The objective of this dissertation is the development of the necessary processing steps needed to manufacture infrared photodiodes on InAs1-xSbx material. Preliminary surface preparation steps were performed on both InAs and InSb material, thus covering both possible extremes of the antimony mole fraction. The first experiments endeavoured to characterise the effect of several possible etchants with regards to etch rate, repeatability, limitations for photolithographic patterning and the resultant surface roughness. The etchants investigated include a lactic acid based etchant, a sulphuric acid based etchant, an acetic acid based etchant, an ammonium based etchant, a hydrochloric acid based etchant as well as an organic rinse procedure. These cleaning and etching steps were evaluated at several temperatures. Measurements were performed on an Alpha Step stylus profiler as well as an atomic force microscope. Metal-insulator-semiconductor capacitor devices were manufactured, on both InAs and InSb material, in order to investigate the effects of the above-mentioned etchants combined with surface passivation techniques in terms of surface state densities. Capacitance-versus-bias voltage measurements were done to determine the resultant surface state densities and to compare these to the surface state density of an untreated reference sample. The surface passivation techniques included KOH, Na2S as well as (NH4)2S anodisation. Auger electron spectroscopy measurements were done on InAs and InSb material in order to examine possible surface contamination due to the etchants as well as combinations of these etching and anodisation procedures. The extent of surface coverage by contaminants as well as by the intrinsic elements was measured. The results of the cleaning and etching as well as the surface passivation studies were used to manufacture photovoltaic infrared diodes on an MOCVD (metal oxide chemical vapour deposition) grown p-InAs0.91Sb0.09/i- InAs0.91Sb0.09/n-GaSb structure. Current-versus-voltage and electro-optical measurements were performed on the these diodes in order to evaluate the effect of sulphuric acid based etching combined with KOH, Na2S or (NH4)2S anodisation on the detector performance. The results of surface passivated structures were compared to those of an unpassivated reference detector.

published_or_final_version / Industrial and Manufacturing Systems Engineering / Doctoral / Doctor of Philosophy

Metal Organic Frameworks (MOFs) are a new class of nanoporous materials with high surface area, thermal/chemical stability and a taylorable pore size. These properties make MOFs ideal for storage and gas separation applications. Piezoresistive microcantilever sensors are microfabricated devices that are highly sensitive to surface strain due to doped single crystal silicon regions. Changes in resistance generated by surface strain can be measured with a high degree of accuracy using a Wheatstone bridge and basic instrumentation. This thesis will discuss the use of piezoresistive microcantilever sensors as a transduction mechanism for detection of volatile organic compounds (VOC's) using MOF coatings. It will be shown that by coating a microcantilever with MOFs it is possible to detect low levels of different VOC's (hundreds of parts per million). Excellent sensitivity and a simple transduction mechanism make these devices low power and highly compact. Such devices would be capable of detecting a plethora of different analytes at low concentrations. Devices were engineered for maximum response and microfabricated in the cleanroom with high yield. A custom setup for testing the devices was designed and machined. A number of MOFs were selected and tested, their response was recorded and analyzed. Twelve different analytes including eleven VOC's and water were used to characterize the MOFs. Microcantilever sensors were shown to be durable, reliable and stable in long term testing despite being subjected to many different analytes. MOF coatings proved flexible, durable, stable and reversible. This work will show a promising new technology for a next generation gas sensor.

Nanopore covered microporous silicon interfaces have been formed via an electrochemical etch for gas sensor applications. Rapid reversible and sensitive gas sensors have been fabricated. Both top-down and bottom-up approaches are utilized in the process. A nano-pore coated micro-porous silicon surface is modified selectively for sub-ppm detection of NH3, PH3, NO, H2S, SO2. The selective depositions include electrolessly generated SnO2, CuxO, AuxO, NiO, and nanoparticles such as TiO2, MgO doped TiO2, Al2O3, and ZrO2. Flow dynamics are analyzed via numerical simulations and response data. A general coating selection method for chemical sensors is established via an extrapolation on the inverse of the Hard-Soft Acid-Base concept.

