Jon Oiler

Film bulk acoustic-wave resonator based ultraviolet sensor

This letter described ultraviolet (UV) radiation sensing with ZnO based film bulk acoustic-wave resonator (FBAR). The resonant frequency upshifted when there was UV illumination on the FBAR. For 365 nm UV light, the frequency upshift was 9.8 kHz with an intensity of 600 μW/cm2, and the detection limit of the sensor was 6.5 nW. The frequency increase in the FBAR UV sensor was proposed to be due to the density decrease in ZnO film upon UV illumination. When UV was incident on the ZnO film, it can cause oxygen desorption from the ZnO surface, resulting in density decrease in the film. This study has proven the feasibility of detection of low intensity UV using ZnO film based FBAR.

Film Bulk Acoustic-Wave Resonator Based Relative Humidity Sensor Using ZnO Films

This article described relative humidity RH sensing using a ZnO-based film bulk acoustic-wave resonator FBAR . The resonant frequency of the FBAR decreased in a two-stage manner as the RH increased. For low RH, a frequency downshift of 2.2 kHz per 1% RH change was observed. This effect was attributed to water molecules replacing the adsorbed oxygen on the ZnO surface, thus increasing the density of the film. For high RH, a frequency downshift of 8.5 kHz per 1% RH change was obtained, which was due to the mass loading effect of the water layers formed on the ZnO surface.

Development of a micro seismometer based on molecular electronic transducer technology for planetary exploration

Molecular Electronic Transducer (MET) is a recent technology applied in seismic instrumentation that proves highly beneficial to planetary seismology. MET is an electrochemical cell that senses the movement of liquid electrolyte between electrodes by converting it to the output current. Seismometers based on MET technology are attractive for planetary applications due to their high sensitivity, low noise floor, small size, lack of fragile moving parts and independence on the direction of sensitivity axis. This paper reports an approach to build a micro MET seismometer using Micro-Electro-Mechanical Systems (MEMS) techniques. We have reduced the MET cell size, resulting in internal dimensions close to 1 micrometer (μm). The employment of MEMS improves the sensitivity up to 400V (m/s2) and reproducibility of the device, and has reached 1 micro Gee (1.0 ×10-5 m/s2/√Hz) noise level at 1 Hz.

Localized Parylene-C bonding with reactive multilayer foils

This paper describes a novel bonding technique using reactive multilayer Ni/Al foils as local heat sources to bond Parylene-C layers to another Parylene-C coating on a silicon wafer. Exothermic reactions in Ni/Al reactive multilayer foils were investigated by x-ray diffraction (XRD) and differential scanning calorimetry. XRD measurements showed that the dominant product after exothermic reaction was ordered B2 AlNi compound. The heat of reaction was calculated to be ?57.9?kJ?mol?1. A numerical model was developed to predict the temperature evolution in the parylene layers and silicon wafers during the bonding process. The simulation results revealed that localized heating occurred during the reactive foil joining process. Our experimental observation showed that the parylene layer was torn when the bond was forcefully broken, indicating a strong bond was achieved. Moreover, leakage test in isopropanol alcohol showed that reactive foil bonds can withstand liquid exposure. This study demonstrated the feasibility of reactive foil joining for broad applications in bio-microelectromechanical systems and microfluidic systems.

The effects of relative humidity and reducing gases on the temperature coefficient of resonant frequency of ZnO based film bulk acoustic wave resonator

This study describes the influence of relative humidity (RH) and reducing gases on the temperature coefficient of resonant frequency (TCF) of ZnO-based film bulk acoustic wave resonator (FBAR). Upon exposure to moisture or reducing gases, the TCF of FBAR decreased. Water molecules can replace adsorbed oxygen on the ZnO surface. This process was less effective at high temperature, resulting in a lower TCF in high RH. Reducing gases, such as acetone, can reduce the density of ZnO through reaction with the adsorbed oxygen, leading to a lower TCF.

