MEMS Cantilever Sensor for THz Photoacoustic Chemical Sensing and Spectroscopy

Sensitive Microelectromechanical System (MEMS) cantilever designs were modeled, fabricated, and tested to measure the photoacoustic (PA) response of gasses to terahertz (THz) radiation. Surface and bulk micromachining technologies were employed to create the extremely sensitive devices that could detect very small changes in pressure. Fabricated devices were then tested in a custom made THz PA vacuum test chamber where the cantilever deflections caused by the photoacoustic effect were measured with a laser interferometer and iris beam clipped methods. The sensitive cantilever designs achieved a normalized noise equivalent absorption coefficient of 2.83x10-10 cm-1 W Hz-1/2 using a 25 µW radiation source power and a 1 s sampling time. Traditional gas phase molecular spectroscopy absorption cells are large and bulky. The outcome of this research resulted was a photoacoustic detection method that was virtually independent of the absorption path-length, which allowed the chamber dimensions to be greatly reduced, leading to the possibility of a compact, portable chemical detection and spectroscopy system

Toward a Flying MEMS Robot

The work in this thesis includes the design, modeling, and testing of motors and rotor blades to be used on a millimeter-scale helicopter style flying micro air vehicle (MAV). Three different types of motor designs were developed and tested, which included circular scratch drives, electrostatic motors, and comb drive resonators. Six different rotor designs were tested; five used residual stress while one design used photoresist to act as a hinge to achieve rotor blade deflection. Two key parameters of performance were used to evaluate the motor and rotor blade designs: the frequency of motor rotation and the angle of deflection achieved in the rotor blades. One successful design utilized a scratch drive motor with four attached rotor blades to try to achieve lift. While the device rotated successfully, the rotational frequency was insufficient to achieve lift-off. The electrostatic motor designs proved to be a challenge, only briefly moving before shorting out; nonetheless, lessons were learned. Comb drive designs operated over a wide range of high frequencies, lending them to be a promising method of turning a rotary MAV. None of the fabricated devices were able to achieve lift, due to insufficient rotational rates and low angles of attack on the rotor blades. With slight modifications to the current designs, the required rotational rates and rotor blade deflections would yield a viable MAV. The ultimate objective of this effort was to create an autonomous MAV on the millimeter scale, able to sense and act upon targets in its environment. Such a craft would be virtually undetectable, stealthily maneuvering and capable of precision engagement

Effects of SU-8 Cross-linking on Flip-chip Bond Strength When Assembling and Packaging MEMS

New methods to assemble, integrate, and package micro devices are always needed in attempts to simplify and expedite fabrication methods to maximize throughput. Our paper focuses on assessing SU-8 as a viable material for packaging and flip chip bonding processes for MEMS and micro devices. In this paper, we vary the level of cross- linking through post exposure bake (PEB) times and assess rectangular ring test structures bonding strength following flip chip bonding through applied tensile loads. In addition, we performed initial assessments on the etching resiliency of varied cross-linking of SU-8. From initial results, the bonding strength is maximized following a 3-min PEB. Cross-linking appears to have minimal effects on SU-8\u27s etch resiliency as all tested samples etched approximately 1.25 μm. From our initial results, SU-8 appears to be a viable and inexpensive material for wafer bonding, assembling and packaging MEMS devices

A MEMS Photoacoustic Detector of Terahertz Radiation for Chemical Sensing

A piezoelectric Microelectromechanical system (MEMS) cantilever pressure sensor was designed, modeled, fabricated, and tested for sensing the photoacoustic response of gases to terahertz (THz) radiation. The sensing layers were comprised of three thin films; a lead zirconate titanate (PZT) piezoelectric layer sandwiched between two metal contact layers. The sensor materials were deposited on the silicon device layer of a silicon-on-insulator (SOI) wafer, which formed the physical structure of the cantilever. To release the cantilever, a hole was etched through the backside of the wafer and the buried oxide was removed with hydrofluoric acid. Devices were then tested in a custom made THz vacuum test chamber. Cantilever deflection was observed with a laser interferometer in the test chamber and preliminary data indicates the signals were caused by the photoacoustic effect. Future device data will also include the piezoelectric voltage signal analysis

A Micro-Cantilever Based Photoacoustic Detector Of Terahertz Radiation For Chemical Sensing

A Microelectromechanical system (MEMS) cantilever pressure sensor was designed, modeled, fabricated, and tested for sensing the photoacoustic response of gases to Terahertz (THz) radiation. This paper describes manufacturing, experimental set-up and the most recent spectroscopic results, which demonstrate the capabilities of this spectroscopic technique

MEMS Cantilever Sensor for Photoacoustic Detection of Terahertz Radiation

Cantilever structures have long been used in a variety of sensor and actuator applications. In this work, a Microelectromechanical system (MEMS) cantilever pressure sensor was designed, modelled, and fabricated to investigate the photoacoustic response of various gases to terahertz radiation. Cantilever design parameters of length, width, and thickness are investigated using CoventorWare finite element model software. Cantilever tip deflection and resonant frequencies of the beams are of particular interest in order to maximize the effectiveness of the sensor. A few select designs were then fabricated on the device layer of a silicon-on-insulator wafer which was used to create the physical structure of the cantilever. Fabricated devices will then be tested in a custom made vacuum test chamber where the amplitude modulated THz radiation excited acoustic waves in the chamber and cause the cantilever to deflect. To examine the induced deflection in the cantilever, a laser beam reflected off the tip of the cantilever back to a photodiode to analyze tip displacements caused from the photoacoustic effect. Initial test measurements are currently underway and initial data indicates a nearly linear response in signal amplitude from the photodiode which directly correlated to the gases absorption coefficients

A MICRO-CANTILEVER BASED PHOTOACOUSTIC DETECTOR OF TERAHERTZ RADIATION FOR CHEMICAL SENSING

Author Institution: Department of Electrical and Computer Engineering, Air Force Institute of Technology, 2950 Hobson Way, Wright-Patterson AFB, OH 45433, USA; Department of Physics, Wright State University, 3640 Colonel Glenn Highway, Dayton, OH 45435, USAIn this paper we describe a novel photoacoustic detector that can detect radiation in the Terahertz/sub-millimeter (THz/smm) spectral range, is immune to the effect of standing waves, and potentially can have spectral response that is independent of the absorption path length, thus offering crucial advantages for acquisition of THz/smm molecular spectra. The photoacoustic effect occurs when the energy from electromagnetic waves is absorbed by molecules and collisionally transferred into translational energy, thus resulting in local heating induced by the radiation. If radiation produced by the source is modulated, an acoustic wave results which can be detected by a pressure sensitive device such as a microphone or a cantilever. This transduction of the THz signal into a photoacoustic wave is what makes this approach insensitive to the detrimental standing waves associated with traditional THz sensors and allows for a significant reduction in the size of the absorption cell. A Microelectromechanical system (MEMS) cantilever pressure sensor was designed, modeled, fabricated, and tested for sensing the photoacoustic response of gases to THz/smm radiation. Here we present our manufacturing, experimental set-up and most recent spectroscopic results, which demonstrate the capabilities of this spectroscopic technique