Thermoluminescent Microparticles used as Harsh Environment Temperature Sensors Characterized using MEMS Device

The measurement of glow curves from thermoluminescent materials has had important applications in geological/archeological dating and radiation dosimetry. A method for using thermoluminescent materials in a temperature sensing application will be described in this thesis. Thermoluminescence is a process by which an ionizing radiation source excites carriers that eventually settle into trap states. Thermal energy due to a temperature profille is then used to empty the carriers from these trap states allowing them to radiatively recombine. Measuring the thermoluminescent intensity versus temperature is called a glow curve and contains information about the traps in wide bandgap (> 5.5eV) insulating materials. One such material, yttrium oxide with a terbium impurity, was deposited as a thin film on a silicon substrate in order to characterize the use of lanthanides in a insulating host material for thermoluminescent applications. Lanthanides can act as both a trap and recombination center. Eventually microparticles of lanthanide doped magnesium borate and calcium sulfate where determined to be the best samples for testing. When the microparticles of magnesium borate or calcium sulfate are exposed to a temperature profile like those that occur during explosives testing the filled trap density will decrease different amounts depending on the physical properties of a given trap. The temperature profile can be calculated by comparing the altered glow curve of a sample that experienced the explosive event to the glow curve of a sample that was not in the explosive event, this technique has been shown to be effective in measuring temperatures up to just above 500C. The limitation in maximum temperature is in large part due to the maximum temperature possible during a glow curve measurement before thermal emission from the heat source overwhelms the thermoluminescence of the sample. To combat this parasitic thermal emission, and extend the usable temperature range of this sensing technique, two methods are demonstrated to reduce thermal emission. The first method uses a microheater with the metal heating element placed around the perimeter and an aperture placed over the center where a thermoluminescent microparticle is placed blocking thermal emission from the heating element but allowing the light from the microparticle to escape. The second method deposits a distributed Bragg reflector on the top and bottom of a microheater which reduces its emissivity at wavelengths that match the microparticle emission spectrum.