Novel MEMS pressure and temperature sensors fabricated on optical fibers

Abstract

This thesis presents the design, fabrication, and testing of novel MEMS pressure and temperature sensors fabricated on optical fiber end faces. A simple micromachining process compatible with MEMS was developed in fabricating sensors directly on optical fibers. The pressure sensor configuration involves anodic bonding of a piece of an extremely thin silicon wafer onto the fiber end face over a cavity etched in the central portion of the fiber end face. Final device diameter is thus the same as that of the optical fiber. The temperature sensor is based on anodically bonding a thin piece of silicon onto the fiber end face. The pressure sensors were fabricated on 400 µm diameter fibers while temperature sensors were fabricated on both 200 and 400 µm diameter fibers. Pressure measurements were made over the 14 to 80 psi range while temperature measurements were made over the 23 to 300 0 C range. Pressure sensor sensitivities of 0.1 mV/psi and 0.2 mV/psi were obtained. The pressure sensors were designed with cavity diameter d=150 µm, and cavity depth h=0.640 µm. Diaphragm thickness for the two sensors were t=7.1, and t=3.4 µm. Higher sensitivity was achieved by design of a sensor with the thinner diaphragm. A sensor array fabrication effort demonstrated that our micromachining process could be extended to simultaneous processing of an array of fibers. The temperature sensor was fabricated by bonding 3.1 µm thick silicon onto the fiber end face. An oxidant-resistant encapsulation scheme for the temperature sensor was proposed, namely aluminum coated silicon nitride (Al/Si 3 N 4). The uncoated side of silicon was bonded to a fiber end face using the anodic bonding method. The measured values of κ φ =λ m-1 dλ m /dT for capped and uncapped sensors were κ φ =(7.5±0.6)×10-5 / 0 C, and κ φ =(7.2±0.1)×10-5 / 0 C respectively. The measured κ φ value for the uncapped sensor is equal to that which was iii determined using the published material properties for crystalline silicon (κ φ 7.9×10-5 / 0 C) within measurement uncertainty. The micromachining process developed for micromachining fiber end faces along with the bonding of silicon to fiber end faces can be extended to fabrication of other MEMS based microoptic devices where fiber optic interrogation is advantageous. First of all, I want to thank my co-advisers Professors Joseph T. Boyd, and Howard E. Jackson for their invaluable guidance, and generous support throughout my thesis project. Their formative influence on my way of thinking about research will continue well beyond the completion of this thesis. I am indebted to Dr. Boyd for introducing me to an exciting thesis project in the area of Optical MEMS and supervising me in such a manner that enabled me to progress and learn in a timely manner. I feel fortunate in associating such a kind and good person. This thesis would not exist without Dr. Jackson, who accepted me as a doctoral student, at a very difficult time of my life, and who believed in my declaration of dedication. His professionalism, guidance, energy, humor...

Discharge-Based Pressure Sensors for High-Temperature Applications Using Three-Dimensional and Planar Microstructures

“…Operating temperatures up to 800 • C have been achieved with sapphire membranes [1]. An interferometer-based sensor has also been fabricated inside a fiber-optic cable [2]. Another sensing technology uses Bragg gratings, which are photoinscribed into fibers and used to trace wavelength shifts caused by pressure and temperature changes at temperatures exceeding 350 • C and potentially over 1500 • C [3].…”

3D mask modules using two-photon direct laser writingtechnology for continuous lithography process on fibers

“…In order to realize more functionality and applications, it is necessary to directly integrate electronic, computational and other functionality into textile fibers. Therefore, there are strong academic and industry interests in developing high resolution micromachining technology on fiber substrates [1][2][3][4]. As a matter of facts, practical applications cannot be expected unless the aforementioned micromachining technology can be utilized for mass production because the fiber substrates are not compatible with batch processes.…”

Continuous photolithography system and technology for fiber substrate

“…Although good results had been achieved, both the processes are mainly shadow-mask-based so that their applications are limited. Abeysinghe et al [4] and Sasaki et al [5] successfully demonstrated single fiber-based sensor for optical communication application but both sensors are made on the optical fiber end by using traditional photolithography technology. Therefore, we have recently suggested a so-called three-dimensional photolithography method for realizing the continuous photolithography process on the fibers [1].…”