Acetone sensor based on Film Bulk Acoustic Resonator

This paper described acetone sensing using ZnO based Film Bulk Acoustic Resonator (FBAR). The resonant frequency of the FBAR increased as the concentration of acetone increased. The detection limit of acetone was around 4 ppm. The density decrease of the ZnO induced by releasing carbon dioxide generated from the reaction between acetone and the adsorbed oxygen ions on the ZnO surface was assumed to be responsible for the frequency upshift. Upon exposure to ethanol (a major environmental crosstalk for traditional acetone sensors), an opposite response (decrease of resonant frequency) was observed. Water was generated and absorbed on the ZnO surface during the ethanol sensing process. Thus, the density of the ZnO film increased, resulting in a frequency drop. FBAR sensor possessed the unique ability to distinguish acetone from ethanol due to their different reaction behaviors.

Reactive multilayer foils for MEMS wafer level packaging

We present a novel room temperature bonding technique using reactive multilayer Ni/Al foils as local heat sources to heat intermediate adhesion layers and thus bond silicon wafers to form wafer level package. Exothermic reactions in Ni/Al multilayer foils were investigated by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). XRD measurements showed that the dominant product after the exothermic reaction was ordered B2 AlNi compound. The heat of reaction was calculated to be −57.9 kJ/mol. Two bonding approaches were realized. One used AuSn solder as an intermediate layer to bond two silicon wafers together; the other approach conducted bonding between Parylene-C and silicon wafers with a thin Parylene-C coating. Either silicon or Parylene-C was torn when the bond was forcefully broken, indicating a strong bond was achieved. Moreover, leakage test in isopropanol alcohol (IPA) showed that the joints possessed good hermeticity to liquid. Numerical simulation results demonstrated that both localized heating and rapid cooling occurred during the bonding process, which made reactive foil bonding an ideal method for MEMS wafer level packaging applications.

The effects of ultraviolet radiation, humidity and reducing gases on the temperature coefficient of resonant frequency of ZnO based film bulk acoustic-wave resonator

This paper described the influence of ultraviolet (UV) radiation, relative humidity (RH) and reducing gases on the temperature coefficient of resonant frequency (TCF) of ZnO based Film Bulk Acoustic-wave Resonator (FBAR). Under UV illumination, the TCF of the FBAR increased. This was attributed to the adsorption of oxygen due to the electrons generated by UV absorption. Water molecules can replace adsorbed oxygen on the ZnO surface. However at high temperature, less water can be sustained by the ZnO film due to its energetically unstable nature. In this way, the TCF in high RH became smaller. When reducing gases, such as acetone, were exposed to FBAR, a smaller TCF was observed.

Lateral Field Excitation Film Bulk Acoustic Resonator as infrared sensor

This paper investigated an infrared (IR) sensitive Lateral Field Excitation (LFE) Film Bulk Acoustic Resonator (FBAR). The resonant frequency of the LFE FBAR decreased when there was IR (peak wavelength at 750nm) illumination on the device. A linear relationship between the resonant frequency and the IR intensity was obtained with a detection limit of 9 µW/mm2. The sensing mechanism is attributed to the fact that the Youngs modulus of the resonator material (ZnO) depends on temperature. In general, for a resonator operating in a bulk mode, a change in the Youngs modulus translates into a shift of the resonant frequency. Thus, the sensitivity of the FBAR relies on its temperature coefficient of resonant frequency (TCF). Thickness Field Excitation (TFE) FBAR possessed a larger TCF. However, it showed a lower sensitivity to IR compared with the LFE FBAR. This was due to the reflection of IR radiation from the top electrode on the TFE FBAR.

Directional acoustic underwater thruster

This study describes a tested prototype for a controllable directional underwater thruster with no moving parts. During operation, a high-intensity acoustic wave creates directional water jets and the device moves itself in the opposite direction. When the underwater thruster moves along a non-vertical angle, it can produce straight backward thrust of 2.3 mN and lateral thrust of 0.6 mN in parallel with the device surface, with a total thrust-to-weight ratio of 2:1. To enhance the acoustic streaming effect, a self-focusing acoustic transducer (SFAT) with air reflectors is used to focus the acoustic wave.