based piezoresistiors connected in full bridge structure, the capability of monitoring probe mechanical behavior was firstly examined with the probe buckling experiments and further proven through in vivo implantations on rat brain. Besides the large buckling mechanics (during probe insertion), the physiological brain micro-motion (e.g. caused by respiration) was successfully picked up by integrated SiNWs strain sensors. The integrated neural device (including both neural electrode and localized strain sensor) provides the possible research platform to practically understand the correlation between the recorded electrical neural signal and the brain micro-motion.

Recent work with cyclical electrical field-flow fractionation systems has shown promise for the technique as a separation and analysis tool, but little is understood about how the carrier composition in the system affects its capabilities. The electrical properties of microscale CyElFFF systems change when the carrier ionic conditions are altered, and it is well known that the effects of increasing ionic strength carriers on retention in normal ElFFF systems are severe. Specifically, retention levels fall significantly. Accordingly, this work seeks to understand the effect that increasing carrier ionic strength in CyElFFF has on nanoparticle retention in the channels. The retention of polystyrene particles in the CyElFFF microsystem is reported at various ionic strengths of ammonium carbonate and at a variety of pH levels. The experiments are compared to the theory of CyElFFF available in the literature. The results indicate that the ionic strength of the carrier has a significant impact on retention and that high ionic strength carrier solutions lead to poor performance of the CyElFFF system. These results have significant impact on the possible uses of the technique and its applications, especially in the biomedical arena.

Cyclical electrical field flow fractionation (Cy/ElFFF) is demonstrated in a standard electrical field flow fractionation (ElFFF) channel for the first time. Motivation for the use of alternating current (AC) fields in a traditionally direct current (DC) technique are discussed. The function of the system over a wide range of operating conditions is explored and challenges associated with various operating conditions reported. Retention of polystyrene nanoparticle standards is accomplished and the effect of varying parameters of the applied field, such as voltage and frequency, are explored. The first separations using this technique are demonstrated. The experimental results are compared to analytical models previously reported in the literature. The general trend of the experimental results is similar to those predicted in theoretical models and possible reasons for discrepancies are elucidated. Suggestions are made for improving the separation and analysis method, and possible applications explored.

Cyclical electrical field flow fractionation (CyElFFF) is a variation on electrical field flow fractionation (ElFFF) where cyclical electrical fields are used instead of steady DC fields to increase the effective field experienced by particles in the flow channel. Even though the effective field increases more than 20-fold compared to normal ElFFF, the retention and resolution in CyElFFF has not been shown to be better than in ElFFF. In this paper we report how one can optimize operational parameters in CyElFFF to obtain good retention and resolution in CyElFFF. The effects of offset voltage, frequency, flowrate, concentration of particles and sample size on retention, resolution and retained peak/void peak ratio have been observed. The results obtained from these experiments were analyzed and suggestions have been made to improve both retention and resolution. A 4-fold improvement in retention without a significant increase in band broadening is reported.

We present the fabrication of highly P-doped single crystal silicon electrodes on a silicon probe through complementary metal-oxide-semiconductor (CMOS)-compatible processes. The electrode with diameter of 50 μm and a separation of 200 μm is designed for recording/stimulating purposes. Electrochemical impedance spectroscopy indicates that the interfacial impedance of silicon electrodes at 1 KHz is 2.5 ± 0.4 MΩ, which is equivalent to the result reported from the gold (Au) electrode. To further enhance the charge storage capacity, composites of multi-wall carbon nanotubes (MWCNTs) and Au nanoparticles are electroplated onto the highly P-doped silicon electrode after surface roughness treatments. With optimized electroplating processes, MWCNTs and Au nanoparticles are selectively coated onto the electrode site with only a minimum enlargement in physical diameter of electrode (

A microscale cyclical electrical field flow fractionation (CyElFFF) channel is characterized with regard to the effect of various operating parameters and comparison made to recent theoretical developments. Challenges associated with various operating conditions are reported along with some of the optimized operating parameters. The effect of retention wall choice, an offset voltage, relaxation steps, and flow rates, along with the basic operating parameters of voltage, frequency, and electrophoretic mobility are reported. Retention of polystyrene nanoparticle standards is accomplished and the first separations using this technique in a microscale system are also demonstrated. Relaxation steps and offset voltages are found to be effective in eliminating early peaks and in improving plate heights. Plate heights were also found to decrease with increasing flow rates, which is the opposite of the behavior seen in most existing chromatographic systems. The experimental results are compared to the analytical and empirical models of CyElFFF and found to be compatible. Suggestions are made for improving the separation and analysis methods used with CyElFFF.