Design, fabrication and characterization of novel directional thermoelectric IR sensors

This thesis project reports on implementation of the thermoelectric effect in conjunction with 3D microfabricated silicon structures to create a novel pixel detector that is capable of directional sensing in the infrared (IR) regime. Previous works have focused on use of thermoelectric sense materials in 2D pixel detectors for room temperature IR imaging. This work uses the effect in conjunction with a 3D design to not only sense the presence of an IR target, but also to recalculate its incidence angle using known trigonometric relationships that arise from the silicon micromachining process. Room temperature (RT) IR sensing applications use thermoelectric (thermoelectric) material such as transition metal oxides (TMOs) which depict an inverse relationship between the materials temperature and its electrical resistance. The incident IR radiation is detected via measuring the induced change in the material’s electrical resistance as a result of materials temperature change due to IR radiation absorption. Depending on the distance to the target and the magnitude of the induced change (indicated by the material’s temperature coefficient of resistance (TCR)), the detector creates an image of the IR radiative source. There has been no prior report on use of such effect in tracking an IR target’s angular path as it traverses a pixel detector hence recalculate the incidence angle of an IR target using thermoelectric effect. In this work, standard silicon micromachining techniques were employed to create 3D micro pixels that were further coated with vanadium pentoxide via dip coating. The desired sense regions were then created via patterning of the deposited vanadium pentoxide thin film through an innovative process flow that allowed for selective removal of the material from across the surface of the fabricated device die. Prior to deposition, the material underwent extensive synthesis and characterization routines in order to achieve an optimum recipe that produces the maximum TCR and least possible sheet resistance. Electrodes were put in place across the inclined (111) facets of the micromachined pixels through photoresist spray coating and photolithography and lift off process. The device responses were measured using a test setup comprised of an automated NI LabView ® data capture interface, Keithley digital source meters, IR source and calcium fluoride lenses to illuminate the devices in an angular fashion. Two generation of the devices were designed prototyped in order to investigate the effects of optical and thermal noise and parasitic factors on the proposed functionality of the device. The results show an improvement in the capability of the devices to measure the angle of incidence of an IR source using thermal IR sensing at room temperature.