The objective of this research is to develop miniature infrared (IR) spectrometers for portable or handheld chemical/biosensors. The approach is to use novel micro-electro-mechanical system (MEMS) techniques to miniaturize the mirror scanning mechanism and the IR detector. A unique interferometer design is also proposed to compensate mirror tilting.
Fourier transform spectroscopy, especially in infrared range, or FTIR, is very powerful in chemical/biosensing. However, most of FTIR systems are bulky and expensive. MEMS technology has been used to miniaturize FTIR systems, but researchers still face several challenges: low spectral resolution due to small displacements of the MEMS mirrors; tilting of scanning MEMS mirrors; and lack of small-sized uncooled IR detectors for FTIR. This research will address these challenges with several innovative techniques: a new MEMS mirror whose scan range will reach over 1 mm that is 10?e improvement compared to its counterparts; a single-mirror Michelson interferometer design capable of tilt-insensitive scanning; and a capacitive MEMS uncooled IR detector that is small, inexpensive and highly-sensitive.
The proposed integrated technology has a broad range of applications including homeland security, antiterrorism, food safety, and environmental monitoring. Due to their small size and low cost, such devices can be used onsite by first responders such as soldiers or border guards, so that explosives, chemical weapons, toxic hazards and biological agents can be identified quickly to prevent or minimize damage and save lives. Through this project, efforts will be made to attract more young students especially minority students into engineering and science areas.
The objective of this project is to develop miniature portable spectrometers and chemical/biosensors. Fourier transform spectroscopy (FTS), especially in infrared range, is very powerful in chemical/biosensing. However, most of FTS systems are bulky and expensive. MEMS technology has been used to miniaturize FTS systems, but one big challenge is the small displacement of MEMS actuators that leads to low spectral resolution. In this project, several MEMS actuator designs with large linear scan range and MEMS scanning mirrors have been proposed and demonstrated. Compact FTS systems based on the MEMS mirrors developed in this project have also been demonstrated. Furthermore, even more compact solid-state GaN chemical sensors have been developed. The developed techniques have a broad range of applications including homeland security, antiterrorism, food safety, health care, and environmental monitoring. Due to their small size and low cost, such devices can be used onsite by first responders such as soldiers or border guards, so that explosives, chemical weapons, toxic hazards and biological agents can be identified quickly to prevent or minimize damage and save lives. MEMS Mirrors Development (1) Electrothermal bimorph actuator: A large-vertical-displacement (LVD) thermal MEMS mirror (Fig. 1a) was demonstrated, which is capable of generating 600mm vertical displacement, a factor of 10x improvement compared to the state of the art. (2) Ladder bimorph actuator: A large-piston (~100mm) micromirror based on a novel ladder-type electrothermal actuator was developed (Fig. 1b). The undesired tilt of the mirror plate is reduced by a factor of 10. (3) Curved bimorph actuator: Another large-piston micromirror based on a curved concentric electrothermal actuator design was developed (Fig. 2a), which has very small lateral shift and tilting. The MEMS mirror tilts less than 0.4° through the entire 200 mm piston scan range, and the driving voltage is only ~1V. (4) Hidden bimorph actuator: A unique high-fill-factor (40%) electrothermal MEMS mirror with hidden actuators was developed (Fig. 2b). This micromirror is flip-chip bonding ready and large two-axis scan optical angles up to 46° have been achieved at only 4.8 V. (5) Piezoelectric actuator: In order to overcome the relatively slow thermal response of electrothermal bimorph actuators, a unique folded unimorph piezoelectric actuator design has been developed to build large-scan-range and fast piezoelectric micromirrors (Fig. 2c). MEMS mirror-based Fourier-Transform (FT) Spectrometers Development (1) An MEMS mirror based miniature FT spectrometer was demonstrated. A spectral resolution of 19.2 cm-1 has been achieved with a 261μm physical scan range generated by an LVD bimorph MEMS mirror (Fig. 3). (2) A mirror-tilt-insensitive FT spectrometer based on an LVD bimorph MEMS micromirror with dual reflective surface has been demonstrated. The combination of a corner-cube retroreflector and the dual reflection from the MEMS mirror is used to compensate the scanning mirror tilting. Tilting compensation of up to 1.7° and spectral resolution of up to 8.1 cm-1 have been experimentally demonstrated. Chemical and Biological Sensing A sensor platform based on AlGaN/GaN high electron mobility transistors (HEMTs) has been developed to detect chloride ion, glucose and vitellogenin. AlGaN/GaN HEMTs with anti-vitellogenin (Vtg) antibodies attached to the gate region showed rapid changes in the drain current when exposed to different concentrations of Vtg solutions. The sensor was able to detect as low as 2µg/mL. Fig. 4 illustrates a ZnO nanorod-gated AlGaN/GaN HEMT sensor chip, which can be used for carbon monoxide detection. The sensor sensitivity is in the range of 100 parts per million. International Collaboration An international collaboration has been established between the PI and a French research group led by Prof. Philippe Lutz at FEMTO-ST. Several researchers from both sides have visited the other side and started working on two joint projects.