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Ohio University, March, 2009. / Title from PDF t.p. Includes bibliographical references.

The monitoring of harmful ambient vapors is of major concern in the industrial environment. To this end, the development of systems which detect and respond in real time to specific vapors is a highly desirable goal. Surface Acoustic Wave (SAW) devices have been used for chemical analysis since 1978. While sensitive to mass changes occurring on their surfaces, they are not selective to the mass they will detect. Their use as chemical sensors requires the development of specificity for a vapor (or class of vapors) using selective chemical reagents suspended in film media that can have their permeability easily changed. This dissertation presents the development of an automated dosimeter for the detection of phosgene using SAW devices. By changing the film media from a very permeable material to a film exhibiting less permeability, the analytical range of the device using the same suspended selective chemical reagent is expanded to concentrations which the very permeable film is incapable of accurately measuring. / Ph. D.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 164-176).

A miniature, ultra-low power, sensitive, microbridge gas sensor has been developed.The heat loss from the bridge is a function of the thermal conductivity of thegas ambient. Miniature thermal conductivity sensors have been developed for gaschromatography systems [1] and microhotplates have been built with MEMS technologywhich operates within the mW range of power [2]. In this work a lower power microbridgewas built which allowed for the amplification of the effect of gas thermalconductivity on heat loss from the heated microbridge due to the increase inthe surface-to-volume ratio of the sensing element. For the bridge fabrication,CMOS compatible technology, nanolithography, and polysilicon surfacemicromachining were employed. Eight microbridges were fabricated on each die,of varying lengths and widths, and with a thickness of 1 μm. A voltagewas applied to the sensor and the resistance was calculated based upon thecurrent flow. The response has been tested with air, carbon dioxide, helium,and nitrogen. The resistance and temperature change for carbon dioxide was thegreatest, while the corresponding change for helium was the least. Thus the selectivity of the sensor todifferent gases was shown, as well as the robustness of the sensor. Another aspect of the sensor is that it hasvery low power consumption. The measuredpower consumption at 4 Volts is that of 11.5 mJ for Nitrogen, and 16.1 mJ forHelium. Thesensor responds to ambient gas very rapidly. The time constant not only showsthe fast response of the sensor, but it also allows for more accuratedetection, given that each different gas produces a different correspondingtime constant from the sensor. The sensor is able to detect differentconcentrations of the same gas as well. Fromthe slopes that were calculated, the resistance change at 5 Volts operation wasfound to be 2.05mΩ/ppm, 1.14 mΩ/ppm at 4.5 Volts, and 0.7 mΩ/ppm at 4 Volts. Thehigher voltages yielded higher resistance changes for all of the gases thatwere tested. Theversatility of the microbridge has been studied as well. Experiments were donein order to research the ability of a deposited film on the microbridge, inthis case tin oxide, to act as a sensing element for specific gases. In thissetup, the microbridge no longer is the sensing element, but instead acts as aheating element, whose sole purpose is to keep a constant temperature at whichit can then activate the SnO film, making it able to sense methane. In conclusion,the microbridge was designed, fabricated, and tested for use as an electrothermalgas sensor. The sensor responds to ambient gas very rapidly with differentlevels of resistance change for different gases, purely due to the differencein thermal conductivity of each of the gases. Not only does it have a fastresponse, but it also operates at low power levels. Further research has beendone in the microbridge's ability to act as a heating element, in which the useof a SnO film as the sensing element, activated by the microbridge, was studied. REFERENCES: 1. D. Cruz,J.P. Chang, S.K. Showalter, F. Gelbard, R.P. Manginell, M.G. Blain," Microfabricated thermal conductivity detector for themicro-ChemLabTM," Sensors andActuators B, Vol. 121 pp. 414-422, (2007). 2. A. G. Shirke, R. E. Cavicchi, S. Semancik, R. H. Jackson, B.G. Frederick, M. C. Wheeler. "Femtomolar isothermal desorption usingmicrohotplate sensors," J Vac Sci TechnolA, Vol. 25, pp. 514-526 (2007).