Publications

Abstract not provided.

We report measurements of the power handling and intermodulation distortion of piezoelectric contour mode resonators and filters operating near 500 MHz. The output power capability scales as the inverse of the motional impedance squared, and the power handling of resonator filter circuits scales with the number of resonators combined in series and parallel. Also, the third-order intercept depends on the measurement tone spacing. Individual AlN resonators with 50 Ω motional impedance demonstrate output power capability of +10 dBm and OIP3 > +20 dBm, while an eight resonator filter demonstrates output power handling of +14 dBm and a OIP3 > +32 dBm. © 2011 IEEE.

Frequency tuning of aluminum nitride (AlN) micromechanical resonators has been demonstrated by reactance manipulation via termination with variable capacitors. Shunting one electrode with a variable capacitor in a 13 MHz fourth overtone length-extensional mode resonator effected resonator stiffening to yield a ∼600 ppm frequency shift. Tunability could be further increased by dedicating two electrodes for tuning doubling the frequency tuning range to ∼1500 ppm. A tunable bandwidth balun filter has been constructed by parallel coupling of independently tunable resonators demonstrating almost three-fold increase in the bandwidth from 12 kHz to 33 kHz. Also a voltage-controlled frequency tuning printed circuit board (PCB) was implemented. © 2011 IEEE.

Abstract not provided.

We report a new wafer-level packaging technology for miniature MEMS in a hermetic micro-environment. The unique and new feature of this technology is that it only uses low cost wafer-level processes such as eutectic bonding, Bosch etching and mechanical lapping and thinning steps as compared to more expensive process steps that will be required in other alternative wafer-level technologies involving thru-silicon vias or membrane lids. We have demonstrated this technology by packaging silicon-based AlN microsensors in packages of size 1.3 1.3 mm2 and 200 micrometer thick. Our initial cost analysis has shown that when mass produced with high yields, this device will cost $0.10 to $0.90. The technology involves first preparing the lid and MEMS wafers separately with the sealring metal stack of Ti/Pt/Au on the MEMS wafers and Ti/Pt/Au/Ge/Au on the lid wafers. On the MEMS wafers, the Signal/Power/Ground interconnections to the wire-bond pads are isolated from the sealring metallization by an insulating AlN layer. Prior to bonding, the lid wafers were Bosch-etched in the wirebond pad area by 120 um and in the center hermetic device cavity area by 20 um. The MEMS and the lid wafers were then aligned and bonded in vacuum or in a nitrogen environment at or above the Au-Ge Eutectic temperature, 363C. The bonded wafers were then thinned and polished first on the MEMS side and then on the lid side. The MEMS side was thinned to 100 ums with a nearly scratch-free and crack-free surface. The lid side was similarly thinned to 100 ums exposing the wire-bond pads. After thinning, a 100 um thick lid remained over the MEMS features providing a 20 um high hermetic micro-environment. Thinned MEMS/Lid wafer-level assemblies were then sawed into individual devices. These devices can be integrated into the next-level assembly either by wire-bonding or by surface mounting. The wafer-level packaging approach developed in this project demonstrated RF Feedthroughs with 0.3 dB insertion loss and adequate RF performance through 2 GHz. Pressure monitoring Pirani structures built inside the hermetic lids have demonstrated the ability to detect leaks in the package. In our preliminary development experiments, we have demonstrated 50% hermetic yields. © 2011 IEEE.

Abstract not provided.

Abstract not provided.

Phononic crystals (PnCs) are acoustic devices composed of a periodic arrangement of scattering centers embedded in a homogeneous background matrix with a lattice spacing on the order of the acoustic wavelength. When properly designed, a superposition of Bragg and Mie resonant scattering in the crystal results in the opening of a frequency gap over which there can be no propagation of elastic waves in the crystal, regardless of direction. In a fashion reminiscent of photonic lattices, PnC patterning results in a controllable redistribution of the phononic density of states. This property makes PnCs a particularly attractive platform for manipulating phonon propagation. In this communication, we discuss the profound physical implications this has on the creation of novel thermal phenomena, including the alteration of the heat capacity and thermal conductivity of materials, resulting in high-ZT materials and highly-efficient thermoelectric cooling and energy harvesting. © 2011 SPIE.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Recently reported narrow bandwidth, <;2%, aluminum nitride microresonator filters in the 100-500 MHz range offer lower insertion loss, 100x smaller size, and elimination of large external matching networks, when compared to similar surface acoustic wave filters. While the initial results are promising, many microresonators exhibit spurious responses both close and far from the pass band which degrade the out of band rejection and prevent the synthesis of useful filters. This paper identifies the origins of several unwanted modes in overtone width extensional aluminum nitride microresonators and presents techniques for mitigating the spurious responses.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

A two-dimensional phononic crystal (PnC) that can operate in the GHz range is created in a freestanding silicon substrate using NanoFIBrication (using a focused ion beam (FIB) to fabricate nanostructures). First, a simple cubic 6.75 x 6.75 ?m array of vias with 150 nm spacing is generated. After patterning the vias, they are backfilled with void-free tungsten scatterers. Each via has a diameter of 48 nm. Numerical calculations predict this 2D PnC will generate a band gap near 22 GHz. A protective layer of chromium on top of the thin (100 nm) silicon membrane confines the surface damage to the chromium, which can be removed at a later time. Inspection of the underside of the membrane shows the vias flaring out at the exit, which we are dubbing the 'trumpet effect'. The trumpet effect is explained by modeling the lateral damage in a freestanding membrane.

Abstract not provided.