Chuang Yuan Lee

Electrical Frequency Tuning of Film Bulk Acoustic Resonator

This paper describes the design, fabrication, and measurement of an electrically tunable film bulk acoustic resonator (FBAR) that is formed by integrating FBAR with an electrostatic microelectromechanical systems actuator. Around 1.47% tuning of the series resonant frequency ( Deltaf cong 22.5 MHz) at 1.5 GHz is experimentally obtained with an electrostatic actuation voltage of 7 V. This is the highest frequency tuning reported for FBAR operating at above 1 GHz without any extra power consumption. Two integration approaches of FBAR and air-gap capacitor are presented and compared, in terms of fabrication process and Q factor. The approach that minimizes any possible energy loss in the acoustic wave propagation path shows a quality factor (160-304) significantly higher than the one having a capacitor right on top surface of the FBARs piezoelectric film. Furthermore, we have characterized the electrical tuning of FBAR through piezoelectric stiffening due to an applied DC electric field and report a linear frequency shift of about -8 ppm/V at 3.4 GHz.

Acoustic Ejector with Novel Lens Employing Air-Reflectors

This paper describes a novel droplet ejector with an acoustic lens employing air-reflectors. The lens focuses the acoustic beams at the liquid surface, and facilitates uniform and consistent droplet ejections. This acoustic ejector requires no nozzle, nor heat for actuation, but uses a novel lens. When excited with RF pulses (7μs pulsewidth) of 18 MHz (corresponding to the fundamental thickness-mode resonant frequency), the ejector ejects uniform droplets of 70 μm in diameter at a rate up to 10 kHz. The ejector is integrated with reservoirs and channels on a single chip, and is shown to produce continuous and stable ejections without any liquid refilling or frequency tuning.

Droplet-Based Microreactions With Oil Encapsulation

This paper reports a microreaction technology for biochemical assay using nanoliter droplets encapsulated inside oil droplets. Microreaction chambers are constructed on a glass substrate by accumulating oil droplets that are dispensed by a directional droplet ejector. Droplets of different aqueous reagents are then directionally ejected (by other directional droplet ejector adjacent to the oil droplet ejector) into the oil microchambers for parallel and combinatory analysis. Because the reagents are encapsulated in oil, the evaporation rate is reduced by several orders of magnitude, and only small amounts of reagents are required for each assay. The microchamber size and the reagent amount are digitally controlled by the number of ejected oil and reagent droplets, respectively. The ejectors for oil and reagents have been integrated on a single chip so that each assay is performed efficiently without any mechanical movement and alignment. We have carried out both physical and chemical microreactions with this method and observed a negligible difference in response from conventional macroreactions.

HBAR-Based 3.6 GHz oscillator with low power consumption and low phase noise

We have designed and built 2 oscillators at 1.2 and 3.6 GHz based on high-overtone bulk acoustic resonators (HBARs) for application in chip-scale atomic clocks (CSACs). The measured phase noise of the 3.6 GHz oscillator is -67 dBc/Hz at 300 Hz offset and -100 dBc/Hz at 10 kHz offset. The Allan deviation of the free-running oscillator is 1.5 times 10-9 at one second integration time and the power consumption is 3.2 mW. The low phase noise allows the oscillator to be locked to a CSAC physics package without significantly degrading the clock performance.

Subpicoliter droplet generation based on a nozzle-free acoustic transducer

This letter reports picoliter liquid droplet generation using an orifice-free acoustic ejector operating at its harmonic frequencies. For an acoustic ejector working at the thickness-mode resonance, the droplet size is primarily determined by the acoustic wavelength, which is proportional to the piezoelectric substrate thickness. In our design, we do not need to lap the bulk piezoelectric lead zirconate titanate (PZT) substrate or deposit high temperature processing PZT thin film, but we use harmonic frequencies of the bulk form to reduce the wavelength. The fabricated acoustic ejector with a size of 1200×1200μm2 has been shown to be very effective up to the ninth harmonic (180MHz), continuously ejecting ∼10μm diameter droplets, corresponding to droplet volumes as small as 0.5pl.

Multi-Cantilever-Driven Rotational Micrograting for MOEMS Spectrometer

For the purpose of detecting biological fluorescence, a rotational actuator with integrated diffraction grating is designed as the central part of a MOEMS spectrometer. In order to produce scanning with a lithographically defined micrograting, angular displacement is produced with multiple balanced beams placed in opposition around a semi-floating pivot point. Piezoelectrically driven, the beams rotate a suspended micro grating linearly with voltage, directly tuning the angularly spread spectral outputs. The design advantages, optimizations and fabrication are discussed. The fabricated actuator is used in a fluorescence scanning of paper cellulose fibers and Rhodamine B dye, and shown to be effective in rotating a diffraction grating for fluorescence spectroscopy.

Nanoliter droplet coalescence in air by directional acoustic ejection

This letter presents a controlled coalescence of nanoliter liquid droplets in air by acoustic directional ejections. An asymmetrical electric field is created within a piezoelectric transducer to produce lopsided acoustic waves, which are focused (through a lens based on the innate impedance mismatch between solid and gas) onto a spot on the liquid surface. The focused acoustic beam is shown to obliquely eject 80-μm-diameter droplets at a traveling speed of 2.3m∕s. Up to four such obliquely ejected droplets coalesce in air into a single droplet, which then continue to travel, rotating at 16000rad∕s and producing effective micromixing in air.

Surface micromachined GHz tunable capacitor with 14:1 continuous tuning range

This paper reports a new simply-supported bridge structure and its use for GHz tunable capacitor application. Unlike traditional MEMS bridges with fully-clamped boundary condition (B.C.) at the anchors, the new bridge structure has simply-supported B.C. Through the implementation of a simply-supported bridge driven by two 100-mum-long ZnO-actuated cantilevers, a compact surface-micromachined tunable capacitor has been fabricated on a single chip without any warping, and shown to be capable of a 1,400% continuous tuning from 0.13 pF to 1.82 pF.

Airborne Particle Generation Through Acoustic Ejection of Particles-In-Droplets

This article reports a method to produce airborne particles by generating uniformly sized droplets that contain particles, where the droplets are made with an acoustic ejector that does not need any small orifice or nozzle which might become clogged. We demonstrate stable and continuous ejection for more than 10 minutes of 14-μ m droplets containing 1-μ m polystyrene latex (PSL) particles at a concentration of 1% solids. There was no indication of clogging. We have demonstrated ejection of droplets containing PSL at rates up to 3,000 droplets/s (90,000 1-μ m-PSL particles/s). This method should produce, at a known rate, (1) uniform particles of known volume when the particles are soluble in the liquid and/or (2) particles with a statistical distribution (e.g., Poisson distribution) when the particles are aggregates of primary particles. The method should be useful for aerosol generation systems requiring no volatile organic compounds (VOC).

Surface micromachined, complementary-metal-oxide-semiconductor compatible tunable capacitor with 14:1 continuous tuning range

This letter reports a surface micromachined, complementary-metal-oxide-semiconductor compatible tunable capacitor utilizing a simply supported bridge structure, unlike traditional microelectromechanical-system bridges that use fully clamped boundary condition at the anchors. Through the implementation of a simply supported bridge driven by two 100-μm-long ZnO-actuated cantilevers, a compact tunable capacitor has been fabricated on silicon without any warping and shown to be capable of a 1400% continuous tuning from 0.13to1.82pF.